BiologyQ1–100 of 167 questions
Page 1 of 3 · English
1
BiologyMediumMCQAIPMT · 2000
Which of the following is grouped under phanerogams?
A
Pteridophytes
B
Gymnosperms
C
Angiosperms
D
Both $(b)$ and $(c)$
Solution
(D) Phanerogams are seed-bearing plants.
Both gymnosperms and angiosperms produce seeds,whereas pteridophytes are cryptogams (seedless plants).
Therefore,both $(b)$ and $(c)$ are grouped under phanerogams.
Both gymnosperms and angiosperms produce seeds,whereas pteridophytes are cryptogams (seedless plants).
Therefore,both $(b)$ and $(c)$ are grouped under phanerogams.
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2
BiologyEasyMCQAIPMT · 2000
Metazoans without tissue grade organization are called as
A
Parazoa
B
Protozoa
C
Eumetazoa
D
Deuterostomia
Solution
(A) The animal kingdom is divided into two sub-kingdoms: $Parazoa$ and $Eumetazoa$.
$Parazoa$ includes multicellular organisms that lack tissue-level organization,such as sponges ($Phylum$ $Porifera$).
In these organisms,cells are loosely aggregated and do not form tissues or organs.
$Protozoa$ are unicellular organisms,not metazoans.
$Eumetazoa$ refers to animals that possess true tissues.
Therefore,the correct answer is $A$.
$Parazoa$ includes multicellular organisms that lack tissue-level organization,such as sponges ($Phylum$ $Porifera$).
In these organisms,cells are loosely aggregated and do not form tissues or organs.
$Protozoa$ are unicellular organisms,not metazoans.
$Eumetazoa$ refers to animals that possess true tissues.
Therefore,the correct answer is $A$.
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3
BiologyMediumMCQAIPMT · 2000
According to their modes of nutrition,the fungi are classified into
A
One category
B
Three categories
C
Four categories
D
Six categories
Solution
(B) Fungi are classified into three categories based on their modes of nutrition:
$(a)$ Saprophytic: Fungi that absorb soluble organic matter from dead substrates.
$(b)$ Parasitic: Fungi that live on living plants and animals.
$(c)$ Symbiotic: Fungi that live in association with other organisms,such as lichens (with algae) or mycorrhiza (with roots of higher plants).
$(a)$ Saprophytic: Fungi that absorb soluble organic matter from dead substrates.
$(b)$ Parasitic: Fungi that live on living plants and animals.
$(c)$ Symbiotic: Fungi that live in association with other organisms,such as lichens (with algae) or mycorrhiza (with roots of higher plants).
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4
BiologyEasyMCQAIPMT · 2000
The reserve food material in fungi is:
A
Starch
B
Protein
C
Glucose
D
Glycogen
Solution
(D) Fungi are heterotrophic organisms that do not perform photosynthesis.
They store their reserve food material in the form of glycogen and oil droplets.
Starch is the reserve food material in plants,whereas glycogen is the primary storage polysaccharide in fungi and animals.
They store their reserve food material in the form of glycogen and oil droplets.
Starch is the reserve food material in plants,whereas glycogen is the primary storage polysaccharide in fungi and animals.
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5
BiologyMediumMCQAIPMT · 2000
Which of the following is obtained from algae?
A
Wax
B
Butter
C
Chocolate
D
Carrageenan
Solution
(D) is the correct answer. Carrageenan is a phycocolloid obtained from the cell wall of red algae,specifically $Chondrus$ $crispus$. It belongs to the class $Rhodophyceae$.
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6
BiologyEasyMCQAIPMT · 2000
The product of conjugation of $Spirogyra$ is called
A
Zoospore
B
Akinete
C
Chlamydospore
D
Zygospore
Solution
(D) In $Spirogyra$,sexual reproduction occurs through a process known as conjugation.
During this process,two filaments come together,and their protoplasts fuse to form a diploid structure.
This resulting diploid structure is known as a $Zygospore$.
The $Zygospore$ is a thick-walled,resistant resting spore that allows the organism to survive unfavorable environmental conditions.
During this process,two filaments come together,and their protoplasts fuse to form a diploid structure.
This resulting diploid structure is known as a $Zygospore$.
The $Zygospore$ is a thick-walled,resistant resting spore that allows the organism to survive unfavorable environmental conditions.
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7
BiologyMediumMCQAIPMT · 2000
In $Pteridophytes$ / $Dryopteris$,meiosis occurs at the time of:
A
Gamete formation
B
Spore formation
C
Formation of prothallus
D
Formation of sex organs
Solution
(B) In $Pteridophytes$ like $Dryopteris$,the main plant body is a sporophyte $(2n)$.
Inside the sporangium,specialized cells called spore mother cells $(2n)$ undergo meiosis (reduction division) to produce haploid $(n)$ spores.
These spores germinate to form the prothallus (gametophyte).
Therefore,meiosis occurs at the time of spore formation.
Inside the sporangium,specialized cells called spore mother cells $(2n)$ undergo meiosis (reduction division) to produce haploid $(n)$ spores.
These spores germinate to form the prothallus (gametophyte).
Therefore,meiosis occurs at the time of spore formation.
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8
BiologyMediumMCQAIPMT · 2000
Cell-tissue organisation occurs in
A
Liver fluke
B
Sponge
C
Hydra
D
Starfish
Solution
(C) In the animal kingdom,organisms are classified based on their level of organization.
$1$. Sponges exhibit a cellular level of organization.
$2$. $Hydra$ (a member of Phylum $Cnidaria$) exhibits a tissue level of organization,where cells performing the same function are arranged into tissues.
$3$. Liver fluke (Phylum $Platyhelminthes$) and Starfish (Phylum $Echinodermata$) exhibit organ and organ-system levels of organization,respectively.
Therefore,tissue-level organization is characteristic of $Hydra$.
$1$. Sponges exhibit a cellular level of organization.
$2$. $Hydra$ (a member of Phylum $Cnidaria$) exhibits a tissue level of organization,where cells performing the same function are arranged into tissues.
$3$. Liver fluke (Phylum $Platyhelminthes$) and Starfish (Phylum $Echinodermata$) exhibit organ and organ-system levels of organization,respectively.
Therefore,tissue-level organization is characteristic of $Hydra$.
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9
BiologyMediumMCQAIPMT · 2000
Members of phylum Porifera are
A
Exclusively marine animals
B
Exclusively fresh water animals
C
Mostly fresh water animals but few are marine animals
D
Mostly marine animals but few are fresh water animals
Solution
(D) Members of the phylum $Porifera$ are commonly known as sponges.
Most of the species belonging to this phylum are marine,meaning they live in saltwater environments.
However,there are a few exceptions,such as the genus $Spongilla$,which is found in freshwater habitats.
Therefore,the correct statement is that they are mostly marine animals with a few freshwater representatives.
Most of the species belonging to this phylum are marine,meaning they live in saltwater environments.
However,there are a few exceptions,such as the genus $Spongilla$,which is found in freshwater habitats.
Therefore,the correct statement is that they are mostly marine animals with a few freshwater representatives.
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10
BiologyMediumMCQAIPMT · 2000
Hydra receives impulses and stimuli through
A
Nerve net
B
Sensory cells
C
Nematocytes
D
All of these
Solution
(D) $Hydra$ possesses a primitive nervous system consisting of a nerve net composed of interconnected neurons.
Sensory cells are distributed throughout the epidermis to detect environmental stimuli.
$Nematocytes$ (or $Cnidocytes$) are specialized cells that contain stinging organelles and also function as sensory receptors to trigger the discharge of the nematocyst in response to external stimuli.
Therefore,all these structures contribute to the reception of impulses and stimuli in $Hydra$.
Sensory cells are distributed throughout the epidermis to detect environmental stimuli.
$Nematocytes$ (or $Cnidocytes$) are specialized cells that contain stinging organelles and also function as sensory receptors to trigger the discharge of the nematocyst in response to external stimuli.
Therefore,all these structures contribute to the reception of impulses and stimuli in $Hydra$.
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11
BiologyEasyMCQAIPMT · 2000
Coenocytic epidermis is present in
A
Ascaris
B
Cockroach
C
Earthworm
D
Housefly
Solution
(A) coenocytic condition refers to a multinucleated state where multiple nuclei are present within a single cell or cytoplasm without being separated by cell membranes.
In the phylum $Aschelminthes$ (roundworms),the epidermis of $Ascaris$ is syncytial or coenocytic,meaning it contains many nuclei within a continuous mass of cytoplasm.
In the phylum $Aschelminthes$ (roundworms),the epidermis of $Ascaris$ is syncytial or coenocytic,meaning it contains many nuclei within a continuous mass of cytoplasm.
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12
BiologyMediumMCQAIPMT · 2000
Enteronephric nephridia of earthworm are concerned with
A
Excretion
B
Respiration
C
Digestion
D
Osmoregulation
Solution
(D) In earthworms,nephridia are classified based on their opening into the body.
$1$. Integumentary nephridia open directly to the exterior.
$2$. Enteronephric nephridia open into the alimentary canal (intestine).
These nephridia discharge nitrogenous wastes into the gut,which are then eliminated along with the feces.
This mechanism helps in the conservation of water,thus playing a significant role in osmoregulation.
$1$. Integumentary nephridia open directly to the exterior.
$2$. Enteronephric nephridia open into the alimentary canal (intestine).
These nephridia discharge nitrogenous wastes into the gut,which are then eliminated along with the feces.
This mechanism helps in the conservation of water,thus playing a significant role in osmoregulation.
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13
BiologyMediumMCQAIPMT · 2000
Ascaris and Cockroach resemble each other in
A
Pseudocoel
B
Sexual dimorphism
C
Nephridia
D
Dorsal tubular nerve cord
Solution
(B) Both $Ascaris$ (roundworm) and Cockroach exhibit sexual dimorphism,meaning the male and female individuals are morphologically distinct from each other.
In $Ascaris$,the male is smaller than the female and has a curved posterior end.
In Cockroach,the male possesses anal styles,which are absent in the female.
In $Ascaris$,the male is smaller than the female and has a curved posterior end.
In Cockroach,the male possesses anal styles,which are absent in the female.
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14
BiologyMediumMCQAIPMT · 2000
Tube feet are the characteristic structures of
A
Jellyfish
B
Cuttlefish
C
Starfish
D
Crayfish
Solution
(C) Tube feet are the characteristic structures found in the phylum $Echinodermata$.
They are part of the water vascular system,which is unique to this phylum.
These structures function primarily in locomotion,capture of food,and respiration.
Among the given options,$Starfish$ (Asterias) belongs to the phylum $Echinodermata$,and therefore,possesses tube feet.
They are part of the water vascular system,which is unique to this phylum.
These structures function primarily in locomotion,capture of food,and respiration.
Among the given options,$Starfish$ (Asterias) belongs to the phylum $Echinodermata$,and therefore,possesses tube feet.
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15
BiologyMediumMCQAIPMT · 2000
The animal that possesses a notochord throughout its life is
A
Fish
B
Amphioxus
C
Bird
D
Snake
Solution
(B) $Amphioxus$ $(Branchiostoma)$ belongs to the subphylum $Cephalochordata$. In this group,the notochord is present throughout the entire life and extends from the head to the tail region.
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16
BiologyEasyMCQAIPMT · 2000
Which of the following is a poisonous snake?
A
Eryx
B
Natrix
C
Tree snake
D
Russel's viper
Solution
(D) The $Russel's$ $viper$ ($Daboia$ $russelii$) is a highly venomous snake found in the Indian subcontinent. It belongs to the family $Viperidae$. $Eryx$ (sand boa) is non-poisonous,$Natrix$ (water snake) is generally considered non-poisonous,and most tree snakes are also non-poisonous.
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17
BiologyEasyMCQAIPMT · 2000
Bats belong to which order?
A
Carnivora
B
Chiroptera
C
Dermaptera
D
Cetacea
Solution
(B) Bats are unique mammals capable of true flight. They are classified under the order $Chiroptera$ within the class $Mammalia$. The name $Chiroptera$ is derived from Greek words meaning 'hand-wing',referring to the structure of their wings,which are formed by elongated digits covered by a thin membrane.
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18
BiologyEasyMCQAIPMT · 2000
Pneumatophores occur in plants of
A
Sandy soil
B
Saline marshy soil
C
Marshy soil
D
Water
Solution
(B) The correct answer is $B$.
Pneumatophores are specialized respiratory roots found in plants growing in saline marshy areas (mangroves).
In these environments,the soil is often waterlogged and oxygen-deficient.
To overcome this,some branches of the tap root grow vertically upwards into the air from the horizontal secondary roots to facilitate gaseous exchange.
These specialized roots are known as pneumatophores.
Pneumatophores are specialized respiratory roots found in plants growing in saline marshy areas (mangroves).
In these environments,the soil is often waterlogged and oxygen-deficient.
To overcome this,some branches of the tap root grow vertically upwards into the air from the horizontal secondary roots to facilitate gaseous exchange.
These specialized roots are known as pneumatophores.
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19
BiologyMediumMCQAIPMT · 2000
Wound healing is due to
A
Primary meristem
B
Secondary meristem
C
Ventral meristem
D
All of the above
Solution
(B) . The secondary meristems,such as the cork cambium $(phellogen)$,are responsible for the formation of secondary tissues. These tissues are essential for the repair of injured plant parts and provide effective protection to the plant body through the formation of periderm.
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20
BiologyMediumMCQAIPMT · 2000
The main organelle involved in the modification and routing of newly synthesized proteins to their destinations is:
A
Chloroplast
B
Mitochondria
C
Lysosome
D
Golgi apparatus
Solution
(D) The $Golgi$ $apparatus$ is the primary organelle responsible for the modification, sorting, and packaging of proteins synthesized by the $Endoplasmic$ $reticulum$.
After proteins are synthesized in the $Rough$ $Endoplasmic$ $reticulum$ $(RER)$, they are transported to the $Golgi$ $apparatus$ in vesicles.
Within the $Golgi$ $apparatus$, these proteins undergo modifications such as glycosylation and are then sorted and routed to their specific destinations, such as the plasma membrane, lysosomes, or for secretion outside the cell.
After proteins are synthesized in the $Rough$ $Endoplasmic$ $reticulum$ $(RER)$, they are transported to the $Golgi$ $apparatus$ in vesicles.
Within the $Golgi$ $apparatus$, these proteins undergo modifications such as glycosylation and are then sorted and routed to their specific destinations, such as the plasma membrane, lysosomes, or for secretion outside the cell.
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21
BiologyMediumMCQAIPMT · 2000
Which of the following is related to the glycosylation of proteins?
A
$ER$
B
Peroxisome
C
Lysosome
D
Mitochondria
Solution
(A) Glycosylation is the process of adding carbohydrate chains to proteins to form glycoproteins.
This process primarily occurs in the lumen of the rough Endoplasmic Reticulum $(ER)$ and is further modified in the Golgi apparatus.
Therefore,the $ER$ is the site where the initial glycosylation of proteins synthesized by ribosomes attached to its membrane takes place.
This process primarily occurs in the lumen of the rough Endoplasmic Reticulum $(ER)$ and is further modified in the Golgi apparatus.
Therefore,the $ER$ is the site where the initial glycosylation of proteins synthesized by ribosomes attached to its membrane takes place.
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22
BiologyMediumMCQAIPMT · 2000
Lysosomes are known as suicidal bags because of
A
Catalytic enzymes
B
Hydrolytic enzymes
C
Parasitic on nucleus
D
Proteolytic enzymes
Solution
(B) Lysosomes are membrane-bound vesicular structures formed by the process of packaging in the Golgi apparatus.
They contain a wide variety of hydrolytic enzymes (hydrolases like lipases,proteases,and carbohydrases) that are optimally active at the acidic $pH$.
When the cell gets damaged or dies,lysosomes burst and the enzymes digest their own cell organelles,which is why they are known as suicidal bags.
They contain a wide variety of hydrolytic enzymes (hydrolases like lipases,proteases,and carbohydrases) that are optimally active at the acidic $pH$.
When the cell gets damaged or dies,lysosomes burst and the enzymes digest their own cell organelles,which is why they are known as suicidal bags.
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23
BiologyMediumMCQAIPMT · 2000
The function of the centrosome is:
A
Inhibition of cell division
B
Initiates cell division
C
To increase protein synthesis
D
None of these
Solution
(B) The centrosome is a non-membrane-bound organelle usually containing two cylindrical structures called centrioles.
It plays a crucial role in organizing the microtubule cytoskeleton.
During cell division,the centrosome acts as the microtubule-organizing center $(MTOC)$ and helps in the formation of the spindle apparatus,which is essential for the separation of chromosomes.
Therefore,it initiates and regulates the process of cell division.
It plays a crucial role in organizing the microtubule cytoskeleton.
During cell division,the centrosome acts as the microtubule-organizing center $(MTOC)$ and helps in the formation of the spindle apparatus,which is essential for the separation of chromosomes.
Therefore,it initiates and regulates the process of cell division.
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24
BiologyEasyMCQAIPMT · 2000
Spindle chromosomes have
A
Centriole
B
Kinetochore
C
Chromocentre
D
Chromomere
Solution
(B) Chromosomes that attach to spindle fibers are designated as spindle chromosomes.
The specific site on the centromere where the spindle fibers attach is known as the kinetochore.
Therefore,spindle chromosomes possess a kinetochore for the attachment of spindle fibers during cell division.
The specific site on the centromere where the spindle fibers attach is known as the kinetochore.
Therefore,spindle chromosomes possess a kinetochore for the attachment of spindle fibers during cell division.
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25
BiologyMediumMCQAIPMT · 2000
Enzymes are basically or all enzymes contain:
A
Sugars
B
Proteins
C
Fats
D
Vitamins
Solution
(B) All enzymes are proteins,as they are composed of amino acid chains folded into specific three-dimensional structures. However,it is important to note that not all proteins are enzymes. Ribozymes are a notable exception,as they are catalytic $RNA$ molecules,but in the context of general biological classification,enzymes are primarily proteinaceous in nature.
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26
BiologyMediumMCQAIPMT · 2000
Enzymes are absent in
A
Algae
B
Fungi
C
Bacteria
D
Virus
Solution
(D) . Viruses are acellular entities that lack their own metabolic machinery,including enzymes for independent biochemical reactions. They rely entirely on the host cell's machinery for replication and protein synthesis.
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27
BiologyMediumMCQAIPMT · 2000
Mitosis is the process by which eukaryotic cells
A
Expose the genes for protein synthesis
B
Become specialized in structure and function
C
Multiply
D
Grow
Solution
(C) Mitosis is a type of cell division in which one parent cell divides to produce two identical daughter cells. This process is essential for the growth,development,and repair of tissues in multicellular organisms. Therefore,it is the fundamental process by which eukaryotic cells multiply.
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28
BiologyMediumMCQAIPMT · 2000
When,during the meiotic division,do the centromeres divide?
A
Diplotene
B
Metaphase $-I$
C
Pachytene
D
Anaphase $-II$
Solution
(D) During meiosis,the centromeres do not divide in Meiosis $-I$.
In $Anaphase-II$,the centromeres of each chromosome split,allowing the sister chromatids to separate.
These separated chromatids then move toward opposite poles and are referred to as individual chromosomes.
This process is similar to the mitotic division of centromeres.
In $Anaphase-II$,the centromeres of each chromosome split,allowing the sister chromatids to separate.
These separated chromatids then move toward opposite poles and are referred to as individual chromosomes.
This process is similar to the mitotic division of centromeres.
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29
BiologyMediumMCQAIPMT · 2000
Exchange of chromosome segments between maternal and paternal chromatids during meiosis is called
A
Linkage
B
Dominance
C
Crossing over
D
$DNA$ multiplication
Solution
(C) During the pachytene stage of prophase-$I$ of meiosis,the exchange of genetic material occurs between non-sister chromatids of homologous chromosomes.
This process is known as crossing over.
It leads to genetic recombination,which is essential for genetic diversity in sexually reproducing organisms.
This process is known as crossing over.
It leads to genetic recombination,which is essential for genetic diversity in sexually reproducing organisms.
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30
BiologyMediumMCQAIPMT · 2000
Increase in $CO_2$ concentration around the leaf results in:
A
Rapid opening of stomata
B
Partial closing of stomata
C
Complete closure of stomata
D
There will be no effect on stomatal opening
Solution
(B) Mansfield $(1965)$ reported that the removal of $CO_2$ maintains stomatal opening even in the dark.
Conversely,stomata tend to close in the presence of light if the $CO_2$ concentration is increased around the leaf surface.
Therefore,an increase in $CO_2$ concentration leads to the partial closing of stomata.
Conversely,stomata tend to close in the presence of light if the $CO_2$ concentration is increased around the leaf surface.
Therefore,an increase in $CO_2$ concentration leads to the partial closing of stomata.
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31
BiologyEasyMCQAIPMT · 2000
Plants absorb $Zn$ in the form of:
A
$Zn$
B
$Zn^{2+}$
C
$ZnO$
D
$ZnSO_4$
Solution
(B) Plants absorb essential mineral elements from the soil primarily in their ionic forms. Zinc $(Zn)$ is absorbed by plants from the soil solution in the form of divalent zinc ions,denoted as $Zn^{2+}$.
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32
BiologyMediumMCQAIPMT · 2000
Which of the following is the initiating step in photosynthesis?
A
$ATP$ formation
B
Glucose formation
C
Photolysis of water
D
Activation of chlorophyll by sunlight
Solution
(D) The process of photosynthesis begins with the absorption of light energy by chlorophyll pigments.
When chlorophyll molecules absorb photons from sunlight,they become excited and reach a higher energy state.
This activation of chlorophyll is the primary and initiating step that triggers the subsequent light-dependent reactions,including the photolysis of water and the synthesis of $ATP$ and $NADPH$.
When chlorophyll molecules absorb photons from sunlight,they become excited and reach a higher energy state.
This activation of chlorophyll is the primary and initiating step that triggers the subsequent light-dependent reactions,including the photolysis of water and the synthesis of $ATP$ and $NADPH$.
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33
BiologyMediumMCQAIPMT · 2000
How many turns of the Calvin cycle are required to form one hexose molecule?
A
$2$
B
$6$
C
$4$
D
$8$
Solution
(B) The Calvin cycle fixes one molecule of $CO_2$ per turn.
Since a hexose molecule (glucose,$C_6H_{12}O_6$) contains $6$ carbon atoms,the cycle must complete $6$ turns to incorporate $6$ molecules of $CO_2$ to produce one molecule of glucose.
Since a hexose molecule (glucose,$C_6H_{12}O_6$) contains $6$ carbon atoms,the cycle must complete $6$ turns to incorporate $6$ molecules of $CO_2$ to produce one molecule of glucose.
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34
BiologyMediumMCQAIPMT · 2000
The first reaction in photorespiration is
A
Carboxylation
B
Decarboxylation
C
Oxygenation
D
Phosphorylation
Solution
(C) Photorespiration occurs under specific conditions:
$(1)$ High $O_2$ concentration.
$(2)$ Low $CO_2$ concentration.
$(3)$ High light intensity.
In the presence of high $O_2$ and low $CO_2$,the enzyme $RuBisCO$ acts as an oxygenase rather than a carboxylase. Therefore,the first reaction in photorespiration is the oxygenation of $RuBP$ (Ribulose$-1,5-$bisphosphate),which leads to the formation of one molecule of phosphoglycerate and one molecule of phosphoglycolate.
$(1)$ High $O_2$ concentration.
$(2)$ Low $CO_2$ concentration.
$(3)$ High light intensity.
In the presence of high $O_2$ and low $CO_2$,the enzyme $RuBisCO$ acts as an oxygenase rather than a carboxylase. Therefore,the first reaction in photorespiration is the oxygenation of $RuBP$ (Ribulose$-1,5-$bisphosphate),which leads to the formation of one molecule of phosphoglycerate and one molecule of phosphoglycolate.
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35
BiologyEasyMCQAIPMT · 2000
Cristae are associated with which of the following?
A
Cytoplasm
B
Protoplasm
C
Mitochondria
D
Ribosomes
Solution
(C) Cristae are the inward folds of the inner mitochondrial membrane. These folds significantly increase the surface area of the inner membrane,which is essential for the attachment of enzymes and proteins involved in the electron transport chain and oxidative phosphorylation during cellular respiration.
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36
BiologyMediumMCQAIPMT · 2000
The link between glycolysis and the Kreb's cycle is:
A
Citric acid
B
Acetyl $CoA$
C
Succinic acid
D
Oxaloacetic acid
Solution
(B) The link between glycolysis and the Kreb's cycle is Acetyl $CoA$.
Glycolysis occurs in the cytoplasm and produces pyruvate.
This pyruvate is then transported into the mitochondria,where it undergoes oxidative decarboxylation to form Acetyl $CoA$.
Acetyl $CoA$ acts as a connecting link because it is the substrate that enters the Kreb's cycle ($TCA$ cycle) for further oxidation.
Glycolysis occurs in the cytoplasm and produces pyruvate.
This pyruvate is then transported into the mitochondria,where it undergoes oxidative decarboxylation to form Acetyl $CoA$.
Acetyl $CoA$ acts as a connecting link because it is the substrate that enters the Kreb's cycle ($TCA$ cycle) for further oxidation.
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37
BiologyMediumMCQAIPMT · 2000
The movement of auxin is largely
A
Basipetal
B
Acropetal
C
Centripetal
D
Centrifugal
Solution
(A) Auxin exhibits polar transport. In the stem,the movement is primarily basipetal (from the apex towards the base),whereas in the root,it is acropetal (from the root tip towards the shoot). Therefore,the most characteristic and widely recognized movement of auxin in the plant body is basipetal.
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38
BiologyMediumMCQAIPMT · 2000
Which of the following is a coconut milk factor?
A
Auxin
B
Cytokinin
C
Morphactin
D
None of the above
Solution
(B) The coconut milk factor is a substance that promotes cell division. It was identified as a cytokinin,specifically zeatin,which is present in the liquid endosperm of coconut. Therefore,the correct option is $B$.
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39
BiologyMediumMCQAIPMT · 2000
Which gastric enzyme acts on milk protein?
A
Casein
B
Rennin
C
Pepsin
D
Caseinogen
Solution
(B) The enzyme $Rennin$ (also known as $Chymosin$) is a proteolytic enzyme found in the gastric juice of infants. It specifically acts on the milk protein $Caseinogen$ (a soluble protein) and converts it into $Paracasein$ (an insoluble protein),which then reacts with calcium ions to form calcium paracaseinate (curd). This process facilitates the digestion of milk protein by $Pepsin$.
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40
BiologyMediumMCQAIPMT · 2000
Vitamins that we must consume daily are:
A
Fat-soluble
B
Water-soluble
C
Both $(A)$ and $(B)$
D
None of these
Solution
(B) Vitamins are classified into two groups based on their solubility: fat-soluble and water-soluble.
Fat-soluble vitamins (e.g.,$A, D, E, K$) can be stored in the body's adipose tissue and liver,so they do not need to be consumed every single day.
Water-soluble vitamins (e.g.,$B$-complex and $C$) are not stored in the body in significant amounts and are excreted through urine.
Therefore,water-soluble vitamins must be replenished through our daily diet to maintain optimal health.
Fat-soluble vitamins (e.g.,$A, D, E, K$) can be stored in the body's adipose tissue and liver,so they do not need to be consumed every single day.
Water-soluble vitamins (e.g.,$B$-complex and $C$) are not stored in the body in significant amounts and are excreted through urine.
Therefore,water-soluble vitamins must be replenished through our daily diet to maintain optimal health.
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41
BiologyMediumMCQAIPMT · 2000
$A$ balanced diet should have approximately
A
$1/5$ protein,$3/5$ fat and $1/5$ carbohydrate
B
$3/5$ protein,$1/5$ fat and $1/5$ carbohydrate
C
$1/5$ protein,$1/5$ fat and $3/5$ carbohydrate
D
$1/2$ protein,$1/4$ fat and $1/4$ carbohydrate
Solution
(C) balanced diet is defined as a diet that contains the proper proportions of carbohydrates,fats,proteins,vitamins,minerals,and water necessary to maintain good health.
According to standard nutritional guidelines,carbohydrates are the primary source of energy and should constitute the largest portion of the diet,typically around $60\%$ or $3/5$ of the total caloric intake.
Proteins are essential for growth and repair and typically make up about $20\%$ or $1/5$ of the diet.
Fats are also required for energy and cell structure,accounting for the remaining $20\%$ or $1/5$ of the diet.
Therefore,the correct ratio is $1/5$ protein,$1/5$ fat,and $3/5$ carbohydrate.
According to standard nutritional guidelines,carbohydrates are the primary source of energy and should constitute the largest portion of the diet,typically around $60\%$ or $3/5$ of the total caloric intake.
Proteins are essential for growth and repair and typically make up about $20\%$ or $1/5$ of the diet.
Fats are also required for energy and cell structure,accounting for the remaining $20\%$ or $1/5$ of the diet.
Therefore,the correct ratio is $1/5$ protein,$1/5$ fat,and $3/5$ carbohydrate.
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42
BiologyEasyMCQAIPMT · 2000
The first heart sound occurs at:
A
Opening of semilunar valve
B
Closing of semilunar valve
C
Onset of auricular systole
D
Sudden closure of $A.V.$ valves
Solution
(D) The first heart sound,known as $LUBB$,is produced by the sudden closure of the atrioventricular $(A.V.)$ valves (tricuspid and bicuspid valves).
This closure occurs at the beginning of ventricular systole due to a sharp rise in intraventricular pressure,which prevents the backflow of blood into the atria.
This closure occurs at the beginning of ventricular systole due to a sharp rise in intraventricular pressure,which prevents the backflow of blood into the atria.
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43
BiologyMediumMCQAIPMT · 2000
The intestinal excretory organs (septal nephridia) of $Pheretima$ have a function of:
A
Locomotion
B
Respiration
C
Water balance
D
Excretion of nitrogenous waste
Solution
(D) In $Pheretima$ (earthworm),nephridia are the primary excretory organs.
Septal nephridia,which are located on both sides of the intersegmental septa behind the $15^{th}$ segment,open into the intestine.
These nephridia are enteronephric,meaning they discharge their nitrogenous waste (primarily urea) directly into the intestinal lumen.
This adaptation helps in the conservation of water by reabsorbing water from the waste before it is excreted,thus playing a crucial role in osmoregulation and the excretion of nitrogenous waste.
Septal nephridia,which are located on both sides of the intersegmental septa behind the $15^{th}$ segment,open into the intestine.
These nephridia are enteronephric,meaning they discharge their nitrogenous waste (primarily urea) directly into the intestinal lumen.
This adaptation helps in the conservation of water by reabsorbing water from the waste before it is excreted,thus playing a crucial role in osmoregulation and the excretion of nitrogenous waste.
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44
BiologyEasyMCQAIPMT · 2000
The vertebrae in birds are mostly
A
Procoelous
B
Amphicoelous
C
Opisthocoelous
D
Heterocoelous
Solution
(D) The vertebrae of birds are mostly $Heterocoelous$.
In $Heterocoelous$ vertebrae,the articular surfaces of the centrum are saddle-shaped,which allows for extensive movement of the neck while preventing rotation,providing stability and flexibility required for flight and feeding.
In $Heterocoelous$ vertebrae,the articular surfaces of the centrum are saddle-shaped,which allows for extensive movement of the neck while preventing rotation,providing stability and flexibility required for flight and feeding.
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45
BiologyEasyMCQAIPMT · 2000
Which of the following bones is related to the skull?
A
Atlas
B
Coracoid
C
Arytenoid
D
Pterygoid
Solution
(D) . The $Pterygoid$ is a paired bone that forms part of the skull,specifically contributing to the lateral walls of the nasal cavity and the posterior roof of the mouth cavity.
$Atlas$ is the first cervical vertebra.
$Coracoid$ is a bone of the pectoral girdle.
$Arytenoid$ is a cartilage associated with the larynx.
$Atlas$ is the first cervical vertebra.
$Coracoid$ is a bone of the pectoral girdle.
$Arytenoid$ is a cartilage associated with the larynx.
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46
BiologyMediumMCQAIPMT · 2000
The joint between the ribs and the sternum is a:
A
Cartilaginous joint
B
Angular joint
C
Fibrous joint
D
Gliding joint
Solution
(A) The joint between the ribs and the sternum is known as a cartilaginous joint. Specifically,these are synchondroses where the hyaline cartilage connects the ribs to the sternum,allowing for limited movement during respiration.
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47
BiologyEasyMCQAIPMT · 2000
Which cranial nerve has the highest number of branches?
A
Trigeminal
B
Facial nerve
C
Vagus nerve
D
None of these
Solution
(C) The $Vagus$ nerve (Cranial nerve $X$) is the longest and most complex cranial nerve, possessing the most extensive distribution and the highest number of branches.
Its primary branches include:
$(i)$ Superior laryngeal nerve
$(ii)$ Recurrent laryngeal nerve
$(iii)$ Cardiac branches
$(iv)$ Pulmonary branches
$(v)$ Esophageal branches
It provides parasympathetic innervation to the heart, lungs, and digestive tract.
Its primary branches include:
$(i)$ Superior laryngeal nerve
$(ii)$ Recurrent laryngeal nerve
$(iii)$ Cardiac branches
$(iv)$ Pulmonary branches
$(v)$ Esophageal branches
It provides parasympathetic innervation to the heart, lungs, and digestive tract.
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48
BiologyEasyMCQAIPMT · 2000
The chemical causing the transmission of nerve impulse across synapses is
A
Acetylcholine
B
Cholinesterase
C
Choline
D
Acetic acid
Solution
(A) When a nerve impulse reaches the synaptic knob,it triggers the release of neurotransmitters,primarily $Acetylcholine$,into the synaptic cleft.
These neurotransmitters then bind to receptors on the postsynaptic membrane,facilitating the transmission of the impulse to the next neuron.
These neurotransmitters then bind to receptors on the postsynaptic membrane,facilitating the transmission of the impulse to the next neuron.
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49
BiologyEasyMCQAIPMT · 2000
The osphradium of $Pila \text{ } globosa$ is
A
Photoreceptor
B
Chemoreceptor
C
Thermoreceptor
D
Tangoreceptor
Solution
(B) The osphradium is a small, bipectinate sensory organ found in the mantle cavity of $Pila$.
It functions as a chemoreceptor, which is sensitive to chemical stimuli in the water, helping the organism to test the quality of water.
It functions as a chemoreceptor, which is sensitive to chemical stimuli in the water, helping the organism to test the quality of water.
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50
BiologyEasyMCQAIPMT · 2000
Otoconium is found in
A
Perilymph
B
Haemolymph
C
Synovial fluid
D
Otolithic membrane
Solution
(D) The otolithic membrane contains numerous minute,irregular particles called otoliths or otoconia.
These structures are composed of calcium carbonate and protein.
They play a crucial role in the vestibular system by providing inertia to the sensory hair cells during head movement,which helps in maintaining balance.
These structures are composed of calcium carbonate and protein.
They play a crucial role in the vestibular system by providing inertia to the sensory hair cells during head movement,which helps in maintaining balance.
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51
BiologyMediumMCQAIPMT · 2000
Plasmid is used as a carrier (vector) because:
A
It has antibiotic resistance genes.
B
Its both ends are replicating points.
C
It can go between eukaryotic and prokaryotic cells.
D
It is circular $DNA$ which has the capacity to bind with eukaryotic $DNA$.
Solution
(D) The correct answer is $(d)$.
Plasmids are small,circular,extrachromosomal $DNA$ molecules found in bacteria that are used as vectors in genetic engineering.
They are ideal carriers because they possess an origin of replication $(ori)$,which allows them to replicate independently within the host cell.
Furthermore,they have the capacity to integrate or bind with foreign $DNA$ (such as eukaryotic $DNA$) to form recombinant $DNA$,which can then be introduced into a host organism for cloning or expression.
Plasmids are small,circular,extrachromosomal $DNA$ molecules found in bacteria that are used as vectors in genetic engineering.
They are ideal carriers because they possess an origin of replication $(ori)$,which allows them to replicate independently within the host cell.
Furthermore,they have the capacity to integrate or bind with foreign $DNA$ (such as eukaryotic $DNA$) to form recombinant $DNA$,which can then be introduced into a host organism for cloning or expression.
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52
BiologyMediumMCQAIPMT · 2000
The hair present on the cob of corn are:
A
Seed hairs
B
Modified hairs of bracts
C
Styles
D
Stigmas and styles
Solution
(D) The silken threads or 'hair' found on a cob of corn are elongated $styles$ that extend from the ovary to the exterior of the husk to receive pollen. The terminal portion of these threads acts as the $stigma$. Therefore, they are collectively referred to as $stigmas$ and $styles$.
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53
BiologyMediumMCQAIPMT · 2000
In angiosperms,the endosperm is formed by:
A
Free nuclear divisions of megaspore
B
Division of fused polar nuclei
C
Division of fused polar nuclei and male gamete
D
Division of fused synergids and male gamete
Solution
(C) In angiosperms,the process of double fertilization involves the fusion of one male gamete with two polar nuclei (or the secondary nucleus) to form the Primary Endosperm Nucleus $(PEN)$.
This process is known as triple fusion.
The $PEN$ subsequently undergoes repeated mitotic divisions to develop into the endosperm,which provides nourishment to the developing embryo.
Therefore,the endosperm is formed by the division of the product of the fusion of two polar nuclei and one male gamete.
This process is known as triple fusion.
The $PEN$ subsequently undergoes repeated mitotic divisions to develop into the endosperm,which provides nourishment to the developing embryo.
Therefore,the endosperm is formed by the division of the product of the fusion of two polar nuclei and one male gamete.
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54
BiologyMediumMCQAIPMT · 2000
$A$ man known to be a victim of haemophilia marries a normal woman whose father was known to be a bleeder. Then it is expected that:
A
All their children will be bleeders
B
Half of their children will be bleeders
C
One fourth of their children will be bleeders
D
None of their children will be bleeder
Solution
(B) Haemophilia is an $X$-linked recessive disorder.
Let $X^h$ represent the haemophilic allele and $X$ represent the normal allele.
The man is a victim of haemophilia,so his genotype is $X^hY$.
The woman is normal but her father was a bleeder $(X^hY)$,which means she must have inherited the $X^h$ allele from him. Thus,her genotype is $X^hX$.
When they marry,the cross is $X^hY \times X^hX$.
The possible offspring genotypes are:
$1. X^hX^h$ (Haemophilic daughter)
$2. X^hX$ (Carrier daughter)
$3. X^hY$ (Haemophilic son)
$4. XY$ (Normal son)
Out of these four possibilities,two are affected (haemophilic). Therefore,half of their children will be bleeders.
Let $X^h$ represent the haemophilic allele and $X$ represent the normal allele.
The man is a victim of haemophilia,so his genotype is $X^hY$.
The woman is normal but her father was a bleeder $(X^hY)$,which means she must have inherited the $X^h$ allele from him. Thus,her genotype is $X^hX$.
When they marry,the cross is $X^hY \times X^hX$.
The possible offspring genotypes are:
$1. X^hX^h$ (Haemophilic daughter)
$2. X^hX$ (Carrier daughter)
$3. X^hY$ (Haemophilic son)
$4. XY$ (Normal son)
Out of these four possibilities,two are affected (haemophilic). Therefore,half of their children will be bleeders.
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55
BiologyEasyMCQAIPMT · 2000
Two bacteria found to be very useful in genetic engineering experiments are
A
Nitrosomonas and Klebsiella
B
Escherichia and Agrobacterium
C
Nitrobacter and Azotobacter
D
Rhizobium and Diplococcus
Solution
(B) The correct answer is $B$.
$Escherichia coli$ $(E. coli)$ is widely used in genetic engineering as a host organism for cloning and the production of recombinant proteins like insulin (humulin) and growth hormones.
$Agrobacterium tumefaciens$ is a soil bacterium that contains the $Ti$ (Tumor-inducing) plasmid,which is extensively used as a vector for gene transfer in plants.
$Escherichia coli$ $(E. coli)$ is widely used in genetic engineering as a host organism for cloning and the production of recombinant proteins like insulin (humulin) and growth hormones.
$Agrobacterium tumefaciens$ is a soil bacterium that contains the $Ti$ (Tumor-inducing) plasmid,which is extensively used as a vector for gene transfer in plants.
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56
BiologyMediumMCQAIPMT · 2000
The latest trend in plant disease control is:
A
Chemical control
B
Biological control
C
Use of fertilizers
D
Use of disease resistant varieties
Solution
(D) The latest and most sustainable trend in plant disease control is the use of disease-resistant varieties. This approach involves breeding or genetic engineering to develop plant cultivars that can naturally withstand or resist pathogens,thereby reducing the reliance on harmful chemical pesticides and promoting environmentally friendly agriculture.
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57
BiologyEasyMCQAIPMT · 2000
The enzyme restriction endonuclease:
A
Cuts $RNA$ strand
B
Cuts double strand of $DNA$
C
Joins the strands of $DNA$
D
Cuts single strand of $DNA$
Solution
(B) Restriction endonucleases are enzymes that recognize specific nucleotide sequences in $DNA$ and cleave both strands of the $DNA$ molecule at or near these recognition sites. They are essential tools in recombinant $DNA$ technology.
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58
BiologyMediumMCQAIPMT · 2000
Which of the following is a correct statement?
A
Drone is diploid
B
Apis indica is largest wild bee
C
Wax is excretory product of bee
D
Karl von Frisch discovered communication in bees
Solution
(D) The correct statement is that Karl von Frisch discovered communication in bees (the waggle dance).
- Drones are haploid,not diploid.
- Apis dorsata is the largest wild bee,not Apis indica.
- Wax is a secretion from the wax glands of worker bees,not an excretory product.
- Drones are haploid,not diploid.
- Apis dorsata is the largest wild bee,not Apis indica.
- Wax is a secretion from the wax glands of worker bees,not an excretory product.
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59
BiologyMediumMCQAIPMT · 2000
Which aquatic fern is an excellent biofertilizer?
A
Salvinia
B
Azolla
C
Marsilea
D
Pteridium
Solution
(B) $Azolla$ $pinnata$ (an aquatic fern) contains symbiotic nitrogen-fixing cyanobacteria ($Anabaena$ $azollae$) in its leaf cavities.
It is widely used as a biofertilizer in rice fields,particularly in south-eastern Asia.
It helps in nitrogen fixation and has been found to increase crop yield by up to $50\%$.
It is widely used as a biofertilizer in rice fields,particularly in south-eastern Asia.
It helps in nitrogen fixation and has been found to increase crop yield by up to $50\%$.
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60
BiologyEasyMCQAIPMT · 2000
Plant genes of endangered species are stored in:
A
Gene library
B
Gene bank
C
Herbarium
D
None of the above
Solution
(B) The correct answer is $B$.
Gene banks are specialized facilities where germplasm,including seeds,pollen,or tissue cultures of endangered plant species,is stored under controlled conditions to preserve genetic diversity.
In India,the $NBPGR$ (National Bureau of Plant Genetic Resources),located in New Delhi,serves as the primary institution for maintaining gene banks of various crop species and wild relatives.
Gene banks are specialized facilities where germplasm,including seeds,pollen,or tissue cultures of endangered plant species,is stored under controlled conditions to preserve genetic diversity.
In India,the $NBPGR$ (National Bureau of Plant Genetic Resources),located in New Delhi,serves as the primary institution for maintaining gene banks of various crop species and wild relatives.
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61
BiologyMediumMCQAIPMT · 2000
Biosphere reserves are being threatened with
A
Population growth
B
Rains
C
Pollution
D
All the above
Solution
(D) Biosphere reserves are protected areas intended to conserve biodiversity and sustainable development.
However,they face significant threats from various human-induced activities.
$1$. Population growth leads to encroachment on forest lands and increased demand for resources.
$2$. Pollution from industrial,agricultural,and urban sources degrades the quality of soil,water,and air within these reserves,harming the flora and fauna.
While rains are a natural phenomenon,the other two factors are major anthropogenic threats. Since the question asks for threats,and both population growth and pollution are significant,the most appropriate choice in this context is $D$.
However,they face significant threats from various human-induced activities.
$1$. Population growth leads to encroachment on forest lands and increased demand for resources.
$2$. Pollution from industrial,agricultural,and urban sources degrades the quality of soil,water,and air within these reserves,harming the flora and fauna.
While rains are a natural phenomenon,the other two factors are major anthropogenic threats. Since the question asks for threats,and both population growth and pollution are significant,the most appropriate choice in this context is $D$.
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62
BiologyEasyMCQAIPMT · 2000
The lemur $Indri indri$ occurs in
A
India
B
Mauritius
C
Fiji
D
Madagascar
Solution
(D) $Indri indri$, commonly known as the Indri, is a large lemur species. Lemurs are primates that are endemic to the island of Madagascar. They are not found naturally in the wild anywhere else in the world.
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63
BiologyEasyMCQAIPMT · 2000
Which of the following is a recently cloned species?
A
Dolly - goat
B
Molly - sheep
C
Dolly - sheep
D
None of these
Solution
(C) Dolly the sheep was the first mammal to be cloned from an adult somatic cell using the process of nuclear transfer. This landmark scientific achievement occurred in $1996$ at the Roslin Institute in Scotland. Therefore,the correct option is $C$.
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64
BiologyEasyMCQAIPMT · 2000
Who is famous in the field of palaeobotany?
A
Bose $J$.$C$.
B
Birbal Sahni
C
Metha $K$.$C$.
D
Maheshwari $P$
Solution
(B) Birbal Sahni is widely recognized as the father of Indian palaeobotany.
He made significant contributions to the study of fossil plants and the geology of the Indian subcontinent.
He founded the Birbal Sahni Institute of Palaeosciences in Lucknow.
He made significant contributions to the study of fossil plants and the geology of the Indian subcontinent.
He founded the Birbal Sahni Institute of Palaeosciences in Lucknow.
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65
BiologyMediumMCQAIPMT · 2000
$A$ magnification of up to $100$ million times is possible in
A
Scanning electron microscope
B
Transmission electron microscope
C
Scanning probe microscope
D
Photon tunneling microscope
Solution
(C) The $Scanning \text{ } probe \text{ } microscope$ $(SPM)$ is a type of microscope that uses a physical probe to scan the surface of a specimen. Among the various types of $SPM$, the $Scanning \text{ } tunneling \text{ } microscope$ $(STM)$ is capable of achieving atomic-level resolution and magnifications of up to $100$ million times, allowing for the visualization of individual atoms on a surface.
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66
BiologyMediumMCQAIPMT · 2000
Which of the following is correctly matched?
A
Saliva - taste of food
B
Humerus - hind limb
C
Sweat - temperature regulation
D
Sebum - sexual attraction
Solution
(C) The correct match is $C$.
$1$. Saliva helps in the digestion of starch and lubrication of food,not primarily in the taste of food.
$2$. The $Humerus$ is a bone of the forelimb (arm),not the hind limb.
$3$. Sweat is produced by sweat glands and is essential for thermoregulation (temperature regulation) in the body.
$4$. Sebum is an oily secretion that lubricates the skin and hair,not primarily for sexual attraction.
$1$. Saliva helps in the digestion of starch and lubrication of food,not primarily in the taste of food.
$2$. The $Humerus$ is a bone of the forelimb (arm),not the hind limb.
$3$. Sweat is produced by sweat glands and is essential for thermoregulation (temperature regulation) in the body.
$4$. Sebum is an oily secretion that lubricates the skin and hair,not primarily for sexual attraction.
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67
BiologyEasyMCQAIPMT · 2000
$A$ place where endangered genetic materials of plants are kept is:
A
Gene library
B
Gene bank
C
Gene pool
D
Herbarium
Solution
(B) $Gene \text{ } bank$ is a type of biorepository that preserves genetic material. For plants, this could be by freezing cuttings from the plant, or stocking the seeds (e.g., in a seed bank). These facilities are crucial for the conservation of endangered plant species and the maintenance of genetic diversity.
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68
BiologyMediumMCQAIPMT · 2000
Wild varieties of plants must be conserved to
A
Maintain ecosystem
B
Feed wild animals
C
Future evolution
D
Incorporate useful traits in future crop varieties
Solution
(D) Wild varieties of plants are essential reservoirs of genetic diversity. They often contain genes for resistance to diseases,pests,and environmental stresses (like drought or salinity) that may have been lost in domesticated crop varieties during selective breeding. By conserving these wild relatives,scientists can use them in plant breeding programs to incorporate these beneficial traits into future crop varieties,thereby improving yield and resilience.
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69
BiologyEasyMCQAIPMT · 2000
Major autotrophic biomass in oceans is contributed by
A
Forests
B
Algae and phytoplanktons
C
Crops
D
None of these
Solution
(B) In marine ecosystems,the primary producers responsible for the majority of autotrophic biomass are microscopic organisms known as phytoplanktons and various forms of algae.
These organisms perform photosynthesis,converting solar energy into chemical energy,which forms the base of the marine food web.
Unlike terrestrial ecosystems where forests contribute significantly to biomass,the vast majority of oceanic primary production is carried out by these small,floating autotrophs.
These organisms perform photosynthesis,converting solar energy into chemical energy,which forms the base of the marine food web.
Unlike terrestrial ecosystems where forests contribute significantly to biomass,the vast majority of oceanic primary production is carried out by these small,floating autotrophs.
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70
BiologyMediumMCQAIPMT · 2000
$A$ change in the amount of yolk and its distribution in the egg will affect
A
pattern of cleavage
B
number of blastomeres produced
C
fertilization
D
formation of zygote.
Solution
(A) : Cleavage is a series of rapid mitotic cell divisions by which a single fertilized egg cell (zygote) is transformed into a multicellular structure called the blastula.
During cleavage,there is no significant growth in the size of the embryo,and the shape remains largely unchanged except for the formation of a central cavity known as the blastocoel.
The ratio of nuclear material $(DNA)$ to cytoplasm increases with each division.
The pattern or mode of cleavage is primarily determined by the amount of yolk present in the egg and its distribution (pattern of yolk deposition).
Based on the yolk content,cleavage is classified as holoblastic (total) or meroblastic (partial).
During cleavage,there is no significant growth in the size of the embryo,and the shape remains largely unchanged except for the formation of a central cavity known as the blastocoel.
The ratio of nuclear material $(DNA)$ to cytoplasm increases with each division.
The pattern or mode of cleavage is primarily determined by the amount of yolk present in the egg and its distribution (pattern of yolk deposition).
Based on the yolk content,cleavage is classified as holoblastic (total) or meroblastic (partial).
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71
BiologyMediumMCQAIPMT · 2000
$Cu$ ions released from copper-releasing intrauterine devices $(IUDs)$:
A
make uterus unsuitable for implantation
B
increase phagocytosis of sperms
C
suppress sperm motility
D
prevent ovulation
Solution
(C) $Cu$ ions released from copper-releasing $IUDs$ (e.g.,$CuT$,$Cu7$,$Multiload$ $375$) act by suppressing the motility and fertilizing capacity of sperms.
While $IUDs$ also increase the phagocytosis of sperms within the uterus,the primary effect of the copper ions specifically is the inhibition of sperm motility and their ability to fertilize the egg.
While $IUDs$ also increase the phagocytosis of sperms within the uterus,the primary effect of the copper ions specifically is the inhibition of sperm motility and their ability to fertilize the egg.
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72
BiologyMediumMCQAIPMT · 2000
Relative Biological Effectiveness $(RBE)$ is associated with damage caused by ................
A
Low temperature
B
High temperature
C
Encephalitis
D
Radiation
Solution
(D) Relative Biological Effectiveness $(RBE)$ is a term used in radiobiology to compare the effectiveness of different types of ionizing radiation in causing biological damage.
It is defined as the ratio of the absorbed dose of a reference radiation (usually $250 \ keV$ $X$-rays) to the absorbed dose of the radiation in question that produces the same biological effect.
Therefore,$(RBE)$ is directly associated with the damage caused by ionizing radiation.
It is defined as the ratio of the absorbed dose of a reference radiation (usually $250 \ keV$ $X$-rays) to the absorbed dose of the radiation in question that produces the same biological effect.
Therefore,$(RBE)$ is directly associated with the damage caused by ionizing radiation.
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73
BiologyEasyMCQAIPMT · 2000
Small proteins produced by vertebrate cells in response to viral infection,which inhibit further viral multiplication,are known as.............
A
Immunoglobulins
B
Interferons
C
Antitoxins
D
Lipoproteins
Solution
(B) Interferons are a group of signaling proteins made and released by host cells in response to the presence of several viruses.
They act as a type of cytokine.
When a cell is infected by a virus,it secretes interferons,which signal neighboring cells to heighten their antiviral defenses,thereby inhibiting further viral multiplication.
Thus,they provide innate immunity against viral infections.
They act as a type of cytokine.
When a cell is infected by a virus,it secretes interferons,which signal neighboring cells to heighten their antiviral defenses,thereby inhibiting further viral multiplication.
Thus,they provide innate immunity against viral infections.
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74
BiologyMediumMCQAIPMT · 2000
What is a plasmid?
A
$A$ piece of $DNA$ that acts as a vector
B
$A$ piece connecting two genes
C
An $mRNA$ that acts as a carrier
D
$A$ photosynthetic fragment
Solution
(A) plasmid is a small,circular,double-stranded $DNA$ molecule that is distinct from a cell's chromosomal $DNA$.
Plasmids are naturally found in bacterial cells and some eukaryotes.
In biotechnology,plasmids are extensively used as vectors to carry foreign genetic material into another cell,where it can be replicated and/or expressed.
Plasmids are naturally found in bacterial cells and some eukaryotes.
In biotechnology,plasmids are extensively used as vectors to carry foreign genetic material into another cell,where it can be replicated and/or expressed.
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75
BiologyMediumMCQAIPMT · 2000
What is required to initiate the development of endosperm in angiosperms after double fertilization?
A
One polar nucleus and one male gamete
B
Two polar nuclei and one male gamete
C
Four or more polar nuclei and one male gamete
D
All of the above types of fusions in various angiosperms
Solution
(B) In angiosperms,double fertilization involves two processes: syngamy and triple fusion.
During triple fusion,one male gamete $(n)$ fuses with two polar nuclei $(n + n)$ or the secondary nucleus $(2n)$ present in the central cell.
This fusion results in the formation of the Primary Endosperm Nucleus $(PEN)$,which is triploid $(3n)$.
This $PEN$ subsequently develops into the endosperm,which provides nourishment to the developing embryo.
During triple fusion,one male gamete $(n)$ fuses with two polar nuclei $(n + n)$ or the secondary nucleus $(2n)$ present in the central cell.
This fusion results in the formation of the Primary Endosperm Nucleus $(PEN)$,which is triploid $(3n)$.
This $PEN$ subsequently develops into the endosperm,which provides nourishment to the developing embryo.
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76
BiologyMediumMCQAIPMT · 2000
An $8$-nucleate embryo sac is $..........$.
A
Always tetrasporic
B
Always monosporic
C
Always bisporic
D
Sometimes monosporic,sometimes bisporic,and sometimes tetrasporic
Solution
(D) The development of the embryo sac from a single megaspore is called monosporic development (e.g.,Polygonum type).
In some plants,two megaspore nuclei participate in the development of the embryo sac (bisporic).
In others,all four megaspore nuclei contribute to the formation of the embryo sac (tetrasporic).
Despite these different developmental pathways,the final mature embryo sac in many angiosperms is $8$-nucleate.
Therefore,an $8$-nucleate embryo sac can be monosporic,bisporic,or tetrasporic depending on the species.
In some plants,two megaspore nuclei participate in the development of the embryo sac (bisporic).
In others,all four megaspore nuclei contribute to the formation of the embryo sac (tetrasporic).
Despite these different developmental pathways,the final mature embryo sac in many angiosperms is $8$-nucleate.
Therefore,an $8$-nucleate embryo sac can be monosporic,bisporic,or tetrasporic depending on the species.
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77
BiologyMediumMCQAIPMT · 2000
Cleavage in the mammalian egg is $.........$.
A
Holoblastic equal
B
Holoblastic unequal
C
Superficial meroblastic
D
Discoidal meroblastic
Solution
(A) In mammals,the egg is alecithal (containing very little yolk) or microlecithal.
Due to the minimal amount of yolk,the cleavage process involves the entire zygote.
This type of cleavage is known as holoblastic cleavage.
Since the blastomeres formed are of approximately equal size,it is specifically termed as holoblastic equal cleavage.
Due to the minimal amount of yolk,the cleavage process involves the entire zygote.
This type of cleavage is known as holoblastic cleavage.
Since the blastomeres formed are of approximately equal size,it is specifically termed as holoblastic equal cleavage.
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78
BiologyMediumMCQAIPMT · 2000
Progesterone is a very important component of oral contraceptive pills. It prevents implantation by ..........
A
inhibiting ovulation
B
inhibiting cleavage in the fertilized egg
C
creating an unfavorable chemical environment for sperm survival in the female reproductive tract
D
altering the quality of cervical mucus to prevent/retard entry of sperms
Solution
(D) Oral contraceptive pills contain either progesterone alone or a combination of progesterone and estrogen.
These hormones act by inhibiting ovulation and implantation as well as altering the quality of cervical mucus to prevent or retard the entry of sperms.
Specifically,progesterone prevents implantation by altering the endometrial lining of the uterus,making it unsuitable for the attachment of the blastocyst.
These hormones act by inhibiting ovulation and implantation as well as altering the quality of cervical mucus to prevent or retard the entry of sperms.
Specifically,progesterone prevents implantation by altering the endometrial lining of the uterus,making it unsuitable for the attachment of the blastocyst.
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79
BiologyDifficultMCQAIPMT · 2000
What is the cause of $Down's$ syndrome?
A
Crossing over
B
Linkage
C
Sex-linked inheritance
D
Non-disjunction of chromosomes
Solution
(D) $Down's$ syndrome is a chromosomal disorder caused by the presence of an additional copy of chromosome number $21$ (trisomy of $21$).
This condition arises due to the failure of homologous chromosomes or sister chromatids to separate properly during meiosis,a phenomenon known as non-disjunction.
As a result,one gamete receives an extra chromosome,and upon fertilization,the zygote develops with $47$ chromosomes instead of the normal $46$.
This condition arises due to the failure of homologous chromosomes or sister chromatids to separate properly during meiosis,a phenomenon known as non-disjunction.
As a result,one gamete receives an extra chromosome,and upon fertilization,the zygote develops with $47$ chromosomes instead of the normal $46$.
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80
BiologyMediumMCQAIPMT · 2000
Which of the following traits was dominant in the garden pea studied by Mendel?
A
Green seed color
B
Terminal flower position
C
Green pod color
D
Wrinkled seed shape
Solution
(C) Mendel studied $7$ pairs of contrasting traits in garden pea $(Pisum \text{ } sativum)$.
According to his findings:
$1$. Seed color: Yellow is dominant, Green is recessive.
$2$. Flower position: Axial is dominant, Terminal is recessive.
$3$. Pod color: Green is dominant, Yellow is recessive.
$4$. Seed shape: Round is dominant, Wrinkled is recessive.
Therefore, among the given options, 'Green pod color' is the dominant trait.
According to his findings:
$1$. Seed color: Yellow is dominant, Green is recessive.
$2$. Flower position: Axial is dominant, Terminal is recessive.
$3$. Pod color: Green is dominant, Yellow is recessive.
$4$. Seed shape: Round is dominant, Wrinkled is recessive.
Therefore, among the given options, 'Green pod color' is the dominant trait.
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81
BiologyMediumMCQAIPMT · 2000
Mutations generally produce:
A
Recessive genes
B
Lethal genes
C
Polygenic traits
D
Dominant genes
Solution
(A) Mutations are sudden,heritable changes in the $DNA$ sequence. In most cases,mutations result in the loss of function or alteration of a gene product,which typically manifests as a recessive trait. Since the wild-type allele is usually dominant and functional,a mutated allele that produces a non-functional or altered protein is generally recessive to the wild-type allele. Therefore,mutations generally produce recessive genes.
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82
BiologyMediumMCQAIPMT · 2000
$A$ $XXY$ genotype in Drosophila is a female,whereas in humans,it is an abnormal male. This indicates that...
A
$Y$ chromosome is essential for sex determination in Drosophila.
B
$Y$ chromosome is female-determining in Drosophila.
C
$Y$ chromosome is the male-determining factor in humans.
D
$Y$ chromosome has no role in sex determination in either Drosophila or humans.
Solution
(C) ड्रोसोफिला में लिंग निर्धारण $X$ गुणसूत्रों की संख्या और ऑटोसोम के सेट के अनुपात ($X/A$ अनुपात) द्वारा निर्धारित होता है। यहाँ $Y$ गुणसूत्र नर प्रजनन क्षमता के लिए आवश्यक है,लेकिन यह लिंग निर्धारित नहीं करता है। मनुष्यों में,$Y$ गुणसूत्र पर मौजूद $SRY$ जीन नर लिंग के विकास के लिए जिम्मेदार होता है,इसलिए $XXY$ जीनोटाइप वाला व्यक्ति पुरुष होता है (क्लाइनफेल्टर सिंड्रोम)। अतः,$Y$ गुणसूत्र मनुष्यों में नर का निर्धारण करने वाला कारक है।
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83
BiologyMediumMCQAIPMT · 2000
In $Drosophila$,during organ differentiation,if one organ is transformed into another (e.g.,legs instead of wings),what is the gene responsible for such transformation called?
A
Double dominant gene
B
Plastid genes
C
Complementary gene
D
Homeotic gene
Solution
(D) Homeotic genes are a group of genes that control the pattern of body formation during early embryonic development of organisms.
These genes encode transcription factors that determine the identity of body segments along the anterior-posterior axis.
In $Drosophila$,mutations in homeotic genes can lead to homeotic transformations,where one body part is replaced by another,such as the development of legs in place of wings (e.g.,the $Antennapedia$ mutation).
Therefore,the correct answer is $D$.
These genes encode transcription factors that determine the identity of body segments along the anterior-posterior axis.
In $Drosophila$,mutations in homeotic genes can lead to homeotic transformations,where one body part is replaced by another,such as the development of legs in place of wings (e.g.,the $Antennapedia$ mutation).
Therefore,the correct answer is $D$.
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84
BiologyMediumMCQAIPMT · 2000
Which is the initiation codon for protein synthesis in eukaryotes?
A
$GUA$
B
$GCA$
C
$CCA$
D
$AUG$
Solution
(D) In protein synthesis,the process of translation begins with an initiation codon.
For both prokaryotes and eukaryotes,the codon $AUG$ serves as the initiation codon.
$AUG$ codes for the amino acid Methionine.
Therefore,the correct option is $D$.
For both prokaryotes and eukaryotes,the codon $AUG$ serves as the initiation codon.
$AUG$ codes for the amino acid Methionine.
Therefore,the correct option is $D$.
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85
BiologyMediumMCQAIPMT · 2000
During $DNA$ replication, the two strands separate. Each of these acts as a template for the synthesis of a new strand. This mode of replication is called:
A
Non-conservative
B
Semi-conservative
C
Dispersive
D
Conservative
Solution
(B) During $DNA$ replication, the two strands of the double helix separate, and each strand serves as a template for the synthesis of a new complementary strand.
As a result, each of the two new $DNA$ molecules consists of one parental (old) strand and one newly synthesized strand.
This mechanism is known as $Semi-conservative$ replication, which was experimentally proven by $Meselson$ and $Stahl$.
As a result, each of the two new $DNA$ molecules consists of one parental (old) strand and one newly synthesized strand.
This mechanism is known as $Semi-conservative$ replication, which was experimentally proven by $Meselson$ and $Stahl$.
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86
BiologyMediumMCQAIPMT · 2000
Which of the following is a common feature between $DNA$ and $RNA$?
A
Polymers of nucleotides
B
Ability to replicate
C
Contain the same sugar
D
Contain the same pyrimidines
Solution
(A) Both $DNA$ $(Deoxyribonucleic \text{ acid})$ and $RNA$ $(Ribonucleic \text{ acid})$ are nucleic acids.
They are both polymers of nucleotides, which consist of a nitrogenous base, a pentose sugar, and a phosphate group.
$DNA$ contains deoxyribose sugar, while $RNA$ contains ribose sugar.
$DNA$ contains thymine as a pyrimidine, whereas $RNA$ contains uracil.
Therefore, the common feature is that both are polymers of nucleotides.
They are both polymers of nucleotides, which consist of a nitrogenous base, a pentose sugar, and a phosphate group.
$DNA$ contains deoxyribose sugar, while $RNA$ contains ribose sugar.
$DNA$ contains thymine as a pyrimidine, whereas $RNA$ contains uracil.
Therefore, the common feature is that both are polymers of nucleotides.
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87
BiologyEasyMCQAIPMT · 2000
What does the $3D$ structure of a transfer $RNA$ $(tRNA)$ molecule look like?
A
$L$-shaped
B
$E$-shaped
C
$Y$-shaped
D
$S$-shaped
Solution
(A) The secondary structure of $tRNA$ is often depicted as a cloverleaf model. However,in its actual $3D$ conformation,the $tRNA$ molecule folds into a compact $L$-shaped structure. This $3D$ shape is essential for its function in protein synthesis,allowing it to interact with both the ribosome and the $mRNA$ template.
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88
BiologyEasyMCQAIPMT · 2000
Coconut milk is used in tissue culture because it contains:
A
Gibberellin
B
Cytokinin
C
Auxin
D
Ethylene
Solution
(B) Coconut milk is widely used in plant tissue culture media because it is a rich natural source of $Cytokinin$ (specifically $Zeatin$).
$Cytokinins$ are plant hormones that promote cell division (cytokinesis) and help in the growth and differentiation of plant tissues in vitro.
Therefore,the presence of $Cytokinin$ makes coconut milk an essential supplement for successful tissue culture.
$Cytokinins$ are plant hormones that promote cell division (cytokinesis) and help in the growth and differentiation of plant tissues in vitro.
Therefore,the presence of $Cytokinin$ makes coconut milk an essential supplement for successful tissue culture.
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89
BiologyEasyMCQAIPMT · 2000
Which of the following is not a vestigial organ in humans?
A
Auricular muscles of the pinna
B
Finger nails
C
Third molars
D
Coccyx
Solution
(B) Vestigial organs are anatomical structures that have lost most or all of their original ancestral function through evolution.
$A$. Auricular muscles of the pinna are considered vestigial in humans as they are non-functional for moving the ears.
$B$. Finger nails are functional structures in humans used for protection and manipulation of objects; they are not vestigial.
$C$. Third molars (wisdom teeth) are often considered vestigial due to the reduction in jaw size in modern humans.
$D$. The coccyx (tailbone) is a vestigial remnant of the ancestral tail.
Therefore,finger nails are not vestigial organs.
$A$. Auricular muscles of the pinna are considered vestigial in humans as they are non-functional for moving the ears.
$B$. Finger nails are functional structures in humans used for protection and manipulation of objects; they are not vestigial.
$C$. Third molars (wisdom teeth) are often considered vestigial due to the reduction in jaw size in modern humans.
$D$. The coccyx (tailbone) is a vestigial remnant of the ancestral tail.
Therefore,finger nails are not vestigial organs.
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90
BiologyEasyMCQAIPMT · 2000
Which of the following primates is the closest relative of humans?
A
Rhesus monkey
B
Orangutan
C
Gorilla
D
Gibbon
Solution
(C) Among the given options,the $Gorilla$ is the closest relative to humans. Based on molecular evidence and genomic studies,$Gorilla$ and $Chimpanzee$ share a very high percentage of $DNA$ sequence similarity with humans. Among the choices provided,$Gorilla$ represents the closest evolutionary relative.
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91
BiologyMediumMCQAIPMT · 2000
Which of the following traits is a characteristic of human evolution and indicates a close relationship with primates?
A
Loss of tail
B
Reduction in jaw size
C
Binocular vision
D
Flat nails
Solution
(C) Binocular vision is a key characteristic shared by humans and other primates. It allows for depth perception,which was crucial for the survival of ancestors living in trees. While other features like the loss of tail,reduction in jaw size,and flat nails are also evolutionary traits,binocular vision is a fundamental primate characteristic that indicates a close evolutionary relationship.
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92
BiologyEasyMCQAIPMT · 2000
When did $Homo$ $sapiens$ emerge?
A
Pleistocene
B
Oligocene
C
Pliocene
D
Miocene
Solution
(A) The evolution of $Homo$ $sapiens$ (modern humans) occurred during the $Pleistocene$ epoch.
This epoch began approximately $2.58$ million years ago and ended about $11,700$ years ago.
$Homo$ $sapiens$ evolved in Africa and subsequently spread across the globe.
Therefore,the correct option is $A$.
This epoch began approximately $2.58$ million years ago and ended about $11,700$ years ago.
$Homo$ $sapiens$ evolved in Africa and subsequently spread across the globe.
Therefore,the correct option is $A$.
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93
BiologyMediumMCQAIPMT · 2000
The presence of endemic species in South America and Australia is due to which of the following?
A
These species have become extinct in other regions.
B
Continental drift
C
There was a terrestrial route to these places.
D
Retrogressive evolution
Solution
(B) The presence of unique or endemic species in South America and Australia is primarily attributed to $Continental \text{ } drift$.
During the process of continental drift, large landmasses separated from each other, leading to the isolation of flora and fauna.
Because these regions remained isolated for millions of years, the species present there evolved independently, resulting in high levels of endemism.
During the process of continental drift, large landmasses separated from each other, leading to the isolation of flora and fauna.
Because these regions remained isolated for millions of years, the species present there evolved independently, resulting in high levels of endemism.
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94
BiologyEasyMCQAIPMT · 2000
In vertebrates,a small protein is produced by cells in response to viral infection,which inhibits further viral replication. Identify this protein.
A
Immunoglobulins
B
Interferons
C
Antitoxins
D
Lipoproteins
Solution
(B) In vertebrates,cells infected with a virus produce special proteins called $Interferons$ $(IFNs)$.
These proteins are released into the surrounding cells and protect non-infected cells from further viral infection.
$Interferons$ act as a part of the innate immune system,specifically as a cytokine barrier,by inhibiting the replication of the virus within the host cells.
These proteins are released into the surrounding cells and protect non-infected cells from further viral infection.
$Interferons$ act as a part of the innate immune system,specifically as a cytokine barrier,by inhibiting the replication of the virus within the host cells.
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95
BiologyMediumMCQAIPMT · 2000
Which of the following is one of the most important reasons why wild varieties of plants should be preserved?
A
They are a source of unsaturated edible oils.
B
They provide high-nutrient animal feed.
C
They are a source of genes for resistance to diseases and pests.
D
They are rare plants with high medicinal value.
Solution
(C) Wild varieties of plants are crucial for plant breeding programs.
They possess a diverse gene pool that includes genes for resistance to various biotic stresses such as diseases,pests,and insects,as well as abiotic stresses like drought or salinity.
By preserving these wild relatives,breeders can introduce these beneficial traits into cultivated crops to improve their yield and resilience.
Therefore,they serve as a vital reservoir of genetic diversity for crop improvement.
They possess a diverse gene pool that includes genes for resistance to various biotic stresses such as diseases,pests,and insects,as well as abiotic stresses like drought or salinity.
By preserving these wild relatives,breeders can introduce these beneficial traits into cultivated crops to improve their yield and resilience.
Therefore,they serve as a vital reservoir of genetic diversity for crop improvement.
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96
BiologyEasyMCQAIPMT · 2000
Which of the following is a biofertilizer reported to increase rice production by more than $50\%$?
A
Mycorrhiza
B
Azolla pinnata
C
Cyanobacteria
D
Legume-Rhizobium symbiosis
Solution
(B) $Azolla$ $pinnata$ is a small aquatic fern that has a symbiotic relationship with the nitrogen-fixing cyanobacterium $Anabaena$ $azollae$.
This fern is widely used as a biofertilizer in rice fields because it fixes atmospheric nitrogen and provides it to the rice plants.
Studies have shown that the use of $Azolla$ can increase rice production by more than $50\%$ due to the enrichment of soil nitrogen content.
This fern is widely used as a biofertilizer in rice fields because it fixes atmospheric nitrogen and provides it to the rice plants.
Studies have shown that the use of $Azolla$ can increase rice production by more than $50\%$ due to the enrichment of soil nitrogen content.
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97
BiologyMediumMCQAIPMT · 2000
Plasmids are suitable vectors for gene cloning because...
A
They are small circular $DNA$ molecules that can integrate with the host chromosomal $DNA$.
B
They are small circular $DNA$ molecules that possess their own origin of replication.
C
They can shuttle between prokaryotes and eukaryotes.
D
They often carry antibiotic resistance genes.
Solution
(B) Plasmids are extrachromosomal,self-replicating,circular $DNA$ molecules found in bacteria.
For a molecule to act as a vector in gene cloning,it must be able to replicate independently within the host cell.
This ability is provided by the presence of an 'origin of replication' $(ori)$ site.
While plasmids often carry antibiotic resistance genes (which serve as selectable markers),the fundamental reason they are suitable vectors is their ability to replicate autonomously due to the presence of an $ori$ sequence.
For a molecule to act as a vector in gene cloning,it must be able to replicate independently within the host cell.
This ability is provided by the presence of an 'origin of replication' $(ori)$ site.
While plasmids often carry antibiotic resistance genes (which serve as selectable markers),the fundamental reason they are suitable vectors is their ability to replicate autonomously due to the presence of an $ori$ sequence.
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98
BiologyEasyMCQAIPMT · 2000
Which was the first successful cloned animal that gained worldwide fame?
A
Molly (Sheep)
B
Polly (Sheep)
C
Chance (Bull)
D
Dolly (Sheep)
Solution
(D) Dolly the sheep was the first mammal to be cloned from an adult somatic cell. It was created by researchers at the Roslin Institute in Scotland and was born on $5$ July $1996$. This achievement gained worldwide fame as it demonstrated that a specialized cell from an adult animal could be used to create an exact genetic copy of the entire organism.
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99
BiologyMediumMCQAIPMT · 2000
The production of giant mice in the laboratory has been possible due to $..........$.
A
Gene mutation
B
Gene manipulation
C
Gene synthesis
D
Gene duplication
Solution
(B) The production of giant mice in the laboratory is a classic example of creating transgenic animals. This was achieved by introducing the growth hormone gene from another species (such as a rat or human) into the mouse genome. This process of altering the genetic makeup of an organism by introducing foreign $DNA$ is known as gene manipulation or genetic engineering. Therefore,the correct answer is $B$.
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100
BiologyDifficultMCQAIPMT · 2000
Which of the following has the largest biomass of autotrophs in the world's oceans?
A
Benthic brown algae,coastal red algae,and diatoms
B
Benthic diatoms and marine viruses
C
Sea grasses and slime molds
D
Free-floating microscopic algae,cyanobacteria,and nanoplankton
Solution
(D) In the world's oceans,the primary producers (autotrophs) are predominantly microscopic organisms.
Although large seaweeds exist,the vast majority of the biomass of autotrophs is contributed by free-floating microscopic algae,cyanobacteria,and nanoplankton,which form the base of the marine food web.
These organisms are collectively known as phytoplankton.
Therefore,the correct option is $D$.
Although large seaweeds exist,the vast majority of the biomass of autotrophs is contributed by free-floating microscopic algae,cyanobacteria,and nanoplankton,which form the base of the marine food web.
These organisms are collectively known as phytoplankton.
Therefore,the correct option is $D$.
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