BiologyQ51–103 of 167 questions
Page 2 of 3 · English
51
BiologyMediumMCQAIPMT · 2000
In the myopia eye defect,the rays of light
A
Do not enter the eye at all
B
Come to a focus at the back of the retina
C
Come to a focus in front of the retina
D
Come to a focus in between the retina and the iris
Solution
(C) Myopia,also known as near-sightedness,is a refractive defect of the eye.
In this condition,the eyeball becomes too long or the curvature of the cornea is too steep.
As a result,the light rays entering the eye converge at a point in front of the retina rather than directly on it.
This causes distant objects to appear blurred,while near objects remain clear.
In this condition,the eyeball becomes too long or the curvature of the cornea is too steep.
As a result,the light rays entering the eye converge at a point in front of the retina rather than directly on it.
This causes distant objects to appear blurred,while near objects remain clear.
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52
BiologyMediumMCQAIPMT · 2000
The feedback control mechanism is related to:
A
Bile secretion
B
$HCl$ secretion
C
Hormonal secretion
D
Hering-Breuer reflex
Solution
(C) The feedback control mechanism is a fundamental process in the endocrine system used to regulate the levels of hormones in the blood.
In this mechanism,the output of a system acts as an input to regulate the process,ensuring that hormone levels remain within a specific physiological range.
Negative feedback is the most common type,where an increase in the concentration of a hormone inhibits its further production,while positive feedback is less common.
Therefore,hormonal secretion is directly controlled by this mechanism to maintain homeostasis.
In this mechanism,the output of a system acts as an input to regulate the process,ensuring that hormone levels remain within a specific physiological range.
Negative feedback is the most common type,where an increase in the concentration of a hormone inhibits its further production,while positive feedback is less common.
Therefore,hormonal secretion is directly controlled by this mechanism to maintain homeostasis.
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53
BiologyMediumMCQAIPMT · 2000
Protein synthesis in an animal cell occurs
A
Only on the ribosomes present in cytosol
B
On ribosomes present in cytoplasm as well as in mitochondria
C
Only on ribosomes attached to the nuclear envelope and endoplasmic reticulum
D
On ribosomes present in the nucleolus as well as in cytoplasm
Solution
(B) The correct answer is $B$. Protein synthesis occurs on ribosomes. In an animal cell,ribosomes are found in the cytoplasm (either free or attached to the endoplasmic reticulum) and within the mitochondria. Mitochondria are semi-autonomous organelles that possess their own $DNA$,$RNA$,and $70S$ ribosomes,allowing them to synthesize a portion of their required proteins independently.
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54
BiologyMediumMCQAIPMT · 2000
$A$ patient suffering from cholera is given a saline drip because:
A
$Cl^-$ ions are an important component of blood plasma.
B
$Na^+$ ions help to retain water in the body.
C
$Na^+$ ions are important in the transport of substances across membranes.
D
$Cl^-$ ions help in the formation of $HCl$ in the stomach for digestion.
Solution
(B) Cholera is a severe diarrheal disease caused by the bacterium $Vibrio$ $cholerae$.
During cholera,the patient loses a significant amount of water and electrolytes (especially $Na^+$ and $Cl^-$) through watery stools.
$Na^+$ ions are the primary extracellular cations that play a crucial role in maintaining osmotic pressure and fluid balance in the body.
By administering a saline drip (an isotonic solution of $NaCl$),the body's fluid volume is restored,and the $Na^+$ ions help in retaining water within the extracellular fluid,preventing severe dehydration and circulatory collapse.
During cholera,the patient loses a significant amount of water and electrolytes (especially $Na^+$ and $Cl^-$) through watery stools.
$Na^+$ ions are the primary extracellular cations that play a crucial role in maintaining osmotic pressure and fluid balance in the body.
By administering a saline drip (an isotonic solution of $NaCl$),the body's fluid volume is restored,and the $Na^+$ ions help in retaining water within the extracellular fluid,preventing severe dehydration and circulatory collapse.
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55
BiologyMediumMCQAIPMT · 2000
The most important characteristic of all living systems is:
A
Use of oxygen to generate energy
B
Self-replication of genetic information
C
Production of gametes
D
Use of solar energy for metabolic activities
Solution
(B) The most fundamental and essential characteristic of all living systems is the ability to store and pass on genetic information through self-replication. This process ensures the continuity of life and the transmission of hereditary traits from one generation to the next. While metabolic activities and energy usage are vital,self-replication is the defining feature that distinguishes living organisms from non-living matter at the molecular level.
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56
BiologyMediumMCQAIPMT · 2000
Black rust in wheat is caused by $..........$.
A
$Puccinia$
B
$Mucor$
C
$Aspergillus$
D
$Rhizopus$
Solution
(A) Black rust of wheat is a fungal disease caused by the pathogen $Puccinia \, graminis \, tritici$.
It belongs to the class Basidiomycetes.
This fungus infects wheat plants, leading to the formation of reddish-brown (rust-colored) pustules on the leaves and stems, which eventually turn black as the teliospores develop.
Therefore, the correct option is $A$.
It belongs to the class Basidiomycetes.
This fungus infects wheat plants, leading to the formation of reddish-brown (rust-colored) pustules on the leaves and stems, which eventually turn black as the teliospores develop.
Therefore, the correct option is $A$.
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57
BiologyEasyMCQAIPMT · 2000
The stored food material in fungi is $........$.
A
Glycogen
B
Starch
C
Sucrose
D
Glucose
Solution
(A) Fungi are heterotrophic organisms that obtain nutrients through absorption.
Unlike plants,which store food as starch,fungi store their reserve food material in the form of $Glycogen$ and oil droplets.
$Glycogen$ is a polysaccharide of glucose,similar to the storage form found in animals.
Unlike plants,which store food as starch,fungi store their reserve food material in the form of $Glycogen$ and oil droplets.
$Glycogen$ is a polysaccharide of glucose,similar to the storage form found in animals.
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58
BiologyEasyMCQAIPMT · 2000
The largest ovules,largest male and female gametes,and the largest plants are found in ........
A
Angiosperms
B
Arborescent ferns and some monocots
C
Gymnosperms
D
Dicotyledons
Solution
(C) Gymnosperms are plants in which the ovules are not enclosed by any ovary wall and remain exposed,both before and after fertilization.
They include some of the largest living plants,such as the giant redwood tree $Sequoia$.
In gymnosperms like $Cycas$,the male and female gametes are the largest in the plant kingdom,and they also possess the largest ovules.
They include some of the largest living plants,such as the giant redwood tree $Sequoia$.
In gymnosperms like $Cycas$,the male and female gametes are the largest in the plant kingdom,and they also possess the largest ovules.
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59
BiologyMediumMCQAIPMT · 2000
In $Dryopteris$ (fern),meiosis occurs during:
A
Spore germination
B
Gamete formation
C
Spore formation
D
Antheridia and archegonia formation
Solution
(C) In $Dryopteris$ (a pteridophyte),the main plant body is the sporophyte $(2n)$.
It produces sporangia,which contain spore mother cells.
These spore mother cells undergo meiosis to produce haploid $(n)$ spores.
Therefore,meiosis occurs during spore formation.
It produces sporangia,which contain spore mother cells.
These spore mother cells undergo meiosis to produce haploid $(n)$ spores.
Therefore,meiosis occurs during spore formation.
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60
BiologyMediumMCQAIPMT · 2000
$A$ research student collects and observes some algae. The cells contain both chlorophyll $a, b, c$ and chlorophyll $d$,in addition to phycoerythrin. This alga belongs to:
A
Rhodophyceae
B
Bacillariophyceae
C
Chlorophyceae
D
Phaeophyceae
Solution
(A) The presence of phycoerythrin is a characteristic feature of red algae,which belong to the class Rhodophyceae.
Red algae typically contain chlorophyll $a$ and $d$,along with phycoerythrin (a red pigment) and phycocyanin.
While the question mentions chlorophyll $a, b, c$ and $d$,the presence of the accessory pigment phycoerythrin is the diagnostic feature for Rhodophyceae.
Therefore,the correct classification is Rhodophyceae.
Red algae typically contain chlorophyll $a$ and $d$,along with phycoerythrin (a red pigment) and phycocyanin.
While the question mentions chlorophyll $a, b, c$ and $d$,the presence of the accessory pigment phycoerythrin is the diagnostic feature for Rhodophyceae.
Therefore,the correct classification is Rhodophyceae.
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61
BiologyEasyMCQAIPMT · 2000
Which of the following is an oviparous mammal?
A
Kangaroo
B
Platypus
C
Koala
D
Whale
Solution
(B) Mammals are generally viviparous,meaning they give birth to live young. However,there is a small group of mammals known as monotremes that lay eggs. The $Ornithorhynchus$ (Platypus) and $Tachyglossus$ (Echidna) are examples of oviparous mammals. Therefore,the correct option is $B$.
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62
BiologyMediumMCQAIPMT · 2000
What is common among whales,bats,and rats?
A
Absence of neck
B
Muscular diaphragm between thorax and abdomen
C
Extra-abdominal testes to protect from high body temperature
D
Presence of external ears
Solution
(B) Whales,bats,and rats are all members of the class $Mammalia$.
One of the defining characteristics of mammals is the presence of a muscular diaphragm that separates the thoracic cavity from the abdominal cavity.
This structure plays a crucial role in respiration.
While some mammals have external ears (pinnae),not all do (e.g.,whales have internal ear openings).
Extra-abdominal testes are not a universal feature of all mammals (e.g.,in whales,testes are abdominal).
Therefore,the presence of a muscular diaphragm is the most accurate common feature among these organisms.
One of the defining characteristics of mammals is the presence of a muscular diaphragm that separates the thoracic cavity from the abdominal cavity.
This structure plays a crucial role in respiration.
While some mammals have external ears (pinnae),not all do (e.g.,whales have internal ear openings).
Extra-abdominal testes are not a universal feature of all mammals (e.g.,in whales,testes are abdominal).
Therefore,the presence of a muscular diaphragm is the most accurate common feature among these organisms.
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63
BiologyMediumMCQAIPMT · 2000
What is common between $Ascaris$ $lumbricoides$ and $Anopheles$ $stephensi$?
A
Diapause
B
Metamerism
C
Anaerobic respiration
D
Sexual dimorphism
Solution
(D) $Ascaris$ $lumbricoides$ (roundworm) belongs to the phylum $Aschelminthes$ (Nematoda),and $Anopheles$ $stephensi$ (mosquito) belongs to the phylum $Arthropoda$.
Both of these organisms exhibit sexual dimorphism,meaning the male and female individuals can be morphologically distinguished from each other.
In $Ascaris$,the male is smaller than the female and has a curved posterior end.
In $Anopheles$,the female is larger and possesses different antennae compared to the male.
Therefore,sexual dimorphism is the common feature between them.
Both of these organisms exhibit sexual dimorphism,meaning the male and female individuals can be morphologically distinguished from each other.
In $Ascaris$,the male is smaller than the female and has a curved posterior end.
In $Anopheles$,the female is larger and possesses different antennae compared to the male.
Therefore,sexual dimorphism is the common feature between them.
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64
BiologyMediumMCQAIPMT · 2000
Match the following families with their representative plants and identify the correct pair.
A
Cucurbitaceae $-$ Orange
B
Malvaceae $-$ Cotton
C
Brassicaceae $-$ Wheat
D
Leguminosae $-$ Sunflower
Solution
(B) The correct pair is $Malvaceae - Cotton$.
$1$. $Cucurbitaceae$ includes plants like cucumber and pumpkin, not orange $(Rutaceae)$.
$2$. $Malvaceae$ includes $Gossypium$ (cotton) and $Hibiscus$.
$3$. $Brassicaceae$ includes mustard, not wheat $(Poaceae)$.
$4$. $Leguminosae$ $(Fabaceae)$ includes pulses and peas, not sunflower $(Asteraceae)$.
$1$. $Cucurbitaceae$ includes plants like cucumber and pumpkin, not orange $(Rutaceae)$.
$2$. $Malvaceae$ includes $Gossypium$ (cotton) and $Hibiscus$.
$3$. $Brassicaceae$ includes mustard, not wheat $(Poaceae)$.
$4$. $Leguminosae$ $(Fabaceae)$ includes pulses and peas, not sunflower $(Asteraceae)$.
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65
BiologyMediumMCQAIPMT · 2000
What is observed during the formation of vascular bundles in plants?
A
Procambium differentiates immediately into secondary xylem and phloem.
B
Procambium differentiates into xylem and phloem as they develop.
C
Procambium,xylem,and phloem differentiate sequentially.
D
After the differentiation of procambium,primary phloem develops first,followed by primary xylem.
Solution
(D) During the development of vascular bundles in plants,the procambium is the meristematic tissue that gives rise to the vascular tissues.
As the procambium differentiates,it gives rise to the primary vascular tissues.
Specifically,the procambium differentiates into primary phloem and primary xylem.
In most vascular bundles,the primary phloem develops first (protophloem),followed by the development of primary xylem (protoxylem).
As the procambium differentiates,it gives rise to the primary vascular tissues.
Specifically,the procambium differentiates into primary phloem and primary xylem.
In most vascular bundles,the primary phloem develops first (protophloem),followed by the development of primary xylem (protoxylem).
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66
BiologyEasyMCQAIPMT · 2000
The polysaccharide found in the matrix of cartilage is known as ..........
A
Cartilagin
B
Ossein
C
Chondroitin
D
Casein
Solution
(C) The matrix of cartilage is composed of a firm but flexible material. It contains a protein called chondrin and a polysaccharide known as chondroitin sulfate. Chondroitin sulfate is a glycosaminoglycan that provides structural support and resilience to the cartilage tissue. Ossein is found in bone matrix,while casein is a protein found in milk.
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67
BiologyMediumMCQAIPMT · 2000
The cells of simple epithelial tissue are . . . . . . .
A
Hardened to provide support to organs.
B
Directly cemented to each other to form a single layer.
C
Continuously dividing to form organs.
D
Loosely connected to each other to form irregular organs.
Solution
(B) Simple epithelial tissue is composed of a single layer of cells that are directly cemented to each other. These cells rest on a basement membrane and function as a lining for body cavities,ducts,and tubes. Because they form a single,continuous layer,they are specialized for absorption,secretion,and filtration.
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68
BiologyMediumMCQAIPMT · 2000
If a bone piece,such as a frog's femur,is kept in dilute $HCl$ for a week,it will become .......
A
Turn black
B
Shrink in size
C
Become flexible
D
Break into pieces
Solution
(C) Bone is composed of an organic matrix (collagen) and an inorganic mineral component (calcium salts/hydroxyapatite).
When a bone is placed in dilute $HCl$,the acid reacts with the calcium salts (inorganic component) and dissolves them.
This process is known as decalcification.
After the removal of calcium,only the flexible organic matrix (collagen) remains.
As a result,the bone loses its rigidity and becomes flexible,allowing it to be bent easily.
When a bone is placed in dilute $HCl$,the acid reacts with the calcium salts (inorganic component) and dissolves them.
This process is known as decalcification.
After the removal of calcium,only the flexible organic matrix (collagen) remains.
As a result,the bone loses its rigidity and becomes flexible,allowing it to be bent easily.
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69
BiologyMediumMCQAIPMT · 2000
Which cells do not form layers and remain structurally distinct?
A
Epithelial cells
B
Muscle cells
C
Neurons
D
Glandular cells
Solution
(C) Neurons (nerve cells) are the structural and functional units of the neural tissue. Unlike epithelial cells,which form continuous sheets or layers to cover surfaces or line cavities,neurons are specialized cells that remain structurally distinct. They are designed to receive,process,and transmit electrical impulses throughout the body. While they are supported by neuroglial cells,they do not form layers themselves.
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70
BiologyMediumMCQAIPMT · 2000
Which cell organelle is associated with the glycosylation of proteins?
A
Ribosome
B
Peroxisome
C
Endoplasmic Reticulum
D
Mitochondria
Solution
(C) Glycosylation is the process of adding carbohydrate chains to proteins to form glycoproteins.
This process primarily occurs within the lumen of the Endoplasmic Reticulum $(ER)$ and is further modified in the Golgi apparatus.
Among the given options,the Endoplasmic Reticulum is the correct site where the initial glycosylation of proteins takes place.
This process primarily occurs within the lumen of the Endoplasmic Reticulum $(ER)$ and is further modified in the Golgi apparatus.
Among the given options,the Endoplasmic Reticulum is the correct site where the initial glycosylation of proteins takes place.
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71
BiologyMediumMCQAIPMT · 2000
Lysosomes are the storage sacs of ..........
A
$RNA$ and proteins
B
Fats
C
Secretory glycoproteins
D
Hydrolytic enzymes
Solution
(D) Lysosomes are membrane-bound vesicular structures formed by the process of packaging in the Golgi apparatus.
These organelles are rich in various hydrolytic enzymes (hydrolases like lipases,proteases,and carbohydrases).
These enzymes are optimally active at the acidic $pH$ level.
Therefore,lysosomes are known as the storage sacs of hydrolytic enzymes,which are capable of digesting carbohydrates,proteins,lipids,and nucleic acids.
These organelles are rich in various hydrolytic enzymes (hydrolases like lipases,proteases,and carbohydrases).
These enzymes are optimally active at the acidic $pH$ level.
Therefore,lysosomes are known as the storage sacs of hydrolytic enzymes,which are capable of digesting carbohydrates,proteins,lipids,and nucleic acids.
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72
BiologyMediumMCQAIPMT · 2000
Patients suffering from cholera are given saline drips because:
A
$Cl^-$ ions are an important component of blood plasma.
B
$Na^+$ ions help in retaining water in the body.
C
$Na^+$ ions play a role in the transport of substances across membranes.
D
$Cl^-$ ions help in the formation of $HCl$ for digestion in the stomach.
Solution
(B) Cholera is caused by the bacterium $Vibrio$ $\text{cholerae}$, which leads to severe diarrhea and vomiting. This results in a massive loss of water and electrolytes from the body, leading to dehydration. Saline drips (containing $NaCl$ solution) are administered to replace the lost water and electrolytes. Specifically, $Na^+$ ions are crucial because they help in maintaining osmotic balance and retaining water in the body, thereby preventing circulatory collapse due to dehydration.
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73
BiologyMediumMCQAIPMT · 2000
In vertebrates,the ability to produce concentrated urine is generally associated with the ............ .
A
epithelial area of Bowman's capsule
B
length of the loop of Henle
C
length of the proximal convoluted tubule
D
network of capillaries forming the glomerulus
Solution
(B) The ability to concentrate urine in vertebrates is primarily dependent on the counter-current mechanism. This mechanism is facilitated by the $Loop$ $of$ $Henle$ and the $vasa$ $recta$. $A$ longer $Loop$ $of$ $Henle$ allows for a greater osmotic gradient in the renal medulla,which enables more water to be reabsorbed from the collecting duct,resulting in the production of concentrated urine. Therefore,the length of the $Loop$ $of$ $Henle$ is directly associated with the concentration ability of the kidney.
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74
BiologyMediumMCQAIPMT · 2000
In earthworms,the septal nephridia are primarily associated with:
A
Digestion
B
Respiration
C
Osmoregulation
D
Excretion of nitrogenous wastes
Solution
(D) In earthworms ($Pheretima$ $posthuma$),nephridia are the excretory organs.
Septal nephridia are present on both sides of the intersegmental septa of segment $15$ to the last segment.
These nephridia open into the intestine and are primarily responsible for the excretion of nitrogenous waste products like urea and ammonia.
While they play a role in osmoregulation,their primary function is the removal of metabolic nitrogenous wastes.
Septal nephridia are present on both sides of the intersegmental septa of segment $15$ to the last segment.
These nephridia open into the intestine and are primarily responsible for the excretion of nitrogenous waste products like urea and ammonia.
While they play a role in osmoregulation,their primary function is the removal of metabolic nitrogenous wastes.
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75
BiologyEasyMCQAIPMT · 2000
In organisms,ammonia is converted into urea through the ............ cycle.
A
Ornithine cycle
B
Citrulline cycle
C
Fumarine cycle
D
Arginine cycle
Solution
(A) In mammals and some other organisms,the liver converts toxic ammonia into less toxic urea through a metabolic pathway known as the $Ornithine$ cycle,also commonly referred to as the $Urea$ cycle or $Krebs-Henseleit$ cycle.
This process involves the conversion of ammonia and carbon dioxide into urea using $ATP$ and specific enzymes.
This process involves the conversion of ammonia and carbon dioxide into urea using $ATP$ and specific enzymes.
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76
BiologyMediumMCQAIPMT · 2000
Which of the following pairs is correctly matched regarding the secretion and its primary physiological role in humans?
A
Sebum - Sexual attraction
B
Sweat - Thermoregulation
C
Saliva - Taste of food
D
Tears - Excretion of salts
Solution
(B) The correct match is $Sweat - Thermoregulation$.
$1$. Sweat is produced by sweat glands and its primary physiological role is to facilitate cooling of the body surface through evaporation, which is essential for thermoregulation.
$2$. Sebum is an oily secretion that lubricates the skin and hair, not primarily for sexual attraction.
$3$. Saliva helps in the lubrication and digestion of food, but its primary role is not the 'taste' of food (which is mediated by taste buds).
$4$. Tears are primarily for lubricating and cleaning the eyes, not for the excretion of salts.
$1$. Sweat is produced by sweat glands and its primary physiological role is to facilitate cooling of the body surface through evaporation, which is essential for thermoregulation.
$2$. Sebum is an oily secretion that lubricates the skin and hair, not primarily for sexual attraction.
$3$. Saliva helps in the lubrication and digestion of food, but its primary role is not the 'taste' of food (which is mediated by taste buds).
$4$. Tears are primarily for lubricating and cleaning the eyes, not for the excretion of salts.
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77
BiologyMediumMCQAIPMT · 2000
The joint between the ribs and the sternum in humans is a/an .......... .
A
Hinge joint
B
Fibrous joint
C
Cartilaginous joint
D
Gliding joint
Solution
(C) In humans,the ribs are attached to the sternum via hyaline cartilage.
This type of joint,where the articulating bones are joined by hyaline cartilage,is known as a cartilaginous joint.
Specifically,these are synchondroses,which allow for very limited movement,providing flexibility to the thoracic cage during respiration.
Therefore,the joint between the ribs and the sternum is a cartilaginous joint.
This type of joint,where the articulating bones are joined by hyaline cartilage,is known as a cartilaginous joint.
Specifically,these are synchondroses,which allow for very limited movement,providing flexibility to the thoracic cage during respiration.
Therefore,the joint between the ribs and the sternum is a cartilaginous joint.
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78
BiologyEasyMCQAIPMT · 2000
Which of the following is a bone of the skull?
A
Atlas
B
Coracoid
C
Arytenoid
D
Pterygoid
Solution
(D) The skull consists of cranial and facial bones. The $Pterygoid$ bone is a paired bone that forms part of the skull,specifically located in the skull base.
$Atlas$ is the first cervical vertebra $(C1)$.
$Coracoid$ is a process or bone associated with the pectoral girdle (scapula).
$Arytenoid$ refers to the cartilages found in the larynx,not a bone of the skull.
$Atlas$ is the first cervical vertebra $(C1)$.
$Coracoid$ is a process or bone associated with the pectoral girdle (scapula).
$Arytenoid$ refers to the cartilages found in the larynx,not a bone of the skull.
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79
BiologyMediumMCQAIPMT · 2000
If a person has a deficiency of the visual pigment $Rhodopsin$, they are advised to consume more of which of the following?
A
Carrots and potatoes
B
Apples and grapes
C
Carrots and ripe papayas
D
Guavas and ripe bananas
Solution
(C) $Rhodopsin$ (also known as visual purple) is a biological pigment found in the rod cells of the retina that is responsible for vision in low-light conditions.
$Rhodopsin$ is composed of a protein called $Opsin$ and a derivative of $Vitamin A$ called $Retinal$.
$A$ deficiency of $Vitamin A$ leads to a reduced synthesis of $Rhodopsin$, which causes night blindness (nyctalopia).
Carrots and ripe papayas are rich sources of $\beta$-carotene, which is a precursor to $Vitamin A$.
Therefore, consuming these foods helps in the synthesis of $Rhodopsin$ and improves vision in low light.
$Rhodopsin$ is composed of a protein called $Opsin$ and a derivative of $Vitamin A$ called $Retinal$.
$A$ deficiency of $Vitamin A$ leads to a reduced synthesis of $Rhodopsin$, which causes night blindness (nyctalopia).
Carrots and ripe papayas are rich sources of $\beta$-carotene, which is a precursor to $Vitamin A$.
Therefore, consuming these foods helps in the synthesis of $Rhodopsin$ and improves vision in low light.
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80
BiologyMediumMCQAIPMT · 2000
An action potential in a nerve fiber is generated when the $+ve$ and $-ve$ charges on the outside and inside of the axon membrane are reversed because ...........
A
More potassium ions enter the nerve fiber than sodium ions leave.
B
More sodium ions enter the nerve fiber than potassium ions leave.
C
All potassium ions leave the nerve fiber.
D
All sodium ions enter the nerve fiber.
Solution
(B) When a stimulus is applied to a site on the polarized membrane,the permeability of the membrane to $Na^+$ ions increases rapidly.
This leads to a massive influx of $Na^+$ ions into the axon from the extracellular fluid.
As a result,the inner side of the membrane becomes positively charged relative to the outer side,which is known as depolarization.
This rapid influx of $Na^+$ ions is significantly greater than the efflux of $K^+$ ions,causing the reversal of polarity (action potential).
This leads to a massive influx of $Na^+$ ions into the axon from the extracellular fluid.
As a result,the inner side of the membrane becomes positively charged relative to the outer side,which is known as depolarization.
This rapid influx of $Na^+$ ions is significantly greater than the efflux of $K^+$ ions,causing the reversal of polarity (action potential).
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81
BiologyEasyMCQAIPMT · 2000
In mammals,the scent-producing glands are known as:
A
Rectal glands
B
Prostate glands
C
Adrenal glands
D
Bartholin's glands
Solution
(A) In many mammals,scent glands are specialized structures used for communication,marking territory,or defense. These are often modified sebaceous or sweat glands. Among the given options,rectal glands (or anal glands) are well-known scent-producing glands in many mammals,such as carnivores,used for marking territory. Therefore,the correct option is $A$.
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82
BiologyMediumMCQAIPMT · 2000
Melanocyte-stimulating hormone $(MSH)$ is produced by the ...... .
A
Anterior pituitary
B
Posterior pituitary
C
Pars intermedia of the pituitary
D
Parathyroid
Solution
(C) The pituitary gland is divided into three parts: the anterior pituitary (pars distalis),the intermediate lobe (pars intermedia),and the posterior pituitary (pars nervosa).
In humans,the pars intermedia is almost merged with the pars distalis.
The pars intermedia secretes only one hormone called Melanocyte-stimulating hormone $(MSH)$,which regulates skin pigmentation by stimulating melanocytes.
In humans,the pars intermedia is almost merged with the pars distalis.
The pars intermedia secretes only one hormone called Melanocyte-stimulating hormone $(MSH)$,which regulates skin pigmentation by stimulating melanocytes.
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83
BiologyMediumMCQAIPMT · 2000
Melatonin is secreted by ..........
A
Skin
B
Thymus
C
Pituitary
D
Pineal gland
Solution
(D) The pineal gland is located on the dorsal side of the forebrain.
It secretes a hormone called melatonin.
Melatonin plays a very important role in the regulation of a $24$-hour (diurnal) rhythm of our body.
For example,it helps in maintaining the normal rhythms of sleep-wake cycle,body temperature,and also influences metabolism,pigmentation,the menstrual cycle,as well as our defense capability.
It secretes a hormone called melatonin.
Melatonin plays a very important role in the regulation of a $24$-hour (diurnal) rhythm of our body.
For example,it helps in maintaining the normal rhythms of sleep-wake cycle,body temperature,and also influences metabolism,pigmentation,the menstrual cycle,as well as our defense capability.
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84
BiologyMediumMCQAIPMT · 2000
The blastopore is the ....................
A
opening of the neural tube
B
opening of the archenteron
C
future anterior end of the embryo
D
opening found in the blastocoel
Solution
(B) The blastopore is the opening that connects the archenteron (primitive gut) to the outside of the embryo during the gastrulation stage of embryonic development.
In protostomes,the blastopore develops into the mouth,while in deuterostomes,it develops into the anus.
In protostomes,the blastopore develops into the mouth,while in deuterostomes,it develops into the anus.
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85
BiologyEasyMCQAIPMT · 2000
Who proposed the "Signal Hypothesis" for the biosynthesis of secretory proteins?
A
Camillo Golgi
B
Blobel and Sabatini
C
Baltimore
D
Schiller and Biachi
Solution
(B) The "Signal Hypothesis" was proposed by $Gunter$ $Blobel$ and $David$ $Sabatini$ in the $1970s$.
This hypothesis explains how secretory proteins are targeted to the endoplasmic reticulum during their synthesis.
It states that a specific signal sequence at the $N$-terminus of the nascent polypeptide chain directs the ribosome-mRNA complex to the endoplasmic reticulum membrane.
This hypothesis explains how secretory proteins are targeted to the endoplasmic reticulum during their synthesis.
It states that a specific signal sequence at the $N$-terminus of the nascent polypeptide chain directs the ribosome-mRNA complex to the endoplasmic reticulum membrane.
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86
BiologyMediumMCQAIPMT · 2000
$ATP$ stands for which of the following?
A
Nucleotide
B
Nucleosome
C
Nucleoside
D
Urine
Solution
(A) $ATP$ stands for Adenosine Triphosphate.
It consists of an adenine base,a ribose sugar,and three phosphate groups.
Because it contains a nitrogenous base,a pentose sugar,and phosphate groups,it is classified as a nucleotide.
$A$ nucleoside consists only of a nitrogenous base and a sugar,whereas a nucleotide includes the phosphate group as well.
It consists of an adenine base,a ribose sugar,and three phosphate groups.
Because it contains a nitrogenous base,a pentose sugar,and phosphate groups,it is classified as a nucleotide.
$A$ nucleoside consists only of a nitrogenous base and a sugar,whereas a nucleotide includes the phosphate group as well.
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87
BiologyMediumMCQAIPMT · 2000
Which of the following is an essential amino acid?
A
Serine
B
Aspartic acid
C
Glycine
D
Phenylalanine
Solution
(D) Essential amino acids are those that cannot be synthesized by the human body and must be obtained through the diet.
Among the given options,$Phenylalanine$ is an essential amino acid.
$Serine$,$Aspartic$ $acid$,and $Glycine$ are non-essential amino acids as they can be synthesized by the human body.
Among the given options,$Phenylalanine$ is an essential amino acid.
$Serine$,$Aspartic$ $acid$,and $Glycine$ are non-essential amino acids as they can be synthesized by the human body.
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88
BiologyMediumMCQAIPMT · 2000
Enzymatic activity is inhibited by which of the following?
A
End product
B
Substrate
C
Enzyme
D
Increase in temperature
Solution
(A) The phenomenon where the end product of a metabolic pathway inhibits the activity of an enzyme that catalyzes an earlier step in the pathway is known as feedback inhibition. This is a common regulatory mechanism in cells to maintain homeostasis and prevent the overproduction of metabolites. Therefore,the end product acts as an inhibitor.
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89
BiologyMediumMCQAIPMT · 2000
How is the rate of an enzymatic reaction increased?
A
By forming an enzyme-product complex.
B
By changing the equilibrium point of the reaction.
C
By binding and immediately forming the product.
D
By lowering the activation energy of the reaction.
Solution
(D) Enzymes are biological catalysts that accelerate chemical reactions.
They function by providing an alternative reaction pathway with a lower activation energy $(E_a)$.
By reducing the energy barrier that reactants must overcome to reach the transition state, a larger fraction of molecules can successfully convert into products at a given temperature.
Enzymes do not alter the equilibrium point of a reaction, nor do they change the overall free energy change $(\Delta G)$ of the reaction.
They function by providing an alternative reaction pathway with a lower activation energy $(E_a)$.
By reducing the energy barrier that reactants must overcome to reach the transition state, a larger fraction of molecules can successfully convert into products at a given temperature.
Enzymes do not alter the equilibrium point of a reaction, nor do they change the overall free energy change $(\Delta G)$ of the reaction.
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90
BiologyEasyMCQAIPMT · 2000
What is a conjugated protein called if it contains a carbohydrate as a prosthetic group?
A
Chromoprotein
B
Glycoprotein
C
Lipoprotein
D
Nucleoprotein
Solution
(B) Conjugated proteins are proteins that contain a non-protein component known as a prosthetic group.
When the prosthetic group is a carbohydrate,the protein is classified as a $Glycoprotein$.
$Chromoproteins$ contain a pigment,$Lipoproteins$ contain lipids,and $Nucleoproteins$ contain nucleic acids as their prosthetic groups.
When the prosthetic group is a carbohydrate,the protein is classified as a $Glycoprotein$.
$Chromoproteins$ contain a pigment,$Lipoproteins$ contain lipids,and $Nucleoproteins$ contain nucleic acids as their prosthetic groups.
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91
BiologyEasyMCQAIPMT · 2000
During cell division,what is the structure called where spindle fibers attach to the chromosomes?
A
Chromocenter
B
Kinetochore
C
Centriole
D
Chromomere
Solution
(B) During cell division,the spindle fibers attach to the chromosomes at a specific disc-shaped protein structure located on the centromere known as the $Kinetochore$.
These structures are essential for the proper alignment and segregation of chromosomes during mitosis and meiosis.
These structures are essential for the proper alignment and segregation of chromosomes during mitosis and meiosis.
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92
BiologyEasyMCQAIPMT · 2000
What happens during the $S$ phase of the cell cycle?
A
The amount of $DNA$ in each cell doubles.
B
The amount of $DNA$ in each cell remains the same.
C
The number of chromosomes increases.
D
The amount of $DNA$ in each cell is halved.
Solution
(A) The $S$ phase (Synthesis phase) is a critical stage of the cell cycle occurring during interphase. During this phase,$DNA$ replication takes place. As a result,the amount of $DNA$ per cell doubles,although the number of chromosomes remains the same (the sister chromatids are formed).
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93
BiologyMediumMCQAIPMT · 2000
Plants grow in a magnesium-deficient soil,but what happens if urea is added to the soil?
A
Leaves become dark green
B
Flowering occurs early
C
Leaves turn yellow
D
Pigments are removed from the petals
Solution
(C) Magnesium is a central component of the chlorophyll molecule. Its deficiency leads to chlorosis,where leaves turn yellow because chlorophyll cannot be synthesized.
Urea is a nitrogen-rich fertilizer. When urea is added to the soil,it provides nitrogen,which promotes vegetative growth and increases chlorophyll synthesis.
However,if the soil remains deficient in magnesium,the plant cannot form functional chlorophyll despite the presence of nitrogen. In many cases,the rapid growth induced by nitrogen without sufficient magnesium exacerbates the chlorosis,causing the leaves to turn yellow more prominently or fail to green up.
Urea is a nitrogen-rich fertilizer. When urea is added to the soil,it provides nitrogen,which promotes vegetative growth and increases chlorophyll synthesis.
However,if the soil remains deficient in magnesium,the plant cannot form functional chlorophyll despite the presence of nitrogen. In many cases,the rapid growth induced by nitrogen without sufficient magnesium exacerbates the chlorosis,causing the leaves to turn yellow more prominently or fail to green up.
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94
BiologyEasyMCQAIPMT · 2000
Plants absorb zinc from the soil in the form of .........
A
$Zn$
B
$Zn^{2+}$
C
$ZnO$
D
$ZnSO_4$
Solution
(B) Plants absorb mineral nutrients from the soil primarily in the form of ions.
Zinc is an essential micronutrient for plants.
It is absorbed by plants from the soil in the form of divalent zinc ions,represented as $Zn^{2+}$.
Zinc is an essential micronutrient for plants.
It is absorbed by plants from the soil in the form of divalent zinc ions,represented as $Zn^{2+}$.
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95
BiologyMediumMCQAIPMT · 2000
Which enzyme catalyzes $CO_2$ fixation in $C_4$ plants?
A
$RuBP$ carboxylase
B
$PEP$ carboxylase
C
Carbonic anhydrase
D
Carboxydismutase
Solution
(B) In $C_4$ plants,the primary $CO_2$ fixation occurs in the mesophyll cells.
The enzyme responsible for this initial fixation is $PEP$ carboxylase (Phosphoenolpyruvate carboxylase).
This enzyme catalyzes the reaction between $CO_2$ and $PEP$ (a $3$-carbon compound) to form oxaloacetic acid $(OAA)$,which is a $4$-carbon compound.
$RuBP$ carboxylase (Rubisco) is involved in the Calvin cycle within the bundle sheath cells,but the initial fixation in $C_4$ plants is mediated by $PEP$ carboxylase.
The enzyme responsible for this initial fixation is $PEP$ carboxylase (Phosphoenolpyruvate carboxylase).
This enzyme catalyzes the reaction between $CO_2$ and $PEP$ (a $3$-carbon compound) to form oxaloacetic acid $(OAA)$,which is a $4$-carbon compound.
$RuBP$ carboxylase (Rubisco) is involved in the Calvin cycle within the bundle sheath cells,but the initial fixation in $C_4$ plants is mediated by $PEP$ carboxylase.
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96
BiologyMediumMCQAIPMT · 2000
In the light-dependent reaction of photosynthesis,the chloroplast is directly involved in which of the following processes?
A
Formation of phosphoglyceric acid
B
Fixation of $CO_2$
C
Formation of glucose and starch
D
Photolysis of water and phosphorylation
Solution
(D) The light-dependent reaction (light reaction) of photosynthesis occurs in the thylakoid membranes of the chloroplast.
During this process,light energy is captured by chlorophyll pigments.
This energy is used for two primary events:
$1$. Photolysis of water $(H_2O \rightarrow 2H^+ + 2e^- + 1/2 O_2)$,which releases oxygen as a byproduct.
$2$. Photophosphorylation,which involves the synthesis of $ATP$ and $NADPH$ using the energy derived from the electron transport chain.
Options $A$,$B$,and $C$ are associated with the light-independent reaction (Calvin cycle),which occurs in the stroma of the chloroplast.
During this process,light energy is captured by chlorophyll pigments.
This energy is used for two primary events:
$1$. Photolysis of water $(H_2O \rightarrow 2H^+ + 2e^- + 1/2 O_2)$,which releases oxygen as a byproduct.
$2$. Photophosphorylation,which involves the synthesis of $ATP$ and $NADPH$ using the energy derived from the electron transport chain.
Options $A$,$B$,and $C$ are associated with the light-independent reaction (Calvin cycle),which occurs in the stroma of the chloroplast.
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97
BiologyMediumMCQAIPMT · 2000
What is required for the fixation of one $CO_2$ molecule in the Calvin cycle?
A
$1\, ATP$ and $2\, NADPH$
B
$2\, ATP$ and $2\, NADPH$
C
$3\, ATP$ and $2\, NADPH$
D
$2\, ATP$ and $1\, NADPH$
Solution
(C) In the Calvin cycle,the fixation of one molecule of $CO_2$ requires $3\, ATP$ molecules and $2\, NADPH$ molecules.
Specifically,the process involves two stages of energy consumption:
$1$. Reduction phase: $2\, ATP$ and $2\, NADPH$ are used per $CO_2$ molecule.
$2$. Regeneration phase: $1\, ATP$ is used per $CO_2$ molecule to regenerate $RuBP$.
Therefore,the total requirement for the fixation of one $CO_2$ molecule is $3\, ATP$ and $2\, NADPH$.
Specifically,the process involves two stages of energy consumption:
$1$. Reduction phase: $2\, ATP$ and $2\, NADPH$ are used per $CO_2$ molecule.
$2$. Regeneration phase: $1\, ATP$ is used per $CO_2$ molecule to regenerate $RuBP$.
Therefore,the total requirement for the fixation of one $CO_2$ molecule is $3\, ATP$ and $2\, NADPH$.
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98
BiologyMediumMCQAIPMT · 2000
The first step of photosynthesis is:
A
Excitation of an electron from chlorophyll by a photon of light.
B
Formation of $ATP$.
C
Attachment of $CO_2$ to a $5$-carbon sugar.
D
Ionization of water.
Solution
(A) The first step of photosynthesis is the absorption of light energy by chlorophyll molecules.
When a photon of light strikes the chlorophyll molecule,it excites an electron to a higher energy state,causing it to be released or ejected from the chlorophyll molecule.
This process is known as photo-excitation of chlorophyll,which initiates the light-dependent reactions.
When a photon of light strikes the chlorophyll molecule,it excites an electron to a higher energy state,causing it to be released or ejected from the chlorophyll molecule.
This process is known as photo-excitation of chlorophyll,which initiates the light-dependent reactions.
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99
BiologyMediumMCQAIPMT · 2000
How many turns of the Calvin cycle are required for the formation of one molecule of glucose?
A
Eight
B
Two
C
Six
D
Four
Solution
(C) The Calvin cycle operates to fix $CO_2$ into organic compounds.
Each turn of the Calvin cycle fixes one molecule of $CO_2$ into a three-carbon sugar $(G3P)$.
Since one molecule of glucose $(C_6H_{12}O_6)$ contains $6$ carbon atoms,the cycle must turn $6$ times to incorporate $6$ molecules of $CO_2$ to produce one molecule of glucose.
Therefore,$6$ turns are required.
Each turn of the Calvin cycle fixes one molecule of $CO_2$ into a three-carbon sugar $(G3P)$.
Since one molecule of glucose $(C_6H_{12}O_6)$ contains $6$ carbon atoms,the cycle must turn $6$ times to incorporate $6$ molecules of $CO_2$ to produce one molecule of glucose.
Therefore,$6$ turns are required.
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100
BiologyEasyMCQAIPMT · 2000
Abscisic acid $(ABA)$ regulates which of the following?
A
Cell division
B
Leaf abscission and dormancy
C
Shoot elongation
D
Cell elongation and cell wall formation
Solution
(B) Abscisic acid $(ABA)$ is a plant growth inhibitor.
It plays a crucial role in the abscission of leaves and fruits.
It also induces dormancy in seeds and buds,which helps plants survive unfavorable environmental conditions.
Therefore,$ABA$ is primarily associated with the regulation of leaf abscission and dormancy.
It plays a crucial role in the abscission of leaves and fruits.
It also induces dormancy in seeds and buds,which helps plants survive unfavorable environmental conditions.
Therefore,$ABA$ is primarily associated with the regulation of leaf abscission and dormancy.
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101
BiologyEasyMCQAIPMT · 2000
The endangered largest lemur,$Indri$ $indri$,is native to which of the following regions?
A
Madagascar
B
Mauritius
C
Sri Lanka
D
India
Solution
(A) The $Indri$ $indri$,also known as the babakoto,is the largest living lemur species. It is endemic to the island of Madagascar,specifically found in the eastern rainforests of the island. Lemurs are primates that are found exclusively in Madagascar.
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102
BiologyMediumMCQAIPMT · 2000
Relative Biological Effectiveness $(RBE)$ is usually considered as the damage caused by ..........
A
Low temperature
B
High temperature
C
Radiation
D
Pollution
Solution
(C) Relative Biological Effectiveness $(RBE)$ is a comparison of the biological effectiveness of different types of ionizing radiation.
It is defined as the ratio of the dose of a standard radiation (usually $250 \text{ kV}$ $X$-rays) to the dose of the radiation in question that produces the same biological effect.
Therefore,$RBE$ is specifically used to measure the damage caused by radiation exposure.
It is defined as the ratio of the dose of a standard radiation (usually $250 \text{ kV}$ $X$-rays) to the dose of the radiation in question that produces the same biological effect.
Therefore,$RBE$ is specifically used to measure the damage caused by radiation exposure.
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103
BiologyMediumMCQAIPMT · 2000
What is the function of Copper-$T$?
A
Checks mutation
B
Stops fertilization
C
Stops zygote formation
D
Stops obliteration of blastocoel
Solution
(B) Copper-$T$ is a copper-releasing intra-uterine device $(IUD)$. It increases the phagocytosis of sperms within the uterus,suppresses sperm motility,and reduces the fertilizing capacity of sperms,thereby preventing fertilization.
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