Algae (General) Questions in English

(C) In $Spirogyra$,sexual reproduction occurs through conjugation. The gametes involved are morphologically similar (isogametes) in size and shape,although they may be physiologically distinct. Therefore,it is classified as isogamy.

(C) $Spirogyra$ is a filamentous green alga that exhibits both asexual and sexual modes of reproduction.
$1$. Asexual reproduction occurs primarily through fragmentation,where the filament breaks into smaller pieces,each capable of growing into a new individual.
$2$. Sexual reproduction occurs through a process called conjugation,where two filaments align and form a conjugation tube,allowing the transfer of genetic material to form a zygospore.

(C) Prof. $M.O.P.$ Iyengar, a renowned Indian phycologist, extensively studied the genus $Spirogyra$.
In $1958$, he reported the phenomenon of direct lateral conjugation in the species $Spirogyra \text{ jogensis}$.
In this type of conjugation, the conjugation tubes are formed between adjacent cells of the same filament, and the protoplast of one cell moves into the other directly through the lateral wall.

(C) $Spirogyra$ is a filamentous green alga that exhibits isogamy or physiological anisogamy. It is homothallic,meaning the same filament or different filaments of the same mating type can undergo conjugation. Therefore,the statement that it exhibits heterothallism is incorrect. $Spirogyra$ possesses polycentric chromosomes,a complex nucleolus,and spiral chloroplasts containing multiple pyrenoids (not a single pyrenoid in each chloroplast).

(A) In $Spirogyra$,the zygote undergoes a resting period and is known as a $zygospore$.
During the germination of the $zygospore$,meiosis occurs,resulting in the formation of haploid zoospores.
Therefore,the spores produced after the resting period of the $zygospore$ are haploid.

(B) The plant body of $Spirogyra$ is haploid $(n)$.
During sexual reproduction,gametes fuse to form a diploid $(2n)$ zygote,which is often referred to as a zygospore.
Since the organism is haploid,the zygote must undergo meiosis to restore the haploid condition.
Therefore,$Spirogyra$ exhibits a haplontic life cycle where zygotic meiosis occurs.

(D) In $Spirogyra$,the gametes are morphologically identical (isogamous) but show physiological differences in their behavior during conjugation,which is termed as physiological anisogamy.
In this process,one filament acts as the male (active) and the other as the female (passive) during the formation of the zygospore.

(A) The life cycle in $Spirogyra$ is haplontic.
In this type of life cycle,the dominant phase is the haploid $(n)$ vegetative body.
The diploid phase is represented only by the zygospore $(2n)$,which undergoes meiosis to produce haploid zoospores or filaments.

(D) $Ulothrix$ contains a characteristic chloroplast that is girdle-shaped or ring-shaped (collar-shaped). This type of chloroplast typically occupies the peripheral region of the cell and extends around the cell like a band or girdle.

(A) $Ulothrix$ produces isogametes.
These gametes are biflagellate and morphologically similar in size and shape,but they differ in their physiological nature (mating types).

(B) In $Ulothrix$,the life cycle is haplontic. The zygote undergoes a period of dormancy and forms a thick-walled zygospore. When favourable conditions return,the zygospore undergoes meiosis $(reduction\, division)$ to produce $4-16$ haploid meiospores. Each of these meiospores germinates to form a new $Ulothrix$ filament.

(B) The basal cell of $Ulothrix$ is elongated and colourless. It is known as the holdfast or hapteron,which helps in the attachment of the filament to the substratum.

(D) $Ulothrix$ is a green alga belonging to the class $Chlorophyceae$.
In $Ulothrix$,the gametes are produced through sexual reproduction.
These gametes are flagellated and motile,which allows them to swim in the aquatic environment to facilitate fertilization.
Specifically,the gametes of $Ulothrix$ are biflagellate,meaning they possess exactly $2$ flagella.

(C) $Ulothrix$ is a filamentous green alga.
The filament consists of a single row of cylindrical cells.
The lowermost cell of the filament is specialized for attachment to the substratum (like rocks or wood).
This specialized,colorless,and elongated basal cell is called the $Holdfast$.

(D) The basal cell in $Ulothrix$ is a specialized,non-green cell that serves as a holdfast for attachment to the substrate.
Although it lacks chlorophyll,it contains a nucleus and cytoplasm,indicating that it is a living cell.
Its specialized function of attachment,distinct from the photosynthetic function of other cells in the filament,represents the beginning of the division of labour in multicellular organisms.

(D) In $Ulothrix$,when two biflagellate gametes of $(+)$ and $(-)$ strains fuse,they form a zygote.
This zygote is initially motile and possesses four flagella,hence it is called a tetraflagellate zygote.
Subsequently,the zygote secretes a thick wall and becomes non-motile to form a resting structure known as a zygospore.

(A) In $Ulothrix$,sexual reproduction occurs through the fusion of morphologically similar gametes,a process known as $Isogamy$.
These gametes are flagellated and motile.
Therefore,the correct mode of sexual reproduction in $Ulothrix$ is $Isogamy$.

(B) $Ulothrix$ is a filamentous green alga.
Each cell of $Ulothrix$ contains a single,girdle-shaped chloroplast.
This chloroplast contains a few pyrenoids (typically $1-3$),which are specialized centers for starch storage.

(A) $Ulothrix$ is a genus of non-branching filamentous green algae.
It is typically found attached to stones,wood,or other submerged objects in freshwater environments by a specialized basal cell called a holdfast.
Therefore,it is an attached unbranched filament.

(C) $Ulothrix$ is an unbranched filamentous green alga.
It consists of numerous cylindrical cells joined end to end in a single row.

(A) $Ulothrix$ is a genus of non-branching filamentous green algae.
It is primarily found in fresh water environments.
It typically inhabits cool,aerated fresh water such as rain puddles,lakes,cold springs,or the slow-moving water of streams.

(C) $Ulothrix$ belongs to the class Chlorophyceae,which are commonly known as green algae.
Green algae contain chlorophyll $a$ and chlorophyll $b$ as their primary photosynthetic pigments.
They also possess accessory pigments such as carotenes and xanthophylls.
Therefore,the correct set of pigments present in $Ulothrix$ is chlorophyll $a$,chlorophyll $b$,carotenes,and xanthophylls.

(A) $Ulothrix$ is a genus of non-branching filamentous green algae. Each vegetative cell of $Ulothrix$ contains a single,girdle-shaped or parietal chloroplast.

(B) The zoospores of $Ulothrix$ are motile,flagellated asexual spores. During their release,a small pore is formed in the lateral wall of the parent cell. The zoospores are then liberated through this pore,typically enclosed within a thin vesicle of mucilage.

(A) $Ulothrix$ is a genus of non-branching filamentous green algae. It is found in fresh and marine water. Its reproductive stages,such as zoospores and gametes,are flagellated and motile,which allows them to move in the aquatic environment.

(D) Sexual reproduction in $Spirogyra$ occurs through conjugation.
In this process,the two gametes involved are morphologically identical (isogamous),meaning they look the same under a microscope.
However,they are physiologically distinct,where one acts as the male (donor) and the other as the female (recipient) gamete.
Therefore,it is described as morphological isogamy and physiological anisogamy.

(C) . Scalariform conjugation is the most common and advanced type of conjugation observed in the genus $Spirogyra$. In this process,two filaments lie side-by-side,and conjugation tubes are formed between the cells of opposite mating types,resembling a ladder-like structure.

(D) In $Spirogyra$,the zygote undergoes meiosis to form four haploid nuclei.
However,three of these nuclei degenerate,and only one functional nucleus remains.
This single functional nucleus develops into a new haploid $Spirogyra$ filament upon germination.
Therefore,each zygospore gives rise to only one plant.

(D) In $Spirogyra$,the zygote (zygospore) undergoes meiosis to form $4$ haploid nuclei. Out of these $4$ nuclei,$3$ degenerate and only $1$ remains functional. This functional nucleus develops into a new $Spirogyra$ filament. Therefore,it does not produce zoospores. Thus,the correct option is $(d)$.

(B) Sexual reproduction in $Spirogyra$ occurs through a process called conjugation. In this process,two morphologically identical (isogamous) but physiologically dissimilar non-motile (non-ciliated) gametes fuse to form a zygospore. This type of reproduction is known as physiological anisogamy.

(C) $Spirogyra$ increases its body length because every cell of the filament is capable of growth,division,and self-maintenance.
Each cell in the $Spirogyra$ filament contains a nucleus and is physiologically independent,allowing all cells to divide by mitosis to contribute to the elongation of the filament.

(D) $Stigeoclonium$ shows a heterotrichous habit,which is differentiated into a prostrate system and an erect system.
In this type of growth,the thallus consists of a creeping prostrate portion that attaches to the substratum and an erect portion that grows upwards for photosynthesis and reproduction.

(B) $A.$ Cyanophyceae: The blue-green colour is due to the presence of phycobilin pigments like $c-phycocyanin$.
$B.$ Chlorophyceae: The green colour is due to the dominance of chlorophyll $a$ and $b$,along with carotenoids.
$C.$ Phaeophyceae: The brown colour is due to the presence of the pigment $fucoxanthin$.
$D.$ Rhodophyceae: The red colour is due to the presence of the red pigment $r-phycoerythrin$.

(A) Some red algae (Rhodophyceae) deposit calcium carbonate on their cell walls.
These are known as coralline algae,for example,$Corallina$.
Due to the deposition of calcium carbonate,they appear hard and rock-like,similar to corals,and contribute to the formation of coral reefs along with corals.

(D) The coenocytic condition refers to a multinucleated cell or organism where the cytoplasm is continuous and not divided by cell walls. Among the given options,$Vaucheria$ (a genus of yellow-green algae) exhibits a coenocytic thallus,meaning it consists of a single,large,tubular cell containing many nuclei.

(A) In most algae,the chloroplasts are structurally simpler compared to higher plants.
Specifically,the thylakoids in algal chloroplasts are often arranged singly or in groups of two or three,but they do not form the highly organized,stacked structures known as $Grana$.
$Grana$ are characteristic features of the chloroplasts in higher plants,where thylakoids are stacked like coins.
Therefore,the chloroplasts of algae usually lack $Grana$.

(A) In most higher plants (like pea and gram) and green algae,thylakoids are stacked together to form grana,where each granum consists of multiple thylakoids.
However,in red algae (Rhodophyta),the thylakoids are not stacked into grana; instead,they occur singly within the chloroplast.
Therefore,the number of thylakoids per granum is effectively one in red algae.

(D) Formalin is a chemical fixative used to preserve biological specimens.
When a $Spirogyra$ filament is preserved in formalin,the cell membrane and cytoplasm are chemically fixed and denatured,rendering the cell dead and non-functional.
Osmosis and plasmolysis are physiological processes that require a living,semi-permeable membrane to occur.
Since the cells are dead,they lose their selective permeability,and therefore,no osmotic movement of water occurs when placed in a hypertonic solution.
Thus,nothing happens to the filament.

(D) During the day,algae perform photosynthesis,which releases $O_2$ gas as a byproduct.
These $O_2$ bubbles get trapped within the algal filaments or thalli,making them buoyant and causing them to float on the water surface.
At night,photosynthesis stops,and the $O_2$ bubbles are either consumed in respiration or escape into the water,causing the algae to lose buoyancy and sink.

(D) Chlorophyll $e$ is a rare form of chlorophyll found in certain algae. It is specifically reported in some members of the class $Xanthophyceae$ (yellow-green algae),which are commonly known as Xanthophytes. It is not found in Rhodophytes (red algae),which typically contain chlorophyll $a$ and $d$.

(D) The brown colour of brown algae $(Phaeophyceae)$ is primarily due to the presence of a specific carotenoid pigment called $Fucoxanthin$.
$Fucoxanthin$ masks the green colour of chlorophyll $a$ and $c$,giving these algae their characteristic brown appearance.

(B) The antibiotic "chlorellin" is a broad-spectrum antibiotic extracted from the green alga $Chlorella$ (specifically $Chlorella$ $vulgaris$).
It exhibits antibacterial properties against various Gram-positive and Gram-negative bacteria.
Therefore, the correct genus is $Chlorella$.

(C) Hydrophytes are plants that grow in water or in very wet environments.
In these plants,vascular tissues (xylem and phloem) are often absent or poorly developed because water is readily available and does not need to be transported over long distances.
They possess well-developed aerenchyma,which is a specialized tissue containing large air spaces.
This aerenchyma provides buoyancy,helping the plants to float on the water surface,and facilitates the exchange of gases in submerged conditions.

(A) The correct answer is $A$.
In certain submerged hydrophytes,such as $Wolffia$,roots are completely absent.
Furthermore,submerged hydrophytes lack stomata because they absorb water and gases directly through their body surface.
While some floating hydrophytes possess stomata on their upper surface,submerged hydrophytes generally lack them entirely to prevent water loss or because they are not needed for gas exchange in an aquatic environment.

(D) Phycobilins are water-soluble accessory photosynthetic pigments. They are characteristic pigments found in $Cyanobacteria$ (Blue-green algae) and $Rhodophyceae$ (Red algae). Since $Rhodophyceae$ is the class name for Red algae, and Blue-green algae are $Cyanobacteria$, all the given options represent organisms that contain phycobilins. Therefore, the correct answer is $All \text{ of the above}$.

(D) Photosynthesis is the process by which green plants and other organisms convert light energy into chemical energy.
While terrestrial plants like trees and shrubs contribute to photosynthesis,the vast majority of photosynthesis on Earth occurs in aquatic environments.
Algae,particularly phytoplankton in oceans,are responsible for approximately $90\%$ or $9/10$th of the total global photosynthesis.
Therefore,the correct answer is $D$.

(D) Chlorophyll $e$ is a rare form of chlorophyll found primarily in certain algae. Specifically,it is characteristic of the class Xanthophyceae (yellow-green algae),also known as Xanthophytes. It is not found in higher plants or most other algal groups.

(A) Professor $M.O.P. Iyengar$ is widely recognized as the father of modern phycology in India. He made significant contributions to the study of algae,particularly in the taxonomy and morphology of Indian algae. His extensive research and dedication to the field established a strong foundation for phycological studies in the country.

(B) The scientific study of algae is known as Phycology (also called Algology). Botany is the study of plants in general,while Protistology is the study of protists.

(C) Among the given options,$Algae$ (specifically cyanobacteria or blue-green algae) are considered the first photosynthetic organisms to have evolved on Earth. They played a crucial role in oxygenating the Earth's atmosphere through the process of photosynthesis. Viruses and viroids are non-cellular entities that require a host cell to replicate,and fungi are heterotrophic organisms that typically evolved after the establishment of autotrophic life forms.