Test: Ulothrix - Class 11 MCQ

Asexual reproduction in algae is by production of different types of spores,the most common being the Zoospores. They are flagellated (motile) and on germination gives rise to new plants.

The above mentioned pigments produce the colour of green. 

Ulothrix is a genus of filamentous green algae, generally found in fresh and marine water. Its cells are normally as broad as they are long, and they thrive in the low temperatures of spring and winter. They become attached to surfaces by a modified holdfast cell. Reproduction is normally vegetative.

Zygospore undergoes zygotic meiosis and forms 4 haploid nuclei of which three degenerate. So one haploid nuclei take part and one new filament is formed.

Chlamydomonas is a motile unicellular alga and belongs to the genus of green algae. This is found in stagnant water, freshwater, seawater, damp soil and even in snow. Asexual reproduction in algae takes place through the production of spores. When zoospores lose their motility these are referred to as aplanospores and in certain green algae these aplanospores have thickened walls and are known as hypnospores. These are resting spores released in the dormant state. 

Therefore, the correct answer is option A

The cells of the filaments are arranged end to end. They are barrel-shaped or cylindrical in shape. The apical cell is somewhat rounded at its terminal end whereas, the basal cell is elongated and does not have chlorophyll. It is also called as the basal holdfast, which attaches the filament to the substratum.

Reduction division is nothing but meiosis. In Ulothrix, reduction division occurs at the time of zygospore germination.

Ulothrix is a genus of green algae in the family Ulotrichaceae. Ulothrix is a genus of filamentous green algae, generally found in fresh and marine water.

An akinete is an enveloped, thick-walled, non-motile, dormant cell formed by filamentous, heterocyst-forming cyanobacteria under the order Nostocales and Stigonematales. Once conditions become more favorable for growth, the akinete can then germinate back into a vegetative cell.

Ulothrix is a genus of filamentous green algae, generally found in fresh and marine water. Its cells are normally as broad as they are long, and they thrive in the low temperatures of spring and winter. They become attached to surfaces by a modified holdfast cell. Reproduction is normally vegetative.

Asexual reproduction takes place in winter, during its active growth. It takes place by the formation of zoospores, akinetes and palmella stage. a.The protoplast either develops into single zoospore (U. fimbriata) or undergoes division and form 2, 4, 8, 16 or 32 units.

The eyespot or stigma is a photoreceptive organelle found in the flagellate of green algae like Chlamydomonas and some other unicellular photosynthetic organisms such as euglenoids. It allows the cells to sense light direction and intensity and respond to it by swimming either towards the light (positive phototaxis) or away from the light (negative phototaxis). A related response occurs when cells are briefly exposed to high light intensity, causing the cell to stop, briefly swim backward, then change swimming direction. Eyespot-mediated light perception helps the cells in finding an environment with optimal light conditions for photosynthesis. Eyespots are the simplest and most common "eyes" found in nature, composed of photoreceptors and areas of bright orange-red pigment granules. Signals relayed from the eyespot photoreceptors result in alteration of the beating pattern of the flagella, generating a phototactic response.

Sexual reproduction of Ulothrix begins after the growth period/ Vegetative season. Sporophytic generation is represented only by the zygote. In the life cycle of Ulothrix, Zygote is very short in duration. Gametes are formed in semi drying condition and released in the morning.

When zoospores settle on any substratum, the cysts almost invariably germinate towards the host. This raises the possibility that zoospores might pre- align during encystment.
Calcium has an important role in zoospores motility. It is also required for cyst adhesion and subsequent cyst germination.

An akinete is formed under an unfavourable condition. It is an enveloped, thick- walled, non- motile, dormant cell formed by filamentous, heterocyst- forming cyanobacteria, ulothrix under the order Nostocales and Stigonematales. Akinetes are resistant to cold and desiccation.

Hypnospores: Under certain conditions the aplanospores secrete thick walls around them and store abundant food reserves. These thick walled aplanospores are called the hypnospores. Because of the thick wall, hypnospore may undergo a long resting period and may survive even in some unfavourable conditions (Ulothrix).

In most species, all the cells can form reproductive bodies. Ulothrix reproduces vegetatively by fragmentation, asexually by nonmotile resting spores (aplanospores) and motile quadriflagellate spores (zoospores), and sexually by biflagellate gametes.

Ulothrix is heterothallic. It means fusing isogametes have different strains genetically. Sexual reproduction of Ulothrix begins after the growth period/ Vegetative season.

Ulothrix is a genus of filamentous green algae, generally found in fresh and marine water. Its cells are normally as broad as they are long, and they thrive in the low temperatures of spring and winter. They become attached to surfaces by a modified holdfast cell. Reproduction is normally vegetative.

Filaments unbranched, attached by a single basal rhizoidal cell, or rhizoids arising from other cells. Cells cylindrical, longer or shorter; chloroplast parietal, girdle-shaped, usually lobed, encircling normally over three quarters of the cell, with one or more pyrenoids.

Unlike carboxysomes, pyrenoids are not delineated by a protein shell (or membrane). A starch sheath is often formed or deposited at the periphery of pyrenoids, even when that starch is synthesised in the cytosol rather than in the chloroplast.

Linear means no connections.
But Ulothrix is having plasmodesmatal connections. They are the connections of cytoplasms of neighbouring cells established through the plasmodesmata. The plant cells exchange small molecules with their neighboring cells through these plasmodesmatal connections.

The thallus of Ulothrix is multicellular, filamentous, unbranched and bright green in colour. All the cells of the filament are similar but basal cell and apical cell are different. The upper most or apical cell is somewhat dome-shaped and basal cell is elongated and narrow at the base.

Ulothrix is a genus of filamentous green algae which are found in marine and fresh waters habitats.
They have a single girdle-shaped or band-shaped chloroplast near the peripheral region of the cytoplasm (near the cell wall).
So, the correct answer is 'Girdle-shaped'.

The plant body consists of unbranched, uniseriate filaments. The cells of the filaments are arranged end to end. They are barrel-shaped or cylindrical in shape. The apical cell is somewhat rounded at its terminal end whereas, the basal cell is elongated and does not have chloroplast. It is also called as the basal holdfast, which attaches the filament to the substratum.
 

A red colour eyespot is found in zoospores for reception of light, which is made up of carotenoids (Hematochrome).

The stage of Palmella occurs in the Chlamydomonas and Euglena. They are the green algae, and have 325 species all of which are the unicellular flagellates.

The gametangia then fuse into a zygosporangium. In other fungi, cells from two hyphae with opposing mating types fuse, but only the cytoplasm is fused (plasmogamy). The two nuclei do not fuse, leading to the formation of a dikaryon cell that gives rise to a mycelium consisting of dikaryons.

In most species, all the cells can form reproductive bodies. Ulothrix reproduces vegetatively by fragmentation, asexually by nonmotile resting spores (aplanospores) and motile quadriflagellate spores (zoospores), and sexually by biflagellate gametes.