Algae (NCERT) - NEET Free MCQ Test with solutions

Dictyoia is a ribbon shaped dichotomously branched marine brown alga that grows in shallow waters. Its frond is flat and dichotomously branched.

Polysiphonia is a small, upright, bushy marine red alga, fixed to the substratum by rhizoids, hold fast, etc.

Vegetative reproduction in algae occurs through fragmentation. When a part of the algal thallus breaks off, it can develop into a new individual. This method of reproduction is common in many types of algae.

Volvox is colonial green alga. The cells are like unicelled alga chlamydomonas and are definitely organized in the form of a colony called coenohimn. The coenobia of Volvox are largest, highly differentiated and well evolved among motile forms. Each coenobium is motile, the movement is brought about by the joint action of the flagella of individual call.

Certain red and brown algae are sources of hydrocolloids used in various commercial applications. Algin is extracted from brown algae, while carrageen is obtained from red algae. These hydrocolloids are used in industries for their thickening, stabilizing, and gelling properties in products like food, cosmetics, and pharmaceuticals.

Volvox shows advanced oogamy which takes place by the formation of antheridia and oogonia. They may be formed on the same plant (monoeclous) or on different plants(dioecious). The sex-organs are produced fewer in number.

The underwater forest consists of a variety of seaweed species. These "seaweeds" are not only essential for the ocean's ecosystem, but they also have a significant impact on human life. The three primary types of seaweeds that form these underwater forests include:

• Kelps: This is a common type of seaweed. It grows in "forests" in the cold waters of the world's oceans. Kelp plays a crucial role in ocean ecosystems and is a source of food and habitat for a variety of marine species.
• Laminaria: This is another type of kelp that forms dense, forest-like groupings underwater. Laminaria serves as a habitat for many marine species. Besides, it is used in food and medicine due to its high iodine and potassium content.
• Macrocystis: Also known as giant kelp, Macrocystis is the largest of all algae and can grow up to 50 meters in length. It forms dense forests that provide shelter and food for a diverse range of marine species. It is also used in the food industry as a thickener and stabilizer.

Hence, the correct answer is D: All of these, as all three - Kelps, Laminaria, and Macrocystis - are types of "seaweeds" that form the underwater forest.

Isogamous type of sexual reproduction is found in Ulothrix and in majority, the plants are heterothallic. The gametes are found in large number, I.e. 32 to 64 in each gametangium.

Nostoc and Anabaena are nitrogen fixing blue-green algae, Azotobacter is free-living nitrogen fixing bacterium, while Spirogyra is a green alga which does not fix atmospheric nitrogen.

Seaweeds are rich in minerals such as iodine, calcium sodium, magnesium, potassium, iron, zinc, copper. Seaweeds also provide fibre, vitamins, enzyme and high quality protein.

Phaeophyceae, commonly known as Brown Algae, predominantly inhabit marine environments. They are most commonly found in cold water regions and are especially abundant in the temperate and polar zones.

Adaptation: Brown algae are well adapted to survive in marine environments due to their strong holdfasts, which help them attach securely to rocks and other substrates, preventing them from being swept away by strong currents or waves.

Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic (both fresh water and marine) organisms. They occur in a variety of other habitats: moist stones, soils and wood.

The plant body is usually attached to the substratum by a holdfast, and has a stalk, the stipe and leaf like photosynthetic organ – the frond. Vegetative reproduction takes place by fragmentation.