Test: Algae (NCERT) - NEET MCQ

• Algae are primarily characterized by being chlorophyll-bearing, which allows them to carry out photosynthesis.
• They are simple, thalloid (lacking differentiated stems, leaves, and roots), autotrophic (producing their own food through photosynthesis), and are commonly found in aquatic environments, including both freshwater and marine habitats.
• Some can also thrive in various other habitats such as moist stones, soils, and wood.
• It's important to note that algae are not heterotrophic as they produce their own food through photosynthesis.

Fig: Chlorophyll bearing and mostly aquatic algae

Line in NCERT: "They are chlorophyll-bearing and largely aquatic."

The photosynthetic pigments in green algae mainly consist of two types, namely chlorophyll a and chlorophyll b. These pigments play a pivotal role in the process of photosynthesis by aiding in the absorption of light energy.

They harness the energy from sunlight and use it to power the process of photosynthesis, which is vital for the survival and growth of the algae. They do not possess other pigments like chlorophyll c, d or fucoxanthin, or phycoerythrin as indicated in the other options. Therefore, the correct answer is Option A: Chl a and b.

Line in NCERT: "Their plant body may be unicellular, colonial or filamentous. They are usually grass green due to the dominance of pigments chlorophyll a and b."

Statement (i): Plant body is thalloid.

• Algae, being simple plants, do not have well-differentiated plant bodies. Instead, they have a thalloid plant body, which means their bodies are not differentiated into stems, leaves, and roots like higher plants. This statement is true.

Statement (ii): Largely aquatic.

• Algae are predominantly aquatic organisms. They are found in a variety of habitats, ranging from freshwater to marine environments, and some can even be found on moist stones, soils, or wood. Thus, this statement is also true.

Statement (iii): Reproduction by vegetative, asexual and sexual methods.

• Algae reproduce through a variety of methods including vegetative (by fragmentation), asexual (by the formation of spores), and sexual (by the fusion of gametes) reproduction. So, this statement is accurate as well.

Statement (iv): Chlamydomonas, Volvox, and Ulothrix are the multicellular algae.

• This statement is partially correct. Chlamydomonas is a unicellular green alga, not multicellular. On the other hand, Volvox and Ulothrix are indeed multicellular algae. Therefore, as a whole, this statement is not completely accurate.

Based on the analysis of each statement, options (i), (ii), and (iii) are true. Therefore, the correct answer is Option C: Statements (i), (ii), and (iii) are true.

Line in NCERT: "Algae usually reproduce vegetatively by fragmentation, asexually by formation of different types of spores and sexually by formation of gametes which may show isogamy, anisogamy or oogamy."

The algae shown in figure are Chlamydomonas, Volvox and Chara respectively, belonging to class Chlorophyceae.

Class Chlorophyceae (Green Algae):

• These algae are commonly known as green algae.
• They are usually found in fresh water and marine environments.
• The pigments include chlorophyll a and b, which gives them a bright green color.
• They store food in the form of starch.
• Most of them are unicellular, but some are multicellular.

Line in NCERT: "The algae are divided into three main classes: Chlorophyceae, Phaeophyceae and Rhodophyceae."

Cell wall of green algae is thin, transparent andd form and consists of outer pectic and inner cellulosic layers. It is smooth but in most of species it gets thickened at the anterior end to form an apical papilla.

Line in NCERT: "Green algae usually have a rigid cell wall made of an inner layer of cellulose and an outer layer of pectose."

Pyrenoids are cellular micro-compartments, and are not membrance bound organelles. Pyrenoids are found within chloroplast. Chloroplasts generally contain one to many pyrenoids for storage of starch. 

Line in NCERT: "Most of the members have one or more storage bodies called pyrenoids located in the chloroplasts."

Ulothrix is a filamentous form of algae. Filamentous algae are characterized by their thread-like structures composed of a chain of cells.

Fig: Ulothrix

Other examples of filamentous algae include Spirogyra and Cladophora. Volvox (Option A) is a colonial alga, Fucus (Option B) is a marine brown alga, and Porphyra (Option C) is a red alga.

Line in NCERT: "The form and size of algae is highly variable, ranging from colonial forms like Volvox and the filamentous forms like Ulothrix and Spirogyra."

Fusion of two gametes dissimilar in size, as in species of Eudorina is termed as anisogamous acc. to ncert textbook.

Line in NCERT: "Fusion of two gametes dissimilar in size, as in species of Eudorina is termed as anisogamous."

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.

Line in NCERT: "Some commonly found green algae are: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara (Figure 3.1a)."

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.

Line in NCERT: "Vegetative reproduction is by fragmentation. Each fragment develops into a thallus."

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.

Line in NCERT: "Fusion between one large, non-motile (static) female gamete and a smaller, motile male gamete is termed oogamous, e.g., Volvox."

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.

Line in NCERT: "Certain marine brown and red algae produce large amounts of hydrocolloids (water holding substances), e.g., algin (brown algae) and carrageen (red algae) which are used commercially."

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.

Line in NCERT: "Fusion between one large, non-motile (static) female gamete and a smaller, motile male gamete is termed oogamous, e.g., Volvox, Fucus."

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.

Line in NCERT: "Such reproduction is called isogamous."

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.

Line in NCERT: "The members of phaeophyceae or brown algae are found primarily in marine habitats."

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.

Line in NCERT: "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."