Multiple Choice Questions (MCQs): Algae - Grade 11 MCQ

Thallophyta (algae) reproduce sexually when male gametes and female gametes fuse to form zygote. Zygote immediately undergoes meiosis and it gives haploid gametes. Thus, embryo is not formed.
So, the correct option is 'Zygotic meiosis'.

Chlamydomonas is best example for the evolution of sexual reproduction as the evolution of sex in algae has not taken place in any one phylogenetic line. This has taken place along several independent lines. For example, in Volvocales, where Gonium is isogamous, Pandorina slightly anisogalnous, Eudorina and Pleodorina marked by anisogamy and Volvox oogamous. It is correlated with the evolution from isogamy to oogamy through anisogamy. Whereas on the other hand, in another genus of Volvocales, i.e., Chlamydomonas, where species within the genus show all gradations from isogamy to oogamy, e.g., Chlamydomonas snowiae is isogamous, C. braunii is anisogamous and C. coccifera is oogamous.  
Thus, the correct answer is option A.

• Multiple fission is a process through which many individuals are produced by repeated nuclear division.
• Multiple fission takes place under unfavourable conditions.
• During multiple fission, an outer layer called cyst is formed.
• Nucleus divides repeatedly and new individuals are formed inside the cyst after which cyst breaks to release new individuals.

• Most of the algae reproduce using spore formation.
• Asexual spores are called as zoo-spores and the reproductive part in algae is called zoosporangium.
• Under favourable conditions, these organisms germinate to form new organism.
• Zoo-spores are motile and flagellated.

Classification of algae is mainly based upon the nature of their pigments.
Red Algae (Rhodophyceae) are characterized by the pigments - Phycoerythrin and Phycocyanin.
Brown Algae (Phaeophyceae) are brown due to the pigment Fucoxanthin.
Green Algae (Chlorophyceae) are characterized by pigments Chlorophyll-a, b, Carotenes, Xanthophyll. Hence option C is correct.

A species of yellow-green alga called Vaucheria sessilis is an example of a sexually reproducing alga. The reproductive structures consist of an antheridium, which contains male gametes, and two oogonia, which contain female gametes.

Correct option is D. Fucus
 Fucus are brown algae which is found in the intertidal zones of rocky seashores. These algae belong to the class Phaeophyceae and order Fucales, which stored food in the form of laminarin, mannitol, and oil. Mannitol is stored as a food reserve in Fucus. They are common littoral seaweed growing in the hard-rocky areas of the sea.

The green algae are a large, informal grouping of algae consisting of the Chlorophyta and Charophyta/Streptophyta, which are now placed in separate divisions, as well as the potentially more basal Mesostigmatophyceae, Chlorokybophyceae and Spirotaenia.

Clamydomonas and Ulothrix in green algae best explains the evolution of sexual reproduction. 
The first sexuality was seen in the Clamydomonas and Ulothrix in the from of isogamy that the gamates formed were of plus and minus strains. Next evolution is seen is the ansiogamy that the gametes are of different size. Hence, the correct option is Option A. 
The further more advanced evolution in the sex repdroduction is seen in the red algae and brown algae. so the Options B and C are not correct.

• The vegetative cells in Phaecophyceae are made up of two layers with the inner one being made of cellulose and the other being made of gelatinous coating of algin.
• A leaf like photosynthetic organ in Phaecophyceae is called as frond.
• They also have a stalk called stipe and a substratum called as holdfast.

The brown algae contains xanthophyll pigment fucoxanthin, chlorophyll 'a' and 'c' (no chlorophyll b), beta-carotene. 
Red algae contain chlorophyll  'a'  and 'd' as well as phycobilins, red and blue pigments involved in photosynthesis. 
Yellow green algae contains chlorophyll 'a' but lack chlorophyll 'b'. They possess chlorophylls 'e' or 'c'. Besides these they also possess xanthophylls and beta carotene.
Therefore, the correct answer is option B.

• The male gamete in sexual reproduction of algae is called antherozoid and the female gamete is called egg.
• These two gametes fuse to form a zygote which will further develop to form spores.

The fact that the land surface is covered in plants, not algae, indicates that plants are the most effective photoautotroph in most terrestrial habitats. In the open ocean, however, you will find mostly microalgae and some cyanobacteria, such as Prochlorococcusare particularly numerous. If you are wondering why these algae, which have a higher photosynthetic efficiency (measured as carbon fixed per quantity of photons), lose out to plants on land, then the short answer is that efficiency very rarely confers a reproductive or competitive advantage in biology.
As for why cyanobacteria and microalgae are more efficient at photosynthesis, it is mostly because they are small, (usually) single-celled, and have a enzymes to actively pump carbon dioxide into their cells (plants rely on passive diffusion). Being small gives them a very high surface-to-volume ratio. Being single-celled means that all cells are doing photosynthesis as opposed to a plant which needs to feed non-photosynthetic tissues. The carbon dioxide pumping enzymes lets cyanobacteria and microalgae avoid some of the harmful byproducts of photosynthesis that accumulate when there isn’t enough carbon dioxide in the cell to match the supply of energy from the light reactions.