The seven divisions of organisms that are considered within the algae are the Euglenophyta, Chrysophyta, Pyrrophyta, Chlorophyta, Rhodophyta, Paeophyta, and Xanthophyta. These divisions are separated on the basis of various features including their morphology and the biochemistry of their pigments, cell walls, and energy-storage compounds. The colors of these various algae types differ according to their particular mixtures of photosynthetic pigments, which typically include a combination of one or more chlorophylls and various accessory pigments.

One of the simplest multicellular organisms is algae. They are seen growing in the freshwater of marine habitats. They are also eukaryotic organisms. Algae can grow rapidly when exposed to stagnant waters. An adequate amount of sunlight, temperature and aquatic habitat leads to the rapid growth of slimy, green patches containing chlorophyll called algae.

The cell wall of the unicellular green alga Chlamydomonas consists of glycoproteins, which also occurs in the extracellular matrix of multicellular green algae and higher plants.

Algae have a cell wall containing cellulose, Galatians, and mannan.

Heterocysts are the thick-walled cells formed in cyanobacteria (Nostoc) and are responsible for nitrogen fixation in the state of nitrogen starvation by the use of enzyme nitrogenase. These are specialized pale yellow structures  which help in nitrogen formation during aerobic conditions.

The correct answer is D.

Binary fission is a form of asexual reproduction in Amoeba. Zoospore is the flagellated spores present in algae for the means of asexual reproduction. Conidia are unicellular asexually produced spores in penicillium. Hydra reproduces by budding by the use of regenerative cells. Sponge reproduce asexually by gemmules which are the internal buds found in sponges.

The correct answer is B.

Algae are important as primary producers of organic matter at the base of the food chain. They also provide oxygen for other aquatic life. Algae may contribute to mass mortality of other organisms, in cases of algal blooms, but they also contribute to economic well- being in the form of food, medicine and other products. In tropical regions, coralline algae can be as important as corals in the formation of reefs. They may form important constituent of human food (diet) in future. In future when world population will be very much, to provide them all nutritious food, algae will be used as alternate source of energy.

The major pigments present in algae is chlorophyll. It is a photosynthetic pigment. Apart from it, algae contain carotenoids and phycobilins pigments. Haemoglobin pigment is present in the red blood cells. It carries oxygen from the lungs to different parts of the body. Plasma is the colourless liquid part of the blood which contains all the components of blood except red blood cells, white blood cells and platelets.

Algae growing on a rock is called as epilithic. Endolithic algae live in porous rocks or coral and chasmolithic algae grow in rock fissures. So, option C is the correct answer.

Algae are unicellular or multicellular photosynthetic, eukaryotic organisms that can occur in salt or fresh waters, or on the surfaces of moist soil or rocks. Algae make their own energy or food from the sun but they also need water, correct temperature and nutrients to grow. Hence they usually live in water or damp environments. Algal growth is a natural occurrence in all water bodies and is the base of the aquatic food chain.

Phycology is the scientific study of algae. Phycology or Algology is a branch of life science and often is regarded as a sub-discipline of botany. Algae are important as primary producers in aquatic ecosystems. Hence, the phycology deals with the study of algae.

• One can clearly found algae in a waterbody as algae are found in a large range in aquatic habitats. 
• They are able to prepare their own food by the process of photosynthesis by the help of chlorophyll which gives green colour to algae. 
• Hence the green colour scum is visible over water bodies.
• The correct answer is A. 

Volvox is colonial green alga. The cells are like unicellular alga Chlamydomdnas and are definitely organised in the form of a colony called coenobium. 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 cell.

Algae have become significant organisms for self purification of wastewater since they are able to accumulate plant nutrients, heavy metals, pesticides, organic and inorganic toxic substances and radioactive matters in their cells or bodies.

Non-embryonic plants are included under the division Thallophyta. In non-embryonic plants, the zygote or the fertilized egg does not form the embryo. It directly forms a new plant. It mainly includes algae such as Spirogyra, Ulothrix, and Ulva. Hence, all the given options are correct.

So, the correct answer is ' Anthocyanin'.

Algae are hte diverse group of aquatic organisms that have the ability to conduct photosynthesis.Certain algae are familiar to most people;for instance seaweeds, pond scum or the algal blooms in the lakes.

Haplontic life cycle generally occurs in most algae such as volvox, Spirogyra and some species of Chlamydomonas.

 The cell walls of diatoms are embedded with silica and thus the walls are indestructible. Thus, diatoms have left behind a large number of cell deposits in their habitat; this accumulation over billions of years is referred to as 'diatomaceous earth'. Being gritty this soil is used in polishing, filtration of oils and syrups.

The constant number of cells or nuclei in individuals of a species or in parts of their bodies is known as eutely.

The members of Rhodophyceae are commonly called red algae because of the predominance of the red pigment r-phycoerythin in their body. Apart from this, other major pigments found in them are chlorophyll a and chlorophyll d.

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.

The $CO _2$ present in the oceans in the form of dissolved gas or carbonates is estimated about 11.2 X {10}$^{14}$ tonnes which is more than 50 times of the amount present in the atmosphere.