Q.1. What is Algae ? Give general characters of Algae.
Ans. The algae is a group of chlorophyll bearing thallophytes. These posses unicellular sex organs or multicellular one in which every cell forms a gamete. The branch of botany dealing with study of algae is known phycology.
The characteristics features of algae are as follows :
1. These are cholorphyll bearing plants with thallose plant body.
2. They have little differentiation of true tissue.
3. Even the complex forms of algae lack vascular tissue (xylem, phloem, etc.)
4. Sex organs are unicellular and non-jacketed and when multicellular, each cell is fertile.
5. There is no embryo formation after fertilization in life cycle.
6. Most of the algae are aquatic.
7. When there are two phases, i.e. gametophytic and sporophytic phase in life cycle, they are independent of each other.
Q.2. Describe the distinguishing characteristics of myxophyceae, Chlorophyceae, Rhodophyceae and phoeophyceae. (1994, 95, 96, 98, 99)
Ans. Characteristics of Class-Myxophyceae (Blue green algae): -
1. Class-Myxophyceae is commonly known as blue green algae.
2. It is also known as cynophyceae due to presence of cyanin pigment.
3. Cell is prokaryotic type.
4. The nucleous is inupiant type i.e. no nuclear membrane present.
5. The flagella are completely absent.
6. Storage food product is cynophycean starch and protein.
7. The phyobilin pigments unique to this class are blue c-phycocynin, and red c-phycoerythrin with chlorophyll a - carotene.
8. Sexual reproduction is absent.
9. Thylakoids occur singly.
10. Cell content is divisble into two regions-
(i) Outer denser region i.e. chromoplasm as pigments are located in this region.
(ii) The inner is centroplasm in which diffused nuclear material in present.
Characteristics of Class-Chlorophyceae (Grass Green Algae): -
1. The thallus is typically green colour due to the presence of green pigment, the chlorophyll.
2. The member of chlorophyceae may be aquatic, amphibious, terrestrial or subaerial. Mainly these are aquatic.
3. Majority of them are fresh water, few are marine.
4. The cell of thallus are eukaryotic.
5. Chlorophyll a and b, and carotene pigment are present.
6. Reserve food material are starch and oil.
7. Cell contains one or more pyronoid commonly surrounded by starch sheath.
8. Cell wall is made up of cellulose.
9. Thallus unicellular or multicellular.
10. The flagella are of equal length and of whiplash type.
11. Asexual reproduction by zoospores, aplanospores, plamella stage anes akinetes.
12. Sexual reproduction may be isogamous (Chlamydomonas) anisogamous (zygnema) and oogamous (Oedogonium) type.
Characteristic of Class-Rhodophyceae (Red Algae): -
1. The group is popularly known as red algae.
2. They are found in marine mostly are in warmer sea.
3. The red colour is due to presence of two phycobilin pigment i.e. r-phycoerythrin and c-phycocynin.
4. The motile stages are absent.
5. Reserve food material is Floridean starch and galactan Sulphate.
6. Cell show typically eukaryotic structure.
7. The cell wall consist of two layer (i) outer poetic mattered, and (ii) inner cellulose.
8. Nucleus distinct with nucleolus, spindle and centromeric chromosomes.
9. Reproduction takes place by both asexual and sexual means.
10. Sexual reproduction is highly advanced. Spores are non-motile. Male gametes called “Spermatic” and female carpospore.
Characteristics of Class-phaeophyceae: -
1. The brown algae are distinguished by their golden colour due to presence of Xanthophyll pigment - Fucoxanthin along with chlorophyll and b Carotene.
2. Phaeophyceae are marine and commonly called “brown sea weeds”. Three genera are fresh water.
3. Pigment are chlorophyll a, b, and c, carotenes and other Xanthophylls.
4. Plant body is multicellular and sessile.
5. Reserve food material are mannital, laminarin and rarely fats.
6. Motile reproductive cells are commonly found in the brown algae.
7. Pyrenoids are projecting and naked.
8. The two flagella are unequal in length.
9. Cell wall is two layered inner cellulosic and outer pectic.
10. All kind of reproduction present i.e. vegetative, asexual and sexual.
Q.3. Describe the thallus organisation in Algae.
Related Question -
Q. Describe the range of thallus organization in algae. (2013)
Q. Draw a labelled diagram of thallus structure of chlamydomonas. (2012)
Ans. Thallus organisation in Algae: -
The plant of algae is thalloid (i.e., not differentiated into true root true stem and true leaves). There are different types of vegative structures in algae. The plants may be unicellular or multicelluar, flagellated or non-flagllated, filamentous or non-filamentous, branched or unbranched, small microscopic mostly or very large and highly organized. Fritsch (1935) fundamentally considered mostly two categories - unicellular and multicellular forms.
(A) Unicellular Forms: - The plant body is made of a single cell. It is the simplest form among algae. The unicellular forms may be motile (Flagmented) or non-motile (non-flagmented). The motile unicellular forms are - Chlamydomonas (green algae),Chlorochromonas (Xanthophyta) and the non-motile unicellular forms are Anacystis, Chroococcus, Gloeocapsa (blue greenalgae), Porphyridium (red algae), chlorella, Chlorococcum (green algae). However, unicellular forms are not found in Phaeophyta.
(B) Multicellular forms: - As against unicellular plant body, multicellular forms is more specialized and highly evolved. A multicellular body has many cells which share the life activities of an organism and exhibit division of labour. Multicellular forms may be following four types.
(i) Plamelloid forms: - It is a colonial form of algae where many cells constitute a plant body. Plamelloid forms are distinguished by having no definite of fixed number and size of cells.
The cells become dormant secrete gelatinous matrix and have an irregular outline of the thallus. They are - Aphanocapsa (Cyanophyta), Tetraspora (Chlorophyta), Mischococcus (Xanthophyta), Asterocystis (Rhodophyta), etc.
(ii) Coenobial forms: - Coenobium is a multicellular colonial plant body with fixed number of cells arranged in a definitie manner. It may be motile or non-motile. Hydrodictyon (green algae) is the best example of motile coenobium, where hundreds of cells coenobium is present.
(iii) Dendroid forms: - It is multicellular colonial form where the plant body appears as a microscopic tree, examples - Ecballocystis and Ecballocystopsis.
(iv) Siphonaceous forms or Coenocytic thallus: - The thallus enlarges in size, becomes multinucleate but the septa are not formed. Such a body is related as a cellular (or unicellular) coenocytic. It takes the shape of a siphon, example of this type of thallus are Vaucheria (Xanthophyta) and Caulerpa (Chlorophyta).
