Frequently asked questions (FAQs).

Transcription

1 Frequently asked questions (FAQs). Q.1. What is The term algae (singular: alga), has been derived from a Latin word algere, meaning seaweeds. Algae include a diverse group of mostly autotrophic, eukaryotic living organisms, presently classified under the kingdom Protista. The scientific study of algae is known as algology or very often phycology. The term phycology is derived from the Greek word phycos, which means seaweeds. Although, algae practically occur in every habitable environment on earth, they are predominantly abundant in aquatic habitats. Q. 2. What are the algal blooms? Ans: The free-floating assemblage of algae is collectively known as phytoplankton. Such planktonic algae under eutrophic conditions increase enormously in number and extent, and form algal blooms. Q. 3. Write a concise note on the range of thallus structure in Ans: The term thallus (plural: thalli) - often used in describing the algal plant body- refers to a simple, relatively undifferentiated vegetative body. The thallus varies from the relative simplicity of a single cell to the more striking complexity exhibited by the giant kelps. While unicellular algae, such as Chlorella (2-8 micrometer) are in the range of bacterial size, kelps may attain a length of 60 m. Unicellular, colonial, filamentous, membranous or foliose and tubular types of algal plant body occur, together with more highly differentiated blade-like types and those that have root-like, stem-like and leaf-like organs are of frequent occurrence. Q. 4. What are the various types of asexual spores found in

2 Ans: Algae produce a variety of spores. The spores are produced within an ordinary algal vegetative cell, or within special cells or groups of cells. The specialized sporeproducing structures are known as sporangia. Among the various types of spores in algae, akinetes are of widespread occurrence, especially in green algae. An akinete is a vegetative algal cell that has enlarged and formed an envelope external to its wall. In many non-motile algae, flagellate zoospores are the agents of asexual reproduction. In some cases, zoospores omit their motile phase and start their development within the parental cell wall, and are called as aplanospores; and the aplanospores that thicken their walls are known as hypnospores. Other types of non-motile spores produced by algae include: autospores (green algae), monospores, tetraspores, paraspores and carpospores (red algae), and statospores and auxospores (diatoms). Q.5. Discuss briefly the modes of sexual reproduction in Ans: Algae generally show three modes of sexual reproduction. (i) Isogamy: It involves the fusion of motile or non-motile gametes which are morphologically and physiologically alike. (ii) Anisogamy: It involves the fusion of motile or non-motile gametes which are morphologically dissimilar. The larger gamete is the female and the smaller one is the male. (iii) Oogamy: It involves the fusion of a large non-motile gamete (egg or ovum) with a smaller motile gamete (sperm). Usually, the eggs are formed within an oogonium and the sperm within an antheridium. Q. 6. Highlight the photosynthetic pigments found in Ans: In algae, three main types of photosynthetic pigments are as follows.

3 Chlorophylls: The photosynthetic algae possess chlorophylls in their chloroplasts. Five kinds of chlorophylls-a,-b,-c,-d,-e have been reported among algae. Carotenoids: These are a group of protective pigments that pass on the light energy to chlorophylls, after screening. They occur usually inside plastids. Generally, the carotenoids can be divided into 2 classes. (a) Carotenes: These are linear unsaturated oxygen-free hydrocarbons. B-carotene is present in most algae and is replaced by alpha, gamma, epsilon carotenes and lycopene in some algae. (b) Xanthophylls: These are oxygen derivatives of carotenes. As xanthophylls, such as fucoxanthin, peridinin, myxoxanthin, and teraxanthin are unique to particular algal phyla, they are important in classification. Phycobilins: A pigment-protein complex, phycobilins are tetra-pyrrolic compounds joined to globulin proteins. These are water soluble, blue or red pigments located on or inside the thylakoids of algal chloroplasts of two algal phyla. Based on their absorption spectra, three types of phycobilins recognized are phycocyanin, phycoerythrin and allophycocyanin. Q.7. What is haptonema? Ans: In the phylum Haptophyta, a thread-like structure, called haptonema, extends from the cell along with the 2 flagella. Haptonema differs from flagella both in structure and properties; these do not show typical arrangement of microtubules, and can bend and coil, but can t beat like flagella. Q.8. What are frustules? Ans: In diatoms, the cell wall is silicified. The cell wall consists of two halves, known as frustules, which fit together like a laboratory petri-dish.

4 Q. 9. Underline the main characters used in the classification of Algae? Ans. The main characters that have been widely used in the classification of algae include: photosynthetic pigments, biochemical nature of food reserve, cell wall composition, and flagella. Q. 10. Enlist the different divisions recognised under Algae? Ans. At present, the Algae are divided into following nine phyla: Chlorophyta (Green algae), Chrysophyta (Chrysophytes), Bacillariophyta (Diatoms), Cryptophyta (Cryptomonads), Dinophyta (Dinoflagellates), Euglenophyta (Euglenoids), Phaeophyta (Brown algae), Haptophyta (Haptophyte algae), Rhodophyta (Red algae). Q. 11. What is a theca? Ans. In the Dinoflagellates, a typical cell wall is absent. Instead, there is a layer of vesicles beneath the plasma membrane with or without cellulose plates. Such stiff cellulose plates look like a helmet, forming a structure known as theca. Q. 12. What are the coccoliths? Ans. In the Haptophyte algae, scales of cellulose or calcified organic material are present on the outer surface of the cell. These calcified scales are known as coccoliths. Q.13. Highlight the diagnostic features of Green Algae? Ans. Some of the diagnostic features of Green Algae are as follows: Mostly occur in aquatic, freshwater or marine habitats, and many show symbiotic association. The photosynthetic pigments include chlorophylls -a, -b, and carotenoides

5 They store starch as reserve food inside plastids. Mostly occur in aquatic, freshwater or marine habitats, and many show symbiotic association. The cell wall is composed of cellulose, hemicelluloses and pectic substances. Flagella either absent, or when present, 2 or more in number, apical or subapical in position, equal or unequal in size, and mainly of the whiplash type. Q. 14. Underline the two main characters by which Algae differ from higher plants? Ans. The Algae differ from higher plants (i.e., bryophytes, pteridophytes, gymnosperms and angiosperms): (i) in their production of gametes and/or gametangia without a covering of sterile cells and (ii) in lacking a true vascular system. Q. 15. Briefly discuss the habit and habitat in Algae? Ans. Algae practically occur in every habitable environment on earth; however, they are predominantly abundant in aquatic habitats. The occurrence of algae in habitats, such as thermal springs, ice-damp soil, rocks, tree trunks, old walls etc is not uncommon. A number of algae can be found as endophytes (i.e., live inside the tissue of other plants), epiphytes (i.e., live on other plants without causing any harm) and symbionts (i.e., live in association with other organisms for deriving mutual benefit).