Question 1: What is the basis of classification of algae?
Answer: The presence or absence of pigments is the main basis of classification of algae.
Chlorophyceae: Chlorophyll a and b are present in them and impart green colour. Chlorophyceae are also called ‘blue-green algae’.
Phaeophyceae: Chlorophyll a and c and fuxoxanthin are present. Fucoxanthin imparts brown colour. Phaeophyceae are also called ‘brown algae’.
Rhodophyceae: Chlorophyll a and d and phycoerythrin are present. Phycoerythrin imparts red colour. Rhodophyceae are also called ‘red algae’.
Question 2: When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?
Answer: In case of liverwort, moss and fern; the saprophytic plant produces haploid spores after meiosis. In case of gymnosperm and angiosperm, meiosis takes place in antheridium and ovary; for the formation of pollen grains and ovules.
Question 3: Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Answer: Gymnosperms are heterosporous. Haploid microspores and megaspores are produced. Spores are produced within sporangia. Sporangia are borne on sporophylls which are arranged spirally along an axis. The Sporophylls form lax or compact strobili or cones.
Male Cone: The male strobili are called microsporangiate. Microspores develop into a male gametophytic generation which is highly reduced and is confined to only a limited number of cells. This small-sized gametophyte is called pollen grain.
Female Cone: The female strobili are called megasporangiate. The male or female cones can be found on the same tree (pinus) or on different trees (cycas). The megaspore mother cell is differentiated from one of the cells of the nucellus. Nucellus is protected by envelopes and the composite structure and is called an ovule. Meiotic division in the megaspore mother cell produces four megaspores. One of the megaspores develops into a multicellular female gametophyte. The female gametophyte bears two or more archegonia or female sex organs. The female gametophyte is retained within the megasporangium.
Fertilization: The pollen grains are released from the microsporangium and carried by air currents. They come in contact with the opening of the ovules on the female cone. A pollen tube develops in the pollen grain. The male gamete travels through the pollen tube to reach near the mouth of archegonia. After fertilization, zygote develops into an embryo. The ovule develops into seed.
Question 4: Mention the ploidy of the following:
Protonemal cell of a moss
Primary endosperm nucleus in dicot
The secondary necleus in embryo sac is diploid because it is formed after fusion of two polar nuclei. When a pollen nucleus fuses with secondary nucleus, the result is a triploid Primary Endosperm Nucleus.
Leaf cell of a moss
Prothallus cell of a fern
Gemma cell in Marchantia
Meristem cell of monocot
Ovum of a liverwort
Zygote of a fern.
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