NEET-XI-Biology
03: Plant Kingdom
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- Qstn #6Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
Ans : Gymnosperms and angiosperms are seed-producing plants with diplontic life cycles.
In gymnosperms, the sporophylls are aggregated to form compact cones. The microsporophylls are broad and are not distinguished into filaments and anthers. The megasporophylls are woody and lack the ovary, style, and stigma, because of which the ovules lie exposed. The female gametophyte consists of archegonia. The fertilisation process involves the fusion of a male gamete with the female gamete. Their endosperm is haploid. The produced seeds are naked as there is no fruit formation.
Angiosperms are also known as flowering plants. They have sporophylls that aggregate to form flowers with the perianth. The microsporophylls consist of stamens containing pollen sacs. These sacs bear the male gametes called pollen grains. The megasporophylls are delicate and rolled, forming carpels that contain the ovary, style, and stigma. The ovules are present inside the ovary. The archegonium is replaced by an egg apparatus. Two male gametes enter the egg apparatus at the time of fertilisation. One male gamete fertilises the egg and the other fuses with the diploid secondary nucleus to form an endosperm. The resulting endosperm is thus triploid. In addition, in angiosperms, the development of seeds takes place inside the fruits.
- Qstn #7What is heterospory? Briefly comment on its significance. Give two examples.
Ans : Heterospory is a phenomenon in which two kinds of spores are borne by the same plant. These spores differ in size. The smaller one is known as microspore and the larger one is known as megaspore. The microspore germinates to form the male gametophyte and the megaspore germinates to form the female gametophyte. The male gametophyte releases the male gametes and these reach the female gametophyte to fuse with the egg. The development of the zygote takes place inside the female gametophyte.
This retention and germination of the megaspore within the megasporangium ensures proper development of the zygote. The zygote develops into the future sporophyte. The evolution of the seed habit is related to the retention of the megaspore.
Heterospory is thus considered an important step in evolution as it is a precursor to the seed habit.
Heterospory evolved first in pteridophytes such as Selaginella and Salvinia.
SECTION I SECTION I Page No 45:
- Qstn #8-iprotonemaAns : Protonema - It is the first stage in the life cycle of a moss, developing directly from the spore. It consists of creeping, green, branched, and often filamentous structures.
- Qstn #8-iiantheridiumAns : Antheridium - It is the male sex organ present in bryophytes and pteridophytes and is surrounded by a jacket of sterile cells. It encloses the sperm mother cells, which give rise to the male gametes.
- Qstn #8-iiiarchegoniumAns : Archegonium - It is the female sex organ present in bryophytes, pteridophytes, and gymnosperms. In bryophytes and pteridophytes, it generally has a swollen venter and a tubular neck, and contains the female gamete called the egg.
- Qstn #8-ivdiplonticAns : Diplontic - It is the term used for the life cycles of seed-bearing plants (gymnosperms and angiosperms). In these plants, the diploid sporophyte is dominant, photosynthetic, and independent. The gametophyte is represented by a single-celled (or a few-celled) structure.
- Qstn #8-vsporophyllAns : Sporophyll - In pteridophytes, the sporophytic plant body bears sporangia. These sporangia are subtended by leaf-like appendages known as sporophylls. In gymnosperms, microsporophylls and megasporophylls are found. These bear microspores and megaspores respectively.
- Qstn #8-viisogamyAns : Isogamy - It is a type of sexual reproduction involving the fusion of morphologically-similar gametes. This means that the gametes are of the same size, but perform different functions. This type of reproduction is commonly observed in Spirogyra.
- Qstn #9-ired algae and brown algaeAns : Red algae and brown algae
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Red algae Brown algae
1. Red algae are grouped under the class Rhodophyceae. 1. Brown algae are grouped under the class Phaeophyceae. 2. They contain floridean starch as stored food. 2. They contain mannitol or laminarin as stored food. 3. They contain the photosynthetic pigments chlorophylls a and d, and phycoerythrin. 3. They contain the photosynthetic pigments chlorophylls a and c, and fucoxanthin. 4. Their cell walls are composed of cellulose, pectin, and phycocolloids. 4. Their cell walls are composed of cellulose and algin. 5. Flagella are absent 5. Two flagella are present
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- Qstn #9-iiliverworts and mossAns : Liverworts and moss
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Liverworts Moss
1. They have unicellular rhizoids. 1. They have multicellular rhizoids. 2. Scales are present very often 2. Scales are absent 3. They are generally thalloid, with dichotomous branching. 3. They are foliage, with lateral branching. 4. Gemma cups are present 4. Gemma cups are absent 5. Sporophyte has very little photosynthetic tissue 5. Sporophyte has abundant photosynthetic tissue
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- Qstn #9-iiihomosporous and heterosporous pteridophyteAns : Homosporous and heterosporous pteridophyte
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Homosporous pteridophytes Heterosporous pteridophytes 1. They bear spores that are of the same type. 1. They bear two kinds of spores - microspores and megaspores. 2. They produce bisexual gametophytes. 2. They produce unisexual gametophytes.
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- Qstn #9-ivsyngamy and triple fusionAns : Syngamy and triple fusion
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Syngamy Triple fusion
1. It is the process of fusion of the male gamete with the egg in an angiosperm. 1. It is the process of fusion of the male gamete with the diploid secondary nucleus in an angiosperm. 2. A diploid zygote is formed as a result of syngamy. 2. A triploid primary endosperm is formed as a result of triple fusion.
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- Qstn #10How would you distinguish monocots from dicots?
Ans : Monocots and dicots can be differentiated through their morphological and anatomical characteristics.
Characteristic
Monocot
Dicot
Morphology
Roots
Fibrous roots Tap roots Venation
Generally parallel venation Generally reticulate venation Flowers
Trimerous flowers Pentamerous flowers Cotyledons in seeds
One Two Anatomy
No. of vascular bundles in stem
Numerous Generally 2 - 6 Cambium
Absent Present Leaves
Isobilateral Dorsiventral