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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Sexual Reproduction in Angiosperms Page 1

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1.

 

 

  1. Flower: It is a modified shoot, highly specialised for sexual reproduction.
  2. Thalamus: It is the basal portion of a flower from where the floral whorls arise.
  3. Pedicel: Stalk of the flower.
  4. Floral Whorls: Floral members are arranged on the thalamus in a cyclic manner one inside the other, thus called whorls.
  5. There are four whorls namely calyx, corolla, androecium and gynoecium.
  6. Out of these, calyx and corolla are accessory whorls while androecium and gynoecium are called essential whorls.
  7. Members of calyx are sepals, corolla are petals, androecium are stamens and gynoecium are carpels.
  8. Sometimes calyx and corolla are not differentiated. Such undifferentiated whorl is called 'perianth'. The members of perianth are tepals.
  9. Complete Flower: When a flower contains all the four floral whorls, it is called a complete flower.
  10. Incomplete Flower: When one of the floral whorls is missing, the flower is called incomplete flower.
  11. Bisexual and unisexual flower: When a flower contains, both the essential whorls, i.e., stamen as well as carpel, then the flower is bisexual. But if only one essential whorl is present i.e., either stamen or carpel then it is called unisexual flower.
  12. Male flower is called 'staminate' flower while female flower is called 'pistillate' flower.
  13. Depending upon the arrangement of floral whorls on the thalamus, with respect to position of ovary, there are three types.
  14. Hypogynous Flower: Here thalamus is elongated and ovary is superior in position. Stamen, petals and sepals are situated below ovary. Example: Hibiscus flower.
  15. Epigynous Flower: Here thalamus is cup-shaped and ovary is present in this cup-like thalamus. Thus it is inferior and other whorls arise from the top of ovary. Example: Guava flower.
  16. Perigynous Flower: Here, the thalamus is cup-shaped. Stamens, petals and sepals arise from the cup-shaped thalamus. They encircle the ovary. Example: Rose.
  17. Inflorescence: It is a branch system which bears flowers. The stalk of inflorescence is called 'peduncle'.
  18. Two main types of inflorescence are 'cymose' and 'racemose'.
  19. Racemose: Here, the growth of peduncle is indefinite. The flowers arranged are in 'acropetal' succession, i.e., older flowers at the base and younger towards apex.
  20. Cymose: Here, the growth of peduncle is limited because peduncle ends in a flower. The flowers are arranged in 'basipetal' succession, i.e., younger flowers at the base and older flowers at the tip.

 

 

2.

 

 

  1. Pollination: Transfer of pollen grains from anthers to the stigma is called pollination.
  2. Types of Pollination: Two main types of pollination are 'self pollination' and 'cross pollination'.
  3. Self Pollination: Also called 'autogamy'. Here, pollen grains are transferred from anthers to the stigma of same flower.
  4. Cross Pollination: Also called 'allogamy'. Here, pollen grains are transferred from anthers to the stigma of other flower. For this transfer of anthers, some pollinating agents are required.
  5. If pollinating agent is wind, it is called 'anemophily'. Pollination by water is called 'hydrophily' while pollination by animals is called 'zoophily'.
  6. For self pollination to take place, the flowers should be 'bisexual', i.e., stamens and carpels both should be present and they should mature at one time, i.e., 'Homogamy'.
  7. In some plants, the flowers do not open at all. In such closed flowers, self pollination becomes a rule. This is 'cleistogamy'. Example: Commelina.
  8. For cross pollination to take place, the flowers should have attractive colours, sufficient large size, presence of spiny, sticky pollen grains and nectarines to produce sugary solution.
  9. The flowers should be 'unisexual', i.e., either stamen or carpel should be present and their maturity time should be different. If anthers mature first, it is 'protandry' and if gynoecium matures first, it is 'protogyny'.
  10. Adaptations seen in the flower to carry out a specific type of pollination is called 'contrivances'. For cross pollination, if the lengths of styles is different i.e., 'Heterostyly', then only cross pollination takes place. If pollens of the same flowers do not germinate on its stigma, then cross pollination takes place. This is 'self-sterility'.

 

 

3.

 

 

  1. Angiospermic plant is diploid and produces two types of haploid spores called microspores and megaspores.
  2. A typical anther is made up of two anther lobes. Each anther lobe contains microspore (pollen) mother cells. These microspore mother cells undergo meiosis and produce haploid microspores.
  3. Each pollen or microspore is with two coverings, namely, outer 'exine' and inner 'intine'. Exine shows 'germ pores'.
  4. Initially, unicellular pollen divides unequally to give tube cell and generative cell. This bicelled structure is 'male gametophyte'. Tube cell helps in the formation of pollen tube and generative cell forms two male gametes.

 

 

4.

 

 

  1. Inside the ovary ovules are present which are arranged on a special tissue called 'placenta'.
  2. Each ovule consists of a central mass of tissue called 'nucellus'. The nucellus is covered over by two protective layers called 'outer and inner integuments'.
  3. The integuments leave an aperture at one end. It is called 'micropyle' through which pollen tube enters during fertilisation. This end of ovule is called 'micropylar end' while opposite end is called 'chalazal end'.
  4. The stalk of ovule is called 'funicle'.
  5. One of the cells of nucellus becomes large to form 'megaspore mother cell', which undergoes meiosis to produce 'four megaspores'.
  6. Out of four, three degenerate and one megaspore remains functional which gives rise to 'female gametophyte', i.e., embryo sac.
  7. During development, nucleus of functional megaspore undergoes successive divisions, to form eight nuclei. Out of these eight nuclei, three are at one end, three at the opposite end and two in the middle part.
  8. The group of three nuclei at chalazal end is called 'antipodal cells'. The nuclei in the centre are called 'secondary nucleus'. Out of the three nuclei at micropylar end, the central large cell is 'egg' cell and the other two are called 'synergids'. The egg with two synergids is called 'egg apparatus'.

 

 

5.

 

 

  1. Fertilisation: Fusion of male and female gametes is called fertilisation.
  2. Pollen grains on the stigma absorb moisture and produce pollen tube which passes through the style and reaches the ovule.
  3. Pollen tube carries two male gametes. It enters the ovule through micropyle and reaches the embryo sac.
  4. The tip of the pollen tube ruptures and two male gametes are released in the embryo sac.
  5. Out of two male gametes, one fuses with the egg cell to form zygote while the other fuses with the secondary nucleus to form primary endosperm nucleus.
  6. This act where both the male gametes participate in the fertilisation is called 'double fertilisation'.
  7. The significance of double fertilisation is formation of a triploid tissue which is nutritive in function, and nourishes the developing embryo.
  8. After fertilisation, the ovary forms fruits, ovules form seeds and the two integuments form seed coats called testa and tegmen.

 

 

6.

 

 

  1. The fusion product of male and female gametes results into 'zygote' which after a short resting period divides by mitosis to give rise to 'embryo'.
  2. First the zygote divides to form a two-celled stage called 'proembryo'. These two cells are 'basal cell' and 'terminal cell'.
  3. Basal cell forms 'suspensor' and terminal cell forms 'embryo proper'.
  4. Terminal cell divides to give rise to eight-celled structure called 'octant'.
  5. Four terminal cells from octant forms cotyledons and plumule. Four basal cells form radicle and hypocotyl.
  6. In some seeds, during the development, the endosperm is completely used by the developing embryo. Thus, the seeds are without endosperm and are called 'non-endospermic' or 'ex-albuminous' seeds. Example: Pea, bean.
  7. Those seeds which contain endosperm at maturity are called 'endospermic' or 'albuminous' seeds. Example: Maize, castor.
  8. Fruit is the fertilised ovary. It has a covering called 'pericarp' which may be 'dry' or 'fleshy'. The pericarp consists of outer 'epicarp', middle 'mesocarp' and inner 'endocarp'.
    In most of the fleshy fruits, the mesocarp is thick, fleshy and edible but in coconut it is fibrous.
  9. When a fruit develops from the ovary, it is called a true fruit. Sometimes the fruit may develop from parts other than ovary such as thalamus. Such fruit is called a false fruit or pseudo fruit. For example, in cashew, peduncle forms a fruit while in apple it is thalamus.
  10. True fruit is either simple or aggregate or composite.
  11. Simple fruit is formed from a single ovary. Simple fruits are of two types, namely, dry and fleshy. Some simple, dry fruits do not split or dehisce. They are called indehiscent fruits. Example: Achene, caryopsis, cypsela, nut, etc. Some simple dry fruits spilt or dehisce along one or more margins. They are called dehiscent fruits. Example: Legume, follicle, capsule, siliqua.
  12. In aggregate fruit, a combined fruit is formed from different free carpels of the same flower. Example: Strawberry, custard apple, etc.
  13. In composite fruit, an inflorescence gives rise to a single fruit. Example: Fig, jackfruit, etc.
  14. Sometimes, the ovary develops into a fruit without fertilisation. This is called parthenocarpy. Parthenocarpic fruits are seedless. Example: Banana, pineapple, etc.

 

 

 

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