Class 12 Biology

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  Male reproductive system 1.Sperms have a tail whereas eggs do not. Why so? (C.B.S.E. 2007) 2.Why does failure of testes to descend into scrotum produce sterility? 3.Mention the difference between spermiogenesis and spermiation.(C.B.S.E. 2012) 4.Where is acrosome present in humans? Write its functions. (C.B.S.E. 2012) 5.Mention the location and function of Leydig cells in humans. (C.B.S.E. 2012) 6.Mention the function of mitochondria in sperm. (C.B.S.E. 2012) (a) Give a schematic representation of spermatogenesis in humans. (b) At which stage of life does gametogenesis begin in human male? (c)Describe the structure of a human sperm. Fate of Germ Layers List the following events observed in human reproduction in chronological order.  Fertilization, gametogenesis, insemination, gestation, parturition, implantation. State the significance of cervix in the female reproductive system. What is the reason for the absence of menstrual cycles during conception or pregnancy? Fill up th...

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  What is the number of microsporangia in each lobe of an angiosperm anther? (1) Four (2) Two (3) Eight (4) One The cells of which of the following layers of the anther wall are multinucleated due to endomitosis? (1) Epidemis (2) Endothecium (3) Middle layer (4) Tapetum A typical angiosperm anther is dithecous which means that it is: (1) One lobed and the lobe has two theca (2) Two lobed and each lobe has two theca (3) Two lobed and each lobe has one theca (4) Four lobed and each lobe has two theca Which of the following layers in the wall of an anther nourishes the developing pollen grains? 1. Tapetum 2. Epidermis 3. Endothecium 4. Middle layers Pollen intine is made of: 1. Sporopollenin 2. Cellulose and pectin 3. Ergosterol 4. Phospholipids and cholesterol Pollen grains lose their viability within 30 minutes of their release in: 1. Rose 2. Potato 3. Pea 4. Wheat Pollen grains are shed at which stage? (1) 2 celled  (2) 3 celled (3) Usually at 2-celled, but sometimes 3-celled ...

 Vegetative propagation :  Reproduction by vegetative parts of plants i.e. other than the reproductive parts(flower, Fruit). Vegetative parts= Roots, Stem, Leaves Types : Natural and Artificial Natural methods i) Roots: Buds grow in 2 types of roots(Tap and fibrous) eg: Dahlia, Dalbergia, sweet potato, Asparagus ii) Underground stem (a) Tubers : Potato (b) Bulbs: Onion and Garlic (c) Rhizomes: Banana, Turmeric, Ginger (d) Corms: Colocasia, crocus, Amorphophilus (e) Sucker : Mint, Crysenthemum (f) Runner:Oxalis (g) Stolon:Strawberry, Valisneria (h)Offset: Pistia,Eichhornia