Sample 1Medium
A figure shows the transverse section of one microsporangium of a young anther, with four wall layers from outside inwards. A is a single outer layer. B is a single layer just inside A. C is one to three layers inside B. D is the innermost layer, whose cells have dense cytoplasm and generally more than one nucleus, surrounding the sporogenous tissue. What is D, and what does it do?
- A
Tapetum; it nourishes the developing pollen grains
- B
Endothecium; it protects the anther and helps it dehisce
- C
Middle layers; they nourish the developing pollen grains
- D
Epidermis; it releases the pollen grains
Show the answer
The answer is A.The microsporangium wall has four layers: epidermis, endothecium, middle layers and tapetum. The innermost layer, the tapetum, has cells with dense cytoplasm and usually more than one nucleus, and it nourishes the developing pollen grains.
- B.
The endothecium is layer B, just inside the epidermis. The innermost layer with multinucleate cells is the tapetum.
- C.
The middle layers are C. Pollen grains are nourished by the innermost layer, the tapetum.
- D.
The epidermis is the outermost layer, A. D lies innermost, next to the sporogenous tissue.
NCERT: Class 12 Biology, Chapter 1
Sample 2NEET level
Consider the following statements about the female gametophyte of a typical angiosperm: 1. In monosporic development, only one of the four megaspores is functional. 2. The mature embryo sac is 8-nucleate and 7-celled. 3. The filiform apparatus is present in the antipodal cells. 4. The nucleus of the functional megaspore undergoes three successive mitotic divisions to form the 8-nucleate stage. Which of the statements above are correct?
- A
1 and 2 only
- B
2, 3 and 4 only
- C
1, 3 and 4 only
- D
1, 2 and 4 only
Show the answer
The answer is D.In most flowering plants one megaspore is functional and three degenerate (monosporic development); its nucleus divides mitotically three times to give 8 nuclei, and the mature embryo sac is 8-nucleate and 7-celled. The filiform apparatus is a special cellular thickening at the micropylar tip of the synergids, not the antipodals, so statement 3 is false.
- A.
Leaves out statement 4, which is correct: three mitotic divisions give 8 nuclei.
- B.
Includes statement 3; the filiform apparatus is in the synergids, and leaves out the correct statement 1.
- C.
Includes statement 3, which is false, and leaves out the correct statement 2.
NCERT: Class 12 Biology, Chapter 1 (Sexual Reproduction in Flowering Plants), The pistil, megasporangium (ovule) and embryo sac