What is Amitosis and Where Does it Occur?
Amitosis is a method of asexual reproduction, which occurs in acellular organisms such as bacteria, protozoans, diseased cells, old cells, mammalian cartilage cells and in fetal membranes, yeast budding, etc. It was first discovered by the scientist, REMAK.
Mechanisms:
-- Nucleus of the cell elongates.
-- Constriction appears in the nucleus, which gradually deepens and divides the nucleus into two daughter nuclei.
-- A constriction appears in the cytoplasm, which divides the cytoplasm and the nuclei into two daughter cells each with a nucleus.
-- In direct division, no spindle formation and no direct chromosome formation occurs.
Q. What is the minimum number of meiotic divisions required to produce 100 wheat grains?
a) 100 b) 125 c) 150 d) 200
Ans (b)
Explanation: Usually, one meiotic division forms 4 pollen grains
One meiotic division forms 1 egg cells
So, to produce 100 wheat grains, we need 100 pollen grains and 100 eggs
To produce 100 pollen, only 25 meiotic divisions are required and to produce 100 eggs, 100 meiotic divisions are required. Therefore, a total of 125 meiotic divisions are required to produce 100 wheat grains.
Shortcut:
No of meiotic divisions required to produce 'n' number of seeds / grains
No. of grains = n + n / 4
= Egg + Pollen
= 100 + 100 /4
= 125
Q. Number of mitotic divisions required for the formation of 100 cells:
a) 100 b) 50 c) 25 d) 99
Ans: (d)
Explanation:
Number of mitotic divisions for the formation of ‘n’ number of cellls = (n - 1)
Mechanisms:
-- Nucleus of the cell elongates.
-- Constriction appears in the nucleus, which gradually deepens and divides the nucleus into two daughter nuclei.
-- A constriction appears in the cytoplasm, which divides the cytoplasm and the nuclei into two daughter cells each with a nucleus.
-- In direct division, no spindle formation and no direct chromosome formation occurs.
Q. What is the minimum number of meiotic divisions required to produce 100 wheat grains?
a) 100 b) 125 c) 150 d) 200
Ans (b)
Explanation: Usually, one meiotic division forms 4 pollen grains
One meiotic division forms 1 egg cells
So, to produce 100 wheat grains, we need 100 pollen grains and 100 eggs
To produce 100 pollen, only 25 meiotic divisions are required and to produce 100 eggs, 100 meiotic divisions are required. Therefore, a total of 125 meiotic divisions are required to produce 100 wheat grains.
Shortcut:
No of meiotic divisions required to produce 'n' number of seeds / grains
No. of grains = n + n / 4
= Egg + Pollen
= 100 + 100 /4
= 125
Q. Number of mitotic divisions required for the formation of 100 cells:
a) 100 b) 50 c) 25 d) 99
Ans: (d)
Explanation:
Number of mitotic divisions for the formation of ‘n’ number of cellls = (n - 1)
