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NCERT Solutions Cell Growth And Development




Question 1
Why is meiosis so important for the production of gametes or sex cell? How would the offering of sexual reproduction be affected if sex cell underwent mitosis instead of meiosis?
Answer
Meiosis is important because it ensures that all organisms produced via sexual reproduction contain correct number of chromosomes. Meiosis also produces genetic variation by the way of the process recombination.
If mitosis occur in gametes, then the offering produces would be done to the parents.

Question 2
Name two proteins which are responsible for contraction of muscles.
Answer
Actin and myosin

Question3
What is meant by G0in the cell cycle?
Answer
G0 phase is also referred to as resting phase. In the late G, phase, all cell follows one of the two pathways. They may either become committed to start DNA synthesis and complete the cell cycle or withdraw from cell cycle to enter resting phase go phase). Cells that enter Go phase remain viable and metabolically active but are non-dividing cells may remain in Go phase days to years, but may be stimulated to enter G, phase and re-enter cell cycle.
Question 4
Differentiate between heterochromatin and euchromatin.
Answer

Heterochromatin

Euchromatin
1
It is tightly coiled chromatin
1
It is loosely coiled chromatin
2
It stains darkly
2
It stains less.
3
It is used to express a large no. of genes.
3
A less number of genes are expressed

Question 5
Name 5 different classes of antibodies.
Answer
5 different classes of antibodies are :
(a) Ig A
(b) Ig E
(c) Ig M
(d) Ig D
(e) Ig G

Question 6
Name some of the secondary metabolites produced by plants, which have medicinal value for human beings.
Answer
Some of useful secondary metabolites are :
phenols, alkaloids, tannins and resins.
Question 7
How is vascular system of plants different from circulatory system of animal?
Answer

Vascular system of plants

Circulatory system of animals
1
This transport system comprises vascular bundle called xylem and phloem.
1
This system comprises arteries, veins, capillaries and a pumping organ called heart.
2
Heart is absent
2
Heart is present
3
It transports water minerals and food.
3
It transports blood.

Question8
At interphase cell is highly active. Tree or false?
Answer
False.
Question 9
The alveoli constitutes large surface area. True or false.
Answer
False.
Question 10
Briefly explain apoptosis.
Answer
Cell undergoing programmed cell death show distinctive morphological features, which are collectively termed as apoptosis.

Question 11
Compare and contrast the essential features of asexual and sexual reproduction
Answer

Sexualreproduction.

Asexual reproduction.
1
Involves two parents
1
Involve only one parent
2
Gametes are produced
2
Gametes are not produced
3
Offspring show genetic variation
3
Offspring’s are genetically identical to the parent
4
Gametes are produced by meiotic division
4
The cell division are only mitotic
5
Comparatively the number produced is less.
5
Large number of organisms are produced in a very short period of time
6
Eg-In human beings.
6
Eg-In hydra.

Question 12
Explain briefly how fertilization takes place in flowering plants.
Answer
The process of fertilization in flowering plants is known as double fertilization. It takes place in embryo sac. The steps of process are stated below :
i) The pollen tube enters the egg apparatus that contain one egg cell and two synergid.
ii) Release of two male gametes from the pollen tube takes place.
iii) One male gamete fuse with egg cell (syngamy)
iv) The other male gamete fuses with two polar nuclei to form endosperm (triple fusion.)
Fusion of male game with egg cell results in the formation of zygote.
Question 13
Differentiate b/w active and passive defense in plants.
Answer

Passive defense

Active defense
1
It depends on the defenses that are contitutively expressed in plants
1
It relies on defense that are induce a after infection or attack
2
It is inbuilt
2
It is induced after the attack of pest or pathogen
3
Secondary metabolites are released in passive defense.
3
It occurs at the specific site.

Question 14
Fill in the blanks :
(a) The development of embryos and seeds without fertilization is known as ___________.
(b) The process of cell death, which results from acute injury, is called…………
Answer
1.The development of embryo and seed without fertilization is called apomixis.
2. The process of cell death, which results from acute injury programmed cell death (PCD).
Question 15
What is the major utility of in vitro fertilization.
Answer
IVF is carried out to help infertile couples who are unable to war children due to medical problems, IVF is a part of larger discipline called ART (desisted reproductive technology in which such infertile couples are helped in variety of ways to solve problems related to their reproductive health.
Question 16
Explain what is meant by apomixes?
Answer
In apomixes embryos and seeds are developed without fertilization. It is of two types.
(i) obligate apomixes
(ii) facultative apomixes
Question17
How internal environment is maintained in living organism?
Answer
When a living organism is too warm, it sweats to release heat. When any living organism gets thrown off balance, its body or cells help it to return to normal. In other words, they have the ability to keep internal environment stable. Maintaining a balance inside the body or cells organism is known as homeostasis.



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