NCERT Class X Science Class: Chapter –8. How Do Organisms Reproduce? – Part-6

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Question 31:

Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes?

Answer:

Reduction division (meiosis) during gamete formation halves the chromosome number in both male and female gametes. Since these two gametes fuse during fertilization, the original number of chromosomes (as in the parent) is restored in the offspring.

Question 32:

Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.

Answer:

Yeast are living organisms hence require a food source to respire.

The sugar solution provides yeast along with food source.

Sugar solution provides energy to yeast cells and so they can be observed to multiply rapidly.

Water does not contain any water source and also does not provide energy to the yeast cells.

Question 33:

Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?

Answer:

Moisture is an important factor for the growth of hyphae. Moistened bread slice offers both moisture and nutrients to the bread mould, hence it grows profusely. Dry slice of bread offers nutrients but not moisture hence hyphae fail to grow.

Question 34:

Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.

Answer:

(a) Sexual reproduction involves two parents with different sets of characters

(b) The gene combinations are different in gametes.

Question 35:

Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure D and E by indicating the regenerated regions.

Image Planaria cut vertically

Image Planaria Cut Vertically

Image Planaria cut vertically

Answer:

Yes, shaded part in Figures D and E represent the regenerated halves.

Image shaded part in Figures D and E represent

Image Shaded Part in Figures D and E Represent

Image shaded part in Figures D and E represent

Question 36:

From the internet, gather information about the chromosome numbers of five animals and five plants. Correlate the number with the size of organism and answer the following questions.

(a) Do larger organisms have more number of chromosomes/cells?

(b) Can organism with fewer chromosomes reproduce more easily than organisms with more number of chromosomes?

(c) More the number of chromosomes/cells greater is the DNA content. Justify.

Answer:

(a) No, there is no relationship between size of organism and its chromosome number.

(b) No, process of reproduction follows a common pattern and is not dependent on the number of chromosomes

(c) Yes, since the major component of chromosome is DNA, if there are more chromosomes in a cell, the quantity of DNA will also be more.

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