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*Self-practice*

10 th -Science Part 2

Topic 2: *Life Process in Living organisms Part-1*

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 *Today's exercise*

Explain the difference between mitosis and meiosis. Use the following points.

# Meaning

# Type of reproduction

# Takes place in

# Necessary for

# Produces 

# No. Of divisions

# Mother cell

# Chromosome numbers

# Steps involved

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 *Resolve doubts *

1) *What is the sight of meiosis in the body?*

 Answer:

 ◆ Meiosis occurs in the sex cells of an organism.  But it is also misinterpreted to mean that cell division occurs in sperm and ovum.  Sperm and ovum are the names of the progenitor cells formed by meiosis. 

◆ Sperm are formed by meiotic division in the germinal epitheliul cells of the male testicles.

◆ A female child borns with about 1 million eggs in the ovary. By the time a female reaches puberty nearly 3 lakh eggs are in her ovary. In mature female generally every month an ovum is released in oviuct.

That is, both the sperm and the ovum are haploid gametes formed by meiosis.

2) *What is the duration of meiosis in humans?*

 Answer:

◆ Sperm production begins when a man reaches puberty and continues throughout his life. A healthy adult male produces millions of sperm in a single day.

◆ In female, an ovum is released each month by ovulation process. The ovulation process lasts for 40 to 45 years of her age.

3) *What are homologous chromosomes?*

Answer:

◆ A pair of diploid chromosomes one from the mother and another from the father is called a homologous chromosome.

◆ The height, thickness, gene sequence and location of the centromere of both these chromosomes are identical. 

4) *What are sister chromatids?*

Answer:

◆ Duplicate copies of genes are made in cell division.

◆ The 'n' chromosome from the mother and its duplicate together form the 2n diploid chromosome. They are both identical in all respects so they are called as sisters chromosomes. 

◆ Similarly, 2n chromosome are formed from the n chromosome from the father. (See accompanying figure.)

We will deal with the rest of the questions tomorrow.

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