Question

1. How does the number of chromosomes in parents and offspring of a particular species remain constant? 2. What do you mean by bisexual flower? Give any one example of it. 3. What is the reason behind the fact that the offspring formed as a result of sexual reproduction exhibit more variations? 4. In tobacco plant, the male gametes have twenty four chromosomes. What is the number of chromosomes in the female gamete? What is the number of chromosomes in the zygote? 5. Why cannot fertilisation take place in flowers if pollination does not occur? 6. Give two reasons for the appearance of variations among the progeny formed by sexual reproduction. 7. In a bisexual flower inspite of the young stamens being removed artificially, the flower produces fruit. Provide a suitable explanation for the above situation.​

Answer 1

1) The number of chromosomes in parents and offsprings of a particular species remains constant due to the halving of chromosomes under the meiosis process during gamete formation.

2) The flowers which contain both male and female reproductive organs are known as full or bisexual flowers. They will self-pollinate themselves. Examples: Tulip, Sunflower and Lily.

3) Offspring formed by sexual reproduction exhibit more variation than those formed by asexual reproduction because gametes of parents have qualitatively different genetic composition. In asexual reproduction due to involvement of only one parent, so there is no chance of variation.

4) Number of chromosomes in the female gamete is 24, the number of chromosomes in the zygote is 48.

5) If pollination does not occur then fertilization cannot take place because male gametes will not be available. For fertilization both male and female gametes must be present.

6) the two major reasons for appearance of variation among the progeny formed from sexual reproduction are; crossing over in which the DNA gets exchanged between the homologous chromosomes during the meiosis that causes variation in the offspring.

7) A bisexual flower has the male as well as female reproductive organs. If the young stamens, (i.e., male unit) is removed artificially, the flower still has its pistil, (i.e., female unit) intact. Thus, cross pollination can occur.