Class 10 Science Chapter 7 Question Answers - How do Organisms Reproduce?

Q1: Write the full form of DNA. Where is it located? What does it consist of?
Ans: DNA = Deoxyribo Nucleic Acid. It is located in the nucleus of the cell. It consists of nucleotides which make nucleic acids.

Q2: Mention the information source for making proteins in the cell. What is the basic event in reproduction?
Ans: The information source for making proteins in the cell is deoxyribo nucleic acid (DNA). The basic event in reproduction is the replication of DNA and cell division.

Q3: How does the creation of variation in a species promote survival?
Ans: Creation of variation increases the probability or chances of survival of some members of the population under adverse conditions. This ensures the survival of the species under unfavourable conditions.

Q4: Protozoans reproduce by binary fission as well as multiple fission. Which process is better and why? Give your opinion.
Ans: Multiple fission is better than binary fission because it produces many daughter cells inside a protective structure called cyst which ensures their survival under adverse conditions.

Q5: Name the kind of organisms that reproduce by spore formation. How will an organism be benefitted if it reproduces through spores?
Ans: Rhizopus (Fungus) reproduces by spore formation. The organism is benefitted because the spores are covered by thick walls that protect them until they come in contact with a moist surface and begin to grow.

Q6: Compare the vegetative propagation in Bryophyllum and money plant.
Ans:

• Bryophyllum reproduces by the adventitious buds present on the margins of its leaves.
• Money plant reproduces by stem cutting which can produce the whole plant when placed in moist soil.

Q7: List any two pubertal changes that appear in both boys and girls.
Ans: The two pubertal changes which appear in both boys and girls are:

• The skin becomes oily and pimples appear
• Pubic hairs appear

Q8: (a) Specify the events which occur in the reproductive system of a human female.
(i) if egg is fertilised
(ii) if egg is not fertilised.
(b) Mention the changes that take place in uterus in both the above events.
Ans: (a) (i) Pregnancy
(ii) Menstruation
(b) If the egg gets fertilised then the wall of the uterus becomes thick and spongy with a rich supply of blood vessels to receive the fertilised zygote.
If the egg does not get fertilised then the blood vessels in the wall of the uterus along with the spongy uterine tissue is shed in the form of blood and mucus through the vagina.

Q9: Prenatal sex determination has been prohibited by law, state two reasons.
Ans: Prenatal sex determination has been prohibited by law to:

• Check the female foeticide
• Prevent the decline in female sex ratio

Q10: How can pregnancy be prevented surgically?
Ans: The pregnancy can be prevented surgically by:

• Vasectomy: The vas deferens of male is blocked to prevent sperm transfer.
• Tubectomy: The fallopian tube of female is blocked to prevent egg to reach uterus.

Q11: 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?
Ans: Number of chromosomes in female gamete is 24.
Number of chromosomes in zygote is 48.

Q12: How are general growth and sexual maturation different from each other?
Ans: General growth comprises of the different types of developmental process in the body like increase in height, weight gain, changes in shape and size of the body. Sexual maturation refers to the specific changes which occur at puberty like cracking of voice, new hair patterns, development of breast in female, etc.

Q13: Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.
Ans: Sperm comes out from testis into the vas deferens and pass through the urethra before ejaculation. The secretions of seminal vesicle and prostate glands provide nutrition to the sperms and also facilitate their transport.

Q14: What changes are observed in the uterus if fertilisation does not occur?
Ans: If fertilisation does not occur then the thick and spongy lining of the uterus slowly breaks and comes out through the vagina in the form of blood and mucus.

Q15: What changes are observed in the uterus subsequent to implantation of young embryo?
Ans: After implantation, a special tissue called placenta develops which connects embryo to the uterine wall. Placenta provides nutrients and oxygen to the embryo which are obtained from the rich blood supply of the uterine wall.

Q16: Differentiate between reproduction and regeneration. Name any two organisms which grow by regeneration.
Ans: Reproduction is the process by which an organism produces its young ones for perpetuation of its race. Some organisms have the ability to form new organisms from the pieces of its body which has been cut into different pieces. This process by which new organisms develop from the parts of an organism is called regeneration. Planaria and Hydra have the ability of regeneration.

Q17: Name the female reproductive part of a flower. Which part of a flower develops into a seed and a fruit? Where are the male germ cell and female gamete present in the flower?
Ans: Female reproductive part of a flower is carpel. Ovule develops into a seed and a fertilised ovary develops into fruit. Male germ cells are present in the pollen grain of a flower. Female gamete are present in the ovules located in ovary of a flower.

Q18: (a) Trace the path of sperms from where they are produced in human body to the exterior.
(b) Write the functions of secretions of prostate gland and seminal vesicle in humans.
Ans: Sperm comes out from testis into the vas deferens and pass through the urethra before ejaculation. The secretions of seminal vesicle and prostrate glands provide nutrition to the sperms and also facilitate their transport.

Q19: Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes.
Ans: The process of cell division called meiosis halves the number of chromosomes present in the cell of an organism. The gametes produced as a result of meiosis, fuse during sexual reproduction and restore the number of chromosomes in the offsprings of the individual.

Q20: Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?
Ans: Moist slice of bread is able to provide both moisture and nutrients needed for the growth of the hyphae. Dry slice of bread is able to provide only the nutrients but not moisture, so the hyphae do not grow on the dry slice of bread.