BIOLOGY CLASSWORK NOTES
CLASS: X
HOW DO ORGANISMS REPRODUCE?
1. What is the importance of DNA copying reproduction?
DNA copying is the basic event of reproduction through which genetic
information of the parents pass to the offspring. It maintains the body
design features in different generations of the species. Also produces
variations. Such variations are essential for the survival of species over
time.
2. How are binary fission different from multiple fission?
Binary fission of the parent cell results in the formation of two small,
nearly equal sized daughter individuals whereas multiple fission results
in the formation of several daughter individuals.
3. How will an organism be benefited if it reproduces through spores?
• Spores are widely dispersed by wind.
• A large number of organisms are produced from a single parent
through sporulation.
• Spores are covered by thick wall to withstand unfavourable
conditions of the environment.
• Spores are small and light in weight, thus easily dispersed
through wind, water and animals.
4. Can you think of a reason why more complex organisms cannot give rise to
new individuals through regeneration?
Complex organisms have several kind of specialised organs and organ
systems. They have less number of undifferentiated cells so the
power of regeneration is limited and only restricted to certain cells.
For example, stem cells can form some tissues and organs but not
the complete individuals.
5. Why is vegetative propagation practiced for growing some type of plants?
• Vegetative propagation is used in plants which lost their capacity
to produce seeds or do not produce viable seeds.
• Plants produced through this method are genetically similar.
• Flowers and fruits are grown in shorter duration.
• It is a cheaper, rapid and easier method of propagation.
6. Why is DNA copying essential part of the process of reproduction?
Reproduction results in the production of offspring which are exactly
similar to parents. The exact blue prints of body design is inherited in
the offspring due to DNA replication in the parent cell. Thus DNA
copying is essential part of the process of reproduction.
7. What is the role of seminal vesicle and prostate gland?
• Seminal vesicle secrete fluid for nourishment of sperms.
• Prostate gland also produces fluid which along with the secretion
of seminal vesicle help in motility of sperms.
• The secretions of these glands with sperms is semen. It affects
the vaginal pH so that sperms move smoothly inside the vagina.
8. How does embryo gets nourishment inside the mother’s body?
The embryo gets nourishment from the mother’s blood through
placenta. The placenta is a disc shaped tissue embedded in uterine
wall. It contains villi on the embryo side and blood spaces on the
mother’s side. This provides large surface area for glucose and oxygen
to pass from the mother to the embryo.
9. What are the advantages of sexual reproduction over asexual reproduction?
• In asexual reproduction, the offspring are identical to their
parents because they have same genes as of their parents. Thus
genetic variations are not possible.
• Sexual reproduction involves fusion of male and female gametes
coming from both the parents. Offspring receive genes from
mother as well as from the father. This results in genetic
variations.
• Sexual reproduction promote diversity of characters of offspring
by providing genetic variations. This genetic variations lead to
evolution of species.
9. Why does menstruation occur?
Menstruation occurs in the human female when the egg is not fertilised
by male sperm. The thick and soft uterus lining having a lot of blood
capillaries ruptures. The unfertilised egg disintegrates within a day.
This results in shedding of blood along with mucus through vagina.
10. How does reproduction help in providing stability to population of species?
Reproduction help in increasing the number of organisms. Stability of
the population is attained when the rate of birth is approximately equal
to rate of death. Through reproduction, population increases and
compensates for the dead organisms and maintains stability.
11. What could be the reason for adopting contraceptive methods?
• Prevent unwanted conception
• Keep a check on population explosion
• Improve standard of living
• Pave sufficient gap between successive birth of child
• Protection from sexually transmitted diseases.
12. Explain how, offspring and parents of organisms reproducing sexually have
the same number of chromosomes.
Sexual reproduction involves two diploid (2x) parents. During gamete
formation, meiosis occurs which results in formation of haploid
gametes. Fertilisation of male and female gametes, restores the
diploid chromosome number in the zygote (2x).
Draw all the diagrams and label .
