HOW DO ORGANISMS REPRODUCE?
1) Draw a well labelled diagram of the human male reproductive system.
DRAW THE DIAGRAM IN PAGE 137 fig. 8.10
2) Draw a well labelled diagram of the human female reproductive system.
DRAW THE DIAGRAM IN PAGE 137 fig. 8.11
3) How are the modes of reproduction different in unicellular and
multicellular organisms?
1
Unicellular organisms
They have only one cell
1
2
No separate tissue for reproduction
2
3
They can reproduce asexually by
the process of fission(binary or
multiple) or budding as in yeast.
3
Multicellular Organisms
They contain various cells and
have separate systems
Separate systems for reproduction
They can reproduce by both sexual
and asexual means.
4) How does reproduction help in providing stability to populations of a
species?
➢ The consistency of DNA copying during reproduction is important for
maintenance of body design features that allow the organism to live in
a particular area.
➢ This consistency of DNA copying provides stability to the population
of a species.
➢ Reproduction is responsible for continuation of a species.
➢ Stability to populations of species is attained by equalizing the birth
and death ratio of individuals.
➢ Birth is possible only due to reproduction.
5) Reproduction is essentially a phenomenon that is not for survival of an
individual but for the continuation of a species. Justify.
➢ For survival, an individual needs energy which it obtains from life
processes such as nutrition and respiration.
➢ Reproduction does not provide energy for survival.
➢ Instead it ensures transfer of genetic material from one generation to
the next which helps in continuation of a species.
➢ Hence it is an important phenomenon for maintaining continuity of a
species.
6) Can you consider cell division as a type of reproduction in unicellular
organisms? Give one reason.
➢ Yes. For example, let us take the case of amoeba, which undergoes
asexual reproduction through binary fission, resulting in the
formation of two daughter cells.
➢ Reproduction is basically the production of more number of
individuals.
➢ Here one amoeba has become two, which is reproduction.
7) What is sexual reproduction? List its four significances.
➢ Sexual reproduction is the fusion of the male and female gamete
leading to the formation of a zygote.
➢ The two major processes namely formation of gametes and fusion of
gametes constitute the process.
Its significances are:
➢ Incorporates the process of combining the DNA from two different
individuals during reproduction.
➢ Increases genetic variation.
➢ Promotes diversity in the offspring.
➢ Plays a role in the origin of a new species.
8) Explain how the parents and offspring of a sexually reproducing
organism have the same number of chromosomes.
➢ During asexual reproduction, organisms undergo only mitotic
division.
➢ The DNA of the cells involved are copied and then equally divided
among the two daughter cells formed.
➢ Thus the chromosome number remains unchanged.
➢ In sexual reproduction, organisms produce gametes through meiosis
which is called reduction division, in which the original number of
chromosomes becomes half.
➢ These two gametes combine to form the zygote and the original
number of chromosomes is restored.
➢ For example, in humans, the parents each have 23 pairs of
chromosomes. In the gametes, the sperm has half the number of
chromosomes that is 23 and the egg also has 23 chromosomes. When
the sperm and the egg fuse, the zygote has 46 chromosomes.
➢ Thus the number remains constant.
9) Mention the information source for making proteins in the cell. What is
the basic event in reproduction?
➢ The DNA in the nucleus of a cell is the information source for making
the proteins.
➢ If the information is changed different proteins will be made.
➢ Cells use chemical reactions to build copies of their DNA.
➢ This creates 2 copies of the DNA in a reproducing cell and they need
to get separated from each other.
➢ DNA copying is accompanied by the creation of an additional cellular
apparatus.
10)
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What is placenta? Mention its role in pregnancy.
Placenta is a special tissue which is in the form of a disc embedded in
the uterine wall.
It serves as a connection between the embryo and the uterine wall.
It possesses villi on the embryo’s side and blood filled spaces on the
maternal side which surrounds the villi.
This increases the surface area for absorption of nutrients.
It facilitates passage of nutrients and oxygen to embryo from mother
through blood.
Waste produced by embryo is removed through placenta into the
mother’s blood.
.
11) Assertion(A): Ovary releases one egg every month.
Reason(R): The lining of the uterus is always thick and spongy. Identify the
correct option.
A) Both assertion and reason are true and reason is the correct explanation of
assertion.
B) Both assertion and reason are true but reason is not correct explanation of
assertion.
C) Assertion is true but reason is false.
D)Both assertion and reason are false
Answer: C
12). A news paper headline incorrectly stated that the use of condoms can result in
erectile dysfunction, which may lead to problems during sexual intercourse.
Scientists are concerned that this incorrect statement could lead to an increase in
HIV.
(i) What name is used to describe the method of birth control involving the use of
condoms?
(ii) Explain how a condom acts as a method of birth control.
(iii) Explain how a decrease in the use of condoms may lead to an increase in the
incidence of HIV.
(iv) State two ways by which a person who does not have sexual intercourse might
still become infected with HIV.
(v) Name any other two STDs.
(i)
Barrier Method
(ii)
Condoms are coverings worn over the penis during sexual intercourse.
It creates a mechanical barrier so that the sperms do not reach the egg
preventing fertilisation.
(iii)
Condoms not only prevent pregnancy but also prevent the spread of STD
as they reduce the chance of skin tearing and thus transmission of
sexually transmitted diseases.
(iv)
HIV can spread through blood transfusion as well as by using a needle
which was used by an infected person
(v)
Gonorrhoea, syphilis.
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