CBSE Class X Science Chapter 7 How do Organisms Reproduce? Questions and Answers

In-Text Questions (Page 114)

Q1: What is the importance of DNA copying in reproduction?

The importance of DNA copying in reproduction includes:

• It passes on the information source for making proteins, ensuring features are inherited from parents to the next generation.
• It provides the blueprint for maintaining consistent body design features necessary for a species to inhabit a specific niche.
• It generates subtle variations during copying, which form the basis for evolution and help species adapt to changing environments.

Q2: Why is variation beneficial to the species but not necessarily for the individual?

Variation may not benefit a single individual if the change offers no immediate advantage or if a drastic DNA copying error causes the cell to die. However, variation is beneficial to the species over time because if environmental conditions or niches change drastically (such as a rise in water temperature due to global warming), variant individuals (like heat-resistant bacteria) can survive and keep the population from being completely wiped out.

In-Text Questions (Page 119)

Q1: How does binary fission differ from multiple fission?

Binary Fission	Multiple Fission
A single cell splits into two equal halves during division.	A single cell divides into many daughter cells simultaneously.
Observed in organisms like Amoeba and Leishmania.	Observed in the malarial parasite, Plasmodium.

Figure 7.1(a): Binary fission in Amoeba

Figure 7.2: Multiple fission in Plasmodium

Q2: How will an organism be benefited if it reproduces through spores?

An organism benefits from reproducing through spores because the spores are covered by thick protective walls that allow them to survive unfavorable conditions. They remain protected until they come into contact with a moist surface where they can begin to grow into new individuals.

Figure 7.6: Spore formation in Rhizopus

Q3: Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Complex multi-cellular organisms cannot reproduce through regeneration because:

• They are not a random collection of cells; specialized cells are organized into tissues, and tissues into organs positioned at definite locations in the body.
• Cell-by-cell division or growing an entire organism from a body part is impractical in such a highly organized structure.
• Regeneration requires specific specialized cells that can proliferate and make other cell types, which complex organisms lack throughout their entire body structure.

Q4: Why is vegetative propagation practised for growing some types of plants?

Vegetative propagation is practised because:

• Plants raised this way can bear flowers and fruits earlier than those produced from seeds.
• It allows the propagation of plants that have lost the capacity to produce seeds, such as banana, orange, rose, and jasmine.
• All new plants produced are genetically similar enough to the parent plant to retain all its desirable characteristics.

Figure 7.5: Leaf of Bryophyllum with buds

Q5: Why is DNA copying an essential part of the process of reproduction?

DNA copying is essential because DNA contains the information source for making proteins and building the structural blueprint of an organism. Copying DNA ensures that genetic features are passed from parents to offspring, accompanied by the creation of an additional cellular apparatus so each new cell can function and maintain life processes.

In-Text Questions (Page 126)

Q1: How is the process of pollination different from fertilisation?

Pollination	Fertilisation
It is the transfer of pollen grains from the anther to the stigma of a flower.	It is the fusion of the male germ-cell (from the pollen grain) with the female gamete (egg cell in the ovule).
Achieved by external agents like wind, water, or animals.	Occurs internally after the pollen tube grows down to the ovary.
Precedes fertilisation.	Results in the formation of a zygote.

Figure 7.8: Germination of pollen on stigma

Q2: What is the role of the seminal vesicles and the prostate gland?

The seminal vesicles and the prostate gland add their secretions along the path of the vas deferens. These secretions make the transport of sperms easier by placing them in a fluid medium and provide nutrition to the sperms.

Figure 7.10: Human male reproductive system

Q3: What are the changes seen in girls at the time of puberty?

The changes seen in girls at the time of puberty include:

• Increase in breast size and darkening of the skin of the nipples at the tips of the breasts.
• Beginning of menstruation.
• Growth of thick hair in new parts of the body such as armpits and the genital area.
• Appearance of thinner hair on legs, arms, and face.
• Skin frequently becoming oily, leading to pimples.

Q4: How does the embryo get nourishment inside the mother's body?

The embryo receives nourishment through a special disc-like tissue called the placenta embedded in the uterine wall. The placenta contains villi on the embryo's side and blood spaces surrounding the villi on the mother's side. This structure provides a large surface area for glucose and oxygen to pass from the mother's blood to the embryo.

Figure 7.11: Human female reproductive system

Q5: If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?

No, using a copper-T will not help in protecting her from sexually transmitted diseases. A copper-T is a contraceptive device placed inside the uterus to prevent pregnancy, but it does not act as a mechanical barrier to prevent the transmission of infectious fluids during sexual intercourse.

Chapter End Exercises (Page 127)

Q1: Asexual reproduction takes place through budding in

(a) Amoeba.
(b) Yeast.
(c) Plasmodium.
(d) Leishmania.

Answer: (b) Yeast.

Q2: Which of the following is not a part of the female reproductive system in human beings?

(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube

Answer: (c) Vas deferens (It is part of the male reproductive system).

Q3: The anther contains

(a) sepals.
(b) ovules.
(c) pistil.
(d) pollen grains.

Answer: (d) pollen grains.

Q4: What are the advantages of sexual reproduction over asexual reproduction?

The advantages of sexual reproduction over asexual reproduction are:

• It combines DNA from two different individuals, creating novel combinations of variants in each generation.
• It speeds up the process of generating variation compared to slow DNA-copying errors in asexual reproduction.
• The generated variations ensure the survival of species over time when exposed to changing environmental conditions.

Q5: What are the functions performed by the testis in human beings?

The functions of the testes in human beings are:

• Production of male germ-cells or sperms.
• Secretion of the hormone testosterone, which regulates sperm formation and brings about secondary sexual characteristics in boys at puberty.

Q6: Why does menstruation occur?

Every month, one ovary releases an egg, and the uterus prepares its lining by making it thick and spongy to nourish a potential embryo. If the egg is not fertilised by a sperm, it lives for about one day and the prepared uterine lining is no longer needed. Consequently, the lining slowly breaks down and exits through the vagina as blood and mucous, causing menstruation.

Q7: Draw a labelled diagram of the longitudinal section of a flower.

Figure 7.7: Longitudinal section of flower

Key parts to label include:

• Stamen (Male reproductive part): Anther and Filament.
• Pistil (Female reproductive part): Stigma, Style, and Ovary.
• Other parts: Sepal and Petal.

Q8: What are the different methods of contraception?

The main methods of contraception are:

• Mechanical Barriers: Condoms on the penis or coverings in the vagina prevent sperms from reaching the egg.
• Chemical/Hormonal Methods: Oral pills change the body's hormonal balance so eggs are not released.
• Contraceptive Devices: Devices like the loop or copper-T are placed in the uterus to prevent pregnancy.
• Surgical Methods: Blocking the vas deferens in males (preventing sperm transfer) or blocking the fallopian tubes in females (preventing egg movement).

Q9: How are the modes for reproduction different in unicellular and multicellular organisms?

Unicellular Organisms	Multicellular Organisms
Reproduction happens through simple cell division or fission (e.g., binary fission, multiple fission).	Reproduction involves complex modes such as fragmentation, vegetative propagation, spore formation, budding, or sexual reproduction.
The entire single organism divides to form new individuals.	Reproduction is carried out by specialized cells, tissues, or organs.

Q10: How does reproduction help in providing stability to populations of species?

Reproduction maintains consistent DNA copying, which preserves body design features that allow a species to reliably occupy a specific niche in an ecosystem. Furthermore, the variations introduced during reproduction enable some individuals to survive environmental changes, preventing population extinction and providing overall species stability.

Q11: What could be the reasons for adopting contraceptive methods?

Reasons for adopting contraceptive methods include:

• To avoid unwanted pregnancies and family planning.
• To protect female physical and mental health from frequent or premature pregnancies.
• To prevent the transmission of sexually transmitted diseases (STDs) like HIV-AIDS, gonorrhoea, and syphilis using mechanical barriers.
• To control population growth and help improve living standards.