Question 1

What is the importance of DNA copying in reproduction?

Accepted Answer

DNA copying is crucial in reproduction because it ensures that the genetic information is accurately passed from the parent organism to the offspring. This copying allows the offspring to inherit traits and characteristics of the parent, maintaining the continuity of species. Without DNA copying, reproduction would not result in offspring with the same genetic makeup, leading to loss of hereditary information. — During reproduction, the DNA in the parent cell is duplicated so that each new cell or organism receives a complete set of genetic instructions. This process maintains genetic stability across generations.

Question 2

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

Accepted Answer

Variation is beneficial to a species because it increases the genetic diversity within the population, which helps the species adapt to changing environments and survive over time. Different traits may provide advantages under different conditions, ensuring the species' survival. However, for an individual, variation may not always be beneficial because some variations can be harmful or disadvantageous, reducing the individual's chances of survival or reproduction. — While variation promotes adaptability and evolution at the species level, individual variations can be neutral, beneficial, or harmful. Therefore, variation benefits the species by providing a pool of traits for natural selection but does not guarantee benefit for every individual.

Question 3

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

Accepted Answer

More complex organisms have highly specialised tissues and organs that perform specific functions. Regeneration requires the ability to regrow entire body parts or whole organisms from fragments. In complex organisms, cells are differentiated and cannot revert to a pluripotent state easily, limiting their ability to regenerate whole new individuals. Additionally, the complexity of body organisation and the need for precise coordination of multiple systems make regeneration of a whole organism unfeasible. — Regeneration depends on the ability of cells to divide and differentiate into all required cell types. In simple organisms, many cells retain this ability. In complex organisms, cells are specialised and lose this ability, preventing regeneration of whole new individuals.

Question 4

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

Accepted Answer

Vegetative propagation is practised because it allows the production of new plants that are genetically identical to the parent plant, ensuring the preservation of desired traits. It is also faster than growing plants from seeds and can be used to propagate plants that do not produce viable seeds or have seeds that take a long time to germinate. — Vegetative propagation uses parts like stems, roots, or leaves to grow new plants. This method bypasses seed formation, leading to quicker and reliable reproduction of plants with desirable characteristics.

Question 5

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

Accepted Answer

DNA copying is essential because it ensures that the genetic information is passed from the parent organism to the offspring. This copying allows the offspring to inherit traits and characteristics of the parents, enabling continuity of species and proper development of the new individual. — During reproduction, cells divide and DNA is copied so that each new cell receives a complete set of genetic instructions. Without accurate DNA copying, offspring would not develop correctly or inherit parental traits.

Question 6

Asexual reproduction takes place through budding in
(a) Amoeba.
(b) Yeast.
(c) Plasmodium.
(d) Leishmania.

Accepted Answer

The correct answer is (b) Yeast. Yeast reproduces asexually by budding, where a new cell grows out of the body of a parent cell. — Budding is a form of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. Yeast reproduces by budding, unlike Amoeba which reproduces by binary fission.

Question 7

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

Accepted Answer

The correct answer is (c) Vas deferens. Vas deferens is a part of the male reproductive system, not female. — The female reproductive system includes ovary, uterus, and fallopian tube. Vas deferens is a duct in males that transports sperm from the epididymis to the ejaculatory ducts.

Question 8

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

Accepted Answer

The correct answer is (d) pollen grains. The anther is the part of the stamen that produces pollen grains. — Anther is the male reproductive part of the flower that produces pollen grains which contain male gametes. Sepals are part of the calyx, ovules are inside the ovary, and pistil is the female reproductive part.

Question 9

What are the advantages of sexual reproduction over asexual reproduction?

Accepted Answer

Advantages of sexual reproduction over asexual reproduction include:
1. Genetic Variation: Sexual reproduction combines genetic material from two parents, leading to offspring with genetic variation, which helps in adaptation and evolution.
2. Evolutionary Benefits: Genetic diversity increases the chances of survival under changing environmental conditions.
3. Disease Resistance: Variation helps populations resist diseases and parasites better.
4. Elimination of Harmful Mutations: Sexual reproduction can help eliminate harmful mutations through recombination.
5. Better Adaptability: Populations can adapt to new environments more effectively. — Sexual reproduction involves the fusion of gametes from two parents, resulting in offspring with a mix of traits. This genetic recombination leads to diversity, which is beneficial for survival and evolution. In contrast, asexual reproduction produces genetically identical offspring, limiting adaptability.

Question 10

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

Accepted Answer

Functions of the testis in human beings:
1. Production of Sperm: Testes produce male gametes called spermatozoa necessary for fertilization.
2. Secretion of Male Hormones: Testes secrete testosterone which is responsible for the development of male secondary sexual characteristics such as facial hair, deep voice, and muscle development.
3. Regulation of Male Reproductive System: Testosterone also regulates libido and the functioning of male reproductive organs. — Testes are the primary male reproductive organs that produce sperm for reproduction and secrete hormones that regulate male characteristics and reproductive functions.

Question 11

Why does menstruation occur?

Accepted Answer

Menstruation occurs because the thickened lining of the uterus (endometrium) is not needed if fertilization does not take place. The lining breaks down and is shed through the vagina as menstrual blood. — Each month, the uterus prepares for pregnancy by thickening its lining. If the egg released during ovulation is not fertilized, the lining is not required and hence it breaks down and is expelled from the body as menstruation.

Question 12

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

Accepted Answer

A labelled diagram of the longitudinal section of a flower should include the following parts:
- Petal
- Sepal
- Stamen (Anther and Filament)
- Pistil (Stigma, Style, Ovary)
- Ovule
- Receptacle
- Pedicel

The diagram should clearly show the arrangement of these parts in the flower. — The longitudinal section of a flower shows the internal structure and arrangement of reproductive parts. Labeling helps identify each part and understand their functions in reproduction.

Question 13

What are the different methods of contraception?

Accepted Answer

Different methods of contraception include:
1. Barrier Methods: Condoms, diaphragms prevent sperm from reaching the egg.
2. Chemical Methods: Oral contraceptive pills, spermicides prevent ovulation or kill sperm.
3. Intrauterine Devices (IUDs): Devices inserted into the uterus to prevent implantation.
4. Surgical Methods: Vasectomy in males and tubectomy in females to permanently prevent reproduction.
5. Natural Methods: Rhythm method, withdrawal method based on timing of ovulation.
6. Hormonal Methods: Injectable contraceptives that prevent ovulation. — Contraception methods aim to prevent fertilization or implantation to avoid pregnancy. They vary in effectiveness, reversibility, and usage.

Question 14

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

Accepted Answer

Differences in modes of reproduction:
- Unicellular organisms reproduce mainly by asexual methods such as binary fission, budding, or spore formation because they consist of a single cell.
- Multicellular organisms reproduce by both asexual and sexual reproduction. Sexual reproduction is more common in multicellular organisms to increase genetic diversity.
- Unicellular reproduction results in genetically identical offspring, while multicellular reproduction often involves genetic recombination.
- Multicellular organisms have specialized reproductive organs, whereas unicellular organisms do not. — Unicellular organisms reproduce quickly and simply by dividing their single cell. Multicellular organisms have complex structures and often reproduce sexually to ensure variation and adaptability.

Question 15

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

Accepted Answer

Reproduction helps provide stability to populations by ensuring the continuation of species. It replaces individuals that die, maintains population size, and allows adaptation through genetic variation (in sexual reproduction). This stability helps ecosystems function properly. — Without reproduction, species would become extinct as individuals die. Reproduction maintains population numbers and genetic diversity, which is essential for survival in changing environments.

How do Organisms

How do Organisms — Study Notes

How do Organisms Reproduce?

7.1 DO ORGANISMS CREATE EXACT COPIES OF THEMSELVES?

7.1.1 The Importance of Variation

Practice Questions — How do Organisms

All 13 Chapters in Science