Intext Questions (Page 115)
Question 1: What is the importance of DNA copying in reproduction?
Answer-
The basic event in reproduction is the creation of a DNA copy. The chromosomes in the nucleus contain information for the inheritance of features from parents to the next generation in the form of DNA molecules. DNA is the information source for making proteins, and these proteins determine the body design. If the body designs of new individuals are to be similar to the parents, the blueprints for these designs must be similar. Thus, DNA copying is essential to maintain the body design features and the stability of populations of species.
Question 2: Why is variation beneficial to the species but not necessarily for the individual?
Answer-
Variation is beneficial to the species because it is useful for the survival of the species over time. Populations fill well-defined niches. Niches can change drastically due to reasons beyond the organism’s control (e.g., temperature changes, water level variations). If the entire population is uniform and the niche is drastically altered, the population could be wiped out. However, if variations are present, the few variants resistant to the change would survive and grow further, ensuring the species survives the niche alteration.
Variation is not necessarily beneficial for the individual because some variations might be so drastic that the new DNA copy cannot work with the cellular apparatus it inherits, and such a newborn cell will simply die.
Intext Questions (Page 119)
Question 1: How does binary fission differ from multiple fission?
Answer-
Fission leads to the creation of new individuals in unicellular organisms.
In binary fission, many bacteria and protozoa (like Amoeba) simply split into two equal halves during cell division. In some organisms, like Amoeba, the splitting can occur in any plane.
In multiple fission, single-celled organisms, such as the malarial parasite (Plasmodium), divide into many daughter cells simultaneously.
Question 2: How will an organism be benefited if it reproduces through spores?
Answer-
Organisms that reproduce through spores, like the bread mould (Rhizopus), benefit primarily from the protection and dissemination provided by the spores.
- Protection: The spores are covered by thick walls that protect them until they come into contact with another moist surface.
- Survival and Growth: Once conditions are favourable (e.g., moist surface), the spores can begin to grow and develop into new individuals.
Question 3: Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer-
More complex multi-cellular organisms cannot simply give rise to new individuals through regeneration because they have a complex and carefully organised body design.
- Specialisation: In complex organisms, specialized cells are organised as tissues, and tissues are organised into organs, which have to be placed at definite positions in the body.
- Impracticality: In such a complex situation, cell-by-cell division would be impractical. Regeneration, though carried out by specialized cells, involves an organised sequence referred to as development, but it is not the same as reproduction, as most organisms do not normally depend on being cut up to be able to reproduce.
Question 4: Why is vegetative propagation practised for growing some types of plants?
Answer-
Vegetative propagation is practised for growing some types of plants because it offers several advantages over growing plants from seeds:
- Early Bearing: Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds.
- Seedless Propagation: This method makes it possible to propagate plants, such as banana, orange, rose, and jasmine, that have lost the capacity to produce seeds.
- Genetic Similarity: All plants produced are genetically similar enough to the parent plant to have all its characteristics.
Question 5: Why is DNA copying an essential part of the process of reproduction?
Answer-
DNA copying is an essential part of the process of reproduction because it serves as the mechanism for transferring the blueprint of the body design from one generation to the next.
- Information Source: The DNA in the cell nucleus is the information source for making proteins, which eventually lead to the body design.
- Body Design Maintenance: For the new individual to look similar to the parent, the DNA copies must be made so that the body designs are similar.
- Cellular Apparatus: DNA copying is accompanied by the creation of an additional cellular apparatus. When the cell divides, each resulting cell receives a copy of the DNA along with the cellular apparatus necessary for maintaining life processes.
Intext Questions (Page 127)
Question 1: How is the process of pollination different from fertilisation?
Answer-
Pollination is the process that precedes fertilisation in flowering plants:
- Mechanism: Pollination is the transfer of pollen grains from the stamen (male reproductive part) to the stigma (terminal part of the pistil, the female reproductive part).
- Types: Pollination can be self-pollination (transfer within the same flower) or cross-pollination (transfer between different flowers), often achieved by agents like wind, water, or animals.
Fertilisation is the subsequent fusion of germ-cells:
- Mechanism: Fertilisation is the process where the male germ-cell produced by the pollen grain fuses with the female gamete (egg cell) present in the ovule.
- Product: This fusion gives rise to the zygote, which is capable of growing into a new plant.
Question 2: What is the role of the seminal vesicles and the prostate gland?
Answer-
The seminal vesicles and the prostate gland are glands located along the path of the vas deferens in the male reproductive system.
Their role is to add their secretions to the sperms. This fluid serves two main functions:
- Transport: It makes the transport of the sperms easier.
- Nutrition: The fluid also provides nutrition to the sperms.
Question 3: What are the changes seen in girls at the time of puberty?
Answer-
Puberty is the period during adolescence when the maturation of reproductive tissue begins. Changes seen in girls include:
- Hair Growth: Thick hair begins growing in new parts of the body such as armpits and the genital area. Thinner hair can also appear on legs, arms, and face. The skin may become oily.
- Breast Development: Breast size begins to increase, often accompanied by darkening of the skin of the nipples at the tips of the breasts.
- Menstruation: Girls begin to menstruate around this time.
Question 4: How does the embryo get nourishment inside the mother’s body?
Answer-
The embryo gets nourishment from the mother’s blood with the help of a special tissue called the placenta.
- Structure: The placenta is a disc-like tissue embedded in the uterine wall. It contains villi on the embryo’s side and is surrounded by blood spaces on the mother’s side.
- Exchange: This arrangement provides a large surface area for glucose and oxygen to pass from the mother to the embryo.
- Waste Removal: The placenta also removes waste substances generated by the developing embryo by transferring them into the mother’s blood.
Question 5: If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?
Answer-
No, if a woman is using a copper-T, it will not help in protecting her from sexually transmitted diseases (STDs).
- Copper-T Function: The copper-T is a contraceptive device placed in the uterus to prevent pregnancy by creating a mechanical barrier or affecting the uterine environment.
- STD Protection: To prevent the transmission of STDs (like gonorrhoea, syphilis, warts, and HIV-AIDS) during the sexual act, a covering, called a condom, for the penis during sex helps to prevent transmission of many of these infections to some extent.
Exercise Questions (Page 127-128)
Question 1: Asexual reproduction takes place through budding in
(a) Amoeba.
(b) Yeast.
(c) Plasmodium.
(d) Leishmania.
Answer-
Asexual reproduction takes place through budding in (b) Yeast. Amoeba uses binary fission, and Plasmodium uses multiple fission.
Question 2: 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-
The (c) Vas deferens is a component of the male reproductive system, responsible for delivering sperms from the testes.
The correct option is (c) Vas deferens.
Question 3: The anther contains
(a) sepals.
(b) ovules.
(c) pistil.
(d) pollen grains.
Answer-
The anther is part of the stamen (male reproductive part) of a flower. It produces the pollen grains, which contain the male germ-cells.
The correct option is (d) pollen grains.
Question 4: What are the advantages of sexual reproduction over asexual reproduction?
Answer-
Sexual reproduction is advantageous over asexual reproduction because it allows for greater variation to be generated.
- Creation of Novel Combinations: Sexual reproduction involves the combination of DNA from two different individuals, creating new, novel combinations of variants. This allows the process of making variants to be speeded up compared to the slow variations accumulated through DNA copying errors alone.
- Survival of Species: The increased variation is crucial for the survival of the species over time by providing individuals capable of adapting if the niche is drastically altered.
- Restoring DNA Content: The sexual mode uses meiosis to halve the number of chromosomes in germ-cells; fusion then re-establishes the DNA content in the new generation.
Question 5: What are the functions performed by the testis in human beings?
Answer-
The testes are located outside the abdominal cavity in the scrotum. They perform two main functions:
- Germ-cell Formation: The testes are the site for the formation of the germ-cells or sperms. Sperm formation requires a lower temperature than the normal body temperature.
- Hormone Secretion: The testes are involved in the secretion of the hormone testosterone. Testosterone regulates the formation of sperms and brings about the changes in appearance seen in boys at the time of puberty.
Question 6: Why does menstruation occur?
Answer-
Menstruation occurs when the egg released by the ovary is not fertilised.
- Uterine Preparation: The uterus prepares itself every month to receive a fertilised egg by making its lining thick and spongy and richly supplied with blood to nourish a potential embryo.
- Shedding of Lining: If fertilisation does not take place, the prepared lining is not needed any longer. Consequently, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle, known as menstruation, takes place roughly every month.
Question 7: Draw a labelled diagram of the longitudinal section of a flower.
Answer-
(The source provides Fig 7.7 as the diagram, which shows the longitudinal section of a flower. The key labelled parts are the sepals, petals, stamen (consisting of anther and filament), and pistil (consisting of stigma, style, and ovary, with ovules inside the ovary)).
Question 8: What are the different methods of contraception?
Answer-
Contraceptive methods are devised ways to avoid pregnancy. They fall into several categories:
- Mechanical Barriers: Devices that create a mechanical barrier so that sperm does not reach the egg. Examples include condoms (for the penis or worn in the vagina).
- Chemical Methods (Hormonal Balance): Methods that change the hormonal balance of the body so that eggs are not released and fertilisation cannot occur. These are usually oral pills.
- Intrauterine Devices (IUDs): Devices like the loop or the copper-T that are placed in the uterus to prevent pregnancy.
- Surgical Methods (Creating Blocks): Methods used to create physical blocks to prevent the fusion of gametes. These include blocking the vas deferens in the male or blocking the fallopian tube in the female.
Question 9: How are the modes for reproduction different in unicellular and multicellular organisms?
Answer-
The modes of reproduction depend fundamentally on the body design of the organisms.
| Feature | Unicellular Organisms | Multicellular Organisms |
|---|---|---|
| Complexity | Simple body organization. | Complex body organization where specialized cells are organized into tissues and organs. |
| Mode | Reproduction is typically through fission (binary or multiple) or budding (as in yeast). | Requires more complex ways of reproduction. Reproduction is the function of a specific cell type. |
| Mechanism | Simple cell division leads directly to new individuals. Cell-by-cell division is practical. | Cannot divide cell-by-cell. Asexual modes involve vegetative parts (plants) or regeneration/budding using specialised cells (simple animals like Hydra or Planaria). Sexual modes involve specialized germ-cells and complex reproductive systems. |
Question 10: How does reproduction help in providing stability to populations of species?
Answer-
Reproduction provides stability to populations of species in the following ways:
- Continuity of Species: Organisms reproduce to create new individuals and ensure the continued existence of their kind.
- Niche Maintenance: The consistency of DNA copying during reproduction maintains the body design features that allow the organism to effectively use its particular niche in the ecosystem.
- Variation and Survival: Reproduction, especially sexual reproduction, introduces variation. This variation is crucial because if the environmental niche is drastically altered, individuals with variations resistant to the change will survive and grow further, thus preventing the entire species from being wiped out.
Question 11: What could be the reasons for adopting contraceptive methods?
Answer-
Contraceptive methods are adopted primarily to avoid pregnancy. Reasons for adopting these methods include:
- Health of the Woman: Pregnancy makes major demands on the body and mind of the woman. If she is not ready for it, her health will be adversely affected.
- Personal Choice/Responsibility: Sexual maturation does not necessarily mean the body or mind is ready for the responsibility of having and bringing up children. Contraception allows for responsible choice.
- Population Control: The size of the human population is a cause for concern, as an expanding population makes it harder to improve everybody’s standard of living. Contraception helps in controlling population size.
- Spacing Children: Families may choose to space out births to ensure better care and resources for existing children.