How do Organisms Reproduce?Class 10 Biology NCERT Solutions
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Q1EXERCISES
Asexual reproduction takes place through budding in
(a)
Amoeba.
(b)
Yeast.
(c)
Plasmodium.
(d)
Leishmania.
Solution
(b) Yeast.
Explanation: Amoeba and Leishmania reproduce by binary fission. Plasmodium reproduces by multiple fission. Yeast reproduces asexually by putting out small buds that separate and grow into new individuals.
Q2EXERCISES
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
Solution
(c) Vas deferens
Explanation: The vas deferens is a part of the male reproductive system. It is the tube that transports sperms from the testes. The ovary, uterus, and fallopian tube are all parts of the female reproductive system.
Q3EXERCISES
The anther contains
(a)
sepals.
(b)
ovules.
(c)
pistil.
(d)
pollen grains.
Solution
(d) pollen grains.
Explanation: The anther is part of the stamen, which is the male reproductive part of a flower. The anther's function is to produce and store pollen grains, which contain the male germ-cells.
Q4EXERCISES
What are the advantages of sexual reproduction over asexual reproduction?
Solution
Sexual reproduction has several key advantages over asexual reproduction, primarily related to genetic variation:
- Generation of Variation: Sexual reproduction involves combining DNA from two different individuals. This creates new combinations of genes and variations in the offspring. Asexual reproduction produces offspring that are genetically identical to the parent, so variation only arises from rare, slow DNA copying errors.
- Adaptation and Evolution: The greater variation generated by sexual reproduction provides the raw material for natural selection. It increases the chances that some individuals in a population will have traits suitable for surviving in a changing environment, thus ensuring the survival of the species and driving evolution.
- Elimination of Harmful Genes: In asexual reproduction, harmful mutations are passed on to all offspring. In sexual reproduction, the shuffling of genes can lead to offspring that do not inherit a particular harmful gene from a parent.
Q5EXERCISES
What are the functions performed by the testis in human beings?
Solution
The testes (singular: testis) are the primary reproductive organs in males and perform two main functions:
- Sperm Production: The primary function of the testes is the formation and maturation of male germ-cells, called sperms. This process is known as spermatogenesis. Sperm formation requires a temperature slightly lower than the normal body temperature, which is why the testes are located outside the abdominal cavity in the scrotum.
- Hormone Secretion: The testes produce the male sex hormone, testosterone. Testosterone regulates the formation of sperms and is also responsible for the development of secondary sexual characteristics in boys during puberty, such as the growth of facial hair, deepening of the voice, and muscle development.
Q6EXERCISES
Why does menstruation occur?
Solution
Menstruation occurs as part of the monthly reproductive cycle in females when the egg released by the ovary is not fertilised.
Each month, the uterus prepares itself to receive a fertilised egg. Its inner lining (endometrium) becomes thick, soft, and richly supplied with blood vessels to nourish a potential embryo. If fertilisation does not happen, the egg disintegrates after about a day. Consequently, the thickened uterine lining is no longer needed. The body then sheds this lining, which slowly breaks and comes out through the vagina as a mixture of blood and mucous. This monthly discharge is called menstruation, and the cycle typically lasts for about two to eight days.
Q7EXERCISES
Draw a labelled diagram of the longitudinal section of a flower.
Solution
To draw a labelled diagram of the longitudinal section of a flower, you should include and label the following parts, as shown in Figure 7.7 of the textbook:
- Pedicel: The stalk of the flower.
- Receptacle: The part of the flower stalk where the parts of the flower are attached.
- Sepals: The green, leaf-like structures at the base that protect the bud.
- Petals: The often colourful parts that attract pollinators.
- Stamen (Male reproductive part):
- Anther: The top part that produces pollen grains.
- Filament: The stalk that holds up the anther.
- Pistil/Carpel (Female reproductive part):
- Stigma: The sticky tip that receives pollen.
- Style: The tube-like structure connecting the stigma to the ovary.
- Ovary: The swollen base containing ovules.
- Ovule: Structure within the ovary that contains the female egg cell and develops into a seed after fertilisation.
(A diagram should be drawn based on Figure 7.7 in the textbook, clearly showing these parts.)
Q8EXERCISES
What are the different methods of contraception?
Solution
Contraceptive methods are ways to avoid pregnancy and can be categorised as follows:
-
Mechanical/Barrier Methods: These methods physically prevent sperm from reaching the egg.
- Condoms: A covering worn over the penis or inside the vagina. They also help prevent the transmission of sexually transmitted diseases (STDs).
-
Hormonal Methods: These methods alter the hormonal balance of the body to prevent the release of eggs (ovulation).
- Oral Pills: These drugs are taken orally and can have side effects due to the change in hormonal balance.
-
Intrauterine Devices (IUDs): These are devices placed in the uterus to prevent pregnancy.
- Copper-T or Loop: These can cause side effects due to irritation of the uterus.
-
Surgical Methods (Sterilisation): These are permanent methods that block the transport of gametes.
- Vasectomy (in males): The vas deferens is blocked to prevent sperm transfer.
- Tubectomy (in females): The fallopian tube is blocked to prevent the egg from reaching the uterus.
Q9EXERCISES
How are the modes for reproduction different in unicellular and multicellular organisms?
Solution
The modes of reproduction in unicellular and multicellular organisms differ significantly due to the complexity of their body designs.
-
Unicellular Organisms: These organisms have a simple body structure consisting of a single cell. Reproduction is typically asexual and involves the division of the entire cell. Common methods include:
- Fission: The cell splits into two (binary fission, e.g., Amoeba) or many (multiple fission, e.g., Plasmodium) new individuals.
- Budding: A small outgrowth or bud forms on the parent cell and detaches to become a new individual (e.g., Yeast).
-
Multicellular Organisms: These organisms have complex bodies with specialised cells, tissues, and organs. Their reproductive methods are more complex.
- Simple Multicellular Organisms: Some with simple body organisation can reproduce asexually through methods like fragmentation (e.g., Spirogyra) or regeneration (e.g., Planaria).
- Complex Multicellular Organisms: Most use sexual reproduction, which involves specialised reproductive organs and the production of specific germ-cells (gametes) from two different parents. This allows for genetic variation. Some plants also use vegetative propagation, an asexual method where new plants grow from parts like roots, stems, or leaves.
Q10EXERCISES
How does reproduction help in providing stability to populations of species?
Solution
Reproduction is crucial for providing stability to populations of species in the following ways:
- Continuity of Population: Reproduction is the process by which new individuals are created, replacing older individuals that die. This ensures the continuity of the population from one generation to the next, preventing the species from becoming extinct.
- Maintaining Niche Occupancy: The consistency of DNA copying during reproduction ensures that offspring have the same basic body design and features as their parents. These features are what allow the species to live successfully in a particular, well-defined place or niche in the ecosystem. By consistently producing well-adapted individuals, reproduction helps maintain the population's hold on its niche.
- Adaptation through Variation: While DNA copying is consistent, it is not perfect, leading to variations. In sexual reproduction, variations are generated more rapidly. This variation is essential for the long-term stability of a population, as it provides the raw material for the population to adapt to changes in the environment, ensuring survival even if the niche is altered.
Q11EXERCISES
What could be the reasons for adopting contraceptive methods?
Solution
People may adopt contraceptive methods for several personal, health, and social reasons:
- To Prevent Unwanted Pregnancy: This is the primary reason. It allows individuals and couples to choose if and when they want to have children.
- Family Planning and Spacing: Contraceptive methods help in planning the size of the family and maintaining a desired gap between the births of children, which is important for the health of the mother and the children.
- Protecting Health: Pregnancy places major demands on the body and mind of a woman. If she is not physically or mentally ready, her health can be adversely affected. Contraception helps avoid such health risks.
- Preventing Sexually Transmitted Diseases (STDs): Barrier methods like condoms are effective in preventing the transmission of STDs, including HIV-AIDS.
- Population Control: On a larger scale, family planning and the use of contraceptives are essential for managing the size of the human population, which helps in better management of resources and improving the standard of living.
Q1QUESTIONS (In-text, Page 2)
What is the importance of DNA copying in reproduction?
Solution
DNA copying is of fundamental importance in reproduction for the following reasons:
- Inheritance of Traits: The DNA in the cell nucleus contains the genetic information for the inheritance of features from parents to the next generation. DNA copying ensures that this information, which acts as a blueprint for body design, is passed on.
- Maintenance of Body Design: For an organism to produce new individuals of its own kind, its body design must be replicated. DNA copying allows for the creation of new individuals that look very much like their parents because they inherit a similar genetic blueprint.
- Continuity of Species: The process ensures that the essential information for making proteins and building a functional organism is transmitted, allowing the species to continue its existence over generations.
Q2QUESTIONS (In-text, Page 2)
Why is variation beneficial to the species but not necessarily for the individual?
Solution
Variation is beneficial to a species for its long-term survival, but it may not always benefit an individual organism.
-
Benefit to the Species: Variations within a population mean that some individuals might have traits that allow them to survive drastic environmental changes (like a sudden increase in temperature or a new disease). For example, if a population of bacteria living in temperate water faces a sudden temperature rise due to global warming, most may die. However, a few variants that are resistant to heat will survive, reproduce, and ensure the continuation of the species. Thus, variation provides a survival advantage to the species over time.
-
Not Necessarily for the Individual: For an individual organism, a new variation might be neutral or even harmful. A drastic variation could result in a DNA copy that cannot work with the existing cellular apparatus, leading to the death of the new cell. If the environment is stable and the individual is well-adapted, any change or variation from the proven successful blueprint is not necessarily advantageous and could be detrimental.
Q1QUESTIONS (In-text, Page 6)
How does binary fission differ from multiple fission?
Solution
Binary fission and multiple fission are both modes of asexual reproduction in unicellular organisms. The main differences are:
| Feature | Binary Fission | Multiple Fission |
|---|---|---|
| Number of Daughter Cells | The parent cell divides into two equal daughter cells. | The parent cell divides into many daughter cells simultaneously. |
| Process | The nucleus divides first, followed by the cytoplasm, splitting the cell into two. | The nucleus divides repeatedly to form multiple nuclei, each of which then gets surrounded by a bit of cytoplasm to form a daughter cell. |
| Example Organisms | Amoeba, bacteria, Leishmania. | Plasmodium (malarial parasite). |
Q2QUESTIONS (In-text, Page 6)
How will an organism be benefited if it reproduces through spores?
Solution
An organism that reproduces through spores benefits in two main ways:
- Survival in Unfavourable Conditions: Spores are covered by thick, protective walls. This allows them to withstand harsh environmental conditions such as high temperatures, lack of moisture, and scarcity of food. They can remain dormant for long periods and germinate only when conditions become favourable again.
- Wide Dispersal: Spores are typically small and light, which allows them to be easily dispersed by wind, water, or animals over large distances. This helps the organism to colonise new habitats and reduces competition for resources in one location.
Q3QUESTIONS (In-text, Page 6)
Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Solution
More complex organisms cannot give rise to new individuals through regeneration because of their high degree of organisation and specialisation.
- Specialised Tissues and Organs: Multicellular organisms are not just a random collection of cells. Their cells are organised into specialised tissues, which in turn form organs. These organs are placed at definite positions in the body to perform specific functions.
- Complexity of Body Design: In such a carefully organised structure, simple cell-by-cell division is impractical for recreating the entire organism. The process of development from a single cell (or a small group of cells) involves a complex, organised sequence of cell division, differentiation, and morphogenesis to form all the different tissues and organs in their correct places. Regeneration from a random body part cannot replicate this complex developmental process.
Q4QUESTIONS (In-text, Page 6)
Why is vegetative propagation practised for growing some types of plants?
Solution
Vegetative propagation is practised for growing certain types of plants due to its several advantages:
- Faster Growth: Plants raised by vegetative propagation can bear flowers and fruits much earlier than those grown from seeds.
- Propagation of Seedless Plants: It makes it possible to grow plants like bananas, oranges, roses, and jasmine that have lost their capacity to produce viable seeds.
- Genetic Uniformity: All plants produced through vegetative propagation are genetically identical to the parent plant. This ensures that desirable characteristics of the parent, such as fruit quality or flower colour, are preserved in the offspring.
Q5QUESTIONS (In-text, Page 6)
Why is DNA copying an essential part of the process of reproduction?
Solution
DNA copying is an essential part of reproduction because DNA (Deoxyribonucleic Acid) contains the genetic blueprint for an organism's body design and functions. For reproduction to occur, this blueprint must be passed from the parent to the offspring. The process of DNA copying (replication) creates a new copy of this genetic information. This copied DNA is then passed to the new individual, ensuring that it inherits the characteristics and body features of its parent's species. Without DNA copying, there would be no mechanism to transmit the essential information for life from one generation to the next.
Q1QUESTIONS (In-text, Page 13)
How is the process of pollination different from fertilisation?
Solution
Pollination and fertilisation are two distinct stages in the sexual reproduction of flowering plants.
| Feature | Pollination | Fertilisation |
|---|---|---|
| Definition | It is the transfer of pollen grains from the anther (male part) to the stigma (female part) of a flower. | It is the fusion of the male germ-cell (gamete) from the pollen grain with the female gamete (egg cell) present in the ovule. |
| Nature of Process | It is an external physical process. It can be achieved by agents like wind, water, or animals. | It is an internal cellular and biochemical process that occurs after pollination. |
| Outcome | It brings the male gamete-containing pollen grain to the female reproductive part. | It results in the formation of a zygote, which develops into an embryo. |
Q2QUESTIONS (In-text, Page 13)
What is the role of the seminal vesicles and the prostate gland?
Solution
The seminal vesicles and the prostate gland are accessory glands in the male reproductive system. Their role is to add their secretions to the sperms as they pass through the vas deferens. This fluid serves two main purposes:
- Provides a Medium for Transport: The secretions form a fluid medium (semen) which makes the transport of sperms easier through the reproductive tract.
- Provides Nutrition: The fluid contains nutrients like fructose, which provide energy to the sperms, keeping them active and motile.
Q3QUESTIONS (In-text, Page 13)
What are the changes seen in girls at the time of puberty?
Solution
The changes seen in girls at the time of puberty are part of their sexual maturation. These include:
- Increase in breast size, with the darkening of the skin of the nipples.
- Growth of hair in new parts of the body, such as the armpits and the genital area.
- The onset of menstruation (the monthly cycle of bleeding).
- The skin may become more oily, sometimes leading to the development of pimples.
- The hips widen as part of the overall change in body proportions.
Q4QUESTIONS (In-text, Page 13)
How does the embryo get nourishment inside the mother's body?
Solution
The embryo gets nourishment inside the mother's body through a special tissue called the placenta. The placenta is a disc-like structure embedded in the uterine wall. It is connected to the embryo via the umbilical cord.
On the embryo's side of the placenta, there are villi which create a large surface area for absorption. On the mother's side, there are blood spaces that surround these villi. This arrangement allows for the efficient transfer of nutrients like glucose and oxygen from the mother's blood to the embryo's blood. Simultaneously, waste products generated by the embryo are transferred into the mother's blood through the placenta to be eliminated by her body.
Q5QUESTIONS (In-text, Page 13)
If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?
Solution
No, a copper-T will not help in protecting a woman from sexually transmitted diseases (STDs). The copper-T is an intrauterine contraceptive device (IUCD) placed inside the uterus to prevent pregnancy. It works by preventing the implantation of the embryo. It does not create a physical barrier to prevent the exchange of body fluids during sexual intercourse. STDs like HIV-AIDS, gonorrhoea, and syphilis are transmitted through direct contact with infected bodily fluids. Only barrier methods, such as condoms, can help prevent the transmission of many of these infections.