CBSE Class 10 Science How Do Organisms Reproduce VBQs Set 05

Sexual Reproduction

Sexual Reproduction in Flowering Plants

Question. The number of chromosomes in parents and offsprings of a particular species undergoing sexual reproduction remain constant due to
(a) doubling of chromosomes after zygote formation
(b) halving of chromosomes after zygote formation.
(c) doubling of chromosomes before gamete formation
(d) halving of chromosomes at the time of gamete formation.

Answer: (d) halving of chromosomes at the time of gamete formation.

Question. The stamen contains
(a) stigma
(b) pollen grain
(c) sepal
(d) ovule.

Answer: (b) pollen grain

Question. Seeds are called products of sexual reproduction because they
(a) give rise to new plants
(b) are formed by fusion of gametes
(c) are formed by the fusion of pollen tubes
(d) can survive for a longer period.

Answer: (b) are formed by fusion of gametes

Question. Fertilisation is the process of
(a) transfer of male gamete to female gamete
(b) fusion of nuclei of male and female gamete
(c) adhesion of male and female reproductive organs
(d) the formation of gametes by a reproductive organ.

Answer: (b) fusion of nuclei of male and female gamete

Question. What are all organisms called which bear both the sex organs in the same individual? Give one example of such organism.
Answer: Bisexual (or hermaphrodite) organisms. Example: Earthworm / Hibiscus (China rose).

Question. List two unisexual flowers.
Answer: Papaya and Watermelon.

Question. Why is fertilisation not possible without pollination?
Answer: Pollination is the process that brings the male gametes (in pollen grains) to the female part of the flower (stigma). Fertilization is the fusion of these gametes. Without the physical proximity provided by pollination, the gametes cannot meet and fuse.

Question. Name the parts of a bisexual flower that are not directly involved in reproduction.
Answer: Sepals and Petals.

Question. No two individuals are absolutely alike in a population. Why?
Answer: This is due to genetic variations that occur during DNA copying and the shuffling of genes during sexual reproduction (meiosis and fertilization).

Question. Mention the changes that occur in the following after fertilisation in a flower : (a) Petals (b) Zygote (c) Ovary (d) Ovule
Answer: (a) Petals wither and fall off. (b) Zygote develops into an embryo. (c) Ovary grows rapidly and ripens to form a fruit. (d) Ovule develops a tough coat and is converted into a seed.

Question. Name the reproductive parts of an angiosperm. Where are these parts located? Explain the structure of its male reproductive part.
Answer: Reproductive parts: Stamen (male) and Carpel/Pistil (female). They are located in the flower. The stamen consists of a stalk called the filament and a swollen top called the anther, which produces pollen grains containing male gametes.

Question. (a) Which of the following flowers will have higher possibility of self-pollination? Mustard, Papaya, Watermelon, Hibiscus (b) List the two reproductive parts of a bisexual flower.
Answer: (a) Mustard and Hibiscus (as they are bisexual). (b) Stamen and Carpel.

Question. Define the term pollination. Differentiate between self-pollination and cross-pollination. What is the significance of pollination?
Answer: Pollination is the process of transfer of pollen grains from the anther of a stamen to the stigma of a carpel. In self-pollination, the pollen transfer occurs within the same flower or between flowers of the same plant. In cross-pollination, pollen is transferred from the anther of one flower to the stigma of a flower on another plant of the same species. Significance: It is a prerequisite for fertilization, which leads to the formation of seeds and fruits. Cross-pollination also introduces genetic variations.

Question. State the basic requirement for sexual reproduction. Write the importance of such reproductions in nature.
Answer: The basic requirement for sexual reproduction is the fusion of male and female gametes (germ cells). Importance: It leads to genetic variation in offspring, which promotes diversity, allows for better adaptation to changing environments, and is a key driver of evolution.

Question. List any two steps involved in sexual reproduction and write its two advantages.
Answer: Two steps involved are: (i) Gametogenesis (formation of gametes) and (ii) Fertilization (fusion of gametes). Two advantages are: (i) It produces variations among offspring and (ii) Offspring have better chances of survival in changing environmental conditions.

Question. How do organisms, whether reproduced asexually or sexually maintain a constant chromosome number through several generations? Explain with the help of suitable example.
Answer: Organisms maintain a constant chromosome number through a special type of cell division called meiosis, which occurs during gamete formation. Meiosis reduces the chromosome number to half in germ cells (gametes). When a male gamete (n) and a female gamete (n) fuse during fertilization, the original diploid number (2n) is restored in the zygote. Example: In humans, parents have 46 chromosomes. Gametes (sperm and egg) contain 23 chromosomes each. Their fusion results in a zygote with 46 chromosomes.

Question. What is sexual reproduction? List its four significances.
Answer: Sexual reproduction is the process of producing offspring through the fusion of male and female gametes. Four significances are: (i) Promotes genetic diversity, (ii) Ensures species survival through better adaptation, (iii) Facilitates evolution, and (iv) Restores the diploid chromosome number through fertilization.

Question. Name the reproductive parts of an angiosperm. Where are these parts located? Explain in brief the structure of its female reproductive parts.
Answer: The reproductive parts are the Stamen (male) and Carpel/Pistil (female). They are located in the flower. The female reproductive part (carpel) consists of: (i) Stigma: The sticky top part that receives pollen, (ii) Style: The elongated tube, and (iii) Ovary: The swollen basal part containing ovules (female gametes).

Question. List six specific characteristics of sexual reproduction.
Answer: (1) Requires two parents (usually), (2) Involves the formation of gametes, (3) Meiosis occurs during gamete formation, (4) Fusion of gametes (fertilization) takes place, (5) Offspring are genetically different from parents, and (6) It is a slower process compared to asexual reproduction.

Question. Write one main difference between asexual and sexual mode of reproduction. Which species is likely to have comparatively better chances of survival - the one reproducing asexually or the one reproducing sexually? Justify your answer.
Answer: Difference: Asexual reproduction involves a single parent without gamete fusion, while sexual reproduction involves two parents and the fusion of male and female gametes. Species reproducing sexually have better chances of survival because sexual reproduction generates variations, which help the species adapt to environmental changes and resist diseases.

Question. Why is DNA copying an essential part of the process of reproduction? What are the advantages of sexual reproduction over asexual reproduction?
Answer: DNA copying is essential because it ensures the transfer of genetic information from parents to offspring, maintaining the continuity of characteristics. Advantages of sexual reproduction: (i) It leads to genetic variations and (ii) It enhances the ability of a species to adapt and evolve.

Question. Describe in brief the function of the various parts of the female reproductive part of a bisexual flower.
Answer: (i) Stigma: Receives and provides a surface for pollen germination. (ii) Style: Supports the stigma and guides the pollen tube. (iii) Ovary: Protects the ovules and eventually becomes the fruit. (iv) Ovule: Contains the female germ cell and becomes the seed after fertilization.

Question. Name the two reproductive parts of a bisexual flower which contain the germ cells. State the location and function of its female reproductive part.
Answer: The reproductive parts containing germ cells are the Anther (pollen/male) and Ovule (egg/female). Location of female part: It is located in the center of the flower. Function: It facilitates pollination, fertilization, and the development of seeds and fruit.

LA 

Question. (i) What happens when: (1) Leaves of Bryophyllum fall on the soil? (2) Planaria is cut into many pieces? (3) Sporangia of Rhizopus on maturation liberate spores? Mention the modes of reproduction in each of the above three cases. (ii) Write the changes that occur in a flower once the fertilization has taken place.
Answer: (i) (1) Buds present on the leaf margins develop into new plantlets. Mode: Vegetative Propagation. (2) Each piece regenerates into a complete new organism. Mode: Regeneration. (3) Spores are dispersed by air and germinate into new hyphae upon reaching a suitable substrate. Mode: Spore formation.
(ii) Post-fertilization changes: (a) The zygote divides to form an embryo, (b) Ovule develops a tough coat and converts into a seed, (c) Ovary grows rapidly and ripens into a fruit, (d) Petals, sepals, stamens, style, and stigma usually shrivel and fall off.

Question. (a) Identify the modes of asexual reproduction in each of the following organisms: (i) Hydra (ii) Planaria (iii) Amoeba (iv) Spirogyra (v) Rhizopus (b) List three advantages of vegetative propagation. (c) Why cannot fertilisation take place in flowers if pollination does not occur?
Answer: (a) (i) Hydra: Budding/Regeneration, (ii) Planaria: Regeneration, (iii) Amoeba: Binary Fission, (iv) Spirogyra: Fragmentation, (v) Rhizopus: Spore formation.
(b) Advantages: (1) Plants can be grown faster, (2) Offspring are genetically identical (clones) to parents, (3) Helpful for plants that have lost the capacity to produce seeds.
(c) Fertilization is the fusion of male and female gametes. Pollination is the process that brings the male gamete (in pollen) to the female part (stigma). Without pollination, the male germ cell cannot reach the female germ cell, hence fertilization cannot occur.

Question. Define pollination. Explain the different types of pollination. List two agents of pollination. How does suitable pollination lead to fertilisation?
Answer: Pollination is the transfer of pollen grains from anther to stigma. Types: (i) Self-pollination (within the same flower/plant) and (ii) Cross-pollination (between different plants of the same species). Agents: Wind and Insects. Suitable pollination leads to fertilization because the pollen grain germinates on the stigma, producing a pollen tube that carries male gametes to the egg cell in the ovule.

Question. (a) Give one example each of unisexual and bisexual flower. (b) Mention the changes a flower undergoes after fertilisation. (c) How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals?
Answer: (a) Unisexual: Papaya; Bisexual: Hibiscus.
(b) Sepals/Petals fall off, ovary becomes fruit, ovule becomes seed.
(c) DNA remains constant because gametes are formed by meiosis, which halves the chromosome number. When two haploid (n) gametes fuse, the diploid (2n) status is restored.

Sexual Reproduction in Human Beings

MCQ

Question. Assertion (A): Sexual reproduction involves two parents of different sexes, a male and female, which produce male and female gametes respectively.
Reason (R): The male and female gametes fuse to form a zygote in sexual reproduction, which develops into a new individual.
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A).

Question. Which one of the following is not a part of the human female reproductive system?
(a) Ovary
(b) Oviduct
(c) Uterus
(d) Seminal vesicle
Answer: (d) Seminal vesicle

Question. Assertion (A): Testes are located outside the abdominal cavity in the scrotum.
Reason (R): Because sperm formation requires lower temperature than the normal body temperature.
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A).

VSA 

Question. List two functions of ovary of human female reproductive system.
Answer: (i) Production of female gametes (eggs/ova) and (ii) Secretion of female sex hormones (estrogen and progesterone).

SA I 

Question. Give reasons: (i) Placenta is extremely essential for fetal development. (ii) Uterine lining become thick and spongy after fertilisation.
Answer: (i) It provides nutrients and oxygen to the developing fetus and removes waste products like \( CO_2 \) and urea. (ii) The uterine lining thickens to support the implantation of the embryo and provide nourishment for its development.

Question. What is puberty? Mention any two changes that are common to both boys and girls in early teenage years.
Answer: Puberty is the period during which an individual reaches sexual maturity and becomes capable of reproduction. Common changes: (i) Growth of hair in armpits and pubic area and (ii) Skin becomes oily and may develop pimples.

Question. What are testes? List two functions performed by testes in human beings.
Answer: Testes are the primary male reproductive organs located in the scrotum. Functions: (i) Production of sperm and (ii) Secretion of the hormone testosterone.

Question. What is the main difference between sperms and eggs of humans? Write the importance of this difference.
Answer: Difference: Sperms are small, motile cells with a tail, while eggs are larger, non-motile, and contain stored food. Importance: Motility allows sperm to swim to the egg for fertilization, while the egg's size and food store nourish the early embryo.

Question. List two preparations shown every month by the uterus in anticipation of pregnancy in humans.
Answer: (i) The inner lining of the uterus (endometrium) thickens and (ii) The lining becomes rich in blood supply to nourish a potential embryo.

SA II 

Question. What is placenta? Explain its function in humans.
Answer: Placenta is a disc-like tissue embedded in the uterine wall. Functions: It facilitates the transfer of glucose and oxygen from the mother to the embryo and allows waste generated by the embryo to be transferred to the mother's blood.

Question. What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.
Answer: Chromosomes are thread-like structures made of DNA and proteins, located in the nucleus, carrying genetic information. Maintenance: During gamete formation, meiosis reduces the chromosome number to half (haploid). During fertilization, the fusion of two haploid gametes restores the original diploid number in the progeny.

Question. (a) What provides nutrition to human sperms? State the genetic constitution of a sperm. (b) Mention the chromosome pair present in a zygote which determines the sex of (i) a female child and (ii) a male child.
Answer: (a) Secretions from seminal vesicles and the prostate gland provide nutrition. Genetic constitution: Either 22 + X or 22 + Y chromosomes.
(b) (i) Female child: XX chromosome pair, (ii) Male child: XY chromosome pair.

Question. State the changes that take place in the uterus when: (a) Implantation of embryo has occurred. (b) Female gamete/egg is not fertilised.
Answer: (a) The uterine wall thickens further, becomes highly vascularized, and the placenta develops to support the fetus. (b) The thick lining of the uterus is no longer needed; it breaks down and is expelled through the vagina as blood and mucous (menstruation).

Question. What are the functions of testes in the human male reproductive system? Why are these located outside the abdominal cavity? Who is responsible for bringing about changes in appearance seen in boys at the time of puberty?
Answer: Functions: Sperm production and testosterone secretion. Location: They are outside to maintain a temperature \( 2-3^\circ C \) lower than body temperature, which is essential for sperm survival. Responsibility: The hormone testosterone is responsible for changes at puberty.

Question. (a) Mention the role of the following organs of human male reproductive system. (i) Testes (ii) Scrotum (iii) Vas deferens (iv) Prostate gland (b) What are the two roles of testosterone?
Answer: (a) (i) Testes: Produce sperm. (ii) Scrotum: Maintains low temperature for sperm production. (iii) Vas deferens: Transports sperm from testes to urethra. (iv) Prostate gland: Adds fluid for sperm motility and nutrition.
(b) Roles of testosterone: (1) Regulates sperm production and (2) Stimulates secondary sexual characteristics in boys.

Question. Write names of those parts of a flower which serve the same function as the following do in the animals (i) testes (ii) sperm (iii) ovary (iv) egg.
Answer: (i) Anther, (ii) Pollen grain/Male germ cell, (iii) Ovary, (iv) Ovule/Egg cell.

LA 

Question. (a) In the female reproductive system of human beings, state the functions of: (i) Ovary (ii) Oviduct. (b) Mention the changes which the uterus undergoes, when (i) it has to receive a zygote. (ii) no fertilisation takes place. (c) State the functions of placenta.
Answer: (a) (i) Ovary: Produces eggs and hormones. (ii) Oviduct (Fallopian tube): Site of fertilization and transports egg/zygote to the uterus.
(b) (i) It thickens its walls and blood supply increases. (ii) The lining breaks down and menstruation occurs.
(c) Functions of placenta: Nutrient and oxygen supply to fetus, waste removal, and secretion of pregnancy hormones.

Question. (a) What is puberty? (b) Describe in brief the functions of the following parts in the human male reproductive system. (i) Testes (ii) Seminal vesicle (iii) Vas deferens (iv) Urethra (c) Why are testes located outside the abdominal cavity? (d) State how sperms move towards the female germ cell.
Answer: (a) Period of attaining sexual maturity. (b) (i) Testes: Sperm/testosterone production. (ii) Seminal vesicle: Adds nutritive fluid to sperm. (iii) Vas deferens: Carries sperm. (iv) Urethra: Common passage for urine and sperm. (c) For lower temperature required for sperm production. (d) Sperms use their long tails to swim through the female reproductive tract (vagina and uterus) to the oviduct.

Question. (a) Write the function of following parts in human female reproductive system: (i) Ovary (ii) Oviduct (iii) Uterus (b) Describe in brief the structure and function of placenta.
Answer: (a) (i) Ovary: Egg production. (ii) Oviduct: Path for egg/site of fertilization. (iii) Uterus: Site of implantation and fetal development.
(b) Structure: A disc-like tissue with villi on the embryo side and blood spaces on the mother's side. Function: Exchange of nutrients, gases, and waste between mother and fetus.

Question. (a) Name the organ that produces sperms as well as secretes a hormone in human males. Name the hormone it secretes and write its functions. (b) Name the part of the human female reproductive system where fertilisation occurs. (c) Explain how the developing embryo gets nourishment inside the mother's body.
Answer: (a) Organ: Testes. Hormone: Testosterone. Function: Regulates sperm production and pubertal changes. (b) Oviduct (Fallopian tube). (c) The embryo gets nourishment through the placenta, which facilitates the passage of glucose and oxygen from the mother's blood into the embryo's blood.