7. How do Organisms Reproduce ?

Class 10 Chapter 7. How do Organisms Reproduce ?

Chapter 7: How do Organisms Reproduce ?

Multiple Choice Questions

1. In the list of organisms given below, those that reproduce by the asexual method are

(i) banana (ii) dog (iii) yeast (iv) Amoeba

(a) (ii) and (iv) (b) (i), (iii) and (iv)

Answer: (b) (i), (iii) and (iv)

[ The organisms that reproduce by the asexual method in the given list are: (i) Banana (through rhizomes or suckers) (iii) Yeast (through budding or fission) (iv) Amoeba (through binary fission) ]

2. In a flower, the parts that produce male and female gametes (germ cells) are

(a) stamen and anther

(b) filament and stigma

(d) stamen and style

Answer : (c) Anther and ovary

[ In a flower, the parts that produce male and female gametes (germ cells) are the anther (produces pollen containing male gametes) and the ovary (contains ovules, which produce female gametes).]

3. Which of the following is the correct sequence of events of sexual reproduction in a flower?

(a) pollination, fertilisation, seedling, embryo

(b) seedling, embryo, fertilisation, pollination

(d) embryo, seedling, pollination, fertilization

Answer : (c) Pollination, fertilisation, embryo, seedling

[ The correct sequence of events in sexual reproduction in a flower is pollination, fertilization, embryo development, and then the growth of the seedling.]

4. Offspring formed by asexual method of reproduction have greater similarity among themselves because

(i) asexual reproduction involves only one parent

(ii) asexual reproduction does not involve gametes

(iii) asexual reproduction occurs before sexual reproduction

(iv) asexual reproduction occurs after sexual reproduction

(a) (i) and (ii) (b) (i) and (iii)

Answer : (a) (i) and (ii)

[ Offspring formed by asexual reproduction have greater similarity among themselves because: (i) Asexual reproduction involves only one parent. (ii) Asexual reproduction does not involve gametes, and there is no mixing of genetic material from different individuals. ]

5. Characters transmitted from parents to offspring are present in

(a) cytoplasm

(b) ribosome

(d) genes

Answer : (d) Genes

[ Characters transmitted from parents to offspring are present in genes. Genes are segments of DNA that carry the information needed to determine the traits and characteristics of an organism. They are passed from one generation to the next during reproduction.]

6. Characters that are transmitted from parents to offspring during reproduction show

(a) only similarities with parents

(b) only variations with parents

(d) neither similarities nor variations

Answer : (c) Both similarities and variations with parents

[ Characters transmitted from parents to offspring during reproduction can exhibit both similarities and variations with the parents. While certain traits may be inherited and show similarities, variations can also arise due to genetic recombination and mutations.]

7. A feature of reproduction that is common to Amoeba, Spirogyra and Yeast is that

(a) they reproduce asexually

(b) they are all unicellular

(d) they are all multicellular

Answer : (a) They reproduce asexually

[ A feature of reproduction that is common to Amoeba, Spirogyra, and Yeast is that they reproduce asexually. They all have mechanisms for asexual reproduction, such as binary fission in Amoeba, fragmentation in Spirogyra, and budding in Yeast.]

8. In Spirogyra, asexual reproduction takes place by

(a) breaking up of filaments into smaller bits

(b) division of a cell into two cells

(d) formation of young cells from older cells.

Answer : (a) Breaking up of filaments into smaller bits

[ In Spirogyra, asexual reproduction takes place by the breaking up of filaments into smaller bits, each of which can grow into a new filament under suitable conditions. ]

9. The ability of a cell to divide into several cells during reproduction in Plasmodium is called

(a) budding

(b) reduction division

(d) multiple fission

Answer : (d) Multiple fission

[ The ability of a cell to divide into several cells during reproduction in Plasmodium is called multiple fission. This is a form of asexual reproduction in which a single cell divides into multiple daughter cells.]

10. The correct sequence of reproductive stages seen in flowering plants is

(a) gametes, zygote, embryo, seedling

(b) zygote, gametes, embryo, seedling

(d) gametes, embryo, zygote, seedling

Answer : (a) Gametes, zygote, embryo, seedling

[ The correct sequence of reproductive stages in flowering plants is gametes (pollen and egg cells) → zygote (formed after fertilization) → embryo (develops from the zygote)→ seedling (develops from the germinating seed).]

11. The number of chromosomes in parents and offsprings of a particular species remains constant due to

(a) doubling of chromosomes after zygote formation

(b) halving of chromosomes during gamete formation

(d) halving of chromosomes after gamete formation

Answer : (b) halving of chromosomes during gamete formation

[ Halving of chromosomes during gamete formation ensures that the number of chromosomes remains constant in parents and offspring. This process occurs during meiosis, where gametes are produced with half the chromosome number. ]

12. In Rhizopus, tubular thread-like structures bearing sporangia at their tips are called

(a) filaments

(b) hyphae

(d) roots

Answer : (b) Hyphae

[ In Rhizopus, tubular thread-like structures bearing sporangia at their tips are called hyphae. These structures play a crucial role in the asexual reproduction of Rhizopus by producing and releasing spores from the sporangia. ]

13. Vegetative propagation refers to formation of new plants from

(a) stem, roots and flowers

(b) stem, roots and leaves

(d) stem, leaves and flowers

Answer : (b) Stem, roots, and leaves

[ Vegetative propagation refers to the formation of new plants from structures such as stems, roots, and leaves.]

14. Factors responsible for the rapid spread of bread mould on slices of bread are

(i) large number of spores

(ii) availability of moisture and nutrients in bread

(iii) presence of tubular branched hyphae

(iv) formation of round shaped sporangia

(a) (i) and (iii) (b) (ii) and iv)

Answer : (c) (i) and (ii)

[ The factors responsible for the rapid spread of bread mold on slices of bread are: (i) Large number of spores (ii) Availability of moisture and nutrients in bread ]

15. Length of pollen tube depends on the distance between

(a) pollen grain and upper surface of stigma

(b) pollen grain on upper surface of stigma and ovule

(d) upper surface of stigma and lower part of style

Answer : (d) Upper surface of stigma and lower part of style

[ The length of the pollen tube depends on the distance between the upper surface of the stigma and the lower part of the style. This is the path the pollen tube must traverse to reach the ovule for fertilization in the process of plant reproduction.]

16. Which of the following statements are true for flowers?

(i) Flowers are always bisexual

(ii) They are the sexual reproductive organs

(iii) They are produced in all groups of plants

(iv) After fertilisation they give rise to fruits

(a) (i) and (iv) (b) (ii) and (iii)

Answer : (d) (ii) and (iv)

[ (ii) Flowers are the sexual reproductive organs. (iv) After fertilization, they give rise to fruits.

Flowers can be either bisexual (containing both male and female reproductive structures) or unisexual (containing either male or female reproductive structures) ]

17. Which among the following statements are true for unisexual flowers?

(i) They possess both stamen and pistil

(ii) They possess either stamen or pistil

(iii) They exhibit cross pollination

(iv) Unisexual flowers possessing only stamens cannot produce fruits

(a) (i) and (iv) (b) (ii), (iii) and (iv)

Answer : (b) (ii), (iii) and (iv)

[ Unisexual flowers:

(ii) They possess either stamen or pistil, not both.

(iii) They exhibit cross-pollination in many cases.

(iv) Unisexual flowers possessing only stamens cannot produce fruits, as the pistil (female reproductive structure) is required for fruit formation.]

18. Which among the following statements are true for sexual reproduction in flowering plants?

(i) It requires two types of gametes

(ii) Fertilisation is a compulsory event

(iii) It always results in formation of zygote

(iv) Offspring formed are clones

(a) (i) and (iv) (b) (i), (ii) and (iv)

Answer : (c) (i), (ii) and (iii)

[ In sexual reproduction in flowering plants:

(i) It requires two types of gametes (male and female gametes).

(ii) Fertilization is a compulsory event for the fusion of male and female gametes.

(iii) It always results in the formation of a zygote.

(iv) "Offspring formed are clones" is not true for sexual reproduction, as sexual reproduction introduces genetic variation, and the offspring are not clones of the parents.]

19. In Figure 8.1, the parts A, B and C are sequentially

(a) cotyledon, plumule and radicle

(b) plumule, radicle and cotyledon

(d) radicle, cotyledon and plumule

Answer : (c) plumule, cotyledon and radicle

20. Offspring formed as a result of sexual reproduction exhibit more variations because

(a) sexual reproduction is a lengthy process

(b) genetic material comes from two parents of the same species

(d) genetic material comes from many parents

Answer : (b) Genetic material comes from two parents of the same species

[ Offspring formed as a result of sexual reproduction exhibit more variations because genetic material is inherited from two parents of the same species. This combination of genetic material leads to a mixing of genes, promoting genetic diversity and the potential for a wide range of variations in the offspring.]

21. Reproduction is essential for living organisms in order to

(a) keep the individual organism alive

(b) fulfill their energy requirement

(d) continue the species generation after generation

Answer : (d) Continue the species generation after generation

[ Reproduction is essential for living organisms to ensure the continuation of their species from one generation to the next.]

22. During adolescence, several changes occur in the human body. Mark one change associated with sexual maturation in boys

(a) loss of milk teeth

(b) increase in height

(d) weight gain

Answer : (c) Cracking of voice

[ The cracking or deepening of the voice is a change associated with sexual maturation in boys during adolescence. This change is a result of the growth of the larynx (voice box) and the lengthening of the vocal cords, which is influenced by the increased production of testosterone during puberty.]

23. In human females, an event that reflects onset of reproductive phase is

(a) growth of body

(b) changes in hair pattern

(d) menstruation

Fig. 8.10

Answer : (d) Menstruation

[ The onset of menstruation (menarche) in human females is an event that marks the beginning of the reproductive phase. It typically occurs during puberty and signifies the ability to menstruate and potentially conceive.]

24. In human males, the testes lie in the scrotum, because it helps in the

(a) process of mating

(b) formation of sperm

(d) all the above

Answer : (b) Formation of sperm

[ The main reason the testes are located in the scrotum in human males is to regulate the temperature for sperm production. The slightly lower temperature in the scrotum compared to the internal body temperature is conducive to the formation of sperm.]

25. Which among the following is not the function of testes at puberty?

(i) formation of germ cells

(ii) secretion of testosterone

(iii) development of placenta

(iv) secretion of estrogen

(a) (i) and (ii) (b) (ii) and (iii)

Answer : (c) (iii) and (iv)

[ The functions of the testes at puberty include the formation of germ cells (sperm), and the secretion of testosterone. However, the development of the placenta and the secretion of estrogen are not functions of the testes; these are associated with female reproductive physiology.]

26. The correct sequence of organs in the male reproductive system for transport of sperms is

(a) testis → vasdeferens → urethra

(b) testis → ureter → urethra

(d) testis → vasdeferens → ureter

Answer : (a) Testis → Vas deferens → Urethra

[ Sperms are produced in the testes, travel through the vas deferens, and exit through the urethra during ejaculation.]

27. Which among the following diseases is not sexually transmitted?

(a) Syphillis

(b) Hepatitis

(d) Gonorrhoea

Answer : (b) Hepatitis

[ Hepatitis is not exclusively a sexually transmitted disease.]

Short Answer Questions

28. In a bisexual flower inspite of the young stamens being removed artificially, the flower produces fruit. Provide a suitable explanation for the above situation.

Answer: In a bisexual flower, even if the young stamens are removed, the flower can still produce fruit due to the presence of functional pistils. If pollination occurs from an external pollen source, fertilization can take place, leading to the development of fruit despite the absence of its own stamens.

29. Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.

Answer: Yes, cell division can be considered a type of reproduction in unicellular organisms because it results in the creation of new, independent organisms. For example, during binary fission, a single unicellular organism divides to form two genetically identical daughter cells, each functioning as a new organism.

30. What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?

Answer: A clone is an organism or cell that is genetically identical to the original organism or cell from which it was derived. Offspring formed by asexual reproduction exhibit remarkable similarity because they inherit their genetic material from a single parent without the mixing of genetic material from two different parents, resulting in identical genetic copies.

31. Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes?

Answer : In sexually reproducing organisms, offspring and parents have the same number of chromosomes due to the process of meiosis and fertilization. Meiosis reduces the chromosome number by half, producing gametes (sperm and egg) with a single set of chromosomes (haploid). During fertilization, two gametes combine to form a zygote with a full set of chromosomes (diploid), restoring the original chromosome number. Thus, the offspring have the same number of chromosomes as their parents.

32. Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.

Answer: Colonies of yeast fail to multiply in water because they lack an energy source for growth and reproduction. In a sugar solution, yeast cells have access to sugars, which they can metabolize to obtain energy, allowing them to grow and multiply.

33. Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?

Answer: Bread mold grows profusely on a moist slice of bread because moisture provides an ideal environment for mold spores to germinate and proliferate. Moist conditions support the mold's growth by offering necessary water for metabolic activities, while a dry slice lacks sufficient moisture, hindering mold development.

34. Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.

Answer: Variations among progeny formed by sexual reproduction arise due to:

(i) During meiosis, homologous chromosomes exchange genetic material through crossing over, resulting in new combinations of genes.

(ii) Chromosomes are distributed randomly to gametes, leading to diverse combinations of genetic traits in the offspring.

35. Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure 8.2 D and E by indicating the regenerated regions.

Answer: Yes, a Planaria cut vertically into two halves can regenerate into two individuals. Planaria have remarkable regenerative abilities, allowing each half to develop into a complete organism, as long as the cut sections contain essential parts like a portion of the head and tail.

36. From the internet, gather information about the chromosome numbers of five animals and five plants. Correlate the number with the size of organism and answer the following questions.

(a) Do larger organisms have more number of chromosomes/cells?

(b) Can organism with fewer chromosomes reproduce more easily than organisms with more number of chromosomes?

Answer: The chromosome numbers of five animals and five plants are :

Animals:

Human: 46 chromosomes (23 pairs)

Fruit fly (Drosophila melanogaster): 8 chromosomes (4 pairs)

Dog: 78 chromosomes (39 pairs)

Horse: 64 chromosomes (32 pairs)

Elephant: 56 chromosomes (28 pairs)

Plants:

Common wheat (Triticum aestivum): 42 chromosomes (21 pairs)

Pea (Pisum sativum): 14 chromosomes (7 pairs)

Rice (Oryza sativa): 24 chromosomes (12 pairs)

Potato (Solanum tuberosum): 48 chromosomes (24 pairs)

Sunflower (Helianthus annuus): 34 chromosomes (17 pairs)

(a) Not necessarily. The number of chromosomes does not directly correlate with the size or complexity of an organism. For example, humans have more chromosomes than fruit flies, but both organisms have different sizes and complexities. Similarly, plants like wheat and potatoes, which are larger, have varying numbers of chromosomes, and there is no consistent pattern of larger organisms having more chromosomes.

(b) The number of chromosomes does not directly determine the ease of reproduction. Reproductive success is influenced by various factors, including genetic stability, adaptability, and environmental conditions. Organisms with fewer chromosomes might reproduce efficiently, but so can those with more chromosomes. The complexity of chromosome number affects genetic diversity and stability, but not the fundamental ease of reproduction.

(c) Not always. While more chromosomes often imply more DNA, the total DNA content also depends on the size of the chromosomes and the amount of non-coding DNA. For example, some plants with high chromosome numbers, like wheat, may have a large amount of DNA, but this is not a strict rule. The total DNA content is also influenced by the genome size, which can vary widely even among organisms with similar chromosome numbers.

37. In tobacco plant, the male gametes have twenty four chromosomes. What is the number of chromosomes in the female gamete? What is the number of chromosomes in the zygote?

Answer: In tobacco plants, if the male gametes have 24 chromosomes, the female gametes will also have 24 chromosomes, as both male and female gametes are haploid.

When these gametes fuse during fertilization, they form a zygote, which is diploid. Therefore, the number of chromosomes in the zygote will be the sum of the chromosomes from both gametes:

24 (male gamete)+24 (female gamete)=48 chromosomes in the zygote.24

38. Why cannot fertilisation take place in flowers if pollination does not occur?

Answer: Fertilization cannot take place in flowers if pollination does not occur because pollination is the essential process that transfers pollen (which contains male gametes) to the stigma of the flower (where the female gametes are located). Without pollination, the male gametes do not reach the female gametes, preventing fertilization and the formation of seeds. Pollination ensures that the pollen and ovules meet, enabling the fusion of gametes necessary for fertilization and subsequent seed development.

39. Is the chromosome number of zygote, embryonal cells and adult of a particular organism always constant? How is the constancy maintained in these three stages?

Answer : Yes, the chromosome number of a zygote, embryonal cells, and an adult organism remains constant throughout its development.

This constancy is maintained through the process of cell division. During fertilization, the zygote receives a full set of chromosomes from each parent, restoring the diploid number. As the zygote divides and develops into an embryo and then into an adult, mitotic divisions ensure that each new cell retains the same chromosome number. This precise duplication and distribution during cell division preserve chromosomal integrity across all stages of development.

40. Where is the zygote located in the flower after fertilization?

Answer: After fertilization, the zygote in the flower is located within the ovule, which is found inside the ovary of the pistil. The ovary eventually develops into a fruit, and the ovule becomes the seed, containing the developing embryo.

41. Reproduction is linked to stability of population of a species. Justify the statement.

Answer: Reproduction is crucial for population stability as it ensures the continuation of a species. High reproductive rates produce offspring that maintain or increase population numbers, countering deaths and environmental changes. Effective reproduction stabilizes population size, prevents extinction, and supports genetic diversity, which enhances adaptability and survival.

42. How are general growth and sexual maturation different from each other?

Answer: General growth refers to the overall increase in size and development of an organism, including physical and physiological changes. Sexual maturation specifically pertains to the development of reproductive organs and systems, enabling an organism to reproduce. While general growth encompasses the entire body, sexual maturation focuses on reproductive capabilities.

43. Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.

Answer: During ejaculation, sperm travel from the testes through the epididymis, into the vas deferens, and merge with seminal fluid from the seminal vesicles, prostate gland, and Cowper’s glands. The mixture is then expelled through the urethra. The seminal vesicles provide nutrients, the prostate adds fluid for mobility, and Cowper’s glands secrete pre-ejaculatory fluid.

44. What changes are observed in the uterus if fertilisation does not occur?

Answer: If fertilization does not occur, the uterus undergoes several changes: the endometrial lining, which thickened to support implantation, begins to break down and shed. This results in menstruation, where the lining is expelled through the vagina. Hormone levels drop, signaling the end of the cycle and preparing for a new one.

45. What changes are observed in the uterus subsequent to implantation of young embryo?

Answer: After implantation, the uterus undergoes several changes: the endometrial lining thickens and becomes more vascular to support the developing embryo. The uterine wall develops into a placenta, which facilitates nutrient and oxygen exchange. Additionally, hormonal changes, primarily increased levels of progesterone and estrogen, help maintain the pregnancy and prevent further ovulation.

46. What are the benefits of using mechanical barriers during sexual act?

Answer: Mechanical barriers, like condoms, offer several benefits during sexual activity: they prevent the transmission of sexually transmitted infections (STIs), reduce the risk of unintended pregnancies by blocking sperm entry, and can help in controlling certain sexual health conditions. They also promote sexual health and safety by ensuring protection for both partners.

47. In the given Figure 8.3 label the parts and mention their functions

(a) Production of egg

(b) Site of fertilisation

(d) Entry of the sperms

Answer: The functions are :

(a) Production of egg: The ovaries produce eggs (ova) through oogenesis.

(b) Site of fertilisation: The fallopian tubes (oviducts) are the site where sperm and egg meet and fertilization occurs.

(c) Site of implantation: The endometrium, the inner lining of the uterus, is where the fertilized egg implants and develops.

(d) Entry of the sperms: The vagina is the entry point for sperm during intercourse, which then travel through the cervix and uterus to reach the fallopian tubes.

48. What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?

Answer: The chromosome number in an egg is haploid (n), meaning it has half the chromosome number of a zygote, which is diploid (2n). Therefore, the ratio of chromosome number between an egg and its zygote is 1:2.

Genetically, sperm differ from eggs in that they carry a single set of chromosomes (haploid), which includes either an X or Y sex chromosome, determining the offspring's sex. Eggs also have a single set of chromosomes (haploid) but always carry an X chromosome. The combination of these sex chromosomes from the sperm and egg results in the genetic diversity of the offspring.

Long Answer Questions

49. Why are budding, fragmentation and regeneration all considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria.

Answer: Budding, fragmentation, and regeneration are all considered asexual types of reproduction because they do not involve the fusion of gametes or genetic material from two parents. Instead, new organisms are produced from a single parent through various mechanisms of self-replication.

Regeneration in Planaria involves a remarkable ability to regrow lost body parts. When a Planaria is injured, specialized cells near the wound site, called neoblasts, rapidly proliferate and differentiate into the various cell types needed to reconstruct the missing structures. This process is guided by complex interactions between signaling molecules and genetic instructions, ensuring the precise rebuilding of organs and tissues. Consequently, Planaria can regenerate entire body segments, highlighting their extraordinary regenerative capabilities.

50. Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction.

Answer: Differences Between Asexual and Sexual Reproduction:

Genetic Variation:

Asexual Reproduction: Produces offspring genetically identical to the parent, as it involves a single organism and does not involve the exchange of genetic material.

Sexual Reproduction: Involves the fusion of male and female gametes, resulting in offspring with genetic variation due to the combination of different sets of genes from both parents.

Reproductive Mechanism:

Asexual Reproduction: Typically involves processes like binary fission, budding, or vegetative propagation, where offspring are direct clones of the parent organism.

Sexual Reproduction: Involves the production of gametes through meiosis, fertilization of these gametes, and the subsequent development of a genetically unique organism.

Variations in Offspring Formed by Sexual Reproduction:

Variations arise in sexual reproduction due to the recombination of genetic material from two parents. During meiosis, the process of crossing over and independent assortment of chromosomes leads to the shuffling of genetic information. This genetic recombination ensures that offspring inherit a unique combination of genes from each parent, contributing to genetic diversity within a population. This variation is crucial for evolution and adaptation, as it provides a pool of genetic traits that may enhance survival and reproduction in changing environments.

51. Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.

Answer: The distinction Between Pollination and Fertilization:

Process:

Pollination: The transfer of pollen grains from the male anther of a flower to the female stigma. It can occur via wind, water, or animal pollinators and is a prerequisite for fertilization.

Fertilization: The fusion of male gametes (sperm) from pollen with female gametes (egg) within the ovule, resulting in the formation of a zygote.

Purpose:

Pollination: Ensures that pollen reaches a compatible stigma, initiating the process leading to fertilization.

Fertilization: Results in the formation of seeds, combining genetic material from both parents to create a new organism.

Site and Product of Fertilization in a Flower:

Site: Fertilization occurs in the ovule, located within the ovary of the flower's pistil.

Product: The product of fertilization is a zygote, which develops into a seed containing the embryo. This seed then matures into a fruit or seed pod.

52. Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.

Answer: Distinction Between a Gamete and a Zygote:

Genetic Composition:

Gamete: A gamete is a haploid cell, meaning it contains one set of chromosomes (half the number of chromosomes typical of the species). In animals, gametes are sperm and eggs; in plants, they are pollen and ovules.

Zygote: A zygote is a diploid cell formed by the fusion of two haploid gametes. It contains two sets of chromosomes, one from each parent.

Roles in Sexual Reproduction:

Gamete: Gametes are specialized reproductive cells that carry genetic information from each parent. Their primary role is to combine during fertilization to restore the diploid number of chromosomes and introduce genetic diversity.

Zygote: The zygote results from the fertilization of gametes and is the first stage of development in the life cycle of an organism. It divides and differentiates into various cell types, eventually forming a complete organism. The zygote’s role is crucial in developing and propagating genetic traits from both parents.

53. Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower.

Answer: The diagram of a flower :

In flowering plants, the gamete-producing organs are:

(i) Stamens: The male reproductive organs, which produce pollen grains containing male gametes (sperm cells).

(ii) Pistils (or Carpels): The female reproductive organs, which include the ovary, where ovules containing female gametes (egg cells) are produced.

54. What is placenta? Mention its role during pregnancy?

Answer: The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta.

The placenta plays a crucial role during pregnancy by acting as an interface between the mother and the developing embryo. Embedded in the uterine wall, the placenta features villi on the side of the embryo, creating an extensive surface area. This structure allows for efficient exchange of essential nutrients, such as glucose and oxygen, from the mother’s blood to the embryo. Simultaneously, the placenta facilitates the removal of waste products generated by the embryo, transferring them into the mother's bloodstream for excretion. This vital organ supports the growth and development of the embryo throughout the nine months of pregnancy, ensuring that the developing child receives the necessary resources for healthy development. The birth of the child is then triggered by rhythmic contractions of the uterine muscles, culminating in delivery.

55. What are various ways to avoid pregnancy? Elaborate any one method.

Answer: Various ways to avoid pregnancy include hormonal contraceptives (like pills, patches, and injections), barrier methods (such as condoms and diaphragms), intrauterine devices (IUDs), sterilization (like vasectomy and tubal ligation), and natural methods (such as the rhythm method).

Hormonal contraceptives work by releasing hormones that prevent ovulation, thicken cervical mucus, and alter the uterine lining, making it less suitable for implantation. They are effective in preventing pregnancy when used consistently and correctly.

56. How does fertilisation take place? Fertilisation occurs once in a month. Comment.

Answer: Fertilization occurs when a sperm cell from the male combines with an egg cell from the female. This typically takes place in the fallopian tube after sexual intercourse, where sperm travels through the female reproductive tract to meet the egg released from the ovary during ovulation. Upon successful fusion, the sperm’s genetic material merges with the egg’s, forming a zygote.

The comment about fertilization occurring once a month refers to the female’s ovulation cycle. Generally, ovulation happens once per menstrual cycle, about midway through the cycle, making it the primary period when fertilization is possible. However, fertilization can only occur if intercourse happens around this time. If fertilization does not occur, the egg disintegrates and is expelled along with the uterine lining during menstruation.

57. Reproduction is essentially a phenomenon that is not for survival of an individual but for the stability of a species. Justify.

Answer: Reproduction serves primarily to ensure the continuity and stability of a species rather than the survival of an individual. While individual organisms have limited lifespans and may face various threats, the process of reproduction ensures that genetic material is passed on to the next generation, maintaining the species' presence over time. Through reproduction, species can adapt to environmental changes and evolve, contributing to their long-term survival. Thus, while an individual may not endure forever, reproduction secures the perpetuation and evolution of the species.

58. Describe sexually transmitted diseases and mention the ways to prevent them.

Answer: Sexually transmitted diseases (STDs) are infections transmitted through sexual contact, including vaginal, anal, or oral sex. Common STDs include chlamydia, gonorrhea, syphilis, herpes, human papillomavirus (HPV), and HIV/AIDS. These diseases can affect various body parts and may lead to serious health issues if left untreated, such as infertility, chronic pain, or increased risk of certain cancers.

Prevention Methods:

Condom Use: Consistently and correctly using condoms during sexual activity can significantly reduce the risk of many STDs by providing a barrier that prevents the exchange of bodily fluids.

Regular Testing: Routine screening for STDs, especially for sexually active individuals or those with multiple partners, can help detect infections early and reduce transmission.

Mutual Monogamy: Engaging in sexual activity with a mutually monogamous partner, who has been tested and is free of STDs, can lower the risk of infection.

Vaccination: Vaccines are available for certain STDs, such as HPV and hepatitis B, which can prevent infection and related health complications.

Abstinence: Refraining from sexual activity is the most effective way to avoid STDs, but it may not be a practical or desired option for everyone.

Open Communication: Discussing sexual health and STD status with partners can help make informed decisions and reduce risk.