8. How do Organisms Reproduce ?

SEBA Class 10 Science Chapter 8. How do Organisms Reproduce ?

Chapter 8. How do Organisms Reproduce ?

Class 10 Chapter How do Organisms Reproduce Multiple Choice Questions and Answers :

Question : Asexual reproduction takes place through budding in

(a) amoeba.

(b) yeast.

(d) leishmania.

Answer: (b) yeast.

Question : Which of the following is not a part of the female reproductive system in human beings?

(a) Ovary

(b) Uterus

(d) Fallopian tube

Answer: (c) Vas deferens

Question : The anther contains

(a) sepals.

(b) ovules.

(d) pollen grains.

Answer: (d) pollen grains.

Question : The process of giving rise to new individual organisms from the body parts of many fully differentiated organisms is known as : [SEBA 2023]

(a) Regeneration

(b) Budding

(d) Fission

Answer: (c) Fragmentation.

[ Fragmentation is the process of giving rise to new individual organisms from the body parts of many fully differentiated organisms. In this reproductive method, the parent organism breaks into fragments, and each fragment has the potential to develop into a new individual. ]

Question : Binary fission occurs in : [SEBA 2023]

(a) Amoeba

(b) Paramoecium

(d) All of these

Answer : (d) All of these.

[ Binary fission is a form of asexual reproduction in which a single organism divides into two equal and identical individuals. All the mentioned organisms undergo binary fission for reproduction. ]

Question : and are the reproductive parts of a flower which contain the germ-cells . [SEBA 2023]

Answer : Stamens and pistil .

[Stamens and pistil are the reproductive parts of a flower which contain the germ-cells.]

Question : 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) ]

Question : 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).]

Question : 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.]

Question : 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. ]

Question : 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.]

Question : 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.]

Question : 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.]

Question : 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. ]

Question : 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.]

Question : 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).]

Question : 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. ]

Question : 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. ]

Question : 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.]

Question : 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 ]

Question : 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.]

Question : 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) ]

Question : 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.]

Question : 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.]

Question : 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

Question : 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.]

Question : 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.]

Question : 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.]

Question : In human females, an event that reflects onset of reproductive phase is

(a) growth of body

(b) changes in hair pattern

(d) menstruation

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.]

Question : 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.]

Question : 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.]

Question : 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.]

Question : 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.]

16. Where is the zygote located in the flower after fertilisaion ?

Answer : After fertilization, the zygote is located in the ovule within the ovary of the flower. The ovule will eventually develop into a seed.

17. Given an example of a flower which contains both stamens and carpels .

Answer : An example of a flower containing both stamens and carpels is the Lily (Lilium spp.). Lilies have both male (stamens) and female (carpels) reproductive organs.

18. Name the largest cell present in the human body .

Answer : The largest cell in the human body is the female egg cell, or ovum. The ovum is also commonly known as the egg and is produced by the ovaries.

19. State the method used for growing rose plants .

Answer : Rose plants can be grown through various methods, but one common approach is propagation through cuttings. This involves taking a stem cutting from a healthy rose plant and planting it in suitable soil under proper conditions to encourage root development and growth.

OR State what type of method is used for growing jasmine plant .

Answer : Jasmine plants are commonly grown through propagation methods such as stem cuttings. These cuttings are taken from healthy plants and rooted in soil or water until they develop into independent plants.

20. What is the effect of DNA copying which is not perfectly accurate on the reproduction process ?

Answer : The effect of imperfect DNA copying on the reproduction process can lead to genetic variations and mutations. These variations contribute to biodiversity and can influence the traits of offspring.

SECTION = B

1. Define the terms unisexual and bisexual giving one example of each .

Answer: Unisexual refers to organisms that have either male or female reproductive organs. Example: Papaya plants (separate male and female flowers).

Bisexual (or hermaphroditic) organisms have both male and female reproductive organs. Example: Earthworms.

2. What are the different methods of contraception ?

Answer: Different methods of contraception include barrier methods such as condoms and diaphragms, hormonal methods like birth control pills and patches, intrauterine devices (IUDs), sterilization procedures like tubal ligation and vasectomy, fertility awareness methods, emergency contraception (morning-after pill), and behavioral methods such as withdrawal and abstinence.

3. What are the advantage of sexual reproduction over asexual reproduction ?

Answer : Sexual reproduction offers several advantages over asexual reproduction, including genetic diversity, which enhances adaptation to changing environments, increased genetic variation, which can improve resistance to diseases, and the ability to produce offspring with new combinations of traits, potentially leading to evolutionary advantages.

4. How does the embryo get nourishment inside the mother’s body ?

Answer: The embryo receives nourishment inside the mother's body through the placenta. The placenta is an organ formed during pregnancy that facilitates the exchange of nutrients, oxygen, and waste products between the mother's bloodstream and the developing embryo.

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

Answer: DNA copying, or DNA replication, is essential in the process of reproduction because it ensures that genetic information is accurately passed on to offspring. It allows cells to duplicate their genetic material so that each new cell or organism receives a complete set of instructions for its development and function.

6. How is the process of pollination different from fertilization ?

Answer : Pollination is the transfer of pollen grains from the anther to the stigma of a flower. Fertilization, on the other hand, occurs when the sperm from pollen combines with the egg cell in the ovule, leading to the formation of a zygote and the development of seeds.

7. Why is vegetative propagation practiced for growing some types of plants ?

Answer : Vegetative propagation is practiced for certain plants because it allows growers to reproduce plants with desirable traits without relying on seeds. This method ensures the preservation of specific characteristics, such as disease resistance, fruit quality, or flower color, which may not be consistently reproduced by seeds.

8. Differentiate between self-pollination and cross-pollination . Describe double fertilization in plants .

Answer : The difference between self-pollination and cross-pollination are :

Self-Pollination	Cross-Pollination
Pollen from the same flower fertilizes the stigma of the same flower.	Pollen from one flower fertilizes the stigma of a different flower of the same species.
Pollen transfer within the same flower.	Pollen transfer between different flowers, typically by wind, insects, or other agents.
Limited genetic diversity as offspring inherit traits from a single parent.	Promotes genetic diversity as offspring inherit traits from two different parents.
Example : Peas, beans, tomatoes.	Example : Apple trees, sunflowers, squash plants.

Double fertilization in plants involves the fusion of one sperm cell with the egg cell to form the zygote and another sperm cell with the polar nuclei to form endosperm, which provides nourishment for the developing embryo.

9. Write any two differences between binary fission and multiple fission in a tabular form as observed in cells of organisms .

Answer : The two differences between binary fission and multiple fission are :

Binary Fission

Multiple Fission

A single parent cell divides into two daughter cells, each identical to the parent cell.

A single parent cell divides into multiple daughter cells, often more than two, each

identical to the parent cell.

Commonly observed in unicellular organisms such as bacteria and amoebas.

Typically observed in certain protists and parasites like Plasmodium species.

10. What are the changes seen in girls at the time of puberty ?

Answer : During puberty in girls, common changes include the growth of thick, darker hair in areas like armpits and genital regions, increased oiliness of the skin leading to pimples, and heightened awareness of body changes. Specific to girls, breast size increases, nipples darken, and menstruation begins. Puberty varies among individuals in timing and progression.

SECTION = C

1. (a) What is the importance of DNA copying in reproduction ?

(b) Draw a labeled diagram of the longitudinal section of a flower .

Answer : (a) DNA copying, or replication, is crucial in reproduction as it ensures the faithful transmission of genetic information from parent to offspring. During cell division, DNA replication produces identical copies of the genetic material, allowing each new cell or organism to inherit the necessary instructions for proper growth, development, and functioning.

(b)

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

Answer : Reproduction contributes to population stability by maintaining a balance between birth and death rates. While individuals reproduce to ensure the continuation of their species, factors such as limited resources, predation, and environmental conditions act as natural checks on population growth. This equilibrium helps prevent overpopulation, ensures a sustainable utilization of resources, and enhances the species' ability to adapt to changing environments for long-term survival.

3. (a) How are the modes for reproduction different in unicellular and multicellular organisms ?

(b) What could be the reasons for adopting contraceptive methods ?

Answer : (a) Modes of Reproduction in Unicellular and Multicellular Organisms:

	Unicellular Organisms	Multicellular Organisms
Type of Reproduction	Primarily asexual reproduction through processes like binary fission or budding.	Can undergo both asexual and sexual reproduction.
Genetic Diversity	Limited genetic diversity as offspring are genetically identical to the parent.	Allows for greater genetic diversity, promoting adaptation.
Examples	Bacteria, amoebas, yeast.	Plants, animals, fungi.

(b) Contraceptive methods are adopted for various reasons, are :

(i) Contraceptives enable individuals or couples to plan and space their pregnancies, allowing them to achieve their desired family size and timing.

(ii) Contraceptives help prevent unintended pregnancies, which may occur due to inadequate use of protection during sexual intercourse.

(iii) Some individuals may have health conditions that make pregnancy risky or undesirable. Contraceptives provide a means to prevent pregnancies that could pose health risks to the mother or fetus.

(iv) Contraceptives can help individuals and families manage their financial resources more effectively by allowing them to have children when they are financially stable. They also offer individuals the opportunity to pursue education and career goals before starting a family.

4. (a) What is fertilization ? Distinguish between external fertilization and internal fertilization .

(b) What is the site of fertilization in human being ?

Answer : (a) Fertilization is the process in which the male germ-cell, produced by the pollen grain, fuses with the female gamete in the ovule. This fusion, known as fertilization, results in the formation of a zygote, capable of developing into a new plant.

The difference between external fertilization and internal fertilization are :

	External Fertilization	Internal Fertilization
Definition	Fertilization occurs outside the organism's body	Fertilization occurs inside the organism's body
Function	Occurs typically in aquatic environments, where eggs and sperm are released into water.	Occurs within the reproductive tract of the female, protecting gametes from external environment
Example	Fish, amphibians (e.g., frogs), most marine invertebrates.	Mammals (e.g., humans, dogs, cats), birds, reptiles (e.g., snakes, lizards).

(b) In human beings, fertilization typically occurs in the fallopian tubes, also known as the uterine tubes. After ovulation, the egg is released from the ovary and moves into the fallopian tube, where it may encounter sperm for fertilization.

5. (a) What is the role of the seminal vesicles and the prostate gland ?

(b) Draw a labeled diagram of the human female reproductive system .

Answer : (a) The seminal vesicles and prostate gland play vital roles in semen production. Seminal vesicles contribute fructose and other nutrients to nourish sperm, while the prostate gland secretes alkaline fluid that enhances sperm motility and neutralizes acidity in the female reproductive tract.

(b)

6. (a) Mention the mode of reproduction used by :

(i) Amoeba (ii) Planaria

(b) Draw a diagram showing germination of pollen on stigma of a flower .

Answer: (a) (i) Amoeba reproduces asexually by binary fission, where the parent cell divides into two daughter cells with equal genetic material.

(ii) Planaria reproduces asexually by regeneration, where a new organism can develop from a fragment of the original planaria's body.

(b)

7. (i) What is placenta ? Mention its role during pregnancy ?

(ii) Draw a labeled diagram of a human male reproductive system .

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

It facilitates the exchange of nutrients, oxygen, and waste products between the mother's blood and the embryo. The placenta nourishes the embryo, removes waste, and supports fetal development during the nine-month gestation period.

(ii)

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

Answer :

	Gamete	Zygote
Definition	Haploid reproductive cell; either sperm (male) or egg (female).	Diploid cell resulting from the fusion of sperm and egg during fertilization.
Chromosome	Contains half the number of chromosomes compared to somatic cells.	Contains the full complement of chromosomes,one set from each parent.
Formation	Produced by gametogenesis (spermatogenesis or oogenesis) in the gonads.	Formed as a result of fertilization when the male and female gametes fuse.

In sexual reproduction, gametes serve as the specialized cells responsible for fertilization. Sperm and egg cells, or male and female gametes respectively, are produced through meiosis. Their main role is to combine during fertilization to form a zygote, which is the initial cell of a new organism.

The zygote, formed by the fusion of gametes, contains a full set of chromosomes necessary for the development of the new individual. It undergoes subsequent cell divisions and differentiation to form tissues, organs, and eventually, a complete organism. Thus, the zygote marks the beginning of embryonic development in sexual reproduction.

9. Explain : (i) Regeneration (ii) Budding

Answer : (i) Regeneration: Regeneration is a biological process by which an organism can replace or restore lost or damaged body parts. This ability is most prominent in simple organisms like planaria, starfish, and certain types of worms. In these organisms, if a part of their body is lost or damaged, they can undergo cell division and tissue differentiation to regenerate the missing or damaged part. This process is not limited to specific body structures and can involve various tissues and organs. Regeneration is a remarkable adaptive mechanism that enhances the survival and resilience of certain organisms.

(ii) Budding: Budding is a form of asexual reproduction observed in some organisms, where a new individual develops as an outgrowth or bud from the parent organism. During budding, a small projection or bulge, known as a bud, forms on the parent organism. This bud grows and develops into a genetically identical or slightly modified individual. Once the bud reaches a sufficient size, it detaches from the parent, becoming an independent organism. Budding is common in organisms like hydra, yeast, and some types of sponges, providing a simple and efficient means of reproduction .

10. (i) What is spore formation ? Draw a diagram showing spore formation in Rhizopus .

(ii) List two advantages for organisms to reproduce themselves through spores .

Answer : (i) Spore formation is a method of reproduction in certain organisms, such as the bread mold Rhizopus. Specialized structures called sporangia produce cells known as spores. These spores, protected by thick walls, can develop into new individuals when they encounter a suitable environment with moisture.

(ii) Two advantages of spore reproduction are :

(a) Spores are lightweight and easily dispersed by wind, water, or animals, allowing organisms to colonize new habitats efficiently.

(b) Spores are protected by thick walls, enabling them to withstand harsh environmental conditions and remain dormant until conditions become favorable for growth and reproduction.