7 . How do Organisms Reproduce ?

CBSE Class 10 Science Chapter 7 . How do Organisms Reproduce ?

Chapter 7. How do Organisms Reproduce ?

CBSE Class 10 Science Chapter 7. How do Organisms Reproduce ? Previous Years Questions ans Answers :

Question : What is the effect of DNA copying which is not perfectly accurate on the reproduction process ? [CBSE 2008 1M]

Answer : The imperfect accuracy of DNA copying introduces variations in the offspring. Drastic variations may lead to non-functional cells, causing cell death. However, subtle variations contribute to genetic diversity, serving as the basis for evolutionary processes.

Question : After observing the prepared slides of binary fission in Amoeba and Budding in Yeast , the following observations were reported :

(i) Single cells of amoeba and Yeast were undergoing binary fission and budding respectively .

(ii) Cytokinesis was observed in the Yeast cell .

(iii) Elongated nucleus was dividing to form two daughter in Amoeba .

(iv) A chain of buds were observed due to reproduction in Amoeba .

The correct observation(s) is/are : [2012 1M]

(a) (iv) , (i) and (iii) (b) (iii) and (iv) (c) (ii) only (d) (i) and (iii)

Answer : (d) (i) and (iii)

[Note : (i) states that single cells of amoeba and yeast were undergoing binary fission and budding, respectively, which is accurate.

(iii) mentions that an elongated nucleus was dividing to form two daughter cells in amoeba, which is a characteristic of binary fission in amoeba.]

Question : A student after observing a slide showing different stages of binary fission in Amoeba draws the following diagrams . However these diagrams are not in proper sequence . [2011,2013 1M]

The correct sequence is :

(a) (I) , (V) , (IV) , (III) , (II) (b) (I) , (V) , (III) , (IV), (II)

Answer : (d) None of these .

Question : In the figure , the parts marked A, B and C are sequentially . [2013 , 2014 1M]

(a) Plumule , Cotyledon and Radicle

(b) Radicle , Cotyledon and Plumule

(d) Plumule , Radicle and Cotyledon

Answer : (d) Plumule , Radicle and Cotyledon

Question : Select the correct statements for the process of budding in Yeast : [2013 1M]

(i) A bud arises from a particular region on a parent body .

(ii) A parent cell divides into two daughter cells ; here the parental identity is lost .

(iii) Before detaching from the parent body a bud may form another bud .

(iv) A bud when detached from the parent body grows into a new individual .

(a) (ii) , (iii) and (iv) (b) (i) , (ii) and (iii) (c) (iii) , (iv) and (i) (d) None of the above

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

[ Note : (iii) is correct because before detaching from the parent body, a bud may indeed form another bud.

(iv) is correct because when a bud detaches from the parent body, it has the potential to grow into a new individual.

(i) is correct because a bud arises from a specific region on the parent body.

(ii) is incorrect because in budding, the parent cell does not divide into two daughter cells; rather, a smaller daughter cell (the bud) forms on the parent cell. ]

Question : When you study a slide showing different stages of budding in yeast you observe the following stages : [2014 1M]

(i) The bud may get separated from the parent body and develop into new individual .

(ii) The body of the bud develops and gives rise to another baby bud .

(iii) A bud comes out in any direction from the body of the parent cell .

(iv) Thus they may form a colony . The proper sequence of the above stages is :

(a) (ii) , (i) , (iii) , (iv) (b) (ii) , (iii) , (i) , (iv) (c) (iii) , (ii) , (i) , (iv) (d) (iii) , (i) , (ii) , (iv)

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

Question : Name two simple organisms having the ability of generation . [2015 1M]

Answer : The names of two simple organisms that have the ability to regenerate are Hydra and Planaria .

Question : A student was asked to observe and identify the various parts of an embryo of a red kidney bean seed . He identified the parts and listed them as under : [2015 1M]

(i) Tegmen (ii) Testa (iii) Cotyledon (iv) Radicle (v) Plumule

The correctly identified parts among these are :

(a) (i) , (ii) and (iii) (b) (ii) , (iii) and (iv) (c) (iii) , (iv) and (d) (i) , (iii) , (iv) and (v)

Answer : (d) (i), (iii), (iv), and (v)

[ Note : Tegmen (i) is a seed coat.

Cotyledon (iii) is the embryonic leaf in seed-bearing plants.

Radicle (iv) is the embryonic root.

Plumule (v) is the embryonic shoot. ]

Question : List two functions of ovary of human female reproduction system . [2016 1M]

Answer : Two functions of the ovary in the human female reproductive system are:

(i) Ovaries produce and release eggs (oocytes) during the menstrual cycle, typically one egg per month, which can potentially be fertilized by sperm during sexual intercourse.

(ii) Ovaries secrete important hormones such as estrogen and progesterone, which regulate the menstrual cycle, support pregnancy, and maintain the female reproductive system's health and function.

Question : A student while observing an embryo of a pea seed in the laboratory listed various parts of the embryo as given below :

Testa , Tegmen , Radicle , Plumule , Micropyle , Cotyledon

On examining the list the teacher remarked that only three parts are correct . Select three correct parts from the above list ; [2016 1M]

(a) Testa , Radicle , Cotyledon (b) Tegmen , Radicle , Micropyle

Answer : (d) Radicle, Cotyledon, Plumule

[Note: Radicle: The embryonic root.

Cotyledon: The seed leaf or the first leaf of the embryo.

Plumule: The embryonic shoot or the bud. ]

Question : Answer question numbers 11(a) to 11(d) on the basis of your understanding of the following paragraphs and the related studied concepts .

The growing size of the human population is a cause of concern for all people . The rate of birth and death in a given population will determine its size . Reproduction is the process by which organisms increase their population . The process of sexual maturation for reproduction is gradual and takes place while general body growth is still going on . Some degree of sexual maturation does not necessarily mean that the mind or body is ready for sexual acts of for having and bringing up children . Various contraceptive devices are being used by human beings to control the size of population .

(a) List two common signs of sexual maturation in boys and girls . [2020 4M]

(b) What is the result of reckless female foeticide ?

(d) Write two factors that determine the size of a population .

Answer : (a) Two common signs of sexual maturation in boys and girls are:

(i) Development of secondary sexual characteristics such as breast development in girls and facial hair growth in boys.

(ii) Onset of menstruation in girls and production of sperm in boys.

(b) The result of reckless female foeticide are :

(i) Gender imbalance in the population.

(ii) Social and psychological consequences for families and societies.

(iii) Disruption of the natural sex ratio, leading to long-term societal issues.

(c) A contraceptive method that changes the hormonal balance of the body is hormonal contraception, such as birth control pills, patches, injections, or implants. These methods contain synthetic hormones that prevent ovulation, alter the cervical mucus, or change the uterine lining to prevent pregnancy.

(d) Two factors that determine the size of a population are:

(i) Birth rate: The number of live births per thousand people in a population within a given time period.

(ii) Death rate: The number of deaths per thousand people in a population within a given time period.

Question : With the help of diagrams show the different stages of binary fission in Amoeba . [2010 , 17 , 18 2M]

Answer : The diagram of a amoeba :

In Amoeba, binary fission begins with the elongation of the cell. The nucleus then divides, followed by cytoplasmic division, forming two daughter cells. The splitting can occur in any plane due to the absence of a fixed axis. Each daughter cell inherits a nucleus and other essential organelles, resulting in independent organisms.

Question : List any four reasons for vegetative propagation being practiced in the growth of some type of plants . [2011 2M]

Answer : Four reasons for vegetative propagation being practiced in the growth of some types of plants are :

(i) Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds, which is advantageous for agricultural purposes.

(ii) Vegetative propagation allows for the propagation of plants such as bananas, oranges, roses, and jasmine that have lost the capacity to produce seeds or are seedless varieties.

(iii) Vegetative propagation ensures that all plants produced are genetically similar enough to the parent plant to inherit all its desirable characteristics, such as disease resistance, fruit quality, and flower color.

(iv) Methods such as layering or grafting facilitate the mass production of plants like sugarcane, roses, or grapes for agricultural and commercial purposes, ensuring consistent quality and characteristics in the propagated plants.

Question : State the role of : (i) Seminal vesicle (ii) Prostate gland in the human body [2011 2M]

Answer : (i) Seminal vesicle: The seminal vesicle secretes a fluid rich in fructose, prostaglandins, and other substances that provide energy and nourishment to sperm. This fluid also helps in the transportation of sperm by providing a medium that enhances their motility and survival.

(ii) Prostate gland: The prostate gland secretes a milky fluid that constitutes a significant portion of semen. This fluid contains enzymes, citric acid, and zinc, which help to activate and nourish sperm, contributing to their motility and viability.

Question : Define the term puberty . List two changes observed in girls at the time of puberty . [2012 2M]

Answer : Puberty is the period during adolescence when the reproductive tissues begin to mature. It is characterized by the gradual development of secondary sexual characteristics.

Two changes observed in girls at the time of puberty are :

(i) The onset of the menstrual cycle, marking the beginning of reproductive capability.

(ii) The enlargement and development of breast tissue, a secondary sexual characteristic.

Question : What is meant by asexual reproduction ? List any two of its different forms . [2012 2M]

Answer : Asexual reproduction is a type of reproduction where offspring arise from a single parent, and they inherit the genetic material of that parent only. There is no fusion of gametes (sex cells) involved in asexual reproduction.

Two different forms of asexual reproduction are:

Binary Fission: This is a process where a single organism divides into two equal-sized daughter organisms. Examples include bacteria and amoebas.

Budding: In budding, a small outgrowth or bud forms on the parent organism, which eventually detaches and develops into a new individual. Yeast and Hydra are examples of organisms that reproduce through budding.

Question : Mention two functions of the human testis . [2013 2M]

Answer : Two functions of the human testis are:

(i) The primary function of the testes is the formation of germ cells or sperms through a process called spermatogenesis. Sperms are essential for sexual reproduction.

(ii) The testes secrete the male sex hormone, testosterone. Testosterone plays a crucial role in the development of secondary sexual characteristics, such as deepening of the voice, facial hair growth, and the development of muscle mass during puberty.

Question : Draw labeled diagrams to illustrate budding in Hydra.[2014 2M]

Draw a labeled diagram in proper sequence to show budding in hydra . [2019 2M]

Answer :

In Hydra, reproduction occurs through budding, where regenerative cells undergo repeated division at a specific site, leading to bud formation. The buds grow into small individuals and, upon maturation, detach from the parent Hydra. These detached buds then develop into independent organisms, marking the completion of the budding process.

Question : Give reasons :

(i) Placenta is extremely essential for foetal development .

(ii) Uterine lining becomes thick and spongy after fertilization . [2022 2M]

Answer : (i) Placenta is extremely essential for foetal development:

(a) The placenta is a vital organ that forms during pregnancy and serves as a connection between the developing foetus and the mother's uterus.

(b) It facilitates the exchange of nutrients, oxygen, and waste products between the mother and the developing foetus.

(c) The placenta produces hormones, such as human chorionic gonadotropin (HCG), which helps in maintaining the pregnancy and supporting the growth and development of the foetus.

(d) It acts as a protective barrier, preventing harmful substances from reaching the foetus.

(ii) Uterine lining becomes thick and spongy after fertilization:

(a) After fertilization, the fertilized egg (zygote) undergoes several cell divisions, forming a ball of cells called the blastocyst.

(b) The blastocyst travels through the fallopian tube and reaches the uterus for implantation.

(d) This thickened uterine lining provides a nourishing environment for the developing embryo and ensures that it receives the necessary nutrients and support for initial growth.

Question : (a) Name the reproductive and non- reproductive parts of bread mould (Rhizopus) .

(b) List any two advantages of vegetative propagation . [2002 2M]

Answer : (a) Reproductive Parts of Bread Mould (Rhizopus):

Sporangium : A structure that produces and releases spores.

Spores : Reproductive cells capable of developing into new individuals.

Non-Reproductive Parts of Bread Mould (Rhizopus):

Hyphae: Thread-like structures that make up the body (mycelium) of the bread mould.

Stolon: Horizontal, stem-like structures that spread over the surface of the substrate, facilitating the absorption of nutrients

(b) Two advantages of vegetative propagation:

(i) Vegetative propagation allows for the preservation of desirable traits in plants, such as disease resistance, fruit quality, and flower color, ensuring consistency in characteristics across generations.

(ii) Plants propagated vegetatively often grow and establish more quickly compared to those grown from seeds. This is because vegetative propagation bypasses the seed germination and establishment phase, allowing for rapid growth and development.

Question : Name the reproductive parts of an angiosperm . Where are these parts located ? Explain the structure of its male reproductive part . [2022 2M]

Answer : The reproductive parts of an angiosperm are located within the flower. These parts include the stamen and the pistil.

The stamen is the male reproductive part of an angiosperm. It consists of two main structures:

Anther: The part of the stamen where pollen grains are produced.

Filament: The slender stalk that supports the anther, positioning it for efficient pollen dispersal.

Together, the anther and filament comprise the male reproductive structure of the angiosperm.

Question : What is puberty ? Mention any two changes that are common to both boys and girls in early teenage years . [2022 2M]

Answer : Puberty is a transitional stage in human development during which a child's body matures into an adult capable of sexual reproduction. It is characterized by various physical, physiological, and psychological changes.

Two changes that are common to both boys and girls during early teenage years are :

(i) Both boys and girls experience the growth of thick hair in new areas of the body such as armpits and the genital area between the thighs. This hair can also become darker in color. Additionally, thinner hair may appear on legs, arms, and the face.

(ii) The skin frequently becomes oily during puberty, leading to an increased likelihood of developing pimples or acne. This change is common to both boys and girls and is often associated with the hormonal fluctuations that occur during puberty.

Question : (a) Explain the terms : (i) Implantation (ii) Placenta

(b) What is the average duration of human pregnancy ? [2009 3M]

Answer : (a) (i) Implantation: Implantation refers to the process by which the fertilized egg (zygote) embeds itself into the thickened lining of the uterus. This occurs after the zygote undergoes several divisions and forms a ball of cells known as the embryo. Implantation is crucial for the continued development of the embryo, as it allows the embryo to receive nutrients and support from the mother's body.

(ii) Placenta: The placenta is a specialized organ that develops during pregnancy and is essential for the exchange of nutrients, oxygen, and waste products between the mother and the developing embryo/fetus. It is a disc-shaped structure embedded in the wall of the uterus, containing villi on the embryo's side and blood spaces on the mother's side. The placenta facilitates the transfer of substances like glucose and oxygen from the mother's blood to the embryo, while also removing waste products from the embryo's blood.

(b) The average duration of human pregnancy is approximately nine months.

Question : Write the full form of DNA . Name the part of the cell where it is located . Explain its role in the process of reproduction of the cell . [2010 3M]

Answer : The full form of DNA is Deoxyribonucleic Acid.

DNA is located in the nucleus of a cell, which is a membrane-bound organelle found in eukaryotic cells.

DNA plays a crucial role in the process of cell reproduction, specifically in cell division. During cell division, DNA replicates itself in a process called DNA replication. This ensures that each new cell receives a complete set of genetic information. In eukaryotic cells, which have a nucleus, the DNA is replicated during the S phase of the cell cycle. The accurate transmission of genetic information through DNA replication is vital for maintaining the genetic integrity and continuity of species during cellular reproduction.

Question : What does HIV stand for ? Is AIDS an infectious disease ? List any four modes of spreading AIDS . [2011 3M]

Answer : HIV stands for Human Immunodeficiency Virus.

Yes, AIDS (Acquired Immunodeficiency Syndrome) is an infectious disease caused by the Human Immunodeficiency Virus (HIV).

Four modes of spreading AIDS are :

(i) Unprotected sexual intercourse with an infected person.

(ii) Sharing contaminated needles or syringes, particularly among intravenous drug users.

(iii) From an HIV-infected mother to her child during pregnancy, childbirth, or breastfeeding.

(iv) Blood transfusions or organ transplants from HIV-infected donors (though this is rare in areas where blood is screened for HIV).

Question : Explain the meaning of sexually transmitted diseases (STD’s) . Give two examples of STD’s each , caused due to

(i) bacterial infection (ii) viral infection .

State in brief how the spread of such diseases may be prevented . [2008 , 12 ,13 3M]

Answer : Sexually Transmitted Diseases (STDs) are infections that are primarily transmitted through sexual contact, including vaginal, anal, and oral sex. These infections can be caused by bacteria, viruses, parasites, or fungi.

Examples of STDs caused by bacterial infection:

(i) Gonorrhea: A bacterial infection caused by Neisseria gonorrhoeae, which can affect the genitals, rectum, and throat.

(ii) Syphilis: An infection caused by the bacterium Treponema pallidum, which progresses through several stages and can affect various organs.

Examples of STDs caused by viral infection:

(i) HIV/AIDS: Human Immunodeficiency Virus (HIV) causes Acquired Immunodeficiency Syndrome (AIDS), affecting the immune system.

(ii) Herpes: Herpes simplex virus (HSV) can cause oral or genital herpes, characterized by painful sores in the affected areas.

Preventive measures for the spread of STDs:

(i) Using condoms or dental dams consistently and correctly during sexual activities can reduce the risk of transmission.

(ii) Getting tested for STDs regularly, especially if sexually active with multiple partners, can help in early detection and treatment.

(iii) For certain viral STDs like HPV (Human Papillomavirus), vaccination is available to prevent infection.

(iv) Promoting awareness and education about safe sex practices and the importance of regular screenings can contribute to prevention.

Question : (a) Explain the process of regeneration in Planaria .

(b) How is generation different from reproduction ? [2013 3M]

Answer : (a) In Planaria, regeneration is a process by which a complete organism can regenerate from a fragment of its body. Specialized cells called neoblasts are responsible for regeneration. When a Planaria is cut into pieces, these neoblasts proliferate and differentiate to form the necessary cell types and tissues to rebuild the missing parts. Over time, each fragment develops into a complete organism, possessing all the essential organs and structures required for survival.

(b) Generation refers to the production of offspring by sexual reproduction, where genetic material from two parents combines to create a new individual with a unique combination of traits. It involves the fusion of gametes (sperm and egg) to form a zygote, which develops into a new organism. Reproduction, on the other hand, is a broader term that includes both sexual and asexual processes of producing offspring. Asexual reproduction methods like regeneration in Planaria do not involve the fusion of gametes or genetic recombination, and offspring are genetically identical to the parent.

Question : Write one difference between asexual and sexual mode of reproduction . Which species is likely to have better chances of survival – the one reproducing asexually or the one reproducing sexually ? Justify your answer . [2014 3M]

Answer : The difference between asexual and sexual modes of reproduction are :

In asexual reproduction, offspring are genetically identical to the parent, as they arise from a single parent organism.

In sexual reproduction, offspring inherit genetic material from both parents, resulting in genetic variation.

Species reproducing sexually are likely to have better chances of survival in the long run. The genetic diversity introduced through sexual reproduction provides a population with the potential to adapt to changing environmental conditions. This diversity increases the chances of some individuals possessing advantageous traits that can contribute to the population's survival in the face of environmental challenges, diseases, or other selective pressures. In contrast, asexually reproducing species may lack this genetic diversity, making them more vulnerable to threats that can affect the entire population simultaneously.

Question : What is the effect of DNA coping , which is not perfectly accurate , on the reproduction process ? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals ? [ 2014 , 2018 3M]

Answer : The imperfect accuracy of DNA copying during reproduction can lead to mutations, introducing genetic variations. These variations contribute to the diversity within a population and are essential for evolution.

The amount of DNA remains constant through precise processes like DNA replication during cell division. Each new generation inherits a combination of DNA from two individuals through sexual reproduction, maintaining the overall quantity of genetic material while introducing variability through genetic recombination.

Question : List any four methods of contraction used by humans . State in brief two advantages of adopting such preventive methods . [2022 3M]

Answer : Four methods of contraception used by humans are :

(i) Barrier method that prevents sperm from reaching the egg.

(ii) Hormonal method that inhibits ovulation or fertilization.

(iii) Devices inserted into the uterus to prevent implantation of fertilized eggs or alter the uterine environment.

(iv) Permanent method that involves surgical procedures like vasectomy for males or tubal ligation for females to prevent sperm or eggs from reaching each other.

Two advantages of adopting contraceptive methods are:

(i) Contraceptives help individuals and couples to plan and space pregnancies according to their desires, reducing the likelihood of unintended pregnancies and associated challenges.

(ii) Contraceptive methods provide individuals with control over their reproductive health by allowing them to make informed decisions about when and if to have children, contributing to overall well-being and autonomy.

Question : (a) List two reason for the appearance of variations among the progeny formed by sexually reproduction .

(b)

(i) Name the part marked A in the diagram .

(ii) How does ‘A’ reaches part ‘B’ ?

(iii) State the importance of the part ‘C’ .

(iv) What happens to the part marked ‘D’ after fertilization is over ? [2016 3M]

Answer : (a) Two reasons for the appearance of variations among the progeny formed by sexual reproduction are:

(i) Genetic recombination during meiosis, which results in the shuffling and mixing of genetic material from two parent organisms.

(ii) Random assortment of chromosomes during gamete formation, leading to different combinations of alleles in offspring .

(b) (i) Pollen grain .

(ii) Pollen grains are transferred to the stigma through various means such as wind, insects, birds, or other animals.

(iii) The pollen tube plays a crucial role in fertilization by delivering the male gametes (sperm cells) from the pollen grain to the female gametes (ovules) within the ovary.

(iv) After fertilization, the female germ-cell develops into the embryo, which eventually grows into a new plant inside the seed.

Question : Define reproduction . How does it help in providing stability to the population of species ? [2016 3M]

Answer : Reproduction is the biological process by which new individuals of the same species are produced, ensuring the continuation of the species.

Reproduction contributes to the stability of a population by maintaining a balance between births and deaths. It replaces aging or deceased individuals, preventing extinction. Variability introduced through reproduction allows populations to adapt to changing environments, enhancing their resilience and overall stability over time.

Question : Explain the term “Regeneration” as used in relation to reproduction of organisms . Describe briefly how regeneration is carried out in multi-cellular organisms like Hydra . [2016 3M]

Answer : Regeneration refers to the ability of organisms to regrow lost or damaged body parts to restore their original form or function.

In multicellular organisms like Hydra, regeneration is achieved through specialized cells called interstitial cells, located between the epithelial cells. When a Hydra is cut into pieces, interstitial cells migrate to the wound site, proliferate, and differentiate into various cell types, eventually forming complete individuals from the fragments.

Question : List the two type of production . Which one of the two is responsible for bring in more variation in its progeny and how ? [2017 3M]

Answer : The two types of reproduction are sexual reproduction and asexual reproduction.

Sexual reproduction is responsible for bringing in more variation in its progeny. This is because sexual reproduction involves the fusion of gametes from two different parents, resulting in genetic recombination and the mixing of genetic material from both parents. This process creates offspring with unique combinations of traits, leading to increased genetic diversity within a population.

Question : List three techniques that have been developed to prevent pregnancy . Which one of these techniques is not meant for males ? How does the use of these techniques have a direct impact on the health and prosperity of a family ? [2017 3M]

Answer : Three techniques developed to prevent pregnancy are:

(i) Barrier method used by both males and females.

(ii) Hormonal method primarily used by females.

(iii) Devices inserted into the uterus, primarily used by females.

Condoms are not specifically meant for males, as female condoms are also available.

The use of these techniques has a direct impact on the health and prosperity of a family by allowing individuals and couples to plan and space their pregnancies according to their desires. This can lead to improved maternal and child health outcomes, reduced financial strain, increased educational and career opportunities for women, and overall greater family well-being and stability.

Question : What is vegetative propagation ? state two advantages and two disadvantages of this method . [2017 3M]

Answer : Vegetative propagation is a form of asexual reproduction in plants where new individuals are produced from vegetative parts such as stems, roots, or leaves, without the involvement of seeds.

Advantages of vegetative propagation are :

(i) Vegetative propagation allows for the preservation of desirable traits in plants, ensuring the propagation of high-quality characteristics.

(ii) It enables rapid multiplication of plants, allowing for the production of numerous offspring in a short period.

Disadvantages of vegetative propagation are :

(i) Since vegetative propagation produces offspring from the same parent plant, there is limited genetic variation, which may make the population susceptible to diseases and environmental changes.

(ii) Uniformity among plants propagated vegetatively can make them more vulnerable to pests and diseases, as a single pathogen can affect the entire population.

Question : (a) List in tabular form two differences between binary fission and multiple fission .

(b) What happens when a mature spirogyra filament attains considerable length ? [2020 3M]

Answer : (a) The differences between binary fission and multiple fission are :

	Binary Fission	Multiple Fission
Number of Offspring	Produces two offspring	Produces multiple offspring
Occurrence	Common in unicellular organisms	Common in some unicellular and multicellular organisms

(b) When a mature Spirogyra filament attains considerable length, it undergoes fragmentation. The filament breaks into smaller fragments due to mechanical forces or environmental factors. Each fragment then develops into a new filament, leading to vegetative reproduction and the propagation of Spirogyra.

Question : With the help of suitable diagrams, explain the various steps of budding in Hydra .[2011 5M]

Answer :

In Hydra, budding begins with the development of an outgrowth due to repeated cell division at a specific site. The bud grows and develops into a tiny individual while remaining attached to the parent Hydra. As the bud matures, it eventually detaches from the parent body and becomes a new independent individual, capable of further growth and reproduction through budding.

Question : What is binary fission in organisms ? with the help of suitable diagrams , describe the mode of reproduction in Amoeba . [2011 5M]

Answer : Binary fission is a form of asexual reproduction in which a single organism divides into two daughter organisms of equal size. This process is commonly observed in unicellular organisms such as bacteria, protists, and some algae.

In Amoeba, a single-celled organism, reproduction occurs primarily through binary fission. The process begins with the nucleus of the Amoeba dividing by mitosis, resulting in two identical nuclei. The cell then elongates and eventually divides into two daughter cells, each containing one of the nuclei. These daughter cells are genetically identical to the parent Amoeba and are capable of independent existence and further growth. Binary fission allows Amoeba to rapidly multiply and populate their environment under favorable conditions.

Question : Define the terms pollination and fertilisation . Draw a diagram of a pistil showing pollen tube growth into the ovule and label the following : pollen grain , male gamete , female gamete and ovary .[2012 5M]

Answer : Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a pistil within the same flower (self-pollination) or between different flowers (cross-pollination), facilitated by agents like wind, water, or animals.

Fertilization is the fusion of the male germ-cell produced by the pollen grain with the female gamete present in the ovule, resulting in the formation of a zygote capable of developing into a new plant.

Question : Describe in brief the role of : (i) Testis (ii) Seminal vesicle (iii) Vas deferens (iv) Ureter (v) Prostate gland in human male reproduction system . [2012 5M]

Answer : (i) Testis: The testes are responsible for producing sperm cells through a process called spermatogenesis. They also produce the hormone testosterone, which is crucial for the development of male reproductive tissues and secondary sexual characteristics.

(ii) Seminal vesicle: Seminal vesicles produce a significant portion of the fluid that makes up semen. This fluid provides nourishment for sperm cells and helps to protect them as they travel through the female reproductive system.

(iii) Vas deferens: The vas deferens is a duct that transports mature sperm from the epididymis to the ejaculatory ducts in anticipation of ejaculation. It also plays a role in propelling sperm through peristaltic contractions of its smooth muscle layers.

(iv) Ureter: The ureter is not directly involved in the male reproductive system. It is part of the urinary system and carries urine from the kidneys to the bladder for storage and eventual elimination from the body.

(v) Prostate gland: The prostate gland secretes a fluid that mixes with sperm and seminal vesicle fluid to form semen. This fluid helps to nourish and protect sperm, and it also plays a role in activating sperm for fertilization. The prostate gland surrounds the urethra and is located just below the bladder.

Question : (a) Write the function of placenta in females .

(b) List four ways of preventing pregnancy . State two advantages of using such preventive methods . [2013 5M]

Answer : (a) The placenta in females serves as a vital organ during pregnancy, facilitating the exchange of nutrients, oxygen, and waste products between the mother and the developing fetus. It acts as a barrier, preventing harmful substances from reaching the fetus while allowing essential substances to pass through. Additionally, the placenta produces hormones that help maintain the pregnancy and support fetal development.

(b) Four ways of preventing pregnancy are:

(i) Condoms are barriers worn over the penis during sexual intercourse to prevent sperm from reaching the egg. They also offer protection against sexually transmitted infections (STIs).

(ii) Birth control pills contain hormones that prevent ovulation and thicken cervical mucus, making it difficult for sperm to reach the egg.

(iii) IUDs are small, T-shaped devices inserted into the uterus to prevent pregnancy. They can either release hormones or contain copper, which affects sperm motility and fertilization.

(iv) Sterilization procedures, such as vasectomy for males and tubal ligation for females, involve surgical methods to block or cut the fallopian tubes (in females) or the vas deferens (in males) to prevent sperm from reaching the egg.

Advantages of using preventive methods:

(i) These methods are highly effective when used correctly, providing reliable protection against unintended pregnancy.

(ii) Some preventive methods, such as condoms, not only prevent pregnancy but also offer protection against sexually transmitted infections, promoting sexual health and well-being.

Question : (a) Identify A, B and C in the given diagram and write their functions .

(b) Mention the role of gamete and zygote in sexually reproducing organisms . [2013 , 15 5M]

Answer : (a) A - Stigma , B - Male germ-cell , C - Female germ-cell
(i) Stigma: The stigma in a flower receives pollen grains during pollination, facilitating the attachment and germination of pollen for fertilization.

(ii) Male germ-cell: Male germ cells, or sperm, fertilize the female germ cell (egg) during sexual reproduction, contributing genetic material to form a zygote.

(iii) Female germ-cell: The female germ cell, or egg, fuses with a male germ cell during fertilization, forming a zygote that develops into a new organism.

(b) In sexually reproducing organisms, gametes and zygotes play crucial roles in the process of reproduction:

Gametes are reproductive cells (sperm in males, eggs in females) that fuse during fertilization to form a zygote. The gametes carry half of the genetic information (haploid) of the organism.

The zygote, formed by the fusion of gametes, contains a complete set of chromosomes (diploid) from both parents. It develops into an embryo and eventually into a new individual, initiating the process of growth and development in sexually reproducing organisms.

Question : (a) Draw a sectional view of human female reproductive system and label the part where

(i) eggs develop (ii) fertilization takes place .

(iii) fertilization egg gets implanted .

(b) Describe in brief the changes the uterus undergoes

(i) to receive the zygote . (ii) if zygote is not formed . [2014 5M]

Answer : (a)

(i) Eggs develop in the ovaries. (ii) Fertilization takes place in the fallopian tubes (oviducts). (iii) After fertilization, the fertilized egg gets implanted in the endometrium of the uterus.

(b) (i) Uterus changes to receive the zygote: After ovulation, the uterus undergoes changes in its lining, thickening the endometrium to prepare for implantation. Glands secrete nutrients to support potential embryo development, creating a favorable environment for the zygote to implant and develop.

(ii) Uterus changes if zygote is not formed: If fertilization does not occur, the thickened endometrial lining is shed during menstruation. Hormonal changes trigger the breakdown of the endometrium, leading to menstrual bleeding and the expulsion of the unfertilized egg and uterine lining.

Question : (a) Name the parts label as A, B, C and D in the diagram given below :

(b) What is pollination ? State its significance .

(c) How does fertilisation occur in flowers ? Name the parts of the flower that develop into (i) seed and (ii) fruit after fertilization . [2014 5M]

Answer : (a) A - Pollen grain , B - Male germ-cell , C - Ovary , D - Pollen tube .

(b) Pollination is the transfer of pollen grains from the male reproductive organ (anther) of a flower to the female reproductive organ (stigma) of the same or another flower.

Its significance lies in facilitating the fertilization process, leading to the production of seeds and the continuation of plant species. It ensures genetic diversity and contributes to the reproductive success of flowering plants.

(c) Fertilization in flowers occurs when a pollen grain lands on the stigma of a flower and grows a pollen tube down the style to the ovary. Within the ovary, sperm cells from the pollen grain fertilize the egg cell, forming a zygote.

(i) The fertilized ovule develops into a seed.

(ii) The ovary of the flower develops into a fruit after fertilization.

Question : (a) Name the human male reproductive organ that produces sperm and also secretes a hormone . Write the functions of the secreted hormone .

(b) Name the parts of the human female reproductive system where

(i) Fertilisation takes place

(ii) Implantation of the fertilized egg occurs . Explain how the embryo gets nourishment inside the mother’s body . [2015 5M]

Answer : (a) The human male reproductive organ that produces sperm and also secretes a hormone is the testis. The hormone secreted by the testis is testosterone. Testosterone functions to regulate the development of male reproductive tissues and secondary sexual characteristics such as facial hair, deepening of the voice, and muscle growth.

(b) (i) Fertilization takes place in the fallopian tubes, also known as the oviducts, of the human female reproductive system. (ii) Implantation of the fertilized egg occurs in the endometrium, which is the lining of the uterus.

After implantation, the embryo receives nourishment through the placenta. The placenta is a specialized organ that develops during pregnancy and connects the developing fetus to the uterine wall. It serves as a conduit for the exchange of nutrients, oxygen, and waste products between the mother and the fetus. The placenta contains blood vessels that allow for the transfer of substances from the mother's bloodstream to the fetus, providing the necessary nourishment for the embryo's growth and development inside the mother's body.

Question :What is placenta ? Describe its structure . State its functions in case of a pregnant human female .[2016 5M]

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

Structure: The placenta is a disc embedded in the uterine wall, facilitating nutrient exchange between the mother and the embryo. It has villi on the embryo's side, and on the mother's side are blood spaces surrounding the villi. This structure provides a large surface area for the transfer of glucose and oxygen from the mother to the embryo and allows the removal of waste substances from the embryo to the mother's blood.

The functions are :

(i) The placenta transports nutrients and oxygen from the mother's bloodstream to the baby through the umbilical cord.

(ii) It also removes waste products and carbon dioxide from the baby's bloodstream and transfers them to the mother's bloodstream for elimination.

(iii) The placenta produces hormones that help maintain the pregnancy and support the development of the baby.

(iv) It acts as a barrier, protecting the baby from harmful substances and infections that could harm its development. Overall, the placenta is essential for the healthy growth and development of the baby during pregnancy.

Question : (a) write the functions of each of the following parts in a human female reproductive system :

(i) Ovary (ii) Uterus (iii) Fallopian tube

(b) Write the structure and functions of placenta in a human female . [2017 , 2018 5M]

Answer : (a) Functions of each part in the human female reproductive system:

(i) Ovary: The ovary produces eggs (ova) through the process of oogenesis and releases them during ovulation. It also secretes hormones such as estrogen and progesterone, which regulate the menstrual cycle and maintain pregnancy.

(ii) Uterus: The uterus, or womb, is where a fertilized egg implants and develops into a fetus during pregnancy. It provides a nourishing environment for the developing embryo/fetus and undergoes contractions during labor to facilitate childbirth.

(iii) Fallopian tube: The fallopian tube, or oviduct, is where fertilization typically occurs. It transports eggs from the ovaries to the uterus. Cilia lining the fallopian tubes help move the egg towards the uterus and provide a site for sperm-egg interaction.

(b) Structure: The placenta is a disc embedded in the uterine wall, facilitating nutrient exchange between the mother and the embryo. It has villi on the embryo's side, and on the mother's side are blood spaces surrounding the villi. This structure provides a large surface area for the transfer of glucose and oxygen from the mother to the embryo and allows the removal of waste substances from the embryo to the mother's blood.

The functions are :

(i) The placenta transports nutrients and oxygen from the mother's bloodstream to the baby through the umbilical cord.

(ii) It also removes waste products and carbon dioxide from the baby's bloodstream and transfers them to the mother's bloodstream for elimination.

(iii) The placenta produces hormones that help maintain the pregnancy and support the development of the baby.

Question : Define pollination . Explain the different types of pollination . List two agents of pollination ? How does suitable pollination lead to fertilization ? [2019 5M]

Answer : Pollination is the process by which pollen grains are transferred from the anther (male reproductive organ) of a flower to the stigma (female reproductive organ) of the same or another flower, leading to fertilization and seed production.

Types of Pollination are :

Self-pollination: Pollen is transferred from the anther to the stigma of the same flower or another flower on the same plant.

Cross-pollination: Pollen is transferred from the anther of one flower to the stigma of a different flower, either on the same or another plant.

Agents of Pollination:

Wind: Pollen is carried by the wind to reach the stigma of a flower.

Animals: Insects, birds, and other animals transfer pollen as they visit flowers for nectar.

Suitable pollination is essential for fertilization in plants. When pollen reaches the stigma, it germinates and develops a pollen tube down the style, leading to the ovary. Sperm cells move through the pollen tube, reaching the ovule in the ovary. Fertilization occurs when the sperm cell fuses with the egg cell in the ovule, forming a zygote. This zygote develops into a seed, initiating the formation of new plants. Successful pollination ensures the transfer of genetic material and contributes to the production of seeds, supporting the next generation of plants.

Question : (a) Identify the given diagram . Name the parts 1 to 5 .

(b) What is contraception ? List three advantages of adopting contraceptive measures . [2019 5M]

Answer : (a)

1. Oviduct or Fallopian 2. Ovary 3. Uterus 4. Cervix 5. Vagina

(b) Contraception is the methods or techniques used to prevent pregnancy by intentionally inhibiting the fusion of the male and female gametes (sperm and egg).

Three advantages of adopting contraceptive measures:

(i) Contraception allows individuals or couples to plan and control the timing and number of children they want. This helps in spacing pregnancies, promoting responsible parenthood, and ensuring that families can adequately provide for their children's needs.

(ii) Contraceptive methods provide women with the ability to make decisions about their reproductive health. They allow women to delay pregnancies until they are physically and emotionally prepared, reducing the risks associated with maternal and infant health.

(iii) Contraception enables individuals, particularly women, to pursue education and career goals without the immediate pressure of unplanned pregnancies. By having control over reproductive choices, individuals can focus on personal and professional development before starting a family.