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Case Based Questions: How Do Organisms Reproduce? | Science Class 10 PDF Download

Q1: Read the source below and answer the questions that follow:

Riya conducted an experiment where she observed a drop of pond water under a microscope. She noticed a single-celled organism splitting into two identical cells. Her teacher explained that this process is called binary fission, a form of asexual reproduction in which an organism divides to form two new individuals.

(a) What is binary fission? (1 Mark)
(b) How does binary fission occur in Amoeba? (2 Marks)
(c) How is binary fission in Amoeba different from binary fission in Leishmania? (1 Mark) 
OR
(c) What is multiple fission? Give an example.
(1 Mark)

Ans:
(a) Binary fission is a type of asexual reproduction where a unicellular organism splits into two equal daughter cells. 
(b) In Amoeba, binary fission occurs as follows:

  • The nucleus divides first.
  • The cytoplasm then divides, forming two identical daughter cells. 

(c) In Leishmania, binary fission occurs in a fixed orientation along the longitudinal axis, while in Amoeba, it can occur in any plane.
OR
(c) Multiple fission is when a parent cell divides into many daughter cells at the same time. 
Example: Plasmodium (malarial parasite).

Q2: Read the source below and answer the questions that follow:

A farmer noticed that his mango trees produced fruits only after flowers appeared. His son asked how flowers lead to fruit formation. The farmer explained that flowers contain male and female reproductive parts, and pollen grains need to reach the female part for fertilization to occur.

(a) What is pollination? (1 Mark)
(b) Explain the process of fertilization in flowering plants. (2 Marks)
(c) What happens to the ovule and ovary after fertilization? (1 Mark) 
OR
(c) How is cross-pollination different from self-pollination?
(1 Mark)

Ans:
(a) Pollination is the transfer of pollen grains from the anther to the stigma of a flower. (1 Mark)
(b) Fertilization in flowering plants:

  • The pollen grain lands on the stigma and forms a pollen tube.
  • The male gamete travels through the tube and fuses with the egg inside the ovule, forming a zygote. 

(c) After fertilization:

  • The ovule develops into a seed.
  • The ovary grows and becomes a fruit. 

OR
(c) Self-pollination occurs when pollen from the same flower fertilizes the ovule, while cross-pollination happens between different flowers of the same species.

Q3: Read the source below and answer the questions that follow:

Rahul’s teacher explained how human reproduction involves both male and female reproductive systems. He was curious about how a zygote forms and what happens after fertilization.

(a) Where does fertilization occur in humans? (1 Mark)
(b) Explain the process of fertilization and zygote development in humans. (2 Marks)
(c) What is the role of the placenta in embryo development? (1 Mark) 
OR
(c) What happens if fertilization does not occur? (1 Mark)

Ans:
(a) Fertilization occurs in the fallopian tube of the female reproductive system.
(b)

  • A sperm fuses with an egg in the fallopian tube, forming a zygote.
  • The zygote divides and forms a ball of cells (embryo).
  • The embryo attaches to the uterus wall, where it grows into a foetus.

(c) The placenta transfers oxygen and nutrients from the mother to the foetus and removes waste products.
OR
(c)
If fertilization does not occur, the uterine lining sheds, leading to menstruation. 

Q4: Read the source below and answer the questions that follow:

Priya’s grandmother grew roses and potatoes in her garden. Priya was surprised to see that new rose plants grew from cut stems and potatoes sprouted from buds. Her grandmother explained that these plants reproduce by vegetative propagation.

(a) What is vegetative propagation? (1 Mark)
(b) How does vegetative propagation occur in Bryophyllum and potato? (2 Marks)
(c) Why is vegetative propagation useful in agriculture? (1 Mark) 
OR
(c) Give an example of a plant that reproduces using runners.
(1 Mark)

Ans:
(a) Vegetative propagation is a type of asexual reproduction where new plants grow from roots, stems, or leaves of the parent plant.
(b)

  • In Bryophyllum, new plants grow from buds on leaf margins.
  • In potatoes, buds (eyes) on tubers sprout into new plants.

(c) Vegetative propagation allows rapid reproduction and ensures genetic similarity in crops like sugarcane and banana.
OR
(c) Example: Strawberry reproduces using runners. 

Q5: Read the source below and answer the questions that follow:

During a biology class, Anjali asked about family planning methods. Her teacher explained how contraceptive methods help prevent unwanted pregnancies and protect against sexually transmitted diseases (STDs).

(a) What is contraception? (1 Mark)
(b) Explain two different methods of contraception. (2 Marks)
(c) How do hormonal contraceptives prevent pregnancy? (1 Mark) 
OR
(c) Can contraceptives prevent sexually transmitted diseases?
(1 Mark)

Ans:
(a) Contraception refers to methods used to prevent pregnancy. 
(b)

  • Barrier methods: Condoms prevent sperm from reaching the egg.
  • Surgical methods: Vasectomy (males) and tubectomy (females) block the sperm or egg path.

(c) Hormonal contraceptives (e.g., pills) prevent ovulation by altering hormone levels, stopping egg release. 
OR
(c) Barrier methods like condoms help prevent STDs, but other contraceptive methods do not. 

Q6: Read the source below and answer the questions that follow:

During a science discussion, Aman’s teacher explained that offspring look similar to their parents but are not exactly identical. Aman wondered why there are small differences between parents and children even though they belong to the same family. His teacher explained that this happens due to DNA copying and variations during reproduction.

(a) Why is DNA copying important in reproduction? (1 Mark)
(b) How does variation occur during reproduction? (2 Marks)
(c) Why is variation beneficial to a species but not necessarily to an individual? (1 Mark) 
OR
(c) How is variation responsible for the evolution of species? (1 Mark)

Ans:
(a) DNA copying is essential for passing genetic information from one generation to the next and maintaining body design.
(b) Variations occur due to:

  • Errors during DNA copying (minor changes in genetic material).
  • Sexual reproduction, which mixes genetic material from two parents.

(c) Variations help a species survive in changing environments, but they may not always be useful for an individual.
OR
(c) Over generations, useful variations accumulate, leading to the evolution of new traits and species.

Q7: Read the source below and answer the questions that follow:

During a lab activity, Anjali observed that a Planaria (flatworm) was cut into three parts, and after a few days, each part developed into a complete Planaria. Her teacher explained that this happens due to a process called regeneration.

(a) What is regeneration? (1 Mark)
(b) How does regeneration occur in Planaria? (2 Marks)
(c) Why can complex organisms like humans not reproduce through regeneration? (1 Mark) 
OR
(c) Give an example of another organism that reproduces by regeneration.
(1 Mark)

Ans:
(a) Regeneration is the ability of an organism to grow into a complete individual from its cut parts. 
(b) In Planaria, regeneration occurs as follows:

  • Special cells divide rapidly to form a mass of new cells.
  • These cells differentiate to form organs and body parts, leading to a new individual.

(c) Complex organisms have specialized cells, tissues, and organs that cannot regenerate the whole body. 
OR
(c) Example:
Hydra can also regenerate its body parts. 

Q8: Read the source below and answer the questions that follow:

Rohit was observing a Hydra under a microscope when he noticed a small outgrowth on its body. His teacher explained that Hydra reproduces asexually by budding, where new individuals grow as small buds and later detach from the parent body.

(a) What is budding? (1 Mark)
(b) Describe the process of budding in Hydra. (2 Marks)
(c) How is budding in Hydra different from binary fission in Amoeba? (1 Mark) 
OR
(c) Give an example of another organism that reproduces by budding. 
(1 Mark)

Ans:
(a) Budding is a form of asexual reproduction where a new organism develops as an outgrowth (bud) from the parent body.
(b) In Hydra:

  • A small bud appears due to repeated cell division at a specific site.
  • The bud grows, develops tentacles, and then detaches to form a new Hydra.

(c) In binary fission, the parent divides into two equal parts (Amoeba), while in budding, a small bud grows and separates (Hydra).
OR
(c) Example: Yeast also reproduces by budding. 

Q9: Read the source below and answer the questions that follow:

During a biology lecture, Meera asked why women experience menstruation every month. Her teacher explained that the female reproductive system prepares for pregnancy each month, and if fertilization does not occur, the uterus sheds its lining.

(a) What is menstruation? (1 Mark)
(b) Explain what happens during the menstrual cycle. (2 Marks)
(c) Why does menstruation stop when a woman is pregnant? (1 Mark) 
OR
(c) What is the average duration of the menstrual cycle?
(1 Mark)

Ans:
(a) Menstruation is the monthly shedding of the uterine lining along with blood and mucus when fertilization does not occur. 
(b) The menstrual cycle occurs in phases:

  • The ovary releases an egg (ovulation).
  • The uterine lining thickens to receive a fertilized egg.
  • If fertilization does not occur, the lining sheds as menstruation. 

(c) During pregnancy, the fertilized egg implants in the uterus, and hormone levels prevent the shedding of the uterine lining.
OR
(c) 
The average duration of the menstrual cycle is 28 days.

Q10: Read the source below and answer the questions that follow:

During a school seminar, students were taught about sexually transmitted diseases (STDs) and the importance of contraceptive methods. The speaker emphasized that some STDs, like HIV-AIDS, can be life-threatening.

(a) Name any two sexually transmitted diseases (STDs). (1 Mark)
(b) How can the spread of sexually transmitted diseases be prevented? (2 Marks)
(c) What is the importance of using condoms during sexual intercourse? (1 Mark) 
OR
(d) How do contraceptive pills prevent pregnancy? 
(1 Mark)

Ans:
(a) Two STDs: 
HIV-AIDS, Syphilis.
(b) STDs can be prevented by:

  • Using condoms during intercourse.
  • Avoiding multiple partners.
  • Maintaining hygiene and getting medical check-ups. 

(c) Condoms act as a barrier, preventing sperm from entering the female body, thus avoiding pregnancy and reducing STD risks.
OR
(c)
Contraceptive pills alter hormone levels, preventing ovulation (egg release) and making fertilization impossible. 

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FAQs on Case Based Questions: How Do Organisms Reproduce? - Science Class 10

1. What are the two main types of reproduction in organisms?
Ans. The two main types of reproduction in organisms are asexual reproduction and sexual reproduction. Asexual reproduction involves a single organism producing offspring that are genetically identical to itself, while sexual reproduction involves the combination of genetic material from two parent organisms, resulting in genetically diverse offspring.
2. How does asexual reproduction occur in organisms?
Ans. Asexual reproduction can occur through various methods such as binary fission, budding, fragmentation, and vegetative propagation. In binary fission, a single organism divides into two parts. In budding, a new organism grows from a part of the parent. Fragmentation involves breaking into pieces, each of which can grow into a new organism. Vegetative propagation occurs in plants where new individuals arise from vegetative parts like roots, stems, or leaves.
3. What are the advantages of sexual reproduction?
Ans. Sexual reproduction has several advantages, including increased genetic diversity, which enhances the adaptability of a species to changing environments. This genetic variation can lead to better survival rates and the ability to withstand diseases. Additionally, sexual reproduction can promote evolution by allowing beneficial traits to be passed on to future generations.
4. Can you give examples of organisms that reproduce asexually?
Ans. Yes, several organisms reproduce asexually. Examples include bacteria, which commonly reproduce through binary fission, and hydra, which can reproduce by budding. Many plants also reproduce asexually through methods like runners, tubers, or cuttings.
5. What role do gametes play in sexual reproduction?
Ans. In sexual reproduction, gametes are the reproductive cells that fuse during fertilization to form a zygote. Male gametes (sperm) and female gametes (eggs) contain half the genetic material of the parent organisms. The fusion of these gametes results in offspring that have a mix of traits from both parents, contributing to genetic diversity.
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