CBSE Class 10 Science Reproduction Assignment Set 02

This Class 10 Science assignment on Reproduction (chapter How Do Organisms Reproduce) has 24 questions arranged by marks, with step-by-step answers, a simple-words summary and a teacher's note for each. It practises asexual reproduction: DNA copying and variation, fission, budding, fragmentation, regeneration, spore formation and vegetative propagation, with labelled diagrams of Rhizopus, Amoeba and Hydra.

Very Short Answer Questions (1 Mark)

Question 1. How does binary fission differ from multiple fission?
Answer:
1. In binary fission a cell divides into two daughter cells (for example Amoeba, Leishmania).
2. In multiple fission a cell divides into many daughter cells at the same time (for example Plasmodium).
In simple words: Binary fission gives two cells; multiple fission gives many cells.

Teacher's Note:
1. Give one example of each.
2. The difference is the number of daughter cells.

Question 2. Name the part of Bryophyllum where the buds are produced for vegetative propagation.
Answer:
The buds are produced in the notches along the margin of the leaves of Bryophyllum.
In simple words: Bryophyllum makes buds on its leaf edges.

Teacher's Note:
1. Write the part: notches of the leaf margin.
2. These buds grow into new plants when the leaf falls on soil.

Question 3. Name the method by which Hydra reproduces. Is this method sexual or asexual?
Answer:
Hydra reproduces by budding (and also by regeneration). Both are asexual methods, because only one parent is involved and no gametes are formed.
In simple words: Hydra buds, and this is asexual reproduction.

Teacher's Note:
1. Answer both parts of the question.
2. Give the reason for calling it asexual.

Question 4. Name the causative agent of the disease 'kala-azar' and its mode of asexual reproduction.
Answer:
The causative agent of kala-azar is Leishmania. It reproduces by binary fission, in which the cell divides in a definite orientation (longitudinally) with respect to the whip-like structure at its end.
In simple words: Leishmania causes kala-azar and divides by binary fission.

Teacher's Note:
1. Name the organism and the method.
2. Contrast with Amoeba, which divides in any plane.

Question 5. How will an organism be benefitted if it reproduces through spores?
Answer:
1. Spores are covered with thick walls that protect them from dry and other harsh conditions until they reach a moist surface and begin to grow.
2. They are very light and are produced in very large numbers, so they spread easily through air and water and many survive.
3. Reproduction by spores is quick and simple.
In simple words: Thick-walled, light, numerous spores help the organism survive and spread.

Teacher's Note:
1. Write protection, large numbers and easy spread.
2. Name the example: Rhizopus.

Question 6. Select two plants from the following which are grown by vegetative propagation process: Banana, Wheat, Mustard, Jasmine, Gram.
Answer:
Banana and jasmine are grown by vegetative propagation. They do not form seeds easily, so new plants are grown from parts of the plant, for example banana from suckers (side shoots) and jasmine by layering or cutting.
Wheat, mustard and gram are grown from seeds.
In simple words: Banana and jasmine are grown from plant parts, not from seeds.

Teacher's Note:
1. Remember banana, jasmine, rose and sugarcane as common examples.
2. Wheat, mustard and gram are seed crops.

Short Answer Questions I (2 Marks)

Question 7. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer:
1. Simple organisms that regenerate, such as Hydra and Planaria, have bodies with many similar, non-specialised cells and some specialised cells that can form all the missing parts.
2. In complex organisms the cells are differentiated into tissues and organs that perform different functions. Such organisms can repair parts like skin and muscle, but a piece of the body cannot grow into a whole new individual.
In simple words: In complex bodies, cells are specialised, so a piece cannot rebuild the whole organism.

Teacher's Note:
1. Use the words differentiated tissues and organs.
2. Give Hydra and Planaria as simple examples.

Question 8. Why is vegetative propagation practised for growing some types of plants?
Answer:
1. It is used for plants that do not form viable seeds or form very few seeds, for example banana, pineapple and orange.
2. It helps to grow plants where seed germination fails because of change in environment or soil.
3. It is a faster, easier and cheaper method, and the plants flower and fruit earlier.
4. The plants are genetically similar to the parent, so a good quality variety is preserved. (Any two or three points.)
In simple words: It gives quick, exact copies of useful plants, even if seeds are not formed.

Teacher's Note:
1. Write at least two points.
2. Give an example such as banana.

Question 9. Leaves of Bryophyllum fallen on the ground produce new plants, why?
Answer:
The leaves of Bryophyllum have adventitious buds (small plantlets) in the notches along the leaf margin. When the leaf falls on the soil, these buds develop into new plants under favourable conditions.
In simple words: Buds in the leaf notches grow into new plants.

Teacher's Note:
1. Name the buds as adventitious buds.
2. This is vegetative propagation.

Question 10. Why is variation beneficial to the species but not necessary for the individual?
Answer:
1. If the environment changes drastically (for example, the temperature of water rises because of global warming), most individuals of a population may die.
2. A few individuals with a variation that lets them tolerate the change (for example, heat resistant bacteria) will survive and multiply, so the species continues.
3. The individual itself can live its life without the variation, so it is useful for the species over time but not necessary for every individual.
In simple words: Variations let some members survive a change, which saves the species.

Teacher's Note:
1. Give the bacteria and heat example.
2. State that the benefit is for survival of the species over time.

Question 11. What is the importance of DNA copying in reproduction?
Answer:
1. DNA carries the information for making proteins, and so for the body design. By copying its DNA, the cell passes the characters of the parent to the offspring.
2. The DNA copying is not absolutely accurate, so small variations arise. These variations are useful for the survival of the species and lead to evolution.
In simple words: DNA copying passes the body design to the young and also brings small variations.

Teacher's Note:
1. Write two points: transmission and variation.
2. Link variation to survival.

Question 12. 'Cell division is a type of reproduction in unicellular organism'. Justify.
Answer:
In a unicellular organism the cell divides into two or more daughter cells, and each daughter cell becomes a new individual. So cell division produces more individuals, which is what reproduction does.
In simple words: In single-celled organisms, one cell dividing means one more organism.

Teacher's Note:
1. Give Amoeba as an example.
2. Reproduction means production of new individuals.

Question 13. How does the process of budding differ from the process of spore formation?
Answer:
1. In budding a bud develops as an outgrowth of the parent body by repeated cell division, grows into a tiny individual and detaches on maturity (for example Hydra).
2. In spore formation small, thick-walled, single-celled spores are formed inside sporangia on the hyphae. When the sporangium bursts, the spores are released and grow into new individuals in suitable conditions (for example Rhizopus).
In simple words: A bud is an outgrowth of the parent; spores are tiny cells released from a sporangium.

Teacher's Note:
1. Give one example of each.
2. Make a two-column comparison if time permits.

Question 14. Differentiate between unisexual and bisexual flowers and give one example of each.
Answer:
1. Unisexual flower: contains either stamens or carpels, not both (for example papaya, watermelon).
2. Bisexual flower: contains both stamens and carpels (for example hibiscus, mustard).
In simple words: Unisexual flowers have one sex organ; bisexual flowers have both.

Teacher's Note:
1. Stamen is male, carpel is female.
2. Learn two examples of each.

Short Answer Questions II (3 Marks)

Question 15. What is multiple fission? How does it occur in an organism? Explain briefly. Name an organism which exhibits this type of reproduction.
Answer:
1. In multiple fission a single parent cell divides into many daughter cells at the same time.
2. Under unfavourable conditions the cell forms a protective covering (cyst). The nucleus divides repeatedly into many nuclei, each nucleus gets a little cytoplasm and a thin membrane, and many daughter cells form inside the cyst.
3. When conditions become favourable, the cyst bursts and the daughter cells are released, each growing into a new organism.
4. Plasmodium (the malarial parasite) reproduces by multiple fission.
In simple words: One cell breaks up into many cells at once, as in Plasmodium.

Teacher's Note:
1. Mention the protective cyst.
2. Name Plasmodium as the example.

Question 16. Explain the term 'regeneration' as used in relation to reproduction of organisms. Describe briefly how regeneration is carried out in multicellular organisms like Hydra.
Answer:
1. Regeneration is the ability of an organism to give rise to a new individual from its cut or broken body parts.
2. It is carried out by specialised cells that divide and make a large number of cells. From this mass, different cells change into the various cell types and tissues, in an organised sequence, to form the missing parts.
3. If a Hydra is cut into pieces, each piece grows into a complete Hydra.
In simple words: A cut piece of Hydra can grow back into a whole animal.

Teacher's Note:
1. Say that specialised cells do the work.
2. Name Planaria as the second example.

Question 17. In the context of reproduction of species state the main difference between fission and fragmentation. Also give one example of each.
Answer:
1. Fission takes place in unicellular organisms. The cell splits into two or more daughter cells, for example Amoeba and Paramecium.
2. Fragmentation takes place in multicellular organisms. The body breaks into smaller pieces on maturity, and each piece grows into a new individual, for example Spirogyra.
In simple words: Fission is for single-celled organisms; fragmentation is for filament-like multicellular ones.

Teacher's Note:
1. State the type of organism for each method.
2. Give one example each.

Question 18. What happens when (i) Planaria gets cut into two pieces (ii) a mature Spirogyra filament attains considerable length (iii) on maturation sporangia burst?
Answer:
(i) Each piece regenerates into a complete new Planaria.
(ii) The filament breaks into smaller fragments, and each fragment grows into a new Spirogyra (fragmentation).
(iii) The spores are released and spread by air. When they land on a moist, favourable surface, each spore germinates into a new fungus.
In simple words: Each piece or spore can start a new organism.

Teacher's Note:
1. Name the process for each part.
2. All three are asexual reproduction.

Question 19. What is vegetative propagation? State two advantages and two disadvantages of this method.
Answer:
1. Vegetative propagation is a mode of asexual reproduction in which new plants are obtained from vegetative parts such as the stem, root or leaf. No seeds or spores are involved.
2. Advantages: (i) plants that do not produce seeds can be grown, for example banana and sugarcane; (ii) it is cheaper, easier and faster than growing from seeds, and the plants flower earlier.
3. Disadvantages: (i) there is no genetic variation, so no new and better varieties arise; (ii) the plants are all open to the same diseases, which can destroy an entire crop.
In simple words: Vegetative propagation gives quick copies of a plant, but without variation.

Teacher's Note:
1. Write two advantages and two disadvantages separately.
2. Define the term in your first line.

Long Answer Questions (5 Marks)

Question 20. Identify the following methods and give one example of each: (a) Process in which reproduction takes place by breaking up of parent into several fragments. (b) Process of dividing of organisms into many cells simultaneously. (c) Process of reproduction by formation of bud on the parent body. (d) Process of reproduction by formation of spores. (e) Process used by multi-cellular organisms to reproduce by cutting into many pieces and each piece forms a new individual.
Answer:
(a) Fragmentation, for example Spirogyra.
(b) Multiple fission, for example Plasmodium.
(c) Budding, for example yeast or Hydra.
(d) Spore formation, for example Rhizopus.
(e) Regeneration, for example Planaria.
In simple words: Match each description with its name: fragmentation, multiple fission, budding, spores, regeneration.

Teacher's Note:
1. Learn the pairs: Spirogyra-fragmentation, Plasmodium-multiple fission, Hydra-budding, Rhizopus-spores, Planaria-regeneration.
2. Examples are worth marks in this question.

Question 21. (i) Name the mode of reproduction of the following organisms and state the important feature of each mode: (a) Planaria (b) Hydra (c) Rhizopus. (ii) We can develop new plants from the leaves of Bryophyllum. Comment.
Answer:
(i)(a) Planaria reproduces by regeneration: if the body is cut into pieces, each piece can grow into a complete worm, using specialised cells.
(i)(b) Hydra reproduces by budding: a bud forms as an outgrowth by repeated cell division, grows into a small Hydra and then detaches from the parent.
(i)(c) Rhizopus reproduces by spore formation: tiny thick-walled spores are formed in sporangia, and each spore grows into a new individual in a moist, favourable place.
(ii) The leaves of Bryophyllum bear buds in the notches of the leaf margin. These buds fall on the soil and grow into new plants, which is vegetative propagation.
In simple words: Planaria regenerates, Hydra buds, Rhizopus makes spores, and Bryophyllum leaf buds grow into plants.

Teacher's Note:
1. Write the mode first and the feature next for each organism.
2. Part (ii) is about vegetative propagation.

Question 22. How does Rhizopus multiply by spores? Explain in brief. Sketch neat labelled diagram of this method.
Answer:
1. The hyphae of Rhizopus (bread mould) put up erect stalks called sporangiophores. At the tip of each, a round knob called the sporangium develops.
2. Inside the sporangium the nucleus divides many times, and each nucleus with a little cytoplasm and a thick wall becomes a spore. Thousands of spores are formed.
3. On maturity the sporangium bursts and the spores are released into the air.
4. A spore that lands on a moist surface with food germinates into a new hypha and a new fungus grows.

In simple words: Rhizopus makes many tiny spores in sporangia, and each spore can grow into a new mould.

Teacher's Note:
1. Label sporangium, spores, sporangiophore and hypha.
2. Spores need moisture and food to germinate.

Question 23. Name the process by which an Amoeba reproduces. Draw the various stages of its reproduction in a proper sequence.
Answer:
1. Amoeba reproduces by binary fission.
2. The nucleus first elongates and divides into two. Then the cytoplasm divides, a constriction appears and deepens, and the cell splits into two daughter Amoebae, each of which grows into an adult.

In simple words: Amoeba splits into two: first the nucleus divides, then the cytoplasm.

Teacher's Note:
1. Draw four stages in sequence and label them.
2. Nuclear division comes before cytoplasmic division.

Question 24. Draw a labelled diagram in proper sequence to show budding in Hydra.
Answer:
1. A small outgrowth called a bud forms on the side of the parent Hydra, because cells at that point divide repeatedly.
2. The bud grows, develops tentacles and a mouth, and stays attached for some time.
3. When it is fully grown, it detaches from the parent and lives as a new, independent Hydra.

In simple words: A bud grows on the Hydra, becomes a small Hydra and breaks away.

Teacher's Note:
1. Draw the bud at three stages.
2. Label the parent, bud and tentacles.