Class 10 Science · Chapter 7
How do Organisms Reproduce?
434 Class 10 Science questions on How do Organisms Reproduce? from the NCERT textbook, NCERT Exemplar and CBSE board papers 2017–2026, each with its answer and a step-by-step solution.
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Questions · page 19 of 22
- Q361 CBSE 2017How does Plasmodium reproduce. Is this method sexual or asexual ?Step-by-step solution →
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Plasmodium reproduces by multiple fission, which is asexual.
Plasmodium reproduces by multiple fission: its nucleus divides repeatedly, each new nucleus gets some cytoplasm and a membrane, and the parent cell releases many daughter cells at the same time. The method is asexual, because only one parent is involved and no gametes are formed or fused. - Q362 CBSE 2017Name the organs producing sperms and ova respectively in humans.Step-by-step solution →
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Sperms are produced by the testes and ova by the ovaries.
Sperms are produced by the testes, and ova by the ovaries. - Q363 CBSE 2017What is fertilisation ? Where does it occur in a human female ?Step-by-step solution →
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Fertilisation is the fusion of a sperm and an egg to form a zygote; in a human female it occurs in the oviduct.
Fertilisation is the fusion of a male gamete (sperm) with a female gamete (egg, or ovum) to form a zygote. In a human female it takes place in the oviduct (fallopian tube). - Q364 CBSE 2017When a cell reproduces, what happens to its DNA ?Step-by-step solution →
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The DNA is copied, and the two copies separate into the two new cells.
The DNA is copied. The cell uses chemical reactions to build a copy of its DNA, so the reproducing cell holds two copies; additional cellular apparatus is made as well, and the two DNA copies then separate, one going into each of the two new cells. The copying is not absolutely accurate, so the two copies, and hence the two cells, are similar but may differ slightly (variation). - Q365 CBSE 2017Newly formed DNA copies may not be identical at times. Give one reason.Step-by-step solution →
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No biochemical reaction is absolutely reliable, so small errors arise while DNA is copied.
DNA is copied by biochemical reactions, and no biochemical reaction is absolutely reliable. Small errors (variations) therefore arise during copying, so a newly formed copy is similar to the original but may not be identical to it. - Q366 CBSE 2017Why is variation important for a species ?Step-by-step solution →
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Variation helps a species survive a drastic change in its environment, as individuals with suitable variations survive and reproduce.
Variation is important for the survival of a species over time. If its environment (niche) changes drastically - for example, if the water in which a population of bacteria lives becomes much warmer - a population whose members were all alike could be wiped out, but if some individuals carry variations that suit the new conditions, they survive and reproduce, and the species continues. Variations selected in this way are also the basis of evolution. - Q367 CBSE 2017Name the method by which Plasmodium reproduces. Is this method sexual or asexual ?Step-by-step solution →
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Plasmodium reproduces by multiple fission, which is an asexual method.
Plasmodium reproduces by multiple fission, in which the parent cell divides into many daughter cells at the same time. This method is asexual, because only one parent is involved and no gametes are formed or fused. - Q368 CBSE 2017Give an example each of unisexual and bisexual flowers.Step-by-step solution →
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Papaya is a unisexual flower and Hibiscus is a bisexual flower.
Unisexual flower: papaya (watermelon is another example); such a flower contains either stamens or a pistil. Bisexual flower: Hibiscus (mustard is another example); such a flower contains both stamens and a pistil. - Q369 CBSE 2017Name the life-process that is essential for the existence of an organism.Step-by-step solution →
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Reproduction is the life process that keeps a kind of organism in existence from one generation to the next.
Reproduction. Every individual organism lives for a limited time; by producing new individuals of the same kind, reproduction keeps that kind of organism in existence from one generation to the next. - Q370 CBSE 2017List two functions performed by testes in human beings.Step-by-step solution →
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The testes form sperms and secrete the male hormone testosterone.
(1) The testes form the male germ cells, the sperms. (2) The testes secrete the male hormone testosterone, which regulates the formation of sperms and brings about the changes in appearance seen in boys at puberty. - Q371 CBSE 2017What is vegetative propagation ? Write the names of any two plants grown by this method.Step-by-step solution →
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Vegetative propagation is asexual reproduction in which new plants arise from the root, stem or leaves; sugarcane and rose are examples.
Vegetative propagation is a mode of asexual reproduction in which new plants develop from the vegetative parts of a plant, its root, stem or leaves, instead of from seeds. Two plants grown by this method: sugarcane and rose. (Grapes, banana, potato, Bryophyllum and money plant are other examples.) - Q372 CBSE 2017List in tabular form two distinguishing features between the binary fission and fragmentation.Step-by-step solution →
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Binary fission occurs in unicellular organisms, where one cell divides into two; fragmentation occurs in simple multicellular organisms, whose body breaks into pieces.
Binary fission compared with fragmentation (two distinguishing features): (1) Organisms: binary fission is seen in unicellular organisms such as Amoeba and Paramecium; fragmentation is seen in multicellular organisms with a relatively simple body organisation, such as Spirogyra. (2) What happens: in binary fission the single cell divides into two daughter cells (in Amoeba the nucleus divides first, then the cytoplasm); in fragmentation the body simply breaks up into two or more pieces (fragments), each of which grows into a new individual. - Q373 CBSE 2017Describe briefly how regeneration is carried out in Planaria.Step-by-step solution →
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Specialised cells in each piece multiply and change into tissues in order, so the piece grows into a complete Planaria.
If a Planaria is cut into a number of pieces, each piece can grow into a complete organism; this is regeneration. It is carried out by specialised cells present in the body piece. These cells proliferate and make a large number of cells. From this mass of cells, different cells undergo changes to become the various cell types and tissues. These changes take place in an organised sequence called development, so the missing parts are formed and each piece develops into a complete Planaria. - Q374 CBSE 2017Name two types of germ-cells present in human beings. Give any one difference between them.Step-by-step solution →
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The germ cells are the sperm and the egg; the sperm is small and motile, the egg much larger and non-motile.
The two types of germ cells in human beings are the male germ cell, the sperm, and the female germ cell, the egg (ovum). One difference: the sperm is a small cell that is motile, swimming by means of its long tail, whereas the egg is a much larger cell that is not motile and contains stored food. (Other differences also earn the mark: sperms are formed in the testes and eggs in the ovaries; a sperm carries an X or a Y chromosome, while an egg carries an X chromosome.) - Q375 CBSE 2017List any four modes of asexual reproduction.Step-by-step solution →
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Fission, budding, fragmentation and spore formation.
Any four of the following: 1. Fission — a single cell divides into two (binary fission, e.g. Amoeba) or many (multiple fission, e.g. Plasmodium). 2. Budding — a bud grows on the parent and detaches as a new individual, e.g. Hydra, yeast. 3. Fragmentation — the body breaks into pieces and each piece grows into a new individual, e.g. Spirogyra. 4. Spore formation — spores released from sporangia grow into new individuals, e.g. Rhizopus (bread mould). (Also accepted: vegetative propagation, e.g. Bryophyllum; regeneration, e.g. Planaria.) - Q376 CBSE 2017List any four advantages of vegetative propagation.Step-by-step solution →
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Vegetative propagation gives earlier flowering and fruiting, propagates plants that cannot make seeds, keeps the parent's features, and is quick and easy.
(1) Plants raised by vegetative propagation bear flowers and fruits earlier than plants raised from seeds. (2) Plants that have lost the capacity to produce seeds, such as banana, orange, rose and jasmine, can still be propagated. (3) All the plants produced are genetically similar enough to the parent plant to have all its characteristics, so the desirable features of a variety are preserved. (4) It is a quick and easy way to raise many plants from a single parent (for example, from the buds of one potato tuber), since no pollination, seed formation or germination is needed. - Q377 CBSE 2017Differentiate between pollination and fertilisation. What is cross-pollination ? State any two carriers (agents) that carry out this process.Step-by-step solution →
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Pollination is pollen transfer to the stigma; fertilisation is fusion of germ cells in the ovule; insects and wind carry pollen in cross-pollination.
Differences between pollination and fertilisation: (1) Pollination is the transfer of pollen grains from the anther to the stigma; fertilisation is the fusion of the male germ cell with the female germ cell (egg). (2) Pollination ends on the stigma, on the outside of the pistil; fertilisation takes place inside the ovule, in the ovary. (3) Pollination comes first, and when pollen goes from flower to flower it needs an agent to carry it; fertilisation follows after a pollen tube has grown down the style to the ovule, and it forms a zygote, which develops into the embryo. Cross-pollination is the transfer of pollen grains from the anther of one flower to the stigma of another flower of the same kind. Two agents of cross-pollination: insects and wind (water, and animals such as birds, are other agents). - Q378 CBSE 2017How does Hydra reproduce by budding ? Explain with the help of labelled diagrams. Why is this method of reproduction called asexual method ?Step-by-step solution →
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A bud grows on the parent Hydra and detaches as a new Hydra; it is asexual because only one parent is involved.
Budding in Hydra (see the labelled diagrams of the stages): (1) At one specific site on the body of the parent Hydra, cells (regenerative cells) divide repeatedly and form a small outgrowth called a bud. (2) The bud grows, and tentacles and a mouth develop at its free end, so it becomes a tiny Hydra while still attached to the parent. (3) When fully mature, it detaches from the parent body and lives as a new, independent Hydra. It is called an asexual method because only one parent is involved: no gametes are formed and no fertilisation takes place. The new individual is formed from the body cells of a single parent by cell division, so it is genetically similar to that parent. - Q379 CBSE 2017Define pollination. Differentiate between self-pollination and cross-pollination. If from a bisexual flower the young stamen is removed artificially, even then the flower produces fruits. How does it take place ?Step-by-step solution →
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Pollination moves pollen to the stigma; a flower with stamens removed still sets fruit by cross-pollination.
Pollination: the transfer of pollen grains from the anther of a stamen to the stigma of a carpel. Self-pollination and cross-pollination: (i) In self-pollination the pollen reaches the stigma of the same flower; in cross-pollination it is carried from one flower to another flower. (ii) Self-pollination usually needs no outside agent; cross-pollination needs an agent such as wind, water or animals. (iii) Self-pollination gives offspring with less variation; cross-pollination between flowers of different plants combines germ cells from two parents and gives more variation. Fruit without the flower's own stamens: the carpel of the flower is intact, so pollen from another flower reaches its stigma by cross-pollination (carried by wind, water or insects, or placed there by hand). A pollen tube grows through the style to the ovule, fertilisation takes place, and the ovary develops into the fruit while the ovules become seeds. - Q380 CBSE 2017List any four methods that are adopted by human beings for contraception. State in brief how the health of a family and prosperity of a nation is affected, if these methods are adopted either by the husband or the wife.Step-by-step solution →
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Barrier, oral pill, Copper-T and surgical methods let couples limit and space children, improving family health and, by slowing population growth, national prosperity.
Four methods of contraception: (1) Barrier method: a condom on the penis, or a similar covering worn in the vagina, stops sperm from reaching the egg. (2) Oral pills: they change the hormonal balance of the body so that eggs are not released. (3) Loop or Copper-T: a device placed in the uterus to prevent pregnancy. (4) Surgical methods: vasectomy in the man (the vasa deferentia are blocked, so sperm are not transferred) or tubectomy in the woman (the fallopian tubes are blocked, so the egg cannot reach the uterus). Health of the family: whether the husband or the wife adopts a method, the couple can limit the number of children and space them. Fewer, well-spaced pregnancies protect the mother's health, and the family's income, food and care go further for each child, so the family stays healthier. A condom also gives some protection against sexually transmitted infections. Prosperity of the nation: small families slow the growth of the population, which reduces the pressure on food, water, housing, schools, health care and jobs; more resources for each person and a healthier, better-educated population help the nation to prosper.