CBSE Class 10 Science Biology Life Processes Control Reproduction and Heredity Assignment with Answers Set 01

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Teacher's Note: Use the key term in your answer.

Answer: Inhalation: the ribs move up and out and the diaphragm flattens, so the chest cavity gets larger, the pressure falls and air rushes into the lungs.
Exhalation: the ribs move down and in and the diaphragm rises, so the cavity gets smaller, the pressure increases and air is pushed out.
Design: inside the lungs the passage divides into smaller and smaller tubes ending in millions of balloon-like alveoli. Their walls are very thin and have a rich network of blood capillaries, which gives a very large surface area for the exchange of oxygen and carbon dioxide.

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Answer:

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Answer: In humans the blood passes through the heart twice in one complete circuit. In the pulmonary circulation, deoxygenated blood goes from the right ventricle to the lungs through the pulmonary artery, and oxygenated blood returns to the left atrium by the pulmonary vein. In the systemic circulation, oxygenated blood goes from the left ventricle through the aorta to the body, and deoxygenated blood returns to the right atrium by the vena cava.
It is necessary because it keeps oxygenated and deoxygenated blood separate, which supplies oxygen efficiently to the body. Humans are warm-blooded and need a lot of energy, so they need this efficient system.

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Answer: The nephron is the functional unit of the kidney. It has a cup-shaped Bowman's capsule that holds a bunch of capillaries called the glomerulus, followed by a long coiled tubule that ends in a collecting duct.
Functions: (1) Filtration: blood is filtered in the glomerulus. (2) Selective reabsorption: useful substances such as glucose, amino acids, salts and water are taken back into the blood from the tubule. (3) Secretion of extra wastes. The remaining liquid is urine, which goes to the collecting duct, ureter and bladder.

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Answer: A reflex action is a sudden, automatic response to a stimulus, without thinking, such as pulling the hand away from a hot object. The path is called the reflex arc. A receptor senses the stimulus and a sensory neuron carries the message to the spinal cord. There a relay neuron passes it to a motor neuron, which carries it to a muscle (effector), which acts. The brain is not needed, so the reaction is quick.

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Answer:

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Answer:

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Answer: The brain has three parts. The fore-brain (cerebrum) is the thinking part: it controls memory, intelligence, reasoning and voluntary actions, and has centres for hearing, smell, sight and hunger. The mid-brain controls reflex movements of the eyes and head. The hind-brain has the cerebellum, which keeps balance and posture and coordinates voluntary actions such as walking, the pons, and the medulla, which controls involuntary actions such as heartbeat, breathing and vomiting.

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Answer: A neuron has a cell body with the nucleus, short branches called dendrites that receive the message, a long axon that carries the message away from the cell body, and the nerve ending that passes it to the next neuron at the synapse. Neurons carry electrical impulses and are the structural and functional unit of the nervous system.

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Answer: When the leaves of Mimosa (touch-me-not) are touched, the cells at the base of the leaf lose water quickly, and the leaves droop and fold. The signal is passed from cell to cell by electrical-chemical means. No nerves are needed, as plant cells change their water content, and so their shape, in response to the signal.

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Answer: Fission: the parent cell divides into two (binary fission in Amoeba) or many (multiple fission in Plasmodium).
Budding: a bud grows on the parent, then separates, e.g. Hydra and yeast.
Fragmentation: the body breaks into pieces, each of which grows into a new organism, e.g. Spirogyra.
Others: regeneration (Planaria) and spore formation (Rhizopus).

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Answer: Vegetative propagation is the growth of new plants from parts of the parent such as root, stem or leaf, e.g. potato (stem), Bryophyllum (leaf), rose (cutting).
Advantages: plants bear flowers and fruits earlier; seedless plants like banana can be grown; the new plant is identical to the parent.
Disadvantages: there is no variation, so a disease can spread to all plants; the plants may become overcrowded.

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Answer: The diagram shows the parts of a flower: sepal, petal, stamen (filament and anther) and pistil (stigma, style, ovary and ovule).

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Answer:

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Answer: The diagram shows the two ovaries, two fallopian tubes, the uterus, the cervix and the vagina.

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Answer: Barrier methods: condoms, diaphragm and cervical cap stop the sperm from reaching the egg.
Chemical methods: oral pills change the hormones so that eggs are not released.
Intra-uterine devices: copper-T or loop placed in the uterus.
Surgical methods: vasectomy in men and tubectomy in women.
Reasons: (1) to control the population, (2) to space the births of children, (3) to avoid unwanted pregnancy, and (4) to protect from sexually transmitted diseases and to protect the mother's health.

Teacher's Note: Give an example if the question allows.

Answer: In Hydra, a small outgrowth called a bud forms on the body wall by repeated cell division. It grows, develops tentacles and a mouth, and finally separates to become a new Hydra.
In yeast, a small bulge forms on the cell, the nucleus divides and one nucleus moves into the bud. The bud grows and breaks off as a new yeast cell.

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Answer: Natural selection: the survival of organisms with traits suited to the environment, who pass these to their offspring.
Genetic drift: random change in the frequency of genes in a small population by chance.
Geographical isolation: separation of populations by barriers such as rivers and mountains, which stops gene flow.
Speciation: the formation of new species from an existing species.
Vestigial organs: organs that no longer have any use, e.g. the human appendix.

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Answer:

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Answer: Variations make individuals different, so that when the environment changes, some are likely to survive. For example, if the temperature of water rises, heat-resistant bacteria survive while the others die, so the species continues.

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Answer: The sexually reproducing species. Sexual reproduction creates many variations, so some individuals can survive a change in the environment, while asexual reproduction makes identical copies, which could all be killed by a single change.

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Answer: Mendel crossed pea plants differing in two traits, round yellow seeds (RRYY) and wrinkled green seeds (rryy). The F₁ plants were all round and yellow. The F₂ plants showed round yellow, round green, wrinkled yellow and wrinkled green in the ratio 9 : 3 : 3 : 1. New combinations such as round green appeared, so the traits are inherited independently. He chose peas because they have contrasting traits, a short life cycle, produce many seeds, are self-pollinating and are easy to cross.

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Answer: Two traits: tall or dwarf plants, and round or wrinkled seeds. When pure tall (TT) and pure dwarf (tt) plants are crossed, all F₁ plants are tall (Tt), so tallness is dominant. In F₂ the ratio is 3 tall to 1 dwarf, so the dwarf trait, hidden in F₁, appears again. Dwarfness is recessive.

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Answer: Humans have 23 pairs of chromosomes, of which one pair are sex chromosomes. Females have XX and males have XY. All eggs carry X, while sperms carry either X or Y. If an X-sperm fertilises the egg, a girl (XX) is born, and if a Y-sperm fertilises it, a boy (XY) is born. So the sex depends on the father's sperm.

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Answer: Evolution is the formation of diverse species by variation and selection, like a branching tree, and it does not move upwards towards a goal. Bacteria are still very successful although they are simple, and humans are not 'better' than them, only different. Evolution makes organisms better suited to their environment, not 'higher'.

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Answer: Fossils are the remains or impressions of organisms that lived long ago, preserved in rocks.
Relative dating: fossils in deeper rock layers are older than those in upper layers.
Radiocarbon dating: the amount of radioactive carbon-14 left in the fossil is compared with the normal amount; since the half-life of carbon-14 is known, the age can be calculated.

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