CBSE Class 10 Science How do Organisms Reproduce Important Questions Set 01

Answer: Bryophyllum.

Teacher's Note:
1. Buds develop at the notches on the leaf margin and grow into new plants.
2. This is an example of vegetative propagation.

Answer: (a) Ovulation. (b) Menarche.

Teacher's Note:
1. Ovulation occurs around the middle of the menstrual cycle.
2. Menarche marks the beginning of puberty in girls.

Answer: In the oviduct (fallopian tube).

Teacher's Note:
1. The zygote then moves to the uterus for implantation.
2. Remember that implantation takes place in the uterus, not the oviduct.

Answer: (d) anther. The anther is the part of the stamen that makes and releases pollen.

Teacher's Note:
1. Ovules are produced in the ovary.
2. The stigma receives the pollen.

Answer: (a) spore formation. Fungi such as Rhizopus form spore-bearing sporangia, and the spores grow into new individuals.

Teacher's Note:
1. Yeast is the common exception, which reproduces by budding.
2. Spores are protected by a thick wall.

Answer: (d) Placenta. It is a disc-like structure in the uterine wall that also removes the waste of the embryo.

Teacher's Note:
1. The placenta contains villi that increase the surface area for exchange.
2. The embryo is linked to it by the umbilical cord.

Answer: (a) AIDS. It is caused by the human immunodeficiency virus (HIV), whereas gonorrhoea and syphilis are bacterial diseases.

Teacher's Note:
1. Warts are another viral sexually transmitted infection.
2. Bacterial infections can be treated with antibiotics.

Answer: (a) gestation. In humans it lasts about nine months.

Teacher's Note:
1. Ovulation is the release of the egg.
2. Menopause is the stopping of the menstrual cycle.

Answer: (d). A is false because every egg carries one X chromosome, so only one type of gamete is formed. R is true.

Teacher's Note:
1. The sex of the child is decided by the type of sperm that fertilises the egg.
2. Women have XX chromosomes and men have XY.

Answer: (c). A is true because a bisexual flower has both stamens and carpels. R is false because pollen is produced in the anther of the stamen and ova in the ovary of the carpel.

Teacher's Note:
1. Remember stamen is male and carpel is female.
2. Hibiscus and mustard are bisexual flowers.

Answer: DNA copying makes sure that the genetic material, and so the body design, is passed from the parent to the next generation. Small errors in copying also give rise to variations, which help species survive changes in the environment.

Teacher's Note:
1. Cells make copies of DNA along with the cell machinery needed for the new cell.
2. Variation arising from copying errors is the basis of evolution.

Answer: Pollination is the transfer of pollen grains from the anther to the stigma of a flower. Fertilisation is the fusion of the male gamete with the female gamete (egg) to form a zygote.

Teacher's Note:
1. Pollination always comes before fertilisation.
2. Pollination is a physical transfer, whereas fertilisation is the fusion of gametes.

Answer: They add their secretions to the sperms to form semen. These secretions provide nourishment to the sperms and make their movement easier.

Teacher's Note:
1. The sperms and these fluids together form semen.
2. The semen passes out of the body through the urethra.

Answer: A unisexual flower has either stamens or carpels, but not both, for example papaya and watermelon. A bisexual flower has both stamens and carpels, for example hibiscus and mustard.

Teacher's Note:
1. Stamens are the male parts and carpels the female parts.
2. A unisexual flower cannot self-pollinate within the same flower.

Answer: The main organs are the testes, vas deferens, seminal vesicles, prostate gland and urethra. The testes produce sperms and the hormone testosterone.

Teacher's Note:
1. The testes are located in the scrotum outside the abdominal cavity.
2. Sperm production needs a temperature lower than the body temperature.

Answer: 1. It is a quick and economical method of producing new plants.
2. The new plants are exact copies of the parent, so useful traits are preserved.
3. It is the only way to propagate plants which have lost the capacity to produce seeds, such as banana and jasmine.
4. The new plants flower and fruit earlier than those grown from seeds.

Teacher's Note:
1. Layering, grafting and cutting are common artificial methods.
2. The main disadvantage is the lack of variation.

Answer: The embryo gets nourishment through the placenta, a special tissue embedded in the uterine wall. The placenta has villi on the embryo's side and blood space on the mother's side. Glucose and oxygen pass from the mother's blood to the embryo, and waste substances pass from the embryo to the mother's blood.

Teacher's Note:
1. The placenta is the exchange region between mother and embryo.
2. The waste of the embryo is removed by the mother's body.

Answer: (a) AIDS stands for Acquired Immuno Deficiency Syndrome. It weakens the immune system.
(b) The human immunodeficiency virus (HIV).
(c) Transmission is by 1. sexual contact with an infected person, 2. infected blood transfusion, 3. contaminated needles and syringes, and 4. from an infected mother to the child.

Teacher's Note:
1. AIDS does not spread by handshakes, sharing food or mosquito bites.
2. Safe practices and awareness are the only means of prevention.

Answer: 1. Barrier methods: condoms (male) and diaphragm (female) stop the sperm from reaching the egg.
2. Chemical methods: oral pills change the hormonal balance so that eggs are not released; vaginal pills kill sperms.
3. Intrauterine devices such as the copper-T and loop are placed in the uterus to prevent implantation.
4. Surgical methods: vasectomy blocks the vas deferens in males and tubectomy blocks the fallopian tubes in females.

Teacher's Note:
1. Only condoms also protect against sexually transmitted infections.
2. The surgical methods are permanent methods of birth control.

Answer: 1. After pollination, the pollen grain lands on the stigma and absorbs substances, then grows a pollen tube.
2. The pollen tube grows down through the style and reaches the ovary.
3. It enters the ovule and releases the male gametes near the female gamete (egg cell).
4. One male gamete fuses with the egg to form the zygote. This fusion is fertilisation.
5. The zygote divides to form the embryo, the ovule becomes the seed and the ovary ripens into the fruit.

Teacher's Note:
1. Chemical signals guide the pollen tube towards the ovule.
2. Draw a labelled diagram of the carpel to score full marks.

Answer: 1. Binary fission: the parent cell divides into two equal daughter cells, for example Amoeba (in any plane) and Leishmania (in a definite plane).
2. Multiple fission: the nucleus divides many times and then the cell divides into many daughter cells, for example Plasmodium.
3. Fragmentation: the body breaks into pieces and each piece grows into a new individual, for example Spirogyra.
4. Regeneration: a new organism grows from a cut body part, for example Planaria.
5. Budding: a bud develops on the parent body, grows and then separates, for example Hydra.

Teacher's Note:
1. Asexual methods need only one parent and produce identical offspring.
2. Planaria and Hydra are favourite examples of regeneration and budding.

Answer: 1. Ovaries: produce eggs and the hormones oestrogen and progesterone.
2. Oviducts (fallopian tubes): carry the egg from the ovary to the uterus and are the site of fertilisation.
3. Uterus: the site where the embryo gets implanted and develops into a foetus.
4. Cervix: the narrow lower end of the uterus leading to the vagina.
5. Vagina: the passage through which sperms enter and the baby is born.

Teacher's Note:
1. The egg is released from one ovary every month after puberty.
2. If the egg is not fertilised, the thickened uterine lining breaks down in menstruation.