CBSE Class 10 Biology How do Organisms Reproduce MCQs Set 12

Answer: (a) stock

Explanation:
1. In grafting the rooted plant, which provides the roots and is fixed in the soil, is the stock.
2. The shoot of the other plant joined to it is the scion.

Teacher's Note:
1. Stock = root part; scion = shoot part.
2. Grafting joins two plants.

Answer: (a) buds in the notches of leaves

Explanation:
1. Bryophyllum forms small buds in the notches along the leaf margin.
2. These buds fall on the soil and grow into new plants.

Teacher's Note:
1. The leaves of Bryophyllum do the work of propagation.
2. It is an example of natural vegetative propagation.

Answer: (b) germination

Explanation:
1. Under suitable conditions of water, air and temperature the embryo in a seed grows into a seedling.
2. This process is germination.

Teacher's Note:
1. Seeds germinate when conditions are favourable.
2. Radicle emerges first.

Answer: (a) regeneration

Explanation:
1. Regeneration is the ability of an organism to regrow a lost body part or a whole organism from a cut piece.
2. It is shown by Planaria, Hydra and starfish.

Teacher's Note:
1. Regeneration needs specialised cells that divide and form the missing parts.
2. Do not confuse it with simple healing of a wound.

Answer: (c) Multiple fission divides repeatedly; binary fission divides only once

Explanation:
1. In binary fission a cell divides once into two daughter cells.
2. In multiple fission the nucleus divides repeatedly first and then the cytoplasm divides around each nucleus, giving many cells.

Teacher's Note:
1. Count the daughter cells: two in binary fission, many in multiple fission.
2. Both are asexual and need one parent.

Answer: (d) all of these

Explanation:
1. In tissue culture new plants are grown from a small piece of tissue in a nutrient medium.
2. It gives disease-free plants and rapid multiplication, including of sterile plants.

Teacher's Note:
1. Tissue culture is also called micropropagation.
2. Orchids and ornamental plants are raised this way.

Answer: (b) P-(iv), Q-(ii), R-(iii), S-(i)

Explanation:
1. Planaria shows regeneration, fungi form asexual spores, yeast reproduces by budding and Amoeba by binary fission.
2. These give P-(iv), Q-(ii), R-(iii), S-(i).

Teacher's Note:
1. Match each organism with its method.
2. Fission, budding, spore formation and regeneration are asexual methods.

Answer: (d) all of them

Explanation:
1. Cutting, layering and grafting are all common methods of artificial vegetative propagation.
2. Farmers choose among them according to the plant.

Teacher's Note:
1. These are man-made methods of propagation.
2. They give identical plants.

Answer: (b) the anthers produce female gametes

Explanation:
1. Anthers produce pollen grains, which contain the male gametes.
2. The female gametes are produced in the ovules of the pistil, so the statement about anthers is not true.

Teacher's Note:
1. Anther = male; ovule = female gamete.
2. Pollen tube carries the male gamete to the ovule.

Answer: (b) bisexual flower

Explanation:
1. Self-pollination is the transfer of pollen from the anther to the stigma of the same flower.
2. This is possible only in a bisexual flower, which has both stamens and carpel.

Teacher's Note:
1. Unisexual flowers must be cross-pollinated.
2. Bisexual flowers can do both.

Answer: (c) cotyledon, plumule, radicle

Explanation:
1. The embryo consists of the cotyledons, the plumule (future shoot) and the radicle (future root).
2. Testa and tegmen are seed coats and the micropyle is a tiny pore.

Teacher's Note:
1. Embryo = plumule + radicle + cotyledon.
2. Seed coat and micropyle are not parts of the embryo.

Answer: (a) watermelon

Explanation:
1. Watermelon flowers are either male or female.
2. Hibiscus and mustard have bisexual flowers with both stamens and carpels.

Teacher's Note:
1. Unisexual examples: papaya, watermelon, cucumber.
2. Bisexual examples: mustard, hibiscus.

Answer: (c) between fertilisation and parturition

Explanation:
1. Gestation is the time from fertilisation of the egg until the birth of the baby.
2. The birth itself is parturition.

Teacher's Note:
1. Gestation = pregnancy period.
2. In humans it is about 40 weeks.

Answer: (c) (iii) and (iv)

Explanation:
1. The testes form sperms (germ cells) and secrete testosterone at puberty.
2. The placenta develops in the female during pregnancy and oestrogen is secreted by the ovaries, so (iii) and (iv) are not functions of the testes.

Teacher's Note:
1. Testes: sperms and testosterone.
2. Ovaries: eggs, oestrogen and progesterone.

Answer: (b) cervix

Explanation:
1. The uterus has a fundus at the top, a body in the middle and a narrow lower end.
2. This lower narrow end is the cervix, which opens into the vagina.

Teacher's Note:
1. The urethra belongs to the urinary system.
2. The cervix is the neck of the uterus.

Answer: (d) fallopian tube

Explanation:
1. The egg released from the ovary enters the fallopian tube (oviduct).
2. Sperms swim up and fertilise the egg in the fallopian tube; the zygote then moves to the uterus for implantation.

Teacher's Note:
1. Fertilisation occurs in the fallopian tube and implantation in the uterus.
2. Do not mix these two sites.

Answer: (d) vagina

Explanation:
1. Sperms are deposited in the vagina but the egg is not present there.
2. Fertilisation takes place in the oviduct (fallopian tube), whose wider part is the ampulla.

Teacher's Note:
1. Ampulla, fallopian tube and oviduct all refer to the site of fertilisation here.
2. The vagina only receives the sperms.

Answer: (b) sexual maturation

Explanation:
1. These are secondary sexual characters controlled by oestrogen.
2. They show that the body is becoming sexually mature at puberty.

Teacher's Note:
1. Puberty prepares the body for reproduction.
2. Menstruation begins at menarche.

Answer: (a) seminal fluid

Explanation:
1. The seminal vesicles and the prostate gland add their secretions to the sperms.
2. This fluid, the seminal fluid, makes the transport easier and also provides nutrition.

Teacher's Note:
1. Semen is made of sperms and the secretions of the seminal vesicles and prostate.
2. The fluid gives energy to the swimming sperms.

Answer: (d) the formation of sperms will not take place

Explanation:
1. Sperm formation needs a temperature lower than the body temperature.
2. If the testes stay in the abdomen, the sperms cannot be formed, although hormones are still secreted.

Teacher's Note:
1. Testosterone is still made, so secondary sexual characters develop.
2. Only sperm formation is affected.

Answer: (c) (A), (B), (C), (D) and (E)

Explanation:
1. Sex education, medical help, awareness, equal opportunities and a ban on sex-determination tests all improve reproductive health.
2. Encouraging myths and misconceptions harms it, so (F) must be excluded.

Teacher's Note:
1. Prenatal sex determination is banned in India.
2. Good health needs correct information.

Answer: (c) (iii) and (iv)

Explanation:
1. Gonorrhoea and syphilis are caused by bacteria.
2. Warts (human papilloma virus) and AIDS (HIV) are caused by viruses.

Teacher's Note:
1. Bacterial STDs: gonorrhoea, syphilis. Viral STDs: warts, HIV-AIDS.
2. Know the pathogen of each.

Answer: (c) only (P), (Q) and (S)

Explanation:
1. Oral pills work by stopping ovulation itself, so they are not a method that works after the egg is released.
2. Blocking the fallopian tube, a Copper-T (an intra-uterine device) and a condom all prevent the sperm and egg from meeting or developing further even when ovulation has occurred, so (P), (Q) and (S) are correct.

Teacher's Note:
1. Pills act before ovulation; barrier, surgical and IUCD methods act after it.
2. Note the mode of action of each contraceptive method.

Answer: (a) errors in copying DNA

Explanation:
1. DNA copying is not perfectly accurate, so small changes arise in each generation.
2. Together with the mixing of genes of two parents, these errors cause variation.

Teacher's Note:
1. Inexact DNA copying is the source of variation.
2. Variation helps species to survive.

Answer: (c) error in DNA replication

Explanation:
1. Copying of DNA during reproduction is not perfectly accurate, and the genes of the mother are also combined.
2. These differences make the offspring similar but not identical to the parent.

Teacher's Note:
1. Variation arises from DNA copying errors and mixing of genes.
2. Habits and knowledge are not inherited.

Answer: (b) both (i) and (iv) are correct

Explanation:
1. Multiple fission gives many offspring and binary fission gives two, so (i) is correct.
2. Plasmodium shows multiple fission and Leishmania shows binary fission, so (iv) is correct. In both cases the offspring are identical and only one parent is involved.

Teacher's Note:
1. Both types are asexual and use one parent.
2. Offspring are clones in both.

Answer: (c) genetic similarity in offspring

Explanation:
1. Vegetative propagation uses a single parent, so the offspring are genetically identical to it.
2. This preserves the good qualities of the parent plant.

Teacher's Note:
1. Vegetative propagation gives uniform plants.
2. The same feature is a disadvantage when disease strikes.

Answer: (c) cracking of voice

Explanation:
1. At puberty the testes secrete more testosterone in boys.
2. One of its effects is the deepening or cracking of the voice, which is a sign of sexual maturation.

Teacher's Note:
1. Height and weight increase in both boys and girls, but voice change is typical of boys.
2. Milk teeth are lost in childhood.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Vasectomy and tubectomy are nearly permanent and very effective methods.
2. They block the vas deferens or the fallopian tubes, so the gametes cannot meet; this explains the assertion.

Teacher's Note:
1. Vasectomy is done in males and tubectomy in females.
2. Surgical methods do not protect against STDs.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. At the time of birth, the baby is pushed out of the uterus through the cervix and the vagina.
2. This is why the vagina is called the birth canal, so R explains A.

Teacher's Note:
1. Vagina receives the sperms during copulation and also acts as the birth canal.
2. Cervix opens into the vagina.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. With one parent and no mixing of genes, the offspring are copies of the parent except for tiny copying errors.
2. So R correctly explains A.

Teacher's Note:
1. Single parent means identical offspring.
2. Sexual reproduction needs two parents.

Answer: (c) A is true, but R is false.

Explanation:
1. Every month the uterine lining becomes thick and spongy to receive the embryo, so A is true.
2. An unfertilised egg does not implant; the lining breaks down as menstruation, so R is false.

Teacher's Note:
1. Menstruation occurs when the egg is not fertilised.
2. Implantation happens only for the zygote.

Answer: (d) A is false, but R is true.

Explanation:
1. DNA copying is not perfectly accurate, so small variations arise; A is false.
2. No biochemical reaction is absolutely reliable, so R is true, and it is the reason variations occur.

Teacher's Note:
1. DNA copying always allows small errors.
2. These errors are the source of variation.

Answer: (d) A is false, but R is true.

Explanation:
1. Pollen grains come from the anther of the stamen and stick to the stigma of the carpel, so A is false.
2. The fertilised egg (ovule) develops into the seed inside the ovary, so R is true.

Teacher's Note:
1. Pollen: stamen. Stigma: carpel.
2. Ovule → seed; ovary → fruit.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Spores have thick walls that protect them until they reach a moist surface, so A is true.
2. Spores are the reproductive parts of Rhizopus, so R is true, but this fact does not explain why they can survive extreme conditions.

Teacher's Note:
1. The thick wall is the reason for survival.
2. Spores germinate in moist conditions.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. The corolla, made of petals, is one of the parts of a flower, so A is true.
2. Its bright colour attracts insects that help in pollination, so R is true, but R does not explain why the corolla is a floral part.

Teacher's Note:
1. Petals attract insects.
2. Both statements are true but separate.