10th Science Unit 17 Reproduction in Plants and Animals Book Back Answers

In Bryophyllum, small plantlets grow at the leaf notches and develop into new plants when they fall on the soil.

Onion (bulb), ginger (rhizome) propagate by stems; neem is grown from seeds.

In budding, a daughter individual is formed from a small projection (bud) on the parent body, as in yeast.

Amoeba reproduces by fission and bacteria by fission/spore formation.

Syngamy is the fusion of one male gamete with the egg cell.

This fusion forms a diploid zygote, which later develops into the embryo.

Androecium (stamens) produces pollen grains and gynoecium (carpels) bears ovules, so both take part directly in reproduction.

Calyx and corolla are non-essential or accessory whorls.

Anemophilous (wind-pollinated) flowers have stigmas that are comparatively large, protruding and sometimes hairy or feathery.

This helps them trap the small, light, dry pollen grains carried by wind.

A mature pollen grain has a vegetative cell and a generative cell.

The generative cell divides mitotically to form the two male gametes.

Gametes (sperm and ovum) are haploid cells produced by gametogenesis in the gonads — testes and ovaries.

They are not diploid, do not form gonads and do not secrete hormones.

The epididymis is a single, highly coiled tube attached to the testis.

Sperms are stored here, become concentrated and mature before passing into the vas deferens.

Sertoli cells lie in the seminiferous tubules and are the supporting cells.

They provide nutrients to the developing sperms; Leydig cells only secrete testosterone.

As the egg grows, the primary follicle enlarges, fills with fluid and becomes the Graafian follicle.

The Graafian follicle secretes estrogen, whose level rises during the follicular phase.

IUCDs (intra-uterine devices) are contraceptive devices inserted into the uterus, such as Lippe's Loop and Copper-T.

Oral pills are hormonal, diaphragm is a barrier and tubectomy is a surgical method.

The embryo sac is the female gametophyte inside the ovule.

At the time of fertilization it contains seven cells and eight nuclei — egg apparatus (egg + 2 synergids), 3 antipodal cells and 2 polar nuclei (secondary nucleus).

Post-fertilization changes: the ovule becomes the seed and its integuments become the seed coat.

The ovary enlarges and develops into the fruit.

Planaria has a specialized mass of cells that can rebuild lost body parts.

The ability of lost body parts to give rise to a whole new organism is called regeneration.

In humans the sperm is deposited inside the female genital tract.

Fusion of sperm and ovum occurs in the ampulla of the fallopian tube, i.e. inside the body.

After cleavage the blastocyst travels to the uterus.

It attaches to the uterine endometrium about 6 to 7 days after fertilization; this is implantation.

The milk released from the mammary gland in the first 2–3 days after child birth is colostrum.

It contains immune substances and gives immunity to the new born.

Milk production from the alveoli of the mammary glands is stimulated by prolactin.

Prolactin is secreted by the anterior pituitary (oxytocin from the posterior pituitary ejects the milk).

Fission – the parent cell divides into two daughter cells, each growing into a new adult, e.g. Amoeba.

Budding – a daughter individual arises from a small projection (bud) on the parent body, e.g. Yeast.

Fragmentation – the filament breaks into many fragments, each growing into a new filament, e.g. Spirogyra.

a) Parturition – the expulsion of the young one from the mother's uterus at the end of gestation, i.e. delivery of baby from uterus → 3

b) Gestation – the period during which the embryo develops in the uterus (about 280 days), i.e. duration between pregnancy and birth → 1

c) Ovulation – on the 14th day the Graafian follicle ruptures and releases the ovum, i.e. release of egg from Graafian follicle → 4

d) Implantation – the attachment of the blastocyst (fertilised egg/zygote) to the uterine wall or endometrium → 2

The ovule is attached to the ovary wall by a stalk known as the funiculus.

Pedicel is the stalk of a flower, not of an ovule.

Seeds are formed after pollination and fertilization, which involve fusion of male and female gametes.

Hence seeds are the product of sexual reproduction.

In yeast a small projection called bud arises on the parent body and grows into a daughter individual.

This method is budding, not multiple fission.

The pistil (gynoecium) has three parts – ovary, style and stigma.

The stigma is the receptive structure that receives the pollen grains; style is only the connecting stalk.

In entomophily (insect pollination) the pollen grains are larger in size with pitted or spiny exine so that they stick firmly to the sticky stigma.

Small, smooth, dry and light pollen grains are the feature of wind pollinated (anemophilous) flowers.

Gametogenesis produces gametes through meiosis.

Sperms and ova are therefore haploid; only their fusion forms the diploid zygote.

LH and FSH are pituitary gonadotropins secreted by the anterior pituitary.

Oxytocin is the hormone released from the posterior pituitary.

If fertilization takes place, the corpus luteum persists and secretes progesterone.

This maintains the thickened uterine wall and prevents maturation of another follicle till the end of pregnancy, so menstruation stops.

Lack of menstruation generally indicates pregnancy.

Surgical methods are vasectomy (ligation of vas deferens) in males and tubectomy (ligation of fallopian tube) in females.

They only block the transport of gametes; the testes and ovaries still form gametes.

Menstrual flow begins when the uterine endometrial lining breaks down.

This breakdown is caused by a decrease in progesterone and oestrogen levels, not an increase.

In double fertilization each ovule needs two male gametes – one fuses with the egg (syngamy) and the other with the secondary nucleus (triple fusion).

One pollen grain supplies exactly two male gametes, so one pollen grain is enough for one ovule.

For 10 ovules, $10 \times 1 = 10$ pollen grains are needed.

After pollination the pollen grain lands on the stigma of the gynoecium.

There it germinates and puts out the pollen tube, which grows through the style to reach the ovule.

Budding is the formation of a daughter individual from a small projection (bud) on the parent body.

Yeast reproduces by budding; Hydra also gives out buds that mature into new individuals.

The endosperm is formed from the primary endosperm nucleus after triple fusion.

It is triploid and stores food material.

It supplies nourishment to the developing embryo.

At the end of gestation the young one has to be expelled from the uterus (parturition).

Oxytocin from the posterior pituitary stimulates vigorous uterine contractions and provides the force to expel the baby.

The acrosome is the cap-like structure at the anterior part of the sperm head.

It contains the enzyme hyaluronidase, which helps the sperm to enter the ovum during fertilization.

Menstrual Hygiene Day is observed every year on May 28.

It creates awareness among girls and women about maintaining menstrual hygiene for good health.

Contraception is one of the best birth control measures and prevents unwanted pregnancy.

It checks population explosion and supports family planning – 'Small Family, Happy Family'.

IUDs and similar devices give an adequate time interval (spacing) between pregnancies.

Barrier methods like condoms also protect against sexually transmitted diseases such as syphilis and AIDS, thus improving reproductive health.

a. Fertilization: the sperm fuses with the ovum in the oviduct, usually in the ampulla of the fallopian tube.

b. Implantation: the blastocyst attaches to the uterine wall (endometrium) of the uterus about 6–7 days after fertilization.

Planaria reproduces by regeneration — the ability of lost body parts of an organism to give rise to a whole new organism.

It has a specialised mass of cells that can grow into all the missing parts.

So each small fragment will grow into a complete new planaria.

Thus many new individuals, genetically identical to the parent, are produced from one animal.

The new plants are produced from vegetative parts (root, stem, leaf or bud) by mitosis only, so they are genetically similar to the parent — good qualities of the parent are retained.

Plants that do not produce viable seeds (e.g. banana, sugarcane, rose) can be multiplied only this way.

It is a quicker and cheaper method; the plants grow and bear flowers and fruits earlier than seed-grown plants.

Many identical plants can be raised from a single parent in a short time.

Binary fission: the parent cell divides into two equal daughter cells, and each develops into a new adult organism, e.g. Amoeba.

Multiple fission: the nucleus of the parent cell divides repeatedly to form many nuclei, and the cell then splits into many daughter cells at a time, e.g. Plasmodium.

Binary fission usually occurs in favourable conditions; multiple fission helps the organism survive unfavourable conditions and produces many offspring at once.

During double fertilization two male gametes are released into the embryo sac.

One male gamete fuses with the egg (syngamy); the second male gamete fuses with the two polar nuclei (secondary nucleus).

Since three nuclei are involved, this fusion is called triple fusion.

It forms the triploid primary endosperm nucleus, which develops into the endosperm that feeds the embryo.

Pollination by insects is called entomophily (honey bees carry about 80% of insect pollination).

The flowers are large and brightly coloured to attract insects.

They have a sweet smell (fragrance) and secrete nectar as a reward for the visiting insects.

Pollen grains are larger in size and the exine is pitted or spiny, so they stick firmly to the insect body and to the sticky stigma.

The primary sex organs in the male are the testes; the other structures are secondary (accessory) sex organs.

Male accessory sex organs are: vas deferens, epididymis, seminal vesicle, prostate gland and penis.

They help in the transport, nourishment and delivery of the sperms.

Colostrum is the first fluid (milk) released from the mammary glands during the first 2–3 days after child birth.

It contains immune substances and provides immunity to the new born, so it is essential for the baby.

Milk production from the alveoli of the mammary glands is stimulated by the hormone prolactin secreted by the anterior pituitary.

The ejection (release) of milk is stimulated by oxytocin secreted by the posterior pituitary.

Sanitary pads should be changed regularly to avoid infection from microbes of the vagina and sweat of the genitals.

The genitals should be cleaned with warm water; this also helps to relieve menstrual cramps.

Loose clothing instead of tight fitting clothes should be worn to allow airflow around the genitals and prevent sweating.

Used pads or tampons must be wrapped properly and discarded (never flushed in the toilet); napkin incinerators should be used for disposal.

After implantation, a disc shaped structure called the placenta is formed, attached to the uterine wall.

It is a temporary association between the developing embryo and the maternal tissues.

Through the placenta the embryo receives food materials and oxygen from the mother's blood, and gives out carbon dioxide and nitrogenous wastes.

The placenta is connected to the foetus by the umbilical cord, which contains the blood vessels carrying these substances.

The figure shows a mature pollen grain in section (textbook p. 258).

A – Exine (thick outer wall with spiny projections).

B – Intine (the inner wall layer beneath the exine).

C – Generative cell (small cell that divides to form the two male gametes).

D – Vegetative nucleus (the larger nucleus of the vegetative cell).

The testes lie outside the abdominal cavity in a sac like structure called the scrotum.

The scrotum keeps the testes at a temperature about 2–3 °C lower than the body temperature.

This lower temperature is necessary for the normal formation of sperms (spermatogenesis) in the seminiferous tubules.

Inside the warm abdominal cavity, sperm production would be affected.

The luteal phase extends from the 15th to the 28th day of the menstrual cycle.

The emptied Graafian follicle changes into the corpus luteum, which secretes the hormone progesterone.

Progesterone makes the endometrial glands of the uterus secretory, so the uterine lining becomes thick and spongy and is prepared for implantation.

Because of this active glandular secretion in the ovary and uterus, the phase is called the secretory phase.

Illiteracy and ignorance — many people do not know about family planning methods or their benefits.

Superstitions, religious beliefs and social customs make some people oppose contraception.

Preference for a male child makes couples go on having more children.

Early marriage, poverty and the belief that more children mean more earning hands add to the problem.

Lack of proper counselling and fear of side effects of contraceptives also keep people away, so population explosion continues.

In angiosperms two types of fusion take place inside the embryo sac, so two male gametes are needed. This is called double fertilization.

One male gamete fuses with the egg cell (syngamy) and forms the diploid zygote, which develops into the embryo.

The second male gamete fuses with the secondary nucleus (triple fusion) and forms the triploid primary endosperm nucleus.

The primary endosperm nucleus develops into the endosperm, which supplies food to the developing embryo. Without the second gamete there would be no endosperm and the embryo would starve.

The menstrual cycle is controlled by the pituitary gonadotropins (FSH and LH) and the ovarian hormones estrogen and progesterone.

Before puberty these hormones are not secreted in sufficient amounts, so the ovary and uterus are not functional; the first menstruation (menarche) begins only at puberty, at about 11–13 years.

During pregnancy the fertilized egg is implanted in the uterus, so the uterine lining must be maintained and not shed.

The corpus luteum persists and keeps secreting progesterone, which maintains the thickened uterine wall and prevents maturation of another follicle till the end of pregnancy. Hence there is no ovulation and no menstrual flow.