CBSE Class 10 Science How Do Organisms Reproduce Notes Set B

– Asexual Reproduction is extremely useful as a mean of rapid multiplication.
It is common in lower plants and animals.
– Different form of Asexual Reproduction.

1. FISSION : the parent cell divides/splits into two daughter cell-Binary Fission; splits into many cells-multiple Fission 

2. BUDDING : A new organism is produced as an outgrowth of the parent body part. 

3. Spore Formation : Spores are small, bulb like structure develops at the top of the erect hyphae of the fungus plant, released into the air and ge rminate , into new individuals after landing into food or soil. 

4. FRAGMENTATION : It is the accidental process when the broken pieces of an organism (fragments) grows into a complete organism. 

5. REGENERATION : When the simple animals like Hydra Planaria develop a new individual from their broken older part it is known as regeneration. It is carried out by specialised cells which grow large numbers of cells. 

VEGETATIVE PROPAGATION :

A mode of reproduction in which part like the stem, root, leaves develop into new plant under favourable conditions.
Benefits
1. Plants can bear flowers, fruits earlier than those produced from seeds.
2. Growing Banana, orange, rose, jasmine that have lost the capacity to produce seeds.
3. Genetical similarity is maintained in the plants.
eg. Sugarcane, rose, grapes by layering or grafting. 

SEXUAL REPRODUCTION

When reproduction takes place as a result of fusion between two gamets, one from each parent, it is called sexual reproduction.
– This process of fusion between two gamets is called fertilization.
– The formation of gamets involves exchange of chromosomal (genetic) fragments between homologous chromosomes causing genetic recombination which leads to variation.

SEXUAL REPRODUCTION IN PLANTS
It occurs mostly in flowering plants. In fact flowers are the reproductive organ of plants. 

A typical flower consists of four main whorls namely calyx (sepals), Corolla (Petals), Androecium (Stamens) and Gynoecium (Carpels). 

– Pollen grains of a flower transfer to stigma of the carpel of the same flower (Self-Pollination) or to the carpel of the another flower (Cross-Pollination).
– This transfer of pollens is achieved by agent like wind, water or animals.
– After Pollination, the pollen grains reach to the egg cell in the form of a pollen tube.
– Fertilization : The fusion between the pollen grain and female egg cell. It occurs inside the ovary. Zygote is produced in this process. 

– Zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is converted into a seed.
– Ovary grows rapidly and ripens to forms a fruit, while the seed contains the future plant or embryo which develops into a seedling under suitable condition. This process is known as Germination.

REPRODUCTION IN HUMAN BEINGS

– Humans use a Sexual Mode of reproduction.
– It needs sexual maturation which includes creation of the germ cells ie, egg (ova) in the female and sperm in the male partener & this period of sexual maturation is called Puberty.
– Human beings have a well developed male and female reproductive system.
– The formation of male germ cell (sperms) takes place in the testes (male reproducture organ)
– Actually a pair of testes are located inside scrotum situated outside the abdominal cavity. It is meant to keep relatively a low temperature needed for the production of sperms by testes.
– Moreover testes release a male sex hormone called testosterone whose function is to:
1. Regulate the production of sperm
2. Brings about changes in appearance seen in boys at the time of puberty.
– The sperms along with the secretion of prostate gland and seminal vesicle, together constitute semen, which is released and made to enter into the female genital tract during Copulation. 

♦ The female germ cells or eggs are made in the ovaries, a pair of which is located in both side of abdomen.
♦ When a girl is born, the ovaries already contain thousands of immature eggs.
♦ At the puberty, some of these Eggs start maturing. One egg is produced every month by one of the ovaries.
♦ The Egg is carried from the ovary to the womb through a fallopian tube. These two fallopian tube unite into an elastic bag like structure known as Uterus.
♦ The Uterus opens into the vagina through the cervix.
♦ Fertilization occurs in the fallopian tube of female genital tract.
?The fertilized egg also called zygote (2n) gets implanted in the lining of the Uterus, and start dividing. Actually uterus is richly supplied with blood to nourish the growing embryo. If zygote is not formed, the inner wall of uterus breaks which causes bleeding through vagina. This process is called MENSTRUATION. It occurs at a regular interval of 28 days.
♦ The Embroyo gets nutrition fromthe mother's blood with the help of a special tissue called PLACENTA. It provides a large surface area for glucose and oxygen to pass from the mother to the embryo. Similarly the wastes from developing embryo are removed to mother's blood through placenta.
♦ The child is born as a result of rhythmic contractions of the muscles in the uterus. after Nine months (36 weeks) of development inside mother's womb.
It is also called Gestation Period.
The sexual cycle in a woman continues upto the age of 45 to 50 years. After that the ovary do not release egg. This stage is called Menopause. It a also marks the end of menstruation in the woman.

REPRODUCTIVE HEALTH

♦ Reproductive Health means a total well-being in all aspects of reproductive, ie., physical emotional, social and behavioural.
♦ Contraception : It is the avoidance of pregnancy. It can be achieved by 

Multiple Choice Questions

Question. Which of the following is the correct sequence of events of sexual reproduction in a flower?
(a) pollination, fertilisation, seedling, embryo
(b) seedling, embryo, fertilisation, pollination
(c) pollination, fertilisation, embryo, seedling
(d) embryo, seedling, pollination, fertilisation
Answer : C

Question. In the list of organisms given below, those that reproduce by the asexual method are
(i) banana (ii) dog (iii) yeast (iv) amoeba
(a) (ii) and (iv)
(b) (i), (iii) and (iv)
(c) (i) and (iv)
(d) (ii), (iii) and (iv)
Answer : B

Question. Offspring formed by asexual method of reproduction have greater similarity among themselves because
(i) asexual reproduction involves only one parent
(ii) asexual reproduction does not involve gametes
(iii) asexual reproduction occurs before sexual reproduction
(iv) asexual reproduction occurs after sexual reproduction
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)
Answer : A

Question. In a flower, the parts that produce male and female gametes (germ cells) are
(a) stamen and anther
(b) filament and stigma
(c) anther and ovary
(d) stamen and style
Answer : C

Fill in the blanks.

Question. The embedding of embryo in the wall of the uterus is called ...... .
Answer : implantation

Question. After ...... the zygote divides several times to form an ...... within the ovule.
Answer : fertilization, embryo

Question. The ovule gradually develops into a ...... .
Answer : seed

Question. The period during ...... is called puberty.
Answer : adolescence

Question. During sexual reproduction ...... from two individuals fuse.
Answer : germ cells

Question. The ...... forms a common passage for both the sperms and urine.
Answer : urethra

Question. Plants raised by ...... can bear flowers and fruit earlier than those produced from seeds.
Answer : vegetative propagation

Question. The development of the child inside the mother’s body takes approximately ...... .
Answer : nine months

Question. Hydra reproduce commonly by ...... .
Answer : budding

Question. ...... is the result of non-fertilization of egg.
Answer : Menstruation

Question. Sperms travel upwards and reach the ...... where they may fuse with the egg.
Answer : oviduct

Question. Gonorrhoea is caused by ...... .
Answer : bacteria

Question. The ...... prepares itself every month to receive and nurture the growing child.
Answer : uterus

Write Yes/No.

Question. Is multiple fission common in Plasmodium?
Answer : Yes

Question. Can stamens and petals be called reproductive parts of a flower?
Answer : Yes

Question. Is an egg produced daily by one of the ovaries in human beings?
Answer : No

Question. Is regeneration a common feature in Planaria?
Answer : Yes

Question. Are plants produced by vegetative reproduction genetically similar?
Answer : Yes

Question. Will the process of copying DNA have some variations each time?
Answer : Yes

Question. Is spore formation the common method of sexual reproduction in Rhizopus?
Answer : No

Question. Is it true that bacterial diseases are not transmitted through sexual act?
Answer : No

Case Study Questions

Study the table related to sex ratio of females/1000 males in different states and answer the questions that follow:

Question. Which test is responsible for female foeticide?
(a) UV-Spectroscopy
(b) Ultrasound
(c) MRI
(d) X-Ray
Answer : B

Question. Name the state which has males to female ratio to maximum extent in 2013-15.
(a) Haryana
(b) Kerala
(c) West Bengal
(d) Uttar Pradesh
Answer : B

Question. Which of the following state improves sex ratio in 2013-15 from 2012-14?
(a) Delhi
(b) Karnataka
(c) Bihar
(d) Kerala
Answer : C

Question. What is major cause of less females than males in India?
(a) Male Foeticide
(b) Female Foeticide
(c) Natural
(d) None of these
Answer : B

Question. Which state of India has lowest sex ratio in 2013-15?
(a) Punjab
(b) Odisha
(c) Haryana
(d) Delhi
Answer : C