Science [3 Mark Questions]

Advantages of sexual reproduction over asexual reproduction:

1. Sexual reproduction combines DNA from two individuals (male and female) due to which the offspring has lot of variations. On the other hand, in asexual reproduction, only the DNA of one individual is copied due to which the variations in the offspring are extremely small.
2. Due to lot of variations, sexual reproduction allows species to change to more advanced forms from one generation to the next and speed up evolution whereas asexual reproduction does not allow a species to change much from one generation to the next and hence, evolution becomes very slow.

Money plant can be grown by vegetative propagation by using a piece of its stem which has at least one leaf on it. One end of the stem is dipped in water and after a few days new roots appear at the point where the leaf was attached. This piece of stem grows gradually into a new money plant.

In grafting, two plants are chosen which are used as scion and stock. First the stem is removed from the plant chosen to be made scion by giving a slanting cut. The scion is placed over the stock and is fitted together by binding tightly by a piece of cloth or plastic sheet. The cut soon heals and the stock and scion of two plants grow together to become one plant.

In complex multicellular organisms, specialized cells makeup tissues; tissues makeup organs; organs makeup organs systems and finally organs systems makeup organisms. Since complex Multi cellular organisms have a high degree of organisation in their body, they cannot be reproduced from their cut body parts by the process of regeneration.

Bryophyllum can be reproduced by vegetative propagation by using either a piece of its stem or leaves. The leaves of a Bryophyllum plant have special buds in their margins which may get detached from the leaves, fall to the ground and then grow to produce a new plant.

In males, the gonads are testes. The function of testes is to make sex cells called sperms and to make sex hormone called testosterone. In females, the gonads are ovaries. The function of the ovaries is to make mature female sex cell called ova or egg and also to make female sex hormones called oestrogen and progesterone.

A seed is the reproductive unit of a plant (which can be used to grow a new plant). Plumule, radical and cotyledon are the parts of seed.

Layering: In this method, a branch of the plant is pulled towards the ground and the part of it is covered with moist soil leaving the tip of the branch exposed above the ground. After some time, new roots develop from the part of the branch buried in the soil. The branch is then cut off from the parent plant. The part of the plant which has developed roots grows to become a new plant. The layering method is used for the propagation of plants like Jasmine, Strawberry, Raspberry, Lemon and Guava.

1. Barrier method – Condom.
2. Chemical method – Oral pills.
3. Surgical method – Vasectomy.