Chapter 7: How do Organisms Reproduce?

Q1: (b) Yeast (reproduces by budding). Q2: (c) Vas deferens (part of the male system). Q3: (d) pollen grains.

Sexual reproduction combines DNA from two parents, producing more variation among offspring. This variation helps species adapt to changing environments, aids evolution and improves the chances of survival.

Q5: The testes produce sperms (male gametes) and secrete the hormone testosterone (which controls male sexual characters). Q6: Each month the uterus prepares a thick lining to receive a fertilised egg. If the egg is not fertilised, this lining breaks down and is shed along with blood — this is menstruation (about every 28 days).

Label the outer sepals and coloured petals; the stamen (anther on a filament — male part); and the central pistil — stigma at the top, then style, and the ovary at the base containing ovules (female part).

① Barrier methods (condom, diaphragm). ② Chemical/hormonal methods (oral contraceptive pills). ③ IUCD (copper-T placed in the uterus). ④ Surgical methods (vasectomy in males, tubectomy in females).

Q9: Unicellular organisms reproduce mainly by asexual methods (fission, budding). Multicellular organisms use more complex methods, including sexual reproduction with specialised reproductive organs. Q10: Reproduction produces new individuals of the same kind generation after generation, keeping the population numbers steady and thus giving stability to the species.

To prevent unwanted pregnancy, to space or limit the number of children (protecting the mother's health), to control population growth, and (with condoms) to prevent sexually transmitted diseases like AIDS.

Hydra.

Variations.

Tissue culture.

The virus HIV (sexual contact, infected blood, etc.).

Growing new plants from vegetative parts (root, stem, leaf). Advantage: plants can be grown quickly and are identical to the parent (e.g., banana, rose).

It helps some individuals survive changes in the environment, aiding the survival and evolution of the species.

It supplies the developing embryo with nutrients and oxygen from the mother's blood and removes its wastes.

Self-pollination: pollen falls on the stigma of the same flower/plant. Cross-pollination: pollen is carried to the stigma of a different plant of the same kind.

Sexually transmitted diseases spread by sexual contact, e.g., AIDS (HIV), gonorrhoea, syphilis.

It consists of the testes (which produce sperms and testosterone), the vas deferens (which carries sperms), glands that add fluid to form semen, the urethra and the penis (which delivers sperms into the female body).

It has two ovaries (which produce eggs and hormones), fallopian tubes (where fertilisation occurs), the uterus (where the embryo develops), and the vagina. If fertilisation does not occur, the uterine lining is shed as menstruation.

A sperm fuses with an egg in the fallopian tube to form a zygote. The zygote divides and moves to the uterus, where it implants and develops into an embryo. The placenta nourishes it until a baby is born.

Fission (Amoeba), budding (Yeast, Hydra), fragmentation (Spirogyra), regeneration (Planaria), spore formation (Rhizopus) and vegetative propagation (rose, banana, potato).

To prevent unwanted pregnancies, to space and limit children (protecting maternal and child health), to control population growth, and (with barrier methods) to prevent STDs.

Small variations arising during reproduction (especially sexual) accumulate over many generations. Those helpful for survival are selected by nature, gradually leading to new adaptations and evolution.