Reproduction

Step 1: Reproductive organs become active during adolescence. Step 2: Testes and ovaries secrete hormones. Step 3: These hormones control external and internal body changes.

Step 1: Some contraceptive pills are hormone based. Step 2: They may affect release of ovum from ovary. Step 3: If ovum is not released the chance of fertilisation decreases.

Step 1: A condom prevents sperms from entering the female reproductive tract. Step 2: This reduces the chance of pregnancy. Step 3: It can also reduce direct contact with infected fluids.

Step 1: A copper device is placed in the uterus. Step 2: Contraceptive pills may affect hormone levels. Step 3: Both reduce pregnancy chance but by different methods.

Step 1: In sterilisation reproductive tubes are blocked. Step 2: This makes meeting of sperm and ovum difficult. Step 3: Therefore chances of fertilisation and pregnancy decrease.

Step 1: Contraceptive pills act through hormones. Step 2: They do not stop exchange of fluids during sexual contact. Step 3: A barrier method can help more in disease prevention.

Step 1: Fertilisation involves fusion of male and female gametes. Step 2: True fusion joins genetic material. Step 3: Without nuclear fusion a zygote will not form.

Step 1: A zygote forms after fertilisation. Step 2: It divides repeatedly to form a group of cells. Step 3: This group develops into an embryo.

Step 1: In sexual reproduction two gametes fuse. Step 2: If each has half the number the normal number is restored after fusion. Step 3: This keeps chromosome number stable in a species.

Step 1: Asexual reproduction forms similar offspring from one parent. Step 2: Low variation can make all offspring face the same risk. Step 3: This can be a limitation in changing environments.

Step 1: Cross pollination mixes genetic information from different plants. Step 2: This can increase variation in offspring. Step 3: Such variation can benefit a species in changing conditions.

Step 1: The anther produces pollen grains. Step 2: Pollen must settle and germinate on the stigma. Step 3: If stigma is not receptive further fertilisation may fail.

Step 1: Normally ovules become seeds after fertilisation. Step 2: If ovules are not fertilised seeds will not form. Step 3: The ovary may still grow into a fruit like structure in some cases.

Step 1: The embryo depends on the mother in the uterus. Step 2: Placenta supplies nutrients and oxygen. Step 3: It also helps remove wastes.

Step 1: After fertilisation the embryo must attach in the uterus. Step 2: Only after attachment can it get support and nourishment. Step 3: Without proper attachment development may stop.

Step 1: Accurate copying preserves parental traits. Step 2: This similarity is common in asexual reproduction. Step 3: But very high similarity can reduce variation.

Step 1: Slight variation can be useful. Step 2: Too many errors can disturb essential traits. Step 3: This may reduce survival ability of offspring.

Step 1: In sexual reproduction male and female gametes fuse. Step 2: Information from both parents forms new combinations. Step 3: This is a main source of variation.

Step 1: Asexual reproduction can quickly form offspring from one parent. Step 2: Sexual reproduction combines information from two parents. Step 3: Thus the first is important for speed and the second for variation.

Step 1: First pollen reaches the stigma. Step 2: Pollen tube carries male gamete to the ovule. Step 3: After fertilisation ovule becomes seed and ovary becomes fruit.