Reproduction

Step 1: Uterine lining prepares for a possible embryo. Step 2: If fertilisation occurs the lining remains. Step 3: If not it breaks down and comes out.

Step 1: In pregnancy embryo attaches to uterine lining. Step 2: This lining is needed for nourishment and support. Step 3: Therefore it does not come out as menstrual flow.

Step 1: Reproductive organs become active during adolescence. Step 2: Secretion of reproductive hormones increases. Step 3: These hormones affect voice body structure and other changes.

Step 1: Pill can affect chemical control in the body. Step 2: Condom is a barrier that prevents sperm entry. Step 3: Thus both prevent pregnancy in different ways.

Step 1: Many sexually transmitted diseases can spread through body fluid contact. Step 2: Condom forms a barrier. Step 3: It can reduce risk of both pregnancy and disease.

Step 1: In sterilisation reproductive tubes are blocked. Step 2: This makes meeting of sperm and ovum difficult. Step 3: Gametes may form but fertilisation cannot occur.

Step 1: A copper device is placed in the uterus. Step 2: Contraceptive pills may act on body hormones. Step 3: Both aim to prevent pregnancy but methods differ.

Step 1: Preventing pregnancy and preventing infection are different goals. Step 2: Some diseases spread through sexual contact and fluids. Step 3: Safe behaviour and barrier methods are needed.

Step 1: Reaching close is not enough for fertilisation. Step 2: Genetic material of male and female gametes must fuse. Step 3: If nuclei do not fuse zygote will not form.

Step 1: A zygote is one cell. Step 2: Division increases the number of cells. Step 3: Embryo formation also needs proper arrangement and division of roles.

Step 1: Two gametes fuse during fertilisation. Step 2: If both have half number the normal number is restored after fusion. Step 3: This keeps chromosome number stable in the species.

Step 1: Fertilisation combines information from two gametes. Step 2: If two full numbered cells fuse the total number will increase. Step 3: So gametes must have half the number.

Step 1: Cross pollination combines information from different plants. Step 2: This increases variation. Step 3: In changing environments some new combinations may be useful.

Step 1: A mature stigma can receive pollen. Step 2: If anther has no pollen self pollen is unavailable. Step 3: Pollen from another suitable flower can help fertilisation.

Step 1: Normally ovule becomes seed after fertilisation. Step 2: In some cases fruit like growth can occur without normal seeds. Step 3: Thus seed formation remains incomplete in seedless fruit.

Step 1: Placenta provides nutrition and oxygen from mother to embryo. Step 2: It also helps remove wastes from embryo. Step 3: Weak placenta affects exchange in both directions.

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: A small error may create variation. Step 2: Too many errors can disturb genetic information. Step 3: Essential traits may be affected and the offspring may become weak.

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

Step 1: Ovum is released from ovary. Step 2: It may fuse with sperm in oviduct to form zygote. Step 3: After division embryo attaches in uterus.