Reproduction

Step 1: The embryo develops in the uterus and cannot take food independently. Step 2: Placenta helps supply nutrients and oxygen from the mother. Step 3: It also helps remove wastes from the embryo.

Step 1: In each cycle the uterus prepares for possible pregnancy. Step 2: The thick lining helps the embryo attach. Step 3: If fertilisation does not occur the lining breaks down.

Step 1: The uterine lining prepares for an embryo. Step 2: If fertilisation does not occur no embryo forms. Step 3: The prepared lining breaks and comes out with blood and tissue.

Step 1: During adolescence reproductive organs become active. Step 2: Levels of chemical messengers change in the body. Step 3: These influence many physical and emotional changes.

Step 1: Some pills affect chemical control in the body. Step 2: This can influence ovulation. Step 3: Barrier methods prevent sperms from entering the female reproductive tract.

Step 1: Contraceptive pills are mainly related to preventing pregnancy. Step 2: They do not stop contact with infected fluids. Step 3: A condom acts as a barrier and reduces such contact.

Step 1: In sterilisation reproductive tubes are blocked. Step 2: This prevents sperm and ovum from meeting. Step 3: Gametes may be produced but fertilisation cannot occur.

Step 1: A copper device is placed in the uterus. Step 2: It reduces the chance of pregnancy. Step 3: It interferes with later reproductive events inside the body.

Step 1: Some diseases spread through reproductive tract contact. Step 2: Unsafe contact can exchange infected fluids. Step 3: Safe behaviour reduces the risk of infection.

Step 1: Fertilisation is not just coming close. Step 2: Genetic material of male and female gametes must fuse. Step 3: Without fusion the first new cell will not form.

Step 1: A zygote is a single cell formed after fertilisation. Step 2: To form an embryo the number of cells must increase. Step 3: Repeated division forms a group of cells.

Step 1: Two gametes fuse in sexual reproduction. Step 2: If each has half the number fusion restores the normal number. Step 3: This keeps chromosome number stable over generations.

Step 1: Two gametes fuse during fertilisation. Step 2: If both have full number the total would double. Step 3: Therefore half number is necessary for a species.

Step 1: Offspring in asexual reproduction may be very similar. Step 2: If environment changes a shared weakness can affect all. Step 3: Thus low variation becomes a limitation.

Step 1: Cross pollination can combine gametes from different plants. Step 2: This forms new genetic combinations. Step 3: In the long term variation can help the population in changing conditions.

Step 1: Pollen from the correct species is needed for successful fertilisation. Step 2: Pollen from another species may not work properly on the stigma. Step 3: The male gamete may not reach the ovule.

Step 1: Ovules become seeds after fertilisation. Step 2: Ovary can become fruit. Step 3: If ovules are not fertilised seeds may be absent.

Step 1: Placenta is the exchange site between mother and embryo. Step 2: Nutrients and oxygen reach the embryo through it. Step 3: Its weakness can affect embryo development.

Step 1: Wastes are also formed by cellular activities in the embryo. Step 2: Placenta helps remove them. Step 3: If wastes are not removed development can be affected.

Step 1: Accurate copying preserves useful traits but reduces variation. Step 2: Small errors can create variation. Step 3: Too many errors can damage essential traits.

Step 1: Asexual offspring are similar to the parent. Step 2: Due to similarity they may share the same weakness. Step 3: A disaster or disease can affect the whole population.

Step 1: Sexual reproduction creates new combinations. Step 2: In changing environments some combinations may be better adapted. Step 3: Therefore variation can help survival.

Step 1: Pollination transfers pollen to the stigma. Step 2: Pollen tube carries male gamete to the ovule. Step 3: Seed forms after fertilisation.

Step 1: First an ovum is released from ovary. Step 2: Fertilisation in the oviduct forms a zygote. Step 3: After division the embryo attaches in the uterus.

Step 1: Reproduction produces new organisms. Step 2: Genetic information passes to offspring. Step 3: Variation especially in sexual reproduction can be useful in changing environments.