Reproduction

Step 1: Self-pollination uses pollen from the same flower or same plant. Step 2: It may reduce dependence on external pollinating agents. Step 3: So seed formation can still occur in some situations.

Step 1: In cross-pollination, pollen comes from another plant of the same species. Step 2: Traits of two different plants can combine. Step 3: New combinations may produce new traits in offspring.

Step 1: During pollination, pollen reaches the stigma. Step 2: A sticky stigma helps hold pollen grains. Step 3: Without stickiness, successful pollination may decrease.

Step 1: The pollen tube grows from the stigma toward the ovary. Step 2: It carries the male gamete to the egg. Step 3: Fusion of male and female gametes forms the zygote.

Step 1: Pollination brings pollen to the stigma. Step 2: Seed formation needs the male gamete to fuse with the egg. Step 3: Therefore pollination alone is not enough.

Step 1: An ovary may contain one or more ovules. Step 2: After fertilization, each ovule can become a seed. Step 3: If many ovules are fertilized, the fruit may contain many seeds.

Step 1: Wind carries pollen grains in uncertain directions. Step 2: Many pollen grains are lost or scattered on the way. Step 3: Producing many pollen grains increases the chance of successful pollination.

Step 1: Nectar attracts insects to the flower. Step 2: Pollen grains can stick to the insect body. Step 3: When the insect visits another flower, pollen may reach its stigma.

Step 1: Sperm formation needs a temperature slightly lower than normal body temperature. Step 2: Testes remain in an external sac. Step 3: This helps maintain a suitable temperature.

Step 1: Testes produce sperms and male hormones. Step 2: The vas deferens carries sperms forward. Step 3: Cutting the tube blocks sperm transport but does not directly stop hormone production.

Step 1: Sperms are very small motile cells. Step 2: They need supportive fluid for movement and energy. Step 3: Secretions from glands provide a suitable medium.

Step 1: Ovulation releases an egg from the ovary. Step 2: The egg moves through the fallopian tube and fertilization usually occurs there. Step 3: If the tube is blocked, meeting of sperm and egg becomes difficult.

Step 1: The uterine lining prepares for possible pregnancy. Step 2: If fertilization does not occur, this lining breaks down. Step 3: This process is part of the menstrual cycle.

Step 1: After fertilization, an embryo forms. Step 2: For development, it must attach to the uterine wall. Step 3: Without implantation, it does not receive needed nourishment and protection.

Step 1: The embryo needs nutrition and oxygen. Step 2: The placenta helps exchange these materials. Step 3: It also helps move wastes from the embryo toward the mother.

Step 1: After ovulation, the uterus remains prepared for possible pregnancy. Step 2: If fertilization does not occur, no embryo forms. Step 3: Then the uterine lining breaks down and leaves the body.

Step 1: Hormones bring many body changes during adolescence. Step 2: In boys, development of the voice box can be more noticeable. Step 3: This can make the voice deeper.

Step 1: Sperm must reach the egg, so it is small and motile. Step 2: The egg is larger and contains material for early development. Step 3: This structural difference is linked to their functions.

Step 1: A barrier method stops sperm from reaching the egg. Step 2: It can also reduce direct contact of body fluids. Step 3: Therefore it helps prevent pregnancy and some sexually transmitted diseases.

Step 1: Some contraceptive pills are hormone-based. Step 2: They can affect release of egg from the ovary. Step 3: If ovulation does not occur, the chance of fertilization decreases.