Reproduction and genetics, Year 8: more practice

A mate

提示Count how many parents it takes.

为什么With only one parent and no gametes to join, an organism such as a bacterium or a strawberry plant never has to search for a mate, so it can spread fast.

They are genetically identical, so they all share the same weakness

提示Think about how alike clones are inside.

为什么In a varied population some individuals may resist the disease. In clones none has a different gene to help.

The uterus (womb)

提示It is a muscular, stretchy bag in the lower abdomen.

为什么The uterus has a thick, muscular wall that stretches as the baby grows and pushes the baby out at birth.

oviduct

提示It is also called the fallopian tube; it begins with "ovi-".

为什么The egg is released from the ovary into the oviduct. If a sperm reaches it there, fertilisation can happen.

Most pollen is wasted, so many grains are needed for a few to reach a stigma

提示Wind blows randomly, so think about the odds of any one reaching a flower.

为什么The wind does not aim, so most grains never land on a stigma. Making a lot raises the chance that some do.

It sticks to the insect's body so it is carried to another flower

提示Think about how it catches hold of a visiting bee.

为什么When the insect visits the next flower, some pollen rubs off onto the stigma.

Cross-pollination

提示The pollen crosses from one plant to another.

为什么Cross-pollination mixes genes from two plants, so the seeds produced are more varied.

Through a pollen tube that grows down the style

提示A thin pathway forms inside the female part, heading for the ovule.

为什么The pollen tube grows down through the style to the ovary and the ovule, where the male gamete fuses with the female gamete.

The fruit

提示It surrounds and protects the seeds.

为什么The wall of the ovary swells into the fruit, such as a pea pod or an apple.

Less competition with the parent and each other for light, water and nutrients

提示Think about what crowded plants would fight over.

为什么Seeds that land far away also help the species spread into new areas.