Grade 7 Science Practice Test: Cell Division and Reproduction

In mitosis a cell copies its chromosomes and splits into two identical cells with the same number of chromosomes. Four cells with half the chromosomes describes meiosis, which makes sex cells.

Mitosis makes new cells so you can grow and heal, for example when skin closes over a cut. Egg and sperm cells are made by a different kind of division.

Asexual reproduction needs only one parent, and the offspring receive a copy of its genes. Mixing traits from two parents happens only in sexual reproduction.

When a bacterium splits in two, both cells are copies of the parent. Seeds, fertilized frog eggs and puppies all come from two parents.

Mixing genes from two parents creates variety, so a change such as a new disease is less likely to harm every individual. Needing only one parent is an advantage of asexual reproduction.

Sex cells have half the usual number, 23, so that when an egg and a sperm join, the new cell has 46 again. Choosing 46 forgets that the number is halved.

Fertilization joins an egg and a sperm into one cell that has chromosomes from both parents. Splitting into two cells describes cell division.

The anther, at the top of the stamen, makes pollen. The stigma is the sticky tip that receives pollen, and the ovary holds the eggs that become seeds.

As bees collect nectar, pollen sticks to their bodies and rubs off on the next flower, which is pollination. Bees do not plant seeds or water plants.

Normally the cell cycle is carefully controlled. In cancer, damaged cells ignore those controls and keep dividing, forming a mass of cells.