Page 21 - 02 Cells Biology Notes

#20 Sum mary of Cells

Structure

• Cells are the smallest units of living things. They are too small to be
seen with the naked eye, so we need to use microscopes to see their
structures.

• Cells have a cell membrane, cytoplasm and a nucleus. Plant cells
also have a cell wall, and oft en have chloroplasts and a
large vacuole containing cell sap.

• The cell membrane is partially permeable, and it controls what
enters and leaves the cell.

• The cytoplasm is a jelly-like solution of many different substances in
water. It is the site of many different metabolic reactions.

• The nucleus contains the chromosomes, which are made of DNA.
This is the genetic information and it controls the activities of the cell.

• The cell wall of a plant cell is made of criss-crossing fibres
of cellulose. It is fully permeable. It helps to support the cell,
and prevents the cell bursting if it absorbs a lot of water.

• The vacuole of a plant cell contains cell sap, which is a solution
of sugars and other substances in water.

• Chloroplasts contain the green pigment chlorophyll, which absorbs
sunlight for photosynthesis. There may be starch grains inside the