1.1 All living things are made up of cells. The structures of
different types of cells are related to their functions. To get
into or out of cells, dissolved substances have to cross the
1.1.1 Most human and animal cells have the following parts: a nucleus, which controls
the activities of the cell; cytoplasm, in which most of the chemical reactions take
place; a cell membrane, which controls the passage of substances into and out of
the cell; mitochondria, which is where most energy is released in respiration;
ribosomes, which is where protein synthesis occurs.
18.104.22.168 Plant and algal cells also have a cell wall made of cellulose, which
strengthens the cell. Plant cells often have chloroplasts, which absorb
light energy to make food and a permanent vacuole filled with cell sap.
22.214.171.124.1 A bacterial cell consists of cytoplasm and a
membrane surrounded by a cell wall; the
genes are not in a distinct nucleus.
126.96.36.199.1.1 Yeast is a single-celled organism. Yeast
cells have a nucleus, cytoplasm and a
membrane surrounded by a cell wall.
188.8.131.52.1.1.1 Cells may be specialised to carry out a particular function.
2 B2.1.2 Dissolved Substances
2.1 Dissolved substances can move
into and out of cells by diffusion.
2.1.1 Diffusion is the spreading of the particles of a gas, or of
any substance in solution, resulting in a net movement from
a region where they are of a higher concentration to a
region with a lower concentration. The greater the
difference in concentration, the faster the rate of diffusion.
184.108.40.206 Oxygen required for respiration passes
through cell membranes by diffusion.