B2.1.1 CELLS AND SIMPLE CELL TRANSPORT
a) 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 and RIBOSOMES which is where protein synthesis occurs.
b) Plant and agal cells also have a cell wall made of cellulose, which strengthens the cell. Plant cells often have: CHLOROPLASTS which absorb light and make food and a PERMANENT VACUOLE filled with cell sap.
c) A bacterial cell consists of CYTOPLASM and a MEMBRANE surrounded by a cell wall; the genes are not in a distinct nucleus.
d) Yeast is a single-celled organism. Yeast cells have a nucleus, cytoplasm and a membrane surrounded by a cell wall.
e) Cells may be specialised to carry out a particular function.
B2.1.2 DISSOLVED SUBSTANCES
a) Dissolved substances can move into and out of cells by diffusion.
b) 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.
c) Oxygen required by respiration passes through cell membranes by diffusion.