AS Biology

It controls the movement of substances into and out of cells.

Network of channels running through the cytoplasm.

As strands and loops called plasmids, not surrounded by a nulear membrane.

By altering the structure (and therefore shape) of the active site of the enzyme so that the substrate molecules can no longer bind to the active site.

Main component of ligaments and tendons.

A component of the wall of plant cells.

Forms a triglyceride with 3 molecules of fatty acid.

Part of cell membranes.

Stored in plant cells.

It has the same molecular formula as glucose.

Diffusion - the concentration in the air in the alveoli is greater than the concentration of oxygen in the blood. Oxygen therefore passes down the oxygen concentration from the alveoli to the blood.

A heart attack happens when the flow of blood to the heart is interrupted.

A pathogen may rupture the host cells. It may break down and use nutrients in the host cells, so that the host cells starve. Or a pathogen may replicate inside host cells and burst them as it leaves.

Antibodies coat pathogens, making it easier for phagocytes to engulf them and preventing them fro entering the host cells. They also bind to toxins to neutralise them.

A seconday immune response is faster and produces a quicker, stronger response than the primary response. This is becuase memory cells are produced during the primary response which remember the foreign antigen. During the second infection, memory cell B-cells can quickly divide to form plasma cells, which secrete the correct antibody to the antigen. Memory T-cells quickly divide into the right type of T-cells to kill the cell carrying the antigen.

Two amino acids join together in a condensation reaction. A peptide bond forms between the carboxyl group of one amino acid and the amino group of the other amino acid. A molecule of water is released.

Lactose intolerance is an inability to break down lactose, a sugar found in milk/milk products, due to a lack of the anzyme lactase.

A change in the amino acid sequence of an anzyme may alter its tertiary structure. This changes the shape of the active site so that the substrate can't bind to it.

The membrane is described as fluid because the phospholipids are constantly moving. It is described as mosaic becuase the proteins are scattered throughout the membrane like tiles ina mosaic.

Two fatty acid molcules and a phosphate group attached to one glycerol molecule.

Saturated fatty acids don't have double bonds between their carbon atoms. Unsaturated fatty acids have one or more double bonds between their carbon atoms.

In eukaryotes, DNA is linear and wound around proteins (histones). In prokaryotes, DNA molecules are shorter, circular and not associated with proteins.

A gene is a section of DNA that codes for a protein (polypeptide).