BiologiBiology

The manipulated variable is the one the investigator changes on purpose: the amount of fertiliser. The height is the responding variable; seed type and volume of water are kept constant.

Lysosomes contain hydrolytic (digestive) enzymes. Ribosomes make protein, centrioles form the spindle in animal cells and the Golgi apparatus modifies and packages proteins.

Proteins for export are made by ribosomes on the rough endoplasmic reticulum, pass to the Golgi apparatus for modification and packaging, and leave in secretory vesicles that fuse with the plasma membrane. Smooth ER does not carry ribosomes, and the Golgi apparatus does not make protein.

Oxygen is a small non-polar molecule. It passes through the phospholipid bilayer down its concentration gradient by simple diffusion, without a carrier protein or energy.

The mass decreased by 0.6 g, so there was a net loss of water from the cells. Water moves by osmosis from the cell sap (higher water potential) to the stronger solution, so Y is hypertonic to the cell sap.

Sucrose = glucose + fructose. Maltose = glucose + glucose and lactose = glucose + galactose.

Specificity comes from the shape of the active site, which fits only its own substrate (lock and key hypothesis). Enzymes are not used up or changed in the reaction.

Above the optimum temperature the enzyme is denatured: its three-dimensional shape, including the active site, is permanently changed. Heating increases (not decreases) kinetic energy, and enzymes are not used up.

DNA is replicated in the S phase, so each of the 12 chromosomes consists of two sister chromatids at metaphase: 12 × 2 = 24 chromatids.

Glycolysis takes place in the cytoplasm; the complete oxidation of pyruvic acid with oxygen takes place in the mitochondria.

In exhalation the diaphragm relaxes and arches upwards (and the ribs move down and in), so the thoracic volume decreases, the pressure inside rises above atmospheric pressure and air is forced out.

Bile (made in the liver, stored in the gall bladder) has no enzymes. It emulsifies fats into tiny droplets, increasing the surface area for lipase. Lipase digests the lipids.

Gastritis is inflammation of the stomach lining. It is caused when gastric juice acts on the lining of an empty stomach, for example in people who skip meals. Anorexia nervosa and bulimia nervosa are eating disorders about body weight, and muscle dysmorphia is a belief that one's body is too small.

The pulmonary vein is the exception that carries oxygenated blood to the left atrium. The pulmonary artery carries deoxygenated blood to the lungs; the vena cava returns deoxygenated blood from the body; the aorta carries oxygenated blood out of the left ventricle.

A group B patient has anti-A antibody in the plasma, so antigen A in the donor's red blood cells would cause agglutination. Groups B and O (no antigen A) are safe.

After the first infection, memory cells formed by lymphocytes remember the antigen. On the next exposure they produce antibodies immediately and in large amounts. Antibodies do not stay for ever and phagocytes are non-specific.

This is a reflex action. The reflex arc passes through the spinal cord (relay neurone to motor neurone to effector), so the response is made before the impulse reaches the cerebrum, which is why the pain is felt a moment later.

Drinking water lowers the osmotic pressure of the blood. Osmoreceptors in the hypothalamus are less stimulated, less ADH is secreted, the distal tubule and collecting duct become less permeable to water and a large volume of dilute urine is passed.

A hinge joint is a freely movable joint that moves in one plane only (bending and straightening). A ball-and-socket joint (shoulder, hip) rotates in all directions.

Sperm are made (spermatogenesis) in the seminiferous tubules. The epididymis stores and matures them, the vas deferens carries them, and the prostate gland adds fluid to semen.