BiologiBiology

The flame symbol means the substance is flammable. It must be kept away from naked flames, sparks and heat. Heating it directly, storing it warm or smelling it directly are all unsafe.

The Golgi apparatus receives proteins from the rough endoplasmic reticulum, modifies and packages them in vesicles and secretes them. Ribosomes make protein, mitochondria release energy and the nucleus controls the cell.

Several tissues that work together to carry out a function form an organ. Organs working together form an organ system.

Movement of ions against the concentration gradient needs carrier proteins and energy (ATP): active transport. The other processes move substances down a concentration gradient and need no ATP.

Water moves by osmosis from the more dilute (hypotonic) cell X to the more concentrated (hypertonic) cell Y. Cell Y gains water and becomes more turgid; cell X loses water.

Sucrose is a disaccharide made of glucose + fructose. Maltose gives two glucose molecules; lactose gives glucose + galactose.

At low temperature molecules move slowly, so there are fewer effective collisions between enzyme and substrate. Low temperature slows enzymes but does not denature them; denaturation happens at high temperature.

From 8 g dm⁻³ the rate is constant at 50 units: all the active sites are occupied, so enzyme concentration is the limiting factor. Only more enzyme (more active sites) raises the rate.

DNA replicates in the S phase, so by G2 each of the 46 chromosomes consists of two sister chromatids: 46 × 2 = 92 chromatids.

Yeast ferments the sugar in the dough, releasing carbon dioxide gas bubbles that make the dough rise (and ethanol, which evaporates on baking). Yeast produces ethanol, not lactic acid, and does not photosynthesise.

A very thin wall gives a short diffusion distance, so gases diffuse quickly. A large surface area comes from the huge number of alveoli; moisture comes from the thin film of water lining them.

Lipase hydrolyses lipids into fatty acids and glycerol. Amino acids come from protein and glucose from carbohydrate.

Brick-red precipitate with Benedict's = reducing sugar; violet with Biuret = protein; no change with iodine = no starch. The tests given do not show lipid.

Platelets and damaged cells release thrombokinase, which starts the clotting process. Red cells carry oxygen and white cells defend the body.

The left ventricle sends oxygenated blood through the aorta around the whole body, needing a thick muscular wall for high pressure. The right ventricle sends blood only to the nearby lungs.

A vaccine gives artificial active immunity: it stimulates lymphocytes to form memory cells. On later exposure, memory cells recognise the antigen and produce antibodies faster and in larger amounts. Ready-made antibodies are given in passive immunity.

The cerebellum coordinates balance and posture. The cerebrum controls thinking and voluntary actions, the hypothalamus controls body temperature and water balance, and the medulla oblongata controls involuntary actions such as the heartbeat and breathing.

Loss of water raises the osmotic pressure of the blood. The pituitary gland releases more ADH, so the distal tubule and collecting duct reabsorb more water. Less urine is produced and it is more concentrated.

Ligaments are strong, slightly elastic bands that join one bone to another. Tendons join muscle to bone, synovial fluid reduces friction and cartilage absorbs shock.

Progesterone, secreted first by the corpus luteum and later by the placenta, keeps the endometrium thick and prevents menstruation. FSH and LH are inhibited during pregnancy; testosterone is a male hormone.