Stop memorising, start understanding

Diffusion is any particle moving from high to low concentration. Osmosis is specifically WATER moving across a semi-permeable membrane, from where water is more concentrated to where it is less.

Moving substances AGAINST their concentration gradient, using energy (ATP) and carrier proteins.

An enzyme's active site binds a specific substrate (lock and key), speeds the reaction, and is released unchanged.

The double helix unzips; each old strand acts as a template for a new complementary strand (A–T, G–C).

Transcription copies a gene from DNA into mRNA (in the nucleus). Translation reads the mRNA to build a protein (at the ribosome).

A dominant allele shows its effect even with one copy; a recessive allele shows only with two copies.

A cross of two heterozygotes (Aa × Aa) gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio.

In humans, females are XX and males are XY. The sperm decides the sex, because it carries either X or Y.

Alleles I^A and I^B are codominant; i is recessive. O is ii; AB expresses both.

Valves between chambers and in the great vessels open one way, so blood cannot flow backwards.

Oxygen diffuses from alveolar air (high O₂) into blood (low O₂); CO₂ diffuses the other way. Thin walls and huge surface area make it fast.

The glomerulus filters blood indiscriminately; the tubule then REABSORBS the useful things (glucose, most water, salts) back into the blood.

An impulse travels ELECTRICALLY along a neuron, but crosses the gap between neurons CHEMICALLY, via neurotransmitters.

Insulin LOWERS blood glucose (stores it); glucagon RAISES it (releases it). They are opposites that keep glucose stable.

A pathogen's antigen triggers B-cells to make specific antibodies; memory cells remember it for next time.

In chloroplasts, light energy converts CO₂ + water into glucose, releasing O₂. It happens in green parts, in light.

Water evaporates from leaf pores (stomata), creating suction that pulls a continuous water column up from the roots through the xylem.

Xylem carries WATER and minerals UP from the roots (dead cells). Phloem carries FOOD (sugars) in BOTH directions (living cells).

Mitosis makes two IDENTICAL diploid cells (growth, repair). Meiosis makes four genetically DIFFERENT haploid cells (gametes).

In flowering plants, one male gamete fertilises the egg (→ embryo), the other fuses with two nuclei (→ nutritive endosperm).

Hormones (FSH, LH, oestrogen, progesterone) cycle to mature an egg, release it (ovulation ~day 14), and prepare the uterus lining.

Energy flows one way: sun → producers → consumers. Only about 10% passes to the next level; the rest is lost as heat.

Photosynthesis removes CO₂; respiration, decay and combustion return it. Normally these balance.

Bacteria FIX atmospheric N₂ into usable forms, plants absorb them, and other bacteria return N₂ to the air (denitrification).

Variation exists; those best suited to the environment survive and reproduce more, passing on their traits.

Homologous organs share ancestry but differ in function (human arm, whale flipper). Analogous organs share function but not ancestry (bird wing, insect wing).

Repeated heating and cooling, with a heat-stable enzyme (Taq), doubles a DNA segment each cycle — millions of copies fast.

These 'molecular scissors' cut DNA at specific recognition sequences, leaving sticky ends that can join other DNA cut the same way.

A useful gene is cut out, inserted into a vector (often a plasmid), the vector enters a host cell, and the cell then expresses the new gene.

Antibiotics target structures found in BACTERIA (like their cell wall). Viruses have no such structures.

A vaccine shows the immune system a harmless piece of a pathogen, so memory cells form WITHOUT you getting ill.

In the absence of oxygen, microbes like yeast break down sugars to release energy, producing CO₂ and alcohol (or acids).

Fungi and bacteria break down dead matter, returning nutrients to the soil for plants to reuse.