Interdependence Among Organisms Within Their Environment

Classify the interactions between organisms by their effect on each partner; explain intraspecific and interspecific competition, the niche and competitive exclusion; analyse predator–prey cycles and the adaptations of predators, prey and parasites; and explain how saprotrophs, mutualists and commensals depend on other organisms.

2

Transport Across the Cell Membrane

Relate the fluid mosaic structure of the cell membrane to what can cross it; apply Fick's law to diffusion and explain facilitated diffusion; calculate water potential and predict the direction of osmosis; explain turgor, plasmolysis and osmosis in animal cells; describe active transport, the sodium–potassium pump and co-transport; and explain endocytosis and exocytosis.

3

Nucleic Acids and DNA Replication

Describe how DNA is packaged with histones into chromosomes; draw the structure of nucleotides, DNA and RNA and explain the Watson–Crick model; explain the nature of genes, the properties of the genetic code and the role of telomeres; and describe the enzymes and steps of semi-conservative DNA replication and the experimental evidence for it.

4

Cell and Nuclear Division

Describe the cell cycle and how checkpoints, cyclins and CDKs control it; distinguish haploid, diploid and polyploid cells; describe the phases of mitosis and meiosis, including spindle formation, synapsis, bivalents and chiasmata; explain the roles of mitosis and meiosis, the link between abnormal mitosis and cancer, and errors in meiosis; and compare the two divisions.

5

Transport in Plants

Explain why large plants need a transport system; relate the structure of xylem and phloem to their functions; follow water from the soil through the root, stem and leaf; measure transpiration and explain the factors that change its rate; explain translocation by the mass flow hypothesis and weigh the evidence for it; and describe how xerophytes save water and how plants get rid of their waste products.

6

Gas Exchange in Animals and Plants

Explain the features of efficient gas-exchange surfaces and relate them to surface area to volume ratio; compare gas exchange in insects, fish, amphibians and humans; explain ventilation, lung volumes and the spirometer, and how breathing is controlled by the brain; evaluate the effects of smoking on the lungs, heart and blood vessels; and explain how stomata control gas exchange in plants.

7

Excretion and Homeostasis

Distinguish excretion from egestion and relate the nitrogenous waste of an animal to its habitat; compare the excretory organs of different animals; explain homeostasis and negative and positive feedback; explain how blood glucose and body temperature are controlled and what goes wrong in diabetes; and relate the structure of the kidney and nephron to ultrafiltration, selective reabsorption and the control of water by ADH.

8

Behaviour and Response in Mammals

Distinguish innate from learned behaviour; explain reflexes, the fight-or-flight response, taxes and kineses; describe habituation, imprinting, classical and operant conditioning, latent and insight learning; explain communication, altruism, courtship, territories and dominance hierarchies in social animals; and relate biological rhythms, biological clocks and migration to survival.

Units