Interdependence Among Organisms in an Ecosystem

How the organisms of an ecosystem depend on one another: food webs from Akagera, Nyungwe and Lake Kivu; pyramids of numbers, biomass and energy drawn to scale; intraspecific and interspecific relationships and competition; predation, grazing and parasitism; and mutualism, commensalism, neutralism, amensalism and allelopathy.

2

Population Size

What a population is and how its size and density are measured: quadrat sampling for plants and capture–recapture (the Lincoln index) for animals; the factors that limit population size; the S-shaped growth curve with its lag and log phases and the carrying capacity; and the causes and consequences of human population growth, using Rwanda's census data.

3

Nutrient Cycles

How water, carbon, nitrogen and phosphorus move between living things and their surroundings: the water cycle; the carbon cycle and how people are changing it; the nitrogen cycle and biological nitrogen fixation; and the phosphorus cycle, each drawn with its processes and illustrated with Rwandan examples.

4

Effects of Human Activities on Ecosystems and Environmental Conservation

How producing food, clearing habitats, polluting air, water and land, and producing waste affect ecosystems; what sustainable development and good waste management mean, from recycling to sewage treatment and Rwanda's ban on plastic bags; why species become extinct and how endangered species such as the mountain gorilla are conserved; and what Rwanda's conservation programmes, from Gishwati–Mukura to the Rugezi wetland and umuganda, have achieved.

5

Mitosis and Meiosis

How cells divide: chromosomes, chromatids, homologous pairs, haploid and diploid; the cell cycle; the stages of mitosis and why it matters for growth, repair and asexual reproduction; the two divisions of meiosis, crossing over and why meiosis makes gametes and variation; and a full comparison of the two, with chromosome counts drawn and checked at every stage.

6

Heterotrophic Nutrition

How organisms that cannot make their own food get it: holozoic, saprophytic and parasitic nutrition; human teeth and their care; the human digestive system from mouth to anus, with every enzyme's substrate, product and site; digestion in the stomach and small intestine, absorption through the villi and the work of the large intestine; and the common digestive disorders, a balanced diet and what Rwanda's own nutrition surveys show.

7

Circulatory System in Humans

How blood is moved round the body: open and closed, single and double circulation; the structure of the human heart and how its valves keep blood flowing one way; how exercise changes the heart rate; arteries, veins and capillaries, blood pressure and coronary heart disease; the parts of blood and their jobs; clotting, the ABO and Rhesus blood groups and safe transfusion; and the lymphatic system.

8

Cellular Respiration

How cells release energy from food: what respiration is and why every living cell needs ATP; aerobic respiration, its equation and the experiments that show it, including a simple respirometer; anaerobic respiration in yeast, muscles and plants; a comparison of the two and of their energy yields; and how fermentation is used in Rwanda, from urwagwa and bread to fermented milk and biogas.

9

Response and Coordination

How living things detect changes and respond to them: tropisms and nastic responses in plants and the role of auxin; why animals need coordination; the central and peripheral nervous systems; the structure of neurones and how an impulse crosses a synapse; reflex arcs and reflex actions; the endocrine glands and their hormones, including insulin, glucagon and ADH; and how nervous and hormonal coordination compare.

10

Sense Organs and Homeostatic Mechanisms

How the body senses its surroundings and keeps its internal conditions steady: the structure of the eye, how it focuses and controls the light it lets in; eye defects and how lenses, surgery or care correct them; the ear, hearing and balance; smell and taste; the skin as a sense organ; homeostasis by negative and positive feedback; how the skin and hypothalamus control body temperature; and how ADH and the hormones of the pancreas control the water and glucose in the blood, with diabetes insipidus, diabetes mellitus and the eating habits that lower the risk of diabetes.

11

Asexual and Sexual Reproduction in Plants and Microorganisms

How living things make new individuals: asexual reproduction by binary fission, budding and spores in microorganisms; natural vegetative reproduction and artificial propagation of plants, from banana suckers and cassava cuttings to grafting and tissue culture, with their advantages and disadvantages; the structure of a flower; insect and wind pollination; double fertilisation and how seeds and fruits form; how fruits and seeds are dispersed; and the conditions for, and types of, seed germination.

12

Reproduction in Humans

How human reproduction works, at textbook level: the structure and functions of the male and female reproductive systems; how sperm and eggs are made by gametogenesis; the sex hormones and puberty; the menstrual cycle and the hormones that control it; fertilisation, implantation, the placenta and pregnancy; antenatal care and birth; and protecting reproductive health, including preventing STIs and HIV and knowing where to get help, because any sexual contact with a child is abuse and a crime.

13

Genetics and Gene Technology

How characteristics pass from parents to offspring: genes, alleles and the key terms of genetics; monohybrid crosses worked with Punnett squares for complete dominance, incomplete dominance and co-dominance, including the ABO blood groups; how sex is inherited in humans; sex-linked haemophilia and red–green colour blindness; and gene technology: human insulin made by bacteria, gene therapy, and the benefits and drawbacks of genetically modified organisms.

14

Variation and Selection

Why no two organisms are exactly alike: the genetic and environmental causes of variation; continuous and discontinuous variation, shown on histograms and bar charts; gene and chromosome mutations and what causes them; natural selection, with industrial melanism in the peppered moth and sickle-cell and malaria; how new species form; artificial selection, inbreeding and outbreeding in crops and livestock; and the adaptive features of xerophytes and hydrophytes.

Units