O Level Syllabus

Cambridge O Level Biology 5090

1. Cell structure and organisation

1.1 Plant and animal cells
1.2 Specialised cells, tissues and organs
Learning outcomes
Candidates should be able to:
(a) examine under the microscope an animal cell (e.g. from fresh liver) and a plant cell (e.g. from Elodea, a moss, onion epidermis, or any suitable, locally available material), using an appropriate temporary staining technique, such as iodine or methylene blue;
(b) draw diagrams to represent observations of the plant and animal cells examined above;
(c) identify, from fresh preparations or on diagrams or photomicrographs, the cell membrane, nucleus and cytoplasm in an animal cell;
(d) identify, from diagrams or photomicrographs, the cellulose cell wall, cell membrane, sap vacuole, cytoplasm, nucleus and chloroplasts in a plant cell;
(e) compare the visible differences in structure of the animal and the plant cells examined;
(f) state the function of the cell membrane in controlling the passage of substances into and out of the cell;
(g) state the function of the cell wall in maintaining turgor (turgidity) within the cell;
(h) state, in simple terms, the relationship between cell function and cell structure for the following:

  • absorption – root hair cells;
  • conduction and support – xylem vessels;
  • transport of oxygen – red blood cells;

(i) identify these cells from preserved material under the microscope, from diagrams and from photomicrographs;
(j) differentiate cell, tissue, organ and organ system as illustrated by examples covered in sections 1 to 12, 15 and 16.

2. Diffusion and osmosis

2.1 Diffusion
2.2 Osmosis
2.3 Active transport
Learning outcomes
Candidates should be able to:
(a) define diffusion as the movement of molecules from a region of their higher concentration to a region of
their lower concentration, down a concentration gradient;
(b) define osmosis as the passage of water molecules from a region of higher water potential to a region of
lower water potential, through a partially permeable membrane;
(c) describe the importance of a water potential gradient in the uptake of water by plants and the effects of
osmosis on plant and animal tissues;
(d) define active transport as the movement of ions into or out of a cell through the cell membrane, from
a region of their lower concentration to a region of their higher concentration against a concentration
gradient, using energy released during respiration;
(e) discuss the importance of active transport as an energy-consuming process by which substances are
transported against a concentration gradient, as in ion uptake by root hairs and glucose uptake by cells in
the villi.

3. Enzymes

3.1 Enzyme action
3.2 Effects of temperature and pH
Learning outcomes
Candidates should be able to:
(a) define catalyst as a substance that speeds up a chemical reaction and is not changed by the reaction;
(b) define enzymes as proteins that function as biological catalysts;
(c) explain enzyme action in terms of the ‘lock and key’ hypothesis;
(d) investigate and describe the effects of temperature and of pH on enzyme activity.

4. Plant nutrition

4.1 Photosynthesis
4.2 Leaf structure
4.3 Mineral nutrition
Learning outcomes
Candidates should be able to:
(a) understand that photosynthesis is the fundamental process by which plants manufacture carbohydrates
from raw materials;
(b) investigate the necessity for chlorophyll, light and carbon dioxide for photosynthesis, using appropriate
(c) state the equation (in words or symbols) for photosynthesis;
(d) investigate and state the effect of varying light intensity, carbon dioxide concentration and temperature
on the rate of photosynthesis (e.g. in submerged aquatic plants);
(e) understand the concept of limiting factors in photosynthesis;
(f) describe the intake of carbon dioxide and water by plants;
(g) understand that chlorophyll traps light energy and converts it into chemical energy for the formation of
carbohydrates and their subsequent storage;
(h) explain why most forms of life are completely dependent on photosynthesis;
(i) identify and label the cuticle, cellular and tissue structure of a dicotyledonous leaf, as seen in cross-
section under the microscope, and describe the significance of these features in terms of function, i.e.

  • distribution of chloroplasts – photosynthesis;
  • stomata and mesophyll cells – gas exchange;
  • vascular bundles – transport;

(j) understand the effect of a lack of nitrate and magnesium ions on plant growth.

5. Animal nutrition

5.1 Nutrients
5.2 Diet
5.3 World food supplies
5.4 Human alimentary canal
5.5 Chemical digestion
5.6 Absorption and assimilation
Learning outcomes
Candidates should be able to:
(a) list the chemical elements that make up:

  • carbohydrates;
  • fats;
  • proteins;

(b) describe tests for:

  • starch (iodine in potassium iodide solution);
  • reducing sugars (Benedict’s solution);
  • protein (biuret test);
  • fats (ethanol emulsion test);

(c) list the principal sources of, and describe the dietary importance of carbohydrates, fats, proteins,
vitamins (C and D only), mineral salts (calcium and iron only), fibre (roughage) and water;
(d) name the diseases and describe the symptoms resulting from deficiencies of vitamin C (scurvy),
vitamin D (rickets), mineral salts calcium (rickets) and iron (anaemia);
(e) understand the concept of a balanced diet;
(f) explain why diet, especially energy intake, should be related to age, sex and activity of an individual;
(g) state the effects of malnutrition in relation to starvation, heart disease, constipation and obesity;
(h) discuss the problems that contribute to famine (unequal distribution of food, drought and flooding,
increasing population);
(i) identify the main regions of the alimentary canal and the associated organs: mouth (buccal) cavity, salivary
glands, oesophagus, stomach, duodenum, pancreas, gall bladder, liver, ileum, colon, rectum and anus;
(j) describe the main functions of these parts in relation to ingestion, digestion, absorption, assimilation and
egestion of food, as appropriate;
(k) identify the different types of human teeth and describe their structure and functions;
(l) state the causes of dental decay and describe the proper care of teeth;
(m) describe peristalsis;
(n) explain why most foods must be digested;
(o) describe:

  • digestion in the alimentary canal;
  • the functions of a typical amylase, protease and lipase, listing the substrates and end-products;

(p) describe the structure of a villus, including the roles of capillaries and lacteals;
(q) describe the significance of villi in increasing the internal surface area;

6. Transport in flowering plants

6.1 Water and ion uptake
6.2 Transpiration and translocation
Learning outcomes
Candidates should be able to:
(a) relate the structure and functions of root hairs to their surface area and to water and ion uptake;
(b) state that transpiration is the evaporation of water at the surfaces of the mesophyll cells followed by the
loss of water vapour from the leaves through the stomata;
(c) describe:

  • how water vapour loss is related to cell surfaces, air spaces and stomata;
  • the effects of air currents (wind), and the variation of temperature, humidity and light intensity on transpiration rate;
  • how wilting occurs;

(d) investigate, using a suitable stain, the pathway of water in a cut stem;
(e) explain the movement of water through the stem in terms of transpiration pull;
(f) identify the positions of xylem and phloem tissues as seen in transverse sections of unthickened,
herbaceous, dicotyledonous roots, stems and leaves;
(g) state the functions of xylem and phloem.

7. Transport in humans

7.1 Circulatory system
Learning outcomes
Candidates should be able to:
(a) describe the circulatory system as a system of tubes with a pump and valves to ensure one-way flow of
(b) describe the double circulation in terms of a low pressure circulation to the lungs and a high pressure
circulation to the body tissues and relate these differences to the different functions of the two circuits;
(c) name the main blood vessels that carry blood to and from the heart, lungs, liver and kidneys;
(d) describe the structure and function of the heart in terms of muscular contraction and the working of
(e) compare the structure and function of arteries, veins and capillaries;
(f) investigate and state the effect of physical activity on pulse rate;
(g) describe coronary heart disease in terms of the occlusion of coronary arteries and state the possible
causes (diet, stress and smoking) and preventive measures;
(h) identify red and white blood cells as seen under the light microscope on prepared slides, and in
diagrams and photomicrographs;
(i) list the components of blood as red blood cells, white blood cells, platelets and plasma;
(j) state the functions of blood:

  • red blood cells – haemoglobin and oxygen transport;
  • white blood cells – phagocytosis, antibody formation and tissue rejection;
  • platelets – fibrinogen to fibrin, causing clotting;
  • plasma – transport of blood cells, ions, soluble food substances, hormones, carbon dioxide, urea,
    vitamins and plasma proteins;

(k) describe the transfer of materials between capillaries and tissue fluid.

8. Respiration

8.1 Aerobic respiration
8.2 Anaerobic respiration
8.3 Human gas exchange
Learning outcomes
Candidates should be able to:
(a) define respiration as the release of energy from food substances in all living cells;
(b) define aerobic respiration as the release of a relatively large amount of energy by the breakdown of food
substances in the presence of oxygen;
(c) state the equation (in words or symbols) for aerobic respiration;
(d) state the uses of energy in the human body: muscle contraction, protein synthesis, cell division, active
transport, growth, the passage of nerve impulses and the maintenance of a constant body temperature;
(e) define anaerobic respiration as the release of a relatively small amount of energy by the breakdown of
food substances in the absence of oxygen;
(f) state the equation (in words or symbols) for anaerobic respiration in humans and in yeast;
(g) describe the effect of lactic acid production in muscles during exercise;
(h) know the percentages of the gases in atmospheric air and investigate and state the differences between
inspired and expired air;
(i) investigate and state the effect of physical activity on rate and depth of breathing;
(j) identify on diagrams and name the larynx, trachea, bronchi, bronchioles, alveoli and associated
(k) state the characteristics of, and describe the role of, the exchange surface of the alveoli in gas exchange;
(l) describe the role of cilia, diaphragm, ribs and intercostal muscles (external and internal) in breathing.

9. Excretion

9.1 Structure and function of kidneys
9.2 Kidney dialysis
Learning outcomes
Candidates should be able to:
(a) define excretion as the removal of toxic materials and the waste products of metabolism from
(b) describe the removal of carbon dioxide from the lungs;
(c) identify on diagrams and name the kidneys, ureters, bladder, urethra and state the function of each (the
function of the kidney should be described simply as removing urea and excess salts and water from the
blood; details of kidney structure and nephron are not required);
(d) describe dialysis in kidney machines as the diffusion of waste products and salts (small molecules)
through a membrane; large molecules (e.g. protein) remain in the blood.

10. Homeostasis

10.1 Structure and function of the skin
Learning outcomes
Candidates should be able to:
(a) define homeostasis as the maintenance of a constant internal environment;
(b) explain the concept of control by negative feedback;
(c) identify, on a diagram of the skin, hairs, sweat glands, temperature receptors, blood vessels and fatty
(d) describe the maintenance of a constant body temperature in humans in terms of insulation and the role
of temperature receptors in the skin, sweating, shivering, blood vessels near the skin surface and the
coordinating role of the brain.

11. Coordination and response

11.1 Nervous system
11.2 Receptors
11.3 Reflex action
11.4 Hormones
Learning outcomes
Candidates should be able to:
(a) state that the nervous system (brain, spinal cord and nerves) serves to coordinate and regulate bodily functions;
(b) identify, on diagrams of the central nervous system, the cerebrum, cerebellum, pituitary gland and hypothalamus, medulla, spinal cord and nerves;
(c) describe the principal functions of the above structures in terms of coordinating and regulating bodily functions;
(d) describe the gross structure of the eye as seen in front view and in horizontal section;
(e) state the principal functions of component parts of the eye in producing a focused image of near and distant objects on the retina;
(f) describe the pupil reflex in response to bright and dim light;
(g) outline the functions of sensory neurones, relay neurones and motor neurones;
(h) discuss the function of the brain and spinal cord in producing a coordinated response as a result of a
specific stimulus (reflex action);
(i) define a hormone as a chemical substance, produced by a gland, carried by the blood, which alters the
activity of one or more specific target organs and is then destroyed by the liver;
(j) state the role of the hormone adrenaline in boosting the blood glucose concentration and give examples of situations in which this may occur;
(k) state the role of the hormone insulin in controlling blood glucose concentration;
(l) describe the signs (increased blood glucose concentration and glucose in urine) and treatment (administration of insulin) of diabetes mellitus.

12. Support, movement and locomotion

12.1 Bones
12.2 Joints
12.3 Antagonistic muscles
Learning outcomes
Candidates should be able to:
(a) identify and describe, from diagrams, photographs and real specimens, the main bones of the forelimb
(humerus, radius, ulna and scapula) of a mammal;
(b) describe the type of movement permitted by the ball and socket joint and the hinge joint of the forelimb;
(c) describe the action of the antagonistic muscles at the hinge joint.

13. The use and abuse of drugs

13.1 Antibiotics
13.2 Effects of heroin
13.3 Effects of alcohol
13.4 Effects of tobacco smoke
Learning outcomes
Candidates should be able to:
(a) define a drug as any externally administered substance that modifies or affects chemical reactions in the body;
(b) describe the medicinal use of antibiotics for the treatment of bacterial infection;
(c) describe the effects of the abuse of heroin: a powerful depressant, problems of addiction, severe withdrawal symptoms and associated problems such as crime and infection, e.g. AIDS;
(d) describe the effects of excessive consumption of alcohol: reduced self-control, depressant, effect on reaction times, damage to liver and social implications;
(e) describe the effects of tobacco smoke and its major toxic components (nicotine, tar and carbon monoxide) on health: strong association with bronchitis, emphysema, lung cancer and heart disease, and the association between smoking during pregnancy and reduced birth weight of the baby;
(f) recognise the fact that many people regard smoking as no longer socially acceptable.

14. Microorganisms and biotechnology

14.1 Microorganisms
14.2 Food biotechnology
14.3 Industrial biotechnology
Learning outcomes
Candidates should be able to:
(a) list the main characteristics of the following groups: viruses, bacteria and fungi;
(b) outline the role of microorganisms in decomposition;
(c) explain the role of yeast in the production of bread and alcohol;
(d) outline the role of bacteria in yoghurt and cheese production;
(e) describe the use of fermenters for large-scale production of antibiotics and single cell protein;
(f) describe the role of the fungus Penicillium in the production of penicillin.

15. Relationships of organisms with one another and with the environment

15.1 Energy flow
15.2 Food chains and food webs
15.3 Carbon cycle
15.4 Nitrogen cycle
15.5 Parasitism
15.6 Effects of humans on the ecosystem
15.7 Pollution
15.8 Conservation
Learning outcomes
Candidates should be able to:
(a) state that the Sun is the principal source of energy input to biological systems;
(b) describe the non-cyclical nature of energy flow;
(c) define the following terms and establish the relationship of each in food webs:
•  producer – an organism that makes its own organic nutrients, usually using energy from sunlight
through photosynthesis;
•  consumer – an organism that gets its energy by feeding on other organisms;
•  herbivore – an animal that obtains its energy by eating plants;
•  carnivore – an animal that obtains its energy by eating other animals;
•  decomposer – an organism that obtains its energy from dead or waste organic matter;
•  food chain – a chart showing the flow of energy (food) from one organism to the next, beginning with
the producer (e.g. mahogany tree → caterpillar → songbird → hawk);
(d) describe energy losses between trophic levels and infer the advantages of short food chains;
(e) describe and interpret pyramids of numbers and of biomass;
(f) describe and state the importance of the carbon cycle;
(g) describe the nitrogen cycle in making available nitrogen for plant and animal protein, including the role of
bacteria in nitrogen fixation, decomposition and nitrification (details of denitrification and the names of
individual bacteria are not required);
(h) understand the role of the mosquito as a vector of disease;
(i) describe the malarial pathogen as an example of a parasite and describe the transmission and control of
the malarial pathogen (details of the life cycle of the pathogen are not required);
(j) describe the effects of humans on the ecosystem with emphasis on examples of international
importance (tropical rainforests, oceans and important rivers);
(k) describe the consequences of deforestation in terms of its effects on soil stability, climate and local human populations;
(l) evaluate the effects of:
water pollution by sewage, by inorganic waste and by nitrogen-containing fertilisers; air pollution by greenhouse gases (carbon dioxide and methane), contributing to global warming; air pollution by acidic gases (sulfur dioxide and oxides of nitrogen), contributing to acid rain; pollution due to insecticides;
(m) discuss reasons for conservation of species with reference to maintenance of biodiversity, management
of fisheries and management of timber production;
(n) discuss reasons for recycling materials, with reference to named examples.

16. Development of organisms and continuity of life

16.1 Asexual reproduction
16.2 Sexual reproduction in plants
16.3 Sexual reproduction in humans
16.4 Sexually transmitted diseases
Learning outcomes
Candidates should be able to:
(a) define mitosis as cell division giving rise to genetically identical cells in which the chromosome number
is maintained and state the role of mitosis in growth, repair of damaged tissues, replacement of worn out cells and asexual reproduction;
(b) define asexual reproduction as the process resulting in the production of genetically identical offspring from
one parent and describe one named, commercially important application of asexual reproduction in plants;
(c) define meiosis as a reduction division in which the chromosome number is halved from diploid to haploid;
(d) state that gametes are the result of meiosis (reduction division);
(e) define sexual reproduction as the process involving the fusion of haploid nuclei to form a diploid zygote and the production of genetically dissimilar offspring;
(f)  identify and draw, using a hand lens if necessary, the sepals, petals, stamens and carpels of one, locally
available, named, insect-pollinated, dicotyledonous flower, and examine the pollen grains under a light microscope;
(g) state the functions of the sepals, petals, anthers and carpels;
(h) use a hands lens to identify and describe the anthers and stigmas of one, locally available, named, wind-pollinated flower, and examine the pollen grains under a light microscope;
(i)  outline the process of pollination and distinguish between self-pollination and cross-pollination;
(j)  compare, using fresh specimens, an insect-pollinated and a wind-pollinated flower;
(k) describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (production of endosperm and details of development are not required);
(l)  investigate and describe the structure of a non-endospermic seed in terms of the embryo (radicle, plumule and cotyledons) and testa, protected by the pericarp (fruit wall);
(m) state that seed and fruit dispersal by wind and by animals provides a means of colonising new areas;
(n) describe the external features of one, locally available, named example of a wind-dispersed fruit or seed and of one named example of an animal-dispersed fruit or seed;
(o) investigate and state the environmental conditions that affect germination of seeds: suitable temperature, water and oxygen;
(p) describe the uses of enzymes in the germination of seeds;
(q) identify on diagrams of the male reproductive system and give the functions of the testes, scrotum,
sperm ducts, prostate gland, urethra and penis;
(r)  identify on diagrams of the female reproductive system and give the functions of the ovaries, oviducts, uterus, cervix and vagina;
(s) compare male and female gametes in terms of size, numbers and mobility;
(t)  describe the menstrual cycle, with reference to the alternation of menstruation and ovulation, the natural variation in its length and the fertile and infertile phases of the cycle;
(u) explain the role of hormones in controlling the menstrual cycle (including FSH, LH, progesterone and oestrogen);
(v) describe fertilisation and early development of the zygote simply in terms of the formation of a ball of cells that becomes implanted in the wall of the uterus;
(w) state the function of the amniotic sac and the amniotic fluid;
(x) describe the function of the placenta and umbilical cord in relation to exchange of dissolved nutrients,
gases and excretory products (no structural details are required);
(y) describe the special dietary needs of pregnant women;
(z) describe the advantages of breast milk compared with bottle milk;
(aa) describe the following methods of birth control: natural, chemical (spermicides), mechanical, hormonal and surgical;
(bb) explain that syphilis is caused by a bacterium that is transmitted during sexual intercourse;
(cc) describe the symptoms, signs, effects and treatment of syphilis;
(dd) discuss the spread of human immunodeficiency virus (HIV) and methods by which it may be controlled.

17. Inheritance

17.1 Variation
17.2 Chromosomes and DNA
17.3 Monohybrid inheritance
17.4 Selection
17.5 Genetic engineering
Learning outcomes
Candidates should be able to:
(a) describe the difference between continuous and discontinuous variation and give examples of each;
(b) state that a chromosome includes a long molecule of DNA;
(c) state that DNA is divided up into sections called genes;
(d) explain that genes may be copied and passed on to the next generation;
(e) define a gene as a unit of inheritance and distinguish clearly between the terms gene and allele;
(f) describe complete dominance using the terms dominant, recessive, phenotype and genotype;
(g) describe mutation as a change in the structure of a gene (e.g. sickle cell anaemia) or in the chromosome
number (e.g. 47 in Down’s syndrome instead of 46);
(h) name radiation and chemicals as factors that may increase the rate of mutation;
(i) predict the results of simple crosses with expected ratios of 3:1 and 1:1, using the terms homozygous,
heterozygous, F 1 generation and F 2 generation;
(j) explain why observed ratios often differ from expected ratios, especially when there are small numbers
of progeny;
(k) explain codominance by reference to the inheritance of the ABO blood group phenotypes (A, B, AB, O,
gene alleles I A , I B and I O );
(l) describe the determination of sex in humans (XX and XY chromosomes);
(m) describe variation and state that competition leads to differential survival of organisms, and reproduction
by those organisms best fitted to the environment;
(n) assess the importance of natural selection as a possible mechanism for evolution;
(o) describe the role of artificial selection in the production of economically important plants and animals;
(p) explain that DNA controls the production of proteins;
(q) state that each gene controls the production of one protein;
(r) explain that genes may be transferred between cells (reference should be made to transfer between organisms of the same or different species);
(s) explain that the gene that controls the production of human insulin can be inserted into bacterial DNA;
(t) understand that such genetically engineered bacteria can be used to produce human insulin on a commercial scale;
(u) discuss potential advantages and dangers of genetic engineering.