Cytokinesis is the division of the cytoplasm of a cell that follows nuclear division (karyokinesis) to form two separate daughter cells. In animal cells it occurs by the formation of a cleavage furrow that deepens and constricts the cell from the outside inward. In plant cells, because of the rigid cell wall, it occurs by the formation of a cell plate that grows from the centre outward to divide the cell.

Diffusion is the net movement of molecules of a substance from a region of higher concentration to a region of lower concentration until they are evenly distributed; it does not require a membrane or energy. Osmosis is the movement of solvent (water) molecules from a region of higher water potential to a region of lower water potential across a semipermeable membrane. Its two types are endosmosis (water entering the cell) and exosmosis (water leaving the cell).

Plasmolysis is the shrinkage of the protoplasm (cell contents) away from the cell wall when a plant cell is placed in a hypertonic solution, due to loss of water by exosmosis. Turgor pressure is the pressure exerted by the cell contents (the water-filled protoplast) against the cell wall when the cell is fully turgid (swollen with water); it keeps herbaceous plant parts firm and erect.

Macronutrients are mineral elements required by plants in large amounts (more than 10 millimole per kg of dry matter); they include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. Micronutrients (trace elements) are required in very small amounts (less than 10 millimole per kg of dry matter); they include iron, manganese, copper, zinc, boron, molybdenum and chlorine.

Biological nitrogen fixation is the conversion of atmospheric nitrogen (N2) into ammonia (a usable form) by living organisms using the enzyme nitrogenase. Rhizobium is a symbiotic bacterium that lives in the root nodules of leguminous plants (such as pea and gram); it fixes atmospheric nitrogen into ammonia, which the plant uses to make amino acids, while the plant provides the bacterium with food and shelter.

Photosynthesis is the process by which green plants and some other organisms synthesise their own food (glucose) from carbon dioxide and water using light energy trapped by chlorophyll, releasing oxygen as a by-product. Overall equation: 6CO2 + 12H2O -> (in the presence of light and chlorophyll) C6H12O6 + 6H2O + 6O2. It takes place in the chloroplast.

6CO2 + 12H2O -> C6H12O6 + 6H2O + 6O2

In non-cyclic photophosphorylation both photosystems (PS I and PS II) take part, the electron travels in a one-way path, water is split (releasing oxygen), and both ATP and NADPH are produced. In cyclic photophosphorylation only PS I is involved, the electron is recycled back to the same photosystem, no water is split (so no oxygen is released) and only ATP is produced (no NADPH).

The main photosynthetic pigments are chlorophyll a (the primary pigment, bluish-green), chlorophyll b (yellowish-green) and the carotenoids (carotenes and xanthophylls, which are yellow to orange). Chlorophyll a is the chief pigment that traps light and drives the light reaction. Chlorophyll b and the carotenoids are accessory pigments: they absorb light at wavelengths that chlorophyll a cannot and pass the energy to chlorophyll a, and carotenoids also protect chlorophyll from harmful photo-oxidation.

Blackman's law of limiting factors states that when a process is affected by more than one factor, its rate is limited by the factor that is nearest to its minimum (the limiting factor); it is that factor which directly determines the rate at that moment. The main factors affecting photosynthesis are external factors - light intensity, concentration of carbon dioxide, temperature and water - and internal factors such as the amount of chlorophyll.

Respiration is the process of breaking down food (glucose) to release energy stored as ATP. Aerobic respiration occurs in the presence of oxygen, completely oxidises glucose to carbon dioxide and water, and releases a large amount of energy (about 38 ATP per glucose). Anaerobic respiration occurs in the absence of oxygen, incompletely breaks down glucose into products such as ethanol or lactic acid, and releases only a small amount of energy (2 ATP per glucose).

C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy

The Krebs cycle (also called the citric acid cycle or TCA cycle) is the stage of aerobic respiration in which acetyl CoA (formed from pyruvic acid) is completely oxidised. It takes place in the matrix of the mitochondria. Each turn releases carbon dioxide and transfers energy to the reduced coenzymes NADH and FADH2, along with a small amount of ATP (GTP); the NADH and FADH2 then pass electrons to the electron transport chain to make more ATP.

Fermentation is the incomplete breakdown of glucose (anaerobic respiration) that occurs without oxygen. In alcoholic fermentation, pyruvic acid is converted into ethanol and carbon dioxide (for example by yeast), which is used in brewing and baking. In lactic acid fermentation, pyruvic acid is converted into lactic acid (for example in our muscles during vigorous exercise and by Lactobacillus in curd formation). Both release only a small amount of energy.

The respiratory quotient (RQ) is the ratio of the volume of carbon dioxide released to the volume of oxygen consumed during respiration. RQ = volume of CO2 evolved / volume of O2 consumed. For carbohydrates, which are completely oxidised, the value of RQ is 1. For fats the RQ is less than 1 (about 0.7) and for organic acids it is greater than 1.

RQ = CO2 evolved / O2 consumed

Growth is an irreversible and permanent increase in the size, mass or number of cells of an organism or its parts. In plants, growth has three phases along the growing region: (1) the phase of meristematic (cell division) activity at the tips of roots and shoots; (2) the phase of elongation, in which cells just behind the meristem enlarge; and (3) the phase of maturation, in which the enlarged cells differentiate and attain their final form and function.

Abscisic acid (ABA) is a growth inhibitor: it promotes dormancy of seeds and buds, causes closure of stomata during water stress, and promotes abscission (shedding) of leaves and fruits; it is often called the stress hormone. Ethylene is a gaseous hormone that promotes the ripening of fruits, causes ageing and abscission of leaves and flowers, and breaks the dormancy of seeds and buds.

Photoperiodism is the response of plants to the relative lengths of day and night (the photoperiod), especially with regard to flowering; on this basis plants are grouped as short-day, long-day and day-neutral plants. Vernalisation is the promotion of flowering in certain plants by exposing them to a period of low temperature (cold treatment); it prevents premature flowering and enables the plant to flower at the proper time.

The human alimentary canal is a continuous tube from the mouth to the anus. In sequence it consists of: the mouth (buccal cavity), pharynx, oesophagus, stomach, small intestine (duodenum, jejunum and ileum) and large intestine (caecum, colon and rectum), ending at the anus. Associated digestive glands are the salivary glands, liver and pancreas.

The dental formula of an adult human is 2123/2123, which represents, for one half of each jaw, 2 incisors, 1 canine, 2 premolars and 3 molars. Since this is for one half, the total number of teeth is 32. The four types of teeth are incisors (for cutting/biting), canines (for tearing), premolars and molars (for grinding and chewing). Human teeth are thecodont (fixed in sockets), diphyodont (two sets in life) and heterodont (different types).

2123/2123 (total 32 teeth)

Most of the absorption of digested food takes place in the small intestine, mainly the ileum. Its inner surface is highly folded and bears numerous finger-like projections called villi, and each villus has microvilli on its cells. These greatly increase the surface area for absorption. Each villus contains a network of blood capillaries and a lymph vessel (lacteal); simple sugars and amino acids pass into the blood capillaries while fatty acids and glycerol enter the lacteals.

Bile is a greenish-yellow fluid secreted by the liver and stored in the gall bladder; it is released into the duodenum. Although it contains no digestive enzymes, bile salts emulsify fats, that is, they break large fat globules into tiny droplets, thereby increasing their surface area for the action of the enzyme lipase. Bile also makes the medium alkaline (neutralising the acidic food from the stomach) so that intestinal enzymes can work.