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.

Breathing is the physical process of taking in oxygen-rich air (inspiration) and giving out carbon dioxide-rich air (expiration). The human respiratory system consists, in sequence, of the external nostrils, nasal cavity, pharynx, larynx, trachea (windpipe), two bronchi, bronchioles and finally the alveoli of the lungs, where the exchange of gases takes place.

Oxygen is transported mainly (about 97 percent) by binding to the haemoglobin of red blood cells, forming oxyhaemoglobin; a small amount is dissolved in the plasma. Carbon dioxide is transported in three ways: mostly (about 70 percent) as bicarbonate ions in the plasma, about 20 to 25 percent bound to haemoglobin as carbaminohaemoglobin, and a small amount dissolved in the plasma.

Tidal volume (TV) is the volume of air breathed in or out during a normal (quiet) breath, about 500 mL. Residual volume (RV) is the volume of air that remains in the lungs even after a forceful expiration, about 1100 to 1200 mL. Vital capacity (VC) is the maximum volume of air that a person can breathe out after the deepest possible inspiration (it equals tidal volume plus inspiratory reserve volume plus expiratory reserve volume).

VC = TV + IRV + ERV

Blood is a fluid connective tissue made of a liquid plasma (about 55 percent) and formed elements (about 45 percent). Plasma carries dissolved nutrients, wastes, hormones and proteins. The formed elements are: red blood cells (erythrocytes), which carry oxygen using haemoglobin; white blood cells (leucocytes), which defend the body against infection (immunity); and platelets (thrombocytes), which help in the clotting of blood.

The ABO blood group system classifies human blood into four groups - A, B, AB and O - based on the presence or absence of two antigens (A and B) on the surface of red blood cells and the corresponding antibodies in the plasma. The Rh factor is another antigen (Rh antigen or D antigen) first found in rhesus monkeys; people who have it on their red cells are Rh-positive and those who lack it are Rh-negative. Blood groups must be matched before transfusion to avoid clumping (agglutination).

(1) Arteries carry blood away from the heart (usually oxygenated, except the pulmonary artery), whereas veins carry blood towards the heart (usually deoxygenated, except the pulmonary vein). (2) Arteries have thick, elastic muscular walls and a narrow lumen and lack valves, whereas veins have thinner walls and a wider lumen and possess valves that prevent the backflow of blood.

These terms describe the main nitrogenous waste excreted by animals. Ammonotelic animals excrete ammonia, which is highly toxic and needs a lot of water (e.g. many bony fishes and aquatic amphibians). Ureotelic animals excrete urea, which is less toxic and needs less water (e.g. mammals including humans, and adult amphibians). Uricotelic animals excrete uric acid, which is least toxic and almost insoluble, needing very little water (e.g. birds, reptiles and insects).

Haemodialysis is an artificial method of removing nitrogenous wastes such as urea from the blood using a machine (an artificial kidney) when a person's kidneys have failed. The patient's blood is passed through tubes made of a semipermeable membrane that are surrounded by a dialysing fluid; wastes diffuse out of the blood into the fluid while useful substances are retained, and the cleaned blood is returned to the body. It is used to keep patients with kidney failure alive.

The two main contractile proteins of a muscle are actin (the thin filament) and myosin (the thick filament). A muscle fibre contains many myofibrils, each made of repeating units called sarcomeres. A sarcomere is the region of a myofibril between two adjacent Z-lines and is the basic functional (contractile) unit of a striated muscle; it contains an arrangement of actin and myosin filaments whose sliding produces contraction.

A joint is the point of contact between two or more bones (or between bone and cartilage) that allows movement or gives support. Three types of freely movable (synovial) joints are: (1) ball-and-socket joint, allowing movement in all directions, e.g. the shoulder and hip joint; (2) hinge joint, allowing movement in one plane, e.g. the elbow and knee; and (3) pivot joint, allowing rotational movement, e.g. between the atlas and axis vertebrae of the neck.

The human brain has three main parts: the forebrain, midbrain and hindbrain. The cerebrum (part of the forebrain) is the centre for thinking, memory, intelligence and voluntary actions. The cerebellum (part of the hindbrain) maintains balance and coordinates precise voluntary movements. The medulla oblongata (part of the hindbrain) controls involuntary vital activities such as heartbeat, breathing, blood pressure, swallowing and vomiting.