#165 Summary of Genetic technology

 1 Gene technology involves altering the genes in an organism, which is then said to be genetically modifi ed.

 2 The usual way of genetically modifying bacteria is to insert a plasmid containing the desired gene into them.

#154 Summary Biodiversity and conservation

1 All living organisms may be classified into one of the five kingdoms: prokaryotes, protoctists, fungi, plants and animals.

2 Biodiversity includes the range of habitats (environments) and species in an area, and the genetic diversity within a species.

#143 Summary of Selection and Evolution

1 Genetic variation within a population is the raw material on which natural selection can act. 

2 Meiosis, random mating and the random fusion of gametes produce genetic variation within populations of sexually reproducing organisms. Variation is also caused by the interaction of the environment with genetic factors, but such environmentally induced variation is not passed on to an organism’s off spring. The only source of new alleles is mutation. 

#136 Summary of Inherited change

1 Meiosis consists of two divisions. The first division, meiosis I, separates the homologous chromosomes, so that each cell now has only one of each pair. The second division, meiosis II, separates the chromatids of each chromosome. Meiotic division therefore produces four cells, each with one complete set of chromosomes.

#127 Summary of Homeostasis and Co-ordination

 1 Animals and plants have internal communication systems that allow information to pass between different parts of their bodies, and so help them to respond to changes in their external and internal environments.

 2 Mammals keep their internal environment relatively constant, so providing steady and appropriate conditions within which cells can carry out their activities. This is known as homeostasis.

#106 Summary of Photosynthesis

1 In photosynthesis, light energy is absorbed by chlorophyll pigments and converted to chemical energy, which is used to produce complex organic molecules.

 2 In the light-dependent reactions, water is split by photolysis to give hydrogen ions, electrons and oxygen. The hydrogen ions and electrons are used to reduce the carrier molecule, NADP, and the oxygen is given off as a waste product.

#97 Summary of Energy and Respiration

1 Organisms must do work to stay alive. The energy input necessary for this work is either light, for photosynthesis, or the chemical potential energy of organic molecules. Work includes anabolic reactions, active transport and movement. Some organisms, such as mammals and birds, use thermal energy released from metabolic reactions to maintain their body temperature. 

#76 Summary of Practical Skills

1 In an experiment investigating the effect of one variable on another, the independent variable is the one that you change and the dependent variable is the one that you measure. All other variables should be controlled (kept constant).

# 67 Summary of Ecology

1 A habitat is a place where an organism lives. The niche of an organism is the role that it plays in the community.

2 A population is a group of organisms of the same species, living in the same place at the same time, that can interbreed with one another. A community is all the organisms, of all the diff erent species, living in the same place at the same time.

# 63 Summary of Immunity

1 Phagocytes and lymphocytes are the cells of the immune system.

2 The diagram shows how to recognise phagocytes and lymphocytes in microscope slides and photomicrographs of blood.

# 56 Summary of Infectious diseases and Antibiotics

1 The term disease is defined as a disorder or illness that disrupts the normal functioning of the body or mind. Infectious diseases are caused by organisms known as pathogens that invade the body. Non-infectious diseases are all other diseases that are not caused by pathogens. There are many categories of non-infectious diseases including genetic diseases and deficiency diseases, which are caused by malnutrition.

#53 Summary of Smoking

1 Tobacco smoke contains tar, carbon monoxide and nicotine.

 2 Tar settles on the epithelium lining the bronchi and bronchioles and stimulates inflammation, an increase in the secretion of mucus and an accumulation of phagocytes from the blood.

#51 Summary of Gas exchange

1 Multicellular organisms often have surfaces that are specialised to allow exchange of gases to take place between their bodies and the environment. Alveoli in the lungs form the gas exchange surface in mammals.

#48 Summary of The mammalian heart

 1 The human heart, like that of all mammals, has two atria and two ventricles. Blood enters the heart by the atria and leaves from the ventricles. A septum separates the right side of the heart, which contains deoxygenated blood, from the left side, which contains oxygenated blood.

 2 Semilunar valves at the entrances to the blood vessels that leave the heart (aorta and pulmonary
artery) prevent back flow of blood into the heart, and atrioventricular valves prevent backflow of blood from ventricles into the atria.

#47 Summary of The mammalian transport system

 1. Blood is carried away from the heart in arteries, passes through tissues in capillaries, and is returned to the heart in veins. Blood pressure drops gradually as it passes along this system.

2. Arteries have thick, elastic walls, to allow them to withstand high blood pressures and to smooth out the pulsed blood flow. Capillaries are only just wide enough to allow the passage of red blood cells, and have very thin walls to allow effi cient and rapid transfer of materials between blood and cells. Veins have thinner walls than arteries and possess valves to help blood at low pressure flow back to the heart.

#42 Summary of Transport in multicellular plants

1. Multicellular organisms with small surface area to volume ratios need transport systems.

2. Water and mineral salts are transported through a plant in xylem vessels. Movement of water is a  passive process in which the water moves down a water potential gradient from soil to air.

#37 Summary of Genetic control

1. DNA and RNA are polynucleotides, made up of long chains of nucleotides.

2. A nucleotide contains a pentose sugar, a phosphate group and a nitrogen-containing base. In RNA the sugar is ribose, and in DNA it is deoxyribose.

#32 Summary of Cell and Nuclear division

1. Growth of a multicellular organism is a result of parent cells dividing to produce genetically identical daughter cells.

2. During cell division the nucleus divides first, followed by division of the whole cell.

#27 Summary of Cell membrane

1 The basic structure of a membrane is a 7 nm thick phospholipid bilayer with protein molecules
spanning the bilayer or within one or other layer. Phospholipids and some proteins move within the
layers. Hence the structure is described as a fluid mosaic – the scattered protein molecules resemble pieces of a mosaic.

#22 Summary of Enzymes

1  Enzymes are globular proteins which catalyse metabolic reactions.
2  Each enzyme has an active site with a specific shape, into which the substrate molecule or molecules fit precisely. This is the lock and key hypothesis – the substrate is compared with a key which fits precisely into the lock of the enzyme.