Use SI units (eg kg, g, mg; km, m, mm; kJ, J) and IUPAC chemical nomenclature unless inappropriate
Specialised cell
As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function
Microscopy techniques
Electron microscopy has higher magnification and resolving power than a light microscope
Electron microscopy enables biologists to see and understand many more sub-cellular structures
Calculating magnification
Magnification = size of image / size of real object
The nucleus of a cell contains chromosomes made of DNA molecules, and each chromosome carries a large number of genes
In body cells the chromosomes are normally found in pairs
Cell cycle and mitosis
1. Genetic material is doubled and then divided into two identical cells
2. Cell grows and increases sub-cellular structures
3. DNA replicates to form two copies of each chromosome
4. One set of chromosomes is pulled to each end of the cell and the nucleus divides
5. Cytoplasm and cell membranes divide to form two identical cells
Stem cell
An undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation
Stem cell functions
In embryos
In adult animals
In the meristems in plants
Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells
Stem cells from adult bone marrow can form many types of cells including blood cells
Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant
Stem cell use
May help treat conditions such as diabetes and paralysis
Therapeutic cloning
An embryo is produced with the same genes as the patient, so stem cells from the embryo are not rejected by the patient's body and may be used for medical treatment
The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections
Stem cells from meristems in plants can be used to produce clones of plants quickly and economically
Uses of plant stem cell cloning
Protect rare species from extinction
Produce large numbers of identical crop plants with special features such as disease resistance
Diffusion
The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
Substances transported by diffusion
Oxygen and carbon dioxide in gas exchange
Waste product urea from cells into the blood plasma for excretion in the kidney
Factors affecting rate of diffusion
Concentration gradient
Temperature
Surface area of the membrane
A single-celled organism has a relatively large surface area to volume ratio, allowing sufficient transport of molecules into and out of the cell to meet the needs of the organism
In multicellular organisms, surfaces and organ systems are specialised for exchanging materials to allow sufficient molecules to be transported into and out of cells for the organism's needs</b>
The effectiveness of an exchange surface is increased by having a large surface area, a thin membrane to provide a short diffusion path, an efficient blood supply, and (for gaseous exchange) being ventilated
Osmosis
The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
Active transport
Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient), requiring energy from respiration
Processes of transport into and out of cells
Diffusion
Osmosis
Active transport
Cells are the basic building blocks of all living organisms
Tissue
A group of cells with a similar structure and function
Organ
Aggregations of tissues performing specific functions
Organ system
Organs organised to work together to form organisms
The digestive system is an organ system in which several organs work together to digest and absorb food
Enzymes catalyse specific reactions in living organisms due to the shape of their active site
Lock and key theory
A simplified model to explain enzyme action
Digestive enzymes
Carbohydrases (break down carbohydrates to simple sugars)
Amylase (breaks down starch)
Proteases (break down proteins to amino acids)
Lipases (break down lipids to glycerol and fatty acids)
The products of digestion are used to build new carbohydrates, lipids and proteins, and some glucose is used in respiration
Bile
Made in the liver and stored in the gall bladder, it is alkaline to neutralise hydrochloric acid from the stomach and emulsifies fat to form small droplets which increases the surface area and rate of fat breakdown by lipase
The heart is an organ that pumps blood around the body in a double circulatory system, with the right ventricle pumping blood to the lungs and the left ventricle pumping blood around the rest of the body
Blood vessels associated with the heart
Aorta
Vena cava
Pulmonary artery
Pulmonary vein
Coronary arteries
The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker, and artificial pacemakers are electrical devices used to correct irregularities in the heart rate