whole of biology

• 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 cells


  • 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
• Treatment with stem cells may be able to help conditions such as diabetes and paralysis
• In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient's body so they may be used for medical treatment
• Potential risks of using stem cells

  • Transfer of viral infection
  • Ethical or religious objections
• Stem cells from meristems in plants can be used to produce clones of plants quickly and economically
• Rare species can be cloned to protect from extinction
• Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers
• 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 in and out of cells by diffusion

  • Oxygen
  • Carbon dioxide
  • Urea
• Factors affecting the rate of diffusion

  • Concentration gradient
  • Temperature
  • Surface area of the membrane
• A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism
• 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). This requires energy from respiration
• Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth
• Active transport allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration
• Cells


  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 example of 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
• Sites of production and action of digestive enzymes

  • Amylase
  • Proteases
  • Lipases
• Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream
• Types of digestive enzymes

  • Carbohydrases (break down carbohydrates to simple sugars)
  • Proteases (break down proteins to amino acids)
  • Lipases (break down lipids (fats) to glycerol and fatty acids)
• The products of digestion are used to build new carbohydrates, lipids and proteins. 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. It also emulsifies fat to form small droplets which increases the surface area. The alkaline conditions and large surface area increase the rate of fat breakdown by lipase
• The heart is an organ that pumps blood around the body in a double circulatory system. The right ventricle pumps blood to the lungs where gas exchange takes place. The left ventricle pumps blood around the rest of the body
• Blood vessels associated with the heart

  • Aorta
  • Vena cava
  • Pulmonary artery
  • Pulmonary vein
  • Coronary arteries
• Components of the lungs

  • Trachea
  • Bronchi
  • Alveoli
  • Capillary network surrounding the alveoli
• The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker. Artificial pacemakers are electrical devices used to correct irregularities in the heart rate
• Types of blood vessels

  • Arteries
  • Veins
  • Capillaries
• Blood


  A tissue consisting of plasma, in which the red blood cells, white blood cells and platelets are suspended
• In coronary heart disease layers of fatty material build up inside the coronary arteries, narrowing them. This reduces the flow of blood through the coronary arteries, resulting in a lack of oxygen for the heart muscle. Stents are used to keep the coronary arteries open. Statins are widely used to reduce blood cholesterol levels which slows down the rate of fatty material deposit
• In some people heart valves may become faulty, preventing the valve from opening fully, or the heart valve might develop a leak. Students should understand the consequences of faulty valves. Faulty heart valves can be replaced using biological or mechanical valves
• In the case of heart failure a donor heart, or heart and lungs can be transplanted. Artificial hearts are occasionally used to keep patients alive whilst waiting for a heart transplant, or to allow the heart to rest as an aid to recovery
• Health


  The state of physical and mental well-being