Organisation

• Cells are the basic building blocks of all living organisms.

  A tissue is a group of cells with a similar structure and function.

  Organs are aggregations of tissues performing specific functions.

  Organs are organised into organ systems, which work together to form organisms.
• Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.
• Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down starch.
• 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 is 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.
• Benedict’s test for sugars; iodine test for starch; and Biuret reagent for protein.
• 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.
• 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.
• The body contains three different types of blood vessel: • arteries

  • veins

  • capillaries.
• Blood is 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.
• Diseases, both communicable and non-communicable, are major causes of ill health. Other factors including diet, stress and life situations may have a profound effect on both physical and mental health.
• Different types of disease may interact.

  • Defects in the immune system mean that an individual is more likely to suffer from infectious diseases.

  • Viruses living in cells can be the trigger for cancers.

  • Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma.

  • Severe physical ill health can lead to depression and other mental illness.
• A causal mechanism has been proven for some risk factors, but not in others.

  • The effects of diet, smoking and exercise on cardiovascular disease.

  • Obesity as a risk factor for Type 2 diabetes.

  • The effect of alcohol on the liver and brain function.

  • The effect of smoking on lung disease and lung cancer.

  • The effects of smoking and alcohol on unborn babies.

  • Carcinogens, including ionising radiation, as risk factors in cancer.
• Benign tumours are growths of abnormal cells which are contained in one area, usually within a membrane. They do not invade other parts of the body.
• Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours
• Plant tissues include:

  • epidermal tissues

  • palisade mesophyll

  • spongy mesophyll

  • xylem and phloem

  • meristem tissue found at the growing tips of shoots and roots.
• The roots, stem and leaves form a plant organ system for transport of substances around the plant.
• Root hair cells are adapted for the efficient uptake of water by osmosis, and mineral ions by active transport.
• Xylem tissue transports water and mineral ions from the roots to the stems and leaves. It is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream.
• The role of stomata and guard cells are to control gas exchange and water loss.
• Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. The movement of food molecules through phloem tissue is called translocation.
• Phloem is composed of tubes of elongated cells. Cell sap can move from one phloem cell to the next through pores in the end walls.