Organisation

• Specialised cells


  As an organism develops, cells differentiate to form different types of cells.As a cell differentiates:- it may change shape- different sub-cellular structures develop to let it to carry out a specific function.Include cells such as sperm, nerve and muscle cells.

  
• Sperm cell

  Tail: to propel the sperm to fertilise the egg.Mitochondria: sperm have many of these cell components, which are the major site of respiration, to provide energy for their journey.Nucleus: contains only one set of the genetic material.Acrosome: contains enzymes to allow the sperm to penetrate the outer layer of the egg.

  
• Muscle cell

  Contains:- nucleus- many mitochondria for energy- protein fibres that can contract

  
• Motor neurone

  Contains:- dendrites- cell body- axon- sheath (acts as an insulator)

  
• Xylem cell

  The cells are arranged end to end but the end walls break down to form hollow tubes.The cell wall of the cell is strengthened by a substance called lignin.

  
• Phloem cell

  The end wall of the cells allow sugars through but support the tubes.The cells are arranged end to end into tubes.Contain companion cells.

  
• Root hair cell


  Lots of mitochondria for active transport of minerals.Long projection to increase the surface area to absorb water and minerals.

  
• Tissue

  A group of cells with a similar structure and function, which all work together to do a job.

  
• Examples of tissues

  - muscle tissue contracts to produce movement- glandular tissue produces substances such as enzymes and hormones- epithelial tissue covers organs
• Organs


  Groups of different tissues, which all work together to perform a specific job.Each may contain several tissues.

  
• Stomach


  An organ that contains:- muscle tissue that contracts to churn the contents- glandular tissue to produce digestive juices- epithelial tissue to cover the outside and inside of the stomach

  
• Organ systems


  Groups of organs working together to do a particular job.The digestive system is an example of it, in which several organs work together to digest and absorb food.Lots of them work together to make an organism.

  
• The digestive system

  Includes:- mouth- oesophagus - pushes food down to stomach- liver- stomach- pancreas- gall bladder- large intestine- small intestine- rectum- anus

  
• Enzymes

  They are biological catalysts - they speed up chemical reactions in living organisms.They have a number of properties:- they are all large proteins.- each of it catalyses a specific reaction.

  
• Active site

  A space within the protein molecule of the enzyme.

  
• Optimum


  Where enzymes work best at a specific temperature and pH.
• Lock and key theory

  A model used to explain how enzymes work: the chemical that reacts is called the substrate (key) and it fits into the enzyme's active site (lock).

  
• Denaturing


  Where high temperature and extremes of pH make enzymes change shape.The enzyme cannot work once it has been denatured, because the substrate cannot fit into the active site - the lock and key no longer fit together.

  
• Digestive enzymes

  Produced by specialised cells in glands and in the lining of the gut:- the enzymes pass out of the cells into the digestive system.- they come into contact with food molecules.- they catalyse the breakdown of large insoluble food molecules into smaller soluble molecules.
• Examples of digestive enzymes

  Protease: digest proteinsLipase: digest lipids (fats and oils)Carbohydrase: digest carbohydratesThese are to produce smaller molecules that can be easily absorbed into the bloodstream.
• Amylase


  - is produced in the salivary glands and the pancreas- is a carbohydrase that breaks down starch into sugar (maltose).Used to build new carbohydrates.
• Protease


  - is produced in the stomach, pancreas and small intestine- breaks down proteins into peptides or amino acids.Used to build new proteins.
• Lipase


  - is produced in the pancreas and small intestine- breaks down lipids (fats) into fatty acids and glycerol.Used to build new lipids.
• Bile


  It is a liquid 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, increasing the surface area for enzymes to act on.The alkaline conditions and large surface area increase the rate at which fat is broken down by lipase.Does not contain any enzymes, so it does not digest fat molecules. It just breaks up fat droplets into smaller ones.

  
• Good health


  A state of physical and mental wellbeing.

  
• Disease


  Caused by part of the body not working properly.This can affect physical and / or mental health.Can be divided into two main types:- communicable- non-communicable
• Examples of how different diseases can interact with each other

  - viruses infecting cells can be the trigger for cancers, such as cervical cancer.- diseases of the immune system mean that an individual is more likely to catch infectious diseases, e.g. people with HIV are more likely to get tuberculosis.- immune reactions triggered by a pathogen can cause allergies, such as skin rashes and asthma.- if a person is physically ill, this can lead to depression and mental illness.- poor diet, stress, and difficult life situations can increase the likelihood of developing certain diseases.
• Casual mechanism


  The process by which a cause brings about an effect.
• Risk factor


  They make it more likely that a person will develop a certain disease.Non-communicable diseases are often caused by the interaction of a number of factors.They can be:- aspects of a person's lifestyle- substances in the person's body or environment

  
• Examples of diseases and their proven risk factors

  Cardiovascular disease: lack of exercise / smoking / high intake of saturated fatType 2 diabetes: ObesityLiver and brain damage: Excessive alcohol intakeLung diseases, including lung cancer: SmokingSkin cancer: Ionising radiation, e.g. UV lightLow birth weight in babies: Smoking during pregnancyBrain damage in babies: Excessive alcohol intake during pregnancy
• Coronary heart disease

  Layers of fatty material build up inside the coronary arteries and narrow them.Treatment for it include:- stents to keep the coronary arteries open- statins to reduce blood cholesterol levels and slow down the rate at which fatty materials build up
• Heart valve disease


  In some people, heart valves may become faulty, developing a leak or preventing the valve from opening fully.Faulty valves can be replaced using biological or mechanical valves.
• Treatments of heart failure

  - a donor heart, or heart and lungs, can be transplanted- artificial hearts can be used to keep patients alive while waiting for a heart transplant or to allow the heart to recover- drugs such as clot-busting enzymes or warfarin are sometimes used to treat recovering patients, while statins can be given to lower cholesterol levels
• Cancer


  It is a non-communicable disease,Scientists have identified lifestyle risk factors for some types of cancer, e.g. smoking, obesity, common viruses and UV exposure.It is caused by uncontrolled cell division. This can form masses of cells called tumours.There are two main types of tumours:- benign tumours do not spread around the body- malignant tumours spread, in the blood, to different parts of the body where they form secondary tumours

  
• Epidermis


  Covers the outer surfaces of the plant for protection.
• Palisade mesophyll


  The main site of photosynthesis in the leaf.

  
• Spongy mesophyll

  Air spaces between the cells allow gases to diffuse through the leaf.

  
• Xylem vessels

  Transports water and minerals through the plant, from roots to leaves. Also supports the plant.

  
• Phloem vessels


  Transports dissolved food materials through the plant.

  
• Meristem tissue


  Found mainly at the tips of the roots and shoots, where it can produce new cells for growth.