Human activity and the Environment Rapidly growing population The population of the world is growing exponentially which means it is growing very quickly. This is mostly due to modern medicine, making people live longer and more babies to survive at birth. It is also...
Physical and Chemical barriers These are both harnessed by the body to stop pathogens getting in. Physical barriers Skin: Outer layer skin cells contain keratin which makes the skin very effective at protecting against microorganisms. If damaged, blood clots can seal...
Food webs Interdependence: When organisms in an area depend on each other for food. All organisms require food to survive. Some organisms are producers and make their own food, such as green plants, and the rest get their food from other organisms. They are either...
Indicator species An indicator species is an organism whose presence, absences or abundance reflects a specific environmental condition. Indicator species can signal a change in the biological condition of a particular ecosystem and thus may be used to diagnose the...
The Carbon Cycle • The Carbon Cycle: A sequence of processes by which carbon moves from the atmosphere, through living and dead organisms, into sediments and into the atmosphere again. • The only way carbon dioxide is removed from the atmosphere is by photosynthesis –...
The Nitrogen Cycle The Nitrogen Cycle: A sequence of processes by which nitrogen moves from the atmosphere through living and dead organisms, into the soil and back to the atmosphere. There are four main types of bacteria involved in the Nitrogen Cycle: Decomposer...
Insulin and Diabetes Insulin and glucagon control blood sugar levels. Insulin reduces glucose in the blood and glucagon converts glycogen (a store of glucose in the liver) back into glucose. Glucose is added into the body through foods containing carbohydrates....
Uses of plant hormones Selective weedkillers Artificial auxin is used as a selective weedkiller as it makes plants with broad leaves, like dandelions and daisies grow out of control and die. This means plants with narrow leaves, such as wheat and grass, are...
Effects of alcohol Short term effects Alcohol slows down reactions because it is a depressant. Being drunk can lead to blurred vision (making it more difficult to do simple tasks) and can lower inhibitions – people may do things they normally wouldn’t. The more...
Drugs A drug is a chemical substance that changes the way in which the body works, including our behaviour. Some drugs particularly affect the central nervous system and change our psychological behaviour. There are different types of drugs: Narcotic: is a drug that...
Ethics and organ transplants If an organ is severely damage it can be replaced by a donated natural organ. Many people die every year waiting for transplants so the doctors need to decide carefully who to operate on. There is a shortage of organ donors in the UK. Some...
Infectious diseases Pathogens are microorganisms that cause disease. They include bacteria, protozoa, fungi and all viruses. Pathogens are spread in different ways: Water: Water may contain bacteria such as those that cause cholera. Food: Food may contain food...
The Nervous System A stimulus is a change in the environment that you may need to react to. We have five sense organs: eyes, ears, nose, tongue and skin. They all contain different receptors which are groups of cells sensitive to a stimulus. They change stimulus...
Tropisms Tropism: a growth movement in response to a stimulus. Plants grow towards or away from stimuli. A growth movement towards a stimulus is called a positive tropism. A growth movement away from a stimulus is called a negative tropism. Light; phototropism...
Reflexes Reflexes have to be quick and they are so because they are automatic. The message of a reflex does not go up the brain which is why they are involuntary. Many reflexes occur naturally such as accommodation and sneezing but some can be learned e.g. conditional...
Punnett squares and family pedigrees Specific genetic disorders Genetic disorders are diseases which are caused by faulty alleles. The allele for sickle cell anaemia is recessive so two copies are needed to suffer from the illness. Sickle Cell Anaemia is bad as the...
Hormones and Nerves Hormones and Nerves Hormones Hormones are chemical messengers which travel the blood to activate target cells. Hormones are released directly into the blood stream and are carried around the body until they reach their target organ/cells. The...
Homeostasis Conditions in our body need to be maintained and controlled so cells can function properly. For example: Osmoregulation: This is the regulation of water content. A balance needs to be kept between water gained and water lost. Thermoregulation: This is the...
Adaptions Deep under the surface of the sea, conditions are hard to live in. Food is scarce due to lack of sun, thus lack of photosynthesis, and thus organisms survive on scraps that sink down from above. Some animals have adapted to living in the deep ocean: Some...