The menstrual cycle has four stages Stage 1: Day 1 is when the bleeding starts. The uterus lining breaks down and is released. Stage 2: The lining of the uterus builds up again, from day 4 to day 14, into a thick spongy layer of blood vessels ready to receive the...
Sex determination Women have two X chromosomes and men have one X and one Y. The 23rd pair of chromosomes is called the sex chromosomes. When making sperm, the X and Y chromosomes are drawn apart in the first division in meiosis. There’s a 50% chance each sperm cell...
Monoclonal antibodies Monoclonal antibodies: many identical antibodies. These were invented for making large quantities of antibodies for identifying particular substances. A lymphocyte can divide over and again to make identical clones of itself. However, once it...
The kidneys The Kidneys help maintain the internal environment by: Filtering the blood Reabsorbing all the sugar Reabsorbing the dissolved ions needed by the body Reabsorbing as much water as the body needs Releasing urea, excess salts and excess water as urine. Blood...
Microorganism growth Much is done to keep numbers of bacteria in milk as low as possible; the milking equipment is sterilised, the cow’s udders are washed before milking and most milk is cooled rapidly to slow the growth of bacteria. It is then pasteurised. If...
Vaccines Edward Jenner founded the idea of vaccination. He realised that people who got cowpox didn’t get smallpox. In 1796 Jenner took pus from a cowpox blister and rubbed it into the skin of an 8-year-old boy. He got a mild fever but that was all. He did the same...
White blood cells There are two types of white blood cells. Phagocytes and Lymphocytes. They both get rid of pathogens. Phagocytes get rid of pathogens by phagocytosis: Step 1: encounters foreign body or pathogen Step 2: engulfs the foreign body or pathogen Step 3:...
Enzyme Technology Meat contains fibres which are tough if you don’t beat it to break up the fibres. Pineapple juice, which contains enzymes that tenderise the meat, is sometimes added to meat in recipes to break down the protein fibres. Yoghurt production The...
Breeding plants Unfortunately, as the human population grows many people all over the world do not have enough food. The World Health Organisation has said there is a ‘global food security crisis’. Global food security: the ability to produce enough food in the future...
Biofuels Our increasing population also needs more energy for industry, transport and other uses. However, most people agree we need to reduce our use of fossil fuels. Replacements for them are biofuels. Biofuels are fuels that are made from biomass (plants, animals...
Biological rhythms Biological rhythms that happen across one day are circadian rhythms. For example, in human brains there is a timing mechanism called a biological clock which regulates the things that occur in our body over a 24 hour period and can be influenced by...
A GM future Genetically modified maize, soya and cotton are widely grown in both developed and developing countries. Many of these have a gene that makes them resistant to an herbicide. This means crops are not damaged by the chemical but the weeds growing with them...
Photoperiodism This is controlled by plant genes. The way in which living organisms respond to changes in day length. An example of this is deciduous trees as they lose their leaves in winter as the days become shorter. The plants use the change in day length to help...
Plant defences Plants can be attacked by insects or pathogens. If this happens to crops, crop yield can be severely reduced as the plants are eaten, which will increase the price of the crop in the long run. As a result, plants can produce chemicals to protect the...
Enzymes in digestive system Three main types of digestive enzyme: Protease (digests proteins) Carbohydrase (digests carbohydrates) Lipase (digests fats) Digesting carbohydrates Food like bread and pasta are full of large carbohydrates. They simplest carbohydrates are...
Probiotics and prebiotics Functional foods are eaten by people in order to make themselves healthier. Probiotics These contain live bacteria such as Lactobacillus and Bifidobacteria which are ‘friendly’. They are similar to those found naturally in the gut and produce...
Biotechnology Biotechnology: using living organisms (especially microorganisms) to produce useful products (e.g. food, medicines) or to provide people with services (e.g. waste management, water purification). Biomolecule: a chemical or substance produced by a living...
Fermenters Modern biotechnology often involves big steel vessels, called fermenters, in which microorganisms are grown. Inside these fermenters, the microorganisms are provided with exactly the right conditions to encourage them to grown and produce the substances we...
Microorganisms for food In the early 1960s, scientists were looking for cheap sources of protein. They tried cultivating bacteria, fungi and other kinds of microorganisms. Fusarium was the successful fungus found. It is sold commercially as QuornTM. Fusarium is made...
Factors affecting yoghurt making Yoghurt is made from milk by bacteria such as Lactobacillus bulgaricus. The bacteria live on the sugars in the milk. They convert lactose into lactic acid as they aspire anaerobically (glucose à lactic acid) A variety of factors affect...
The heart The heart consists of four chambers and four major blood vessels. Deoxygenated blood goes to the right side and oxygenated blood into the left side. The two sides of the heart are completely separated by the muscular septum. ...
The Digestive System Food contains a lot of large, insoluble molecules that need to be broken down into smaller soluble molecules. This is so they can be absorbed and used by the body. Digestion is the process of breaking down food which takes place in the organ...
Villi These absorb the soluble molecules of food. There are millions of villi covering the interior of the small intestine. Villi massively increase the surface area of the small intestine so more diffusion of substances can take place. Each villus has a good network...
Growth Growth in an organism is the increase in the number of cells and cell size. There are three ways growth can be measured: Size: height, width, length, circumference Wet mass: the mass of the organism including all the water in the body. It can vary from day to...
Fossils and evolution Fossils are the preserved traces of organisms that lived millions of years ago. Fossils are formed in 3 ways: A buried organism in soft material such as clay decays and leaves a cast/imprint of the organism. Footprints can be preserved this way....
Cells make up tissues, organs and systems Tissue: a tissue (e.g. muscle tissue) is a group of similar cells that work together to carry out a particular function. Organ: An organ is a group of different tissues that work together to perform a particular function....