Stem cells A stem cell is an undifferentiated cell of an organism which can produce more cells of the same type. Certain other cells can arise from stem cells when they differentiate. Stem cells can be found in embryos, in adult animals and in the meristems in plants. Use of embryonic stem cells for research Against Many people believe it is morally wrong to experiment on embryos (even those grown in a laboratory) as all embryos could potentially develop into a baby. Stem cells are cultivated using nutrients from animals sources that could carry diseases that could be passed onto humans. People who receive transplants through stem cell therapy could be infected with viruses. Stem cells may turn cancerous. For Embryos from which stem cells are taken are grown in laboratories and are only a few days old, many people see them as a microscopic ball of cells. Embryos provide the most useful stem cells as they are non-specialised, this means they can become any type of specialised cell Stem cells may be able to treat many diseases and conditions in the future Stem cells act as a repair kit for damaged tissues 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. Folded membrane to increase surface area for diffusion of soluble food molecules. Lots of mitochondria to provide energy from respiration for active transport of glucose. Nucleus containing chromosomes. Epithelial cell in small Diffusion Osmosis Active transport Diffusion is the spreading out of particles of any substance in solution or particles of gas. Diffusion results in a net movement from an area of higher concentration to an area of lower concentration. The rate of diffusion is affected by Difference in concentrations (concentration gradient) Temperature Surface area of the membrane Oxygen and carbon dioxide are transported in and out of cells by diffusion during gas exchange. Passive process no energy required. Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane. The water potential of pure water is 0 kpa. Water potentials of solutions have negative values e.g.. -200 kpa Water may move across cell membranes via osmosis. Passive process no energy required. Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants need these mineral 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 is used for cell respiration. Active transport requires energy from respiration.
Cells A tissue Organs Organ systems Principles of organisation The basic building blocks of all living organisms. A group of cells with similar structure and function. Groups of tissues performing specific functions. Groups of organs which work together to form organisms. The human digestive system Bile is made in the liver and stored in the gall bladder. Bile is not an enzyme but it is an alkaline solution that neutralises 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 in the small. Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream. What needs to be broken down? (substrate) What enzyme does this? Where is the enzyme produced? What are the products of digestion? Where does this type of digestion take place? An example of an organ system in which several organs work together to digest and absorb food Enzymes are protein molecules which catalyse specific reactions in living organisms due to the shape of their active site. The lock and key theory is a simple model to explain how enzymes work... Starch Amylase Salivary glands Protein Protease Stomach Maltose and other simple sugars Amino acids Mouth Stomach Lipids (fats) Lipase Fatty acids and glycerol Enzymes are also affected by temperature. 1. At lower temperatures the rate of reaction increases as the molecules gain kinetic energy and there are more successful collisions between the enzyme and the substrate. 2. In humans the optimum temperature is body temperature (around 40 C). 3. Above the optimum temperature the enzyme denatures and the rate of reaction falls. Food test Food type Start - Positive result Iodine Starch Orange blue/black Biuret test Benedicts Protein Some sugars Blue Purple Blue red or green or orange Fat Sudan III Red layer
Measuring the rate of enzyme reactions Enzymes are protein molecules which catalyse specific reactions in living organisms due to the shape of their active site. Hydrogen peroxide water + oxygen This reaction is catalysed by the enzyme catalase. We can find the rate of reaction by measuring the foam caused by bubbles of oxygen. Keyword Enzyme Optimum Denature Anomaly Give the definition here... Enzymes are affected by temperature & ph. 1. Every enzyme has an optimum temperature & an optimum ph. 2. In humans the optimum temperature is body temperature (around 40 C). 3. Optimum ph will vary dependent on where the enzyme needs to work. 4. Above the optimum temperature or ph the enzyme denatures and the rate of reaction falls. Good experimental techniques (part 1) Change one variable the independent variable Measure one variable the dependent variable Keep all other variables the same the control variables. Investigating starch and amylase Starch is broken down into simpler sugars by the enzyme amylase. We can investigate this by testing how long it takes for the amylase to breakdown starch at different temperatures or different phs. When starch is present iodine turns blue/black in colour. When all the starch has been broken down iodine remains an orange/brown colour. Good experimental techniques (part 2) Experiments that are repeated are more reliable. This allows us to spot anomalies. An anomaly is a measurement that doesn t fit the pattern of the other data. If we get an anomaly we would ignore that reading and not include it when we analyse our data. If we want more precise data we could you a greater range of values with a smaller interval in between.
Blood Part of tissue Function Structure & Adaptations Plasma Carries everything except oxygen in the blood. E.g. Carbon dioxide, glucose, amino acids, urea, hormones, antibodies, antitoxins. Pale straw coloured liquid. Red and white blood cells and platelets travel within this liquid. White blood cells Red blood cells Defend against disease. Carry oxygen from the lungs to all the cells in the body. Platelets Help blood clot.. fragments of cells. No nucleus. Coronary heart disease is when the arteries that supply blood to the muscle of the heart get blocked with fatty deposits. This causes the arteries to become narrow and blood flow is restricted. This decreases oxygen supply to the heart muscle which can result in a heart attack. Quick check... 1. Why do we carry out experiments three times? 2. What should we do with an anomalous result in our data in an investigation? 3. How could we investigate the effect of ph on an enzyme? 4. What is blood made up of? 5. Name four substances that are transported in the blood. 6. What type of tissue makes up the walls of the heart? 7. Describe the route of blood around the body starting at the vena cava. 8. What does coronary heart disease do to the heart? 9. If the heart beats faster & more strongly how can this help an athlete during exercise? Large blood cells with a nucleus. Can change shape to engulf microorganisms. Produce antibodies to fight microorganisms. Produce antitoxins to neutralise toxins produced by microorganisms. Biconcave shape to provide large surface area to absorb oxygen. No nucleus so they have more space to carry oxygen. Contain a red pigment called haemoglobin. Haemoglobin + oxygen oxyhaemoglobin Help blood to clot at a wound site. THE HEART is made of muscle which contracts to pump blood around the body.
Biology revision questions 1. Describe the journey of food through the digestive system. 2. What is the role of enzymes in our body? 3. How do enzymes speed up the process of digestion? 4. What is the name of the model given to explain how enzymes work? 5. Describe how amylase breaks down starch and where it does it. 6. What is the effect of temperature on how enzymes work? 7. Explain why ph affects the rate of reaction in enzyme controlled reactions. 8. Describe how to carry out the Benedict s test for sugars. 9. What does iodine test for? What would a positive test look like? 10. Where is bile produced? 11. Bile has two main functions- what are they? 12. Why are all enzymes specific? 13. What is a tissue? 14. In an experiment what do we call the variable that we change? 15. What is an anomaly and what should we do with one? 16. How can we make experimental data more reliable? 17. How can we make data ore valid? 18. What happens to an enzyme when it denatures? 19. What are lipid molecules broken down into? 20. How would you test for the presence of protein in food?