Summary Sheets 8 B. Going for gold!

Transcription

1 B Summary Sheets Going for gold! All living cells need to respire to release energy. Energy is needed by organisms to stay alive, to make new substances and to help them move. Respiration normally requires oxygen and so it is called aerobic (with air) respiration. It is a series of chemical reactions that can be shown by a word equation: B glucose + oxygen carbon dioxide + water Glucose and oxygen are the reactants. Carbon dioxide and water are the products. Energy is released but this is not a chemical substance. Glucose is supplied by the digestion of carbohydrates. It is absorbed into the blood by the small intestine and carried around the body dissolved in the plasma of the blood. The blood travels through blood vessels and is pumped by the heart. The heart and the blood vessels form the circulatory system. capillaries in lungs blood to the lungs blood from the lungs blood to the rest of the body blood from rest of body Valves stop the blood flowing in the wrong direction. heart chambers left side of heart right side of heart capillaries in small intestine capillaries in other parts of the body capillaries in leg The oxygen is absorbed from the air by the lungs. The lungs are part of the breathing system (or respiratory system). trachea (windpipe) flowing blood flowing blood Carbon dioxide goes into the alveolus to be breathed out. Oxygen from inhaled air enters the capillary. bronchus (plural = bronchi) air sac Each air sac contains a number of tiny pockets called alveoli (singular = alveolus). capillaries plasma red blood cell to the heart to be pumped around the body carbon dioxide oxygen Exploring Science edition 57 Pearson Education Limited 200

2 B Summary Sheets (continued) The alveoli give the lungs a large surface area so that oxygen can quickly diffuse from the air inside the lungs into the blood contained in capillaries. The walls of the alveoli and the walls of the capillaries are only one cell thick, which also makes it easy for oxygen to diffuse into the blood. The oxygen is then carried by the red blood cells to capillaries around the body. B Tissue fluid comes out of other capillaries around the body and bathes the tissues in the body. Tissue fluid contains oxygen and glucose. The cells take the oxygen and glucose that they need from the tissue fluid and put the carbon dioxide that is produced back into the tissue fluid. The tissue fluid soaks back into other capillaries and the carbon dioxide dissolves in the blood plasma. Waste products, like carbon dioxide dissolve in the tissue fluid and go back into the blood in another capillary. oxygen and glucose Tissue fluid, carrying oxygen and glucose,leaks out of the capillary. In the lungs the dissolved carbon dioxide diffuses out of respiration the blood and into the air in the lungs. That is why we breathe out (exhale) more carbon dioxide than we breathe in (inhale). The carbon dioxide is excreted by the lungs. Carbon dioxide can be tested for by using limewater, which turns from clear to cloudy. Oxygen diffusing into the blood and carbon dioxide diffusing out of the blood is called gas exchange. Cells around the body take the oxygen and food that they need from the tissue fluid. Composition of inhaled and exhaled air. Inhaled air Exhaled air nitrogen gas 7% 7% oxygen gas 21% 16% carbon dioxide gas 0.03% 4% water vapour variable more When you exercise, your breathing rate (number of breaths in one minute) and your pulse rate (number of heart beats in one minute) increase. This is because your cells need more oxygen and glucose for respiration. In some diseases (e.g. emphysema) or when there is little air (e.g. at the top of a mountain) the body cannot get enough oxygen. People in these situations often feel short of breath and tired. If too little oxygen gets to cells, the cells cannot release energy from food and so they die. Most organisms respire using oxygen. Fish and many water organisms have gills to take oxygen out of the water. Oxygen from the water diffuses into the leaves of underwater plants. Exploring Science edition 5 Pearson Education Limited 200

3 C Summary Sheets Microbes Microbes, or micro-organisms, can only be seen using a microscope. There are three main types of microbes: viruses, bacteria and fungi. The most common fungus microbes are yeasts. C Viruses are smaller than bacteria which are smaller than yeast Viruses are usually not considered to be living because they do not carry out any of the seven life processes for themselves. Bacteria and yeasts are important in making some foods and drinks. Yeasts are used to make bread dough rise. The cells use oxygen, from the air found in pockets in the dough, for aerobic respiration. This process produces carbon dioxide, which makes the bread rise. glucose + oxygen carbon dioxide + water Yeast cells are also used to make beer and wine. In this case there is no air and so the yeast cells use anaerobic respiration. When yeasts cells use anaerobic respiration it is called fermentation. The ethanol is a waste product of this reaction. glucose carbon dioxide + ethanol (a sugar) The number of an organism in an area is called a population. In good conditions (warm, moist, plenty of sugar) a population of yeast cells will grow rapidly. The population stops growing if something runs out (e.g. sugar). The thing that stops the population growing is called a limiting factor. the effect of a limiting factor Number of yeast cells Time Page 1 of 2 Exploring Science edition Pearson Education Limited 200

4 C Summary Sheets (continued) Diseases Some microbes cause infectious diseases (diseases that can be spread from person to person). The microbes are said to infect you. The effects the microbes have on your body are known as symptoms. A doctor observes symptoms to come up with a diagnosis. Microbes can be spread by the air, water, touch, food, animals and sex. Disease Microbe that causes it Symptoms How it is spread colds and flu virus sore throat, running nose, fever air food poisoning bacteria vomiting, diarrhoea food cholera bacteria vomiting, diarrhoea water athlete s foot fungus sore cracked skin between the toes touch C Some ways that diseases can be stopped from spreading are: making sure sewage is treated and disposed of properly adding chlorine to water to kill bacteria drying, freezing or refrigerating foods pasteurising milk using disinfectants, antiseptics and soaps immunising people with vaccines. Your body has natural defences to stop microbes getting in (e.g. skin, mucus in the trachea and nose, ciliated epithelial cells to sweep mucus away). Your body also has ways of destroying microbes. These include: a chemical in tears that kills some bacteria acid in the stomach that kills some bacteria white blood cells that engulf microbes other white blood cells that make antibodies to help destroy microbes. Babies do not have fully developed immune systems. Antibodies can pass through the placenta and are found in breast milk. These help the baby to fight infections. For many diseases, once you have had the disease (or been immunised) you will not get it again (e.g. chickenpox). This is because the antibodies against these microbes stay in the blood. Some diseases can be cured using antibiotics. These are medicines that kill off bacteria. Some bacteria, however, are unaffected by antibiotics they are resistant to them. Using too many antibiotics only leaves behind the resistant bacteria, which then cause diseases that are difficult to treat. Page 2 of 2 Exploring Science edition 9 Pearson Education Limited 200

5 J Summary Sheets Forces Balanced forces are forces that are the same size but work in opposite directions. If forces are balanced: J A car or motorbike uses the energy stored in fuel to move at a steady speed because it needs a force from the engine to balance the forces of air resistance and friction. a stationary object stays stationary; a moving object continues to move at the same speed. The amount of air resistance on something can be reduced by giving it a smooth, streamlined shape. The air resistance increases as the speed increases, so cars use up more fuel per mile when they are travelling fast. Air resistance is caused by air particles hitting the moving object. The particles transfer energy to the object, which is why objects moving through air can get hot. Pressure on solids Pressure is the amount of force pushing on a certain area. For a certain area, the bigger the force, the bigger the pressure. For a certain force, the bigger the area, the smaller the pressure. In this picture, the thumb is putting a force onto the head of the pin. The force is transferred to the point of the pin. The point has a very small area, so there is a very large pressure on the board, and the pin goes in. In this picture, the thumb is putting a force directly on the board. The area of the thumb is much larger than the area of the pin point, so there is only a small pressure on the board. The thumb does not go into the board. Sharp knife a small area giving a large pressure. Snow shoes a large area giving a small pressure. Magnets and electromagnets Magnetism is a non-contact force. A magnet does not have to be touching something to attract it. Magnets attract magnetic materials. Iron, nickel and cobalt are magnetic materials. Mixtures, like steel, that include a magnetic material will also be attracted to a magnet. Other metals, such as aluminium or copper, are not magnetic and will not be attracted to a magnet. The two ends of a bar magnet are called the north-seeking pole and the south-seeking pole, or north pole and south pole for short. A north pole and a south pole attract each other. Page 1 of 2 Exploring Science edition 24 Pearson Education Limited 200

6 J Summary Sheets (continued) Two north poles or two south poles repel each other. A bar magnet is a permanent magnet, because it is always magnetic. A wire with electricity flowing through it has a magnetic field around it. An electromagnet is a coil of wire with an electric current flowing through it. It is only magnetic while the current is flowing. You can make an electromagnet stronger by: J increasing the number of coils of wire increasing the size of the current (by increasing the voltage) using an iron core. Magnetic fields The space around a magnet where it has an effect is called its magnetic field. You can find the shape of the magnetic field using iron filings or using a plotting compass. S N The Earth has a magnetic field. A compass is a small magnet that will point towards the Earth s North pole. But magnetic materials placed near a compass can change the direction that the compass points towards. This is the shape of the magnetic fi eld of a bar magnet. The magnetic fi eld of an electro magnet is a similar shape. Levers Forces can be used to turn objects around pivots. A pivot is also known as a fulcrum. Levers work by magnifying the force that is put in (the effort) or they can make the load move further than the effort. The amount the force or distance is multiplied depends on the distances between the load and the pivot and the effort and the pivot. The hammer is acting as a force multiplier. force from han biceps muscle effort triceps muscle radius bone pivot The arm is acting as a distance multiplier. Page 2 of 2 Exploring Science edition 25 Pearson Education Limited 200

7 J Summary Sheets Magnets and electromagnets J Magnetism is a non-contact force. Magnets attract magnetic materials. Iron, nickel and cobalt are magnetic materials. Mixtures, like steel, that include a magnetic material will also be attracted to a magnet. Other metals, like aluminium, are not magnetic and will not be attracted to a magnet. Iron oxide is a compound that is a magnetic material. It is used to make video and music cassettes and computer discs. Magnetic materials can also block magnetism. You can make a magnet from a piece of iron or steel. Always stroke in the same direction. magnet magnetic material The two ends of a bar magnet are called the north seeking pole and the south seeking pole or north pole and south pole for short. A north pole and a south pole attract each other. Two north poles or two south poles will repel each other. The space around a magnet where it has an effect is called its magnetic field. S N This is the shape of the magnetic field of a bar magnet. You can find the shape of the magnetic field using iron filings or using a plotting compass. The Earth has a magnetic field. A compass is a small magnet that always points north. But magnetic materials placed near a compass can change the direction that it points. Magnets can be used to sort iron and aluminium cans for recycling. Only the iron cans are attracted to the magnet. Magnets can also be used for holding fridge doors shut, and in compasses that sailors or walkers use. A wire with electricity flowing through it has a magnetic field around it. An electromagnet is a coil of wire with an electric current flowing through it. Exploring Science for QCA Copymaster File Page 1 of Pearson Education Limited 2002

8 J Summary Sheets (continued) You can make an electromagnet stronger by: increasing the number of coils of wire increasing the size of the current (by increasing the voltage) using an iron core. J Electromagnets can be used for lifting things. They are also used in electric bells, relays and in video and music recording. Electromagnets are used to make bells work. cell pivot electromagnet gong springy metal contact armature A reed switch has two thin pieces of iron inside it. If a magnet is held near the switch, the pieces of iron are magnetised and touch each other. A reed switch can also be switched on using an electromagnet. Any switch that is worked by electricity is called a relay. Relays are used to make things safer. For example, the starter motor in a car uses a high current and needs thick wires for the current to flow through. A relay is used in a car so that the driver does not have to touch any part of the circuit that has a high current. contacts circuit 1 When current flows in circuit 1 the coil becomes an electromagnet. circuit 2 iron armature When the armature moves the iron connects the two contacts and electricity can flow in circuit 2. coil of wire The iron armature is attracted by the electromagnet. Exploring Science for QCA Copymaster File Page 2 of Pearson Education Limited 2002

9 F Summary Sheets Elements An element is a simple substance that cannot be split into anything simpler by chemical reactions. Atoms are the smallest particles of an element. Atoms of one element are all the same, and are different from atoms of all the other elements. All the elements are shown in the periodic table. There are 117 known elements. Each element has a chemical symbol, which is usually one or two letters. A symbol is written with the first letter as a capital, and the second letter lower case, for example F oxygen O carbon C iron Fe aluminium Al Compounds Elements can join together to make compounds. The name of the compound tells you the elements that are in it. Compounds made from two elements always have a name that ends in -ide. These elements join together carbon, oxygen sodium, chlorine magnesium, oxygen to make these compounds carbon dioxide sodium chloride magnesium oxide A chemical formula tells you the name and number of atoms in a compound. The smallest particle of many compounds is called a molecule. Molecules are made up of groups of atoms. Some elements are also made of molecules. For example, a molecule of oxygen contains two oxygen atoms joined together. The formula is O 2. Water contains two atoms of hydrogen and one of oxygen. The formula is H 2 O. Elements Compounds Mixtures atoms of helium (He) molecules of carbon dioxide a mixture of helium and oxygen (CO 2 ) molecules of oxygen (O 2 ) molecules of water (H 2 O) a mixture of carbon dioxide and oxygen a lump of iron (Fe) a lump of sodium chloride (NaCl) a lump of bronze (a mixture of copper and tin) Page 1 of 2 Exploring Science edition 175 Pearson Education Limited 200

10 F Summary Sheets (continued) Metals and non-metals The properties of a substance describe the way the substance behaves, or measurements that we can make on it. Metals and non-metals have different properties. F Metals good conductors of heat and electricity shiny solids with a high melting point (except for mercury) Mainly found on the left-hand side and in the centre of the periodic table three metals are magnetic flexible Non-Metals poor conductors of heat and electricity dull most are solids or gases found on the right-hand side of the periodic table no non-metals are magnetic brittle (break easily instead of bending) Re-use and recycling Materials can be classified according to their properties. All the different materials in the world are made up of about 90 different elements. Some useful materials occur naturally, but others have to be manufactured using chemical reactions. In many cases, raw materials are non-renewable. If we can recycle these materials, then we reduce the demand for raw materials. There may also be energy savings as well. A process that uses recycled or renewable materials is sustainable. Waste can also be reduced by re-using objects such as glass bottles or plastic bags. Page 2 of 2 Exploring Science edition 176 Pearson Education Limited 200

11 G Summary Sheets Compounds and mixtures Elements are simple substances that cannot be split up in chemical reactions. Atoms are the smallest particles of an element that can exist. Atoms in an element are all the same. Each element has its own chemical symbol. For example, the chemical symbol for oxygen is O. The symbols and names for all the known elements are shown in the periodic table. G Some elements have their atoms joined to each other in small groups called molecules. Oxygen is an example. Elements can join together to make compounds. A compound contains two or more elements joined together by bonds. The name of the compound tells you the elements that are in it. Compounds made from two elements always have a name that ends in -ide. an atom of oxygen O A molecule of oxygen consists of two oxygen atoms joined together. O another atom of oxygen Many compounds exist as atoms attached to each other in small groups molecules. H H O A molecule of water (hydrogen) A compound always contains the same elements in the same ratio. The chemical formula of a compound tells you the ratio of atoms of each element that are bonded together. For compounds that are molecules it tells you the numbers of atoms of each element in a compound. Each element in the chemical formula is shown by its chemical symbol. For example: The properties of a compound are different from the elements that make it up. For example, hydrogen is an explosive gas and oxygen will relight a glowing splint, but water is a liquid that will put fires out. the symbol for hydrogen 2 atoms of hydrogen H 2 O the symbol for oxygen No number after a symbol means that there is only one atom of that element. Chemical reactions Compounds can be made to react by mixing them with other chemicals, or by using heat or electricity. You can tell that a chemical reaction has occurred if there is a colour change or when a gas is given off. Page 1 of 2 Exploring Science edition 202 Pearson Education Limited 200

12 G Summary Sheets (continued) Most chemical reactions also involve an energy change. This is usually in the form of heat, for example in burning (combustion). In a chemical reaction a new substance is always formed. Most chemical reactions are not easily reversed (they are irreversible). Some chemical reactions take place just by mixing substances together. (e.g. when a solid (a precipitate) forms by mixing two liquids in a precipitation reaction). Other chemical reactions need energy to start them off. (e.g. when some compounds are broken up, decomposed, by heat). G Word equations show what happens in a chemical reaction. The chemicals that you start with are called the reactants. The chemicals at the end are called the products. For example: magnesium + oxygen magnesium oxide { reactants { product Physical changes melting evaporating In a physical change no new substance is formed and the changes are usually easily reversed. Melting, evaporating, condensing and freezing are all examples of physical changes. ice water steam Mixtures freezing condensing Elements and compounds can also be mixed together. A mixture is easier to separate than the elements in a compound. Soil, river water and sea water are examples of mixtures that occur naturally. A pure substance contains a single substance, element or compound, nothing else. Elements and compounds melt and boil at a fixed temperature. Mixtures do not have definite melting points and boiling points. Alloys Alloys are mixtures of metals with one or more other elements. Alloys have different properties from the pure metal. Pure gold is too soft for making jewellery. An alloy of gold mixed with other metals, like copper or silver, is used because it is stronger. The original method used to measure the purity of gold alloys was the carat system. One carat is 1 part in 24. So pure gold is 24 carats and 12 carat gold contains 50% gold. Page 2 of 2 Exploring Science edition 203 Pearson Education Limited 200