Bio.

• light microscopes magnify up to about X2000, and have a resolving power of about 200nm 
• electron microscopes magnify up to about X2,000,000, and have a resolving power of about 0.2nm

resolving power is the ability to establish between two seperate points 

• euk means nuc- plants and animals are euk. all have a cell membrane, cytoplamsm and genetic material enclosed in a nucleus
• in prokaryotic cells, the genetic material is not surrounded by a nucleus
• bacteria are all prokaryotes 

• as an organism develops, cells differentiate to form different types of cells
• as an animal cell differentiates to form a specialised cell, it aquires different subcellular structures to enable it to carry out a certain function
• examples of specialised animal cells: nerve cells, muscle cells and sperm cells
• animal cells may be specialised to function within a tissue, an organ, organ systems or whole organisms 

• plant cells may be specialised to carry ot a particular function 
• examples of specialised plant cells: root hair cells, photosynthetic cells, xylem cells and phloem cells
• plant cells may be specialised to function within tissues, organs, organ systems or whole organisms 

• diffusion is the movement of particles of any substance, in a solution or gas, resulting in a net movement from an area of high concentration to an area of lower concentration, down a concentration gradient 
• the rate of diffusion is impacted by the difference in concentration, the temperature, and the available surface area 
• dissolved substances such as glucose and urea and gases such as oxygen and carbon dioxide move in and out of cells by diffusion

• osmosis is the movement of water from a dilute to a more concentrated solute solution through a partially permeable membrane that allows water to pass through
• differences in the concentration of solutions inside and outside a cell cause water to move into or out of the cell by osmosis 
• animal cells can be damaged if the concentration outside the cell changes dramatically 

• osmosis is important to maintain turgor in plant cells
• there are a variety of practical investigations that can be used to show the effect of osmosis on plant tissues  

• active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient)
• it uses energy from food in respiration to provide the energy required 
• it allows pkant root hairs to absord mineral ions required for healthy growth from very dilute solutions in the soil against a conentration gradient 
• active transport enables sugar molecules used fo cell respiration to be absorbed from lower concentrations in the gut into the blood where the concentration of sugar is higher 

• single-celled organisms have a relatively large surface area to volume ratio so all necessary exchanges with the environment take place over this surface
• in multicellular organisms, many organs are specialise with effective exchnage surfaces 
• exchange surfaces usually have a large surface area and thin walls, which give short diffusion distances. in animals, exchange surfaces will have an efficient blood supply or, for gaseous exchange, be ventilated

• in body cells, chromosomes are found in pairs, there are 23 pairs 
• during the cell cycle the genetic material is doubled. it then divides into two identical nuclei in a process called mitosis 
• before a cell can divide it needs to grow, replicate the DNA to form two copies of each chromosome and increase the number of sub-cellular structures. in mitosis, one set of chromosomes is pulled to each end of the cell and the nucleus divides. finally the cytoplasm and cell membranes divide to form two identical cells 
• mitotic cell division is important in the growth, repair, and development of multicellular organisms.

• in plant cells, mitosis takes place throughout life in the meristems found in the shoot and root tips 
• many types of plant cells retain the ability to differentiate throughout life 
• most types of annimal cell differentiate at an early stage of development

• embryonic stem cells (from human embryos) and adult stem cells (from adult bone marrow) can be cloned and made to differentiate into many different types of cell
• treatment with cell cells may be able to help conditions such as diabetes and paralysis 
• stem cells from plant meristems are used to produce new plant clones quickly and economically for research, horticulture, and agriculture

• treatment with stem cells, from embryos or adult cell cloning, may be able to help with conditions such as diabetes 
• in therapeutic cloning, an embryo is produed with the same genes as the patient so the stem cells produced are not rejected and may be used for medical treatment 
• the use of stem cells has some potential risks and some people have ethical or religious objections

• all substances are made up of atoms 
• the periodic table lists all the chemical elements, with eight main groups each containing elements with similar chemical properties 
• elements contain only one type of atom 
• compounds contain more than one type fo atom 
• an atom has a tiny nucleus at its centre, surrounded by electrons.

• no new atoms are ever created or destroyed in a chemical reaction: the total mass of reactants=the total mass of products 
• there is the same number of eah type of atom on eah side of a balanced symbol eqaution 
• you can include state symbols to give extra information in balanced symbol equations. 

• a mixture is made up of two or more substances that are not chemically combined together 
• mixtures can be seperated by physcial means, such as filtration, crystallisation, and simple distillation

• fractional distillation is an effective way of seperating miscible liquids, using a fractioning column. the seperation is possible because of teh diffrent boling points of the liquids in the mixture
• paper chromatography seperates mixtures of substances dissolved in a solvent as they move up a piece of chomatography paper. the different substances are seperated becuase of their different solubilities in the solvent used

• the ideas about atoms have changed over time 
• new evidence has been gathered from the experiments of scientists who have used their model of the atom to explain their observations and calculations 
• key ideas were proposed successively by Dalton, Thomson, Rutherford , and Bohr, before arriving at the model of the atom 
• 1800s, John Dalton suggested that substances were made of tiny atoms. he believed atoms couldnt be split-end of 1800's J.J. Thomson discovered the nucleus-1914Niels Bohr discovere electrons in shells 

• atomes are made of protons, neutrons and electrons 
• atoms contain an equal number of protons and electrons so they carry no overall charge 
• atomic number=number of protons (=numner of electrons)
• mass number=number of protons+neutrons
• atoms of the same element have the same number of protons (and hence electrons) in their atoms

• atoms that gain electrons form negative ions. if atoms lose electrons they form positive ions 
• isotopes are atoms of the same element with different numbers of neutrons. they have identical chemical properties, but their physical properties, such as density, can differ 

• the electrons in an atom are arranged in energy levels or shells 
• the lowest energy level (1st shell) can hold up to 2 electrons and the next energy level (2nd shell) can hold up to 8 electrons
• the 4th shell starts to fill ater 8 electrons occupy the 3rd shell
• the number of electrons in the outermost shell of an element's atoms determines the way in which that element reacts

• the periodic table of elements developed as chemists tried to classify the elements. it arranges them in an order in whcih similar elements are grouped together 
• the periodic table is so named because of th regularly repeating patterns in teh properties of elements 
• mandeleev's periodic table left gaps for the unknown elements, which when discovered matched his predictions, and so his table was accepted by the scientific community 

• the atomic (proton) number of an element determines its position in the periodic table 
• the number of electrons in the outermost shell (highest energy level) of an atom determines its chemical properties 
• the group number in the periodic table equals the number of electrons in the outermost shell
• the atoms od metals tend to lose electrons, whereas those of non-metals tend to gain electrons
• the noble gases in group0 are unreactive because of their very stable electronic arrangements

• the elements in grp1 are called the alkali metals 
• thir melting points and boiling points decrease going down the group
• the metals all react with water to produce hydrogen and an alkaline solution containing the metal hydroxide 
• they form 1+ions in reactions to make ionic compounds. these are generally white and dissolve in water, giving colourless solutions
• the reactivity of the alkali metals increases going down the group
• lose an electron when becoming positive 

• the halogens all form ions with a single negative charge in tehir ionic compounds with metals 
• the halogens form colavent compounds by sharing electrons with other non-metals 
• a more reactive halogen can displace a less reactive halogen from a solution of one of its salts
• the reactivity of the halogens decreases going down the group
• their mpt and bpt increases going down the group 
• gain an electron when becoming a negative ion 

• you can explain trends in reactivity as you go down a group in terns of the attraction between electrons in the outermost shell and the nucleus
• this electrostatic attraction depends on:-the distance between the outermost electrons and the nucleus --the number of occupied inner shells (energy levels)of electrons, which provide a shielding effect ---the size of the positive charge on the nucleus (called teh nuclear charge)
• in deciding how easy it is for atoms to gain or lose electrons from their outermost shell, these three factors must be taken into account. the increased nuclear charge, due to extra protons in the nucleus, going down a group is outweighed by the other two factors
• therefore electrons are easier for the larger atoms to lose going down a group, and harder for them to gain going down a group 

• high melting points and densities. they are stronger and harder but are much less reactive
• do not react vigorously with oxygen or water 
• can form ions with different charges, in compounds that are often coloured
• transition elements and their compounds are important industrial catalysts
• are shiny 
• they can change the cahrge on their ions. use roman numerals in the compounds to show the ion used

• energy can be stored in a variety of different energy stores 
• energy is transferred by heating, by waves, by an electric current, or by a force when it moves an object
• when an object falls and gains speed, its store of gravitational potential energy decreases and its kinetic energy store increases
• when a falling object hits the ground without bouncing back, its kinetic energy store decreases. some or all of its energy is transferred to the surroundings- the thermal energy store of the surroundings increases, and energy is also transferred by sound waves

• enrgy cannot be created or destroyed
• conservation of energy applies to all energy changes
• a closed system is a system in which no energy transfers take place out of or into the energy stores of the system 
• energy can be transferred between energy stores within a closed system. the total energy of the system is always the same, before and after, any such transfers

• work is done on an object when a force makes the object move
• energy transferred=work done
• work done to overcome friction is transferred as energy to the thermal energy stores of the objects that rub together and to the surroundings 

• the gravitional potential energy store of an object increases when it moves up and decreases when it moves down 
• the gravitional potential energy store of an object increases when it is lifted up because work is done on it to overcome the gravitational force 
• the gravitinal field strength at the surface of the Moon is less than on the Earth 

• the energy in the kinetic energy store of a moving object depends on its mass and its speed
• elastic potentialenergy is the energy stored in an elastic object when work is done on the object 

• useful energy is energy in the place we want it and in the form we need it
• wasted energy is the energy that is not useful energy and is transferred by an undesired pathway
• wasted energy is eventually transferred to the surroundings, which become warmer
• as energy dissipates (spreads out), it gets less and less useful 

• no energy transfer can be more than 100% efficient 
• machines waste energy because of friction between their moving parts, air resistance, electrical resistance, and noise 
• H Machines can be made more efficient by reducing the energy they waste. for example, lubrication is used to reduce friction between moving parts

• electricity an dgas and/or oil supply most of the energy you use in your home 
• electrical appliances can transfer energy in the form of useful energy at the flick of a switch 
• uses of everyday electrical appliances include heating, lighting, making objects move (using an electric motor), and producing sound and visual images 
• an electrical appliance is designed for a particular purpose and should waste as little energy as possible 

• power is rate of transfer of energy 

• metals are the best conductors of energy 
• non-metal materials such as wool and fibreglass are the best insulators 
• the higher the thermal conductivity of a material, the higher the rate of energy transfer through it 
• the thicker the layer of insulating material, the lower the rate of energy transfer through it 

• all objects emit and absorb infrared radiation 
• the hotter an object is, the more infrared radiation it emits in a given time 
• blackbody radiation is radiation emitted by a body that absorbs all the radiation incident on it 

• the temperature of an object increases if it absorbs more radiation than it emits 
• the Earth's temperature depends on a lot of factors, including the absorption of infrared radiation from the Sun, and the emission of radiation from the Earth's surface and atmosphere 

• the specific heat capacity of a substance is the amount of energy needed to change the temperature of 1kg of the substance by 1*C
• the greater the mass of an object, the more slowly its temperature increases when it is heated 

• electric and/or gas heaters and gas or oil-fired central heating or solid-fuel stoves are used to heat houses 
• the rate of energy transfer from houses can be reduced by using:-loft insulation--cavity wall insulation---double-glazed windows---aluminium foil behind radiators---external walls with thicker bricks and lower thermal conductivity 
• cavity wall insulation is insulation material that is used to fill the cavity between the two brick layers of an external house wall 

• energy demands are met mostly by burning oil, coal, and gas 
• nuclear power, biofuels, and renewable resources provide energy to generate some of the energy you use 
• uranium or plutonium is used as the fuel in a nuclear power station. much more energy is released per kilogram from uranium or plutonium than from fossil fuels 
• biofuels are renewable sources of energy. biofuels such as methane and ethanol can be used to generate electricity 

• a wind turbine is an electricity generator on top of a tall tower
• waves generate electricty by turning a floating generator 
• hydroelectricty generators are turned by water running downhill
• a tidal power station traps each high tide and uses it to turn generators 

• solar cells are flat solid cells and use the Sun's energy to generate electricity directly 
• solar heating panels use the Sun's energy to heat water directly 
• geothermal energy comes from the energy transferred by radioactive substances deep inside the Earth 
• water pumped into hot rocks underground produces steam to drive turbines at the Earth's surface that generate electricity 

• fossil fuels produce increased levels of greenhouse gases, which could cause global warming 
• nuclear fuels produce radioactive waste 
• renewable energy resources will never run out, they do not produce harmful waste products (e.g greenhouse gases or radioactive waste), and they can be used in remote places. but they can disturb natural habitats
• different energy resources can be evalauted in terms of reliability, envronmental effects, pollution, and waste 

• gas-fired power stations and pumped-storage stations can meet variations in demand 
• nuclear power stations are expensive to build, run and decomission. Carbon capture of fossil fuels emissions is likely to be very expensive. renewable resources are cheap to run but expensive to install
• nuclear power stations, fossil-fuel power stations that use carbon capture technology, and renewable energy resources are all likely to be needed for future energy supplies