Please enable JavaScript.

Coggle requires JavaScript to display documents.

GCSE Science - Coggle Diagram

- - - - The equation is used to work out the change in GPE as an object is moved from height to another
      - Change in Gravitational Potential Energy (joule, J) = Mass (Kilogram, kg) x Change in Vertical Height (metre, m) x Gravitational Field Strength (Newtons per kilogram, N/kg)
      - The equation is used to calculate the amounts of energy associated with a moving object
      - Kinetic energy (joule, J) = 1/2 x Mass (Kilogram, kg) x speed^2 (metre/second^2, m/s^2)
    - - Diagrams show energy input, and the energy output
        
        And the forms that the energy takes
        
        This includes the waste energy output too
        
        Motors also waste energy as heat
    - - Object projected up a slope
        
        KE transferred to GPE (and also to heat if friction is present)
      - Object projected upwards
        
        KE transferred to GPE, then vice versa as it falls down
      - Moving object hitting an obstacle
        
        KE is transferred to sound/KE transferred to obstacle if that moves too
      - Object being accelerated by a constant force
        
        Object is having work done to it, with it gaining KE
        
        Whatever supplies the force is having its energy transferred to KE
      - Vehicle slowing down
        
        KE transferred to heat (through brakes)
      - Boiling water in kettle
        
        Electrical energy to thermal
    - - In physics, conservation of energy means that the total energy of an isolated system remains constant
      - A 'closed system' has no external forces acting on it (e.g.no change in gravitational force, no electrostatic attraction, no external magnetic force etc.)
      - In a closed system,the total energy in the system never changes, regardless of the energy transfers that take place
        
        In other words, in a closed system no energy is lost
      - Once it becomes an open system, energy can be transferred out of the system, and therefore the total energy of the system can change
    - - In mechanical processes (i.e. where forces are involved on objects)
        
        Energy transferred to it can cause a rise in temperature
      - So energy is dissipated to surroundings (heat is transferred to air)
        
        And this makes the process wasteful
    - - Forms: Light, sound, (most commonly) heat
      - To reduce waste:
        
        Lubricate systems, so less friction and less heat is created
        
        Thermal insulation, so less heat is lost to surroundings
      - Buildings:
        
        Thicker walls mean greater thermal insulation, so less heat is lost
        
        Air cavities between walls cause lots of heat loss by convection - cavity wall insulation fills in this gap and prevents air flow
    - - Ratio of useful output over total input of energy
        
        Efficiency = Useful energy transferred by the device/Total energy supplied to the device
    - - Reducing waste output (via lubrication/thermal insulation or other methods
      - Recycling waste output and using it as input (absorbing heat energy dissipated and used as input heat energy)
      - Suitable methods depend on each situation
    - - Fossil fuels
      - Nuclear fuel
      - Bio-fuel
      - Wind
      - Hydro-electricity
      - Tidal
      - Solar
      - Non-renewable energy is used more for large-scale energy supplies due to he large energy output per kilogram of fuel - renewable resources cannot provide such a large amount of energy as easily
        
        Renewable energy has become more important due to the finite lifetime of fossil fuels, and so their development has become more important
    - - During industrial revolution, fossil fuels became an important source of energy as it was easy to mine, and provided a lot of energy
      - Only recently has renewable energy become more suitable - technology has had to develop a lot since the industrial revolution to be able to harness such energy sources efficiently
  - - - Arrows show direction of light travelling
      - The normal is an (imaginary) dashed line which is perpendicular to the surface, and from which all angles are measured from
      - Incident angle is the angle of the entering ray
      - Reflected angle is the angle of the exiting ray
    - - Incident angle = reflection angle
      - Angles are always measured from normal
    - - If entering a denser material, it bends towards the normal
      - If entering a less dense material. it bends away from the normal
    - - This occurs when the light is passing from a denser medium into a less dense medium (glass to air)
      - If the angle of incidence is equal to the critical angle, the refracted ray will pass along the boundary and not exit the medium
    - - If entering a denser material, it bends towards the n
      - If entering a less dense material, it bends away from t
    - - Incident angle = reflection angle
      - Angles are always measured from normal
    - - This occurs when the light is passing from a denser medium into a less dense medium (glass to air)
      - If the angle of incidence is equal to the critical angle, the refracted ray will pass along the boundary and not exit the medium
        
        The critical angle is a unique angle for each two media (the critical angle for glass-air is different to glass-water)
      - For larger angles, the light internally reflects (following the above law of reflection) back into the glass
    - - If angle < critical angle, light refracts away from the normal
      - If angle = critical angle, light passes along the boundaryl
      - If angle > critical angle, light reflectsl
- - - - 1.21 Explain how ionic bonds are formed by the transfer of electrons between atoms to produce cations and atoms, including the use of dot and cross diagrams
        
        Metals + nonmetals: electrons in the outer shell of the atom are transferred
        
        Metal atoms lose electrons to become positively charged ions (cations)
        
        Nonmetal atoms gain electrons to become negatively charged ions (anion)
        
        Electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram
      - 1.22 Recall that an ion is an atom or group of atoms with a positive or negative charge
        
        Since an ion is formed from a metal losing an electron, i.e. becoming a positive metal ion or from a non-metal gaining an electron, i.e. becoming a negative ion… an ion is an atom or group of atoms with a positive or negative charge
      - 1.23 Calculate the numbers of protons, neutrons and electrons in simple ions given the atomic number and mass number
        
        Atomic number = proton number = number of protons
        
        Mass number = nucleon number = number of protons + neutrons
        
        In an atom number of protons = number of electrons, but in an ion, there is a different number of electrons to protons. to work out electrons in an ion:
        
        work out how many electrons an atom of the element would have (same as proton number)
        
        work out how many electrons have been lost or gained (using charge, remember -ve means electrons gained, +ve means electrons lost)
        
        calculate number of electrons in atom plus electrons gained or minus electrons lost
      - 1.24 Explain the formation of ions in ionic compounds from their atoms, limited to compounds of elements in groups 1, 2, 6 and 7
        
        Ions produced by metals in Groups 1 and 2 and by nonmetals in Groups 6 and 7 have the electronic structure of a noble gas (Group 0)
        
        this means group 1 metals will lose 1 electron and form +1 ions
        
        group 2 metals will lose 2 electrons and form +2 ions
        
        group 6 nonmetals will gain 2 electrons and form 2- ions
        
        group 7 nonmetals will gain 1 electron and form 1- ions
        
        remember a compound will have an overall charge of 0 so you need to balance out the + and - charges
      - 1.25 Explain the use of the endings –ide and –ate in the names of
        compounds
        
        these endings are used for the negatively charged ions in a compound
        
        -ide means the compound contains 2 elements (one is the nonmetal -ve ion)
        
        -ate means the compound contains at least 3 elements, one of which is oxygen
      - 1.26 Deduce the formulae of ionic compounds (including oxides, hydroxides, halides, nitrates, carbonates and sulfates) given the formulae of the constituent ions
        
        Oxide -> involves O^2- ion (e.g. sodium oxide: Na2O)
        
        Hydroxide -> involves OH^1- ion (e.g. sodium hydroxide: NaOH)
        
        Halide -> involves a -1 halide ion (e.g. sodium chloride NaCl)
        
        Nitrate -> involves NO3^1- ion (e.g. sodium nitrate: NaNO3)
        
        Carbonate -> involves CO3^2- ion (e.g. sodium carbonate: NaCO3)
        
        Sulfate -> involves SO4^2- ion (e.g. sodium sulfate: NaSO4)
        
        to deduce the formula of ionic compounds, you need to balance out the + and - charges to make the overall charge 0. You do this by writing a little number below the element e.g. Cl3 or for ions with more than one element you draw a bracket round first e.g. (SO4)2
      - 1.27 Explain the structure of an ionic compound as a lattice structure: consisting of a regular arrangement of ions; held together by strong electrostatic forces (ionic bonds) between oppositely-charged ions
        
        A giant structure of ions = ionic compound
        
        Held together by strong electrostatic forces of attraction between oppositely charged ions
        
        The forces act in all directions in the lattice, and this is called ionic bonding
        
        The lattice has a regular arrangement of ions
        
        An example is sodium chloride (salt):
        Na+ (small blue particles) and Cl- (larger green ones)
    - - 1.28 Explain how a covalent bond is formed when a pair of electrons is shared between two atoms
        
        Covalent bonding occurs in most non-metallic elements and in compounds of nonmetals
        
        When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong
      - 1.29 Recall that covalent bonding results in the formation of molecules
        
        Covalently bonded substances may consist of small molecules e.g. HCl, H2, O2, Cl2, NH3, CH4
        
        Some have very large molecules, such as polymers
        
        Some have giant covalent structures (macromolecules) e.g diamond, silicon dioxide
        
        Diagrams to show these substances could be dot and cross, shown as repeat units for polymers using a single line to represent a single bond, ball and stick and two- and three-dimensional diagrams
      - 1.30 Recall the typical size (order of magnitude) of atoms and small molecules
        
        Simple molecular substances consist of molecules in which the atoms are joined by strong covalent bonds
        
        Therefore, atoms are smaller than small molecules
    - - 1.31 Explain the formation of simple molecular, covalent substances, using dot and cross diagrams, including: hydrogen, hydrogen chloride, water methane, oxygen, and carbon dioxide
      - 1.32 Explain why elements and compounds can be classified as: ionic, simple molecular (covalent), giant covalent, metallic and how the structure and bonding of these types of substances results in different physical properties, including relative melting point and boiling point, relative solubility in water and ability to conduct electricity (as solids and in solution)
        
        Properties of ionic compounds
        
        Ionic compounds are made up of a metal and a nonmetal
        
        Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions
        
        They have high melting and boiling points, because a lot of energy is required to break the many strong bonds
        
        When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and carry current, and they do not conduct electricity as solids, because the ions are fixed and are not able to move, carrying charge
        with them
        
        Often dissolve in water to form an aqueous solution
        
        Properties of simple molecular compounds
        
        Substances that consist of small molecules are usually gases or liquids that have low boiling and melting points. They are made up of nonmetal elements
        
        Substances that consist of small molecules have weak intermolecular forces between the molecules. These are broken in boiling or melting, not the covalent bonds
        
        The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points
        
        Substances that consist of small molecules don’t conduct electricity, because small molecules do not have an overall electric charge. although, some breakdown in water to form ions which can conduct electricity
        
        Many are insoluble in water, but some are soluble because they can form intermolecular forces with water which are stronger than those between water molecules or their own molecules already (e.g. CO2 and NH3 are soluble)
        
        Giant Covalent Structures
        
        They are made up of nonmetal elements
        
        Substances that consist of giant covalent structures are solids with very high melting points
        
        All of the atoms in these structures are linked to other atoms by strong covalent bonds
        
        These bonds must be overcome to melt or boil these substances
        
        some giant covalent structures can conduct electricity, whereas others can’t
        
        Properties of metals
        
        Metals consist of giant structures of atoms arranged in a regular pattern. They are always made up of just metallic elements
        
        The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure
        
        The sharing of delocalised electrons gives rise to strong metallic bonds
        
        Metals have giant structures of atoms with strong metallic bonding
        
        Therefore, most metals have high melting and boiling points
        
        They can conduct heat and electricity because of the delocalised
        electrons in their structures
        
        Conduction depends on the ability for electrons to move throughout the metal
        
        The layers of atoms in metals are able to slide over each other, so metals can be bent and shaped
        
        insoluble in water- but some will react with it instead
      - 1.33 Explain the properties of ionic compounds limited to: high melting points and boiling points, in terms of forces between ions and whether or not they conduct electricity as solids, when molten and in aqueous solution
        
        high melting and boiling points- strong electrostatic forces
        
        conduct electricity when molten/dissolved- ions can move
        
        don’t conduct electricity when solid- ions are fixed in place
      - 1.34 Explain the properties of typical covalent, simple molecular compounds limited to: low melting points and boiling points, in terms of forces between molecules (intermolecular forces) and poor conduction of electricity
        
        low melting and boiling points- only weak forces between molecules must be overcome, not covalent bonds
        
        poor conduction of electricity- no charged particles or electrons that are free to move
      - 1.35 Recall that graphite and diamond are different forms of carbon and that they are examples of giant covalent substances & 1.36 Describe the structures of graphite and diamond
        
        Diamond
        
        In diamond, each carbon is joined to 4 other carbons
        covalently
        
        It’s very hard, has a very high melting point and does not
        conduct electricity
        
        Graphite
        
        In graphite, each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings, which have no covalent bonds between the layers
        
        The layers can slide over each other due to no covalent bonds between the layers, but weak intermolecular forces. Meaning that graphite is soft and slippery
        
        One electron from each carbon atom is delocalised
        
        This makes graphite similar to metals, because of its delocalised
        electrons
        
        It can conduct electricity – unlike diamond
      - 1.37 Explain, in terms of structure and bonding, why graphite is used to make electrodes and as a lubricant, whereas diamond is used in cutting tools
        
        Graphite uses
        
        Electrodes – graphite can conduct electricity – unlike Diamond
        
        Lubricant – weak intermolecular forces and no covalent bonds between the layers, therefore it is soft and slippery
        
        Diamond uses
        
        Cutting tools – very hard, due to its rigid structure
      - 1.38 Explain the properties of fullerenes including C60 and graphene in terms of their structures and bonding
        
        Graphene
        
        Single layer of graphite
        
        Has properties that make it useful in electronics and composites
        
        Carbon can also form fullerenes with different numbers of carbon atoms
        
        Molecules of carbon atoms with hollow shapes
        
        They are based on hexagonal rings of carbon atoms, but they may also contain rings with five or seven carbon atoms
        
        The first fullerene to be discovered was Buckminsterfullerene (C60), which has a spherical shape
        
        Carbon nanotubes
        
        Cylindrical fullerenes with very high length to diameter ratios
        
        Their properties make them useful for nanotechnology, electronics and materials
        
        Examples of uses
        
        They can be used as lubricants, to deliver drugs in the body and catalysts
        
        Nanotubes can be used for reinforcing materials, for example tennis rackets
      - 1.39 Describe, using poly(ethene) as the example, that simple polymers consist of large molecules containing chains of carbon atoms
        
        Polymers have very large molecules (the n in the diagram structure shows there are many many repeat units)
        
        Atoms in the polymer molecules are linked to other atoms by strong covalent bonds
        
        Intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature
      - 1.40 Explain the properties of metals, including malleability and the ability to conduct electricity
        
        malleable- the layers of atoms in metals are able to slide over each other
        
        can conduct electricity- delocalised electrons can move
    - - 1.41 Describe the limitations of particular representations and models, to include dot and cross, ball and stick models and two- and three-dimensional representations
        
        Main limitation is that it applies really well only to the small class of solids composed of Group 1 and 2 elements with highly electronegative elements such as the halogens
        
        In covalent molecular, the dot-cross diagrams don’t express the relative attraction of shared electrons due to electronegativity (learn about this at A-level more)
        
        2d diagrams don’t show the 3d arrangement of atoms, and 3d diagrams don’t show the share or transfer of electrons
      - 1.42 Describe most metals as shiny solids which have high melting points, high density and are good conductors of electricity whereas most non-metals have low boiling points and are poor conductors of electricity
- - - - Only in plant cells:
        
        Cell wall (also present in algal cells) - Made from cellulose. Provides strength to the cell.
        
        Permanent vacuole - Contains cell sap. Found within the cytoplasm. Improves cell’s rigidity.
        
        Chloroplasts - Where photosynthesis takes place, providing food for the plant. Contains chlorophyll pigment (which makes it green) high harvests the light needed for photosynthesis.
      - In animal and plant cells:
        
        Ribosomes - Where protein synthesis occur. Found on a structure called the rough endoplasmic reticulum.
        
        Mitochondria - Where aerobic respiration reactions occur, providing energy for the cell.
        
        Cell membrane - Controls what enters and leaves the cell.
        
        Cytoplasm - Liquid structure, in which chemical reactions occur. Contains enzymes (biological catalysts, i.e. proteins that speed up the rate of reaction). Organelles are found in it.
        
        Nucleus - Contains DNA coding for a particular protein needed to build new cells. Enclosed in a nuclear membrane.
      - The structures mentioned above (e.g. cell membrane) are examples of organelles - structures in a cell that have different functions. These organelles all have a specific function.
      - Bacterial cells are prokaryotic and are much smaller. They have a:
        
        ● Single circular strand of DNA and plasmids (small rings of DNA found in the
        cytoplasm)
        
        Cytoplasm
        
        Cell membrane
        
        Cell wall
      - Animal and plant cells are eukaryotic. They have a:
        
        Nucleus containing DNA
        
        Cytoplasm
        
        Cell membrane
      - All living things are made of cells, which can either be prokaryotic or eukaryotic.
      - Bacterial cells are prokaryotic, so do not share as many similarities in the type of organelles as animal and plant cells do.
      - In bacterial cells:
        
        Cytoplasm- See above
        
        Cell membrane - See above
        
        Cell wall - Made of a different compound (peptidogylcan)
        
        Chromosomal DNA (Circular) - As bacterial cells have no nucleus, this floats in the cytoplasm
        
        Plasmids - Small rings of DNA - code for extra genes to those provided by chromosomal DNA
        
        Flagella - Long, thin ‘whip-like’ tails attached to bacteria that allow them to move
    - - Cells specialise by undergoing differentiation: a process that involves the cell gaining new sub-cellular structures in order for it to be suited to its role. Cells can either differentiate once early on or have the ability to differentiate their whole life (these are called stem cells). In animals, most cells only differentiate once, but in plants many cells retain the ability.
      - Examples of specialised cells in animals:
        
        Sperm cells : specialised to carry the male’s DNA to the egg cell (ovum) for successful reproduction
        
        Streamlined head and long tail to aid swimming
        
        Many mitochondria (where respiration happens) which supply the energy to allow the cell to move
        
        The acrosome (top of the head) has digestive enzymes which break down the outer layers of membrane of the egg cell
        
        Haploid nucleus - the word haploid simply means that it has 23
        chromosomes, rather than the 46 that most other body cells have
        
        Egg cells : specialised to accept a single sperm cell and develop into an embryo
        
        Surrounded by a special cell membrane which can only accept one sperm cell (during fertilisation) and becomes impermeable following this
        
        Lots of mitochondria to provide an energy source for the developing embryo
        
        Large size and cytoplasm to allow quick, repeated division as the embryo
        grows
        
        Ciliated epithelial cells : specialised to waft bacteria (trapped by mucus) to the stomach
        
        Long, hair-like processes called cilia waft bacteria trapped by sticky mucus (produced by nearby goblet cells) down to the stomach, where they are killed by the stomach acid. This is one of the ways our body protects against illness.
      - Examples of specialised cells in plants:
        
        Root hair cells : specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots
        
        Have a large surface area due to root hairs, meaning more water can move in
        
        The large permanent vacuole affects the speed of movement of water from the soil to the cell
        
        Mitochondria to provide energy from respiration for the active transport of
        mineral ions into the root hair cell
        
        Xylem cells : specialised to transport water and mineral ions up the plant from the roots to the shoots
        
        Upon formation, a chemical called lignin is deposited which causes the cells to die. They become hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through
        
        Lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water
        
        Phloem cells : specialised to carry the products of photosynthesis (food) to all parts of the plants
        
        Cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell
        
        Despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cells.
    - - Extremely small structures such as cells cannot be seen without microscopes, which enlarge the image.
      - The first cells of a cork were observed by Robert Hooke in 1665 using a light microscope.
        
        It had two lenses
        
        It is usually illuminated from underneath
        
        They have, approximately, a maximum magnification of 2000x and a resolving power (this affects resolution: the ability to distinguish between two points) of 200nm The lower the RP, the more detail is seen
        
        Used to view tissues, cells and large sub-cellular structures
      - In the 1930s the electron microscope was developed, enabling scientists to view deep inside sub-cellular structures, such as mitochondria, ribosomes, chloroplasts and plasmids.
        
        Electrons, as opposed to light, are used to form an image because the electrons have a much smaller wavelength than that of light waves
        
        There are two types: a scanning electron microscope that create 3D images (at a slightly lower magnification) and a transmission electron microscope which creates 2D images detailing organelles
        
        They have a magnification of up to 2,000,000x and resolving power of 10nm (SEM) and 0.2nm (TEM)
      - The discovery of the electron microscope has allowed us to view many organelles more clearly - especially very small structures such as ribosomes (see image). Transmission electron microscopes (TEMs) in particular, have been used to discover viruses such as poliovirus, smallpox and Ebola - and are still used for this function today. This is useful as viruses are much smaller than bacteria, andare very hard to identify using a standard light microscope.
      - Electron microscopes are also used to examine proteins in much greater detail than can be achieved with a light microscope, which has led to many important scientific discoveries.
    - - Common calculations in microscopy:
        
        Magnification of a light microscope: magnification of the eyepiece lens x magnification of the objective lens
        
        Size of an object: size of image/magnification = size of object (this formula can be rearranged to obtain the other values, make sure you are in the same units!)
      - When working with calculations, it is common to come across very large or small numbers. Standard form can be useful when working with these numbers. Through multiplying a certain number by a power of 10, it can get bigger or smaller. To be able to compare the size of numbers while using standard form, the ‘number’ which being multiplied by a power of 10 needs to be between 1 and 10. Examples:
        
        1.5 x 10^-5 = 0.000015
        
        3.4 x 10^3 = 3400
      - Cells and organelles are extremely small, and we can use orders of magnitude to understand how much bigger or smaller one is from another:
        
        If an object is 10 times bigger than another then we say it is 10^1 times bigger.
        
        If an object is 1000 times bigger than another then we say it is 10^3 times bigger.
        
        If an object is 10 times smaller than another then we say it is 10^-1 times smaller.
      - Prefixes go before units of measurement (such as ‘centimetres’) to show the multiple of the unit.
        
        Centi - multiply by 0.01
        
        Milli - multiply by 0.001
        
        Micro - multiply by 0.000,001
        
        Nano - multiply by 0.000,000,001
      - Estimations are useful in Biology when we don’t know how many of something there is, or if it would take too long to count. For example, if we take a 1m x 1m square sample of grassland and count the number of a particular species of plant (e.g dandelions) in that square, we can estimate the number of dandelions in the whole field by multiplying that number by however many 1m x 1m squares can fit in the field. For example:
        
        One 1m x 1m square contains 15 dandelions
        The entire field measures 50m x 50m, so it fits 50 of the 1m x 1m squares
        Multiply 15 by 50: 15 x 50 = 750 dandelions in the whole field
        Remember that 750 is just an estimate - the real number will likely be different! The more squares we look at (or ‘sample’) the closer we will get to the real number.
    - - The total magnification of a microscope with a 10x eyepiece lens and a 40x objective lens is 400x
      - Using microscopes is an important part of investigating biological specimens. We should be familiar with the parts of a light microscope:
        
        Eyepiece - This is the part of microscope that we look through to view specimens.
        
        Barrel - The upper part of the microscope that can be moved up or down to focus the image.
        
        Turret - The part of the microscope that is rotated to change the magnification lens in use.
        
        Lens - The lens increases the magnification of the specimen. See Section 1.13.
        
        Stage - The flat surface on which we place the specimen.
      - To use a light microscope, you should:
        
        Place the slide on the stage and look through the eyepiece lens
        
        Turn the focus wheel to obtain a clear image
        
        Start with the lowest objective lens magnification
        
        Increase the magnification of the objective lens and refocus.
        
        It is important to remember all 4 steps to gain full marks in a question about microscopy.
      - In order to use specimens with a light microscope, you have to first prepare the slide. This is done using the following method:
        
        Take a thin layer of cells from your sample by either peeling them off or using a cotton bud
        
        Add a small amount of the correct chemical stain (you will be told by your teacher which stain to use). Chemical stains are used to make some parts of the specimen more visible when you look at them through the microscope
        
        Apply the cells to your glass slide by placing them on or wiping the cotton bud against it
        
        Carefully lower a coverslip onto your slide, taking care to avoid air bubbles.
      - You should know how to perform magnification calculations. Remember:
        
        Magnification = measured size / actual size
        
        Actual size = measured size / magnification
        
        Total magnification = objective lens magnification x eyepiece lens magnification
    - - Enzymes are biological catalysts (a substance that increases the rate of reaction without being used up)
        
        Enzymes are present in many reactions - allowing them to be controlled.
        
        They can both break up large molecules and join small ones
        
        They are protein molecules and the shape of the enzyme is vital to its function.
        
        This is because each enzyme has its own uniquely shaped active site where the substrate binds.
      - The Lock and Key Hypothesis (a simplified explanation of how enzymes work):
        
        The shape of the substrate is complementary to the shape of the active site (matches the shape of the active site), so when they bond it forms an enzyme-substrate complex
        
        Once bound, the reaction the reaction takes place and the products are released from the surface of the enzyme
      - Enzymes can only catalyse (speed up) reactions when they bind to a substrate that has a complementary shape, as this is the only way that the substrate will fit into the active site. This is called enzyme specificity
      - Enzymes require an optimum pH and temperature, because they are proteins. They also need an optimum substrate concentration
        
        The optimum temperature in humans is a range around 37 degrees Celsius (body temperature). This temperature is different in other organisms
        
        The rate of reaction increases with an increase in temperature up to this optimum, but above this temperature it rapidly decreases and eventually the reaction stops
        
        When the temperature becomes too hot, the bonds that hold the enzyme together will begin to break
        
        This changes the shape of the active site, so the substrate can no longer ‘fit into’ the enzyme
        
        The enzyme is said to be denatured and can no longer work
        
        The optimum pH for most enzymes is 7 (neutral), but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH
        
        If the pH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected
        
        This will change the shape of the active site, so the substrate can no longer fit in
        
        The enzyme is again said to be denatured, and can no longer work
  - - - Sexual reproduction involves the joining of male and female gametes, each containing genetic information from the mother or father
        
        Sperm and egg cells in animals
        
        Pollen and egg cells in flowering plants
      - Gametes are formed by meiosis, as they are non identical
      - A normal cell has 46 chromosomes. There are two sets of chromosomes (i.e. 23 pairs). In each pair, one chromosome is from the father and the second set are from the mother
      - Each gamete has 23 chromosomes and they fuse in fertilisation
      - The genetic information from each parent is mixed, producing variation in the offspring
      - Asexual reproduction involves one parent with no gametes joining
        
        It happens using the process of mitosis, where two identical cells are formed from one cell
        
        There is no mixing of genetic information
        
        It leads to clones, which are genetically identical to each other and the parent
        
        Examples of organisms that reproduce this way are bacteria, some plants and some animals
      - Advantages of asexual reproduction
        
        Only one parent is needed
        
        Uses less energy and is faster as
        organisms do not need to find a mate
        
        In favorable conditions lots of identical
        offspring can be produced
      - Advantages of sexual reproduction
        
        Produces variation in offspring
        
        This means that if the environment
        changes it is likely that an organism in the species will have a
        characteristic that allows them to survive (called a survival
        advantage)
        
        Although some individuals may die,
        variation decreases the chance of the whole species becoming
        extinct
        
        It allows us to use selective breeding
        
        This type of reproduction mixes the
        genetic information from two organisms
        
        Organisms with different desirable characteristics can be bred to produce offspring with even more
        desirable characteristics
        
        This speeds up natural selection
        
        An example is to increase food production by breeding two animals with lots of meat
    - - While mitosis is used for the division of ordinary body cells to produce diploid (2n) daughter cells, meiosis is used to produce haploid gametes (sperm and egg cells). Gametes only have one copy of each chromosome
      - Meiosis is the formation of four non-identical cells from one cell
        
        The cell makes copies of its chromosomes, so it has double the amount of genetic information
        
        The cell divides into two cells, each with half the amount of chromosomes (46)
        
        The cell divides again producing four cells, each with a quarter the amount of chromosomes (23)
        
        These cells are called gametes and they are all genetically different from each other because the chromosomes are shuffled during the process, resulting in random chromosomes ending up in each of the four cells
      - These gametes with 23 chromosomes join at fertilisation to produce a cell with 46 chromosomes, the normal number
        
        This cell divides by mitosis to produce many copies
        
        More and more cells are produced, and an embryo forms
        
        The cells begin to take on different roles after this stage (differentiation)
    - - DNA, found in the nucleus, is a chemical that contains genetic material
        
        DNA stands for deoxyribonucleic acid, and this is a polymer that contains instructions for the body
        
        It is made up of many small parts called nucleotides
        
        Each nucleotide is made up of one sugar molecule, one phosphate molecule (which form the backbone) and one of the four types of organic bases
        
        The four types of organic bases are A, C, G, T
        
        Each DNA molecule is made up of two DNA strands which are twisted together. Each base is connected to another base in the other strand
        
        A bases only connect to T bases, and C bases only connect to G bases. This is called complementary base pairing
        
        The order of the different bases forms a genetic code - e.g. A, G, T, T, C, A, A etc
      - DNA is a polymer (long molecule) made up of two strands which are wound around each other to form a structure called a double helix
      - A gene is a short section of DNA. Each gene codes for many amino acids, which are joined together to make a specific protein
        
        There are 20 types of amino acid
      - The word genome describes all the genetic information (DNA) of a single organism. The human genome has been studied, which has improved our understanding of the genes linked to different types of disease, the treatment of inherited disorders and has helped in tracing human migration patterns from the past
      - Extracting DNA from Fruit
        
        It is possible to extract DNA from fruit using household ingredients:
        
        Gently mix together 50ml cold water, half a teaspoon of salt and 10ml washing up liquid. Gently heat this mixture at 50C for 5-10 minutes
        
        Peel the skins of a kiwi and chop into small pieces. Pulverise the kiwis
        
        Add the solution from Step 1 to the kiwi
        
        Filter the solution using a few sheets of kitchen paper and a sieve. Pour the filtrate into a test tube
        
        Add 10ml of protease (or pineapple juice) to the filtrate and allow to rest for a few minutes
        
        Add 2 teaspoons of cold ethanol to the solution and wait 10 minutes
        
        What should we see?
        
        A white mass should precipitate at the top of the tube after 10 minutes; this is the DNA from the kiwi
        
        Why do we add protease?
        
        Protease contains an enzyme called bromelain which breaks down proteins attached to the DNA. This helps us see the DNA more clearly
        
        Why do we add ethanol?
        
        Ethanol causes the DNA to precipitate out of the solution - making it visible at the top of the container
    - - Each group of three bases (e.g ACT, AGG, GAC) codes for an amino acid
      - The amino acids are joined together and fold to make a protein. It is the different types and order of amino acids that determine which type of protein it is. Often these proteins are enzymes, which need to have a very specific shape
      - Therefore it is the order of bases in DNA that determine which proteins are produced
      - There are also non-coding parts of DNA that do not code for proteins. Some of them are responsible for switching genes on or off, i.e. controlling whether the gene is used to form a protein or not
      - Protein synthesis: the process of producing a protein from DNA
        
        If a gene is coded to make a protein, it has been expressed
        
        DNA contains the genetic code for making a protein, but it cannot move out of the nucleus as it is too big
        
        The mRNA nucleotides themselves are then joined together, creating a new strand called the mRNA strand. This is a template of the original DNA
        
        An enzyme called RNA polymerase binds to non-coding DNA located in front of a gene on the DNA strand
        
        The two strands of DNA pull apart from each other, and RNA polymerase allows mRNA nucleotides (messenger RNA: a different type of nucleotide) to match to their complementary base on the strand
        
        The mRNA then moves out of the nucleus to the cytoplasm and onto structures called ribosomes
        
        At the ribosomes, the bases on the mRNA are read in threes (triplets) to code for an amino acid (the first three bases code for one amino acid, the second three base code for another etc)
        
        The corresponding amino acids are brought to the ribosomes by carrier molecules called tRNAs - transport RNAs
        
        These amino acids connect together to form a polypeptide (amino acids linked by peptide bonds)
        
        When the chain is complete the protein folds to form a unique 3D structure, which is the final protein
    - - Genetic variants are small changes in the order of bases that make up a strand of DNA. They can affect the structure of proteins in different ways, depending on whether they occur in coding DNA or non-coding DNA
      - Genotype refers to the genes present in the DNA of an individual, whereas phenotype refers to the visible effects of those genes (e.g the proteins that they code for)
      - Coding DNA: A genetic variant will alter the sequence of bases (e.g ACT -> AGT) and therefore will change the sequence of amino acids (e.g Glycine -> Valine). This alters the final structure of the protein produced
      - Non-Coding DNA: A genetic variant in the coding DNA can affect phenotype differently. The enzyme RNA polymerase (see Section 3.8B) binds to non-coding DNA, and a change in the order of bases in this non-coding DNA can affect the amount of RNA polymerase that can bind to it. If less RNA polymerase is able to bind, less mRNA can be formed and the structure of the final protein is affected
      - Mutations change the sequences of bases in DNA. Either:
        
        A base is inserted into the code
        
        As they are read in threes, this changes the way it is read
        
        It may change all the amino acids coded for after this insertion
        
        A base is deleted from the code
        
        Like insertions they change the way it is read
        
        It may change all the amino acids coded for after this deletion
        
        A base is substituted
        
        This will only change one amino acid in the sequence or it may not change the amino acid (as the new sequence can sometimes still code for the same amino acid)
      - A change in the type/sequence of amino acids will affect the way it folds and therefore the structure
      - Most mutations do not alter the protein or only do so slightly
      - Some can have a serious effect and can change the shape
        
        The substrate will not fit into the active site so it cannot act as a protein
        
        A structural protein may lose its shape
      - There can also be mutations in the non-coding parts of DNA that control whether the genes are expressed
    - - Gregor Mendel
        
        Trained in mathematics and natural history in Vienna
        
        Worked in the monastery gardens and observed the characteristics passed on to the next generation in plants
        
        He carried out breeding experiments on pea plants
        
        He used smooth peas, wrinkled peas, green peas and yellow peas and observed the offspring to see which characteristics they had inherited
        
        Through keeping a record of everything he did and eventually publishing his work in 1866, he came to these conclusions:
        
        Offspring have some characteristics that their parents have because they inherit ‘hereditary units’ from each
        
        Offspring have some characteristics that their parents have because they inherit ‘hereditary units’ from each
        
        Units can be dominant or recessive, and cannot be mixed together
        
        Mendel was not recognised till after his death as genes and chromosomes were not yet discovered, so people could not understand
        
        In the late 19th century chromosomes as a part of cell division were observed
        
        In the 20th century, it was understood that chromosomes and units had similar behaviours. It was decided that units (now known as genes) were on the chromosomes
        
        The structure of DNA was determined in 1953, which meant we were able to understand how genes worked
    - - Gamete - An organism’s reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23)
      - Chromosome - A structure found in the nucleus which is made up of a long strand of DNA
      - Gene - A short section of DNA that codes for a protein, and therefore contribute to a characteristic.
        Some characteristics are controlled by a single gene, such as fur
        colour in mice and red-green colour blindness in humans. However, most characteristics are the result of many different genes interacting
      - Alleles - The different forms of the gene - humans have two alleles for each gene as they inherit one from each parent
      - Dominant allele - Only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be observed
      - Recessive allele - Two copies are needed for it to be expressed and for the corresponding the phenotype to be observed
      - Homozygous - -When both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles)
      - Heterozygous - When one of the inherited alleles is dominant and the other is recessive
      - Genotype - The combination of alleles an individual has, e.g. Aa
      - Phenotype - The physical characteristics that are observed in the individual, e.g. eye colour
      - Zygote - The stage of development immediately after fertilisation - a diploid (2n) cell formed from the fusion of two haploid gametes
      - Alleles (different forms of the same gene) lead to differences in inherited characteristics. This is because different alleles code for different forms of the same protein - an allele that codes for a damaged form of a protein can cause illness. For example, in a condition called Huntington’s Disease, an allele of the gene that codes for a particular protein is different. This leads to the protein becoming folded incorrectly and causing the condition
    - - Family trees show the inheritance of different phenotypes over generation in the same family
      - A monohybrid (single gene) cross looks at the probability of the offspring of two parents having certain genotypes and phenotypes. This is done using the alleles the two parents have for a gene and a Punnett square diagram
      - Uppercase letters are used to represent dominant characteristics. Lowercase letters represent recessive characteristics. You can choose any letter but usually either A or B is used for simplicity. Notice that combining the alleles shown above results in ¼ chance of having an offspring who is homozygous dominant (BB, or has two dominant alleles), and there is no chance of having a homozygous recessive offspring (as both parents have the allele). Whether or not the Bb (heterozygous recessive) offspring show symptoms depends on whether the condition itself is recessive or dominant
      - Family pedigrees are used to show how a condition (or more specifically, the allele which causes it) are passed down through different generations. We can use them to better visualise certain patterns - for example, the way that recessive alleles normally ‘skip a generation’
        
        We usually use squares to represent males, and circles to represent females in the lineage
        
        Black shapes represent an affected individual, and white shapes represent an unaffected individual
        
        A line through the shape means that the individual is deceased
        
        A line passing directly between two shapes means that the two are partners, and a line overhanging a group of individual means that they are siblings
    - - Human body cells have 23 pairs of chromosomes
        
        22 control characteristics, and the chromosomes in each pair look very similar
        
        The 23rd pair carries sex determining genes, and the two chromosomes can look different to each other (Y chromosomes are much smaller than X chromosomes)
      - The two possible chromosomes in the 23rd pair are X chromosomes and Y chromosomes. When cells undergo meiosis to form a gamete, one sex chromosome goes into each gamete
        
        Females have two X chromosomes, so therefore only pass on X chromosomes in their eggs
        
        Males have one X chromosome and one Y chromosome, so therefore can pass on X or Y chromosomes in their sperm
      - Punnett squares can be used to show sex inheritance. As shown in this diagram, there is a 50% chance of the child being male, and a 50% chance of the child being female
    - - We can use monohybrid crosses (Punnett squares) and pedigree analysis to analyse the probabilities of particular outcomes:
      - If the cystic fibrosis gene is autosomal recessive, and we use C/c for the normal and defective allele respectively:
        
        We can see that the risk of having both defective alleles (CC) is one out of four, or ¼ (25%)
    - - There are often important patterns to be seen in inheritance of particular genes. For example, sometimes 2 dominant alleles can be expressed together in the same individual. This is called codominance. When three or more alleles can be present at the same loci (but not necessarily expressed at once), we say that multiple alleles are present at the same position, or locus
      - An example of codominance and multiple alleles is the ABO blood group system, where there are alleles for A, B and O that can all be expressed at the same locus (position). Only two of them are expressed at once, however, with the following pattern (note that the O allele is recessive, and the A and B alleles are dominant):
        
        A and O alleles: becomes type A
        
        A and B alleles: becomes type AB (codominantly expressed)
        
        A and A alleles: becomes type A
        
        B and B alleles: becomes type B
        
        O and O alleles: becomes type O
        
        It should be clear from the above that Type O blood is significantly more rare than types involving A or B alleles
    - - Some alleles are not found on chromosome pairs 1-22: instead, they are found on the sex chromosomes X and Y. Remember that in humans, males carry an X and a Y chromosome (XY), whereas females carry two X chromosomes (XX). If these alleles cause a genetic disorder, it is known as a sex-linked genetic disorder. The majority of sex-linked conditions are found on the X chromosome
      - When using Punnett squares to demonstrate sex-linked inheritance, we can use XD to represent an X chromosome with the affected gene, and X to represent one that is unaffected, for example
        
        X-linked conditions can be recessive or dominant
      - Usually, X-linked recessive syndromes are more common in males - because in females, there is an extra X chromosome to mask the effect of the recessive allele. However, in males, there is only one X chromosome and if it contains the defective allele, the individual will have the condition
    - - Most phenotypic features are the result of multiple genes acting together, and not single genes. For example, as many as 16 genes are thought to be responsible for human eye colour
      - Variation between individuals is an important factor in allowing natural selection to happen, and it originates from one of two main areas:
        
        Genetic variation - different characteristics can arise as a result of both random mutation and sexual reproduction. Random mutation occurs in gametes to produce offspring with ‘brand new’ phenotypic characteristics, whereas sexual reproduction causes the offspring to have a new combination of characteristics from both its mother, and its father
        
        Environmental variation - characteristics can also be caused by an organism’s environment, but these changes are generally not heritable (there is no change in the DNA of the organism). For example, a child who does not receive adequate nutrition will not grow to their full height, however this has no effect on their potential height as determined by their genetics
    - - Remember - the word genome describes all the genetic information of that organism. The human genome has been studied, or ‘mapped’ as part of the Human Genome Project, which has:
        
        improved our understanding of the genes linked to different types of disease
        
        helped in the treatment of inherited disorders
        
        helped in tracing human migration patterns from the past
      - By mapping the entire human genome, we are better able to understand which genes cause inherited disorders and which genes are linked with each other
      - There is usually extensive genetic variation within a population of a species - this arises through random mutation
      - Genetic mutation can have varying effects on the phenotype. For example, the majority of mutations have no effect on the phenotype as they occur in DNA which does not code for proteins (non-coding DNA). Some mutations can have a small effect on the phenotype, and other mutations, rarely, can significantly affect the phenotype - for example, changing one base can change one amino acid in a protein. If the protein was an enzyme, this has the potential to change the shape of the active site so that substrates can no longer bind to it