Key Biological Concepts - Topic 1

  • Created by: aa_xx
  • Created on: 08-04-19 11:48


  • Magnification - the degree to which the size of an image is larger than the object actually is
  • Resolution - degree to which it is possible to destinguish between two points that are very close together
  • Light microscopes have lower magnification (x1500) whereas electron microscopes are higher (x 2 000 000)
  • Light microscopes also have low resolution (0.1 micrometres) whereas electron microscopes have a higher resolution (0.2 micrometres)
  • Transmission electron microscopes (TEM) - see 2D detail and are black and white
  • Scanning electron microscopes (SEM) - see 3D images and may be in colour
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  • Magnification - the number of times larger an image is than the initial object that produced it
  • To obtain magnification multiply magnification of the eyepiece and objective lens by each other
  •  Resolution - the smallest distance between two points that can still be seen as two points
  • Field of view - circular area you see in a light microscope
  • Magnification = image size / actual size 
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  •  Eukaryote - cell with a true nucleus e.g. plants and animals
  • Prokaryote - cell does not have a true nucleus
  • Bacteria have a large loop of chromosomal DNA in the cytoplasm. They also have small loops of DNA, called plasmids 
  • Bacteria do not have mitochondria or chloroplasts
  • Bacteria contain very small ribosomes
  • Some bacteria have a flagellum for movement
  • Some bacteria have a slime coat for protection
  • The cell wall is more flexible than plant cell walls and is not composed of cellulose
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Transporting substances

  • Diffusion is the movement of particles from a region in which they are in higher concentratiom to regions of lower concentration
  • Concentration gradient is the difference in concentration between two areas. The bigger the differnece, the steeper the gradient.
  • The steeper the gradient the faster the rate of diffusion.
  • Factors the effect the rate of diffusion:
  • Concentration gradient
  • Temperature
  • Surface area (larger the SA the faster the rate of diffusion)
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  • Osmosis is the overall movement of water molecules across a partially permeable membrane from where there are more water molecules to where there are fewer water molecules
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Active transport

Cells may need:

- to transport molecules against a concentration gradient  OR

- transport molecules that are too big to fit through the cell membrane

  • Active transport is carried out by transport proteins in cell membranes
  • The transport proteins capture certain molecules and carry them across the cell membrane
  • This is an active process and therefore requires energy
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  • Halophytes - plants that live in soils with a high salt content
  • Their ability to take up water by osmosis is affected


  • Ability to secrete salt or to store it in old leaves
  • Specialised tissue that allows water (not salt) to enter the roots
  • Tissue tolerence of high salt levels
  • Actively absorb salts into roots so water follows nby osmosis
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  • Enzymes are biological catalysts i.e. they increase the rate of rections
  • Enzymes control chemical reactions inside and outside of cells
  • Enzymes are proteins
  • Enzymes are specific in their action i.e. each enzyme only catalyses a particular chemical reaction 
  • Enzymes catalyse the reaction, but remain unchanged by it. They can therefore be used again and again to catalyse other reactions of the same kind
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Enzyme action

  • enzyme + substrate -> enzyme substrate complex -> enzyme + product
  • The substrate binds to the active site of the enzyme
  • The substrate and enzyme fit like a 'lock and key' - makes the enzyme specific
  • The enzyme catalyses the breakdown of the substrate into products
  • The enzyme is then free to join another substrate molecuoe i.e. it can be used again and again.
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Uses of Enzymes

  • Enzymes can be used to break down molecules e.g. during digestion. Large, insoluble food molecules are broken down into smaller, soluble molecules so that they can be absorbed into the bloodstream
  • Enzymes can also join substrates together i.e. synthesise new molecules e.g. photosynthesis and protein synthesis
  • Enzymes are also used in the food production industry
  • Enzymes are also found in biological washing powders where they 'digest' food stains
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Enzymes in digestion

  • Starch and proteins are both polymers. This means that they are large molecules that consist of repeated units called monomers 
  • During digestion starch is broken down into its monomers called glucose
  • Proteins are digested into their monomers called amino acids
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Examples of enzymes

  • Amylase - found in saliva and the small intestines
  • Catalase - found in most cells (especially liver cell)
  • Starch synthase - found in plants
  • DNA polymerase - found in the nucleus
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Enzyme activity

  • When the shape of the active site changes the substrate can no longer fit into the active site
  • Two factors can cause the active site to change its shape:

- Increased temperature

- Change in pH

  • When the shape of the enzyme (espically the active site) changes, the enzyme can no longer carry out its function snd it is said to be denatured
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Enzymes - temperature

  • As temperature increases, particles move faster. So there is greater chance of a substrate molecule entering an active site and being changed
  • Optimum temperature: when the enzyme is working fastest becayse many fast-moving substrate molecules enter and fit easily into the active site
  • When temperature is above the optimum, the active site changes shape so the substrate molecule no longer function and the enzyme is denatured
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Enzymes - pH

  • When the pH is below optimum, the active site is not quite the same shape. This means a slower rate of reaction
  • Optimum pH - enzyme works fastest
  • When the pH is above optimum the active site changes shape and no longer fit. The reaction is slower
  • Finally the enzyme is dentaured
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Enzymes - substrate concentration

  • The rate of an enzyme-controlled reaction is also dependent on the concentration of the substrate present.
  • At low concentrations, many enzyme molecules have empty active sites si the rate of reaction is low
  • As the substrate concentration increases more active sites are occupied and the rate increases
  • Wheb the active site of every enzyme molecule contains a substrate molecule, others must wait their turn and the reaction cannot go any faster.
  • The maximum rate for that substrate concentration has been reached.
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Food tests


  • Starch - iodine solution - neg: yellow-brown, pos: blue-black
  • Reducing sugar (glucose) - benedicts solution then boiling water - neg: blue, pos: brick red precipitate

Proteins - biuret test, sodium hydroxide and then copper sulphate - neg: blue, pos: purple

Fats and oils -  emulsion test, ethanol and mix and then cold water - neg: clear solution, pos: milky/white emulsion

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  • Food contains enrgy which is released in the cells during respiration.
  • Foods that contain a large amount of sugars and fats are particularly good sources of energy
  • We can measure the amount of energy in foods by burning it in a calorimeter
  • The amount of energy transferred from the burning food to the water can be calculated from the increase in water temperature
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