Key concepts in Biology

• What is diffusion?

  the net movement of particles from an area of high concentration to an area of low concentration, down the concentration gradient.
• What is active transport?

  The movement of particles across a membrane against a concentration gradient using energy transferred during respiration
• Give an example of when active transport is used in the body.

  In the digestive system, if there's a lower concentration of nutrients in the gut then in the blood, active transport allows nutrients to be taken into the blood, despite the fact that the concentration gradient is the wrong way. This stops us from starving.
• What is osmosis?

  The net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration ( or from a region of lower solute concentration to higher concentration)
• Describe an experiment to investigate osmosis

  1. Prepare sucrose solutions of different concentrations ranging from pure water to very concentrated solutions.

  2. Use a cork borer to cut potato into pieces of the same size, around 1cm diameter

  3. Divide cylinders into groups of three and measure the mass of each group.

  4.Leave the groups of cylinders in the solutions for atleast 40 minutes, then remove them and pat dry with a paper towel to remove excess water ( so final masses are more accurate)

  5. Weigh each group again and record results
• What would happen to a potato cylinder in a highly concentrated sucrose solution?

  It would lose mass, as water would move ,via osmosis, into the sucrose solution because the solution has a lower concentration of water and a higher concentration of solute.
• What would happen to a potato cylinder in pure water?

  It would gain mass, since there is a lower concentration of water in the potato then outside in the water, so water enters it via osmosis ( high conc to low conc)
• What is an enzyme?

  a biological catalyst (substance that speeds up the rate of reaction without being used up)
• What is the Lock and Key mechanism?

  The enzyme has a complementary active site to the substrate so it fits into the enzyme like a key does to a lock. They form an enzyme-substrate complex and enzyme catalyses the reaction.
• How does temperature affect enzyme activity?

  temperature increases chance of enzyme substrate collisions so enzyme activity increases as temperature increases, up to an optimal temperature. Beyond the optimum temperature, the bonds holding the enzyme together break, changing the shape of the enzyme's active site, so it can no longer bind to substrate, decreasing activity until enzyme is completely denatured.
• How does pH affect enzyme activity?

  Each enzyme has an optimal pH at which it can perform at its maximum rate. Too high or too low of a pH deviates the enzyme from its maximum rate and it begins to denature, decreasing enzyme activity. Normally, a neutral pH is the optimum, but for stomach enzymes, it is more acidic, around pH 2.
• How does substrate concentration affect enzyme activity?

  A higher substrate concentration means it is more likely that enzyme-substrate complexes will form so enzyme activity increases. However, this is only true up to a certain point, and after a while there is too many substrate molecules and all the enzymes active sites will be full. Adding more will no longer make a difference.
• Describe a test used to determine if a solution contains reducing sugars.

  The Benedict's reagent test is used. First, you need to heat benedict's reagent in a water bath at 75. If the test is positive, a coloured precipitate will form and the further this colour change, the higher the concentration of reducing sugars, with brick red being the highest.
• Describe a test used to determine if a solution contains proteins.
• Describe a test used to identify lipids in a solution.

  The Emulsion test: shake the test substance with ethanol for one minute until it dissolves, then pour this solution into water. If lipids are present, they precipitate out of the liquid and show up as a milky emulsion.
• Describe a test used to identify starch in a solution.

  Iodine test: Add iodine solution to the test sample. If starch is present, the sample will change from a browny-orange colour to a blue-black colour. If not, it will stay browny-orange.
• Amalyse enzyme breaks down starch( carbohydrate) into maltose or other simple sugars
• Carbohydrase enzymes break down carbohydrates into simple sugars such as glucose or fructose
• Protease enzymes break down proteins into amino acids
• Lipase enzymes break down lipids into glycerol and fatty acids
• Energy in food(J) = mass of water(g) x temperature change x 4.2
• Energy per gram of food(J/g)= Energy in food(J)/mass of food(g)
• Advantages of light microscopes

  cheaper, easy to use, can study living cells
• Disadvantages of light microscope

  lower resolution and magnification so images viewed in less detail
• Advantages of electron microscope

  higher resolution and magnification which allows us to see smaller things in more detail, like the internal structure of subcellular structures. This allows us to gain a greater understanding of how cells work, and the role of these subcellular structures.
• Disadvantages of electron microscopes

  expensive, hard to use, can't be used to view living cells, only dead cells
• 1 millimetre(mm)= 0.001m

  1 micrometre(μm)= 0.000001m

  1 nanometre(nm)= 0.000000001m

  1 picometre(pm)= 0.000000000001m