Biology Edexcel GCSE

• The tips of plant roots are where many cells are dividing by mitosis. Which term describes the area of a root where many cells are dividing by mitosis?

  meristem
• Plant root cells contain an enzyme that joins glucose molecules together to make starch. Devise a plan to investigate the effect of pH on the activity of this enzyme.

  • Add enzyme solution/plant root cells to glucose solution
  • test for the presence of starch
  • test each minute until a positive result for starch
  • repeat at more than one pH
  • control variables would be the same volume of solution or the same temperature.
• A student investigated the fat content of two types of milk: milk A and milk B. Before starting the investigation, the student added a drop of oil from a pipette into a test tube of water. The drop of oil rose to the surface of the water. 5 cm^3 of milk B and 1 cm^3 of lipase were added to a different test tube. The pH of this mixture was pH 7. This test tube was placed in a water bath for 10 minutes. The pH of the mixture changed from pH 7 to pH 5. Explain what caused this change in pH

  • lipase digests fat/lipid
  • forming fatty acids and glycerol
  • making the mixture more acidic
• 5 cm^3 of milk B and 1 cm^3 of lipase were added to a different test tube. The pH of this mixture was pH 7. This test tube was placed in a water bath for 10 minutes. The pH of the mixture changed from pH 7 to pH 5. This procedure was repeated with milk A. There was no change in the pH of this mixture after 10 minutes. Explain why there was no change in the pH of the mixture containing milk A.

  • milk A did not contain much fat
  • as there was no substrate
• 5 cm3 of milk B and 1 cm3 of lipase were added to a different test tube. The pH of this mixture was pH 7. This test tube was placed in a water bath for 10 minutes. The pH of the mixture changed from pH 7 to pH 5. The student repeated this procedure with lipase that had been boiled and left to cool. This was added to another sample of milk B. Describe why the pH did not change in this mixture.

  • the temperature is above the optimum
  • the enzyme denatures
  • so active site changes shape
  • no longer complementary to the substrate
• A scientist investigated how the length of starch grains in potatoes changed when the potatoes were stored in the dark. Three potatoes were used in the investigation. The length of starch grains in potato 1 were measured at the start. The length of starch grains were measured in potato 2 after 5 weeks in the dark. The length of starch grains were measured in potato 3 after 10 weeks in the dark. State variables the scientist should have controlled to improve this investigation.

  1. variety of potato
  2. mass of potato
  3. age of potato
  4. temperature
  5. storage conditions / humidity
• State why the potatoes need glucose

  for energy / respiration
• Describe how starch is broken down into glucose.

  • enzyme / amylase / carbohydrase
  • starch fits into the active site
  • bonds between glucose molecules in starch broken
• Carbohydrates, lipids and proteins

  Biological molecules (molecules found in living organisms)
• Testing for biological molecules

  Use different chemicals to test for carbohydrates, lipids and proteins
• Reducing sugars

  Sugars (e.g. glucose) with chemical properties that allow them to be tested using Benedict's reagent
• Testing for reducing sugars using Benedict's reagent

  Add Benedict's reagent (blue) to sample and heat in water bath at 25°C

  2. Positive test forms coloured precipitate, colour change indicates concentration of reducing sugar
• Starch

  Tested for using iodine solution, turns dark blue-black if present
• Testing for lipids using emulsion test


  Shake test substance with ethanol until dissolved, then pour into water

  2. Milky emulsion indicates presence of lipids, more lipid means more milky
• Biuret test for proteins


  Add potassium hydroxide to make solution alkaline

  2. Add copper(II) sulfate solution

  Purple colour indicates presence of protein, blue colour indicates no protein
• A solution mixed with potassium hydroxide and copper(II) sulfate turning purple indicates the presence of protein
• Enzymes


  Biological catalysts produced by living organisms that increase the rate of chemical reactions without being consumed or permanently altered
• Enzymes


  • They have an active site that the substrate must fit into for the reaction to be catalysed (lock and key mechanism)

  Their activity is affected by temperature, pH and substrate concentration
• Investigating effect of pH on enzyme activity


  Add amylase, buffer solution and starch to boiling tube, heat to 35°C

  2. Sample mixture every 10 seconds, test for presence of starch using iodine

  3. Repeat with different pH buffer solutions to see how pH affects time for starch breakdown
• Rate of reaction


  Measure of how much something changes over time, calculated as amount changed / time taken
• The enzyme catalase catalyses the breakdown of hydrogen peroxide into water and oxygen, 24 cm3 of oxygen was produced in an investigation
• How to Calculate the Rate of Reaction


  1. Use a pH meter to accurately measure the pH of solutions

  2. Use the formula 1000/time to get a bigger number that's easier to plot on a graph
• Rate is often useful to calculate the rate of reaction after an experiment
• Rate


  A measure of how much something changes over time
• Calculating the rate of reaction

  Rate = Amount of product formed / Time taken
• If an experiment measures how much something changes over time, you calculate the rate of reaction by dividing the amount that it has changed by the time taken
• The enzyme catalase catalyses the breakdown of hydrogen peroxide into water and oxygen
• You could adapt this experiment to investigate how factors other than pH affect the rate of amylase activity
• An enzyme-controlled reaction was carried out at pH 4. After 2 minutes, 36 cm³ of product had been released
• Calculate the rate of reaction

  Rate of reaction = Amount of product formed / Time taken = 36 cm³ / 2 minutes
• Cells


  The basic building blocks of all living organisms
• When someone first peered down a microscope at a slice of cork and drew the boxes they saw, little did they know that they'd seen the building blocks of early life on the planet
• Types of organisms


  • Eukaryotes
  • Prokaryotes
• Eukaryotic cells


  • Complex
  • Include all animal and plant cells
• Prokaryotic cells


  • Smaller and simpler
  • e.g. bacteria
• Eukaryotes


  Organisms made up of eukaryotic cells
• Prokaryote


  A single-celled organism
• Subcellular structures in animal cells


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Nucleus


  Contains genetic material that controls the activities of the cell
• Cytoplasm


  Gel-like substance where most chemical reactions happen, contains enzymes