Most experiments answer

• Scientists use their knowledge, experience, and observations to make predictions about how things might behave under certain conditions.
• Controlled variables:

  • time of treatment
  • concentration and volume of chemicals(solution)
  • temperature, pH, environmental conditions of the experimental set-up
• Important answer wordings:

  • sample size should be larger
  • repetition is needed
  • randomly assign to groups
  • design of controlled experiment
• Experimental set up

  
• • Soaking serves to induce germination of the barley grains by softening the grain coat
  • during germination, enzymes inside the barley grains are activated, which help break down the starch stored in grains into maltose and then glucose.Glucose is used as the raw material for alcoholic fermentation.
  • boil the wort to drive away all the dissolved oxygen in the wort and to kill all microorganisms in the wort
  • yeast carries out anaerobic respiration to break down glucose to form ethanol

  
• Young seedlings are preferred to mature plants as they do not store minerals and their rapid growth rate gives a more conspicuous result.
• The jar must be covered with black paper or aluminum foil to exclude light.This prevents the algal growth that may consume some minerals and clog the root hairs
• The solution must be renewed weekly for three reasons:

  1. Replace for the elements used up in the experiment
  2. Avoid the accumulation of metabolic wastes that may retard the growth
  3. Avoid excessive use of culture solution that may expose the roots to air
• Less water is absorbed in the small intestine of a lactose intolerant person due to the presence of lactose
• The water potential of the fluid in the small intestine of a lactose intolerant person is lower than that in a person without lactose intolerance
• The water potential difference between the intestinal fluid and the cells lining the intestine in a lactose intolerant person is smaller than that in a person without lactose intolerance
• Less water is absorbed by osmosis in a lactose intolerant person
• Lactose intolerant individuals lose the ability to digest lactose
• The gene that codes for lactase becomes inactive
• With insufficient lactase produced, they are unable to digest lactose properly
• Assumptions in the experiment about the activity of catalase in yeast beads:

  • oxygen released by yeast beads is only contributed by the activity of catalase but not other enzyme
  • amount of catalase in each yeast bead is the same
  • respiration of yeast cells does not affect the pH of the solution
• • When catalase in the yeast beads broke down hydrogen peroxide , oxygen was released.
  • when the amount of oxygen evolved reached a certain level, the oxygen bubbles buoyed up the yeast beads to the surface of the solution
• If there were no catalase present in the yeast beads, then the rate at which oxygen would have been released from the hydrogen peroxide would have been very slow.
• In this case, the control group (the one with no added hydrogen peroxide) would also remain unchanged as there would be no reaction between the yeast beads and the hydrogen peroxide.
• However, if all the yeast beads rose to the top of their respective tubes within 10 minutes, it can be assumed that all the yeast beads contained some catalase.
• More than one sample should be used so that the results obtained would be more reliable since it minimises individual differences
• Copper sulphate is an inhibitor of catalase
• The set-up should be left for at least ten minutes before the start of the experiment to allow the set-up to equilibrate with the surrounding conditions
• The transpiration rate of the lower epidermis is higher than that of the upper epidermis as the number of stomata in the lower epidermis is greater than that of the upper epidermis
• • The cobalt chloride paper test measures directly the amount of water vapour lost from the leaf
  • The results can be obtained within a short period of time
  • This method is more convenient
• • The result of cobalt chloride paper test obtained are less reliable as the time of colour change is affected by a number of other factors, such as humidity of the air, moisture on fingers/leaf surface
  • covering the leaf surface with cobalt chloride paper may affect the normal transpiration rate of the leaf
• Staining with iodine solution: make the cell structure more distinct
• Adding a drop of water: reduce refraction of light