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Sampling techniques:
Quadrats: Small metal frames that are placed on the ground at a given coordinate. Count number of individuals inside quadrat or percentage cover.
Transect: A line drawn with a tape measure where interval sampling can be carried out. Allows change in distribution along a line to be measured.
Samples: Samples must be randomly generated using a random number generator. This ensures there is no bias to the investigation. The sample size (the number of samples taken) must be large, enabling a mean to be calculated and allows anomalies to be identified.
Repeats also allow a mean to be calculated. Aim to repeat an investigation at least three times.
Risk assessment:
-Questions often address certain potential risks or hazards when carrying out a practical investigation. Biology work can often involve sharp scalpels, irritant chemicals, bacteria, or sometimes a naked flame. Precautions must therefore be taken in order to ensure the students safety.
Eye protection, goggles, lab coat, gloves, fume cupboard, safety screens and taking personal care are all measures to ensure a safe laboratory. Be able to identify the risks associated with a given practical, and how to take the right steps to approach the investigation.
Digesting using an enzyme solution & substrate:
-Questions can be directed towards the action of trypsin (protease) of catalase (breaks down H2O2 to O2 and H2O).
-Be careful to remember what you will be controlling in the experiment! Control variables can include:
Temperature: Controlled by using water baths or ice. Controlling temperature is important as it affects both the enzymes structure and the rate of collisions between enzyme and substrate.
pH: Enzymes are highly pH sensitive. Make sure to keep the pH the same (unless its what you're investigating) using buffer solutions and pH probes to monitor pH.
[Enzyme]: Again, unless the concentration of enzyme is what you are investigating, be sure to keep the volume and concentration of enzyme the same. This also applies for the substrate.
Plant experiments: Visualising xylem activity
-Questions can be directed towards how one could visualise water moving up the xylem over a period of time. Here you should look to describe a setup using water and red food dye. Place a celery stick into the solution and leave for a couple of hours. After time has passed, cutting the celery shows the presence of the red solution within the vascular bundle.
Stomata: Practical questions can illustrate scenarios where upper/lower surfaces of leaves are left uncovered or are covered with wax to see how the amount of water inside the leaf changes. Here remember stomata are found on the underside of leaves so only covering the lower surface should have an effect on water loss.
Root tip squash: Staining crushed root tips of plants and staining with toluidine blue or acetic orcein can help show what stage of mitosis the cells are in when viewed under a microscope. Here remember anaphase = apart, metaphase = middle.
Potato tubers + osmosis: Investigating how the tissue of potato either loses or gains water (and therefore mass) from solution can be measured by using a potato borer to cut equal sized cylinders of potato. Remember, the more sugar a solution has in it, the lower its water potential. Expect water to move towards the more sugary environment, down the water potential gradient.
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