required practicals Flashcards
(6 cards)
Practical 1: Investigating the effect of a named variable on the rate of an enzyme-controlled reaction
Prepare a range of substrate concentrations using serial dilutions (e.g. starch for amylase).
Add equal volumes of buffer solution to maintain constant pH.
Add a fixed volume of enzyme to each tube and start a stopwatch.
Take samples at regular intervals and test with iodine on a spotting tile.
Record the time when iodine no longer turns blue-black (reaction complete).
Repeat at least 3 times and calculate mean time or rate for each concentration.
Practical 3: Investigating the effect of a named variable on the permeability of cell-surface membranes
Cut equal-sized beetroot cylinders and rinse to remove surface pigment.
Place them in test tubes containing equal volumes of distilled water.
Vary one condition, e.g. temperature using water baths or solvent concentration.
After a set time, remove beetroot and mix solutions.
Measure absorbance of each solution using a colorimeter.
Plot absorbance vs. temperature or concentration to assess permeability.
Practical 2: Observing mitosis in root tips
Cut 5 mm of root tips (e.g. garlic/onion), place in HCl at 60°C for 5 minutes.
Rinse and place on a microscope slide; add stain (e.g. toluidine blue) to highlight chromosomes.
Gently macerate the tissue with a mounted needle.
Add a coverslip and squash gently to produce a single layer of cells.
View under a microscope at high power and identify mitotic stages.
Count cells in each stage and calculate mitotic index = (cells in mitosis ÷ total cells) × 100.
Practical 4: Investigating the effect of a named variable on the movement of substances by osmosis
Cut equal-sized cylinders or discs of plant tissue (e.g. potato).
Blot dry and weigh each piece before placing in different sucrose concentrations.
Leave samples for a set time (e.g. 20 minutes).
Remove, blot dry again, and reweigh to calculate percentage change in mass.
Plot results on a graph of percentage change vs. concentration.
Identify the concentration where mass doesn’t change — the tissue’s water potential
Practical 5: Dissection of animal or plant gas exchange system (e.g. lungs/heart)
Examine and identify the trachea, bronchi, and lungs.
Use scissors to cut open the trachea to observe cartilage rings.
Follow bronchi into lung lobes and note alveolar structure.
Use appropriate dissection tools and techniques for safety and accuracy.
Record labelled drawings and observations of internal structures.
Dispose of biological waste according to safety guidelines.
Practical 6: Using aseptic techniques to investigate the effect of antimicrobial substances on microbial growth
Sterilise the agar plate surface and equipment using aseptic techniques.
Inoculate a bacterial lawn evenly using a sterile pipette or spreader.
Place paper discs soaked in different antimicrobial agents onto the agar.
Seal the Petri dish with tape (not all the way around) and incubate at 25°C.
Measure the diameter or area of clear zones after incubation.
Compare zones to determine effectiveness of each antimicrobial.
