A Level Biology Practicals Flashcards
What is the purpose of using a microscope and calibration?
- To observe and measure cells.
Why do we stain during microscope and calibration?
- Staining is used to highlight cell structures such as iodine for starch.
Outline the process of root tip squash?
- Adding hydrochloric acid to soften the root tip tissue.
- Staining will make the chromosomes visible.
What is the mitotic index?
Number of cells in mitosis/Number of total cells x100
How do you prepare a root tip squash?
- Cut a root tip
- Soften with hydrochloric acid
- Stain
- Gently squash under a coverslip.
Why is the root tip used for observing mitosis?
- It contains meristematic tissue, where cells are actively dividing.
How do you identify different stages of mitosis?
- Prophase: Chromosomes condense
- Metaphase : Chromosomes alligned at the equator.
- Anaphase: Chromatid pulled apart
- Telophase: Two nuclei form
How do you control variables in an enzyme experiment?
- Use a buffer solution for pH
- use a water bath to maintain temperature
- Keep enzyme/substrate concentration constant.
Why does reaction rate decrease at high temperatures?
- High temperatures denature the enzyme and the active site changes shape.
- Substrate no longer fits, so enzyme substrate complexes cannot form.
How do you measure permeability using a colorimeter? `
- Higher absorbance means more pigment is released and therefore a higher permeability.
Why does temperature affect membrane permeability?
- High temperature disrupts the phospholipid bilayer.
- proteins denature, increasing the permeability.
How do you determine the water potential of plant tissue?
- Find the sucrose concentration where mass change = 0
Why do cells gain/lose mass in different solutions?
- Hypotonic solution: More water otuside than inside so water enters.
- Hypertonic: More water inside than outside so it leaves
Why do small organisms have a higher diffusion rate?
- They have a higher surface area to volume ratio, so diffusion is faster.
How does surface area to volume ratio affect diffusion?
- Larger SA:V ratio means faster diffusion as there is a shorter diffusion distance.
How are fish gills adapted for efficient gas exchange?
- Gill lamellae creates a large surface area
- Thin diffusion distance
- Counter current flow maintains a concentration gradient
How does the tracheal system in insects allow for gas exchange?
- Spiracles open for gas entry
- Trachea delivers oxygen directly to cells.
How do you ensure a valid test when measuring photosynthesis?
- Use the same plant species, temperature and light source
How does light intensity affect the rate of photosynthesis?
- More light means more energy for photosynthesis meaning increased oxygen production.
How do you calculate an Rf value?
Distance moved by pigment/ distance moved by solvent
Why do different pigments travel different distances?
- Different solubilities in the solvent and affinity for the paper
How do you measure the effectiveness of an antibiotic?
- Measure the clear zone diameter around antibiotic discs.
Why do we use aseptic techniques?
- To prevent contamination by unwanted microbes.
- Ensures results are valid and reliable.
