Topics to revise
Cells
Atomic structure
Required practical - Microscopes
Required practical - Osmosis
Microscopes
Use a light microscope to observe, draw and label a selection of plant and animal cells. A magnification scale must be included.
Check your understanding with these quick common questions. Use the drop down boxes to see the correct answers.
Control:
Dependent:
Independent:
Light microscope, prepared slide (onion skin or cheek cell), stain.
Ensure specimen is flat and thin, focus carefully, repeat with more than one sample.
Onion cells show cell wall, cytoplasm, nucleus; cheek cells show cell membrane, nucleus, cytoplasm.
Peel a thin layer of onion skin / collect a cheek cell.
Place on a slide and add a drop of iodine to stain cell wall.
Carefully lower a coverslip onto the sample.
Place under microscope, start with low power.
Focus the image, then move to higher power.
Draw what you see with clear labels, sharp pencil and no shading.
Osmosis
Investigate how water moves in and out of potato cells when placed in solutions of different concentrations.
Independent: concentration of sugar/salt solution.
Dependent: change in mass/length of potato.
Control: same potato type, time left, volume of solution
Balance (for mass), ruler, sugar/salt solutions.
Dry potato before weighing to ensure results are valid.
Use same thickness chips, repeat and calculate mean.
Improve accuracy by drying to measure true change in mass. Use a pan balance with more decimal places.
In dilute solution, potato gains mass (water enters). In concentrated solution, potato loses mass.
Cut equal-sized potato chips using ruler
Weigh or measure them with pan balance
Place into solutions of different concentration of salt.
Leave for set time (at least 10 minutes)
Remove, blot dry, reweigh.
Compare percentage mass change.