Paper 1 practicals Flashcards
What microscope is used in school practicals?
Optical microscope
What is the stage of a microscope?
Centre of the microscope where the microscope slide is place
What is below the stage?
Lamp, where light from the lamp passes through the microscope slide.
What is above the stage?
3 objective lenses
What is above the objective lenses?
Eye piece where you look through, it has a magnification of 10x
What are on the side of the microscope?
- coarse focusing dial
- fine focussing dial
Process of using a microscope?
- Place slide into stage using clips to hold it in place
- Select lowest objective lens , usually 4x
- Position the lens so it almost touches the microscope slide. To do this slowly turn the coarse focussing dial
- look down through eye piece lens
- Turn coarse focussing dial slowly , to increase the distance between objective lens and the slide , until cells come into focus
- use fine focusing dial to bring the cells into clear focus
How to calculate magnification?
Magnification of eye piece lens x magnification of objective lens
Problem with optimal microscopes?
Limited detail, only the cytoplasm , nucleus and cell membrane
What happens when a plant cell is placed into water?
Water will move into it through osmosis
What will happen if a plant cell is placed into a dilute solution?
Water will move out of it by osmosis and the cell will shrivel up
Process of investigating osmosis in vegetables?
- Peel potato , skin can effect osmosis
- Use cork borer to produce 3 cylinders of potato, make them all the same diameter
- Use scalpel to trim cylinders to the same length (around 3 cm)
- Measure length and mass of cylinders
- Place each cylinder into a test tube
- First test tube add 10cm^3 of 0.5 molar sugar solution. Second add 10cm^3 of 0.25 molar sugar solution. Third add 10cm^3 of distilled water
- Leave potato overnight to allow osmosis to take place
- Remove potato cylinders and gently roll them on paper to remove surface moisture
- Measure the mass and length of cylinders to find difference
Why is distilled water used instead of tap water?
Distilled water contains no dissolved substances, which could effect the rate of osmosis
How to work out percentage change?
Change in value/original value X100
How to prepare a slide a microscope slide?
- Place a drop of water on the slide
- using forceps remove thin layer of onion
- Place the specimen on the slide gently
- Using a pipette add 2-3 drops of stain , e.g iodine to specimen
- slowly at a 90 degree angle , lower the cover slip to cover the specimen . Avoid air bubbles.
What are we investigating the osmosis practical?
In this experiment, you can investigate the effect of glucose solution on plant tissue using a potato
What are we investigating in the microscopy experiment?
Using a microscope to look at onion skin cells and estimate their size.
What are we investigating in the food tests?
We are identifyinh the main foods groups using standard food tests.
How do we prepare for the food tests?
Step 1: grind or crush the food sample using a pestle and mortar
Step 2: add the sample to a test tube containing water or ethanol and shake.
Step 3: filter the mixture to remove any solids.
What test for starch?
Iodine
What tests for protein?
Biuret solution
What test for fat?
Ethanol
What test for sugars?
Benedict solution
How to test for starch?
Iodine test for starch , yellow -red iodine solution turns blue -black if starch is present
