AS Practicals

Question 1

Osmosis practical - investigating membrane permeability

Answer 1

Make dilution series with sucrose solution and distilled water
Use scalpel/cork borer to cut equal sizes
Weigh masses ensuring roughly the same
Place in water
Remove after 10 minutes
Blot dry with paper towel
Weigh masses after
Increase in mass shows cells have a lower water potential - at low sucrose concentration
Plot graph of change in mass and sucrose concentration
With beetroot use colorimeter - for permeability of cell membranes
Plot calibration curve

Question 2

Enzyme

Answer 2

Variables - temperature, pH, substrate concentration, enzyme concentration
Test tube of 5cm3 distilled water as a control indicating the absence of enzyme activity
Repeat at temperatures 20,30,40,50
Use a water bath
Add HCl to other - this control indicates the colour of a completely hydrolysed sample
Milk in 3 test tubes
Equal amounts of trypsin to each
Start timer and record how long it takes for each solution to go colourless - indicating completely hydrolysed
repeat steps and different temperatures and work out rate of reaction

Question 3

Heart dissection

Question 4

Lung dissection

Question 5

Plant dissection

Question 6

Fish dissection

Question 7

Aseptic techniques

Answer 7

Use bunsen burner flame to create convection currents that draw microbes away from culture
Wipe down surfaces before and after with antibacterial cleaner
Place wire hoop in flame before using it to transfer bacteria to culture
Flame neck of any bottles which causes air to move out of the container preventing unwanted microbes moving in
Keep all equipment containing bacteria open for minimum amount of time

Question 8

Named environmental factor on distribution of a given species

Question 9

Rate of dehydrogenase activity in chloroplasts

Question 10

Aseptic technique method

Answer 10

Use sterile wire hoop to transfer bacteria to agar plate
Spread bacteria evenly using sterile plastic spreader
Sterile forceps to place multi disc sterile antibiotic ring on plate
Lightly tape lid on, invert and incubate at 25 for 48 hours
Don’t tape tightly as this prevents oxygen entering which would promote the growth of harmful bacteria under anaerobic respiration
Incubated at 25 so harmful pathogens to humans cant develop at 37
Disinfect surfaces and sterilise all equipment used

Question 11

Insect dissection

Answer 11

Fix insect onto dissection tray using dissecting pins
Cut and remove a piece of exoskeleton from along the length of the abdomen
Use a syringe to fill the abdomen with saline solution
Network of thin grey tubes seen as tracheae fill with air
Examine tracheae under optical microscope with a temporary mount slide