required practicals Flashcards
1
Q
outline required practical 2 (root tip squash) (3 points)
A
- preparation of stained squashes of cells from plant root tips
- set up & use of an optical microscope to identify the stages of mitosis in these stained squashes
- calculation of a mitotic index
2
Q
what equipment is needed for RP2 (root tip squashes)? (10 items)
A
- optical microscope
- microscope slides & cover slips
- water bath
- hydrochloric acid
- toludine blue stain
- distilled water
- scalpel
- forceps
- 100ml beaker
- garlic root tip
3
Q
outline the 10 step method of the root tip squash practical
A
- STEP 1 = heat 1 mol dm -3 HCl as 60˚C in a water bath
- STEP 2 = cut a small sample of the garlic root tip using a scalpel
- STEP 3 = transfer the root tip to the HCl & incubate for 5 minutes
- STEP 4 = remove the root tip from the HCL & wash the sample in cold distilled water. Remove the very tip using a scalpel
- STEP 5 = place the tip on a microscope slide & add a few drops of the toludine blue stain. This makes the chromosomes visible & will therefore show which cells are undergoing mitosis
- STEP 6 = lower the coverslip down carefully onto the slide. Make sure there are no air bubbles in the slide that may distort the image, & that the coverslip doesn’t slide sideways (which could damage the chromosomes)
- STEP 7 = place under a microscope & set the objective lens to the lowest magnification
- STEP 8 = use the coarse adjustment knob to move the lens down to just above the slide
- STEP 9 = use the fine adjustment knob to carefully re-adjust the focus until the image is clear. Use a higher magnification if needed
- STEP 10 = to calculate the mitotic index, the number of cells undergoing mitosis (cells with visible chromosomes) must be counted, as well as the total number of cells. Use the equation (number of cells with visible chromosomes/total number of cells) to calculate the mitotic index
4
Q
outline a risk assessment for the root tip squash practical
A
- hydrochloric acid may cause harm/irritation to eyes or cuts so wear eye protection, avoid contact with skin & tie up long hair. In an emergency, wash off skin immediately & flood eyes/cuts with cold water
- toludine blue stain may cause harm/irritation to eyes or cuts so wear eye protection & avoid contact with skin. In an emergency, wash of skin immediately & flood eyes/cuts with water
- scalpels way cause cuts so cut away from fingers, use forceps to hold sample whilst cutting & keep away from the edge of desks. In an emergency, elevate cuts, apply pressure & seek medical assistance
- broken glass may cause cuts so take care when handling slides/coverslips & keep glassware away from the edge of desks. In an emergency, elevate cuts, apply pressure, do not remove glass from wound & seek medical assistance
5
Q
outline required practical 4 (beetroot membranes)
A
- investigation into the effect of a named variable on the permeability of cell-surface membranes
6
Q
what equipment is needed for the beetroot cell membrane practical? (16 items)
A
- beetroot
- scalpel
- forceps
- cutting board
- ruler
- tongs
- distilled water
- boiling tubes
- boiling tube rack
- colorimeter
- cuvettes
- filter paper
- timer
- water bath
- thermometer
- ethanol
7
Q
describe an 8 step method for the beetroot membranes practical for both temperature & solvents (RP4)
A
- STEP 1 = cut beetroot into 6-10 identical cubes using a scalpel
- STEP 2 = wipe/rinse to clean off any pigment released as a result
- STEP 3 = (investigating temperature) - place each of the cubes of beetroot in an equal volume if distilled water (5-15ml)
- STEP 4 = (investigating temperature) - place each test tube in a water bath at a range on temperatures (30˚-80˚C)
- (in investigating solvents: create a dilution series of ethanol using distilled water. Ethanol concentrations should range from 0-100% ethanol)
- STEP 5 = leave the samples for 20 minutes so that the pigment leaks out of the beetroot
- STEP 6 = set the colorimeter to a blue filter & zero using a cuvette filled with distilled water
- STEP 7 = filter each sample into a cuvette using filter paper
- STEP 8 = measure the absorbance for each solution. A higher absorbance indicates a higher pigment concentration, & hence a more permeable membrane
8
Q
outline a risk assessment for the beetroot membranes practical
A
- scalpels may cause cuts so cut away from fingers, use forceps to hold sample while cutting & keep scalpels away from the edge of desks. In an emergency elevate cuts, apply pressure & seek medical assistance
- broken glass may cause cuts so take care when handling glassware & keep away from the edge of desks. In an emergency elevate cuts, apply pressure & seek medical assistance
- ethanol is an irritant & is flammable so wear eye protection & keep away from naked flames. In an emergency, wash eyes & skin with cold water
- hot liquids may cause scalding so handle with care, sue tongs to remove boiling tubes from water bath, wear eyes protection & keep away from the edge of desks. In an emergency run burn under cold water & seek medical assistance
9
Q
what should be on the axis of the graph for the beetroot membranes practical?
A
- plot a graph of absorbance against ethanol concentration/temperature
10
Q
what conclusions can be made about the affect of temperature on the permeability of beetroot membranes? (RP4)
A
- as the temperature increases, the permeability of the cell-surface membrane also increases.
- this is because the proteins in the membrane denature as the heat damages the bonds in their tertiary structure
- this creates gaps in the membrane so it is easier for molecules to pass through it
- at low temperatures phospholipids have little energy & are packed closely together to make the membrane rigid
- this causes a decrease in permeability & restricts molecules from crossing the membrane
- at very low temperatures ice crystals can form which can pierce the cell membrane & increase permeability
11
Q
what can we conclude about ethanol concentration on the permeability of beetroot membranes? (RP4)
A
- ethanol causes the cell-surface membrane to rupture, releasing the betalain pigment from the cell
- higher concentrations of ethanol will cause more disruption to the membrane & more gaps will form
- therefore as the concentration of ethanol increases, the permeability of the cell-surface membrane also increases
12
Q
outline the water potential practical (RP3)
A
- production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue
13
Q
what is a calibration curve? (RP3)
A
- graphs that are used to determine an unknown concentration of a sample by comparing the unknown to a set of standard samples with known concentrations
- also known as standard curves
- a dilution series can be used to create a set of samples with known concentrations
14
Q
what can calibration curves be used for? (RP3)
A
- to determine an unknown water potential in a potato sample
15
Q
what is water potential determined by? (RP3)
A
- by the concentration of solutes
16
Q
what is the movement of water in/out of cells related to? (RP3)
A
- the relative concentration of solutes either side of the cell membrane
17
Q
give an equipment list for the water potential practical (11) (RP3)
A
- potato tuber
- cork borer
- scalpel
- ruler
- distilled water
- 1M sucrose solution
- boiling tube
- boiling tube rack
- timer
- digital balance
- paper towels
18
Q
outline a 7 step method for the water potential practical (RP3)
A
- STEP 1: make a series of dilutions of 1M sucrose solution. These should be at 0.0, 0.2, 0.4, 0.6, 0.8 1M sucrose. Dilute with distilled water
- STEP 2: measure 5cm cubed of each dilution in separate test tubes
- STEP 3: use a cork borer to cut out 6 potato chips & cut down the sections into identically sized chips. Dry each chip with a paper towel to remove excess water but don’t squeeze the chips
- STEP 4: weigh each chip before the start of the experiment & record the mass
- STEP 5: place a potato chips in each test tubes (one per sucrose solution) & leave for 20 mins. Ensure the test tubes are at 30˚C
- STEP 6: remove each potato chip, dry gently using a paper towel & weigh then in turn
- STEP 7: calculate the percentage change in mass for each sucrose solution
19
Q
outline a risk assessment for the water potential practical (RP3)
A
- scalpels may cause cuts so cut away from fingers, use forceps to hold samples whilst cutting, keep away from the edge of desks. In an emergency, elevate cuts, apply pressure & seek medical assistance
- broken glass may cause cuts to handle glassware carefully & keep away from the edge of desks. In an emergency, elevate cuts, apply pressure & seek medical assistance
20
Q
describe the graph produced by the water potential practical (RP3)
A
- change in mass against concentration of sucrose solution
- the point at which the line of best fit crosses the x-axis (zero change in mass) is the point at which the solution is isotonic
- this is when the water potential of sucrose solution is the same as the water potential of the potato tissue, so there is no net movement of water in or out of the potato
21
Q
write a conclusion for the water potential practical (RP3)
A
- potato chips in lower concentrations of sucrose solution will increase in mass, whilst those in higher concentrations of sucrose solution will decrease in mass
- in the dilute sucrose solutions, the solution has a higher water potential than the potato, so water passively moves via osmosis to the area of lower water potential (the potato). This causes the potato to increase in mass
- in concentrated sucrose solutions, water will move out of the potato, therefore it will decrease in mass
22
Q
outline RP1 (enzyme controlled reaction)
A
- investigation into the effect of a named variable on the rate of an enzyme-controlled reaction
23
Q
what 4 factors influence the ROR of an enzyme-controlled reaction? (RP1)
A
- temperature
- pH
- concentration of substrate
- concentration of enzyme
24
Q
state the equipment needed for RP1 (8)(enzymes)
A
- powdered milk solution
- trypsin solution (0.5%)
- distilled water
- pH buffer (7)
- 5cm cubed syringes
- test tubes
- water bath
- timer
25
Q
outline a 7 step method for RP1 (enzymes)
A
- (1) mark 3 test tubes with an ‘X’ & add 10cm cubes of the milk into each of them
- (2) in 3 separate test tubes add 2cm cubed of the trypsin & 2cm cubed of the pH buffer
- (3) place all 6 test tubes in a water bath at 20°C & leave them for 10 minutes to equilibriate
- (4) add the trypsin & pH buffer mixture into each of the milk test tubes & start timers for each of them immediately
- (5) record how long it takes for the casein in the milk to be broken down (go colourless so the ‘X’ can be seen from the other side)
- (6) repeat at temperatures of 30°C, 40°C, 50°C & 60°C
- (7) find the mean time for the casein to be broken down at each temperature & use this to work out the ROR for each temperature
- ROR = 1/mean time
26
Q
outline a risk assessment for RP 1 (3) (enzymes)
A
- broken glass may cause cuts so take care when handling & keep away from the edge of desks. In an emergency elevate wounds, apply pressure, don’t remove glass from wound & seek medical assistance
- hot liquids may cause scaling so handle with care, use tongs to remove tear tubes from water baths & keep away from the edge of desks. In an emergency run burn under cold water & seek medical assistance
- enzymes may cause allergies to avoid contact with skin/eyes & wear eye protection. In an emergency, seek assistance
27
Q
what can we conclude from the results & graph of RP1? (enzymes)
A
- graph of ROR against temperature should be plotted
- milk contains casein, which when broken down causes the milk to turn colourless (trypsin hydrolyses casein)
- as the temperature increases from 20 degrees, kinetic energy increases so more enzyme-substrate complexes form. This means that the ROR increases up to the optimum temperature
- at temps beyond the optimum (40 degrees), bonds in the enzyme’s tertiary structure break, which causes the active site to change shape. This means that the ROR decreases as the substrate & active site are no longer complimentary, so fewer enzyme-substrate complexes form
