Practical Flashcards
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3 - Investigation into the permeability of cell membranes using
beetroot
INTRO
INTRO
Heating the membrane can cause gaps to
form between the phospholipid molecules and the membrane will become more permeable.
The protein in the membrane can be denatured by heat
Beetroot cells contain betalain, a bright red, water soluble pigment, in the cell vacuoles. If the
cell membranes are damaged the pigment can escape from the cells and can be detected in
an aqueous medium around the tissue.
3 - Investigation into the permeability of cell membranes using
beetroot
APPARATUS
Beetroot cylinders
White tile
10 test tubes
Scalpel
250cm3 beaker
Forceps
Water baths at (25, 35,45,55,65 oC)
Thermometer
Stop clock
Colorimeter with a blue filter / colour chart
3 - Investigation into the permeability of cell membranes using
beetroot
METHOD
- Cut 5 same size beetroot peices eg 1cm (control SA)
- Wash, remove pigment from cutting
- Place 1 piece of beetroot into each test tube for 30 minutes, in water bath
- Shake the test tubes gently to make sure any pigment is well-mixed into the water, then remove the beetroot cores.
- Colorimeter, set it to respond to a blue/ green filter measure absorbance. Check the colorimeter reading for distilled water.
- Measure the absorbance/percentage transmission of each tube and plot a graph of absorbance/percentage transmission against temperature.
3 - Investigation into the permeability of cell membranes using
beetroot
RISK
3 - Investigation into the permeability of cell membranes using
beetroot
THINK ABOUT
3- Determination of water potential by measuring changes in mass or length
APPARATUS
Vegetable large enough to extract 50 mm cylinders: potatoes, sweet potatoes, yams,
beetroots, swede, turnip, parsnip and carrot are suitable.
Chopping board/ white tile
Cork borers: sizes 3 and 4 are suitable
Ruler graduated in mm
Fine scalpel
Fine forceps
5 x boiling tubes
Boiling tube rack
50cm3 measuring cylinder
Distilled water
Sodium chloride solutions (0.2, 0.4, 0.6, 0.8 moldm-3 )
3- Determination of water potential by measuring changes in mass or length
METHOD
- Cut 15 cylinders of tissue, each approximately 50mm long, scalpel to remove any periderm (skin) as its suberin makes it waterproof and would prevent osmosis.
- Place 30cm3 distilled water or solution in to each test tube.
- Measure the length of the cylinder to the nearest mm or the mass
- Using the forceps, place 3 cylinders into each boiling tube.
- Leave at room temperature for a minimum of 45 minutes
- Gently blot the cylinders and re-measure the length or re-weigh the cylinders.
- Record your results in a table.
- Plot the mean percentage change against the concentration of solution.
- Estimate the solute potential of the tissue.
3- Determination of water potential by measuring changes in mass or length
RISK
3- Determination of water potential by measuring changes in mass or length
RESULTS
Percentage Change - The calculation is (end mass or length – start mass or length) ÷ start mass or length.
Where the potato tissue has lost mass or length, the answer will be a negative value.
Point at which the water potentials of the tissue and bathing solutions are equal, crosses x axis
The concentration is converted into a solute potential using a standard table. Where the solution and potato tissue have equal water potentials, the solute and water potentials are equal as the cells are in incipient plasmolysis and the pressure potential is 0 kPa.
3- determining solute potential by the degree of incipient plasmolysis
INTRO
3- determining solute potential by the degree of incipient plasmolysis
APPARATUS
White tile
Fine forceps
Fine scissors
Rhubarb petioles or red onion
5 x 9 cm Petri dishes, 100 cm3 beakers or watch glasses
Distilled water
sodium chloride solutions 0.2, 0.4, 0.6, 0.8 mol dm-3
: instructions for making these
solutions is given in the previous experiment.
Stopclock
Microscope slides
Cover slips
Microscope
Dropping pipettes
3- determining solute potential by the degree of incipient plasmolysis
METHOD
- Set up five labelled Petri dishes/ small bottles each containing 10cm3 of one of the
following solutions: distilled water, 0.2, 0.4, 0.6, 0.8 moldm-3 sodium chloride solution. - Insert the fine forceps tip just under the upper epidermis of the onion leaf.
- Keeping the forceps handles parallel with the epidermis, so as not to penetrate the
underlying mesophyll, grip the epidermis and, maintaining the tension in the tissue,
pull the epidermis off the mesophyll, away from you and place into distilled water. - When several square centimetres of epidermis have been peeled, place one square
into each labelled petri dish/small bottle. - Leave at room temperature for a minimum of 30 minutes.
- Carefully spread the tissue out on a microscope slide, so that it is not folded. Take a
scalpel and rock the blade backwards and forwards over the tissue in order to cut out
a 0.5 x 0.5cm square. - Add two drops of bathing solution and apply a cover slip.
- If any solution exudes from the cover slip, blot it with filter paper to dry the slide.
- Using a x10 and then a x40 objective lens, examine all the cells in a field of view and
count the number that are turgid and the number plasmolysed. - Repeat the counts at all concentrations of bathing solution.
- Record your results in a table.
- Plot a graph of % cells plasmolysed against the concentration of the bathing solution.
- Using the graph, read the concentration of bathing solution that would produce
plasmolysis in 50% of the cells. - From the table given in the previous experiment, determine the solute potential of this
solution. This is equal to the solute potential of the cells.
3- determining solute potential by the degree of incipient plasmolysis
RESULTS
3- determining solute potential by the degree of incipient plasmolysis
RISK
