Topic 2: Beetroot core practical

Question 1

Beetroot cells contain large red pigment molecules called _________ in their _________.

Answer 1

betalains

vacuole

Question 2

Normally, the betalains cannot pass through the ________ ________ (tonoplast) or the _______ _________. These membranes are not __________ to betalains.

Answer 2

vacuole membrane

cell membrane

permeable

Question 3

But when beetroot cells are exposed to certain temperatures or put in alcohol this disrupts the vacuole membrane and the cell membrane (they become _________) and betalains can ______ through these membranes and leave the cell.

Answer 3

permeable

diffuse

Question 4

Define diffusion in terms of betalains

1 point

Answer 4

1. the betalains move from where they are in HIGH concentration inside the cell, to where they are in LOWER concentrations outside the cell, down the concentration gradient.

Question 5

What happens when there is no longer a diffusion gradient? (in terms of betalains diffusing)
(2 points)

Answer 5

1. Eventually an equilibrium will be reached between the inside of the cell and the outside of the cell
2. even though the betalains are moving through the disrupted membrane in both directions, there is no NET movement (movement happens at the same rate in both directions).

Question 6

What is the aim of the beetroot practical?

1 point

Answer 6

1. To investigate the effect of temperature on the permeability of beetroot membranes

Question 7

The _______ _____ the solution, the more betalain molecules have been able to move through the vacuole and cell membranes, so the more disrupted the membranes are and the ________ the membrane ____________.

Answer 7

darker pink

greater

permeability

Question 8

Key Summary: What is the method for the beetroot practical?

7 steps

Answer 8

1. Tissue named (e.g. beetroot, red cabbage) – controlled variable - pieces cut to same surface area & from same species of beetroot & same part of beetroot.
2. Soak overnight and rinse to wash betalains off the beetroot pieces.
3. Place one beetroot piece in water in at each temperature.
4. Independent variable = temperature - 5 different temperatures for validity + control (normal temperature for beetroot) so 6 in total - 0, 10, 20, 30, 40, 50 (or alcohol concentrations – 0%, 1%, 2%, 3%, 4%, 5%) using {water bath to maintain different temperatures / dilution of same alcohol stock solution}.
5. Controlled variable eg. same length of TIME in water bath – same {time of 30 minutes/ VOLUME of water in tube} – measure with pipette 5cm^3 (same temperature using water bath at 10⁰C if changing {ethanol/alcohol} concentration).
6. Dependent variable = measure absorbance using a colorimeter, with blue-green filter, as a measure of membrane permeability (higher absorbance = higher membrane permeability).
7. Repeat 5 times FOR EACH TEMPERATURE – identify anomalies, obtain 3 concordant results, calculate mean, increases reliability.

Question 9

A _____ ______ filter ( ____ nm) is used - wavelength of light that the pink solution absorbs the most. This maximises the ________ of the results.

Answer 9

blue green

490

accuracy

Question 10

A beam of ______ passes through the ______, through the _________ ________ and to the _________. The meter records the amount of _______ absorbed by the ________.

Answer 10

light

filter

beetroot solution

photocell

light

solution

Question 11

The more concentrated (darker) the pink solution, the _______ the absorbance.

Answer 11

higher

Question 12

(the effect of temperature on membrane permeability in beetroot practical)
Below 0 degrees C, ___ _________ may form and pierce the membrane, this may __________ the membrane permeability.

Answer 12

ice crystals

increase

Question 13

Key Summary: What is the effect of temperature on membrane permeability?
(5 steps)

Answer 13

1. INCREASED KINETIC ENERGY INCREASES MOVEMENT OF PHOSPHOLIPIDS
2. Membrane PROTEINS ARE DENATURED (look at data if given to determine temperature at which this happens)
3. More denaturation of proteins and disruption of membrane at higher temperatures
4. Vacuole membrane and cell membrane break down, so are disrupted and become more permeable to betalains
5. Betalains can escape FROM THE VACUOLE AND THE CELL through vacuole and cell membranes

Question 14

(beetroot practical)
Name the independent variable (1 point)

How can it be varied? (2 points)

What is the control? (1 point)

Answer 14

1. temperature
2. 5 different temperatures + 1 control
3. Using WATER BATHS at 0, 10, 20, 30, 40, 50 degrees C.
4. control - usual temperature for growing beetroot (10 degrees C)

Question 15

(beetroot practical)
Name the dependent variable (1 point)

How can it be measured? (1 point)

Answer 15

1. % absorbance of the solution around the beetroot piece

1. Measured using a COLORIMETER

Question 16

Why is using a colourimeter (to measure the % absorbance of the solution around the beetroot piece) better than just deciding which solution is darkest by eye?
(2 points)

Answer 16

1. Colourimeter gives QUANTITATIVE data - numbers (colours are qualitative data)
2. LESS SUBJECTIVE (as different people could rank colours differently)

Question 17

(beetroot practical)
What are the controlled organism variables?
(7 points)

Answer 17

1. SAME SURFACE AREA (size) of beetroot pieces - measured using cork borer and ruler
2. same species of beetroot - ideally cloned plants, so genetically identical
3. same age of beetroot – seeds sown and beetroot picked at same time
4. same growth conditions eg. soil pH, soil minerals
5. same part of beetroot used eg. core
6. same storage temperature

Question 18

Betalains are released when {cells / vacuole membranes} are cut and damaged, even though the membrane permeability has not changed.

How can we make sure there are no betalains on the surface of the beetroot piece before it is placed in the water? (1 point)

What if there are betalains on the surface of the beetroot piece when it is placed in the water? (1 point)

Answer 18

1. SOAK AND RINSE BEETROOT PIECES to remove betalains from damaged (cut) cells before placing in water
2. if they are not washed they would make the solution darker pink (higher absorbance), suggesting a higher permeability than there actually is

Question 19

How is the surface area of beetroot pieces controlled? (1 point)

Answer 19

1. Cut cylinders or cubes to the same size using a cork borer, ruler and sharp scalpel

Question 20

Why is the surface area of beetroot pieces controlled? (2 points)

Answer 20

1. If the area is larger there is more {surface area / more tissue} for betalains to be lost from,
2. so solution will be darker (higher absorbance)

Question 21

How is the same beetroot {part/age/species/storage temperature} controlled? (3 points)

Answer 21

1. grow beetroot plants from seeds from same packet.
2. sown and harvested at the same time.
3. stored in same conditions.

Question 22

Why is the beetroot {part/age/species/storage temperature} controlled? (1 point)

Answer 22

1. Different {beetroots/parts of beetroot/ages} may have different {numbers or sizes of cells/number of betalains}

Question 23

(beetroot practical)
What are the controlled procedural variables & how are they controlled?
(3 points)

Answer 23

1. Same VOLUME of water - 5cm3 measured using graduated pipette
2. Incubation time - 30 minutes measured using stopclock
3. Same {wavelength/filter} in colorimeter - set to 490nm

Question 24

(beetroot practical)
What are the controlled environmental variables & how are they controlled?
(1 point)

Answer 24

1. SAME pH OF WATER that beetroot pieces are placed in - use a BUFFER

Question 25

Why is the volume of water in the test tube controlled? (1 point)

Answer 25

1. If there is more water, the solution will be diluted more and solution will be lighter (lower absorbance)

Question 26

Why is the incubation time controlled? (1 point)

Answer 26

1. If longer time there is more time for betalains to diffuse into water and solution will be darker (higher absorbance)

Question 27

Why is the pH of water in the test tube controlled? (1 point)

Answer 27

1. pH may affect membrane proteins, making membrane more permeable

Question 28

(beetroot practical)]
Cut eight 1cm length sections of beetroot (same surface area) from a single beetroot. Soak in distilled water overnight.

What is the {purpose/justification} of this step?
(2 points)

Answer 28

1. Soak and rinse beetroot pieces – to remove betalains released when cells are damaged(before placing in water),
2. as they would make solution darker pink (higher absorbance)

Question 29

(beetroot practical)
Place eight labelled boiling tubes, containing 5cm^3 distilled water, into water baths (at 0, 10, 20, 30, 40, 50 C) and leave for 5 minutes. Place one beetroot section into each boiling tube and leave for 30 minutes.

What is the {purpose/justification} of this step?
(2 points)

Answer 29

1. Leave for 5 minutes for water in tube to reach temperature of water bath
2. Leave for 30 minutes for temperature to have an effect on membranes and any betalains to diffuse into water

Question 30

(beetroot practical)
Remove beetroot sections from boiling tubes, do not squeeze, and discard.

What is the {purpose/justification} of this step?
(1 point)

Answer 30

1. Squeezing may damage cells or force more betalains out of beetroot

Question 31

(beetroot practical)
Switch on colorimeter, set it to read percentage absorbance and the filter to blue-green.

What is the {purpose/justification} of this step?
(1 point)

Answer 31

1. Blue-green filter (490nm) - wavelength of light that the pink solution absorbs the most - maximises accuracy of results

Question 32

(beetroot practical)
Measure 2cm^3 of distilled water into a cuvette. Place in colorimeter. Make sure light is shining through the smooth side. Calibrate colorimeter to read absorbance for clear water.

What is the {purpose/justification} of this step?
(1 point)

Answer 32

1. To calibrate the colourimeter

Question 33

(beetroot practical)
Place 2cm^3 of the beetroot solution into a cuvette and take a reading for absorbance.

What is the {purpose/justification} of this step?
(1 point)

Answer 33

1. Absorbance gives a measure of how dark the solution is. Darker solution = more betalains = membrane more disrupted = more permeable

Question 34

(beetroot practical)
Repeat readings for all temperatures

What is the {purpose/justification} of this step?
(1 point)

Answer 34

1. Identify anomalies, calculate mean, increases reliability

Question 35

If the effects of alcohol on membrane permeability was investigated instead of temperature, what would need to be changed? (4 points)

Answer 35

1. Independent variable is alcohol (ethanol) concentration (%) - 0, 10, 20, 30, 40, 50%
2. Controlled variable is temperature & volume of ethanol
3. Temperature controlled by water bath at optimum temperature for beetroot membranes (e.g. 15 degrees C)
4. Temperature controlled because temperature affects membrane permeability. If temperature increases, the rate of diffusion increases and solution will be darker (higher absorbance) after 30 minutes.

Question 36

Key Summary: How does {ethanol/alcohol} concentration effect the membrane permeability?
(5 points)

Answer 36

1. ethanol causes the membrane to be disrupted (look at data to determine which concentration this happens at)
2. ethanol DISSOLVES THE PHOSPHOLIPIDS
3. ethanol DENATURES MEMBRANE PROTEINS
4. the vacuole membrane and cell membrane break down, so are disrupted and become more permeable to betalains
5. betalains can escape FROM THE VACUOLE AND THE CELL THROUGH VACUOLE AND CELL MEMBRANES

Question 37

List the experimental design question checklist (7 points)

Answer 37

1. IV Independent variable - how many and range
2. C Control (if applicable) + why it is needed
3. DV Dependent variable + how it is measured (equipment and brief method)
4. CVO/E Controlled variables – organism + environment - use the word ‘same’ and state equipment and value
5. M Method – key details to make design hang together
6. R Repeats + why they are needed
7. S Safety (if relevant) - pair points – risk + how to minimise