Unit 3

Question 1

How to produce a calibration curve and find the concentration of (reducing sugars)?

Answer 1

Produce benedicts test for known concentrations of sugars
Use calorimeter to find colour intensity and plot on a calibration curve
Find the concentration of sample from calibration curve

Question 2

Measuring the rate of an enzyme-controlled reaction: How fast product is made:

Answer 2

Use catalase to catalyse the breakdown of hydrogen peroxide into water and oxygen
Boiling tubes of same volume and concentration of hydrogen peroxide and equal volumes of buffer solution - pH the same
Boiling tubes connected to delivery tubes connected to upside-down measuring cylinder submerged in a trough of water
Each boiling tube in a water bath at different temps (10, 20, 30, 40 degrees C)
Use pipette to add equal amounts of catalase to boiling tubes and quickly place bung on
Record how much oxygen is produced in the first minute using stopwatch
Repeat 3 times to find average
Calculate average rate of reaction

Question 3

Measuring the rate of an enzyme-controlled reaction: How fast the substrate is broken down:

Answer 3

Amylase catalyses breakdown of starch to maltose
Spotting tile + dropping pippete + test tube with starch solution and amylase enzyme
Place drop of iodine in potassium iodide in each well of spotting tile
Amylase and starch then mixed together in test tube
Dropping pipette used to drop a sample of the mixture into a well every timed interval and the resulting colour observed
Record how long it takes until the solution no longer turns blue-black and remains browny-orange

Question 4

Melselson and Stahl’s experiment?

Answer 4

To validate semi-conservative replication
Using Heavy Nitrogen (15) and light Nitrogen (14) isotopes
Bacteria grown in broth, one community in heavy and one in light - took up nitrogen into their DNA
When centrifuged the Heavy nitrogen settled lower than the lighter one
The bacteria grown in the heavy broth were placed in light nitrogen for one round of DNA replication
After centrifugation the new DNA settled in the middle as it was half heavy and half light - semi-conservative
If it was conservative it would be two separate bands, one high and one low

Question 5

Process of differential centrifugation?

Answer 5

1. Use homogeniser to break open cell membrane/wall
2. Buffer solution to keep pH the same and prevent enzyme or protein denaturing
3. Add isotonic solution (same water potential as cell) to keep the osmotic movement the same so cells do not burst or shrink
4. Filter to remove debris such as the broken cell wall
5. Centrifugation: homogenate is centrifuged at different speeds to operate organelles based on their size/density, largest first.
   Pellet of organelle will remain at bottom whilst supernatant will be at top after spinning

Question 6

Root tip observation of cells experiment?

Answer 6

Cut 1cm from the tip of a growing root (tip where mitosis occurs)
Prepare a boiling tube containing 1 M hydrochloric acid and put it in a water bath at 60 C
Transfer the root tip in to a boiling tube and leave for 5 mins
Use a pippete to rinse the root tip with cold water and dry on paper towel
Cut 2mm of the very tip and place on microscope slide
Use a mounted needle to break the tip open and spread the cells out thinly
Add a few drops of stain (toluidine blue O)
Place a cover slip over, push down firmly, don’t smear
Can view through optical microscope

Question 7

Calculating size of cells

Answer 7

Measure diameter of field of view and calculate area
Using micrometer slide and eyepiece graticule
Count the number of …. in large number of fields of view and calculate mean
Select fields of view at random

Question 8

How to prepare slides?

Answer 8

Pipette small drop of water onto slide
Tweezers to place small thin specimen on top of water
Add a stain of potassium iodide
Add cover slip using mounting needle

Question 9

Test for permeability of cell membrane?

Answer 9

Use scape and cut five equally sized pieces of beetroot. Rinse to remove and pigment
Add five pieces to the test tube, each containing 5cm3 of water. Use a measuring cylinder or pipette to measure water.
Place each test tube in a water bath at a different temperature for the same time
Remove the pieces of beetroot from the tube leaving just the coloured liquid
Now use a colorimeter - passes light through and see how much is absorbed, higher the absorbance the more pigment released so the higher the permeability
Connect colorimeter to a computer and use software to collect data and create a graph

Question 10

Extra information: Monoclonal Antibodies?

Answer 10

About 20% of women with breast cancer have tumours that produce more than the usual amount of a receptor called HER2
Herceptin is a drug that contains monoclonal antibodies that bind to the HER2 receptor on a tumour cell and prevent the cells from growing and dividing
2005 study: tested Herceptin on women who had already undergone chemotherapy for HER-2 breast cancer
Twice as many women in the control group developed breast cancer again or died than compared to the Herceptin group

Question 11

ELISA test

Answer 11

1. Monoclonal antibody that is complementary to substance is attached to enzyme
2. Antibody binds to substance
3. Dish washed to rid any unbound enzyme and antibody
4. The substrate to the enzyme is added and an enzyme-substrate complex forms to produce a colour change if the antibody did bind and the substance is present

Question 12

Lung dissection?

Answer 12

Lab coat, clean and sharp instruments
Lay lungs on cutting board
Inflate the lungs with rubber tubing and a pump - place in a plastic bag to prevent bacteria escaping and never blow into the tube
To investigate trachea cut straight down the C-shaped ring of cartilage
Continue to see bronchi
Wash hands

Question 13

Fish gill dissection?

Answer 13

Lab coat
Place on cutting board
Gills protected by a bony flap called the operculum and supported by gill arches
Push back the operculum and cut the gill with scissors

Question 14

Insect gas exchange system dissection?

Answer 14

Dissecting board
Dissecting pins in legs to hold in place
Cut and remove a piece of exoskeleton from the length of the insect’s abdomen
Fill the abdomen with saline solution - should see a network of very, thin silvery-grey tubes called the tracheae
Can examine under an optical microscope using a temporary mount slide - should see rings of chitin in the walls - there for support

Question 15

Experiment to demonstrate translocation?

Answer 15

Supply a leaf with an organic substance that has a radioactive label (carbon dioxide containing 14C)
Radioactive carbon with then be incorporated into the organic substances produced by the leaf (sugars produced by photosynthesis) which will be moved around the plant by translocation
The movement tracked by autoradiography. To reveal where the tracer has spread to in the plant, the plant is killed, and the whole plant is placed on photographic film - present where film turns black
Results show the tracer moves from source to sink

Question 16

Investigating different pigments using chromatography - theory

Answer 16

Plants contain several different photosynthetic pigments in their leaves
Can use thin layer chromatography (TLC) to determine what pigments are present
Possible to identify a certain pigment by calculating its Rf value - the distance a substance has moved through the gel in relation to the solvent - each pigment has a specific Rf value

Question 17

Investigating different pigments using chromatography - Method

Answer 17

Grind up several leaves with some anhydrous sodium sulfate - add a few drops of propanone
Transfer the liquid to a test tube, add some petroleum ether and gently shake
Two layers will form - top with pigments
Transfer some of the top layer into a second tube with anhydrous sodium sulphate
Draw a pencil line near the bottom of a TLC plate
Build up a concentrated spot of the liquid - origin point
Put the plate into a small glass of solvent (cyclohexane) - point of origin above the the solvent
Pigments move up
Mark the solvent front with a pencil
Measure how far the separated pigments moved
Calculate Rf values = Distance travelled by spot/ distance travelled by solvent

Question 18

Investigating the activity of dehydrogenase in Chloroplasts: theory?

Answer 18

In light-dependent reaction - NADP acts as an electron acceptor and is reduced - catalysed by dehydrogenase enzyme
Activity of enzyme can be investigated by a redox indicator dye to extract chloroplasts
Is an electron acceptor and is reduced causing a colour change - DCPIP changes from blue to colourless
Can use a calorimeter to measure the rate at which DCPIP loses its blue colour

Question 19

Investigating the activity of dehydrogenase in Chloroplasts: method?

Answer 19

Cut a few leaves into pieces
Grind up using pestle and mortar with some chilled isolation solution (sucrose, potassium chloride and phosphate buffer at pH 7)
Filter the liquid into a beaker through a funnel and filter paper
Transfer the liquid to centrifuge tubes and centrifuge them at high speed for 10 minutes
Chloroplasts gather at bottom of each tube in a pellet
Filter out liquid leaving just pellet
Re-suspend the pellets in fresh, chilled isolation
Set up calorimeter with a red filter and zero it using a cuvette containing the chloroplast extract and distilled water
Set up test tube rack at a set distance from a bench lamp
Add set volume of chloroplast extract and DCPIP in test tube and mix
Immediately take sample and place in clean cuvette
Then place the cuvette in your colorimeter and record the absorbance. Do this every 2 minutes for the next 10.
Repeat for the distances.

Question 20

Investigating Factors affecting respiration in single-celled organisms - aerobic respiration?

Answer 20

Decide on different temperatures for dependent variable
Known volume and concentration of substrate solution in a test tube + buffer solution to keep pH constant
Place in water bath set at one of the temperatures
Leave for 10 mins for substrate to stabilise
Add known mass of dried yeast and stir for 2 mins
When dissolved add a bung on test tube attached to a gas syringe which is set to zero
Measure CO2 formed
At regular intervals measure CO2 released
Control with no yeast
Repeat at different temperatures
Find mean rate of CO2 production

Question 21

Investigating Factors affecting respiration in single-celled organisms - anaerobic respiration?

Answer 21

Known volume and concentration of substrate solution in a test tube + buffer solution to keep pH constant
Place in water bath set at one of the temperatures
Leave for 10 mins for substrate to stabilise
Add known mass of dried yeast and stir for 2 mins
When dissolved add liquid paraffin down the inside of the test tube so it completely covers the surface of the liquid - stops oxygen
add a bung on test tube attached to a gas syringe which is set to zero
Measure CO2 formed
At regular intervals measure CO2 released
Control with no yeast
Repeat at different temperatures
Find mean rate of CO2 production

Question 22

Experiment: Choice Chamber?

Answer 22

Investigates how animals react to changes in environments
1. Construct
2. To investigate light intensity, cover one side with black paper. Put damp filter paper in bot sides of the base.
3. Place 10 woodlice on the mesh in the centre of the chamber and cover with lid.
4. After 10 mins open lid and record how many woodlice are in each section
5. Repeat the experiment by placing the woodlice gently back in the centre
Most should accumulate in the dark region (tactic response to light)
6. To investigate humidity, place some dark filter paper in one side of the base and a desiccating (drying) agent in the other side. Don’t cover the lid with paper.
Can do the same thing with the maze which we did.

Question 23

Extra information: GM Crops?

Answer 23

‘Golden Rice’ - example of biofortification - inserted gene for Beta-cartoene - stops Vit A deficiency
Halophytes - salt resistant rice in Bangladesh

Question 24

Extra information: HD?

Answer 24

HD causes cells in parts of the brain to die: specifically the caudate, the putamen and, as the disease progresses, the cerebral cortex
Degenerative
Is a genetic disorder
The HD gene is dominant, which means that each child of a parent with HD has a 50% chance of inheriting the disease and is said to be “at-risk”.
Males and females have the same risk of inheriting the disease - not sex linked
Since 1986, genetic testing for HD has been available; however, a direct test for the disease was developed in 1993.
Anyone considering taking the test should have genetic counselling
One symptom is loss of motor control
Damage from HD causes the striatum to release a weaker chemical signal, resulting in less inhibitory neurotransmitters, less inhibition of the motor cortex, and more movement - Involuntary movements

Question 25

Terms for results?

Answer 25

Precise - results which don’t vary much from the mean - reduced by random error
Repeatable - If the same person repeats the experiment using the same methods and equipment, they will get the same results
Reproducible - If someone different does the same experiment, using a slightly different method or piece of equipment the results will be the same
Valid - answers the original question
Accurate - results are really close to the true answer - human interpretation of a measurement affects this

Question 26

Extra information: biodiversity?

Answer 26

Biodiversity hotspots cover 2.3% of the Earth’s land surface and have lost at least 70% of its natural vegetation
Over 50% of world’s plant species and 42% of all terrestrial vertebrate species are endemic to the 34 biodiversity hotspots
Zebra Muscles that stick to ships or get in through bilges of ships - alien invasive species
UNESCO Biosphere Reserve: Two cores: so that if one population is under a natural threat it can migrate and is not forced to stay there and die out

Question 27

Advice for carrying out experiments?

Answer 27

Plan - what you’re going to measure and how often
Appropriate apparatus - Sensitive - Technique must be appropriate for maximum accuracy
Measuring cylinders and graduated pipettes - Have a scale for specific volumes - measure from bottom of meniscus at eye level

Question 28

Which graphs to use when?

Answer 28

Qualitative (non-numerical) or discrete (numerical data that can only take certain values in a range e.g. shoe size) - bar charts or pie charts
Continuous data (data that can take any value in a range) - histograms or line graphs
When you want to show two variables are related/correlated/ TWO INDEPENDENT VARIABLES - scatter graph
Independent on X-axis (first column of table)
Dependent on Y-axis

Question 29

Finding rate?

Answer 29

Linear - gradient of the line

Non-linear - gradient of the tangent

Question 30

Extra knowledge: TB?

Answer 30

1042 resistant TB cases 2011 USA
Extensively drug-resistant TB (XDR TB) is resistant to most TB drugs; therefore the patients are left with treatment options that are much less effective.

Question 31

Extra knowledge: Osmoregulation?

Answer 31

Some marine animals such as the sea stars are osmoconformers; their body fluids are similar to seawater in osmolarity, so they gain and lose water at equal rates and have no need to expend energy expelling water or salt from the body
Osmoconformers are stenohaline ( steno means “narrow range,” and hal means “salt”), unable to tolerate much variation in environmental salinity.

Question 32

Extra knowledge: Importance of inorganic ions in plants?

Answer 32

Nitrate	NO3-	growth of stems and leaves
Phosphate	PO43-	root growth
Potassium	K+	healthy leaves and flowers
Calcium	Ca2+	cell wall development
Magnesium	Mg2+	making chlorophyll

Question 33

Extra knowledge: enzymes + synapses

Answer 33

Anti-cholinesterases - Venoms, poisons, nerve agents - paralysis

Question 34

Mitochondrial Disease?

Answer 34

Mitochondrial diseases are the result of either inherited or spontaneous mutations in mtDNA or nDNA which lead to altered functions of the proteins or RNA molecules that normally reside in mitochondria.