Practical skills

Question 1

How to work out percentage increase?

Answer 1

difference / initial x 100

Question 2

How to calculate ratio?

Answer 2

Divide by the smallest one (3 s.f e.g. 1.14:1)

Question 3

Give two pieces of information required to judge whether this is a valid conclusion

Answer 3

• a statistical test
• number of … (to see if large sample size that can be representative

Question 4

use the standard devitations to compare the variation in the data of the two group

Answer 4

• greater variation in … because the standard deviation is bigger

Question 5

Describe how the control group would have been treated

Answer 5

• exactly the same as the experimental group

Question 6

Give two variable that would have been controlled in order to obtain a valid comparison between groups

Answer 6

• the type of …
• age of …

Question 7

Suggest why the student soaked the root tips in hydrochloric acid

Answer 7

• to break down cellulose of cell wall
• to allow stain to diffuse into cells

Question 8

Why do you have to make sure that root tips/shoot tip is fully squashed?

Answer 8

• to make a thin layer of cells
• so that light can pass through

Question 9

What are the 3 ways of measuring rate of reaction?

Answer 9

• colour change
• mass of substrate or product
• bubble formation (using an upside down cylinder)

Question 10

How can you control temperature?

Answer 10

• use a thermostatically controlled water bath
• regularly check the temperature of the water bath using a thermometer

Question 11

How can you control pH?

Answer 11

• using a buffer which will resist pH changes

Question 12

How can you control concentration of enzymes, substrates and inhibitors?

Answer 12

• add the same volumes/concentrations of each other solution in a method

Question 13

What can be a control group for an enzyme controlled reaction?

Answer 13

• denatured enzyme
• no enzyme at all

Question 14

Why is beetroot used to investigate into the effect of named variables on the permeability of the cell surface membrane?

Answer 14

• the molecule that comes out is a coloured pigment which can be visible

Question 15

Why can the pigment in beetroot not leak out until membrane is disrupted?

Answer 15

• the pigment is water soluble

Question 16

What are the 3 variables affecting permeability of cell surface membrane?

Answer 16

• alcohol
• temperature
• pH

Question 17

In an investigation of the effect of alcohol on the permeability of cell surface membrane, what can you do as a control experiment?

Answer 17

• no alcohol
• no leakage shows that it is the alcohol causing the disruption of membrane allowing pigment to diffuse through the membrane and not another factor

Question 19

Why is high alcohol, temperature and pH not good for an investigation in these factors affecting permeability of cell surface membrane?

Answer 19

• they denature carrier and channel proteins in the cell surface membrane
• allowing more of the pigments to diffuse through

Question 20

Safety techniques for during a dissection

Answer 20

• cut away from your hands
• wear a lab coat
• carry scalpel away from you/others

Question 21

Safety techniques after dissection

Answer 21

• wash all equipment with soap and water
• clean and disinfect all surfaces and benches
• dispose of any dissected tissues or gloves in the bin

Question 22

Why do we use aseptic techniques?

Answer 22

• to prevent contamination of apparatus with other microorganisms/bacteria
• to prevent personal contact with bacteria
• to prevent release of bacteria into the air

Question 23

Why is there a clear zone?

Answer 23

• because the substance has diffused into the agar and inhibited growth of bacteria

Question 24

What does the size of the clear zone tell you?

Answer 24

• how effective the substance is at killing the bacteria

Question 25

Does the size of the clear zone always tell you which substance is the most effective?

Answer 25

• no not always because some of the substances might just be slow at diffusing into the agar

Question 26

Why must the origin line be drawn in pencil?

Answer 26

• ink would be carried up by the solvent

Question 27

What colour DCPIP when oxidised?

Answer 27

blue

Question 28

What colour is DCPIP when it is reduced?

Answer 28

colourless

Question 29

What can be a control in the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts?

Answer 29

• wrap foil around a tube • to show light is required • having a tube with no chloroplast to show that decolorisation of DCPIP is caused by chloroplast and not another factor

Question 30

What is the experiment on chloroplast used to demonstrate?

Answer 30

• production of oxygen requires light • origin of oxygen is from water not carbon dioxide • light-dependent reaction occurs first

Question 31

How can you control the presence of oxygen in an investigation of the effect of a named variable on the rate of respiration of a single-celled organism (yeast)

Answer 31

• a layer of oil can be used to prevent oxygen from reaching the yeast from the air

Question 32

Mistakes in biological drawings

Answer 32

• tissue with too much detail • crossing lines • hanging lines • over casual • sketch rather than draw

Question 33

Describe how to reset the drop of coloured liquid back into the right hand end of the tubing

Answer 33

• open the 3 way tap • push the syringe down

Question 34

Suggest a suitable control for a experiment on the effect of temperature on aerobic respiration

Answer 34

• no (IV) AND all other conditions the same • to show it is the (IV) affecting the (DV)

Question 35

What do scientists assume when working out about Herdy Weinberg

Answer 35

• no mutation • the population is isolated • all alleles are likely to be passed on (no selection) • large population • mating is random