NEED TO REVISE

Question 1

What is the equation for determining time in a reaction? (1)

Answer 1

1 / time

Question 2

What is the rate in a reaction? (1)

Answer 2

Rate is change in absorbance over time.

Question 3

What is the dependent variable? (1)

Answer 3

The dependant variable is the thing you measure, in this case it is the initial rate of reaction.

Question 4

What is the independent variable? (1)

Answer 4

The independent variable is the factor you have selected from; pH, temperature, enzyme concentration and substrate concentration.

Question 5

What is the control variable? (1)

Answer 5

The control variable will be all three factors that are not the independent variable.

Question 6

What should you do if the pH is the control variable? (1)

Answer 6

Use a buffer solution in the correct range for the enzyme used and as near to the optimum as possible.

Question 7

What should you do if the temperature is the control variable? (1)

Answer 7

Use a thermostatically controlled water bath set in the correct range for the enzyme used and as near to the optimum as possible.

Question 8

What should you do if the enzyme concentration is the control variable? (1)

Answer 8

Should be in excess is substrate concentration is the independent variable.

Question 9

What should you do if the substrate concentration is the control variable? (1)

Answer 9

Should be in excess is enzyme concentration is the independent variable.

Question 10

What is the effect of temperature on enzyme activity? (2)

Answer 10

As temperature rises to an optimum, increasing kinetic energy causes more collisions and more enzyme substrate complexes are formed. Above the optimum, active site shape changes lead to a fall in rate as the substrate is less likely to enter the active site.

Question 11

What is the effect of pH on enzyme activity? (1)

Answer 11

The concentration of charged particles such as H+, affects the active site shape. Most enzymes have an optimum pH around 7, but some are different.

Question 12

What is the effect of substrate concentration on enzyme activity? (1)

Answer 12

As more substrate is added, more active sites are occupied. When all active sites are occupied, adding more substrate does not increase the rate.

Question 13

What is the effect of enzyme concentration on enzyme activity? (1)

Answer 13

As more enzyme is added, there are more active site to bind to the substrate. At a certain point all substrate is being acted on and adding more enzyme then does not increase the rate.

Question 14

What are competitive inhibitors? (1)

Answer 14

Excess substrate overcomes the inhibition.

Question 15

What is non-competitive inhibition? (1)

Answer 15

Excess substrate has no effect on inhibition (includes end product inhibition)

Question 16

What does competitive inhibition do? (1)

Answer 16

Competitive inhibitors blocks the active site. With excess substrate substrate always occupiers the site before the inhibitor can.

Question 17

What does a non-competitive inhibition do? (1)

Answer 17

Non-competitive inhibitor changes the shape of the active site, excess substrate has no effect.

Question 18

What are allosteric enzymes? (1)

Answer 18

Some enzymes exist in two forms, an active form and an inactive form.

Question 19

What is competitive inhibition? (1)

Answer 19

Inhibitor chemically resembles the substrate molecule and binds to the active site, blocking access by substrate molecules.

Question 20

What happens when a competitive inhibitor is in low concentration? (1)

Answer 20

Increasing the concentration of the substrate eventually overcomes inhibition as substrate molecules displace inhibitor and enzyme - substrate collisions become more likely than enzyme - inhibitor collisions.

Question 21

What is an examples of competitive inhibition? (1)

Answer 21

Oxygen competes with carbon dioxide for the active site of rubisco.

Question 22

What is non-competitive inhibition? (1)

Answer 22

Inhibitor chemically unlike the substrate molecule, but binding to another (allosteric) sites changes the shape of the enzyme molecule including the active site.

Question 23

What happens when the non-competitive inhibitor is in low concentration? (1)

Answer 23

Increasing the concentration of substrate can neither displace inhibitor nor prevent binding further inhibitor molecules.

Question 24

What is an example of non-competitive inhibition? (1)

Answer 24

Alanine non competitively inhibits pyruvate kinase.

Question 25

What are lenticels? (1)

Answer 25

Ares of loosely packed cells forming pores on the surface of plant stems.

Question 26

What are the stomata? (1)

Answer 26

Pores on the leaf surface allowing diffusion of gases into and out of the leaf.

Question 27

What are the spongy mesophyll? (1)

Answer 27

Loosely packed inner leaf tissue.

Question 28

Why do plant cells use less specialised than in animals? (3)

Answer 28

-plants have lower metabolic rates and much lower rates of gaseous exchange, but they do not show advanced adaptations. This is because they are not motile and do not need to maintain a high body temperature.
-Plants exchange different gases at different gases at different times of day.

Question 29

What are plant stems and leaves above ground covered in?

Answer 29

Are covered in cuticle or a bark to prevent water loss and also prevents diffusion of gases. To overcome this stems are often have tiny patches of very loosely packed cells (lenticels).

Question 30

Where do the highest rates of gas exchange occur? (1)

Answer 30

The highest levels of gas exchange occur in the leaves to supply carbon dioxide for photosynthesis.

Question 31

How are leaves adapted to prevent water loss?

Answer 31

Layers of water proof cuticles cover the leaf but the epidermis of the underside of the leaves usually contains many thousands of stomata.

Question 32

What is the function of the guard cells? (3)

Answer 32

The role of the guard cells is to alter the shape of the stomata by changes in their turgor pressure, when turgid, their curved shape means the stoma open and when they loose turgor (becomes flaccid) and straighten, the pores close.

Question 33

What does the spongy mesophyll do? (2)

Answer 33

Carbon dioxide d’issues through open stomata enters the air spaces of the spongy mesophyll inside the leaf. From here it dissolves in the water films surrounding the spongy mesophyll cells and can freely diffuse through the cell membrane into photosynthesising tissues.