Topic 1 - Key Concepts In Biology

Question 1

State 2 ways in which a yeast cell differs from a bacteria cell. (2)

Answer 1

Yeast cell:
Has a nucleus (1)
Doesn’t have a plasmid (1)
Doesn’t have a flagellum (1)

Bacterial cell:
Has circular/chromosomal DNA (1)
Has a capsule (1)
Has a slime coat (1)
Doesn’t have mitochondria (1)

Question 2

Plant cells can produce glucose. Suggest why yeast cells can’t produce glucose. (1)

Answer 2

They don’t have chloroplasts/chlorophyll

Question 3

Describe the functions of white blood cells. (2)

Answer 3

Involved in defence against disease/part of the immune system (1)
Phagocytosis (1)
Antibody/antitoxin production (1)

Question 4

A person has a low number of red blood cells. Suggest an effect this may have on the person. (1)

Answer 4

Tired/lack of energy/lethargy/shortness of breath (1)

Question 5

A student was investigating osmosis in potato cubes. He used the following method:
- He cut the potato into equally sized cubes
- record the mass of each potato cube
- place each potato cube into different concentrations of salt solution
- remove the potato cubes after 30min
- dry the potato cube & record the final mass of each cube
Name 1 other variable that must be controlled (1)

Answer 5

Temperature (1)
Amount of drying (1)
Type of potato (1)
Age of potato (1)

Question 6

Explain a conclusion that can be made about point Q on the graph (where there’s no % change in mass) for the osmosis experiment in potato cubes (2)

Answer 6

1 identification point:
There’s no change in mass at specific mol/dm^3 (1)
This is the isotonic salt solution concentration in the potato (1)

+ a reasoning point:
Because there’s no net movement of water/no salt concentration gradient (1)

Question 7

Give 1 way the student could obtain more data to increase the accuracy of point Q (osmosis experiment on potato cubes) (1)

Answer 7

Repeat the test using intermediate concentrations (between 0.2 and 0.4 mol dm^3)

Question 8

The length of a flagellum in figure 7 is 68mm. Calculate the length of the flagellum in micrometers. (2)

Answer 8

68mm = 68,000 micrometers (1)

Question 9

During which stage of protein synthesis will amino acids be joined up? (1)

Answer 9

Translation

Question 10

Amino acids are joined together at the… (1)

Answer 10

Ribosome

Question 11

Explain the role of the active site in an enzyme. (2)

Answer 11

It has a specific shape (1)
To bind to substrate/form an enzyme substrate construct (1)
For reactions to take place/catalysed (1)
To join together/break down molecules/substrates (1)
Reference to lock and key mechanism (1)

Question 12

Mutations can occur in DNA. Describe what effect a mutation could have on the action of an enzyme. (3)

Answer 12

A mutation is a change in a gene (sequence)/base pairs (1)
(Change in DNA) causes a change in amino acids/sequence of amino acids (1)
Change in shape of the active site/enzyme/protein (1)
Prevent/reduce binding to substrate (1)
Enzyme can no longer function (1)
Enzyme could be more effective (1)

Question 13

Explain why phenolphthalein turns colourless when lipase breaks down the lipids in milk (2)

Answer 13

Fatty acids are formed when the lipids are broken down by lipase (1)
And fatty acids are acidic (so pH increases) (1)

Question 14

Describe the effect of temperature on the activity of lipase (2)

Answer 14

As the temperature increases from __ to __, the rate of lipase activity increases from __ to __. (1)
The rate of lipase activity is optimal at __. (1)
Above __, the rate of lipase activity decreases from __ to __. (1)

Question 15

Explain why the activity of lipase decreases above a temperature of 40 decrees Celsius. (2)

Answer 15

An increase in temperature above 40 degrees causes changes in the active site of an enzyme. (1)
Therefore, the enzyme becomes denatured & no longer functions. (1)

Question 16

A student investigated the time taken for amylase to break down a 10% starch solution into glucose at 37 degrees Celsius. They repeated the experiment 5x.
State 1 other variable the student should’ve controlled during the investigation. (1)

Answer 16

Concentration of the enzyme (1)
Volume of starch solution (1)
Volume of enzyme solution (1)
pH of the solution (1)

Question 17

Different enzymes catalyse specific reactions. Explain why enzymes can only catalyse specific reactions. (2)

Answer 17

The active shape of an enzyme has a specific shape because of the order of amino acids (1)
The substrate must have a shape that’s complementary to the active site (1)

Question 18

Explain how the lock and key hypothesis models how enzymes work (3)

Answer 18

Enzymes and substrates have complementary shapes (1)
Substrate fits into enzyme/enzyme substrate complex formed (1)
Reference to active site (1)
Enzymes break/form chemical bonds/cause reactions to occur/make products (1)
Idea of products leaving enzyme (so that the enzyme can be used again) (1)

Question 19

Describe what happens to the molecule produced by transcription before it’s translated (2)

Answer 19

Leaves the nucleus/moves to the cytoplasm (1)
Through the nuclear membrane (1)
Attaches to ribosome (1)

Question 20

Describe how named factors affect the rate of enzyme catalysed reactions (6)

Answer 20

Temperature
(Temperature) is too low, not enough energy to make reactions occur fast enough
Reference to optimum temperature
Optimum temperature for most humans is 37 degrees Celsius
Over 37 degrees, changes the shape of the active site/enzyme
Therefore rate of reaction stops/decreases
Enzyme is denatured (if temperature is too high)

pH
For most enzymes, the optimum temperature is 6-8
Optimum pH for pepsin is 2-3 (specific optimum pH for an enzyme)
pH on either side of the optimum changes the shape of the enzyme/active site
Therefore, rate of reaction decreases/stops
Enzyme is denatured if pH is too high/low

Substrate/enzyme concentration
Higher concentrations, faster reactions
Due to more collisions
Until maximum rate reached/all enzymes being used

Question 21

Osmosis is one method that single-celled organisms, such as bacteria, use to obtain molecules from their environment.
Which of the following is a correct description of a process involving the transport of molecules?
A Diffusion is used to transport molecules against the concentration gradient
B Active transport is used to obtain molecules in a low concentration environment
C Active transport moves substances along the concentration gradient
D Diffusion uses energy to transport molecules into cells
(1)

Answer 21

B (1)