Edexcel IAL Biology Unit 4 Energy, Environment, Microbiology and Immunity

Connect molecular energy transfer to ecological processes, then apply microbial growth and immune responses using precise terminology, quantitative evidence and evaluation.

[Maximum number: 8]

The light-independent reactions of photosynthesis use the products of the light-dependent reactions to produce simple sugars.

(a)

Which row of the table shows the products of the light-dependent reactions that are used in the light-independent reactions? □ A □ B □ C

Table for Question (a) — Edexcel A-Level Biology A2

□ D

[ 1 ]

(b)

Simple sugars have the formula $\mathrm{C}_{n} \mathrm{H}_{2 n} \mathrm{O}_{n}$ . Name the inorganic molecule that provides each element in a simple sugar. (2)

[ 2 ]

(c)

Two types of plant, $\mathrm{C}_{3}$ and $\mathrm{C}_{4}$ , have slightly different pathways of light-independent reactions. The graph shows how the rate of photosynthesis is affected by temperature in these two types of plant. Rate of photosynthesis / a.u.

Figure for Question (c) — Edexcel A-Level Biology A2

[ 5 ]

(i)

Describe three conclusions that can be made about the differences in the effect of temperature on the rate of photosynthesis in these two types of plant.

[ 3 ]

An answer that includes three of the following points:

- (overall / after $20^{\circ} \mathrm{C}$ ) rate of increase in C3 plants is lower (1)

- the optimum temperature is lower for C3 plants (than C4 plants) (1)

- at the optimum temperature, the rate of photosynthesis is slower in C3 plants (1)

- credit appropriate comment about rate below $20^{\circ} \mathrm{C}$ (1)

NB all mark points are comparative ACCEPT converse throughout for C4

ACCEPT above $20^{\circ} \mathrm{C} \mathrm{C3}$ plants have a lower rate of photosynthesis

NB if values are given they must be correct C3 \{26 / $27 / 28\}$ and C4 \{34/35/36\}

ACCEPT the \{fastest / peak\} rate for C3 is lower (than the fastest rate for C4)

IGNORE any values given

e.g. C3 have a higher rate of photosynthesis rate increase in C3 is non-linear but in C4 plants it is linear rate increase in C3 is less steep C3 plants (probably) photosynthesise at lower temperatures

(ii)

Calculate the $\mathrm{Q}_{10}$ for the enzymes in $\mathrm{C}_{4}$ plants. Use the formula:

Q_{10}=\frac{R_{t+10}}{R_{t}}

where $R_{t}$ is the initial rate of reaction at $10^{\circ} \mathrm{C}$ . Give your answer as a whole number.

[ 2 ]

values for $\mathrm{R}_{20}$ and $\mathrm{R}_{10}$ read from the graph (1)

- $\mathrm{Q}_{10}$ given as 4 (1)

6 and \{21.5 / 22\}

DO NOT ACCEPT with units IGNORE a.u.

Bald answer of 4=2 marks

Bald answer between 3.583 and 3.667 = 1 mark

[Maximum number: 8]

Two students, student P and student Q, each cultured bacteria in a liquid medium for 20 hours. The culture conditions used by both students were identical. Every two hours, each student removed a sample of the culture to count the number of bacteria. Each student used a different method to count the number of bacteria in the samples. The graph shows the bacterial growth curve that each student drew using their results. $\log _{10}$ number of bacteria per $\mathrm{cm}^{3}$

Figure for Question Unit 4: Energy, Environment, Microbiology and Immunity question 2 — Edexcel A-Level Biology A2

(a)

Both students used aseptic techniques to culture the bacteria.

[ 4 ]

(i)

Explain the importance of using aseptic techniques to culture bacteria.

[ 2 ]

(ii)

Explain one aseptic technique that should be used when culturing bacteria.

[ 2 ]

(b)

Calculate the growth rate constant ( k ) of these bacteria between 2 hours and 6 hours of culture. Use the equation: $\quad k=\frac{\log _{10} N_{t}-\log _{10} N_{0}}{0.301 \times t}$ where: $\log _{10} N_{t}=\log _{10}$ number of cells at 6 hours $\log _{10} N_{0}=\log _{10}$ number of cells at 2 hours.

[ 2 ]

3.2 (1)

- 3 / 2.7 / 2.66 / 2.658 (1)

ACCEPT $\log 5.2-\log 2=3.2$

ECF 0.3 / 0.34 / 0.345 = 1 mark

Bald answer of $\{3 / 2.7 / 2.66 / 2.658\}=2$ marks Bald answer of 2.6578073089700996677 \{incorrectly rounded up to three decimal places max / correctly rounded to more than three decimal places\} = 1 mark Bald answer of 3.2 = 1 mark

Bald answer of $\{0.3$ / 0.34 / 0.345 $\}=1$ mark

(c)

The number of bacteria in the samples taken after 10 hours were: 398107171 in the culture of student P 6309573 in the culture of student Q.

[ 2 ]

(i)

Student P and student Q used different methods for determining the number of bacteria. State which method each student used. Give a reason for your answer. (2) Student P Student Q

[ 2 ]

[Maximum number: 13]

Photosynthesis consists of the light-dependent reactions and the light-independent reactions.

(a)

In the light-dependent reactions, light energy is converted into energy stored in ATP.

[ 7 ]

(i)

Explain why light energy is converted into energy stored in ATP.

[ 2 ]

(ii)

An equation can summarise the production and breakdown of ATP.

Complete this equation, by writing the names of the substrates and the type of reaction on the three dotted lines provided. +

Figure for Question (ii) — Edexcel A-Level Biology A2

phosphorylation

[ 2 ]

An answer that includes the following points:

- (ADP / adenosine diphosphate) and (inorganic) \{Pi / phosphate / $\mathrm{PO}_{4}{ }^{3-}$ (ion)\} (1)

- hydrolysis (1)

ACCEPT adp DO NOT ACCEPT P / phosphorus

ACCEPT dephosphorylation

(2)

(iii)

Explain the role of light energy in the light-dependent reactions.

[ 3 ]

(b)

The light-independent reactions use products of the light-dependent reactions to produce simple sugars.

[ 6 ]

(i)

Which row of the table shows the products of the light-dependent reactions that are used in the light-independent reactions?
(b) The light-independent reactions use products of the light-dependent reactions to produce simple sugars.

Figure for Question (i) — Edexcel A-Level Biology A2

ATP produced by

NADP

cyclic photophosphorylation

oxidised

cyclic photophosphorylation

reduced

non-cyclic photophosphorylation

oxidised

non-cyclic photophosphorylation

reduced

[ 1 ]

(ii)

Simple sugars have the formula $\mathrm{C}_{n} \mathrm{H}_{2 n} \mathrm{O}_{n}$ .

Name the inorganic molecule from which each element in a simple sugar originated.

C

H

O

[ 2 ]

An answer that includes the following points:

- C and O from carbon dioxide (1)

- H from water (1)

ACCEPT CO2

ACCEPT $\mathrm{H}_{2} \mathrm{O}$

DO NOT ACCEPT O from water

(2)

(iii)

Simple sugars are used in the synthesis of new biological molecules.

Which row of the table shows the inorganic ions that are needed to synthesise these new biological molecules?

Table for Question (iii) — Edexcel A-Level Biology A2

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Covered syllabus points

Unit 4: Energy, Environment, Microbiology and Immunity question 1

Question (a)

Question (b)

Question (c)

Question (i)

Question (ii)

Unit 4: Energy, Environment, Microbiology and Immunity question 2

Question (a)

Question (i)

Question (ii)

Question (b)

Question (c)

Question (i)

Unit 4: Energy, Environment, Microbiology and Immunity question 3

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (b)

Question (i)

Question (ii)

Question (iii)