Edexcel A-Level Biology A2 5 Energy Flow Ecosystems and the Environment Questions

Identify the molecular or ecological energy transfer, use the relevant diagram or formula and connect limiting factors and human pressures to measured system outcomes.

Exam points

Trace light-dependent and Calvin-cycle reactions through chloroplast structures and products.
Calculate productivity or transfer efficiency from GPP, NPP, respiration and trophic data.
Interpret succession, nutrient cycles or environmental change through field evidence.

Covered syllabus points

5.1—Overall reaction of photosynthesis 5.2—Photophosphorylation, ATP and energy supply 5.3—Light-dependent reactions 5.4—Light-independent reactions and Calvin cycle products 5.5—Chloroplast structure and photosynthesis 5.6—Absorption and action spectra 5.7—Chloroplast pigment chromatography 5.8—Core Practical 10 - factors affecting photosynthesis rate 5.9—GPP, NPP and plant respiration 5.10—Biomass and energy transfer efficiency 5.11—Population, community, habitat and ecosystem 5.12—Biotic and abiotic factors 5.13—Niche, distribution and abundance 5.14—Core Practical 11 - habitat ecology study 5.15—Succession and climax community 5.16—Evidence for climate change 5.17—Anthropogenic climate change and greenhouse gases 5.18—Carbon cycle applications 5.19—Climate models and extrapolation 5.20—Climate change effects on plants and animals 5.21—Temperature, enzyme activity and Q10 5.22—Core Practical 12 - temperature and organism development 5.23—Evolution by mutation and natural selection 5.24—Isolation, gene flow and speciation 5.25—Scientific conclusions in controversial issues 5.26—Conservation management and human needs

[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: 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

[ 3 ]

All question bank results loaded

Covered syllabus points

Question 1

Question (a)

Question (b)

Question (c)

Question (i)

Question (ii)

Question 2

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (b)

Question (i)

Question (ii)

Question (iii)