Edexcel A Level Biology Topic 5 Exam Questions

Explain how studying pollen grains in peat bogs can provide evidence of climate change. (3)

• M1: Pollen preserved in peat bogs

• M2: A plant species can be identified by its pollen

• M3: Climate affects the type of plaint growing

• M4: Depth of peat correlates with period of time since pollen was produced

• M5: Change in pollen over time indicates change in climate

Explain why anthropogenic emissions of greenhouse gases are affecting the climate. (3)

• M1: relevant example of human activity (burning fossil fuels/ landfills/ cattle ranching/ deforestation)

• M2: Increasing a named greenhouse gas (CO₂/ Methane)

• M3: Therefore more {heat energy/ infrared radiation} is trapped in the atmosphere

• M4: Causing a mean increase in {surface/ atmospheric} temperature

State what is meant by the term Q₁₀ temperature coefficient. (2)

• The ratio of the rate of enzyme reaction taking place at temperatures differing by 10^oC

State what is meant by the term ecosystem. (1)

• Organisms and {non living components/ abiotic factors}

Explain why the value of GPP is lower than the light energy available to the ecosystem. (3)

• M1: Not all light falls on the {leaves/ plants/ producers}

• M2: Some of the light is reflected from the surface of the leaf

• M3: Some of the light misses the chloroplasts and passes through the leaves

• M4: Some of the light is the {wrong wavelength/ not absorbed by the chlorophyll}

Net primary productivity (NPP) is a measure of the increase in biomass of a plant.

Explain why respiration affects the production of biomass. (2)

• M1: GPP - R = NPP

• M2: {organic molecules/ glucose} used in respiration to provide energy

• M3: Because the more {organic molecules/ glucose} used in respiration, the less is available for the production of biomass.

Tropical rainforests play a role in maintaining biodiversity and in storing carbon.

Explain how reforestation of tropical rainforests can be used to minimise climate change. (3)

• M1: {new/ young/ growing} trees

• M2: resulting in net uptake of CO₂/ more CO₂ taken in by photosynthesis than released by respiration

• M3: Therefore reducing CO₂ in the atmosphere

• M4: Which slows the rate of global warming

Describe how forests can be managed as a sustainable resource. (2)

• M1: Replacing trees that have been cut down

• M2: {remove/ cut down} older trees

• M3: Replace with {seedlings/ young/ rapidly growing} trees

Explain the impact of cutting down trees on climate change. (4)

• M1: Less photosynthesis

• M2: Less carbon dioxide will be fixed/ more CO₂ remains in the atmosphere

• M3: More heat energy trapped in the atmosphere

• M4: More energy in the atmosphere increases atmospheric temperature (allow increasing surface temperature of earth)

Describe how starch is formed from the products of the light-independent reactions of photosynthesis. (4)

• M1: Two GALP used to produce a glucose molecule

• M2: Glucose molecules are joined together by glycosidic bonds to form starch

• M3: By condensation reaction

• M4: Producing amylose and amylopectin

Describe the light-dependent reactions of photosynthesis. (5)

• M1: Use of light energy to excite electrons in chlorophyll

• M2: {photolysis/ splitting} of water to produce oxygen, electrons and hydrogen ions

• M3: Electrons used {in the electron transport chain/ to replace those lost by chlorophyll}

• M4: Generation of ATP/ photophosphorylation

• M5: Reduction of NADP

Explain why this increase in carbon dioxide concentration affects the growth of plants in glasshouses. (3)

• M1: description of CO₂ as a limiting factor

• M2: CO₂ is fixed to produce {GP/ GALP}

• M3: Therefore increasing CO₂ results in more {carbohydrate/ polysaccharide/ glucose} being produced

• Which would lead to greater rate of {growth/ cell division} (allow faster growth)

Describe the roles of the products of the light-dependent reactions in the Calvin cycle. (3)

• M1: The production of ATP and reduced NADP

• M2: ATP is used by the enzyme converting {GP to GALP/ GALP to RuBP}

• M3: Reduced NADP used to convert GP to GALP

Explain the importance of RUBISCO to the productivity of an ecosystem. (3)

• M1: fixes inorganic carbon

• M2: Allowing formation of organic molecules by the Calvin Cycle

• M3: these organic molecules allow transfer of energy to the next trophic level (allow: these organic molecules can be converted to biomass)

Explain the relationship between the structure and functions of a granum in photosynthesis. (3)

M1: Granum is formed from many layers of thylakoid membranes to increase surface area for absorbing light

M2: Thylakoid membranes contain chlorophyll to absorb light

M3: Electron carrier molecules in thylakoid membrane involved in ATP production

Describe the difference between the terms niche and habitat. (2)

• M1: Niche is the way an organism interacts with its environment

• M2: habitat is the place (with distinct set of conditions) where an {organism lives/ community of organisms live}

Explain why a diet on plant protein produces lower greenhouse gas emissions than a diet based on animal protein. (3)

• M1: Because plants produce {organic compounds/biomass} from photosynthesis

• M2: Plants remove carbon dioxide from the atmosphere

• M3: Because animals produce more carbon dioxide by respiration

• M4: Because some animals produce methane

Explain why the conditions in peat bogs prevent decomposition. (3)

• M1: Conditions are anaerobic

• M2: Therefore less aerobic respiration by decomposers

• M3: Acidic conditions {inhibit/ denature} enzymes

• M4: Therefore enzymes cannot {digest/ break down} organic matter (ALLOW breakdown plants/ animals/ peat)

Explain why cells use chemical energy in the form of ATP. (3)

• M1: Contains {phosphate / P-O-P} bonds

• M2: That when hydrolysed {releases / provides supplies} energy

• M3: Description of how energy is used (e.g. to {form / break} bonds / form {carbohydrates / sugars} / used in light independent reactions / for metabolic reactions)

• M4: ATP {immediate source of energy /releases energy rapidly}

Describe how plant photosynthesis converts carbon dioxide from the air into simple organic molecules. (4)

• M1: CO2 combined with RuBP

• M2: By RUBISCO

• M3: Forming molecules of GP

• M4: Each GP is converted to GALP using ATP and reduced NADP

• M5: GALP used to form {glucose / hexose sugars}

Explain how chloroplasts are adapted for their role in photosynthesis. (4)

• M1: Large surface area of thylakoid (membrane)

• M2: Thylakoid (membrane) contain photosynthetic pigments to absorb light (ALLOW contains {chlorophyll / photosystems} to absorb light)

• M3: thylakoid (membrane) enables photophosphorylation

• M4: Stroma contains enzymes for light independent reaction

• M5: Stroma contains {DNA / ribosomes} to produce {enzymes / proteins} involved in photosynthesis

Explain how energy of the electrons along the electron transport chain is used to power the synthesis of ATP. (3)

• M1: By photophosphorylation

• M2: (transfer of) electrons releases energy

• M3: That is used to {pump / move} protons into the thylakoid (space / lumen)

• M4: protons {diffuse / move back down concentration gradient} through ATP synthase

• M5: which forms ATP from ADP and inorganic phosphate

Explain what happened to the bare rock to allow the growth of these trees. (3)

M1: Bare rock colonised by pioneer species

M2: These pioneer species break up the rock

M3: Dead plant add {humus/ organic matter} as they decompose

M4: Eventually trees will be able to grow as the soil {becomes deeper/ can retain more water}