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Date November 2016 Marks available 8 Reference code 16N.2.SL.TZ0.7
Level Standard level Paper Paper 2 Time zone TZ0 / no time zone
Command term Explain Question number 7 Adapted from N/A

Question

In ecosystems, energy is used to convert inorganic compounds into organic matter. Energy enters ecosystems through producers.

Explain the processes by which energy enters and flows through ecosystems.

[8]
a.

Producers extract phosphates and nitrates from soil. Outline how these ions are used in the synthesis of organic molecules.

[3]
b.

Draw a labelled diagram of a pyramid of energy.

[4]
c.

Markscheme

a. light energy is the initial energy source for (all) organisms

b. producers/autotrophs change light/radiant energy into chemical energy
OR
producers/autotrophs convert/trap light/radiant energy by photosynthesis

c. producing C6H12O6 /sugars/carbohydrates

d. carbon/organic compounds used for energy/growth/repair/storage

e. compounds/energy pass as food along food chains/trophic levels WTTE

f. cellular respiration releases energy as ATP from food

g. energy is lost as heat (during cellular respiration)

h. loss of energy at each trophic level
OR
only approximately 10% of energy is passed to the next trophic level / 90% is lost at each trophic level

i. energy lost in bones/hair when they die/not fully eaten by the next trophic level

j. energy lost in feces/urine

k. decomposers/saprotrophs remove energy from wastes/bodies

l. energy is not recycled

a.

a. by photosynthesis / using energy from light

b. attached to carbon compounds

c. phosphates used to make phospholipids/nucleotides/nucleic acids/DNA/RNA/ATP

Other phosphorus-containing metabolites are acceptable if verified.

d. nitrates are used to make amino acids/proteins/nucleotides/nucleic acids/DNA/RNA/ATP

Other nitrogen-containing metabolites are acceptable if verified.

e. transported from roots to leaves (in xylem)

b.

a. drawn in steps rather than triangle

b. drawn to scale (should be at least 1/5 of the box below it)
OR
annotated with appropriate numeric values

c. producer

d. primary consumer

e. secondary consumer

Award no marks if a drawing has not been made.

“Appropriate numeric values” should indicate scale so accept percentage or numbers.

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Core » Topic 4: Ecology » 4.2 Energy flow
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