C4.2 Transfers of Energy and Matter

Question 1

The structure of organisms is based on organic molecules containing carbon. Explain the cycling of carbon in an ecosystem. [7]

Answer 1

a. autotrophs/producers/plants obtain inorganic nutrients from the «abiotic»
environment
b. energy is provided «mainly» by sunlight
c. light energy is converted «to chemical energy» through photosynthesis
d. photosynthesis/producers/autotrophs convert inorganic carbon/carbon dioxide
and water into carbon/organic compounds
e. carbon compounds/foods contain/are a source of «usable» energy «for life»
f. carbon compounds/energy are transferred along food chains when eaten by
consumers/heterotrophs
g. respiration returns carbon «dioxide» to the environment
h. respiration releases stored/chemical energy as heat/ATP
i. energy/ATP is used to carry out life functions/synthesis/growth/movement
j. energy is lost/is not recycled (Both related by “or” required.)
k. nutrients are recycled / example of recycled nutrient e.g. carbon
l. decomposers recycle minerals/inorganic nutrients
Award [5 max] if only energy is mentioned.

Question 2

Outline energy flow through a food chain. [4]

Answer 2

a. energy from the sun/light energy is converted to chemical energy by
photosynthesis
b. «chemical» energy flows through the food chains by feeding
c. energy is released «from carbon compounds» by respiration
OR
energy from respiration is used by living organisms and converted to heat
d. heat is not recyclable / heat is lost from food chains
OR
heat cannot be converted to other forms of energy
e. energy is lost in excretion / uneaten material / egestion / feces
f. energy losses between trophic levels limits the length of food chains
OR
energy transfer is only 10 % between trophic levels