Question
a. Distinguish between the transfers of energy and inorganic nutrients in ecosystems. [2]
b. Outline the role of methanogenic archaeans in the movement of carbon in ecosystems. [2]
c. Describe how autotrophs absorb light energy [3]
▶️Answer/Explanation
a.
- Energy flows in one direction and is lost as heat; it is not recycled.
- Inorganic nutrients like carbon and nitrogen are recycled through the ecosystem.
b.
- Methanogenic archaeans produce methane from organic matter in anaerobic (oxygen-free) environments.
- The methane either enters the atmosphere or is later oxidized to carbon dioxide, continuing the carbon cycle.
c.
- Chlorophyll in photosystems absorbs light, especially red and blue wavelengths.
- Photosystems are in the thylakoid membranes of chloroplasts.
- Absorbed light excites electrons, starting photosynthesis.
———————————————————————————————–Markscheme————————————————————————————————————————
energy is lost (between trophic levels) / not all passed on / not reused / must be supplied;
nutrients are recycled/reused;
a. methane produced from organic matter;
b. in anaerobic conditions;
c. methane diffuses into atmosphere/accumulates in ground/soil;
d. oxidized/converted to carbon dioxide (in atmosphere);
a. light absorbed by (photosynthetic) pigments;
b. chlorophyll absorbs blue and red / drawing of absorption spectrum for chlorophyll;
c. photosystems are groups of pigment molecules/are light harvesting complexes;
d. photosystems are located in thylakoid membranes;
e. electrons excited/raised to higher energy level;