Noesis
Level 2 — RecallEcology & Ecosystems

Ecology & Ecosystems

40 marksprintable — key stays hidden on paper

Level 2 (Recall & Standard Problems)

Time: 30 minutes Total Marks: 40

Instructions: Answer all questions. Show working for calculations. Use ...... for any numerical expressions.

Q1. (4 marks) (a) Define ecology. (1) (b) Arrange the following levels of ecological organization from smallest to largest: ecosystem, population, biosphere, organism, community. (3)

Q2. (4 marks) Distinguish between biotic and abiotic factors. Give two examples of each.

Q3. (4 marks) (a) Define the terms habitat and ecological niche. (2) (b) State one key difference between them. (2)

Q4. (5 marks) Consider the food chain: Grass→Grasshopper→Frog→Snake→Hawk\text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog} \rightarrow \text{Snake} \rightarrow \text{Hawk} (a) Identify the producer and the top consumer. (2) (b) State the trophic level of the frog. (1) (c) Explain one difference between a food chain and a food web. (2)

Q5. (6 marks) A producer traps 10,000 kJ10{,}000\text{ kJ} of energy. Using the 10% rule: (a) State what the 10% rule says. (2) (b) Calculate the energy available at the level of a secondary consumer. (3) (c) Give one reason why energy is lost between trophic levels. (1)

Q6. (4 marks) (a) Name the three types of ecological pyramid. (3) (b) Which pyramid can sometimes be inverted? (1)

Q7. (5 marks) The nitrogen cycle involves several processes. (a) Name the process that converts atmospheric N2N_2 into ammonia/nitrogen compounds. (1) (b) Name the process that converts ammonia into nitrites and then nitrates. (1) (c) Name the process that returns nitrogen gas to the atmosphere. (1) (d) Name one type of organism responsible for nitrogen fixation. (2)

Q8. (4 marks) The carbon cycle moves carbon between organisms and the atmosphere. (a) Name the process by which producers remove CO2CO_2 from the atmosphere. (1) (b) Name two processes that add CO2CO_2 to the atmosphere. (2) (c) Name one long-term carbon store. (1)

Q9. (4 marks) Distinguish between primary and secondary succession. Give one example of where each occurs.

END OF PAPER

Answer keyMark scheme & solutions

Q1. (4 marks) (a) Ecology is the scientific study of the interactions between organisms and their environment (and with each other). (1) (b) Smallest → largest: Organism → Population → Community → Ecosystem → Biosphere. (3) — award 3 for fully correct order; 1–2 for partially correct sequence. Why: each level nests within the next larger, from a single individual up to the global sum of life.

Q2. (4 marks)

  • Biotic factors: living components of an environment (1). Examples: predators, plants, bacteria, competition (any two = 1).
  • Abiotic factors: non-living physical/chemical components (1). Examples: temperature, light, water, pH, soil, salinity (any two = 1).

Q3. (4 marks) (a) Habitat = the place/physical environment where an organism lives (1). Niche = the functional role of an organism in its ecosystem — how it obtains food, its interactions and conditions it tolerates (1). (b) Difference: habitat is the "address" (location) whereas niche is the "profession/role" (function). (2)

Q4. (5 marks) (a) Producer = Grass (1); Top consumer = Hawk (1). (b) Frog is a secondary consumer = 3rd trophic level. (1) (Grass=1, Grasshopper=2, Frog=3.) (c) A food chain shows a single linear pathway of energy flow; a food web shows many interconnected food chains / multiple feeding relationships. (2)

Q5. (6 marks) (a) The 10% rule: only about 10% of the energy at one trophic level is transferred to the next; ~90% is lost. (2) (b) Producer =10,000=10{,}000 kJ. Primary consumer =10,000×0.10=1000=10{,}000\times0.10 = 1000 kJ (1). Secondary consumer =1000×0.10=100 kJ=1000\times0.10 = \mathbf{100\text{ kJ}} (2). Why: two transfers from producer → each multiplies by 0.10. (c) Any one: lost as heat via respiration, undigested material (egestion), movement, excretion. (1)

Q6. (4 marks) (a) Pyramid of numbers, pyramid of biomass, pyramid of energy. (3) (b) Pyramids of numbers (and sometimes biomass) can be inverted; pyramid of energy is never inverted. (1)

Q7. (5 marks) (a) Nitrogen fixation (1). (b) Nitrification (1). (c) Denitrification (1). (d) Any one: Rhizobium bacteria (in legume root nodules), Azotobacter, cyanobacteria/blue-green algae. (2)

Q8. (4 marks) (a) Photosynthesis (1). (b) Any two: respiration, combustion/burning of fossil fuels, decomposition (1 each = 2). (c) Any one: fossil fuels (coal/oil/gas), limestone/sedimentary rock, oceans (dissolved carbonates). (1)

Q9. (4 marks)

  • Primary succession: begins on bare lifeless surface with no soil (e.g. new volcanic rock, bare sand). Pioneer species = lichens/mosses. (2)
  • Secondary succession: occurs where a community has been disturbed/removed but soil remains (e.g. after a forest fire, abandoned farmland). (2)
[
  {"claim":"10% rule: secondary consumer gets 100 kJ from 10000 kJ producer","code":"prod=10000\nsec=prod*0.10*0.10\nresult=(sec==100)"},
  {"claim":"Primary consumer receives 1000 kJ","code":"prod=10000\nprim=prod*0.10\nresult=(prim==1000)"},
  {"claim":"Frog is at trophic level 3 in Grass->Grasshopper->Frog chain","code":"chain=['Grass','Grasshopper','Frog','Snake','Hawk']\nlevel=chain.index('Frog')+1\nresult=(level==3)"},
  {"claim":"Energy lost between two successive transfers is 9900 kJ (99%) from 10000 kJ start","code":"prod=10000\nsec=prod*0.10*0.10\nlost=prod-sec\nresult=(lost==9900)"}
]