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A population is one species in an area; a community includes interacting populations. An ecosystem includes that community and its physical environment. Abiotic factors include temperature, light and water availability; biotic factors include competition, predation and disease. Adaptations help organisms in particular conditions. A change in one population can affect several others through a food web, so do not assume only the immediately connected species responds.
Video by Cognito. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Explain biotic and abiotic influences
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Which is abiotic?
Temperature. It is a physical environmental factor.
After watching 2: Why randomise quadrat placement?
Reduce selection bias. Convenient placement may misrepresent the habitat.
What you'll be able to do
A population is one species in an area; a community includes interacting populations. An ecosystem includes that community and its physical environment. Abiotic factors include temperature, light and water availability; biotic factors include competition, predation and disease. Adaptations help organisms in particular conditions. A change in one population can affect several others through a food web, so do not assume only the immediately connected species responds.
Producers build organic material, while consumers obtain it by feeding. Not all biomass passes to the next trophic level: some material is uneaten or undigested, and respiration transfers energy to surroundings. A pyramid of biomass compares material at a stated time and differs from simply counting individuals. Transfer efficiency is useful transferred biomass or energy divided by input times 100. Matter cycles through ecosystems while energy flows and is eventually dissipated.
Use randomly positioned quadrats for a fair estimate of abundance in a reasonably defined habitat. Repeat enough samples and calculate a mean before scaling to the whole area. A transect is useful for a changing environmental gradient and answers a different question from purely random placement. Keep quadrat size and identification rules consistent. Mark–release–recapture needs assumptions such as mixing, retained marks and limited population change. State which assumptions could bias the estimate.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: A trophic level receives 1000 kJ and passes 120 kJ onward. Find efficiency.
12%.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.