Year 7 Biology: Year 7 Ecosystems: Biotic and Abiotic Factors

Q: Which of the following is an ABIOTIC environmental factor?

Correct Answer: B) Sunlight intensity. Explanation: Light intensity is a physical, non-living factor that determines plant photosynthetic rate. Mark Scheme: 1 mark for Sunlight intensity.

Q: What is the biological term for all the living organisms of ALL species in a habitat?

Correct Answer: B) Community. Explanation: A community consists of all populations of different species coexisting in an area. Mark Scheme: 1 mark for Community.

Q: Why must ecologists place quadrats using random number coordinates?

Correct Answer: A) To ensure representative sampling and avoid experimenter bias.. Explanation: Random sampling eliminates unconscious bias and ensures sample validity. Mark Scheme: 1 mark for avoiding bias / ensuring representative data.

Key Learning Objectives

Define the terms habitat, population, community, and ecosystem.
Classify ecological factors into biotic (predation, disease, food) and abiotic (light, temperature, moisture, pH).
Explain how changes in abiotic conditions alter organism abundance and distribution.

Topic Summary & Core Notes

Explore how organisms interact within habitats, communities, and ecosystems. Distinguish between living (biotic) and physical non-living (abiotic) factors influencing population distributions.

Key Rules, Formulas & Definitions

Ecosystem Definition

Ecosystem = Community of Living Organisms (Biotic) + Non-Living Physical Environment (Abiotic)

Sampling Formula

Estimated Population = (Total Habitat Area ÷ Total Quadrat Sample Area) × Mean Organisms per Quadrat

2 Step-by-Step Worked Examples

Worked Example 1

Worked Example 1: Classifying Environmental Factors

Question: Classify the following as Biotic or Abiotic: 1. Soil pH, 2. Introduction of a new predator, 3. Light intensity, 4. Bacterial infection.

Step-by-Step Solution:

Step 1: Define terms: Biotic = living factors; Abiotic = physical/chemical non-living factors.
Step 2: Classify physical factors: Soil pH and Light intensity are non-living (Abiotic).
Step 3: Classify biological factors: Predators and Bacteria are living organisms (Biotic).

Final Answer: Abiotic: Soil pH, Light intensity. Biotic: Predator introduction, Bacterial infection.

Senior Examiner Insight: Always check if the factor involves living organisms or physical environmental conditions.

Worked Example 2

Worked Example 2: Estimating Dandelion Population with Quadrats

Question: A student samples a 200 m² school field using ten 0.5 m² quadrats. They find 40 dandelions in total across the 10 quadrats. Estimate the total dandelion population.

Step-by-Step Solution:

Step 1: Calculate total sampled area: 10 quadrats × 0.5 m² = 5.0 m².
Step 2: Calculate density: 40 dandelions ÷ 5.0 m² = 8 dandelions per m².
Step 3: Scale to field area: Total population = 8 dandelions/m² × 200 m² = 1,600 dandelions.

Final Answer: 1,600 dandelions

Senior Examiner Insight: State clearly that quadrat sampling assumes random distribution across the entire habitat.

Common Pitfalls & Examiner Warnings

Common Mistake: Calling temperature a biotic factor

Temperature, light, and water are physical/chemical, making them ABIOTIC.

Common Mistake: Throwing quadrats rather than using random coordinates

Throwing is biased; random number generators must be used for coordinates.

Common Mistake: Confusing Community with Population

A population is ONE species; a community includes ALL living species in the habitat.

Interactive Self-Check Quiz (3 Questions)

Question 1 of 3

Which of the following is an ABIOTIC environmental factor?

A) Competition for food

B) Sunlight intensity

C) Parasite load

D) Predation

Click to Reveal Answer & Mark Scheme

Correct Answer: B) Sunlight intensity

Detailed Explanation: Light intensity is a physical, non-living factor that determines plant photosynthetic rate.

Mark Scheme & Scoring Points: 1 mark for Sunlight intensity.

Question 2 of 3

What is the biological term for all the living organisms of ALL species in a habitat?

A) Population

B) Community

C) Ecosystem

D) Biome

Click to Reveal Answer & Mark Scheme

Correct Answer: B) Community

Detailed Explanation: A community consists of all populations of different species coexisting in an area.

Mark Scheme & Scoring Points: 1 mark for Community.

Question 3 of 3

Why must ecologists place quadrats using random number coordinates?

A) To ensure representative sampling and avoid experimenter bias.

B) To make counting faster.

C) To sample only the areas with the most plants.

D) To protect the grass from damage.

Click to Reveal Answer & Mark Scheme

Correct Answer: A) To ensure representative sampling and avoid experimenter bias.

Detailed Explanation: Random sampling eliminates unconscious bias and ensures sample validity.

Mark Scheme & Scoring Points: 1 mark for avoiding bias / ensuring representative data.

Created by Fiaraz Iqbal

Former Headteacher & Senior Science / Maths Examiner

Fiaraz produces structured video walkthroughs, Tier 3 literacy packs, and exam mark scheme breakdowns to help secondary students achieve top grades.

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