Describe two ways pioneer species make a habitat suitable for later colonisers.

They break the rock down into particles by physical and chemical weathering, and their dead remains add humus so that a thin soil forms which can hold water and mineral ions.

What is a climax community?

A climax community is the stable, self-sustaining final stage of a succession, whose species composition does not change further under the prevailing conditions.

Describe how species diversity typically changes during a succession.

Diversity rises steeply through the early and middle stages as more niches become available, and may fall slightly at the climax as a few dominant species out-compete some earlier ones.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

Topic overview The cell cycle and mitosis Apoptosis in growth and repair Stem cells and cell differentiation

The Developing Individual: Meiosis, Growth and Development

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The Development of Species: Evolution and Classification

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The Nervous System and the Identification and Consequences of Damage

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Transport Systems in Plants

Topic overview The need for transport systems in plants Vascular tissue in roots, stems and leaves Water uptake and movement through the plant Transpiration and Its Measurement Translocation in the Phloem

Photosynthesis, Food Production and Management of the Environment

Deflected succession and measuring biodiversity

3 things to know
Components 01, 02 and 03

Overview

Recall questions on succession, pioneer species and climax communities, primary and secondary succession, deflected succession and the plagioclimax maintained by grazing, forestry and ploughing, and sampling with random quadrats and line or belt transects, frequency, percentage cover and species-area curves.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is ecological succession?

Key term

What is a pioneer species? Give an example that colonises bare rock.

Process

Explain why each seral stage is eventually replaced by the next.

Questions from this subtopic

Each one with the model answer underneath.

1
What is ecological succession?
Model answer
Succession is the directional change in the species composition of a community over time, as each stage alters the environment and is replaced by the next.
2
What is a pioneer species? Give an example that colonises bare rock.
Model answer
A pioneer is the first species to colonise a bare and hostile habitat, such as a lichen growing on newly exposed rock.
3
Describe two ways pioneer species make a habitat suitable for later colonisers.
Model answer
They break the rock down into particles by physical and chemical weathering, and their dead remains add humus so that a thin soil forms which can hold water and mineral ions.
4
What is a climax community?
Model answer
A climax community is the stable, self-sustaining final stage of a succession, whose species composition does not change further under the prevailing conditions.
5
Explain why each seral stage is eventually replaced by the next.
Model answer
Each community changes the abiotic conditions and makes them less hostile, which allows other species to establish and out-compete the existing occupants.
6
Describe how species diversity typically changes during a succession.
Model answer
Diversity rises steeply through the early and middle stages as more niches become available, and may fall slightly at the climax as a few dominant species out-compete some earlier ones.

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The Developing Cell: Cell Division and Cell Differentiation

The Developing Individual: Meiosis, Growth and Development

The Development of Species: Evolution and Classification

Cells and Microscopy

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