Biodiversity

This lesson covers biodiversity — the variety of living organisms in an ecosystem — as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand what biodiversity is, why it is important, the threats to biodiversity and the methods used to conserve it.

---

What Is Biodiversity?

Biodiversity is the variety of all the different species of organisms on Earth, or within a particular ecosystem. It includes:

• The number of different species present (species richness)
• The abundance of each species (how many individuals of each)
• The genetic variation within species

A healthy ecosystem typically has high biodiversity — many different species, each with a stable population.

---

Why Biodiversity Matters

Reason	Explanation
Ecosystem stability	Greater biodiversity means food webs are more complex and resilient; if one species declines, others can fill its role
Food security	We depend on a wide variety of plants and animals for food; loss of species reduces food options
Medical resources	Many medicines are derived from plants and microorganisms; undiscovered species may hold future cures
Economic value	Agriculture, fishing, tourism and biotechnology all depend on biodiversity
Aesthetic and ethical value	Many people believe we have a moral duty to protect other species and natural landscapes
Ecosystem services	Pollination, water purification, carbon storage and soil fertility all depend on diverse ecosystems

Exam Tip: If asked why maintaining biodiversity is important, give at least two reasons from different categories (e.g. one ecological, one economic or medical).

---

Threats to Biodiversity

Human activities are the main cause of biodiversity loss:

Threat	How it reduces biodiversity
Deforestation	Destroys habitats; removes food sources and shelter for many species
Pollution	Poisons organisms; air, water and land pollution all harm wildlife
Global warming	Changes habitats; species may not adapt fast enough; coral bleaching
Overfishing	Reduces fish populations below sustainable levels; disrupts marine food webs
Overexploitation	Hunting, poaching and over-harvesting drive species towards extinction
Invasive species	Non-native species outcompete or prey on native species
Habitat fragmentation	Roads, buildings and farmland break habitats into small, isolated patches

---

Extinction

Extinction occurs when there are no more living individuals of a species anywhere on Earth. Once extinct, a species cannot be brought back.

Causes of extinction include:

• Habitat destruction
• Climate change
• New diseases
• New predators or competitors
• Overhunting
• Pollution

graph TD
    A["Threats to Biodiversity"] --> B["Habitat loss"]
    A --> C["Pollution"]
    A --> D["Climate change"]
    A --> E["Overexploitation"]
    A --> F["Invasive species"]
    B --> G["Population decline"]
    C --> G
    D --> G
    E --> G
    F --> G
    G --> H["Extinction risk"]

---

Measuring Biodiversity

Scientists measure biodiversity in several ways:

Method	What it measures
Species richness	The number of different species in an area
Species evenness	How evenly individuals are distributed among species
Genetic diversity	The range of genetic variation within a species
Quadrat sampling	Counting species in random sample areas to estimate abundance
Transect sampling	Surveying species along a line to observe changes across a habitat

---

Conservation Methods

Conservation aims to protect and restore biodiversity. Key methods include:

Habitat Protection

Method	Description
Nature reserves and national parks	Protected areas where human activity is restricted
Marine conservation zones	Protected ocean areas where fishing and development are limited
Hedgerow and wildlife corridor maintenance	Connecting fragmented habitats so species can move between them
SSSIs (Sites of Special Scientific Interest)	Legally protected areas in the UK for rare species or habitats

Species Protection

Method	Description
Breeding programmes	Captive breeding of endangered species in zoos, then releasing them into the wild
Seed banks	Storing seeds from rare and endangered plants at low temperatures for future use
Reintroduction programmes	Returning species to habitats where they have become extinct (e.g. red kites in the UK)
Legal protection	Laws banning hunting, trading or disturbing endangered species (e.g. CITES)
Gene banks	Storing genetic material (DNA, sperm, eggs) to preserve genetic diversity

Exam Tip: Seed banks are a key example of conservation. Seeds are stored dried and at low temperatures to keep them viable for long periods. This protects genetic diversity even if the species becomes extinct in the wild.

---

Sustainability and Biodiversity

Sustainable development means meeting the needs of the present without compromising the ability of future generations to meet their own needs. In the context of biodiversity:

• Sustainable fishing uses quotas and net size regulations to prevent overfishing
• Sustainable forestry replants trees at the same rate they are cut down
• Sustainable agriculture uses crop rotation, organic methods and reduces pesticide use

---

The Role of Zoos and Botanic Gardens

Institution	Contribution to conservation
Zoos	Captive breeding, research, education, reintroduction programmes
Botanic gardens	Growing and preserving rare plant species, seed banking, research
Wildlife trusts	Managing reserves, habitat restoration, community engagement

Exam Tip: If asked about the role of zoos in conservation, go beyond just "keeping animals alive". Mention breeding programmes, education of the public and research into animal behaviour and genetics.

---

Summary