IGCSE · Practice questions · Habitat destruction

Trees do things.

Six original Cambridge-style questions on biodiversity, habitat destruction, food webs and the effects of deforestation, including data on species numbers.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Five effects, five reasons.

Biodiversity: the number of different species in an area.
Reasons: housing, crops and livestock; extracting natural resources; freshwater and marine pollution.
Deforestation: biodiversity down, extinction, soil loss, flooding, more carbon dioxide.
Link each effect to the trees: habitat, roots, water uptake, photosynthesis.

Recall

[3 marks]

Define biodiversity and state two reasons why humans destroy habitats.

Biodiversity is the number of different species that live in an area. ✓
To provide land for housing, crop plants or livestock. ✓
To extract natural resources such as timber or minerals (also accept: freshwater or marine pollution). ✓

Explain

[5 marks]

Explain the undesirable effects of deforestation.

Habitats and food sources are lost, so biodiversity is reduced. ✓
Species that live only in that forest may become extinct. ✓
Without roots to hold it, soil is eroded by rain and wind, and the remaining soil loses its mineral ions. ✓
Water is not absorbed by trees, so it runs off into rivers, causing flooding. ✓
Fewer trees remove carbon dioxide by photosynthesis, and burning releases carbon dioxide, so atmospheric carbon dioxide increases. ✓

Data

[3 marks]

A survey counted the species of birds in an area of forest and in a nearby area cleared for cattle.

Area	Number of bird species
forest	64
cattle pasture	16

(a) Calculate the percentage decrease in bird species. (b) Suggest two reasons for the difference.

(a) (64 − 16) ÷ 64 × 100 = 75%. ✓
(b) The pasture has fewer types of plant, so fewer habitats such as nesting sites. ✓
There are fewer food sources (fruits, seeds, insects) for different bird species. ✓

Explain

[3 marks]

A hillside forest is cleared and planted with crops. Explain why the crop yield falls after a few years.

Without tree roots holding the soil, heavy rain washes the topsoil away (soil erosion). ✓
Topsoil contains most of the mineral ions and humus, so the remaining soil is less fertile. ✓
Crops therefore have fewer mineral ions such as nitrate and grow less. ✓

Analysis

[3 marks]

Explain how humans can damage a habitat by altering a food web, using an example.

Example: overfishing a predator, hunting, or introducing a new species (such as rats on an island). ✓
Removing or adding one species changes the numbers of its prey, predators and competitors. ✓
For example, removing predators lets herbivores increase and overgraze the producers, so the habitat is damaged. ✓

Recall

[2 marks]

Give two ways in which pollution of fresh water or the sea can destroy habitats.

Excess fertiliser or sewage causes eutrophication, killing fish and other organisms that need oxygen. ✓
Plastics, oil or toxic chemicals kill or harm organisms and damage habitats such as coral reefs or shorelines. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.