11+ Reading Comprehension Test 3.

(Multiple choice format)

5

Read the passage carefully and then answer the questions that follow.

Earth's Living Systems

Rainforests: Nature's Treasure Chest

The Amazon rainforest is Earth's largest tropical rainforest, covering an area roughly the size of the United States. If you look at a satellite image of South America, you can see this vast green expanse stretching across the continent. Rainforests cover only about 7% of Earth's surface but are home to more than half of the world's plant and animal species. They are one of the five major types of forests on our planet. The other four are temperate forests, boreal forests, mangroves and cloud forests.

Rainforests have four distinct layers, each supporting unique forms of life. The emergent layer is the uppermost layer which contains the tallest trees. It can reach heights of 60 metres - taller than a 20-storey building. Immediately below this is the canopy, where most rainforest animals live. This layer creates a dense ceiling of leaves and branches that blocks most sunlight. Underneath the canopy is the understory layer, which receives very little sunlight, and which hosts shade-loving plants and insects. The forest floor is the darkest layer, receiving only 2% of available sunlight, yet it plays a crucial role in nutrient recycling.

A typical day in the rainforest is hot and humid, with temperatures rarely dropping below 20°C. Some parts receive over 100 inches of rain per year - that's more than four times the rainfall London receives annually. This constant moisture creates perfect conditions for plant growth. The soil, however, is surprisingly poor in nutrients because the rainfall washes them away. Most of the nutrients are stored in the living plants themselves, creating a delicate recycling system where fallen leaves are quickly broken down and reabsorbed by shallow root systems.

Deserts: Extreme Survival

The Sahara Desert, Earth's largest hot desert, presents a stark contrast to the lush rainforest. Unlike rainforests, deserts receive very little rainfall—less than 25 centimetres per year. The Sahara covers about 31% of Africa, an area roughly three times the size of Europe. It is one of the world's three major hot deserts, alongside the Arabian Desert and the Australian Desert.

Life in the desert requires remarkable adaptations. During the day, temperatures can soar to 50°C, while at night they may plummet below freezing. Desert plants, called xerophytes, have evolved ingenious survival strategies. For example, cacti store water in their thick stems and have spines instead of leaves to reduce water loss. The Welwitschia plant of the Namib Desert can live for over 1,000 years, surviving entirely on fog and dew.

Desert animals display equally impressive adaptations. The fennec fox's enormous ears help regulate its body temperature. Kangaroo rats never need to drink water - they get all their moisture from the seeds they eat. The thorny devil lizard can collect water on its skin, channelling morning dew directly to its mouth through tiny grooves between its scales.

Arctic Tundra: The Frozen World

The Arctic tundra forms Earth's coldest biome, creating a ring around the North Pole and covering about 20% of Earth's land surface. Unlike deserts and rainforests, the tundra has extremely low biodiversity, yet its importance to global climate systems cannot be overstated. The ground remains permanently frozen for most of the year, creating a layer called permafrost that can be hundreds of metres deep.

During the brief summer, which lasts only 6-10 weeks, the top layer of soil thaws. This creates shallow ponds where millions of insects breed, attracting numerous migrating birds. Plants in the tundra grow very close to the ground and cluster together, creating patches of colour against the otherwise barren landscape. These plants must complete their entire life cycle in the short summer season, flowering and producing seeds at remarkable speed.

Human Impact and Future Challenges

Each of these ecosystems faces significant threats from human activity. Rainforests are being cleared at an alarming rate - equivalent to losing 40 football fields every minute. Desert expansion, or desertification, threatens neighbouring farmland, while climate change is causing tundra permafrost to thaw rapidly, releasing stored greenhouse gases.

Scientists are racing to understand these ecosystems better. Recent discoveries include new species in the rainforest canopy, ancient river systems beneath the Sahara Desert, and complex networks of fungi in the tundra soil. This research is crucial for conservation efforts and may hold solutions to human challenges, from new medicines to sustainable farming techniques.