Fig. 1.2 shows a cross-section through a tropical rainforest ecosystem. Deforestation for agriculture, logging and urban expansion is one of the main causes...

(a) Name of the layer labelled B [1]

Layer B is the canopy. [1]

The canopy is the primary layer of the tropical rainforest, formed by the crowns of the tallest mature trees (typically 25-35 m). It forms a continuous cover that intercepts most of the incoming sunlight.

(b) How light intensity changes from layer A to layer E [3]

Light intensity decreases progressively from the top of the forest to the floor:

1. Light intensity is highest at the emergent layer (A), where the tallest trees project above the canopy and receive direct, unobstructed sunlight. [1]
2. Light decreases significantly through the canopy layer (B) because the dense, overlapping leaves absorb and block most of the incoming sunlight. [1]
3. By the forest floor (E), only about 1-2% of the sunlight that hits the canopy reaches the ground, resulting in very low light intensity and deep shade. [1]

This steep light gradient is one of the defining physical characteristics of a tropical rainforest and drives the vertical stratification of plant and animal communities.

(c) How the layered structure supports high biodiversity [5]

The vertical layering of the rainforest creates a wide range of conditions, enabling many different species to coexist:

1. Different layers provide different habitats and microclimates (varying light, humidity, temperature and wind exposure), so species with different requirements can find suitable conditions. [1]
2. The canopy intercepts most light, so shade-tolerant species are adapted to the lower layers, while light-demanding species occupy the upper layers. This partitioning reduces direct competition. [1]
3. Each layer offers different food sources, nesting sites and shelter, supporting distinct communities of animals, insects and birds. [1]
4. The vertical structure creates many ecological niches. The more niches available, the more species can coexist without direct competition for the same resources. [1]
5. Epiphytes (plants that grow on other plants) and climbing plants add further diversity by colonising the trunks and branches of larger trees, exploiting surfaces unavailable to ground-rooted plants. [1]