surface but are home to 50–70% of all plant and animal life-forms
on Earth. Rainforests are the most productive and most complex
ecosystems on Earth.
■ Many trees have wide buttress roots to support them as they grow
very tall because of competition for sunlight.
■ Many leaves in the multilayered canopy block out the sun from the
lower layers. The canopy contains over 50% of the rainforest
wildlife. Lianas (vines) climb to the canopy to reach sunlight.
■ The undercanopy mainly contains bare tree trunks and lianas.
■ The shrub layer has the densest plant growth. It contains shrubs and
ferns and other plants that need less light. Saplings of emergents
and canopy trees can also be found here.
■ The forest floor is usually dark and damp. It contains a layer of
rotting leaves and dead animals called litter.(a) (iii) 1 point possible
Describe what you would expect the soil quality to be like in the
tropical rainforest.Possible answers might include the following points: ■ Tropical soils
are often several yards (meters) deep, but the soils are often strongly
leached, with large amounts of nutrients and minerals being removed
from the subsoils. Over many millions of years, this leaching has left
most of the soils lacking many of the fundamental nutrients needed by
the aboveground vegetation.
■ Forest floor litter (e.g., dead plant material such as leaves, bark,
needles, etc.), found in the O soil horizon, decomposes rapidly to
form a thin humus, rich in nutrients, but is quickly absorbed by
plants, resulting in poor soil quality.
■ Topsoil holds very large amounts of carbon known to have a major
potential influence on atmospheric CO 2 levels and hence a major
potential influence on climate change.(b) 2 points possible. Choice of water test and reason(s) for choosing it must
be related to conditions in or around Lake Gatún.
Describe one water quality test that your class might want to do and
why you chose that test.