Soils, soils, soils
• Discuss the formation of soils
• Compare different soil types
• Relate soil fertility to physical & chemical
properties of soil.
• Discuss soil erosion and its preventative
• Compare farming methods
• Discuss food chains & food webs found in
the terrestrial environment
• Describe the oxygen, carbon, nitrogen &
• Soil formation begins with weathering.
• This is the process by which rocks are
broken up into small particles over long
periods of time.
• There are various ways in which
weathering may occur.
• Physical weathering is caused by changes in
temperature and water pressure.
• Chemical weathering is caused by rainwater in
cracks of rock dissolving away some of the
• Biological weathering is caused by growth of
roots through rocks.
Components of soil
• Mineral particles
• Rock particles
• Living organisms
*Discuss the functions of each
• Clay soils have mainly clay particles with
small air spaces.
• Sandy soils have mainly sand particles
with large air spaces.
• Loam soils are a mixture of sand & clay
particles with medium size air particles.
Size of particles
• The size of the particles affects the
following physical characteristics of the
1) Air content
2) Water-holding capacity
• Soil fertility is determined by
1) Particle size
2) Mineral content
3) Organic content
Nb. Soil which possesses the conditions
needed for optimum plant growth of a plant are
fertile with respect to that plant.
• Erosion is a natural process, whereby the
topsoil is removed by action of wind and
• It has been increased dramatically by
human land use, especially industrial
agriculture, deforestation, and urban
Causes of soil erosion
• Careless farming methods
• Over cropping
• Loss of soil structure
Reducing soil erosion
• Contour ploughing
• Planting trees
• Strip cropping
*Please check text for various farming techniques
• An ecosystem is a system formed by the
interaction of a community of organisms
with their physical environment.
• Forests, deserts, grasslands & savannas
have their own terrestrial ecosystems.
• All organisms interact with each other and
their surroundings within an ecosystem.
• One of these main interactions involve the
various feeding relationships.
• A food chain shows the feeding sequence
of organisms in an ecosystem.
• The 1st member is called the producer. It
is a plant, and it produces its own food.
• All of the other members of the food chain
are called the consumers. These acquire
their food otherwise.
• A food chain always starts with the
• The arrows shows the direction of energy
• The consumers follow thereafter and are
classified primary, secondary, tertiary etc.
Consumers can be:
*Herbivores: feed only on plant material
*Carnivores: feed only other animals
*Omnivores: feed on both plants & animals
*Decomposers: feed on dead organic matter
Can you give examples of these?
• A food web is a network of inter-related
• If the number of one organism in a food
web changes, it can affect the numbers of
all the others.
The Carbon cycle
The Nitrogen cycle
The water cycle