World Geography 3202
Chapter 6
Life Systems
Life Systems - Introduction
• Earth is the only planet in
our solar system capable of
supporting complex life
forms.
• Energy is most important
ingredient for this life which
living organisms usually get
from food sources.
• Energy in food is obtained
from heat and light from sun
(ie solar energy is
converted into food energy).
• See Figure 6.1, 6.2 Pages
92-93.
Figure 6.1 - Components Needed to Produce Food Energy
The Web of Life
• Ecosystem: the
network of
relationships
among plants,
animals and the
non-living
organisms in an
environment.
• See Figure 6.3
Page 94
Figure 6.3 – Typical Ecosystem
Organisms in an Ecosystem
• There are many living things (plants & animals) and
non-living things (soil, water sun, temperature etc.)
that affect each other.
• It is the system of relationships between the
organisms and between the organisms and the
non-living environment that makes up the
ecosystem
• Producers: a plant which can convert the sun's
energy into carbohydrates (food energy) for all
other organisms in the ecosystem. (ie. They
actually produce the food for the ecosystem)
Organisms in an Ecosystem
• Consumers: All those organisms in trophic levels
other than producers. Consumers eat their food.
• For example in figure 6.3 on page 94 all the
animals, Raccoon, bass, duck etc. are consumers.
• 1st-order or primary consumers eat producers.
• 2nd-order or secondary consumers eat primary
consumers.
• 3rd-order or tertiary consumers eat secondary
consumers
Organisms in an Ecosystem
• Decomposers: Simple organisms that obtain their
food from dead organisms and wastes.
• For example in Figure 6.3 on page 94 of your text
the colony of bacteria, protozoa, and flatworms are
all decomposers.
• So named because they are actually responsible
for decomposing dead organisms.
• Similarities——all three are terms referring to the
way organisms obtain food & energy
• Differences——the way they obtain food. Producers
make it, consumers eat it, decomposers feed on
wastes & dead material.
Food Chains
• Food chain: linear
sequence representing the
flow of energy & nutrients
from the simplest plant to
the top carnivore.
• Tree ¬¬ insect ¬¬ insecteating bird ¬¬ hawk
• Producer: Tree
• 1st-order consumer: insect
• 2nd-order consumer: insect
eating bird
• 3rd-order consumer: hawk
Food chain from fig. 6.4. P. 95
Food Webs
• Food web: a series of
interconnecting food chains
in an ecosystem
• Similarity——both food
chains and food webs show
the flow of nutrients and
energy in an ecosystem.
• Differences——Food webs
are: more complex;
composed of several food
chains; a more realistic
picture of an ecosystem.
Food web in a temperate deciduous forest
Figure 6.4 on page 95
Energy Flow in an Ecosystem
• the Sun is the source of all
ecosystem energy;
• producers make food via
photosynthesis;
• consumers eat plants and
other consumers to get
energy;
• each time energy moves
from one organism to
another, energy leaves the
system in the form of heat;
• decomposers return
nutrients to the soil but
energy is not recycled
Figure 6.5 on page 95 main energy
flows in an ecosystem
Food Pyramid
• is a diagram showing each trophic level as a
horizontal bar;
• producers are located on bottom & higher
trophic levels are placed on top of each
other;
• each bar is drawn in proportion to the mass
of organisms, giving the triangle shape
• (See Figure 6.6, Page 96)
Food Pyramids
• Pyramid of Numbers:
– There are fewer organisms at each increasing
trophic level:
• less energy available at each increasing level;
• fewer organisms can obtain energy to live;
• therefore fewer organisms at increasing
levels
Food Pyramids
• Pyramid of Energy
– There is a high degree of energy loss at each trophic level
• The producers only store 1% of the sun's energy as food
energy.
• Each consumer level looses energy for several reasons
– much of the energy is lost as heat;
– most of the energy is used to carry out life functions——ie. we
burn many calories of energy each day. so do all organisms; if
an organism dies without being eaten the energy goes to the
decomposers and not up the trophic levels;
– consequently only about 10-15% of the energy is stored as
usable food energy at each level..
Food Pyramids
• in terms of units of energy and we start with 1000
units of energy at the producer level then:
– the primary consumers would only have 100-150 units of
food energy stored for the next level;
– the secondary consumers would only have 10-15 units of food
energy stored for the next trophic level;
– the tertiary consumers would only have 1-1.5 units of food
energy stored as food energy——it is easy to see why we
do not often see a quaternary trophic level
Implications
• people can gain much more energy from
consuming plants for food than eating animals
higher up food chain
• Much more food energy can be supplied to humans
by using land to grow edible plants/crops than by
using land for pasture to feed animals
Unfortunate Consequence
• Biological Amplification
– Toxic chemicals introduced at low trophic levels build up
through the food chain and reach amplified proportions by
the time higher order consumers join the chain
– Consumers eat organisms that contain toxic chemicals,
they receive a higher concentration of the toxins than did
the lower-level organisms because:
• Toxic chemicals are fat soluble (collect and remain in tissue
of organisms and do not get flushed away in waste)
• Higher up an animal is in food chain, more organisms has to
consume at lower levels in order to get all food energy it
requires thus consuming more of the toxic chemicals