Chapter 20
Food Chains are the
sequence of who eats
who in an ecosystem is
called a food chain.
Living organisms need a constant supply of
energy to maintain cellular activities and stay
alive. In ecosystems the initial source of energy
is light from the sun. This is used by plants
during photosynthesis to produce carbohydrates.
Organisms (i.e. plants) that can
manufacture their own food from
inorganic materials are called
autotrophs.
The initial source of energy in an ecosystem is
light from the sun. Some of the light absorbed by
plants is converted through photosynthesis into
chemical energy in the form of carbohydrates
such as glucose. Photosynthesis is summarised
as:
light
carbon dioxide + water
REACTANTS
glucose + oxygen
ENERGY
SOURCE
PRODUCTS
Some of the glucose produced by photosynthesis is
broken down during the process of respiration.
Respiration can be summarised as follows:
Glucose + oxygen
water + carbon + energy
dioxide
The energy produced during respiration is then
used for cellular processes.
Herbivores are consumers that graze directly on the producers.
Herbivores include:
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Elephants
Giraffes
Pandas
Koalas
Deer
Rhinoceros
Zebras
Horses
Carnivores are consumers that eat other consumers (prey).
Carnivores that catch live prey are called predators. The carnivore
that directly feed on herbivores are known as first order
carnivores. The carnivore that is the last link of the chain is known
as the top carnivore. Carnivores include:
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Lions
Tigers
Eagles
Birds
Snakes
Omnivores are animals that eat both plants and other animals.
Many omnivores will eat the eggs of other animals. Some
omnivores are scavengers which means they eat dead animals.
Most will eat plants that produce fruit and vegetables. They also
eat the fruit and vegetables. Omnivores include:
• Pigs
• Grizzly bears
• humans
Parasites are specialised consumers that live and feed on the
surface of, or inside other organisms causing them harm. Parasites
include:
• Tape worm
• Flat worm
• Nematodes
Scavengers are consumers that eat dead animals . Scavengers
include:
• Tasmanian devil
• Vultures
• Hyenas
Detritivores eat small particles of dead plant and animal organic
matter that accumulates as detritus. They also eat waste products
such as dung. Detritivores include:
• Crustaceans
• Worms
• Snails
Decomposers are consumers that breakdown dead material.
Decomposers work differently to detritivores as they secrete
enzymes over the dead material and then absorb the broken down
products as food. Decomposers include:
• Decomposing bacteria
• Fungi
The interrelationship between many food chains
is called a food web.
Producers
Animals are consumers. An organism that
feeds on plants is a first-order consumer.
An organism that feeds on a first-order
consumer is called a second-order consumer,
and so on. The level occupied by a consumer
in a food chain is referred to as a feeding or
TROPHIC level. First-order consumers
occupy the first trophic level; second-order
consumers occupy the second trophic level,
and so on.
Primary
Consumers
Secondary
Consumers
Tertiary
Consumers
Competition is a relationship in which two
organisms compete for a limited resource.
In the short term this results in a decrease in the
abundance of one of the species. In the long
term it can result in extinction of the less
successful species.
Mutualism is a relationship between two organisms where both of
them benefit.
Mutualism and fungi:
A Lichen consists of a fungus and an alga joined together. The
fungi provides structure and the alga provides food
Mutualism and animals:
Rabbits and horses rely on organisms in their gut because no
vertebrate can break down cellulose. Bacteria have enzymes
which can break down cellulose to substances which they can
use.
Commensalism is where one organism benefits but the
other neither benefits nor comes to any harm. An example
of this are Remoras which are the fish found swimming at
the sides of a shark. In this location the fish are getting a free
ride and access to food scraps form the sharks meal.
This is a relationship between two organisms where
one benefits at the expense of the other organism
Example: the pimple wasp. It lays its eggs on the
leaves of the mangrove. The larvae eat through the
leave when they hatch and the leaf is damaged
Pollination is the transfer of pollen from one flower to
another. Successful reproduction in many flowering plants is
reliant on them attracting insects, birds or small mammals (all
known as pollinators) that will transport pollen from one
flower to another.