Doc Scientia curriculum Grade 8

1. FOOD CHAINS
AND
FOOD WEBS
GENERAAL HERTZOG: MRS F BEUKES

2. Introduction
ECOLOGY: The study of living organisms and the
places where they live..
Living organisms that live together in an environment are interdependent.
But the environmental conditions, e.g. soil, water and climate also play an important
role. Ecosystems vary in size. Examples are the Kruger National Park, Kalagadi, the
Botanical gardens and the Gariep dam.

3. ECOSYSTEM: An area where living (biotic) and non-living (abiotic) things live and interact with each
other.
BIODIVERSITY: The diverse spectrum of life found in one habitat.
ECOSYSTEMS are grouped into biomes, namely:
• SAVANNA
• MIDLATITUDE GRASSLANDS
• BOREAL FOREST
• TROPICAL RAIN FOREST
• SCRUBLAND
• OPEN WOODLAND
• DESERT
• TUNDRA
HABITAT: The area in which plants and animals live.
There are various habitats in an ecosystem. .
Examples:
A cheetah’s habitat is SAVANNA GRASSLANDS.

4. Various plants and animals can be found in each habitat.
The plants and animals in a habitat depend on each other for food and protection
and they form a community.
COMMUNITY: All the living things in one habitat.
Communities consist of a variety of populations, such as herds of kudu, flocks of sparrows and
schools of fish.
POPULATION: One kind of living organism that is found in one habitat.

5. Food chains
Example of a food chain :

6. .
Sun
provides
energy.
Snake is then
eaten by the
Plants (producers)
falcon.
use this energy to
produce their own
food.
Frog is eaten by
the snake (tertiary
consumer).
Grasshopper
(primary
consumer)
Frog
eats the grass.
(secondary
consumer) eats the
grasshopper.

7. After the falcon dies, its body is broken down by detritivores and decomposers and
energy is released into the soil, atmosphere and water.
Energy is transferred from one organism to the other in this manner.
FOOD CHAIN: It is the relationship where energy (in food) flows between living organisms.

8. CIRCULATION OF NUTRIENTS :
Consumers:
• primary
• secondary
• tertiary Die and are
Eaten by decomposed by
Die and are Detritivores and
Producers decomposed by Decomposers
Consumed by
Nutrients
Used in photosynthesis

9. Exercise 10
1 Give one word for the following descriptions :
1.1 The relationship where energy (in food) flows between
FOOD CHAIN
living organisms.
1.2 One kind of living organism that is found in a habitat.
POPULATION
1.3 The variety of life found in an ecosystem.
BIODIVERSITY
1.4 All the living organisms of a specific kind that live
POPULATION
together in an ecosystem.
1.5 The diversity of life in a habitat.
COMMUNITY
1.6 An area where living (biotic) and non-living (abiotic)
ECOSYSTEM
things live and interact with each other, e.g. a jungle.

10. 2 Study the sketch below and answer the questions that follow:
2.1 What does this sketch represent?
An ecosystem
2.2 Use the sketch as reference and give an example of:
2.2.1 a predator: Lion/cheetah/eagle
2.2.2 an omnivore: Ostrich
2.2.3 a herbivore: Giraffe/zebra/springbok/blue wildebeest
2.3 Write down two different food chains that are found in this sketch.
grass → springbok → cheetah
tree → giraffe → lion

11. 2.4 Explain why there are so many more herbivores in the habitat than carnivores.
There is more food for the herbivores to eat than for the carnivores.
If there were more carnivores in this habitat, the herbivores would not have
been a sufficient amount of food for the carnivores.
2.5 Explain why giraffes and zebras do not compete for food.
Giraffes eat leaves from trees, while zebras feed on grass. Therefore these
two animals eat different types of food and thus they do not compete for
food.
2.6 Explain why lions and cheetahs compete against each other in this habitat.
Lions and cheetahs are both carnivores. Both these animals may hunt the same
animals and therefore they are each other’s competitors.

12. 3 Study the diagram below and answer the questions that follow
C
B
D
A
plants
soil surface
decomposers
food
excretion
decomposition
respiration

13. 3.1 What does this diagram represent?
A food chain
3.2 What does the arrow at D represent?
Radiation from the sun
3.3 What is another name that can be given to plants? Give a reason for your answer.
Producers, because plants have the ability to produce their own food.
3.4 What does B represent? Give an example.
Secondary consumers for example snakes
3.5 Can C be a herbivore? Motivate your answer.
No, because herbivores only feed on plants (producers) and they are the primary consumers. C is a tertiary
consumer.
3.6 Complete A, B and C with your own examples so that the diagrams follow logically.
A: mouse
B: snake
C: eagle
3.7 What do plants, A, B and C release into the atmosphere during respiration?
Carbon dioxide (CO 2)
3.8 What does “excretion” mean?
Excretion is waste products that are excreted by humans and animals.
3.9 Give an example of decomposers.
Bacteria/Fungi

14. Food webs
FOOD WEB: A variety of interlinked food chains.

15. Various food chains and how they are linked:
• Worms, grasshoppers, mice, guinea fowls and antelope eat grass and plants.
• Herbivores are a source of food for various predators, carnivores and omnivores.
 The grasshopper is eaten by the frog and the bird.
 The snake catches the mouse.
 The genet catches the mouse, frog, guinea fowl, bird and snake.
 The antelope is eaten by the leopard.
 The genet, guinea fowl and bird are eaten by the eagle.
• Because the food chains overlap, a food web exists.
• Decomposers are always at the top of the food chain or food web.
• Decomposers recycle the nutrients in dead plants and animals and plough it back
• into the soil.
• These nutrients will make the soil fertile and make it possible for plants to grow.

16. Activity 13
Investigate your area. See how many different food chains you can identify and
write them down. Food chains in my environment:
Seed → pigeon/mouse → cat/owl
Flowers → butterfly/moth → spider/gecko → crow
Flowers → plant louse → ladybug → spider → crow
Crops → snale → corn cricket → woodpecker
Crops → mouse → cat/owl
Leaves → worms → hoopoe → cat
Determine how many of these food chains are connected, and then draw your own
food web.
Seed Flowers Crops Leaves
Pigeon Mouse Butterfly Moth Plant-louse Snail Worms
Spider Ladybug Corn cricket Hoopoe
Gecko Wood pecker
Cat Crow WWW.DOCSCIENTIA.CO.ZA

17. 3.4 Fossil fuels
There are some circumstances where animals and plants die and it is
impossible for them to decompose and so their remains become
earthbound.
Over a long period of time the remains of these animals and plants are
CONVERTED BY HEAT AND PRESSURE INTO FOSSIL FUELS, e.g. coal and oil
Energy is released when these fuels are burned.
People all over the world are dependent on this energy for electricity, heating,
petrol, etc.
NON-RENEWABLE RESOURCES: cannot be replenished (made again) in a short space of time..
Fossil fuels are non-renewable resources.

18. The mining and burning of fossil fuels lead to pollution.
Harmful greenhouse gasses are released into the atmosphere – ACID RAIN is formed.
GREENHOUSE GASES: Gases whose molecules can absorb harmful infrared radiation from the
sun and release them within our atmosphere.
INTERDEPENDENCE IN ECOSYSTEMS
Organisms depend on other biotic (living) organisms and abiotic (non-living)
aspects of their habitat.
These dependencies result in certain relationships better known as SYMBIOSIS.
There are three different symbioses (interdependencies):
SYMBIOSIS
Mutualism Parasitism
Commensalism

19. MUTUALISM:
Both parties benefit from the relationship that was created
Examples:
Animal-animal  crocodile and Egyptian plover
A crocodile lies with its mouth open so that the Egyptian plover is able to get rid of
small pieces of meat that got stuck between the crocodile’s teeth.
The plover feeds on the small pieces of meat that were stuck between
the teeth.
Animal-plant  bees and flowers
Bees depend on the flower’s nectar for nutrients.
On the other hand flowers depend on bees to spread their pollen and thus ensure
pollination.
Plant-plant  lichens
Lichens actually consist of two plants – fungi and algae.
The fungi absorbs water and nitrogenous substances and provide them to the
algae. The algae produce carbohydrates through photosynthesis and provide them to the fungi .

20. COMMENSALISM:
In this relationship one party will benefit, while the other will not benefit nor will it
be disadvantaged.
Examples:
Animal-animal  white egret and cattle
While cattle are grazing, insects are driven into the air and are eaten by
white egret. The white egret is benefitting, but there is no benefit or
disadvantage to the cattle.
Animal-plant  finches and trees
Finches build their nests in tall trees. The tree provides protection against
predators and floods, so the finch is benefitting. The tree is not at a disadvantage
due to the nest, but it also does not benefit by this relationship.
Plant-plant  orchids and trees
Orchids are not fed by the trees. They need the trees so that they may
grow higher and thus get more sunlight necessary for photosynthesis.
Since orchids do not feed on the trees, the tree is not disadvantaged but it
also does not benefit from this relationship.

21. PARASITISM:
In this instance one party will be disadvantaged while the other benefits.
Examples: Animal-animal  ticks and dogs
The tick is benefitting from this relationship since it feeds on the dog.
On the other hand the dog is disadvantaged and may even become infected
with an illness like biliary.
Plant-plant  dodder on other plants
Dodder obtains all its water, nutrients and carbohydrates
from its host and all of this is to the host’s disadvantage.
The abiotic aspects in a habitat play just as important role in
the survival of biotic organisms.
Abiotic factors: Water, soil, oxygen and carbon dioxide.

22. Exercise 11
1 Consider the diagram below and answer the questions that follow .
Seed
Birds Mouse
Snake
Eagle
1.1 What does this diagram represent?
A food web
1.2 If there was an increase in snakes, which animal will also increase? Give a reason for your answer.
Eagles, because the more snakes there are, the more food there is for the
eagles. The circumstances are favourable for the eagles to increase.
WWW.DOCSCIENTIA.CO.ZA

23. 1.3 If there was an increase in snakes, which animal would decrease? Give a reason for your answer.
Birds and mice, because they serve as a food source for the snakes. If there
are more snakes to feed on them, the amount of birds and mice will decrease .
1.4 What animals are the ... in this case:
primary consumer: bird; mouse
secondary consumer: snake; eagle
predator: snake; eagle
herbivore: bird; mouse
2 Give one word/term for the following:
2.1 Fuels like oil, natural gasses and petrol FOSSIL FUELS
2.2 Interdependence in ecosystems SYMBIOSIS
2.3 One party benefits, while the other does not benefit nor is it COMMENSALISM
disadvantaged.
2.4 These remains of animals and plants have been converted FOSSIL FUELS
over millions of years.
2.5 A variety of food chains that are linked. FOOD WEB

24. 3. Match column A to column B. Write down the correct letter next to the description.
E A. Parasitism
The relationship between ants and
plant lice.
A variety of food chains that overlap. C B. Ecology
The area where plants and animals live. G C. Food web
The relationship between a clown fish D. Fossil fuels
and an anemone.
F
A herd of springbok on the grasslands. E. Mutualism
H
It is produced from the remains of plants and animals under extreme F. Commensalism
heat and pressure.
D
The study of living organisms and the places where they live. G. Habitat
B
The relationship between humans and H. Population
tapeworms.
A