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Natural sciences

Grade 8

Environment and interactions

Module 35

Ecological relationships

Our study of the roles of organisms in ecosystems has shown that organisms do not exist in isolation. There are mutual relationships amongst all of them. All are dependent on each other to a lesser or greater degree.

Ecological relationships develop for many different reasons.

Activity:

To identify the reasons for the relationships between organisms in nature

[lo 2.4]

See whether you are able to write down a few reasons for the development of relationships between organisms in nature.

  • Discuss your reasons with each other and decide which reason is the most important one:

Assessment of your ability to identify relationships

Were you able to list reasons?

[LO 2.4]

Activity:

To be able to explain and identify food relationships, and to be able to illustrate them using examples

[lo 2.1; lo 2.2; lo 2.3; lo 2.4]

Green plants photosynthesise and produce food in the form of starch.

Animals are not capable of producing their own food and therefore need to make use of plants or other animals that have eaten plants.

However, there are different kinds of consumers. In a previous module on biodiversity it was mentioned that herbivores, carnivores and omnivores together comprise the consumers.

Decomposers are also an important part of the chain.

All the above-mentioned are links in a typical FOOD CHAIN .

A food chain originates when organisms feed off each other, and nutrients, as well as energy from the sun, flow from one organism to the next.

Test your knowledge of food relationships

1. Provide the scientific word for:

1.1 plant-eaters:

1.2 meat-eaters:

1.3 eaters of both plants and meat:

2. Provide the definition of:

2.1 a consumer:

2.2 a producer:

2.3 a food chain:

3. Briefly explain the importance of the following:

3.1 a scavenger:

3.2 decomposers:

4. Name at least TWO important decomposers:

Assessment of QUESTIONS ON THE FOOD CHAIN

Were you able to answer the questions correctly?

[LO 2.1]

Compile a food chain

  • Compile a simple food chain by pasting sketches or pictures in the proper order.
  • In nature food chains do not exist in isolation, in other words they are interlinked. Such a network of food chains is called a FOOD WEB .
  • Food chains are often represented as FOOD PYRAMIDS. A food pyramid indicates the amount of biomass or energy on each level in the food chain.[LO 2.2]

Assessment of your understanding of the FOOD CHAIN

Were you able to represent both?

[LO 2.3]

Read the following and use the information to compile as many food chains as possible.

It is a hot day in the Kalahari. A light breeze is blowing dead matter in the form of fine twigs and organic material over the top of a sand dune. Insects such as ants and beetles scuttle about in an attempt to pick up some of these bits and pieces. In a little funnel in the sand an ant-lion lies in wait for its prey. As it starts to cool down at nightfall, tiny field-mice and other mammals appear.

They nibble at the last few grass seeds and blades of grass on which the little moisture there is in the air will condense again to form droplets of water in the early hours of the morning. On the crown of the dune a black tapping-beetle scurries along. It comes to a standstill with its tail in the air so that some of the moisture from the soil can condense on its hard little body and run down into its thirsty mouth.

In the heat of the day the gecko makes small two-steps to avoid being scorched by the burning sand. A grasshopper on a tuft of grass catches its attention. Scorpions scuttle about with their tails held high, in search of spiders and beetle larvae. Spiders lie in wait for ants and termites and a horned adder chases after a field-mouse. All of this takes place amid the great silence of the sweltering day and the cold night when the jackal’s cries can be heard.

Assessment of the interpretation of the PASSAGE:

Were you able to identify the basic FOOD CHAINS from the passage?

[LO 2.4]

Assessment

LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

  • recalls meaningful information;
  • categorises information;
  • interprets information;

2.4 applies knowledge.

Memorandum

Activity: Reasons for ecological relationships

Reasons: food — e.g. birds that pollinate flowers, animals that serve as prey for other animals, herbivores that eat grass, protection — e.g. gnus, zebras and impalas that graze together (protections against predators), homes — e.g. birds that nest in a tree, decomposition — e.g. fungi and bacteria that depend on dead plants and animals for their food, but in turn are useful to other plants and animals because their action maintains the fertility of the soil.

The most important reason: a class decision

Activity: Explaining, identifying and illustrating food-based relationships / the food chain

Tests your knowledge:

1. 1.1 – herbivores 1.2 – carnivores 1.3 – omnivores

2.

2.1 consumer: not able to produce own food, must eat / live off plants or something else that eats / lives off plants.

2.2 producer: produces its own food by utilising the sun, carbon dioxide and water, e.g. green plants.

2.3 Energy derived from the sun, by means of a range of organisms, usually ranging from a herbivore first, then through a range of consumers to decomposers. Some energy is lost at each link.

3.

3.1 Carrion eaters remove visible animal remains while decomposers see to fine breaking down to mineral level so that the residue can return to the soil.

3.2 Decomposers break down organic material (plant and animal remains) to basic nutrients (nutrients / building materials) that are made available to plants from the soil.

4. Fungi, bacteria (or examples of fungi and bacteria)

The Food chain

  • Accept the learner's answer if the following are correct: producer, 1 st consumer, 2 nd consumer and 3 rd consumer, decomposer.

.

Food chains related to a text for reading

  • E.g. twigs / organic material - ants - antlion - gecko - snake
  • Grass - locust - gecko - snake
  • Twigs / organic material - field mouse - snake

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Graphene has a hexagonal structure
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Source:  OpenStax, Natural sciences grade 8. OpenStax CNX. Sep 12, 2009 Download for free at http://cnx.org/content/col11050/1.1
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