Agricultural Sciences is not a list of breeds and crops to memorise. It is reading the diagram, the table and the farm in front of you and saying what is happening.The GOAT Notes™
The seven levels of organisation run from one animal to the whole planet.
| Level | What it is | Farm example |
|---|---|---|
| Individual | One living organism | One cow |
| Species | One kind of organism that breeds together | All cattle |
| Population | One species living in one place | The cattle grazing in one camp |
| Community | All the plants and animals living in one place | Cattle, grass, insects and birds in the camp |
| Ecosystem | A community together with its non-living surroundings | The camp with its soil, water and sunlight |
| Biome | A large region with a similar climate and vegetation | The grassland biome |
| Biosphere | All the ecosystems on Earth | The whole planet |
An adaptation is a feature of an organism's body or behaviour that helps it survive in its environment. Thorns on an acacia protect it from browsers, and the thick fleshy leaves of an aloe store water.
Agro-ecology applies ecological principles to farming, so that food is produced while soil, water and living things are looked after. An agro-ecosystem is an ecosystem that a farmer manages to produce food, fibre or other products.
| Feature | Natural ecosystem | Agro-ecosystem |
|---|---|---|
| Control | Natural processes | The farmer |
| Species | Many different species | Few, chosen by the farmer |
| Nutrients | Return to the soil when organisms die | Leave the farm in the harvest, so the farmer must replace them |
| Energy | Sunlight only | Sunlight plus extra energy such as fuel and labour |
| Stability | Stable, because the species balance each other | Fragile, because pests spread fast through one crop |
Abiotic factors are the non-living parts of an ecosystem. CAPS groups them in three.
| Group | Factor | What it is and what it does on a farm |
|---|---|---|
| Physiographic (landscape) | Slope | How steep the land is; steep land erodes easily |
| Aspect | The direction a slope faces; in South Africa a north-facing slope is sunnier and warmer | |
| Altitude | Height above sea level; higher places are cooler | |
| Climatic | Sunlight | Energy for plant growth |
| Temperature | Controls growth; frost kills crops | |
| Rainfall | Water for crops and veld | |
| Wind | Dries soil and plants | |
| Edaphic (soil) | Soil texture | Proportions of sand, silt and clay |
| Soil depth | Room for roots | |
| Soil water | Water held for plants | |
| Soil fertility | Nutrients available to plants |
A food chain is one path along which energy moves. A food web joins many chains. A food pyramid stacks the feeding levels with the producers at the base.
Only about one tenth of the energy at one level reaches the next. The rest is lost as heat from respiration, in waste and in parts not eaten, so the pyramid narrows at every step.
Use the food web and pyramid above.
Each ✓ is one mark.
Water and nutrients are used again and again. In the water cycle the sun's heat drives every step.
| Letter | Process | What happens |
|---|---|---|
| A | Evaporation | Heat from the sun turns water into vapour |
| B | Condensation | Water vapour cools and forms clouds |
| C | Precipitation | Water falls as rain, hail or snow |
| D | Transpiration | Plants lose vapour through their leaves |
| E | Run-off | Water flows over the land to rivers and the sea |
A farmer cuts down all the trees on a slope above a dam.
Link each effect to a process in the cycle.
In the carbon cycle plants take carbon dioxide from the air and use it to grow; animals get carbon by eating plants. Respiration, decay and burning return carbon dioxide to the air.
In the nitrogen cycle plants cannot use nitrogen gas. Bacteria in the root nodules of legumes such as lucerne change it into ammonium (fixation). Soil bacteria change ammonium into nitrates (nitrification), which plants absorb. Decomposers return nitrogen as ammonium (ammonification), and other bacteria release nitrogen gas (denitrification).
| Pair | Interaction | Why |
|---|---|---|
| Lucerne roots and bacteria in their nodules | Mutualism | Both benefit |
| Cattle and sheep in a camp with little grass | Competition | Both lose out |
| Mistletoe on a thorn tree, drawing sap from it | Parasitism | Mistletoe benefits, tree harmed |
| A bird roosting in a gum tree | Commensalism | Bird benefits, tree unaffected |
| A caracal hunting a lamb | Predator-prey | One feeds, one is killed |
Ecological farming systems work with natural processes.
| System | Key idea | Example practice |
|---|---|---|
| Organic | No synthetic fertilisers or pesticides | Compost and manure feed the soil |
| Biological | Living organisms and natural processes, such as natural enemies, control pests | Ladybirds eat aphids |
| Conservation | Disturb the soil as little as possible and keep it covered | No-till planting and crop rotation |
| Game | Wild animals on natural veld give meat, hunting and tourism | Springbok and impala on a fenced game farm |
| Sustainable (alternative) | Meets today's needs without harming the future, as in integrated farming | Residues feed animals; manure feeds crops |
Which list shows the levels of organisation in the correct order, from smallest to largest?
A farmer counts 80 sheep grazing in one camp. At which level of organisation is this group of sheep?
A dam, the fish and reeds in it, and its water, mud and sunlight together form an:
Which of these describes an adaptation?
The grassland, savanna and desert regions of southern Africa are each an example of a:
Which one of these is a physiographic (landscape) factor?
Crops on the south-facing side of a hill stay cooler and shadier than crops on the north-facing side. Which factor explains this?
Soil texture, soil depth, soil water and soil fertility all belong to which group of abiotic factors?
Orchards high up a mountain are damaged by frost, but orchards at its foot are not. Which physiographic factor best explains the difference?
Which list contains climatic factors only?
Which one of these organisms is a producer?
What is the role of decomposers in an ecosystem?
A snake eats a frog and the frog eats insects that feed on grass. In this chain the frog is a:
Which one of these is a primary consumer?
Dead leaves on a forest floor rot and their nutrients return to the soil. Which organisms are mainly responsible?
In the food chain grass → locust → lizard → hawk, what do the arrows show?
In the chain grass → grasshopper → frog → snake, which organism is the tertiary consumer?
A disease kills all the frogs that ate grasshoppers in a food web. What is the most likely immediate effect on the grasshoppers?
An energy pyramid has 20 000 units of energy at the producers, and about one tenth passes to each next level. How many units reach the secondary consumers?
Why is there less energy at each higher level of a food pyramid?
Which process turns liquid water from the sea into water vapour?
Plants lose water vapour through their leaves. This process is called:
Bacteria in the root nodules of a lucerne plant change nitrogen gas from the air into a form the plant can use. This process is called:
Which process removes carbon dioxide from the air to build plant material?
A farmer removes all the trees from a slope. Which change is a direct result of less transpiration?
A tick feeds on the blood of a cow. This interaction is:
In which interaction do both organisms benefit?
Two bulls in a small camp fight over one green patch of grass and both lose condition. This is:
An owl catches a field mouse in a maize field. Who benefits and who is harmed?
An orchid grows on a tree branch and gets light and support. The tree is not affected. This is:
Which farming system uses compost and manure and avoids synthetic fertilisers and pesticides?
Which system is based on using the natural enemies of pests, such as ladybirds eating aphids?
No-till planting, leaving crop residue on the land and rotating crops are practices of which system?
A farm keeps springbok and impala on natural veld for meat, hunting and tourism. This is:
Which statement describes sustainable farming?
A food chain on a farm is lucerne → locust → lizard → hawk.
Name the tertiary consumer and explain why it receives the least energy of the four organisms. (3)
The tertiary consumer is the hawk. Energy is lost at every step, as heat from respiration, in waste and in parts that are not eaten. Only a small amount of energy is left to reach the hawk at the end of the chain, so it gets the least.
A farmer cuts down all the trees on a steep slope above his dam.
Explain TWO effects of this on the water cycle on his farm. (4)
There is less transpiration, because there are fewer trees to give off water vapour. So less water vapour reaches the air and there is less rain. There is more run-off, because nothing slows the water down the slope. The soil is eroded and washed into the dam.
Explain how a crop of lucerne can add nitrogen to the soil of a farm. (3)
Nitrogen-fixing bacteria live in the root nodules of lucerne. They change nitrogen gas from the air into a form the plant can use, called fixation. When the plant dies, or through its roots, the nitrates and ammonium end up in the soil where later crops can use them.
Ticks feed on the blood of a farmer's cow. In the same camp a jackal kills lambs.
(a) Name the interaction between the ticks and the cow, and say which of the two is harmed. (2)
(b) Name the interaction between the jackal and a lamb, and say which of the two benefits. (2)
The interaction between the ticks and the cow is parasitism. The cow is harmed, because the ticks feed on its blood. The jackal and the lamb are in a predator-prey interaction. The jackal benefits, because it gets food.
Explain to a Grade 8 learner why a food chain on a farm is never very long.
Explain to a Grade 8 learner how a lucerne field helps the maize that is planted after it.
Explain to a Grade 8 learner the difference between a natural ecosystem and a farm, using a veld and a maize land.
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