Ecology

Biosphere to ecosystems

Life is organised from the whole living layer of Earth down to one organism, and energy moves through that organisation in food chains.

CAPS

Grade 10 · Life Sciences · Ecology

Life Sciences is two papers. Use the strand to know which one.

Where it is examined
Grade 10 is the chemistry of life, cells, tissues, organs, support and transport, and the biosphere, biodiversity and the history of life.
How to write it
Name the structure, then say what it does. A labelled diagram only scores if the labels are the biological names. “It helps the body” is not a function.
How a marker reads it
A common mix-up is to draw a pyramid of energy with the top wider than the producers, or to call a herd of springbok a community.

A 2-mark “explain” wants two facts, or one fact and its reason. Extra sentences that contradict the first one can cancel a mark.

Diagram

Worked theory

Worked theory. A Highveld grassland after rain. Grass is the producer. A locust eats grass. A bird eats locusts. Energy entered as sunlight and was trapped by the grass. Most of that energy was used by the grass itself, so the bird receives only a scrap of the original light. There cannot be more hawks than grass. Fynbos in the Cape is a different biome, not a different definition of ecosystem. Remove the decomposers and nutrients stay locked in dead leaves, so the grass eventually fails.

More worked examples

Numbers on a Kruger food chain
Give the grass 10 000 kJ from the sun. Impala that eat it keep about 1 000 kJ. A lion that eats impala keeps about 100 kJ. That is why one pride needs a huge patch of grass and why you never see more lions than impala. Vultures and dung beetles are not a fourth floor of the same size. They feed on what is left, and without them the 10 000 kJ stays locked in dead bodies.
A rock pool at Kalk Bay
At low tide a pool on the rocks heats up, the water gets saltier as it evaporates, and a limpet that cannot clamp down dries out. High tide brings cooler water back. The animals that live there are the ones that survive those hours, not every animal that can swim. Temperature, salt and drying are abiotic. The limpet is biotic. A food chain drawn for the pool that ignores the tide has missed the limit that actually decides who stays.

In ordinary words

The biosphere is every place life exists. A biome is a large climate region, such as grassland or fynbos. An ecosystem is the living community plus the non-living soil, water and climate. A population is one species in one place. A community is all the populations together. Producers make food. Consumers eat. Decomposers return nutrients. In a food chain, only about a tenth of the energy passes to the next level, so pyramids of energy narrow upwards.

In South Africa

Grassland, savanna, fynbos and Nama Karoo are the biomes a South African map is asking you to picture.

Part 1 / 4

What it is

Life is organised from the whole living layer of Earth down to one organism, and energy moves through that organisation in food chains.

More worked examples

Board walkthroughs on this topic. Open one, copy the working, then try the next.

Example 1 / 20

In a food chain, grass captures 10 000 kJ. Using the 10% rule, how much energy reaches a lion in: grass → zebra → lion?

4. Step-by-step working

01
Multiply
Zebra: 10 000×0,1=1 000 kJ.
02
Multiply
Lion: 1 000×0,1=100 kJ.

How we got there

Read this like a teacher at the board. We go slowly, name every number, and say why we take each step.

Explain in another language · 11

1. What is the question asking?

Read the question twice. Circle the unknown. Underline every number and unit. The paper is asking: In a food chain, grass captures 10 000 kJ. Using the 10% rule, how much energy reaches a lion in: grass → zebra → lion?

In other words — as if you have never seen this before

If you have never seen this before: About 10% passes to each next trophic level. We will name a method in words, write the formula with no numbers, then substitute one line at a time.

2. What do we already know?

Producer 10 000 kJ.

3. Which method — and why this one?

About 10% passes to each next trophic level.

4. Step-by-step working

01 / 05
Multiply
Zebra: 10 000×0,1=1 000 kJ.
Why this step: We only do one job per line so a marker can follow the marks — and so you can find a slip without starting over.
02 / 05
Multiply
Lion: 1 000×0,1=100 kJ.
Why this step: We only do one job per line so a marker can follow the marks — and so you can find a slip without starting over.
03 / 05
Step G — Sense-check the size
Ask: is this the kind of number a Grade 10–12 paper would want? A speed of 3 000 ms for a learner walking, or a probability bigger than 1, means a unit or algebra slip. Estimate first: round the numbers and do the sum in your head.
Why this step: Markers write ‘unrealistic’ in the margin when the method is right but the size is wild. A 10-second head check often finds a missing 10² or a unit that never changed.
04 / 05
Step F — Box the answer with its unit
About 100 kJ reaches the lion.
Why this step: A number without a unit is half a mark on a Physics paper, and a marker can miss a Maths answer that is buried in working.
05 / 05
Step H — What the marker is looking for
On an NSC memo you usually earn: (1) a method mark for naming the right formula or idea in words, (2) an accuracy mark for substituting the given numbers with units, (3) an accuracy mark for the boxed answer with its unit. Write those three lines even if you are unsure of the arithmetic — blank pages score zero.
Why this step: First-timers chase the final number and leave the method blank. The memo still pays out for the idea and the substitution even when the last line is wrong.

5. The answer

About 100 kJ reaches the lion.

Copy onto your answer sheet — in this order

Answer: About 100 kJ reaches the lion.

6. Check it like a marker

Energy is lost as heat in respiration, movement and undigested waste.

7. A trap first-timers fall into

First-timers often grab the first formula they remember, mix units (cm with m, minutes with seconds), or drop a minus sign. Write the formula in words first: “this equals that, because…”

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Biodiversity and classification

Life Sciences

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