Ecology

Human impact on the environment

Human impact is the set of ways people change air, water, soil and other species, and what can still be done about it.

CAPS

Grade 11 · Life Sciences · Ecology

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

Where it is examined
Grade 11 works through energy transformations, gas exchange, excretion, population ecology and human impact. The same two-paper pattern is used.
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 treat the greenhouse effect itself as pollution, or to call a local indigenous tree an alien invader.

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 river below an informal settlement and a ploughed field. Pit latrines and fertiliser both add nutrients. Algae bloom. When they rot, oxygen falls and fish die. Upstream of the settlement the same river still holds fish. The difference is the input, not a change in the definition of a river. On the bank, invasive wattle shades out grassland and uses deep water. Clearing the wattle is a human impact in the other direction. Switching a school’s lights off does not fix a river, but it is the same idea at the scale of a carbon footprint: less waste, less damage.

More worked examples

Day Zero and a mine dump
Cape Town’s Day Zero scare was a city using water faster than the catchment refilled. The rain cycle had not stopped. The dams had. On the Witwatersrand, water running off old mine dumps is acidic and carries metals into streams. Fish die downstream of the dump and not above it. Both are human impact. One is volume. One is poison. Neither is the natural greenhouse effect, which would be there with no city and no mine.
Water hyacinth on the Vaal
Water hyacinth, brought in as an ornamental, covers a stretch of slow water. Light cannot reach the plants underneath. They die, bacteria use up the oxygen, and fish turn up dead. The hyacinth is not pollution from a pipe. It is a living thing in the wrong place, growing faster than anything that eats it here. Pulling one basket out does not finish the job if the fragments grow again. The impact is the lost oxygen, not the colour of the flowers.

In ordinary words

The natural greenhouse effect keeps Earth warm enough for life. Burning fossil fuels and cutting forests add extra carbon dioxide, so more heat is trapped. That is the enhanced greenhouse effect. Alien plants outcompete local ones and drink scarce water. Sewage and fertiliser in a river feed algae, which then die and the decay uses up oxygen. Carbon footprint is the greenhouse gas a person or a process is responsible for. Conservation is not only “being nice”. It is keeping the processes, such as clean water and pollination, that people also need.

In South Africa

Wattles in a catchment, and a fish kill below a sewage leak, are the South African cases.

Part 1 / 4

What it is

Human impact is the set of ways people change air, water, soil and other species, and what can still be done about it.

More worked examples

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

Example 1 / 20

A town's dam is green with algae after fertiliser runoff. Explain the process and its effect on fish.

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: A town's dam is green with algae after fertiliser runoff. Explain the process and its effect on fish.

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

If you have never seen this before: Eutrophication. 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?

Algal bloom.

3. Which method — and why this one?

Eutrophication.

4. Step-by-step working

01 / 07
Step A — Read the question twice
Slow down. Circle the word that names the unknown. Underline every number and its unit. Do not grab a formula yet — first decide what the paper is actually asking.
Why this step: If you can say the method in a sentence, you will pick the right formula. First-timers skip this and grab the first equation they remember.
02 / 07
Step B — Write the given in a column
Algal bloom.
Why this step: A column with units stops you mixing cm with m, or minutes with seconds. Markers can also see you started correctly.
03 / 07
Step C — Name the method in words
Eutrophication.
Why this step: If you can say the method in a sentence, you will pick the right formula. First-timers skip this and grab the first equation they remember.
04 / 07
Explain
Nitrates and phosphates feed algae; algae cover the surface and die; decomposing bacteria use up oxygen; fish suffocate.
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.
05 / 07
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.
06 / 07
Step F — Box the answer with its unit
Eutrophication lowers dissolved oxygen and kills fish.
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.
07 / 07
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

Eutrophication lowers dissolved oxygen and kills fish.

Copy onto your answer sheet — in this order

Answer: Eutrophication lowers dissolved oxygen and kills fish.

6. Check it like a marker

Hartbeespoort Dam is an SA example.

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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