Response

Responding to the environment: humans

Humans respond to the world through nerve impulses, which are fast, and hormones, which are slower and travel in the blood. Both are used to keep the inside of the body steady.

CAPS

Grade 12 · Life Sciences · Response

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

Where it is examined
Paper 1 is reproduction, responding to the environment, and homeostasis. Paper 2 is DNA, meiosis, genetics and evolution. Each paper is 150 marks.
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 send a reflex up to the cerebrum before the hand can move, or to say insulin raises blood glucose.

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 hand on a hot stove, then lunch. The heat receptor fires, the impulse enters the spinal cord, a motor neuron makes the biceps pull the hand away. That is the reflex. A moment later the brain feels the pain. At lunch, glucose from the bread rises in the blood. The pancreas releases insulin. The liver stores glucose. The level falls back. If it falls too far, glucagon tells the liver to release some. ADH is the same style of control for water: too little water, more ADH, the kidney saves water. None of these is a choice you talk yourself through. They are responses. The eye and the ear are the receptors that start two of the others.

More worked examples

A hot afternoon in Upington
Skin receptors report a rising body temperature. The hypothalamus, not a conscious decision, sends signals that widen skin blood vessels and start sweat glands. Heat leaves. When the temperature falls, those signals stop. That is negative feedback, the same pattern as insulin, on a different variable. A learner who only drinks nothing and keeps playing overrides the behaviour, not the reflex. The sweating still happens. ADH will rise later because the sweat cost water.
A dark classroom
Walk from the sunny quad into a dark classroom and the pupils widen without a decision. Receptors in the eye report the drop in light. The brain stem sends a signal to the muscles of the iris. More light enters. Walk back into the sun and the pupils narrow. That is a reflex, faster than a thought, and it protects the retina and then restores the image. A learner who says “I decided to let more light in” has described a choice. The iris did not wait for one.

In ordinary words

A receptor detects a change. A sensory neuron carries the impulse to the central nervous system. A motor neuron carries a reply to a muscle or gland. At a synapse the message crosses as a chemical. A reflex arc, such as pulling a hand from a hot pot, uses the spinal cord and does not wait for a conscious decision. The cerebrum thinks and senses. The cerebellum balances and coordinates. The medulla runs breathing and heart rate. Endocrine glands release hormones. Blood glucose is held steady by insulin, which lowers it, and glucagon, which raises it. The eye bends light onto the retina. The ear turns vibration into a nerve impulse.

In South Africa

A hot pot in a kitchen, and feeling thirsty after soccer, are the two controls in one afternoon.

Part 1 / 4

What it is

Humans respond to the world through nerve impulses, which are fast, and hormones, which are slower and travel in the blood. Both are used to keep the inside of the body steady.

More worked examples

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

Example 1 / 20

Trace the reflex arc when you touch a hot stove.

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: Trace the reflex arc when you touch a hot stove.

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

If you have never seen this before: Stimulus → response. 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?

Reflex arc.

3. Which method — and why this one?

Stimulus → response.

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
Reflex arc.
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
Stimulus → response.
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
Identify the given
Receptor (skin) → sensory neuron → interneuron in spinal cord → motor neuron → effector (arm muscle contracts).
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
Receptor → sensory → interneuron → motor → effector.
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

Receptor → sensory → interneuron → motor → effector.

Copy onto your answer sheet — in this order

Answer: Receptor → sensory → interneuron → motor → effector.

6. Check it like a marker

The brain is not involved in the quick response.

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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Responding to the environment: plants

Life Sciences

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