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Reproduction

Reproduction in vertebrates

Vertebrates reproduce sexually, but the way the embryo is protected is not the same in fish, amphibians, reptiles, birds and mammals.

CAPS

Grade 12 · Life Sciences · Reproduction

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 call every animal that gives birth a placental mammal. Some just retain the egg.

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

cycle

Diagram

Worked theory

Worked theory. A frog, a pigeon and a cow. The frog lays many eggs in water with almost no care. Most are eaten. The pigeon lays few amniotic eggs in a nest and warms them. The cow keeps one calf inside, feeds it across a placenta, and suckles it after birth. The strategy is a trade: many cheap young, or few expensive ones. A shark that keeps eggs inside until they hatch, without a placenta, is ovoviviparous, not a mammal. Feathers do not decide it. Where the embryo is fed does.

More worked examples

  • Ostrich, shark and cow

    An ostrich lays a shelled egg and sits on it. The embryo’s food is the yolk. That is ovipary. Some sharks keep the egg inside until it hatches, and the embryo still feeds on the yolk, not on the mother’s blood. That is ovovivipary. A cow’s calf is fed across a placenta for about nine months and then suckled. That is vivipary. The cow does not lay a shell. The ostrich does not grow a placenta.

  • Frogspawn and a lizard egg

    A frog releases eggs into water and the male releases sperm over them. Fertilisation is external, and the jelly must stay wet or the embryo dries. A lizard mates, and fertilisation is internal, so the egg already holds the embryo before it is laid, often in a shell. The frog cannot use the lizard’s dry bank. The lizard does not need a pond for the sperm to swim. The place of fertilisation is the theory, and it decides the habitat.

In ordinary words

Ovipary means the egg is laid and develops outside. Ovovivipary means the egg is kept inside and hatches there, but the embryo is fed by the egg, not by a placenta. Vivipary means the embryo develops inside and is nourished by the mother, as in placental mammals. An amniotic egg, in reptiles and birds, has membranes and a shell so the embryo is not tied to water. Parental care raises the chance that fewer young still survive.

In South Africa

Cattle on a farm, pigeons on a ledge, and frogs at a vlei are the three strategies in one district.

Part 1 / 4

What it is

Vertebrates reproduce sexually, but the way the embryo is protected is not the same in fish, amphibians, reptiles, birds and mammals.

More worked examples

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

Example 1 / 20

Compare internal and external fertilisation with an example of each.

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: Compare internal and external fertilisation with an example of each.

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

If you have never seen this before: Where sperm meets egg. 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?

Fertilisation types.

3. Which method — and why this one?

Where sperm meets egg.

4. Step-by-step working

  1. 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.

  2. 02 / 07

    Step B — Write the given in a column

    Fertilisation types.

    Why this step: A column with units stops you mixing cm with m, or minutes with seconds. Markers can also see you started correctly.

  3. 03 / 07

    Step C — Name the method in words

    Where sperm meets egg.

    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.

  4. 04 / 07

    Identify the given

    External: in water, many eggs, less parental care — frogs, most fish. Internal: in female's body, fewer eggs, more protected — birds, mammals, reptiles.

    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.

  5. 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.

  6. 06 / 07

    Step F — Box the answer with its unit

    External (frog) vs internal (bird/mammal).

    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.

  7. 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

External (frog) vs internal (bird/mammal).

Copy onto your answer sheet — in this order

Answer: External (frog) vs internal (bird/mammal).

6. Check it like a marker

Internal fertilisation is an adaptation to land.

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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Human reproduction

Life Sciences

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