Fertilisation and the First Cleavages · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

One sperm, then smaller cells

Science · Organisms & Life Processes · ages 19-20
Name ______________________   Date ____________

  1. What stops extra sperm after the first?

    • A fast block and then a slow block
    • The egg bursts open
    • Nothing, polyspermy is normal

  2. What starts a new animal?

    • One egg splitting alone
    • Two sperm joining one egg
    • One sperm joining one egg

  3. Frogs release thousands of eggs and sperm into the pond. What is that called?

    • Internal fertilisation
    • External fertilisation
    • Live birth

  4. Birds lay shelled eggs while mammals guard young inside. What bargain differs?

    • Shell colour
    • Parental cost against survival
    • Egg size only

  5. An embryo runs three cleavage rounds with no growth. What happens to cell size?

    • Cells stay the same size
    • Cells get bigger
    • Cells get smaller

  6. Two eggs cleave in different patterns. What best explains the difference?

    • The season they were laid
    • The amount of yolk in each egg
    • The number of sperm admitted

  7. A student claims cleavage grows the embryo eightfold in three rounds. What is wrong?

    • Mass stays flat, so three rounds make smaller cells, not a bigger embryo
    • Divisions need yolk to work
    • Cleavage happens before fertilisation

  8. Releasing thousands of gametes into water guarantees each egg meets exactly one sperm.

    Circle one:   True   False

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Answer key

For grown-ups. Fold this page away before handing over the rest.

One sperm, then smaller cells W1-mt_9BXQsdP8fI-s1

  1. A fast block and then a slow block · A fast block acts at once and a slow block seals the egg.
  2. One sperm joining one egg · Fertilisation is exactly one sperm joining one egg.
  3. External fertilisation · Meeting outside the body in water is external fertilisation.
  4. Parental cost against survival · Internal guarding costs the parent more but far more young survive.
  5. Cells get smaller · No growth means the same mass cut into ever smaller cells.
  6. The amount of yolk in each egg · Yolk reshapes cleavage: heavy yolk eggs divide differently.
  7. Mass stays flat, so three rounds make smaller cells, not a bigger embryo · Cleavage skips growth, so rounds multiply cells, not mass.
  8. False · Numbers help meetings happen, but the blocks still must stop extra sperm.
Worksheet · LightMySky