Reproduction Notes

Edexcel IGCSE Biology: Revision notes

Key facts

  • Sexual reproduction fuses gametes and gives genetic variety; asexual gives identical offspring.
  • Insect-pollinated flowers have large petals and nectar; wind-pollinated flowers have feathery stigmas and hanging anthers.
  • Seeds need water, oxygen and a suitable temperature to germinate.
  • FSH, oestrogen, LH and progesterone control the menstrual cycle.
  • The placenta exchanges materials between mother and fetus.

Sexual and asexual

Sexual reproduction fuses two gametes and gives varied offspring. Asexual reproduction has one parent and gives identical offspring.

Fertilisation produces a zygote, which divides and develops into an embryo. Plants reproduce asexually naturally by runners, or artificially by cuttings.

  1. 1

    Gamete from each parent

    Sperm and egg

  2. 2

    Fertilisation

    The nuclei fuse

  3. 3

    Zygote

    First cell of the new individual

  4. 4

    Embryo

    The zygote divides and develops

Sexual reproduction: two gametes fuse.

Sexual

Parents:
Two parents
Offspring:
Genetically different offspring
Fertilisation?:
Fertilisation

Asexual

Parents:
One parent
Offspring:
Genetically identical offspring
Fertilisation?:
No fertilisation

Offspring from a cutting are...

Pollination and seeds

Insect-pollinated flowers attract insects; wind-pollinated flowers expose their anthers and stigmas to the wind.

After pollination a pollen grain on the stigma grows a pollen tube down the style to the ovary. The male gamete fuses with the female gamete in the ovule, forming a seed.

Insect-pollinated

Petals:
Large, bright, scented
Nectar:
Present
Pollen:
Small amount, sticky or spiky
Anthers:
Inside, firmly fixed
Stigma:
Inside, sticky

Wind-pollinated

Petals:
Small, dull, no scent
Nectar:
Absent
Pollen:
Large amount, light and smooth
Anthers:
Hang outside, loosely attached
Stigma:
Feathery, hangs outside
  1. 1

    Pollen lands on the stigma

  2. 2

    Pollen tube grows

    down the style to the ovary

  3. 3

    Fertilisation

    male gamete fuses with the female gamete in the ovule

  4. 4

    Seed and fruit form

    the ovule becomes the seed and the ovary becomes the fruit

From pollination to fruit

A flower with feathery stigmas and anthers hanging outside is...

Germination

Water, oxygen and a suitable temperature. Light is not needed until the seedling can photosynthesise.

Water activates enzymes and allows cell expansion. Oxygen supports aerobic respiration. Temperature affects enzyme activity. Until it has leaves, the seedling uses stored food, such as starch, for energy and growth.

  1. 1

    Seed takes in water

    Activates enzymes; cells expand

  2. 2

    Oxygen supports aerobic respiration

    Releases energy from stored starch

  3. 3

    Suitable temperature

    Enzymes work well

  4. 4

    Shoot reaches the light

    Leaves can then photosynthesise

Conditions a seed needs to germinate.
  • Wateractivates enzymes
  • Oxygenaerobic respiration
  • Suitable temperatureenzyme activity

Which is NOT needed for a seed to germinate?

Reproductive systems

The male system makes sperm and delivers it; the female system makes eggs and supports the embryo.

The male system includes the testes, sperm ducts, prostate gland and penis. The female system includes the ovaries, oviducts (where fertilisation usually occurs), uterus (where the embryo implants) and vagina.

  1. 1

    Testes

    Make sperm

  2. 2

    Sperm ducts and prostate gland

    Carry sperm; prostate adds fluid

  3. 3

    Penis

    Delivers semen into the vagina

  4. 4

    Ovaries and oviducts

    Egg released; fertilisation usually in the oviduct

  5. 5

    Uterus

    The embryo implants and develops

The route of sperm and egg through the reproductive systems.

Male

  • Produces sperm in the testes
  • Sperm ducts
  • Prostate gland adds fluid
  • Penis

Female

  • Produces eggs in the ovaries
  • Oviducts: fertilisation
  • Uterus: embryo implants
  • Vagina

Fertilisation usually occurs in the...

Menstrual cycle and pregnancy

FSH matures an egg, oestrogen thickens the uterus lining, LH triggers ovulation and progesterone maintains the lining.

The placenta passes nutrients and oxygen to the fetus and waste back, without the blood supplies mixing. Amniotic fluid protects the embryo. At puberty, oestrogen causes breast development and wider hips; testosterone causes facial hair, a deeper voice and more muscle.

  1. 1

    FSH

    egg matures; ovary makes oestrogen

  2. 2

    Oestrogen

    repairs and thickens the uterus lining; stimulates LH

  3. 3

    LH

    triggers ovulation

  4. 4

    Progesterone

    maintains the uterus lining

Hormones in the menstrual cycle

FSH

  • Matures an egg; stimulates oestrogen

Oestrogen

  • Repairs and thickens lining; stimulates LH

LH

  • Triggers ovulation

Progesterone

  • Maintains the lining

Which hormone triggers ovulation?

Try an exam question

Describe the roles of FSH, oestrogen, LH and progesterone in the menstrual cycle.

[4 marks]

That's the notes covered.

Carry on to the next subtopic.