Complete set of notes for each specification point (3.1 - 3.39) for Topic 3 (Reproduction and Inheritance) of the GCSE Biology Edexcel IGCSE Exam Board. Suitable for 2024 or 2025 exams. Written by a GCSE Student, using lots of resources to create accurate notes to aid exams. Includes paper 1 and pa...
3. REPRODUCTION AND INHERITANCE
A – Reproduction:
o Reproduction – results in the program of more of the same species
3.1 – understand the difference between sexual and asexual reproduction
Asexual reproduction Sexual reproduction
No. of parents needed 1 2 (male – sperm cell, female – egg cell)
How does reproduction occur Cells from break away from the Specialised sex cells (gametes) are produced.
parent body and grows into a new During fertilisation, the sperm moves to the
organisms e.g. budding. egg fuses zygote
Benefits to the organism Population = increase rapidly when Offspring has a great deal of genetic
the conditions are favourable variation
Any change to the environment If conditions change, some may survive,
they cannot survive any longer due to gamete production and fertilisation
Level of genetic similarity The offspring would be exactly A mixture of the parents, 50:50
between offspring identical (clone) to the adult and
have the same genes
Number of offspring produced Usually relatively large numbers Usually smaller limited numbers
Time taken to produce Relatively fast Relatively slowly
offspring
3.2 – understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that
undergoes cell division and develops into an embryo
o Fertilisation – the fusion of gametes
1. During ejaculation in the male, millions of sperm cells move along the sperm duct
2. The sperm are suspended in semen (a fluid secreted by the prostate gland) and the semen passes into the urethra
3. During sexual intercourse, semen is ejaculated into the vagina of the female
4. The sperm cells then follow a chemical trail to reach the uterus (the womb) and enter the oviducts
5. If a sperm cell meets an egg cell in the oviduct, fertilisation can occur
6. During fertilisation, the head of a sperm cell releases enzymes that digest a path through the protective outer
layer of the egg cell, allowing the sperm to pass through the egg cell membrane
7. Once this occurs, the egg cell releases a thick layer of material that prevents any more sperm cells from entering
8. When the male and female gametes fuse, they become a zygote (fertilised egg cell)
9. This zygote contains the 46 chromosomes (23 pairs), half from the father and half from the mother
10. The zygote divides to form an embryo
3.3 – describe the structures of an insect-pollinated and a wind-pollinated flower and explain how each is
adapted for pollination
o Pollination – the transfer of pollen from an anther to a stigma, so that the male gametes can fertilise the female
gametes in sexual reproduction
General structure of a typical flower:
o Sepal – protects the unopened flower
o Petals – brightly coloured in insect-pollinated flowers to attract
insects
Stamen (MALE reproductive part) consists of:
o Anther – produces and releases the male sex cell (pollen grain)
o Filament – the stalk that supports the anther
, 3. REPRODUCTION AND INHERITANCE
Carpel (FEMALE reproductive part) consists of:
o Stigma – end bit that the pollen grains attach to
o Style – rod-like section that supports the stigma
o Ovary – contain the female gametes (eggs) inside ovules
Insect-pollinated flowers structure:
o Insect pollination = transfer of pollen from another anther to stigma
o Pollinating agents are insects (e.g. bees)
o Insects collect nectar for energy
o Bright petals – large and brightly coloured to attract insects
o Scented flowers and nectaries (glands that secrete nectar) to attract insects
o Big, sticky pollen grains – attach to insects as they go from plant to plant
o Sticky stigma – so pollen sticks to it when insects brush past it
Wind-pollinated flowers structure:
o Process of pollination is more random than insect-pollinated flowers
o When the flower is ripe, the anthers open and shed their pollen into open air
o The pollen is blown by the wind until it (by chance) lands on the stigma of a
plant of the same species, resulting in pollination
o Small petals – dull, often green or brown
o No scent or nectar – no need to waste energy produce these as no need to attract insects
o Lots of pollen grain – betters the chance of successful pollination, small and light easily carried by the wind
o Long filaments – hang the anthers outside the plant so release of pollen grains is easier
o Feathery stigma – hangs outside the flower, to catch drifting pollen grains
3.4 – understand that the growth of the pollen tube followed by fertilisation leads to seed and fruit
formation
st
o A pollen grain lands on the stigma of a flower (usually by wind or insects)
o Only happens if the pollen has landed on the right kind of stigma (i.e.
same species as the flower it came from)
o A pollen tube grows out of the pollen grain, down through the style to the te
ovary + the ovule
o A nucleus from the male gamete moves down the tube to join with a
female gamete in the ovule fe
o Fertilisation occurs and the ovule develops into a seed and ovule wall vu
develops into the seed coat (testa)
o Parts of the flower surrounding the ovule (mainly the ovary walls) develop
into the fruit (containing the seeds) vu
eco
3.5 – practical: investigate the conditions needed for seed germination
o Germination – when root/shoot appears + seed splits
Key Equipment: Conditions needed:
o 4 boiling tubes o Oxygen – for respiration provides energy needed for plants to grow
o Cress seeds o Water – activate the enzymes
o Cotton wool o Warmth – optimum temperature of enzymes high temperatures can denature
o Incubator enzymes and so may slow or stop its growth
o Fridge o Light – activate plant growth regulators
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