Unit 2A Flashcards
Reproduction
Required to replace individuals in a population that have died through predation (being eaten), disease or old age.
Keeps the population of a species at a steady number.
Sexual reproduction
Usually involves 2 separate parents which produce sex cells called gametes.
Advantage - variation (can adapt to change)
Disadvantage - energy costs
Fertilisation
The nucleus of an egg (containing chromosomes) fuses with the nucleus of a sperm (which also contains chromosomes) to create a zygote (fertilised egg).
Gametes
Sex cells - sperm and eggs in animals, pollen and ovules in plants.
Sperm
Male gamete in animals. Tiny, streamlined and use a tail to swim towards the egg.
Egg (ovum)
Female gamete in animals.
Much larger than the sperm as its cytoplasm contains a food store.
Unable to move by itself.
Zygote
A fertilised egg.
External fertilisation
Sperms and eggs meet outside the body.
Found in aquatic organisms (that live in water) eg. frogs, fish.
Internal fertilisation
Sperms are released inside the female reproductive system and fertilisation occurs inside the female.
Gametes need a watery environment to survive - they would dry out if released on land.
Found in terrestrial (land living) organisms such as mammals, reptiles and birds.
Features of external fertilisation
Fertilisation is left to chance, so many gametes are produced.
Eggs have a tough outer coating
Developing embryos have a yolk sac as a food supply
There is little or no parental care - offspring look after themselves
Many young are produced as few survive.
Improving the chance of external fertilisation occurring
Parents are close together when gametes are released (eg. frogs)
Gametes are released into a nest (eg. sticklebacks - fish)
Gametes are released at the same time (eg. coral)
Embryo
Formed from a fertilised egg which divides repeatedly to form a a ball of unspecialised embryonic stem cells.
The embryo implants into the uterus lining.
Foetus
Once an embryo implants and starts to specialise, it is known as a foetus.
It develops inside the uterus
Amniotic fluid
Cushions the developing foetus and protects it from knocks.
Placenta
An organ which acts as a barrier to harmful substances.
It provides the developing foetus with food and oxygen from the mother’s blood.
Parental care
Offspring are looked after from birth.
Mammals produce milk to feed their young.
Fewer offspring are produced as most survive.
Flowers
Contain the sex organs of plants
Seed
Formed after the ovule is fertilised during sexual reproduction in plants.
Contains a food store and an embryo, and is covered with a seed coat.
Ovary
Female part of the flower, containing ovules.
Stigma
Top section of the female part of the flower.
The pollen lands here.