Unit 2.3 Reproduction Flashcards
Sexual reproduction
2 separate parents produce specialised sex cells (gametes)
The nuclei of the gametes fuse at fertilisation to form a zygote (fertilised egg).
How does a zygote turn into an embryo?
The zygote divides by repeated mitosis to form a ball of stem cells, which specialise to create a new individual organism.
Why does sexual reproduction result in varaiation?
A zygote has a unique combination of chromosomes from both parents.
Why is variation essential?
The best adapted survive and breed passing on their genes.
This leads to evolution, alowing organisms to adapt to change.
Diploid
All body cells (including the cells that produce gametes) are diploid - they have 2 sets of chromosomes (one from each parent)
Haploid
Gametes are haploid - they contain one set of chromosomes.
The nuclei of haploid gametes fuse at fertilisation to create a zygote with 2 sets of chromosomes.
Plant gametes
The male gamete is pollen, produced in the anther (top part) of the stamen of a flower.
The female gamete is the ovule, produced in the ovary of the flower.
Both gametes are haploid.
Pollination
The transfer of pollen from the anther to the stigma of a flower (by insects or the wind)
Fertilisation (plants)
The pollen grows a tube down through the style to the ovary of the flower.
The pollen tube enters the ovule, the male gamete is released and it fuses with the nucleus of the ovule, creating a zygote.
What is inside a seed?
A seed is an embryo plant + a food store.
Fertilisation (mammals)
Sperm meets egg (ovum) in the oviduct and their nuclei fuse to create a zygote.
Animal gametes
Sperm is the male gamete, produced in the testis.
Eggs (ova) are produced in the ovaries. (Ova is the plural of ovum.)
Ova and sperm are both haploid.
Zygote
A fertilised egg (ovum) containing 2 sets of chromosomes, meaning that it is diploid.
The zygote divides by repeated mitosis to form an embryo.
Sites of gamete production in animals
Sperm cells are produced in the testis, ova in the ovaries.
Sites of gamete production in plants
Pollen is produced in the anthers, ovules in the ovaries of flowers.
