Search for notes by fellow students, in your own course and all over the country.
Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.
Title: AS Biology notes on stem cells
Description: AS biology notes specific for Edexcel unit 2, however can be applied to other exams
Description: AS biology notes specific for Edexcel unit 2, however can be applied to other exams
Document Preview
Extracts from the notes are below, to see the PDF you'll receive please use the links above
Biology – Unit 2: Section 2 – Sexual production
Production of gametes
Gametes
Male and female sex cells found in organisms that produce sexually
They join at fertilisation to form a zygote
...
2
...
Name the male and female gametes of flowing plants
Male gametes are pollen grains and female gametes are ovules
2
...
4
...
What is the zona pellucida?
A protective layer that sperm have to penetrate
What name is given to the process that produces gametes?
Meiosis
Describe how sperm are specialised for their function
Sperm have an acrosome which contains digestive enzymes, this is to penetrate the egg
...
a
...
This means they
contain the same genes but have different combinations of alleles
b
...
2
...
4
...
6
...
8
...
Sperm are deposited high up the female vagina close to the entrance of the cervix
They work their way through the cervix and uterus and into one of the oviducts
The sperm swims towards the egg cell in the oviduct
When the sperm makes contact with zona pellucida the acrosome reaction occurs, digestive enzymes
are released
The enzymes digest the zona pellucida and then the sperm can move through to the membrane
The sperm head fuses with the membrane, this triggers the cortical reaction, this is when the cortical
releases the contents of vesicles called cortical granules
This thickens the zona pellucida and stops it being penetrable to other sperm
The sperm nucleus enters the egg cell and the tail is discarded
The nucleus of the sperm fuses with the nucleus of the egg cell, this is fertilisation
Flowering plant’s fertilisation
1
...
3
...
5
...
A pollen grain lands on the stigma, it absorbs water and splits open
A pollen tube grows out of the pollen grain down the style, it contains three nuclei – one tube nucleus
and two male gamete nuclei (tube nucleus releases digestive enzymes to make a way through for the
pollen tube
When the tube reaches the ovary it grows through the micropyle and into the embryo sac within the
ovule
In the embryo sac the tube nucleus disintegrates, and the tip of the pollen the pollen tube burst and
releases the two male nuclei
One nuclei fuses with the egg nucleus to from the embryo and the other fuses with the polar nuclei to
form the endosperm
This is double fertilisation
Practice questions
1
...
3
...
What is fertilisation?
When a male and female gamete fuse to form a zygote
How many nuclei are found in pollen tubes?
3
What is the purpose of the endosperm
It acts as a food store for the embryo
What type of plant does double fertilisation occur in?
Flowering plants
Title: AS Biology notes on stem cells
Description: AS biology notes specific for Edexcel unit 2, however can be applied to other exams
Description: AS biology notes specific for Edexcel unit 2, however can be applied to other exams