Transcript Fertilisation

Fertilisation
D. Crowley, 2007
Thursday, April 7, 2016
Fertilisation
• To know what happens at fertilisation
Fact Or Opinion?
• Which of the following statements are fact or opinion?
– I think all animals need a male and a female to reproduce
– Sperm cells have a tail to help them swim to the egg
– Some animals can have both sets of sex organs
– I think that the egg cells are the largest human cell
– I think the most babies an organism can have is 20
Opinion
Fact
Fact
Fact
Opinion
• Some opinions are biased – what does this mean?
• A biased opinion is one where someone has a preference
towards a particular idea, making it impartial (i.e. Arsenal are the
best football team in the world…)
Specialised Cells
Look at the following cells: -
Draw out the cells, and try and complete the following:–
–
–
–
Name the cell
Label the cell (the main parts)
Is it an animal cell or plant cell - how do you know?
Explain how each cell is specialised for its function
Specialised Cells
They are both animal cells - no vacuole, chloroplasts or cell walls
Egg cell (female)
Sperm cell (male)
Head - contains
chemicals to help
the cell get inside
the egg
Cytoplasm contains a food
(energy) store
Nucleus
Tail for swimming (note there is little
cytoplasm, making the sperm cell
streamlined for swimming)
Nucleus
Jelly coat - helps
make sure only one
sperm can enter
The sperm cell is extremely streamlined, with a powerful tail for swimming. It also has special chemicals
in its head to help it penetrate the egg cell.
The egg cell is full of cytoplasm, used as an energy store for when fertilisation occurs. It also has a
special barrier, which only allows one sperm to penetrate and fertilise it.
Both contain a nucleus, containing genes…
Fertilisation
Rodin’s The Kiss
• Living organisms must reproduce to survive. Most animals do
this via sexual reproduction, involving a male and a female
• Males produce sperm cells, whilst females produce egg cells these can fuse to produce offspring, in the process known as
fertilisation
• Fertilisation occurs when a sperm cell and egg cell meet, and
join together. This occurs after sexual intercourse, when sperm
from the male travels towards the egg tubes (oviducts) within the
female
• If a sperm cell meets an egg cell there, fertilisation can occur
Fertilisation
• The sperm must reach the egg cell for fertilisation to occur
• If it does, one will burrow into the egg cell and fuse with it. At
this point none of the other sperm cells can enter the egg cell
• Fusing is when the nucleus of the sperm cell and the nucleus of
the egg cell join together
• The nucleus of the sperm cell and egg cell contain only half the
genetic information needed for a new human, so when they fuse
there is enough information for life to begin
Unique
• Because fertilisation requires information (genes) from both the
male and female, the offspring (baby) will have features from
both its mum and dad
• This means that every individual born will be unique - as it will
be made up of an individual egg cell (half mum) and sperm cell
(half dad) (except identical twins). This is why you are not
clones of your mum / dad, and why you will be similar, but not
identical to your siblings
Embryo
• Once the egg cell and sperm cell have fused, they share their
genetic information and divide into a ball of cells known as an
embryo.
• These cells then continue to divide, and the embryo get bigger
and bigger. As it does, it moves towards the uterus where it
implants - the female is now pregnant, and we now call the
embryo a foetus.
Information
• Half of the information comes from the male, the other half from
the dad
• This is known as genetic information - the information is carried
on chromosomes (these are made up of long strands of DNA)
• It is these chromosomes which fuse, during fertilisation, so there
is enough information available for an embryo to form
Fertilisation Stages
•
Complete a labelled flow diagram explaining how fertilisation
occurs
The stages are as follows: 1.
2.
3.
4.
5.
6.
Sperm cells from the male enter the female during sexual
intercourse
Sperm and egg cells meet within the oviducts
1 sperm cell can burrow into the egg cell, and fertilise it
At this point no more sperm cells can enter the egg cell
Genetic information is shared between the nucleus of the
sperm and egg cell
The fertilised egg now divides into two, and then into four,
then eight etc… becoming a ball of cells - an embryo
Fertilisation Stages
1.
2.
3.
4.
5.
6.
Sperm cells from the male enter the female during sexual
intercourse
Sperm and egg cells meet within the oviducts
1 sperm cell can burrow into the egg cell, and fertilise it
At this point no more sperm cells can enter the egg cell
Genetic information is shared between the nucleus of the sperm and
egg cell
The fertilised egg now divides into two, and then into four, then eight
etc… becoming a ball of cells - an embryo