Fertilisation

D. Crowley, 2007

Fertilisation• To know what happens at fertilisation

Wednesday, April 19, 2023

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

• 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…)

Opinion

Fact

Fact

Fact

Opinion

Specialised CellsLook 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 CellsThey are both animal cells - no vacuole, chloroplasts or cell walls

Sperm cell (male) Egg cell (female)

Nucleus

Cytoplasm - contains a food (energy) store

Jelly coat - helps make sure only one

sperm can enter

NucleusHead - contains chemicals to help the cell get inside

the egg

Tail for swimming (note there is little cytoplasm, making the sperm cell

streamlined for swimming)

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• 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

Rodin’s The Kiss

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. Sperm cells from the male enter the female during sexual intercourse

2. Sperm and egg cells meet within the oviducts3. 1 sperm cell can burrow into the egg cell, and fertilise it4. At this point no more sperm cells can enter the egg cell5. Genetic information is shared between the nucleus of the

sperm and egg cell6. The fertilised egg now divides into two, and then into four,

then eight etc… becoming a ball of cells - an embryo

Fertilisation Stages1. Sperm cells from the male enter the female during sexual intercourse2. Sperm and egg cells meet within the oviducts3. 1 sperm cell can burrow into the egg cell, and fertilise it4. At this point no more sperm cells can enter the egg cell5. Genetic information is shared between the nucleus of the sperm and

egg cell6. The fertilised egg now divides into two, and then into four, then eight

etc… becoming a ball of cells - an embryo