1. Internal & External Fertilisation
LO: To know the difference between internal and external fertilisation

2. Learning obejctive
To know the difference between internal and external fertilisation

3. Which of these would create identical twins?
Explain your answer

4. Identical?
Identical twins Are formed when one sperm fertilizes an egg and then this SPLITS into 2 clumps of cells.
Non-identical twins Are formed, when 2 separate eggs are fertilized by 2 separate sperms

5. Fertilization Different organisms fertilize in different ways
Can you think of any organisms which fertilise differently to humans?
For fertilisation to occur, the male sperm cells must get to the female egg cells.
There are two main ways for this to occur - internal and external fertilisation

6. External Fertilisation
Happens outside the body
External Fertilisation
Usually a liquid medium for sperm
Large amounts of eggs produced

7. Internal Fertlisation
Happens in most land mammals.
The sperm have liquid to swim in called semen
Happens inside of the female body
Internal Fertlisation
Much more parental care
Small amounts of eggs produced

8. The chances of fertilisation are much lower
Why do organisms which reproduce using external fertilisation produce so many eggs?
The chances of fertilisation are much lower
The sex cells are more likely to be predated
They can also be separated from one another (due to currents)
There is less parental care.

9. The likelihood of successful fertilisation is higher.
Why do organisms which reproduce using Internal fertilisation produce so few eggs?
The likelihood of successful fertilisation is higher.
producing many sex cells causes problems because:
Limited amount of space within the uterus for a growing foetus
There is more parental care - offspring are more likely to survive

10. Internal & External Fertilisation
Look at the worksheet, and cut out all the cards
Organise the cards into two groups - internal fertilisation and external fertilisation
Stick these into your book
Internal
Fertilisation
External
Fertilisation
etc…
etc…

11. Internal & External Fertilisation
Internal Fertilisation
Eggs produced in small numbers
Method usually by land animals (water is not available for the sperm to swim)
Method has a better chance of the offspring surviving due to improved protection
Human, butterfly, horse
External Fertilisation
Eggs produced in very large numbers
Used by fish because water is available for sperm to swim in
Sperm can get eaten by aquatic predators
Fish, frog

12. Black rat snake
Bullfrog
Cod
Gorilla
Grey squirrel
Grey wolf
Type of animal
Reptile
Amphibian
Fish
Mammal
Time for development
3 months
20 days
25 days
8.5 months
38 days
Number of young 20
5000
3000 1 5
Aftercare
None
2.5 years
13 weeks
1 year
Fertilisation
Internal
External
Development
Survival rate
50% 1% 2%
60%
20%
40%

13. Hare
Harvest mouse
King penguin
Human
Lion
Polar bear
Type of animal
Mammal
Bird
Time for development
1.5 months
19 days
2 months
9 months
3 months
8 months
Number of young 2 6 1 3
Aftercare
1 month
16 days
1 year
16 years
2.5 years
Fertilisation
Internal
Development
External
Survival rate
30%
15%
40%
99%
50%

14. Rat
Salmon
Sea turtle
Stickleback
Tiger
Type of animal
Mammal
Fish
Reptile
Time for development
22 days
2 months
7 days
3.5 months
Number of young 7
200
150 20 3
Aftercare
2 weeks
None
1 week
2 years
Fertilisation
Internal
External
Development
Survival rate
30%
15% 5%
50%

15. Make a list of the animals which use internal fertilization and a list of those which use external fertilization
What is the main difference between animals that use internal fertilization and animals which use external fertilization?
Which animals use internal fertilization but external development? Why do you think this is?
What is the relationship between internal / external fertilization and the number of young?
Which animals have the lowest survival rates? Why do you think this is?

16. 6. Why do you think all the animals which use external fertilization also use external development?
7. How does survival rate relate to the number of young?
8. Which animals have the longest aftercare? Why do you think this is?
9. Why do you think humans have such a high survival rate?
10. What are the main factors which affect the number of young produced? Explain why you think they are important