Section 4 – Reproduction

National 4 & 5 - Multicellular Organisms

Learning Outcomes

• By the end of this section I will be able to:• - identify the difference between asexual & sexual

reproduction• - identify the sites of gamete production in

animals• - identify the key structures of these sites• - explain what happens during fertilisation• - compare the methods of fertilisation in different

animals

Re-Cap

• 1) What are the two types of reproduction called?

• 2) What are gametes?• 3) What do the terms haploid and diploid

mean?

Site of gamete production - humans

• In animals, the gametes are the sperm and the egg

• The sperm are produced in the male testes

• - sperm travel through the sperm duct into the penis

• Egg cells are produced in the female ovaries

• - process known as ovulation• The penis of the male deposits sperm

inside the vagina of the female• The sperm them swim to the fallopian

tube/oviduct to meet the egg• Here fertilisation occurs

Testes

Penis

Oviduct

Fertilisation• When the sperm and egg cell

nuclei fuse together• These haploid cells join to

form a diploid cell• - this is called a zygote• This will then divide to form a

ball of cells• - a blastocyst• This will then implant itself

inside the wall of the uterus• It will then grow and develop

– gestation period

Embryo

Uterus wallPlacenta

Umbilical cord

Amniotic fluid

Development of human embryo

http://www.on101.co.uk/foetal.html

Amniotic sac

The Placenta

The placenta is where the blood of the mother and foetus are brought close together.

Oxygen and dissolved food diffuse into the baby’s bloodstream from the mother.

Carbon dioxide and waste diffuse from the baby into the mother’s blood.

A thin barrier separates the bloodstream of mother and baby.

PLACENTA

Mother’s blood going to placenta

Blood to the

embryo

Mother’s blood leaving to placenta

Blood From the embryo

Twins• Account for around 3% of all births• 2 possible types:• IDENTICAL (MONOZYGOTIC):• - after fertilisation, a zygote will

sometimes split into two • - these will then develop separately into

two different embryos• - these share a placenta and amniotic sac• - genetically identical• NON-IDENTICAL (DIZYGOTIC):• - when two eggs are released and

fertilised by two sperm• - different placenta and amniotic sac• - genetically different

Reproduction in other animals

• Many animals reproduce externally• - e.g. fish/amphibians• - fertilisation occurs in water

outside the body of the female• The chances of success are low• Therefore thousands of eggs are

produced• Other animals reproduce internally• - e.g. reptiles/birds• - fertilisation is within the body of

the female• Chances of success are higher• Fewer eggs are produced

Parental Care• Young fish receive little, or no, care and

protection from their parents• They feed initially from their yolk sac• Once this is used up, they learn to catch

food for themselves• Young mammals obtain food from their

mother (suckling milk)• They are dependent on their parents for

care and protection

Trout Human

No. of eggs per year    

No. of ovulations per year    

Where the egg is fertilised    

How is the food obtained by :-    

(i) Embryo    

(ii) free living offspring    

The protection given to :-    

(i) Embryo    

(ii) free living offspring    

3000 12

1 12

In the water in the oviduct

yolk in the egg from mothers blood

Yolk in egg sac then finds its own from its mother

soft covering mothers body

none parents look after

Comparison

Asexual Reproduction• Doesn’t involve sex cells or fertilisation• All offspring are identical to their

parent• Animals• Usually only occurs in micro-organisms• - yeast reproduce by budding• - bacteria/fungi can reproduce by

fission