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