Section 4 – Reproduction National 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 Penis Testes 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

Development of human embryo Uterus wall Placenta Amniotic sac Umbilical cord Embryo/Foetus Amniotic fluid http://www.on101.co.uk/foetal.html

The Placenta The placenta is where the blood of the mother and foetus are brought close together. A thin barrier separates the bloodstream of mother and baby. 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.

OXYGEN WASTE FOOD CARBON DIOXIDE PLACENTA Mother’s blood going to placenta Mother’s blood leaving to placenta Blood to the embryo 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

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