Section 4 Reproduction National 4 5 Multicellular Organisms

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 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 Amniotic fluid http: //www. on 101. co. uk/foetal. html Embryo/Foetus

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.

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

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

Comparison 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

Comparison Trout Human No. of eggs per year 3000 12 No. of ovulations per year 1 12 Where the egg is fertilised How is the food obtained by : - (i) Embryo In the water in the oviduct yolk in the egg Yolk in egg sac then finds its own from mothers blood from its mother (ii) free living offspring The protection given to : - (i) Embryo soft covering (ii) free living offspring none mothers body Parental care

Asexual Reproduction • Doesn’t involve sex cells or fertilisation • All offspring are identical to their parent • Micro-organisms • Usually only occurs in micro-organisms • - yeast reproduce by budding • - bacteria/fungi can reproduce by fission