11.4: Sexual reproduction

Oogenesis & Spermatogenesis Oogenesis = production of egg cells in the ovaries, starts in the ovaries of a female foetus. Complete the w/s to describe the stages of oogenesis & ovulation. These processes can be summarized in one diagram (pg. 501). Draw and annotate this diagram to explain the stages. Spermatogenesis = production of sperm cells in the testes, produced as necessary after puberty. At any time there are millions of sperm at all ages of development. Complete the w/s to describe the stages of spermatogenesis. These processes can be summarized in one diagram (pg. 501). Draw and annotate this diagram to explain the stages.

Oogenesis & ovulation Draw and label this diagram Pg. 501

Draw and label – spermatogenesis Pg. 501

Mature egg cell Draw and label

Draw and label Mature sperm cell

Polyspermy Polyspermy would occur if more than one sperm fertilized an egg. This is prevented by these 3 processes: Acrosome reaction Enzymes in the acrosome digest the egg membrane Penetration of egg membrane Sperm and egg membrane bind together, allowing sperm nucleus to enter the egg. This is the moment of fertilization. Cortical reaction Cortical granules release enzymes to harden the outer surface of the egg so no other sperm cells can penetrate.

Some animals fertilize eggs externally (corals) in which case fertilization is susceptible to environmental variation e.g. changes in pH. Most terrestrial animals (land) are dependent on internal fertilization. Advantages include stable environment, sperm and egg in close proximity.

Blastocyst After fertilization, the ovum (fertilized egg) divides by mitosis forming an embryo, there are approx. 4 cells in an embryo 48hrs after fertilization. The embryo will continue to divide until the embryo resembles a hollow ball. This is now a blastocyst. After 17 days, the blastocyst contains approx. 125 cells and the zona pellucida breaks down. Blastocyst has no more energy within the egg cell, it sinks into the endometrium lining of the uterus. After implantation the embryo grows rapidly, by 8 weeks bone and tissue has started to form. Foetus. Zona pellucida – protective layer around blastocyst

http://highered. mheducation http://highered.mheducation.com/sites/0072495855/student_view0/chapter3/animation__fetal_development_and_risk.html https://www.youtube.com/watch?v=_5OvgQW6FG4 http://www.sumanasinc.com/webcontent/animations/content/ovarianuterine.html Work through animations, videos and webinars. 15 minutes - ish.

Human Chronic Gonadotropin (HCG) is the hormone in early pregnancy that stimulates the ovary (corpus leuteum) to produce progesterone. Released from the pituitary gland. Progesterone maintains the endometrium lining of the uterus.

The Placenta The placenta facilitates the exchange of materials between the mother and foetus. Not all animals produce a placenta. Monotremes – lay eggs Marsupials – offspring devlope in pouches Diagram, p.g. 507 Placenta is made form fetal tissues, fetus also devops the amniotic sac – membrane around the fetus, contains amniotic fluid (support/protection). Placental villus – exchange of materials, mothers blood is not within a vessel, it flows freely around the inter-villus space around the fetal villi. Very unusual. Layer of cells separate mothers and fetus blood – called the placental barrier. This is a selectively permeable membrane. Placenta also secretes hormones (Estrogen & progesterone) around 9 weeks once the corpus luteum has broken down and is no longer needed. Miscarrige can occur if the switch is not successful. DBQ examples on pg. 507/508

Hormones in parturition Parturition is another term for birth. Birth is controlled by positive feedback involving oestrogen and oxytocin. Oxytocin stimulates contractions in the muscule fibres in the myometrium (uterine wall). The more oxytocin, the more frequent & severe the contractions. During pregnancy, progresterone inhibits the production of oxytocin (produced by the pituitary gland, regulates myometrium aka muscular contractions)

Muscular wall of the cervix relaxes – dilation. Uterine contractions burst the amniotic sac Further uterine contractions, over time, allow the baby to be pushed out. The umbilical cord is then broken, the baby breathes and is now independent of the mother.

Answer: D

Answer: C

Answer: C

Answer: B

Answer: C