11.4 Sexual Reproduction Nature of science: Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm Fertilization involves mechanisms that prevent polyspermy Fertilization in animals can be internal or external Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy hCG stimulates the ovary to secrete progesterone during early pregnancy The placenta facilitates the exchange of materials between mother and embryo Estrogen and progesterone are secreted by the placenta once it has formed Birth is mediated by positive feedback involving estrogen and oxytocin Nature of science: Assessing risks and benefits associated with scientific research: the risks to human male fertility were not adequately assessed before steroids related to progesterone and estrogen were released into the environment as a result of the use of female contraceptive pill Skills: Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis Annotation of diagrams of mature sperm and egg to indicate functions Applications: The average 38 week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals.

Annotate your cells EGG CELL Centrioles Polar cell Plasma membrane Follicle cells Gel of glycoproteins Cortical granules Cytoplasm Haploid nucleus SPERM CELL Haploid nucleus Acrosome Plasma membrane Centriole Helical mitochondria Microtubules Mid piece Protein fibres in tail Tail Skills: Annotation of diagrams of mature sperm and egg to indicate functions

Sperm and egg production in testes and ovaries Stage 1 Sperm and egg production in testes and ovaries

Oogenesis and Spermatogenesis Production of egg cells in the ovaries Spermatogenesis Production of sperm in the testes in seminiferous tubules Skills: Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis

Annotate the ovaries Primary follicle Developing follicles Oocyte Secondary follicle Mature follicle (Graafian follicle) Ovulated ovum Developing corpus luteum Corpus luteum Degenerating corpus luteum Skills: Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis

Oogenesis Production of egg cells in the ovary Starts in the ovaries of a female fetus Start to divide by mitosis when the fetus is 4-5 months old to develop primary follicles. All genetically identical No further development until after puberty Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

Oogenesis At the start of each menstrual cycle some primary follicles develop Only one goes on to produce a mature follicle Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

1. Oogenesis Follicle grows Oocyte divides Primary follicles consist of an oocyte (cell that can become an ovum) surrounded by a layer of follicle cells Follicle grows Oocyte divides Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

2. Oogenesis Every menstrual cycle, a few primary follicles start to grow and the primary oocyte inside completes one division of meiosis (meiosis I) Forms a secondary oocyte First polar body formed from meiosis I (Small cell that does not then develop further) Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

The primary follicle grows and becomes a secondary follicle. 3. Oogenesis The primary follicle grows and becomes a secondary follicle. Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

4. Oogenesis A fluid filled cavity develops and the oocyte starts another division of meiosis (meiosis II) producing mature follicles (Graafian follicle) Second polar body formed Secondary oocyte is now an ootid Differentiates into an ovum Ready for ovulation Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

Overview OOCYTE = DIVIDES FOLLICLE = GROWS Primary oocyte completes meiosis I Forms a secondary oocyte (and a polar body) Primary follicles continue to grow into secondary follicles Secondary follicle containing secondary oocyte Secondary oocyte completes meiosis II Now an ootid (and a second polar body) Differentiates into an ovum Secondary follicles grow into Graafian follicles Graafian follicle containing ovum Ready for ovulation Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

Testes have a mass of narrow tubes called the seminiferous tubules Spermatogenesis Happens in the testes Testes have a mass of narrow tubes called the seminiferous tubules Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

Spermatogenesis Outer layer of cells in seminiferous tubules is the germinal epithelium where the production of sperm begins Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

Cells have various stages of sperm production Spermatogenesis Cells have various stages of sperm production Most mature cells are closest to the fluid filled centre of the seminiferous tubule. Cells that have developed a tail are spermatozoa (abbreviated to sperm) Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm

Annotate the seminiferous tubules Germinal epithelium cells Primary spermatocyte Secondary spermatocyte Spermatogonium Spermatids Basement membrane Sertoli cell Spermatozoa Skills: Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis

1. Spermatogenesis Germinal epithelium cells (outer layer) divide endlessly by mitosis to make more diploid cells (spermatogonium) Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm

Spermatogonium grow larger and are then called primary spermatocytes 2. Spermatogenesis Spermatogonium grow larger and are then called primary spermatocytes Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm

3. Spermatogenesis Each primary spermatocyte carries out first division of meiosis to produce two secondary spermatocytes Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm

4. Spermatogenesis Each secondary spermatocyte carries out second division of meiosis to produce two spermatids each Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm

5. Spermatogenesis Spermatids become associated with nurse cells, called sertoli cells which help the spermatids to develop into spermatozoa Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm

6. Spermatogenesis Spermatozoa detach from sertoli cells and eventually are carried out of the testis by the fluid in the centre of the seminiferous tubule Understanding: Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm

After sperm and egg production…. Stage 2 After sperm and egg production…. FERTILISATION

Fertilisation Union of a sperm and egg cell to form a zygote in the fallopian tube Sperm membranes have receptors to detect chemicals released by the egg. This allows directional swimming. Multiple sperm will arrive at the egg at the same time. Understanding: Fertilization involves mechanisms that prevent polyspermy Fertilization in animals can be internal or external

Preventing Polyspermy Acrosome reaction Penetration of egg membrane Cortical reaction Understanding: Fertilization involves mechanisms that prevent polyspermy Fertilization in animals can be internal or external

1. Acrosome Reaction Gel of glycoproteins also called zona pellucida which is a layer of proteins around the cell Acrosome is a large membrane bound sac of enzymes in the head of the sperm Sperm binds to zona pellucida and the contents of the acrosome are released – including enzymes that digest the zona pellucida Understanding: Fertilization involves mechanisms that prevent polyspermy

2. Penetration of egg membrane An area of the membrane on the tip of the sperm is now exposed. Plasma membrane of the sperm binds with plasma membrane of the egg Sperm nucleus enters the egg cell (fertilisation) Understanding: Fertilization involves mechanisms that prevent polyspermy

3. Cortical Reaction Nucleus entry causes the activation of the egg Affects cortical granules first (vesicles located near the egg membrane) Contents released by exocytosis Results in the digestion of binding proteins so that no further sperm can bind General hardening of the zona pellucida Understanding: Fertilization involves mechanisms that prevent polyspermy

Types of fertilisation Internal External Understanding: Fertilization in animals can be internal or external

Internal Terrestrial animals Some fish Ensures gametes are in close proximity to each other Protection inside female Few babies produced Understanding: Fertilization in animals can be internal or external

External Most fish Release gametes into water directly Large number of offspring Easy to find mates Susceptible to predation and environmental conditions (Temperature, pH, pollution) Gametes not close together Understanding: Fertilization in animals can be internal or external

Stage 3 After fertilisation…. IMPLANTATION

Implantation After fertilisation Ovum divides to form a 2 cell embryo After 48 hours it becomes a 4 cell embryo After this, unequal divisions and migration of cells gives the embryo the shape of a hollow ball: blastocyst Understanding: Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy

Implantation At 7 days old the blastocyst reaches the uterus from the oviduct The zona pellucida breaks down. The blastocyst has used up the reserves of the egg cell and needs an external supply of food Sinks into the uterus lining: Implantation Essential for the continuation of pregnancy Understanding: Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy

Implantation Outer layer of the blastocyst develops finger-like projections allowing the blastocyst to penetrate the uterus lining. Exchange materials to and from mother’s blood At 8 weeks it forms bone tissue and is called a fetus Understanding: Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy

Stage 4 After implantation…. GESTATION

Endometrium Endometrium must be maintained for the pregnancy to be successful Progesterone and estrogen must be continually produced Understanding: hCG stimulates the ovary to secrete progesterone during early pregnancy

hCG hormone Hormone produced by cells surrounding the embryo which then form the placenta. Corpus luteum stimulated in the ovary to continue secreting progesterone and estrogen Continues development of the uterus wall, supplying the embryo with nutrients. Understanding: hCG stimulates the ovary to secrete progesterone during early pregnancy

Pregnancy week 9 Placenta starts to secrete estrogen and progesterone Corpus luteum no longer needed so starts to degenerate Danger of miscarriage if this switch over fails Understanding: Estrogen and progesterone are secreted by the placenta once it has formed

As a fetus grows the surface area to volume ratio decrease Placenta As a fetus grows the surface area to volume ratio decrease Hard to absorb nutrients Placenta allows the fetus to remain in the uterus for longer Understanding: The placenta facilitates the exchange of materials between mother and embryo

Placenta Made of fetal tissues In contact with maternal tissues in the uterus wall Amniotic sac also develops from fetal tissues Contains amniotic fluid which protects and supports the fetus Understanding: The placenta facilitates the exchange of materials between mother and embryo

Placenta Finger-like placental villi Increase to help supply growing demands of the fetus Maternal blood flows in the inter-villous spaces around the villi Fetal blood circulates in capillaries close to the surface of the villlus Understanding: The placenta facilitates the exchange of materials between mother and embryo

Placenta Very small distance between fetal and maternal blood Placental barrier separates maternal and fetal blood Selectively permeable to allow some substances to pass through Understanding: The placenta facilitates the exchange of materials between mother and embryo

Placenta From maternal to fetal Glucose (facilitated diffusion) Oxygen (diffusion) Antibodies (endocytosis) Water (osmosis) From fetal to maternal Carbon dioxide (diffusion) Urea (diffusion) Understanding: The placenta facilitates the exchange of materials between mother and embryo

FETAL BLOOD PLACENTA MATERNAL BLOOD Diffusion Carbon dioxide

Does a baby poop and wee in the womb? FAQ Does a baby poop and wee in the womb? Babies generally do not poop in the womb, given that their digestive systems are not used to process much outside of this swallowed urine. They do accumulate a small amount of fetal poop known as meconium that consists of dead cells, waste, etc, that is pooped out within the first few days of life. Urinate into aminiotic fluid, then re drink again

The Placenta

Pregnancy week 9 Placenta starts to secrete estrogen and progesterone Corpus luteum no longer needed so starts to degenerate Danger of miscarriage if this switch over fails Understanding: Estrogen and progesterone are secreted by the placenta once it has formed

Role of progesterone Inhibits Oxytocin secretions Muscle contractions in uterine wall Understanding: Birth is mediated by positive feedback involving estrogen and oxytocin

Stage 5 After gestation…. PARTURITION

Parturition Time for birth! Fetus produces hormones to stop progesterone from placenta Oxytocin is then secreted Understanding: Birth is mediated by positive feedback involving estrogen and oxytocin

Oxytocin Stimulates contractions of the muscle fibres in the uterus wall. Causes more oxytocin to be secreted Causes more contractions (frequent and vigorous) Understanding: Birth is mediated by positive feedback involving estrogen and oxytocin

Draw one for oxytocin and contractions Positive Feedback Draw one for oxytocin and contractions Understanding: Birth is mediated by positive feedback involving estrogen and oxytocin

Parturition Muscles in the cervix relax and start to dilate Uterine contractions cause the amniotic sac to burst Amniotic fluid leaks out ‘my water has broken’ Understanding: Birth is mediated by positive feedback involving estrogen and oxytocin

Parturition Hours of uterine contractions later the baby is finally pushed out of the cervix and vagina Umbilical cord is broken and the baby takes its first breath – being independent from its mother. Understanding: Birth is mediated by positive feedback involving estrogen and oxytocin

Create a dramatic monologue to describe what happens during parturition to perform in front of the class. Progesterone Contractions Uterus wall Oxytocin Secretion Vigorous Frequent Positive feedback Relaxation Cervix Dilate Amniotic sac Amniotic fluid Vagina Umbilical cord Independence

Altricial Helpless Incompletely developed offspring Relatively immobile No hair Cannot obtain food themselves Applications: The average 38 week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals.

Precocial Open eyes Hair Immediately mobile Able to defend for themselves somewhat Larger mammals Longer gestation period Applications: The average 38 week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals.

What are we? Open eyes Some hair Not mobile Can’t defend for ourselves Cannot obtain food for ourselves Applications: The average 38 week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals.

INTERMEDIATE Open eyes Some hair Not mobile Can’t defend for ourselves Cannot obtain food for ourselves Applications: The average 38 week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals.

Correlation between mammalian body mass and gestation period Applications: The average 38 week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals.