bioknowledgy presentation on 11.4 sexual reproduction

Essential idea: Sexual reproduction involves the development and fusion of haploid gametes.

11.4 Sexual reproduction

By Chris Paine

https://bioknowledgy.weebly.com/

Both sperm and egg cells are the product of reduction division and it is the process of fertilisation that creates a unique diploid (zygote) cell which can develop into a new organism.

http://blogs.discovermagazine.com/science-sushi/files/2015/06/sperm_egg.jpg







UnderstandingsStatement Guidance

11.4.U1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

11.4.U2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm.

11.4.U3 Fertilization in animals can be internal or external.

11.4.U4 Fertilization involves mechanisms that prevent polyspermy.

Fertilization involves the acrosome reaction, fusion of the plasma membrane of the egg and sperm and the cortical reaction.

11.4.U5 Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy.

11.4.U6 HCG stimulates the ovary to secrete progesterone during early pregnancy.

11.4.U7 The placenta facilitates the exchange of materials between the mother and fetus.

11.4.U8 Estrogen and progesterone are secreted by the placenta once it has formed.

11.4.U9 Birth is mediated by positive feedback involving estrogen and oxytocin.

Applications and SkillsStatement Guidance

11.4.A1 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.

11.4.S1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis.

11.4.S2 Annotation of diagrams of mature sperm and egg to indicate functions.


Structure of the mature egg

Haploid (n) contains 23 chromosomes to be passed from mother to child

Consists of a glycoprotein that protects the egg and prevents the entry of sperm.

Not required – will break downContains nutrients to support the early development of fertilised egg

Makes the zona pellucida impenetrable to sperm (after fertilisation) to prevent polyspermy*

Provides nutrients to support the early development of fertilised egg

Diagram from: http://www.slideshare.net/gurustip/reproduction-ahl-1062218

Corticalgranules

Can you match the annotations to the labels?

http://www.slideshare.net/gurustip/reproduction-ahl-1062218




Structure of the mature egg

Haploid (n) contains 23 chromosomes to be passed from mother to child

Consists of a glycoprotein that protects the egg and prevents the entry of sperm.

Not required – will break down

Contains nutrients to support the early development of fertilised egg

Makes the zona pellucida impenetrable to sperm (after fertilisation) to prevent polyspermy*

Provides nutrients to support the early development of fertilised egg

Diagram from: http://www.slideshare.net/gurustip/reproduction-ahl-1062218

Corticalgranules





Structure of the mature sperm

Haploid (n), contains 23 chromosomes to be passed from father to child

Contains enzymes which can digest the zona pellucida

Possesses helical mitochondria which provide the ATP (energy) for swimming (and other processes)

Contains protein fibres and microtubules to strengthen and allow the tail to move respectively.

Can you match the annotations to the labels?


Structure of the mature sperm

Haploid (n), contains 23 chromosomes to be passed from father to child

Contains enzymes which can digest the zona pellucida

Possesses helical mitochondria which provide the ATP (energy) for swimming (and other processes)

Contains protein fibres and microtubules to strengthen and allow the tail to move respectively.

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 the female contraceptive pill. (4.8)

http://www.theguardian.com/environment/2012/jun/02/water-system-toxic-contraceptive-pill

https://www.arhp.org/publications-and-resources/contraception-journal/august-2011

https://www.sciencedaily.com/releases/2010/12/101208125813.htm

Assessing risks and benefits associated with scientific research: pollution from the female contraceptive pill

Use these and other links. How serious is the pollution threat from the female contraceptive pill?

Out for the count: Why levels of sperm in men are falling http://www.independent.co.uk/news/science/out-for-the-cou

nt-why-levels-of-sperm-in-men-are-falling-1954149.html

Don't blame the pillfor estrogen in drinking water

£30bn bill to purifywater system after toxic impact of contraceptive pill

Birth Control Hormones In Water: Separating Myth From Fact










http://www.independent.co.uk/news/science/out-for-the-count-why-levels-of-sperm-in-men-are-falling-1954149.html



11.4.U1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. AND 11.4.U2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm.

http://i-biology.net/


divide to produce spermatocytesspermatogonia



http://highered.mheducation.com/sites/0072495855/student_view0/chapter28/animation__spermatogenesis__quiz_1_.html

http://www.cengage.com/biology/discipline_content/animations/spermatogenesis.html












Roles of hormones are not required, but it is interesting to note that FSH and LH have roles in males as well as females



contains the primary oocyte surrounded by a single layer of supporting follicle cells

contains the secondary oocyte, ready for ovulation

outer layer of cells in the ovary



https://youtu.be/2-VKgdhfNpY

Human ovulation captured on film:







Image edited from: http://www.ib.bioninja.com.au/_Media/oogenesis_med.jpeg

Oogenesis production of ova (female gametes)

during fetal development large numbers of oogonia are formed by mitosis.

oogonia enlarge (growth) and undergo meiosis, but stop in prophase I (until puberty). They are now termed primary oocytes and are held in primary follicles.

(at puberty) some follicles develop each month in response to FSH:• the oocyte completes the first meiotic division• Division of the cytoplasm is unequal creating a polar body• the secondary oocyte continues into meiosis II and halts

at prophase II

polar bodies eventually degenerate

Secondary oocytes develop along with the follicle. When the follicle is mature it rupture to release the secondary oocyte with a small number of cells (the mature egg) into the fallopian tube. The remaining follicle cells remain in the ovary to form the corpus luteum (which secretes progesterone).

The oocyte completes meiosis II (forming the ovum) if the cell is fertilized and another polar body

1

2

4

3b

5

3a

http://www.ib.bioninja.com.au/_Media/oogenesis_med.jpeg

http://www.ib.bioninja.com.au/_Media/oogenesis_med.jpeg


Oogenesis resources:

http://highered.mheducation.com/sites/0072495855/student_view0/chapter28/animation__maturation_of_the_follicle_and_oocyte.html

http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::640::480::/sites/dl/free/0072495855/63089/28_02_1.swf::Structure%20of%20the%20Ovary%20and%20the%20Developmental%20Sequence%20of%20the%20Ovarian%20Follicles

http://www.wiley.com/college/jenkins/0470227583/animations/index_25_03_01.html

















Compare and contrast the processes of spermatogenesis and oogenesis (8 marks)


Compare and contrast the processes of spermatogenesis and oogenesis

Oogenesis Spermatogenesis

Cell division Begin with mitosis and later on involve meiosis

Growth Involve cell enlargement before meiosis

Product Haploid cells (gametes)

Differentiation Produce specialised gametes

Location Eggs/ova produced in the ovaries Sperm produced in the testes

Initiated During development of fetus During puberty

Pauses During prophase I and between prophase II and metaphase II

None

cytokinesis Unequal, producing polar bodies Equal

Number of gametes

One ova, polar bodies degenerate Four sperm

Release 14th day, midpoint of the menstrual cycle

Continuous production, released during sexual intercourse

Ceases At the menopause Continuous until death

(8 marks)

11.4.U3 Fertilization in animals can be internal or external.

http://www.bio1100.nicerweb.com/Locked/media/SAVE/ch31/31_08.jpghttps://i.ytimg.com/vi/q50Yphp1gzI/maxresdefault.jpg

In some aquatic species fertilisation is external (e.g. fish and amphibians) ; eggs are released followed shortly by sperm. This method of fertilisation is susceptible to environmental variation and therefore animals that use it often produce large quantities of eggs and sperm to compensate for losses.

Terrestrial animals (e.g. reptiles, birds and mammals) are mostly internal fertilisers to prevent dehydration of gametes or the developing embryo. Sperm is deposited into the female, in easy reach of the ova, during intercourse.

Internal and external Fertilization

http://www.bio1100.nicerweb.com/Locked/media/SAVE/ch31/31_08.jpg

http://www.bio1100.nicerweb.com/Locked/media/SAVE/ch31/31_08.jpg

https://i.ytimg.com/vi/q50Yphp1gzI/maxresdefault.jpg

https://i.ytimg.com/vi/q50Yphp1gzI/maxresdefault.jpg


There is more to fertilisation than the fusion of the gametes

http://www.abpischools.org.uk/res/coResourceImport/modules/genome/en-flash/fertilisation.swf

Why can only a single sperm fertilise an ova, what prevents polyspermy?

How does the sperm penetrate the zona pellucida?

What causes the pause in the ova’s meiosis process to continue?





1. The sperm pushes through the follicular cells and binds to receptors in the zona pellucida

Fertilisation

https://commons.wikimedia.org/wiki/File:Acrosome_reaction_diagram_en.svg

2. Enzymes are released from the acrosome and digest the glycoprotein based zona pellucida

http://www.vivo.colostate.edu/hbooks/pathphys/reprod/fert/fert.html









Fertilisation



3. The membranes of the sperm and the ova fuse this stimulates:

a. By exocytosis cortical granules (vesicles) release proteases (enzymes) into the zona pellucida causing the zona pellucida to ‘harden’ and become inpenetrable to (subsequent) sperm, preventing polyspermy.

b. An influx of Ca2+ into the ova which prompts the completion of meiosis II










Fertilisation



3. The membranes of the sperm and the ova fuse this stimulates:

a. By exocytosis cortical granules (vesicles) release proteases (enzymes) into the zona pellucida causing the zona pellucida to ‘harden’ and become inpenetrable to (subsequent) sperm, preventing polyspermy.

b. An influx of Ca2+ into the ova which prompts the completion of meiosis II

4. The nucleus of the sperm cell is deposited into the ova’s cytoplasm and subsequently fuses with the ova’s nucleus forming a diploid zygote (cell).



11.4.U5 Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy.

Blastocyst formation occurs in the fallopian tubes and uterus prior to implantation.

When the blastocyst reaches the uterus, it will embed itself in the endometrium.

Once implanted the developing embryo will gain nutrients and oxygen from the endometrium tissue fluid which is supplied, in turn, by a the endometrium’s capillary network.

http://www.ib.bioninja.com.au/_Media/blastocyst_med.jpeg

http://www.as.wvu.edu/~sraylman/physiology/cleavage_implant.swf

Implantation of the blastocyst A ball of cells called a morula form after a series of mitotic divisions

The ball of cells continues to divide, but unequally forming a fluid-filled cavity in the middle - this is now termed a blastocyst which consists of:• Inner mass of cells (develops into the

embryo)• Outer layer (develops into the placenta)• A fluid filled cavity






So can you explain why during pregnancy …

… menstruation ceases?… no further mature eggs are released?

(think about what you know from 6.6)


11.4.U8 Estrogen and progesterone are secreted by the placenta once it has formed.

*The placenta takes over the hormonal role of the corpus luteum at about week ten of the pregnancy:• HCG initially maintains the corpus luteum• Estrogen maintains the lining of the uterus • Progesterone maintains the endometrium and prevents contractions

*


11.4.U7 The placenta facilitates the exchange of materials between the mother and fetus.

Chorionic villi increase surface area for exchange of substances

Placental (chorionic) cells secrete hormones, e.g. HCG, oestrogen and progesterone.


11.4.U9 Birth is mediated by positive feedback involving estrogen and oxytocin.

The process of birth is stimulated by the rise in estrogen levels.

As estrogen increases it is no longer inhibited by progesterone and therefore it initiates contracting in the (smooth) muscular wall of the uterus.

The contractions stimulate stretch receptors signal the brain to release oxytocin from the pituitary gland.

Oxytocin also stimulates the muscle of the uterine wall and contractions to grow stronger.

The contractions again stimulate stretch receptors causing more oxytocin

Contractions continue for short time after birth to eject the placenta. As the stretch receptors are no longer stimulated oxytocin levels fall and contractions cease.

Positivefeedback

Hormonal control of birth

11.4.A1 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.

http://jeb.biologists.org/content/208/9/1731

The graph shows the relationship between (adult) body mass and gestation period (pregnancy) in a range of mammals.

(g)

(days)

Adult size and development of newborn young in mammals

Altricial mammals give birth to relatively helpless, incompletely developed offspring. Precocial mammals give birth to offspring that are mobile and able to defend themselves. These are in reality extremes on a scale.

Although there is a definite positive correlation between body mass and gestation period there are mammals with the same gestation period but widely varying body masses (by an order greater than 103).

The general rule is that animals with a long gestation periods give birth to offspring who are more developed at the time of birth.

humans



Bibliography / Acknowledgments

Bob Smullen

http://commackibbio.blogspot.com/


http://ib.bioninja.com.au/



bioknowledgy presentation on 11.4 sexual reproduction

Education