11.3 The kidney and osmoregulation:  All animals excrete nitrogenous waste products and some animals also balance water and solute concentrations.

Nature of science:  Curiosity about particular phenomena—investigations were carried out to determine how desert animals prevent water loss in their wastes.



∑ - Animals are either osmoregulators or osmoconformers.

  • Osmoregulators maintain a constant internal  solute concentration, even if they live in a marine environment with a very different osmolarity
  • All terrestrial animals, freshwater animals and some marine organisms are osmoregulators 
  • Osmoconformers are animals that have a similar internal solute concentration in comparison to the solute concentration of their surrounding environment  

***Data Based Questions p.486***

∑ - The Malpighian tubule system in insects and the kidney carry out osmoregulation and removal of nitrogenous wastes.

  • Insects have a circulating fluid known as hemolymph, that combines the features of blood and tissue fluid
  • Osmoregulation is a form of homeostasis to keep the concentration of hemolymph or blood within a certain range
  • Nitrogenous waste is created by the breakdown of amino acids and is toxic to the organism
  • In insects, the waste is in the form of uric acid and in mammals it is urea
  • Insects have Malpighian tubules that branch off from their intestinal tract to get rid of this waste
  • Cells in these tubules actively transport the uric acid from the hemolymph into the lumen of the tubules
  • Water is then drawn into the lumen by osmosis from the hemolymph
  • The tubules empty into the gut
  • When it reaches the hindgut, water and salts are reabsorbed and the nitrogenous waste is excreted in the feces of the insect

∑ - The composition of blood in the renal artery is different from that in the renal vein.

  • blood in renal artery is more oxygenated than the blood in the renal vein / oxygenated versus deoxygenated
  • blood in renal artery contains more urea than the blood in the renal vein/urea versus no urea / nitrogenous waste products
  • blood in renal artery contains more glucose than the blood in the renal vein
  • variable water / salt content in renal artery but constant / correct / regulated content in vein
  • Toxins and other substances that are ingested and absorbed but are not yet fully metabolized by the body are present in higher concentrations in the renal artery than in the renal vein

***Data Based p.488***

β - Skill: Drawing and labelling a diagram of the human kidney.

  •  To the right 

Animation of how the kidney works

∑ - The ultrastructure of the glomerulus and Bowman’s capsule facilitate ultrafiltration.

  • Ultrafiltration is the non-specific filtration of the blood as it enters the Bowman’s capsule of the kidney in which hydrostatic pressure created by the high pressure in the glomerulus (capillaries) forces a liquid against a semi-permeable membrane.
  • As blood enters the kidney through the afferent arteriole it becomes a knot-like capillary bed known as the glomerulus.
  • Because of the high pressure created in the capillaries as the blood vessel become smaller and because the glomerulus has fenestrations (small pores), large suspended solids and solutes such as proteins are retained. Water and small solutes such as salts, glucose and waste (urea) pass through the membrane into the Bowman’s capsule.
  • There is a membrane that separates the glomerulus and the Bowman’s capsule called the basement membrane that prevents large molecules such as proteins from entering the filtrate of the kidney.
  • The filtrate now enters the proximal convoluted tubule.



Molecule (mg 100 ml-1)
Blood Plasma
Glomerular Filtrate
> 90

** Please note the concentrations can vary because of diet and salt and water intake**

  • All the glucose contained in the blood will pass into the filtrate during ultrafiltration; however, 100% of the glucose will be quickly reabsorbed in the proximal convoluted tubule by active transport (11.3.6).
  • Therefore, no glucose will be found in the urine of a normal healthy individual. People with diabetes will end up with glucose in their urine.
  • Proteins are too large to leave the blood through the basement membrane during ultrafiltration and are therefore not found in the filtrate or the urine.
  • Urea leaves the blood during ultrafiltration entering the glomerular filtrate. The reason why the concentration of urea in the urine is so high is that much of the water in the filtrate is reabsorbed by the body, thus increasing the urea concentration per 100 ml-1 of urine.

∑ - The proximal convoluted tubule selectively reabsorbs useful substances by active transport.

  • While ultrafiltration is non-specific with regards to the molecules that leave the blood (based on size, no specific channels), selective reabsorption in the proximal convoluted tubule (PCT) is very specific with regards to the molecules that are reabsorbed.
  • Na+ ions are pumped from the filtrate through active transport into the intercellular space surrounding the PCT. The ions then pass into the surrounding capillaries (peritubular capillaries).
  • Cl- ions also leave the filtrate entering the intercellular space and then the capillaries following the charge gradient created by the active transport of Na+ions.
  • Water leaves the filtrate through osmosis following a gradient, but instead of a charge gradient, it follows a solute concentration gradient created by the transport of solutes out of the filtrate into the intercellular fluid and then the surrounding capillaries.
  • About 80% of the salt ions and water in the filtrate are reabsorbed as the filtrate passes through the proximal convoluted tubule.
  • 100% of the glucose lost during ultrafiltration is reabsorbed by active transport through co-transport channels powered by the sodium gradient out of the PCT.
  • The wall of the proximal convoluted tubule is only one cell thick allowing for efficient movement of molecules across a short distance.
  • The wall also contains microvilli (similar to the small intestine) that increase the surface area for reabsorption of important molecules.

Selective Reabsorptionhttps://www.youtube.com/watch?v=2_AvOs9fAlY&nohtml5=False

∑ - The loop of Henle maintains hypertonic conditions in the medulla.

  • The role of the loop of Henle is to create a solute concentration gradient in the medulla of the kidney.
  • The descending loop of Henle is permeable to water but impermeable to salt ions.
  • The ascending loop of Henle is permeable to salt ions but impermeable water.
  • As the filtrate flows up the ascending loop Na+ ions are pumped out of the filtrate into the interstitial fluid of the medulla thus increasing the solute concentration in the medulla.
  • As the filtrate flows down the descending loop (before the ascending loop)water flows out of the filtrate into the interstitial fluid of the medulla by osmosis following the concentration gradient created by pumping Na+ ions out of the ascending loop.
  • Therefore the medulla has a very high concentration of Na+ ions; the maximum level in humans is 1200 mOsm (milliosmole).
  • This system is countercurrent because the flow of the filtrate in the descending and ascending loop is in opposite directions. This allows for a greater concentration gradient to be created in the medulla.
  • The filtrate now leaves the loop of Henle and enters the collecting duct where the water level is fine-tuned.

Countercurrent flow: 


∑ - ADH controls reabsorption of water in the collecting duct.

  • If the solute concentration in the blood is too high, osmoreceptors in the hypothalamus sense this and signal the pituitary gland to produce a hormone called ADH (anti-diuretic hormone).
  • ADH causes special pores called aquaporins in the collecting duct to open, allowing water to be reabsorbed back into the blood, thus making the blood more dilute.
  • If the solute concentration in the blood is too low, osmoreceptors in the hypothalamus sense this and signal the pituitary gland to reduce its production of ADH.
  • This causes the aquaporins in the collecting duct to close, keeping the excess water in the filtrate, which excreted as dilute urine.
  • This is called osmoregulation.

∑ - The length of the loop of Henle is positively correlated with the need for water conservation in animals.

The longer the loop of Henle, the more water will be reabsorbed
Therefore, animals that live in dry habitats such as the desert have a long loop of Henle
This means the medulla of the kidney is also thicker

Animals that live in the desert (loop of Henle in Kangaroo rat 1:10-1:30)


∑ - The type of nitrogenous waste in animals is correlated with evolutionary history and habitat.

  • When animals breakdown amino and nucleic acids, nitrogenous waste is formed in the form of ammonia
  • Ammonia is highly basic, toxic and can be very reactive
  • Marine and freshwater organisms can release the ammonia directly into the surrounding water
  • Terrestrial organisms convert ammonia into a less toxic form (urea or uric acid)  before excretion
  • What form depends on the animals' evolutionary history and habitat
  • Amphibians release waste as ammonia as larvae and urea as adults
  • Birds and insects release ammonia as uric acid. Uric acid does not require water and is highly concentrated.
  • This is beneficial to these organisms as they do not have to carry the extra water around (less energy for flight)
  • Mammals release their waste in the less toxic form known as urea

Crash Course on Excretory System

Applications and skills:

β - Application: Consequences of dehydration and overhydration.

  • Dehydration is the consequence of losing large amounts of water through excessive sweating, diarrhea, vomiting or urination, without the loss of equal amounts of solutes

  • The body fluids become hypertonic
  • This results in dark coloured urine, lethargy, a raised heart rate and low blood pressure

  • Overhydration results when too much water is consumed and the body fluids become hypotonic

  • This results in behavioural changes, confusion, drowsiness, delirium, blurred vision, muscle cramps, nausea, and in acute cases, seizures, coma and finally death

β - Application: Treatment of kidney failure by hemodialysis or kidney transplant.


  • Blood is drawn from a vein in the arm and is passed through a dialysis machine for 3 to 4 hours, 3 times per week
  • As the blood flows through the machine, it passed next to a semi-permeable membrane that contains dialysis fluid
  • Pores in the membrane allow small particles to diffuse in either direction; however, the pores are too small for plasma proteins and cells to pass through and therefore remain in the blood
  • Dialysis fluid (dialysate) has the following characteristics that allow the blood to be cleaned
  • No urea or waste – These products diffuse from the blood into the fluid
  • Ideal concentrations of glucose and other metabolites – ideal concentrations of these molecules is therefore created in the blood of the patient through diffusion onto or out of the blood
  • High concentration of calcium and low concentration of potassium – Excess potassium is extracted out of the blood and calcium is added to the blood
  • HCO3- is added to the blood to make it more basic
  • Correct total solute concentration – Allows for excess water to diffuse from the blood

Kidney Transplant

  • A better long term treatment for a kidney that is not working properly is a kidney transplant
  • Either a living person provides one of their kidneys for transplant or kidneys are removed from someone that has recently died in order to give two kidneys to two individuals
  • It is essential to have matching blood types and tissue matches to minimize the risk of rejection
  • The kidney is grafted to the lower abdomen and the renal artery renal vein and ureter are connected to the individual

β - Application: Blood cells, glucose, proteins and drugs are detected in urinary tests.

Urine tests are used to detect abnormalities and possible diseases

  • Blood cells – blood cells in the urine is an indicator of a variety of diseases, including some cancers and infections
  • Glucose – excess glucose in the urine is almost always an indicator of diabetes
  • Proteins – Larger amounts of proteins in the urine are an indicator of kidney disease. Small amounts of some hormones such as insulin is normal
  • Drugs – Many drugs pass from the body into the urine, therefore a urine test can be conducted to detect drug users in sports or for recreational users tested by the police

β - Application:  The removal of kidney stones by ultrasound treatment.

Kidney stones explanation

Ultrasound surgery of Kidney Stones

Skill: Annotation of diagrams of the nephron including the glomerulus, Bowman’s capsule, proximal convoluted tubule, the loop of Henle, distal convoluted tubule; the relationship between the nephron and the collecting duct should be included.

 Topic 11: Animal Physiology (16 hours)

11.1 Antibody production and vaccination:  Immunity is based on recognition of self and destruction of foreign material.


∑ - Every organism has unique molecules on the surface of its cells.

  • All organisms have unique molecules or markers on the outer surface of the plasma membrane of their cells
  • These highly variable molecules are generally glycoproteins and they identify a cell as being “self” or “non-self”
  • These markers are called major histocompatibility complexes (MHC)
  • These MHC proteins are genetically determined and are unique to that individual

Cell surface glycoproteins on the HIV virus above


β - Application: Antigens on the surface of red blood cells stimulate antibody production in a person with a different blood group.


  • Blood groups such as A, B, AB and O are identified by cell surface antigens
  • Rhesus (Rh) is another antigen that can be present on the surface of the blood cells, being either Rh positive (has antigen) or Rh negative (doesn’t have antigen)
  • A blood transfusion given to an individual with the wrong blood type can stimulate an immune response called agglutination (clumping or clotting of the blood cells)
  • This is followed by the destruction of the RBC (hemolysis)
  • For example, someone with blood type A (antigen A on the surface) contains anti-B antibodies in their plasma. If they get a transfusion with blood type B, their immune system will attack and destroy the foreign blood cells with the B-antigen on the surface
  • People with blood type O just have the basic antigen sequence that all blood cells have and are therefore not attacked by A or B antibodies; therefore, blood type O is known as the universal donor (O negative has no Rhesus factor)

∑ - Pathogens can be species-specific although others can cross species barriers.

  • Invading organisms such as a virus or bacterium that enters the body and causes a disease are known as pathogens
  • Pathogens are generally species-specific, for example, humans are the only known organisms susceptible to pathogens such as polio, syphilis, measles and gonorrhea but are resistant to many pathogens that infect other organisms
  • However, there are pathogens that can cross this species barrier and infect a range of hosts, such as the Rabies virus, bird flu and the Bubonic plague
  •  Diseases from other animals that can infect or be transmitted to humans is called Zoonosis
  • The passing of diseases from different species is a growing global health concern

Video on Zoonosis: https://www.youtube.com/watch?v=PSQPikvU6pc

∑ - B lymphocytes are activated by T lymphocytes in mammals.

  • When a pathogen enters the blood, the specific antigen on the surface of the membrane is identified.
  • Specific phagocytes known as macrophages recognize a pathogen as a foreign entity because of the antigens on the surface.
  • The macrophage engulfs and partially destroys the pathogen.
  • The macrophage takes the antigens from the destroyed pathogen and displays them on the surface of the cell bound to a membrane protein called a MHC protein (called antigen presentation).
  • Specific T-lymphocytes receptors recognize and bind to the antigen presented by the macrophage, thus activating the T-lymphocyte.
  • The activated T-cell binds to a B-lymphocyte specific to the antigen; activating the B-cell through the binding and the release of a signaling protein

∑ - Activated B cells multiply to form clones of plasma cells and memory cells.

  • The active B-cells begin to clone themselves producing cloned plasma B cells that produce antibodies and memory cells.  Memory cells remain in the blood in case a second infection occurs to provide long term protection and a quick response to the new infection.
  • The plasma cells created, produce and release mass amounts of antibodies into the bloodstream.
  • These antibodies surround and bind to the antigens on the foreign pathogens.
  • Through a variety of different methods, the pathogens are destroyed by the antibodies and other white blood cells.

∑ - Plasma cells secrete antibodies.

  • As stated above, plasma cells are specialized B lymphocytes (called B cells as they develop in the bone marrow) that secrete a large number of antibodies during a selective immune response
  • Since they are a cell that produces and secretes a large number of antibodies (proteins), they contain an extensive amount of rER, ribosomes, and mitochondria (for energy)


∑ - Antibodies aid the destruction of pathogens.

Antibodies aid in the destruction of pathogens in a variety of ways

  • Agglutination – antibodies cause the sticking together of pathogens by attaching to the antigens on the surface. These clumped masses of pathogens are then easily ingested and destroyed by phagocytes
  • Opsonization – antibodies make pathogens recognizable by binding to them and linking them to phagocytes
  • Toxin Neutralization – Antibodies bind to toxins produced by pathogens in the blood plasma preventing them from affecting susceptible cells.
  • Complement Activation – After a pathogen is identified by antibodies, complement proteins in the blood plasma form a membrane attack complex that destroys the cell membrane in the pathogen causing the cell to lyse
  • Bacteria and Virus Neutralization – Antibodies can bind to the surface of viruses, preventing them from entering host cells

∑ - Immunity depends upon the persistence of memory cells.

  • Long term specific immunity depends upon the presence of memory cells created during a previous infection from the same pathogen
  • Memory cells are long-lived cells that make an effective response to reinfection of the body by the same antigen (on the pathogen)

∑ - Vaccines contain antigens that trigger immunity but do not cause the disease.

  • Vaccines are introduced to the body usually through injection but can be administered through orally or through a nasal spray
  • Vaccines contain a live attenuated (weakened) or killed version of the pathogen, its toxins or one of its surface antigens.
  • Vaccines stimulate a primary immune response
  • If the body encounters the actual pathogen, it will be destroyed right away by the antibodies during a secondary immune response
  • Vaccines have made great contributions towards public health through the prevention of many deadly or dangerous diseases such as tuberculosis, measles, and smallpox

Herd Immunity http://www.cbc.ca/news/health/measles-vaccinations-of-toddlers-at-89-below-herd-immunity-level-1.3161617 

Anti-Vaxxers in Texas https://www.youtube.com/watch?v=npYocgDntyY

***Do Data Based questions on page 473**

β - Application: Smallpox was the first infectious disease of humans to have been eradicated by vaccination.  Human vaccines are often produced using the immune responses of other animals.

Good video on smallpox 

Eradication of smallpox in South-East Asia 


  • In 1959 a global initiative was undertaken by the WHO in order to eradicate smallpox
  • The effort had mixed results until a well-funded Smallpox Eradication Unit was formed in 1967
  • The last known case of smallpox was recorded in Somalia in 1977
  • It was successful because of the following reasons

  1. Patients were easily identified by obvious clinical features
  2. Transmission was through direct contact only
  3. There were no animal vectors or reservoirs where the disease could remain and reemerge
  4. Contacts of the patients identified were quickly identified and vaccinated
  5. Immunity was long term so reinfection was unlikely
  6. The infection period was short-lived  (3 to 4 weeks)
  7. The virus was stable and didn’t mutate
  8. There was international cooperation organized by the WHO   

Nature of scienceConsider ethical implications of research—Jenner tested his vaccine for smallpox on a child.

  • Edward Jenner was a scientist who infected a small child with cowpox
  • After the boy recovered he then affected the child with the more virulent and possibly fatal smallpox, as he believed the child would be immune because of the original cowpox infection
  • He did this on a young child well below the age of consent

Jenner’s Story 

Ethics in medicine:

β - Skill: Use databases to analyse epidemiological data related to vaccination programmes

Epidemiological Studies on Vaccinations

Vaccines and Autism 

[Polio notifications, Ireland 1948-2010 (as of 14/10/2010)]

∑ - White cells release histamine in response to allergens.

  • Mast cells found in connective tissue and Basophils circulating in the blood secrete histamine in response to antigens from an infection or response to an allergen
  • Histamines cause the blood vessels of the infected area to dilate and increase the flow of fluid containing immune components to the infected area
  • Some of these immune components leave the blood vessels resulting in a non-specific and specific immune response  

∑ - Histamines cause allergic symptoms.

  • A number of symptoms from allergic reactions are caused by histamines
  • Cells throughout the body have histamine receptors
  • The release of histamine causes many of the symptoms from an allergic response such as inflammation, sneezing, itching and mucous secretion
  • Histamines play a role in the formation of rashes and swelling known as anaphylaxis
  • Anti-histamine drugs, counteract these effects by blocking histamine receptors

∑ - Fusion of a tumour cell with an antibody-producing plasma cell creates a hybridoma cell.


∑ - Monoclonal antibodies are produced by hybridoma cells.

  • Monoclonal antibodies are identical antibodies produced by clones of a single parent immune cell that are specific to one type of antigen.
  • A laboratory animal such as a mouse is injected with a specific antigen that corresponds to the needed antibodies.
  • After the animal goes through a primary immune response, a plasma B-cell cell that produces the required antibody is removed from the spleen.
  • Myeloma (cancer) cells are cultured in a petri dish.
  • These dividing myeloma cells are mixed together with the plasma B-cells and are treated to promote fusion between the two cells, forming a cell called a hybridoma.
  • The successful hybridomas have characteristics of both cells; produce antibodies and divide rapidly for a long time.
  • These hybridoma cells are cultured and allowed to divide, producing many clone cells that are able to produce large amounts of antibodies.
  • Monoclonal antibodies can be extracted and used for many different applications.

Video on Monoclonal Antibodies https://www.youtube.com/watch?v=kcxQyIfca4I

β - Application: Monoclonal antibodies to HCG are used in pregnancy test kits.

Use in diagnosis of pregnancy

  • Human chorionic gonadotrophin (HCG) is produced by an embryo in early pregnancy.
  • Monoclonal antibodies can be produced by injecting a lab animal with HCG, as it recognizes this as antigen.
  • HCG Antibodies are combined with color-changing enzymes.
  • When the mixture is introduced into a blood sample of a woman that is pregnant, the antibodies will bind to the HCG in the blood, causing a change in color.
  • If the woman is not pregnant, no HCG will be present in her blood, and therefore there will be no color change.

Use in treatment of rabies

  • Monoclonal antibodies are produced using the method described in 11.1.5.
  • The antibodies are injected directly into the person after a possible rabies infection.
  • The antibodies will control and fight the infection, giving time for the body to produce its own antibodies.
  • If not treated with antibodies after a rabies infection, death can result.

**Other examples are the treatment of cancer cells and detection of HIV**

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

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.


∑ - Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.

  • Spermatogenesis is basically the production of sperm (male gametes) through meiosis.

  • Spermatogenesis starts when 2n cells in the germinal epithelium (spermatogonia) divide by mitosis to form more 2n cells that begin to move towards the middle of the seminiferous tubules.

  • These cells grow and replicate their DNA to prepare for meiosis. These are now called primary spermatocytes.

  • Oogenesis is basically the production of female eggs (female gametes) through meiosis.

  • Germ cells (2n) in the fetal ovary divide by mitosis to produce many 2n germ cells called oogonia.

  • Oogonia will grow in the cortex until they are large enough and ready to go through meiosis; they are called primary oocytes.

  • The primary oocytes begin to go through the first division of meiosis,which is arrested (stopped) in prophase I when follicle cells surround the dividing oocyte.

  • This is called the primary follicle (about 400,000 in a female when she is born).

  • These follicles remain in the first stage of meiosis until the girl reaches puberty and begins her menstrual cycle.

  • These primary spermatocytes undergo their first meiotic division resulting in two haploid (n) cells called secondary spermatocytes.

  • Cells in between the developing spermatocytes called interstitial cells (Leydig cells) produce testosterone in the presence of LH (luteinizing hormone) to aid in the development of the sperm

  • Secondary spermatocytes undergo a second meiotic division resulting in four spermatids (n).

  • Sertoli cells nourish the spermatids as they mature and differentiate into spermatozoa.

  • Sertoli cells are activated by FSH

  • Spermatozoa are released into the lumen of the seminiferous tubules where they are transported to the epididymis. The sperm attain full motility in the epididymis.

  • Every month a primary follicle finishes meiosis I to form two haploid (n) cells (one haploid cell is much larger than the other cell). This development is stimulated by FSH.

  • The large cell is a secondary oocyte and the small cell is called the polar body.

  • The secondary oocyte develops inside what is known as the mature follicle

  • As the large secondary oocyte begins to go through the second meiotic division, it is released from the ovary.  It will not complete the second meiotic division unless the oocyte is fertilized.

  • When meiosis II is complete you have an ovum and another polar body.

Similarities between Spermatogenesis and Oogenesis (use the above information to fill in the table below)

 Spermatogenesis                                    Oogenesis

 ∑ - Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm. (Differences in the outcome of spermatogenesis and oogenesis

Occurs in males (testis)
Occurs in females (ovaries)
Four male gametes (spermatids) are produced through meiosis for every germ cell.
One female gamete (ovum) and 3 polar body cells for every germ cell are produced through meiosis.
Each sperm cell is small and contains little cytoplasm
The large egg cell contains large amounts of cytoplasm and the 3 polar bodies produced degenerate
Millions of sperm produced every day from puberty until a man dies.
One secondary oocyte is ovulated every month during the menstrual cycle until a woman reaches menopause.
Spermatozoa are released during ejaculation.                                                                                         
Secondary oocytes are released during ovulation.

  Skill: Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis.


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

  • Fertilization is the combining of the male and female gametes to produce a zygote.

  • Sperm are ejaculated into the vagina of a female and are stimulated to swim by calcium ions in the vaginal fluids.
  • The sperm follows chemical signals produced by the egg until they reach the fallopian tubes, which is where the majority of fertilization takes place.

  • When the sperm reaches the egg, a reaction called the acrosome reaction takes place that allows the sperm to break through the layer of glycoproteins.

  • The acrosome in the head of the sperm releases hydrolytic enzymes onto the glycoprotein layer surrounding the egg called the zona pellucida.

  • This digests the layer allowing the sperm to force their way through the zona pellucida through vigorous tail beating.

  • The first sperm that makes it through comes into contact and fuses with the egg’s membrane (The membrane at the tip of the sperm has special proteins that can bind to the now exposed membrane of the egg), releasing the sperm’s nucleus into the egg cell.

  • When the membranes fuse together, cortical granules near the surface of the egg membrane are released by exocytosis.

  • The chemicals in the granules combine with the glycoproteins in the zona pellucida. This causes the glycoproteins in the zona pellucida to cross-link with each other, creating a hard layer impermeable to the other sperm.

  • This prevents fertilization of an egg by more than one sperm.  

Fertilization - https://www.youtube.com/watch?v=_5OvgQW6FG4

Skill: Annotation of diagrams of mature sperm and egg to indicate functions.

Sperm Diagram

Egg Diagram

∑ - Fertilization in animals can be internal or external.

  • Without water to prevent drying out of the egg and sperm, terrestrial animals rely on internal fertilization
  • This ensures the close proximity of the sperm and egg in order to ensure fertilization takes place 
  • Most aquatic organisms generally rely on external fertilization, which involves releasing the sperm and egg at close proximity, into the water outside the female’s body
  • External fertilization increases the risk of successfully creating offspring
  • Several risks include predation and changes to the external environment (pH, pollution and temperature etc.)


∑ - Fertilization involves mechanisms that prevent polyspermy.

  • The membranes of the sperm have receptors that detect chemicals that the egg releases in order to move in that direction
  • Once the sperm reaches the egg, the events explained above-involving fertilization, the acrosome reaction and then the cortical reaction prevent multiple sperm from entering the egg (polyspermy)

∑ - Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy.

  • After the male and the female gametes combine to form a zygote, the zygote divides by mitosis to form a two-cell embryo.

  • They two cells grow and replicate their DNA, and undergo another cell division through mitosis to form a four-cell embryo.

  • As the embryo is developing, it is moving along the fallopian tube towards the uterus.

  • The four-cell embryo continues to divide by cell division until it reaches 16 to 32 cells; called the morula.

  • After continued cell divisions, a blastocyst consisting of 100 to 128 cells is formed and is ready for implantation into the endometrium.

  • The blastocyst consists of an inner cell mass that will develop into the body of the embryo, a group of cells surrounding the embryo called the trophoblast that will develop into the placenta, and a fluid-filled cavity called the blastocoel.

  • The outer layer of cells will develop finger-like projections that will allow the embryo to penetrate the uterine wall during implantation.


∑ - HCG stimulates the ovary to secrete progesterone during early pregnancy

  • When a human embryo is implanted into the endometrium or the uterine lining, it starts to produce the hormone, human chorionic gonadotrophin (HCG).

  • HCG promotes the maintenance of the corpus luteum and prevents its disintegration.

  • This allows for the continued production of progesterone which is critical for pregnancy.

  • Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus.

  • HCG might repel the immune cells of the mother thus protecting the fetus during early development.

∑ - The placenta facilitates the exchange of materials between the mother and fetus.

  • The placenta develops from the trophoblast layer of the blastocyst.

  • When developed three blood vessels contained within the umbilical cord connect the placenta to the growing fetus.

  • Two umbilical arteries carry deoxygenated blood and waste away from the fetus to the placenta.

  • As maternal blood enters the placenta it leaves the arteries and enters the intervillous space, where it pools and surrounds the placental villi.

  • The placental villi are finger-like fetal tissues that have a large surface area for the exchange of materials such as gases, nutrients, and wastes.

  • Fetal blood that circulates in capillaries within the villi and microvilli is very close to the surface, allowing for the efficient exchange of materials between the fetal and maternal blood.

  • Materials such as oxygen, nutrients, and vitamins diffuse into the fetal capillaries from the maternal blood in the intervillous space, while carbon dioxide and wastes diffuse out of the fetal capillaries into the intervillous space.

  • One umbilical vein carries oxygenated and nutrient-rich blood back to the fetus from the placenta.

  • The cells that separate the fetal and maternal blood form a semi-permeable placental barrier

Materials are exchanged between the maternal and the fetal blood in the placenta.

Note: maternal and fetal blood is never mixed together.

Materials passed from fetus to mother
Materials passed from mother to fetus
Carbon dioxide
Nutrients (i.e. glucose and amino acids)
Hormones (i.e. HCG)
Vitamins and minerals


Good animations –

Fetal Circulation - 


Diagram of Placenta

∑ - Estrogen and progesterone are secreted by the placenta once it has formed.

  • The placenta also starts to produce progesterone and estrogen after about 9 weeks taking over from the corpus luteum. The placenta produces enough of these steroids to maintain the pregnancy and the corpus luteum is no longer needed.

  • These hormones are necessary to maintain the rich blood supply needed by the placenta.

***Do data based questions on page 507 and 508***


∑ - Birth is mediated by positive feedback involving estrogen and oxytocin.

  • When the pregnancy is at term, the fetus secretes hormones that signal the placenta to stop producing progesterone (progesterone inhibits the secretion of oxytocin by the pituitary gland).

  • Oxytocin secreted by the anterior pituitary gland stimulates the muscle fibers in the uterus to begin to contract.

  • As the muscles in uterus contract, mechanoreceptors in the uterine wall signal the pituitary to produce more oxytocin.

  • More oxytocin increases the frequency and intensity of the contractions, thus stimulating the production of even more oxytocin.

  • This is an example of positive feedback.

  • Contractions of the muscles of the uterus will cause the amniotic sac to break, releasing the amniotic fluid (This is when the “water breaks” in childbirth).

  • Relaxation of the muscles in the cervix causes it to dilate, eventually allowing the increasing contractions to push the baby out through the vagina and the cervix.

  • The placenta is expelled “afterbirth” about 15 min after the baby is born.

***Do the data analysis questions on page 508 and 509***


β -Application: 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.

  • There is a correlation with animal size (mass) and the development of their young (viewed as the length of gestation period)

  • In many cases, the longer the gestation period, the greater the mass size and development at birth

  • ·Species of mammals that give birth to smaller, immature and somewhat helpless offspring are called altricial species

  • Species of mammals that give birth to more mature offspring that are generally larger, have their eyes open at birth and are immediately mobile. These offspring are precocial.

***Do the data analysis on page 510***

β -Application:  Disputes over the responsibility for frozen human embryos.



11.2 Movement:  The roles of the musculoskeletal system are movement, support, and protection.


∑ - Bones and exoskeletons provide anchorage for muscles and act as levers

  • Bones act as levers so the body can move and provide structural support (skeleton).
  • Ligaments are strong bands that connect bone to bone strengthening the joint during movement.
  • Tendons have dense connective tissue that connects muscles to bones, allowing movement of the bone when a muscle contracts.
  • Muscles provide the force for movement by contracting (shortens the muscle fibers)

  • The joint acts as a pivot point or a fulcrum
  • The force applied (when the muscle contracts) is called the effort
  • The force or load needed to overcome for movement to take place is called the resistance
  • Levers are classified by first, second, and third class, depending upon the positions among the fulcrum, the effort, and the resistance.

  • First-class levers have the fulcrum in the middle, like a seesaw. An example of a first class lever is when a human nods their head (top of the spinal column is the fulcrum, the effort force is provided by the muscles in the back of the neck, and the resistance is the weight of the head).

  • Second-class levers have a resistance in the middle, like a load in a wheel-barrow. The body acts as a second class lever when engaged in pushup or calf raise. During a calf raise ball of the foot is the fulcrum, the body’s mass is the resistance and the effort is applied by calf muscle.

  • Third-class levers have the effort from the muscle in the middle of the lever. The majority of the human body's musculoskeletal levers are third class. These levers are built for speed and range of motion. Muscle attachments are usually close to the fulcrum. In the example of the arm, the effort force is provided by the contraction of the biceps, the fulcrum is the elbow joint and the resistance would be provided by whatever weight is being lifted.


  • Exoskeletons in insects and crustaceans can facilitate the movement by providing an anchorage for muscles; similarly to how bones provide anchorage for animals with internal skeletons  

∑ - Synovial joints allow certain movements but not others.

  • The type of joint determines the amount of movement that is possible
  • For ball and socket joints, such as the hip or the shoulder, movement through all three planes is possible. At the hip joint, the head of the femur is the ball the fits into the socket of the pelvis. The movements possible at the joint are flexion, extension, rotation, abduction, and adduction.
  • For hinge joints, such as the knee, flexions (bending) and extensions (straightening) are the possible movements (movement in one plane); however, slight side to side movements are possible

Hip Joint (differences)
Knee joint (differences)
Ball and socket joint
Synovial joints separated by a fluid-filled cavity
Hinge joint
Free movement in all three planes
Fluid is called synovial fluid that lubricates the joint.
Allows movement in one plane (although there can be a slight side to side movement)
Greater range of motion than the knee joint (flexion, extension, adduction, abduction and rotation). Muscles involved are the quads, hamstrings, gluteus maximus and many other smaller muscles
Ends of bones covered in cartilage, a smooth connective tissue which absorbs shocks more easily.
Motions are flexion (contraction of hamstring muscle) and extension (contraction of quadriceps muscles)

β -Skill: Annotation of a diagram of the human elbow: include cartilage, synovial fluid, joint capsule, named bones and named antagonistic muscles.

cartilage - stiff yet flexible connective tissue found in many areas in the bodies such as the joints between bones, nose and ear
cartilage reduces friction in the joint, provides high tensile strength and support, and absorbs compression
synovial fluid – thick, viscous fluid found in the cavity of the synovial joints
synovial fluid reduces friction by providing lubrication between the cartilage and other tissues in joints during movement supplies oxygen and nutrients to and removes carbon dioxide and wastes from the cartilage cells
joint capsule – two-layered sac surrounding the joint made from fibrous tissue
The joint capsule seals the joint space and provides stability to the joint by limiting movements
radius – smaller forearm bone that extends from the lateral side of the elbow to the thumb part of the wrist
Lever attached to the biceps. When the biceps contract, the radius provides a solid structure for lifting
ulna – longer forearm bone on the medial side
A lever connected to the triceps. When the triceps contract, the ulna provides support as a lever as the arm straightens out

biceps – muscle connected to the radius

contracts and causes flexion (arm bending)
triceps – muscle attached ulna
contracts and causes extension (arm straightening)

***Data Based questions on page 477***

∑ - Movement of the body requires muscles to work in antagonistic pairs.

  • Skeletal muscles occur in antagonistic pairs; therefore, when one muscle contracts, the other relaxes
  • These antagonistic pairs produce opposite movements at the joint

  • Examples are 1) biceps and triceps 2) quadriceps and hamstring

β - Application: Antagonistic pairs of muscles in an insect leg.


  • The hind limbs of grasshoppers are specialized for jumping
  • It has a jointed appendage with three parts
  • Below the joint is the tibia, and at the base of the tibia is another joint called the tarsus
  • Above the joint is the femur
  • When the grasshopper jumps, the flexor muscles contract and the femur and tibia are brought closer together (flexing)(extensor muscles are relaxed)
  • As the grasshopper jumps the extensor muscles contract, extending the tibia, creating a powerful jump force

Grasshopper jumping 

Interesting video

∑ - Skeletal muscle fibres are multinucleate and contain specialized endoplasmic reticulum.

  • Skeletal muscles are composed of bundles of muscle fibres and have a striped appearance because of areas of thick and thin filaments (myosin and actin)
  • Muscle cells have many nuclei and are long because the embryonic muscle cells fuse together.
  • Muscle fibres are composed of many parallel elongated fibres called myofibrils. 
  • A modified endoplasmic reticulum, called the sarcoplasmic reticulum (fluid-filled membranous sacs), extends throughout the muscle fibre, wrapping around each myofibril, sending a signal to all parts of the muscle fibre to contract at the same time

∑ - Muscle fibres contain many myofibrils.

∑ -
Each myofibril is made up of contractile sarcomeres.

Myofibrils – rod-shaped parallel bodies consisting of actin and myosin filaments

Sarcolemma – plasma membrane of the muscle cell.
Mitochondria – large numbers; found dispersed around individual myofibrils.


  • Lies between two Z lines which are dense protein discs.
  • Contains the thick filament (myosin) and thin filament (actin).
  • Myosin contains a head that binds to the binding site on the actin; interaction between myosin and actin (cross-bridge) is responsible for muscle contraction.
  • Myosin is seen as dark bands while actin is seen as light bands.
  • A-bands contain a full length of myosin and some of the actin filaments.
  • I bands contain only actin filaments.

β - Skill: Drawing labelled diagrams of the structure of a sarcomere:  include Z lines, actin filaments, myosin filaments with heads, and the resultant light and dark bands.

**Do data-based questions on page 481***

∑ - The contraction of the skeletal muscle is achieved by the sliding of actin and myosin filaments.  Use animations to visualize contraction.

  • During a muscle contraction, myosin filaments pull actin filaments towards the centre of the sarcomere
  • This shortens the sarcomere and the overall length of the muscle fibre
  • When this occurs, the myosin heads bind to sites on the actin filaments, creating cross-bridges, pulling (sliding) the actin filaments along the myosin filaments with energy from ATP 
  • This is called sliding filament theory and is explained further below

Good videos on cross-bridge formation and muscle contraction:



∑ - Calcium ions and the proteins tropomyosin and troponin control muscle contractions.

**The first part in blue is a lead up to the calcium-binding to the troponin in the control of muscle contractions enhancing your understanding of what is occurring; however, it is probably not necessary to answer the understanding above***

  • An action potential propagated along a motor neuron arrives at the neuromuscular junction.
  • This causes the release of the neurotransmitter acetylcholine into the synapse between the terminal axon of the motor neuron and the sarcolemma of the skeletal muscle.
  • The acetylcholine binds to receptors on the sarcolemma, causing voltage-gated channels to open and Na+ ions to flow into the muscle cells.
  • This creates an action potential in the striated muscle.
  • The action potential is further propagated along the sarcolemma of the skeletal muscle.
  • The action potential moves into the interior of the muscle cell through folds called t tubules.
  • The depolarization of the t tubules causes voltage-gated Ca+ channels on the sarcoplasmic reticulum to open, causing an influx of Ca+ ions into the sarcoplasm.
  • Ca+ ions bind to troponin which causes tropomyosin to move, exposing the myosin-binding sites (troponin and tropomyosin are regulatory proteins blocking the myosin-binding sites).

∑ - ATP hydrolysis and cross-bridge formation are necessary for the filaments to slide

  • ATP attaches to the myosin heads breaking the cross-bridges between the myosin heads and actin-binding sites
  • The ATP undergoes a hydrolysis reaction forming ADP + Pi.
  • This causes a positional change in the myosin head (cocked back).
  • The myosin heads bind to actin filaments forming cross-bridges at a site one position further from the centre of the sarcomere
  • When the ADP + Pi are released the myosin heads change conformational position, sliding the actin filaments towards the center of the Sarcomere.
  • This is called the “power stroke”.
  • After the power stroke ATP again binds to the myosin head, causing it to detach from the actin filament ready for another cycle.

β - Skill: Analysis of electron micrographs to find the state of contraction of muscle fibres.  Measurement of the length of sarcomeres will require calibration of the eyepiece scale of the microscope.

Muscle Fiber (contracted and relaxed)

  • Notice in the fully contracted sarcomere the actin filaments slide along the myosin causing the light bands to shorten, even though the dark bands stay the same length.
  • The Z lines get closer together as the sarcomere contracts.
  • The muscle also can be in various states of partial contraction.

β - Skill:  Use of grip strength data loggers to assess muscle fatigue

Nature of science:  Developments in scientific research follow improvements in apparatus—fluorescent calcium ions have been used to study the cyclic interactions in muscle contraction.

**Read through the article and make notes**

Crash Course on Muscles: 


IB Biology - Curriculum Notes 

External Fertilization

​Internal Fertilization

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