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IB Biology Objectives
Topic 5: Human Health and Physiology


Topic 1: Cells
Topic 2: The Chemistry of Life
Topic 3: Genetics
Topic 4: Ecology and Evolution
Topic 5: Human Health and Physiology
Topic 7: Cell Respiration and Photosynthesis
Topic 8: Genetics
Topic 9: Human Reproduction
Topic 10: Defense Against Infectious Disease
Topic 11: Nerves, Muscles, and Movement
Topic 12: Excretion
Topic 13: Plant Science
Option E: Neurobiology and Behaviour
Option H: Further Human Physiology

Topic 5.1 Digestion


5.1.1 Explain why digestion of large food molecules is essential.


Digestion is necessary because it breaks large food molecules into smaller molecules that can be absorbed into the villi of the small intestine and eventually travel through the blood.  Simple molecules can then dissolve in blood and go into circulation to reach every part of the body.


5.1.2 Explain the need for enzymes in digestion.


During digestion, four different groups of molecules are commonly encountered.  Each is broken down into its molecular components by specific enzymes.  Enzymes called amylases break down starch.  Proteins are broken down into short chains of amino acids or individual amino acids by enzymes called proteases.  Fats are broken down into glycerol and fatty acids by enzymes called lipases.  Nucleic acids are broken down into nucleotides by enzymes called nucleases.


5.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase.


One amylase

Source= salivary glands in the mouth and in the pancreas

Substrate= starch

Product= maltose and oligosaccharides

Optimum pH= 7


One protease (pepsin)

Source= glands in stomach wall

Substrate= proteins

Product= peptides

Optimum pH= 2


One lipase

Source= pancreas

Sustrate= fats

Product= fatty acids and monoglycerides

Optimum pH= basic (higher than 7).









5.1.4 Draw a diagram of the digestive system.































5.1.5 Outline the functions of the stomach, small intestine, and large intestine.


Stomach functions


Because of its accordion like folds (called rugae), the wall of the stomach can expand to store two to four liters of material.  Temporary storage is important because you eat considerably faster than you can digest food and absorb nutrients.


The stomach mixes the food with water and gastric juice to produce a creamy medium called chyme.

Physical breakdown

Three layers of smooth muscles in the muscularis externa churn the contents of the stomach, physically breaking food down into smaller particles.  In addition, HCL denatures proteins and loosens the cementing substances between cells.  The HCL also kills most bacteria that may accompany the food.

Chemical breakdown

The enzyme pepsin chemically breaks down proteins.  Only after pepsinogen is secreted into the stomach cavity can protein digestion begin.

Controlled release

A valve at the end of the stomach, the pyloric sphincter, regulates movement of chyme into the small intestine.


Small intestine functions

Mechanical digestion

Segmentation mixes the chyme with enzymes from the small intestine and pancreas.  Bile from the liver separates into smaller fat globules.  Peristalsis moves the chyme through the small intestine.

Chemical digestion

Enzymes from the small intestine and pancreas break down all four groups of molecules found in food into their component molecules.


The small intestine is the primary location in the GI tract for absorption of nutrients.

Carbohydrates, proteins, nucleic acids, water-soluble vitamins, Vitamin B12, lipids, fat-soluble vitamins, water, and electrolytes.


Large intestine functions

Mechanical digestion

Rhythmic contractions of the large intestine produce a form of segmentation called haustral contractions in which food residues are mixed and forced to move from one haustrum to the next.  Peristaltic concentrations produce mass movements of larger amounts of material.

Chemical digestion

Digestion occurs as a result of bacteria that colonize the large intestine.  They break down indigestible material by fermentation, releasing various gases.  Vitamin K and B vitamins are also produced by bacterial activity.


Vitamins B and K, some electrolytes (Na+ and Cl-) and most of the remaining water is absorbed by the large intestine.


Mass movement of feces into the rectum stimulates defecation reflex that opens the internal anal sphincter.  Unless the external and sphincter is voluntarily closed, feces are evacuated through the anus. 


5.1.6 Distinguish between absorption and assimilation.


Absorption is the passage of digested substances through the wall of the intestine into the blood capillaries in bodies.  Assimilation is a process by which food becomes incorporated with the body without being broken down.




5.1.7 Explain how the structure of the villus is related to its role in absorption of the end products of digestion.


Villi (singular villus) are fingerlike projections, in the small intestine,  that cover the surface of the mucosa giving it a velvety appearance.  They increase the surface area over which absorption and digestion occur.  The spaces between adjacent villi lead to deep cavities at the bases of the villi called intestinal crypts.  Glands that empty into the cavities are called intestinal glands, and the secretions are collectively called intestinal juice.


Topic 5.2 - The Transport System


5.2.1 Draw a diagram of the heart showing all four chambers, associate blood vessels and valves.

































5.2.2 Describe the action of the heart in terms of collecting blood, pumping blood and opening and closing valves.


The blood is collected by the atria, and is then pumped out by the ventricles into the arteries.  Atrio-ventricular and semilunar valves control the direction of flow.


5.2.3 Outline the control of the heartbeat in terms of the pacemaker, nerves and adrenalin.


The wall of the right atrium is made of a specialized tissue forming a structure called the sinoatrial node (SAN) also known as the pacemaker.  It spontaneously produces electrical impulses that spread to the two atria causing them to contract.  The brain controls the heart rate and the pacemaker receives two nerves from the brain stem.  One of these nerves, the sympathetic nerve, releases, nor adrenaline, and causes the heart rate to increases.  The parasympathetic nerve releases acetylcholine and lowers the heart rate.  The hormone adrenaline is released by the adrenal gland and prepares the body to situations of stress by increasing the heart rate and also blood sugar levels.


5.2.4 Explain the relationship between the structure and function of arteries, capillaries and veins.


Arteries carry blood that is pumped out by the thick walls of the ventricles.  They have thick walls because this is when the blood has the highest pressure.  These walls are made of connective tissue, elastic and muscle fibers and a layer of endothelial cells.  The elastic tissue allows the arteries to expand and recoil.  This helps push the blood in the circulation.  Veins have thinner walls.  They carry blood from the body back to the heart.  They have thinner layers of connective, elastic, and smooth muscle fibers.  Capillaries only have one layer of endothelium as their walls.  This allows substances to pass in and out of capillaries for exchange of materials.  They have a very narrow diameter, but there are many capillaries allowing a large exchange of materials.


5.2.5 State that blood is composing of plasma, erythrocytes, leucocytes (phagocytes and lymphocytes), and platelets.


Blood is composed of plasma, erythrocytes, leucocytes (phagocytes and lymphocytes), and platelets.


5.2.6 State that the following are transported by the blood: nutrients, oxygen, carbon dioxide, hormones, antibodies and urea.


Nutrients, oxygen, carbon dioxide, hormones, antibodies and urea are transported by blood.





Topic 5.3 - Pathogens and Disease


5.3.1 Define pathogen.

A pathogen is an organism or virus that causes a disease.


5.3.2 State one example of a disease caused by members of each of the following groups: viruses, bacteria, fungi, protozoa, flatworms and roundworms.

Viruses: Influenza

Bacteria: Cholera

Fungi: Athlete's foot

Protozoa: Malaria

Roundworms: Ascaris eggs contained in contaminated food are swallowed, circulate through the blood stream, reach the lungs, grow into larvae in the nasal cavities, swallowed into the stomach where they grow into adult worms and start the cycle again

Flatworms: Pork tapeworm.


5.3.3 List six methods by which pathogens are transmitted and gain entry to the body.

  1. From the air
  2. Direct contact
  3. Through food
  4. Cuts in the skin
  5. Blood transfusion
  6. Animals and insects.


5.3.4 Describe the cause, transmission and effects of one human bacterial disease.


Diptheria is a bacterial disease the is breathed in and infects the nose, throat, and larynx. The bacteria releases toxins that destry tissues in the heart nerves and glands.

Objectives 5.3


5.3.5         Explain why antibiotics are effective against bacteria but not viruses.

Antibiotics block protein synthesis in bacteria but not eukaryotic cells.  Bacteria and animal cells synthesize proteins in a similar manner, though the proteins involved are not the same.  Those antibiotics that are useful as antibacterial agents use these differences to bind or inhibit the function of the bacterial proteins.  In this way, they prevent the synthesis of new proteins and new bacterial cells without damaging the patient.  Viruses consist of genetic material and are not complete cells.  Antibiotics do not, therefore, block virus reproduction. 


5.3.6         Explain the cause, transmission, and social implications of AIDS.

CAUSE:  The HIV virus causes AIDS, but the origin of the virus is unconfirmed.


TRANSMISSION:  AIDS is commonly transmitted via blood (from mother to child, transfusions, or contaminated needles) or via sexual intercourse.


SOCIAL IMPLICATIONS:  Social implications of AIDS includes the ostracizing of homosexuals (or homophobia), the ostracizing of people with the HIV virus, unease over blood transfusions, or changes in sexual behavior, including reductions in promiscuity and the increase use of condoms. 



Objectives 5.4


5.4.1         Explain how skin and mucous membranes act as barriers against pathogens.


If the pathogens never enter the body, they are never dangerous, and the skin plays a key role in keeping the pathogen from entering the body.  When unbroken, it is almost impossible for any microorganisms to penetrate.  Weak points are those not protected by the skin, but these areas usually have defenses of their own:

Lungs: mucus and cilia transport mucus to the throat

Stomach: very acidic environment

Eyes: tears contain enzymes, which destroy bacterial cell walls

Vagina: mucous and acidic environment

Mucus is often used as a barrier against pathogens through trapping microorganisms and preventing further entry.


5.4.2         Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues.


Leucocytes (white blood cells) are the bodys defense against pathogens after they have entered the body.  They can be found in the blood and in the bodys tissues (lungs).  Several different kinds of leucocytes exist, some of which are phagocytic (will eat any cell which is recognized as foreign through a code on the outside of the cell surface membrane).


5.4.3         State the difference between antigens and antibodies.


Antigen-any molecular configuration that certain lymphocytes recognize as nonself and that triggers an immune response

Antibody (or immunogloblin)-a globular protein that recognizes an antigen; antigen-binding receptor; only B cells make antibodies, then position them at their surface or secrete them


5.4.4         Explain antibody production.


Antibodies are produced by the B-lymphocytes or B-cells, a type of leucocyte.  Like all bloods cells, they are produced in the bone marrow and differentiate here before moving to the lymph nodes.  When an antigen has entered the body, a phagocytic leucocyte will ingest the invader and travel to a B-cell in the lymph nodes.  Here the phagocytic leucocyte will present the antigen to the B-cell.  The presence of another leucocyte (a T helper cell) will then cause the B-cell to clone itself many times.  A few of these cloned cells will remain as memory cells but the majority differentiate into plasma cells.  Plasma cells secrete large amounts of antibodies (but only one kind), which are released into the lymph, which drains into the blood.

Memory cells are kept so that the antibody production will be faster at the next invasion of the same antigen.

T-cells also originate from the bone marrow, but travel to the thymus in an immature state and mature there.  Two types develop: T helper cells and cytotoxic T cells.  The T helper cells play a role in the production of antibodies by B-cells and interact with the phagocytes and the B-cells to come to the production of the correct antibodies.  Cytotoxic T cells directly kill pathogens through cell-mediated response.


5.4.5         Outline the effects of HIV on the immune system.


When infected, the HIV virus will specifically infect and destroy the T helper cells (lymphocytes).  This interferes with their specific defense, their ability to produce antibodies, and often leads to a number of opportunistic diseases like rare forms of pneumonia and skin cancer.

Also, HIV replicates in an immune system cell; therefore, by creating more of itself, it is killing the cells that would normally destroy it. 

Objectives 5.5


5.5.1         List the features of alveoli that adapt them to gas exchange.


  • Large surface area through a dense network of capillaries
  • Thin, creating a short diffusion distance
  • Moist (gases need to dissolve before passing through membranes)
  • Good blood supply to maintain the concentration gradient


5.5.2         State the difference between ventilation, gas exchange, and cell respiration.


Ventilation:  Breathing is the ventilation of the lungs.  In involves muscular movement and therefore requires energy.  Oxygen will diffuse from the air in the lungs into the blood only if the concentration of oxygen in the air in the lungs is higher than that in the blood.  As the oxygen diffuses into the blood, the concentration of oxygen in the air of the lungs decreases.  By refreshing the air in the lungs, the concentration gradient is maintained. 


Gas Exchange: the movement of oxygen from the air in the lungs into the blood and the excretion of carbon dioxide

First, oxygen dissolves in the film of water around the cells that make the walls of the alveoli.  The dissolved oxygen then diffuses through the alveoli cells and through the walls of the capillaries into the erythrocytes in the blood.  The circulation of the blood will take the oxygen away from the area of gas exchange, maintaining the concentration gradient.  Carbon dioxide, produced in the tissues, moves in the opposite direction.  The blood carries carbon dioxide to the lungs where it diffuses from the blood, across the walls of the capillaries and the walls of the alveoli into the air in the lungs.  The circulatory system will continue to bring blood carrying carbon dioxide to the lungs, and ventilation of the lungs will refresh the air so that the concentration gradient is maintained. 


Cell Respiration: process of releasing energy from food (large organic molecules), often using oxygen as the ultimate electron acceptor

Catabolic, energy-yielding pathway; electrons fall from organic molecules to oxygen

Three stages: glycolysis, Krebs cycle, and electron transport and ATP synthesis

Glycolysis: glucose to Pyruvate, occurs in cytoplasm; yields 2 ATP

Krebs: Pyruvate to carbon dioxide and water, occurs in the mitochondrial matrix; involves liberation of electrons and hydrogen, which coenzymes deliver to an electron transport system; yields 2 ATP

Electron transport and ATP synthesis: occurs in the inner mitochondrial membrane, 34 ATP yield


All dependent on each other: ventilation requires energy provided by cell respiration, gas exchange depends on a concentration gradient of respiratory gases maintained by ventilation, and cell respiration is more efficient when using oxygen as its electron acceptor; oxygen needed and carbon dioxide produced are exchanged with the environment via gas exchange.


5.5.3         Explain the necessity for a ventilation system.


It is needed to obtain oxygen for the organism and to get rid of carbon dioxide that is produced as a by-product.  It also helps maintain concentration gradients in the alveoli.  A true ventilation system is needed for larger animals when diffusion of oxygen through cells is not enough to supply all the oxygen needed in the organism. 


5.5.4         Draw a diagram of the ventilation system including trachea, bronchi, bronchioles, and lungs.



5.5.5         Explain the mechanism of ventilation in human lungs including the action of the internal and external intercostal muscles, and diaphragm and the abdominal muscles.


The air in the lungs constantly needs to be refreshed.  The intercostal muscles contract and move the ribcage up and outward.  The diaphragm contracts, flattening it downward.  Both actions increase the volume of the chest cavity, resulting in a decreased pressure, and as a result, the air will flow into the lungs. 

When the intercostal muscles and diaphragm relax, they will return to their original position.  The volume decreases, and an increase in pressure will make the air leave the lungs.  In forced expiration the abdominal muscles contract, increasing the pressure in the abdominal cavity.  This pushes the diaphragm up further. 

Objectives 5.6


5.6.1         State that homeostasis involves maintaining the internal environment at a constant level or between narrow limits, including blood pH, oxygen, and carbon dioxide concentrations, blood glucose, body temperature, and water balance.


Homeostasis-state in which physical and chemical aspects of internal environment are being maintained within ranges suitable for cell activities

Examples of homeostasis: maintenance of oxygen and carbon dioxide concentrations, blood glucose levels, body temperature, and water balance


5.6.2         Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms.


Negative feedback- the control of a process by the result or effect of the process in such a way that an increase or decrease in the results or effects is always reversed

Requires sensors to measure the current situation, which need to pass the information to where the desired value or norm is known and compare the current situation to the norm.  If the two are not the same, a mechanism is activated to bring the current value closer to the norm, usually turning off the mechanism.  The action taken aims at changing a situation so that the action is no longer required. 


5.6.3         State that the nervous and the endocrine systems are both involved in homeostasis.


Both the nervous system and endocrine systems are involved in homeostasis. 


5.6.4         State that the nervous system consists of the central nervous system (CNS) and peripheral nerves and is composed of special cells called neurons that can carry electrical impulses rapidly. 


The nervous system can be divided into the Central Nervous System (CNS) and the peripheral nerves.  The CNS is the brain and spinal cord, and everything else is peripheral.  The peripheral nerve cells are called neurons.  Their function is to transport messages in the form of electrical impulses to specific sites.  This is done very quickly by local depolarization of the cell membrane of the neuron. 


5.6.5         Describe the control of body temperature including the transfer of heat in blood, the roles of sweat glands and skin arterioles, and shivering. 


Mammals and birds have thermoreceptors in their skin and in the heat center in their brain, monitoring temperature changes in the environment and in blood temperature. 

If the organism is too hot, it can cool down by:

  • Vasodilation: the blood vessels in the skin become wider which increases the flow of blood to the skin; as a result the skin becomes warmer which increases heat loss to the environment.  Convection and radiation are increased. 
  • Sweating: evaporation of fluid from the skin; change of phase from liquid to gas; requires energy which is taken from the body; panting has the same effect
  • Deceased metabolism: any reaction produces heat as a by product
  • Behavior adaptations (ex, birds bathe, rodents retreat into burrows, dogs dig holes)


If the organism is too cold, it can warm up by:

  • Vasoconstriction: the blood vessels in the skin contract, decreasing the flow of blood to the skin; the skin becomes colder, reducing the heat loss to the environment; convection and radiation are decreased
  • Shivering: any reaction will produce heat as a by product; muscular contractions produce a lot of heat
  • Increase metabolism: increase production of heat
  • Fluffing of hair or feathers: increase the thickness of the insulating layer of air
  • Thick layer of brown fat or blubber
  • Special hair structure


5.6.6 State that the endocrine system consists of glands which release hormones that are transported in the blood.

The endocrine system consists of glands which release hormones that are transported in the blood.


5.6.7 Explain the control of blood glucose concentration, including the roles of glucagon, insulin, and alpha and beta cells in the pancreatic islets.

Insulin and glucagon regulate the sugar level in the body. These two hormones are manufactured in the pancreas and through circulation are carried to the liver where they perform their functions. Enzymes that convert glucose to glycogen though a condensation reaction are stimulated by Insulin. Enzymes that hydrolyze glycogen to glucose are stimulated by glucagon. Receptors in the pancreas are sensitive to the changes in sugar level, thus releasing the necessary requirements of insulin and glucagon depending on the needs of the body. The beta cells found in the islets of the pancreas make insulin and the alpha cells make glucagon.


5.6.8 Define excretion.

Excretion is the removal of excess water, solutes, and wastes, and some harmful substances from body by way of a urinary system or glands.


5.6.9 Outline the role of the kidney in excretion and the maintenance of water balance.

The human body contains two kidneys located at the back of the abdominal cavity. A tube called the ureter connects each kidney and runs downward to empty in a sac-like structure called the urinary bladder. The renal artery supplies each kidney with urea or other unwanted material and also oxygen. The renal vein leaves the kidneys with blood that contains the correct amounts of urea, salts and water. Carbon dioxide is prevalent in the renal vein and this is released by the kidney as respiratory waste. The urinary bladder opens up to two things: the urethra which empties urine to the outside of the body and the sphincter muscles which guard the emptying of urine and provide that urination can be controlled under normal circumstances.




5.7 Reproduction

Alisha George


5.7.1 Draw diagrams of the adult male and female reproductive systems.









5.7.2 Explain the role of hormones in regulating the changes of puberty (testosterone, estrogen) in boys and girls, and in the menstrual cycle (follicle stimulation hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone).

From birth to the age of ten, testosterone level is very low. It increases sharply after that and begins puberty in males. This is when sperm production takes place. Testosterone stays at high levels until the age of 40-50, and then it gradually decreases. It is also responsible for voice change, hair growth in certain parts of the body, and the building of muscles. Estrogen leads to the production of eggs, which leads to the menstrual cycle. In the menstrual cycle, FSH is secreted by pituitary increases; this is responsible for the growth of an oocyte (an immature egg) and its follicle. Two weeks after the start of menstruation, ovulation occurs due to a sudden and sharp increase in LH from the pituitary gland. It also causes the empty follicle to develop into the yellow body which starts releasing the hormone progesterone. This is responsible for maintaining and thickening the endometrium (wall of the uterus) in preparation for implantation.


5.7.3        List the secondary sexual characteristics in both sexes.

Secondary sexual characteristics in males are the growth of hair in certain parts of the body, change in voice, and building of muscles. In females, it is the growth of hair in certain places and the beginning of the menstrual cycle.


5.7.4 State the difference between copulation and fertilization.

Copulation is the physical contact between the male and female reproductive structures that is needed for the sperms to move from the male to the female but does not necessarily result in fertilization due to the use of a contraceptive or being infertile. Fertilization is the fusion of the male and female nuclei to produce the zygote.


5.7.5 Describe early embryo development up to the implantation of the blastocyst. Fertilization occurs and results in the formation of the zygote which starts a series of cell divisions. (Dividing process=cleavage). Cleavage continues, with the embryo becoming a ball of cells by the time is reaches the uterus about 3 to 4 days after fertilization. By about 1 week after fertilization, cleavage has produced an embryonic stage called the blastocyst. During the next 5 days, the blastocyst implants into the endometrium.


5.7.6 State that the fetus is supported and protected by the amniotic sac and amniotic fluid.

The fetus is supported and protected by the amniotic sac and amniotic fluid.


5.7.7 State that materials are exchanged between the maternal and fetal blood in the placenta.

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


5.7.8 Outline the process of birth and its hormonal control, including progesterone and oxytocin.

Labor, delivery and afterbirth mark the three stages of birth. Labor is marked by contractions of the uterus; it is stimulated by a hormone called oxytocin, which is released by the pituitary gland. Dilation of the cervix also occurs at this time. Later, the cervix becomes fully dilated. The most powerful contractions are during the next stage, delivery. Placenta, along with other fluids and blood come out after the baby. This placenta that comes out marks the afterbirth. Labor and delivery are controlled by the actions of oxytocin, progesterone, and estrogen.


5.7.9 Describe four methods of family planning and contraception.

There is sterilization. In this, the female gets a tube legation where the oviducts are tied so the sperm can't reach the egg, or the male gets a vasectomy where the sperm ducts are cut and prevents the release of sperm. Another method is pills. These prevent ovulation by inhibiting FSH and LH. The use of a male condom prevents the release of sperm into vagina. Another method is intrauterine device (IUD) which prevents fertilization or implantation. A behavioral form of contraception is abstinence.


5.7.10 Discuss the ethical issues of family planning and contraception.

Some people believe it is unethical to abort a baby, that is, to kill a fetus formed after fertilization. Other people think it is the right of the woman carrying the fetus to decide what to do with it. Some people, such as Mormons, believe that it is right to produce as many children as possible. Thus, for them any type of family planning is unethical.


5.7.11 Outline the technique of amniocentesis.

Amniocentesis is where some amniotic fluid is drawn by a syringe through the abdomen of the mother. The cells are then grown on a tissue culture to be studied to create a karyotype and are then studied to find out if the are any abnormalities.  It can be used to diagnose nearly 400 conditions from chromosomal abnormalities to biochemical disorders.


5.7.12 Outline the process of in vitro fertilization (IVF).

Eggs are removed from the ovaries of a woman by suction through the vagina. They are sucked into a syringe and placed in a glass dish. The eggs are then cleaned to remove blood and other unwanted material. The egg is then incubated. Then, sperms are added and fertilization takes places and the embryo is then transferred through the vagina to the uterus.


5.7.13 Discuss the ethical issues of IVF.

This is, of course, an artificial process. If one believes that those who cannot have children are meant not to have children, one would not support IVF. In addition, IVF often includes the fertilization of many eggs in order to insure that one will produce a healthy baby. The other zygotes, however, are often thrown away, which is a form of abortion. If one believes abortion is wrong, then one would have to deliver all the babies that are produced via a test tube. This is why mothers who do IVF often have many children in one delivery.