IB Biology/Human Health and Physiology

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[edit]

Topic 6: Human Health and Physiology[edit]

Digestion[edit]


Explain why digestion of large food molecules is essential.

  • The foods that we eat are not necessarily usable in their current form by our tissues. They have to be broken down and rearranged to "human versions".
  • original ingested molecules are often too large to be absorbed by the villi in the small intenstine so they must be broken down to be absorbed.

Explain the need for enzymes in digestion. Without enzymes digestion would still occur, however at a significantly slower pace.

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

  • Enzyme: Salivary Amylase | Pepsin | Pancreatic lipase
  • Source: Salivary glands | Wall of Stomach | Pancreas
  • Substrate: Starch | Proteins | Triglycerides (fats or oils)
  • Products: Maltose | Small polypeptides | Fatty Acids and Glycerol
  • Optimum pH: pH 7 | pH 1.5 - 3 | pH 7

Draw a diagram of the digestive system. Digestive system diagram en.svg

Outline the function of the stomach, small intestine and large intestine.

  • Digestion of proteins begins in the stomach, where the process is sped up by the enzyme pepsin. Harmful bacteria that has entered the body can be killed by the stomach's acidic environment(pH 1.5-2).
  • In the small intestine, enzymes complete the process where the end matter is absorbed by villi.
  • The large intestine absorbs water and passes the unabsorbable rest off as feces.

Distinguish between absorption and assimilation.

  • Absorption is when food molecules pass through a layer of cells such as passing through the villi.
  • Assimilation is when food actually becomes part of the body's tissue.

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

  • It increases the surface area of the small intestine
  • The epithelium has a surface of only a thin layer of cells.
  • Protein channels in the microvilli allow for quick absorption of foods via facilitated diffusion and active transport.
  • Blood capillaries close to epithelium making it only a small distance for diffusion to occur.

The Transport System[edit]


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

see labelled diagram here

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

  • The right atrium relaxes for the blood to be received from the superior and inferior vena cava.
  • The atrioventricular valve opens for blood to go to the right ventricle by the contracting atrium.
  • The right ventricle then relaxes to receive the blood from the atrium. Then it contracts in order to open up the pulmonary valves. Deoxygenated blood goes through to the pulmonary artery, where it enters the lungs so that the blood will be oxygenated.
  • Blood returns from the lungs to the heart through the pulmonary veins, now oxygenated.
  • The left atrium relaxes to receive it and then contracts to pump blood and open the atrioventricular valve where then the blood goes to the relaxed left ventricle.
  • The left ventricle contracts to open the semilunar valves and then the blood goes through the aorta to the rest of the body.

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

  • The pacemaker is located in the wall of the right atrium at the Sinoatrial node (SAN). Each time the pacemaker sends out a signal, the heart carries out a contraction or a beat. The heart beats by itself (myogenic). Nerves and hormones can transmit messages to the pacemaker: Sympathetic nerve secretes adrenaline (also known as "epinephrine") which carries messages from the brain to the pacemaker telling the pacemaker to speed up the beating of the heart. Another nerve tells it to slow it down.

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

  • Arteries:
  • Thick wall to withstand high blood pressure.
  • Thick outer layer of longitudinal collagen and elastic fibers.
  • Thick layers of circular elastic and muscle fibers.
  • walls stretch and recoil for the blood to go from the heart to the small intestine.
  • Narrow lumen to help maintain the high pressure..
  • Veins
  • Thin layers with a few circular elastic and muscle fibers.
  • Thin walls to allow the muscles to squeeze the veins
  • Thin outer layer of longitudinal collagen and elastic fibers.
  • Valves for blood to stay and not flow backwards.
  • Wide lumen to accommodate for the slow flowing of blood
  • Capillaries:
  • Has pores to allow plasma and phagocytes to diffuse in or out.
  • Connects the vein and artery
  • Moist and thin for diffusion and has a short diffusion distance.
  • Narrow diameter and large quantity allow for a large exchange of materials through diffusion

The blood is composed of plasma, erythrocytes, leukocytes (including phagocytes and lymphocytes) and platelets. What is the function of each?

  • Plasma
  • Plasma is largely water and makes up about 55% of the total blood volume.
  • This is the main transporting part of blood and takes advantage of the solvent properties of water.
  • Composed of:
  • Salts (Potassium, Sodium, Chloride, Magnesium, Bicarbonates)
  • Gases (Oxygen, Carbon Dioxide)
  • Plasma Proteins (Albumin [buffer], Fibrinogen [clotting])
  • Nutrients (Glucose, Amino Acids)
  • Waste (Urea)
  • Erythrocytes
  • Red Blood Cells
  • Transports oxygen and assists the transport of carbon dioxide.
  • Leucocytes
  • White blood cells
  • Phagocytes
  • White blood cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells.
  • Lymphocytes
  • White blood cell in the vertebrate immune system.
  • Large granular lymphocytes include natural killer cells (NK cells). Small lymphocytes consist of T cells and B cells.
  • Platelets
  • Cells involved in hemostasis, leading to the formation of blood clots.


Identify at least 6 things that are transported by the blood.

  • Nutrients
  • Oxygen
  • Carbon Dioxide
  • Hormones
  • Antibodies
  • Urea.

Pathogens and Disease[edit]


Define pathogen

  • Pathogen: an organism or a virus that causes a disease.

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

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

  1. Airborne/inhalation
  2. Direct contact
  3. Cuts
  4. Ingestion of contaminated food or water
  5. Sexual intercourse
  6. Insects
  7. Blood transfusions

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

  • Cholera: is a waterborne disease caused by the bacterium Vibrio cholerae.
  • Cause: Cholera is caused by the bacteria Vibrio cholerae which produces potentially lethal secretory diarrhea.
  • Transmission: Cholera is transmitted through the ingestion of feces contaminated by the bacteria. The contamination usually occurs when sewage gets into drinking water. It's a huge problem in developing countries, which lack a developed sewage system, and also right after natural disasters such as floods. The recent Tsunami brought fears of Cholera.
  • Effect: Cholera causes a lethal secretory diarrhea and dehydration. Other symptoms may include cramping, fever, and nausea.

Explain why antibiotics are effective against bacteria but not viruses.

  • Antibiotics are drugs which kill or slow the growth of bacteria. Antibiotics block metabolic pathways of bacteria, inhibiting cell wall formation and protein synthesis, resulting in the death of foreign bacteria. However, viruses are not alive and utilize the organisms host cells to replicate, which are not targeted by antibiotics. In order to kill a virus by antibiotics human cell has to be killed as well

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

  • AIDS or Acquired Immunodeficiency Syndrome is a collection of symptoms and infections caused by infection with the human immunodeficiency virus (HIV).
  • Transmission: HIV is transmitted via direct contact of the mucous membrane with a bodily fluid containing HIV such as blood, semen, or breast milk. The transmission could be through anal or penetrative sex, blood transfusion, contaminated needles, or during pregnancy. Most researches think that the virus originated from the Sub-Sahara, but the exact cause is unknown.
  • Social Implications Fear and apprehension for those associated with the disease, the lifestyle associated with the disease is attacked, trouble getting a job or even getting health insurance- distanced from society

Defense Against Infectious Diseases[edit]

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

  • The skin and mucous membranes form a barrier that prevents most pathogens from entering the body. The other layers of the skin are tough and form a physical barrier. These dry, keratinised layers of skin discourage pathogen growth. The skin also produces a thin layer of acid and oils. Mucus contain an enzyme called lysozyme which kills bacteria.

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

  • Phagocytes are a type of leucocyte which ingest and destroy foreign matter through phagocytosis.
  1. They can easily move through the walls of blood capillaries and the site in which there is an infection.
  2. A phagocyte comes in contact with pathogen cells and does not recognize the glycoprotein struture on its cell wall.
  3. The pathogen is then ingested through endocytosis. Plasma membrane forms around pathogen.
  4. Pathogen vacuole then binds with lysosome containing digestive enzymes which break down the pathogen.
  5. Large numbers of phagocytes form pus.

State the difference between antigens and antibodies.

  • Antigens are macromolecules that elicit an immune response by lymphocytes.
  • Antibodies are proteins secreted by plasma cells that bind to a particular antigen and mark it for elimination.

Explain antibody production.

  • Antibodies are made by lymphocytes, which recognize an enormous number of antigens, but each individual cell recognizes only one type of antigen. Each lymphocyte puts some of the antibody that it makes into its cell surface with the antigen-combining site projecting outwards. When a pathogen enters the body, its antigens bind to the antibodies in the cell surface of one type of lymphocyte. The selected lymphocyte proliferates to give rise to a clone of identical cells bearing receptors for the selecting antigen. Some of the cells develop into short-lived plasma cells that secrete antibody specific for the antigen. Others develop into long-lived memory cells that can respond rapidly upon subsequent exposure to the same antigen.

Outline the effects of HIV on the immune system.

  • HIV attacks T-cells which are part of the immune system that are important for the formation of Beta lymphocytes. The virus enters the T-Cells and replicates there. As reproduction increases, the cell breaks up and the virus RNA is spread to other T-cells. The virus keeps infecting and killing other T-cells, paralyzing the immune system. This enables other organisms usually kept under control by the immune system to be able to affect the body.

Discuss the cause, transmission and social impacts of AIDS

  • The cause of AIDS is that the HIV retro-virus develops further enough to change into AIDS.
  • HIV doesn’t survive outside of the body and can’t easily pass through the skin. Transmission involves the transfer of body fluids from an infected person to an uninfected one.
  1. Through small cuts or tears in the vagina, penis, mouth or intestine during vaginal, anal or oral sex.
  2. In traces of blood on a hypodermic needle that is shared by intravenous drug abusers.
  3. Across the placenta from a mother to a baby, or through cuts during childbirth or in milk during breast feeding.
  4. In transfused blood or with blood products such as Factor VIII used to treat haemophiliacs.

Social implications

  • Friends and families suffer grief.
  • Families become poorer if the individual with AIDS was the wage earner and is refused life insurance.
  • Individuals infected with HIV may become stigmatized and not find partners, housing or employment.
  • Sexual activity in a population may be reduced because of the fear of AIDS.

Gas Exchange[edit]


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

  • Ventilation: Is the process of inhaling and exhaling, with oxygen entering the alveoli (large surface area).
  • Gas exchange: Process of exchanging one gas for the other between the alveoli and capillaries. (Carbon dioxide for oxygen).
  • Cell Respiration: The chemical process occurring in the mitochondria where energy is released as ATP.

Explain the necessity for a ventilation system.

  • A ventilation system is needed in order to obtain oxygen for living organisms and to get rid of carbon dioxide. Surface diffusion utilized by many smaller organisms is not sufficient in supplying the oxygen needs of the body. It is also needed to maintain a concentration gradient in the alveoli.

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

  1. Cells secrete fluid making the inner surface moist.
  2. Increase in surface area.
  3. Single layer of cells allowing for short diffusion distance
  4. Dense network of capillaries near the surface.

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

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

  • (You can try this in an exam room if you can't remember.)
  • When we inhale, the diaphragm moves down and becomes flat because abdominal muscles relax(allowing for more air). The volume of the thorax increases, air flows into the lungs. External intercostal muscles contract.
  • When we exhale, abdominal muscles contract and the diaphragm becomes dome-shaped, moving up. The volume of the thorax decreases and intercostal muscles contract causing pressure to increase. Air flows out to equalize pressure gradient.

Homeostasis and Excretion[edit]


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 involves maintaining the internal environment at a constant level between narrow limits. This includes blood pH, oxygen and carbon dioxide concentrations, blood glucose, body temperature and water balance.

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

  • Homeostasis involves maintaining the body in a environment between narrow limits by negative feedback mechanisms. Negative feedbacks contain a detector which measures the value of a feature to be controlled. This sends information to an effector, which then takes action.

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

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

  • The nervous systems consists of central nervous system and peripheral nerves and is composed of special cells called neurons that can carry electrical impulses rapidly.

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

1) Blood near the skin exchanges heat with the environment to preserve 37°C temperature.

2) Vasoconstriction can decrease blood flow to the skin, preserving heat in cold weather. vasodilation will cause an increase of blood flow close to the skin, which will cool your body.

3) Sweating can cool the body as moisture on skin evaporates.

4) Shivering produces muscle heat.


State that the Endocrine systems consists of glands which release hormones that are transported in blood.

The Endocrine systems consists of glands which release hormones that are transported in blood.'

Explain the control of blood glucose concentration, including the role of glucagons, insulin, Alpha and Beta cells in the pancreatic islets. 1) Glucagons - released by Alpha cells in the pancreatic islets when blood sugar is low, it transforms stored glycogen into glucose that enters the blood stream. 2) Insulin - released by Beta cells in the pancreatic islets when blood sugar is high, it transforms glucose in blood to stored glycogen .

Define excretion.

  • Excretion is the process of eliminating from an organism waste products of metabolism and other products which are of no use.

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

  • The human body has two kidneys located in the back of the abdominal cavity. Each kidney is connected to the urinary bladder by the ureter which dumps toxins filtered by the kidneys into it, along with excess water. The renal artery will supply the kidney with urea and unwanted materials, which it also dumps in the bladder, and sends of the correct amounts of urea, salts, and water through the renal vein. Without the kidney the excess materials would not be able to be filtered out and may cause harm to the body.

Reproduction[edit]


Draw diagrams of the adult male and female reproductive systems. female:[1] male: [2]

Explain the role of hormones in regulating the changes of puberty (testosterone, estrogen) in boys and girls, and in the menstrual cycle (FSH, 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, 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 secreted by pituitary gland increases, this is responsible for the growth of an oocyte (an immature egg) and it's 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 (corpus luteum) which starts releasing the hormone progesterone. This is responsible for maintaining and thickening the endometrium(wall of the uterus) in preparation for implantation.

Reasons for the levels of FSH and LH rising at the end of the reproductive phase.

Estrogen and progesterone levels remain low as no follicles produce estrogen at the end of the reproductive phase. At this stage, this leads for FSH and LH production to not be inhibited. The high levels of FSH and LH do not cause hyper-ovulation in women because the ovary becomes insensitive to FSH and the primary follicles have all degenerated or have all been used.


Reasons for expecting the number of births of male and female babies to be equal.

Gender is determined by sex chromosomes. The chromosomes in females are XX and those in males are XY. Therefore, eggs carry an X chromosome, and a sperm carries either an X or a Y chromosome, as they separate during the first division of meiosis in males. Half of the sperm carry X chromosome and half carry a Y chromosome, therefore the chances that the sperm, which fertilizes the egg, is carrying an X chromosome as opposed to a Y chromosome are the same.


List the secondary sexual characteristics of both sexes.

Secondary sexual characteristics in males are the growth of pubic and armpit hair, growth of the larynx causing a deepening in voice, and building of muscles. In females, it is the growth of pubic hair, vagina, breasts, pelvis, fat deposits in thighs and buttocks, secretion of fluids in vagina, and the beginning of the menstrual cycle.

Explain how levels of other hormones control the FSH level during pregnancy.

Another hormone, HCG, stimulates the maintenance of the corpus luteum and as a result, the production of progesterone. The levels of progesterone rise during pregnancy and inhibit FSH production.

Discuss how many embryos fertility centers should be allowed to transfer.

Reducing the amount of embryos allowed to be transferred reduces the chance of having multiple births, which is beneficial as these types of births increase health risks for both the mother and the child, or children. Restricting the number of embryos allowed for transfer to two would prevent almost all multiple, especially triplet, births from occurring. In older mothers, however, there is a lesser risk of multiple births; therefore, more embryos could be transferred to them.


State the differences 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.

Describe the early embryo development up to the implantation of the blastocyst.

Fertilization occurs, resulting in mitotic divisions or cleavage divisions which lead to the formation of a ball of cells called the morula. The morula reaches the uterus about 4 days after fertilization. Slightly unequal divisions continue until the 7th day, causing a fluid filled spaced in the middle of the morula to form. This is the blastocyst. The outer cells of the blastocyst are called trophoblast and will imbed itself in the endometrium.

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.

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.

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 as levels of progesterone decrease by the pituitary gland. Oxytocin causes dilation of the cervix. 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.

Describe four methods of family planning and contraception. [Chemical, mechanical and behavioral examples should be mentioned].

  • Chemical - Contraceptive pills prevent ovulation by inhibiting FSH and LH.
  • Mechanical - The use of a male condom prevents the release of sperm into vagina. Another method is intrauterine device (IUD) which prevents fertilization or implantation. 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.
  • Behavioral - Abstinence has a 100% success rate of preventing pregnancy. Timing copulation with a woman's ovulation cycle is also effective at preventing pregnancy.


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 that was formed after fertilization. Other people think it is the right of the woman carrying the fetus to decide what to do with it.

Ethical considerations on the use of contraceptives may include: considerations about overpopulation, considerations about the future of the child(ren), religious considerations. Some religions teach that it is wrong to interfere with natural processes such as reproduction.

Outline the technique of amniocentesis.

Amniocentesis is where some amniotic fluid from the amniotic sac 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 there are any abnormalties.

Outline the process of in vitro fertilization (IVF)

  • 1. Various drugs are injected one a day for three weeks to stop the menstral cycle.
  • 2. Large doses of FSH are injected to stimulate ovaries to develop many follicles.
  • 3. HCG hormone is injected 36 hrs. before cell collection, causing the eggs to mature and loosen.
  • 4. Eggs are removed from the ovaries of a woman by suction through the vagina and are placed in a glass dish. The eggs are then cleaned to remove blood and other unwanted material. The egg is then incubated.
  • 5. A male provides sperm which is collected by a doctor.
  • 6. The healthiest sperm are selected and mixed with the egg, to force fertilization.
  • 7. Two or three eggs are selected and implanted in the uterus through the vagina.
  • 8. After a few weeks, a pregnancy test is administered.
  • 9. Later in the pregnancy, a scan is conducted to find a heartbeat.

Discuss the ethical issues of IVF.

  • For IVF - Childless and infertile couples are provided a means to have children. Suffering due to a genetic disease of infertility is reduced.
  • Against IVF - There is a high probability that children conceived using IVF from infertile parents would inherit this genetic disease, going against natural selection. Spare embryos are killed or donated to stem cell research. Once fertilized embryos have been implanted in the uterus, the parents have the option of choosing which eggs shall be removed, essentially allowing humans the right to define life and death. Those who do not remove extra eggs from the uterus have multiple births, increasing the risk of health problems for the fetus.