Biologydidactics

01/08/2026

Lesson 142: Vitamins
Contrary to minerals, vitamins are organic compounds needed for vital functions in the human body. Vitamins can be divided into fat-soluble (Vitamin A, D, E and K) and water-soluble (Vitamin B complex and C). Vitamin C and E are antioxidants.
Vitamin D is required for a normal absorption of calcium in food. Lack of this substance will cause rickets, which supposedly occurs only in children. If you see that you are bandy-legged, however, you might want to increase your intake of vitamin D. The vitamins (calciferol) are present in a huge amount of margarine. However, margarine can also cause atherosclerosis, particularly if it contains trans-fatty acids. Luckily, vitamin D is something the body can synthesize if the skin is exposed to sunlight. This increases the risk of skin cancer. Vitamin D is also abundant in fatty fish. Unfortunately, these also load up dioxins, PCB and other fat-soluble environmental poisons in their tissues and in many areas they are not recommended for frequent consumption. Fat fish is hard to preserve. Desiccation in the sun makes the fat turn rancid and even as frozen it lasts for a limited time span. In northern Europe fat fish is effectively preserved by smoking in special ovens and smoked fish can be stored at low temperature for at least a month.
Vitamin A as retinol, retinal and retinoic acid, is necessary for the production of the photopigment rhodopsin. Deficiency manifests itself as night blindness that may progress to retinal atrophy and permanent blindness. If you can’t see in the dark, you have a vitamin A deficiency. Vitamin A is abundant in liver and fish. Many vegetables and fruits contain carotenes that the body can transform into vitamin A. Carrots, sweet potatoes and mango fruits are rich vegetarian sources of carotenes. However, excess vitamin A is poisonous so you may want to limit your consumption of fruits, vegetables and dairy products. Avoid polar bear liver. 200 Grams of it contains your entire annual requirement!
Vitamin C or ascorbic acid is an antioxidant required for several biochemical reactions in the body. Biosynthesis of the unusual amino acid hydroxyl-proline in connective tissue requires vitamin C. Vitamin C deficiency manifests itself as scurvy – bruises, bleeding gum and teeth falling out. The daily requirement can easily be supplied by eating a citrus fruit or paprika per day. It is now claimed that a lot of vitamin C can prevent colds and cure cancer. For this effect, you must take it in very large doses. Fortunately, it is not dangerous to overdose – the excess just flushes out with the urine. To some extent, vitamin C can be stored in the body – mainly in the adrenal glands.
Vitamin B is a complex of different compounds mostly required for an effective energy metabolism in cells.
B1, thiamine is needed for coenzymes involved in the Kreb’s cycle. Beriberi is a feared disease caused by thiamine deficiency. Thiamine is present in liver, whole grains, yeast and nuts. Or, if you are willing to risk trichinosis, you can get it in pork.
B2, riboflavin is used to form the coenzyme FAD.
B3, niacin is used to form the coenzyme NAD.
B5, pantothenic acid forms part of Coenzyme A.
B6, pyridoxine is needed for coenzymes in amino acid and fatty acid metabolism.
Biotin is needed for fatty acid synthesis and amino acid metabolism.
Folic acid has an important function in nucleic acid synthesis. It is particularly important for the normal development of the fetus. Folic acid is sensitive to UV light and is thought to be the factor providing dark-skinned individuals with an edge of advantage to fair-skinned among people living close to the equator.
B12, cyanocobalamin is necessary for a normal uptake of iron from the intestine. Contrary to other vitamins, it is only present in animal and dairy products. Vegans forgetting to take their vitamin B12 supplements may suffer from megaloblastic anaemia. To have such a serious disease and never be allowed to eat beef or ice cream is just too much.

27/07/2026

Lesson 141: Minerals

Like all biological life, the human body is made up of chemical elements. Normal body functions require access to a limited number of elements in their ionic form. Some transition elements, most prominently iron, copper and zinc make up prosthetic groups of enzymes and other important proteins in the body.
The most important bioelements, minerals and trace elements are summarized in the periodic table.
The table shows the recommended daily intake (RDI) of the most important minerals for the human body functions.

11/07/2026

Lesson 140: Carbohydrates
In most diets, carbohydrates make up the quantitatively largest part of the total energy intake. Most individuals fall within the range 45-75% carbohydrate in the dietary energy intake. Biologically, there is no lower limit for carbohydrate and none of them is essential for human body functions. Some diets with as little as 5-10% carbohydrate as an energy source seem to work. However, the type of carbohydrates ingested has an impact on health. The total rise in blood glucose level after eating a food item is referred to as the glycemic index. The faster the carbohydrates of a food item are broken down and glucose enters the blood, the more strain will be put on the body functions regulating the blood glucose. Excess energy intake as carbohydrates is effectively transferred into fat tissue and in the long run, there will be an increased risk for obesity and type 2 diabetes.
There is no correlation between GI index and energy content of food, so a low GI index may not necessarily mean something that will prevent you from increasing in bodyweight.
The table shows the glycemic index (GI) and energy content for some common food items. Pure glucose has the reference value of 100.
The diagram shows changes in blood glucose after ingestion of two food items of a different glycemic index. The diagram’s time axis can be divided into three zones with regard to scale.

02/07/2026

Lesson 139: Dietary fat

Certain substances in food are tremendously dangerous and cholesterol is among them. Cholesterol is the substance that has ruined pork’s reputation. Although it is a substance that the body needs, it tends to build up plaque on the interior walls of arteries. It is as if the Dartford tunnel gets narrower each time a certain type of vehicle passes it and finally, it is all clogged up causing a major heart attack Brains are exceptionally high in cholesterol (> 2 000 mg/100g) but nowadays rarely eaten due to the risk of prion diseases.
The easiest way to find out if a food contains cholesterol is to taste it. If it tastes good, it is cholesterol. Fortunately, cholesterol ingested as cholesterol is fairly harmless. Most of it is excreted by the liver as bile salts. It is the cholesterol the liver manufactures from saturated fat that is widely considered to be the main problem. Again, saturated fats mainly occur in palatable food. It has a higher melting point and is thus usually solid at room temperature. If saturated fat will be converted into cholesterol transported by High-Density Lipoprotein (HDL) on a one-way tour to the liver and excreted as bile salt or transported to places in the body where needed by Low-Density Lipoprotein (LDL) or, even worse, VLDL (Very Low..), is a matter of genetic constitution and lifestyle. Excess LDL (and particularly VLDL) may cause plaque in susceptible artery walls. Formation of plaques may, in addition to excess cholesterol, also be caused by inflammatory reactions in the artery walls. It is widely believed that unsaturated fat in vegetarian oils is healthy, but omega-6 fatty acids may play a role in promoting inflammatory reactions while omega-3 fatty acids may prevent this. Both types of fatty acids are actually needed by the body as the essential fatty acids linoleic acid (omega-6) and linolenic acid (omega-3). It is the ratio between omega-6 and omega-3 that is critical and something to be kept as low as possible. During the palaeolithic time, this ratio was close to 1, but in a modern western diet based mainly on junk-food, it may have drifted away to values exceeding 30.
The table shows some of the food items that contain most cholesterol.
Annotated A in the diagram represents a hunter’s and gatherers diet with an omega-6 to omega-3 ratio close to 1.
B in the diagram represents a traditional Inuit diet based on seafood and low in carbohydrates.
Picture 3 shows the complexity of different food factors contributing to cardiovascular diseases. Try to figure out what you consider to be the most detrimental food items.

03/04/2026

Lesson 138: A balanced diet

The human body is adapted for an omnivorous diet based on carbohydrates as the main energy source and in most people, this makes up for at least 50% of the total energy consumption. Since the origin in Africa some 200 000 years ago, our species has adapted to most types of environments on earth and there is a wide range of flexibility that seems to have worked out well for several millennia. Among Inuits living in a very cold climate, a seemingly carbohydrate deficient diet of fish and marine mammals can work out well as long as the fats are polyunsaturated. In some parts of the world and among vegetarians, the diet can be very low in proteins.
A recommended daily intake of protein is 1 gram per kilogram body weight. Thus, proteins make up for 15% of the energy intake but its major function is for repair and maintenance of body cells and the production of blood proteins. To keep the body hydrated, water is needed in a quantity of at least 1.5 kg per day and often quite a lot more if living in a hot climate and/or having a significant amount of physical activity in the daily life. To obtain a balanced diet there are also organic compounds called vitamins and inorganic minerals needed for different functions in the human body.
Protein
Proteins are macromolecules made of 20 different amino acids linked together into long chains (polypeptides). Most of those building blocks are exchangeable in transamination reactions. However, there are amino acids the body does not have the biochemical machinery to produce and those are the essential amino acids. As long as the diet contains a modest amount of protein of animal origin, there will be a good supply of these. In a strict vegetarian or vegan diet some of these may be scanty so just like a typograph running out of certain letters, the body’s protein synthesis machinery may run out of certain amino acids. To avoid kwashiorkor (a protein deficiency disease), the vegetarian may thus have to consume huge numbers of beans.
The picture shows the distribution of essential amino acids in protein-rich vegetarian food.

28/02/2026

Lesson 136: Energy requirements of the body
One can see that regardless one is walking or jogging a certain distance, virtually the same amount of energy is spent. 30 minutes of cycling, however, can bring you further than 5 km in 30 minutes and biking is quite an energy-efficient mode of transportation that actually can get you somewhere, while the joggers mainly run around in circles. A sprinter probably hits the limit of possible energy turnover of a human body, but the effort lasts just for 10-20 seconds and cannot be maintained for a sustained period. The amount of extra energy expenditure by normal physical exercise may not seem impressive (corresponds to the energy content of 20-30 gram of butter), but regular exercise usually has a beneficial effect on health and it may reduce the risk of a slow and steady weight gain. Trained muscles do also have more mitochondria, better blood supply and use more energy than the muscles in an untrained individual. The heart will also be increasingly efficient in pumping blood around the body.
If more energy is obtained through food than the energy turnover requires, the excess energy will be stored as body fat to be used during periods when food intake provides an amount of energy that is insufficient for the body’s energy expenditure. A moderately active adult man may utilize 12 000 kJ (2870 kcal) per day while a woman of similar activity level utilizes 9 000 kJ (2150 kcal).

The body of a lean, adult man contains three pools of chemical energy:
A blood glucose level at 5.0 mmol/L (0.90 g/L) in 6 L of circulating blood.
125 g of glycogen stored in liver and muscles
11 kg body fat
Glucose and glycogen contain 4.1 kcal/g and human body fat contains 7.7 kcal/g
For how long will each of these energy pools last if the daily energy expenditure is 2870 kcal.

Blood glucose ……………………….
Glycogen …………………………
Body fat …………………………

17/02/2026

Lesson 135: Diet and nutrition

It has long been known that food is something that is essential to life. Unfortunately, scientists have recently found that food is also a major cause of death. Food causes cardiovascular diseases, cancer and obesity and as soon as famine is eliminated, type II diabetes is not far away. Even the best food, if you eat too much of it, will kill you. Our ancestors did not live long enough to encounter those problems. A diet most similar to what our ancestors have survived on as hunters and gatherers for hundreds of thousands of years is probably the diet to which the human physiology is best adapted. A diet of nuts, berries and brown rice sometimes reinforced with dried meat or fish, will keep you healthy. If you are hungry all the time and never eat anything that tastes good, you are probably on the right track and can look forward to a long and interesting life
Energy requirement of the body
To obtain chemical energy is the main reason why we need food. Energy can be measured as calories (cal) or in Joule (J). For practical reasons, the energy content of food is measured in kilocalories (kcal) or kilojoules (kJ). 1 kcal equals 4.184 kJ. Per definition, it takes 1 Joule to heat one gram of water by 1oC. The basal metabolic rate (BMR) is the minimal amount of energy required to maintain the body’s vital functions. The BMR is highest in infants, decreases rapidly during growth, levels out by the age of 20 and then slowly declines by advancing age. BMR should not be confused with daily energy expenditure which is the total amount of energy the body uses up during a 24 hour period and as it on top of BMR also includes energy spent on different types of physical activity, it is a value that usually exceeds the BMR. Similar to BMR, daily energy expenditure is related to age, but also gender and level of physical activity during a day.

The intensity of physical activity is sometimes measured in watt (W). Watts are convertible to calories and joules in that 1-Watt effect during one second equals one Joule (1 Ws = 1 J = 0.24 cal)
The following values apply for the metabolic energy transfer (MET) at different activities of an adult human being with a body surface of 1.8 m2.

Metabolic energy Energy used during
transfer (W) one hour of activity
(Kcal)
Sleep 95 82
Sitting in armchair 105 90
Walking 350 300
Bicycling moderate intensity 600 520
Jogging 800 690
Fast running (23km/h) 2 300 N.A
Sprinting (100-200m) 3 500 N.A

08/02/2026

31/01/2026

Lesson 134: Liver functions

The liver is the largest gland in the body and as such it secretes bile acting as an emulsifier in the digestion of fat. The bile is made of two major components: Bile pigment bilirubin is a degradation product of the organic heme group of the haemoglobin molecule and bile salt sodium deoxycholate is a metabolite of cholesterol transported to the liver by HDL protein. The recycling system for bile pigments reabsorbed from the intestinal tract and brought back to the liver through the hepatic portal vein is sometimes referred to as the enterohepatic circulation. When used red blood cells are degraded in the liver, degradation of haemoglobin yields iron to be stored in the liver bound to ferritin or transported to the bone marrow by transferrin and other transport proteins. The polypeptides of the globin units are degraded into amino acids that either can undergo deamination for use in catabolic processes with urea formed as a waste product or be used to assemble serum albumin and other plasma proteins.
The liver serves as a filter of the blood carried by the hepatic portal vein from the gastrointestinal tract metabolizing and excreting drugs and other potentially harmful compounds absorbed by the intestines.
The liver receives about 25% of the total cardiac output at rest.
(a) Calculate the amount of blood carried to the liver through the hepatic artery if a total of 1 500 ml of blood leaves the liver through the hepatic vein and 1125 ml blood is carried through the hepatic portal vein.
(b) The hepatic artery carries 30-40% of the total amount of oxygen used by the liver. Calculate from (a) how large percentage of the total quantity of blood that enters the liver through the hepatic artery.
The liver is no compact chunk of cells. The blood flows in sinusoids between plates of liver cells inwards to the central vein in sinusoids. Bile is secreted into canaliculi draining into bile ducts. In a healthy liver, bile and blood are maintained well segregated. Kupfer cells phagocytose used red blood cells and other particles to be cleaned from the circulating blood.

17/01/2026

Lesson 133: Hunger and satiety

Similar to many homeostatic regulatory functions, hunger and satiety are regulated from centres in the hypothalamus region of the brain. Leptin is a peptide produced by several different types of body cells outside the brain and it circumvents the blood-brain barrier by entering the choroid complex.
Ghrelin is a peptide hormone released from the gastric tract. Its transport across the blood-brain barrier is dependent on putting a hydrophobic tail on the peptide by octanoylation (Banks et al. 2002).