Biology: digestive enzymes: pepsin and trypsin

Approaching another biology workshop, the tutor looks at the human body’s two main digestive enzymes aimed at proteins.

For each type of food molecule the body has its own specific digestive enzyme(s). For protein, there are two: pepsin and trypsin.

Why does the human body use two different enzymes to digest protein? The answer is that the enzymes have different optimal environments. Pepsin works at a low (acid) pH of 1 to 3. The body uses it to digest proteins in the stomach, which is an acidic environment.

Trypsin works best in an alkaline, or basic, environment. Specifically, its optimal pH centers around 8. The body uses trypsin to digest proteins in the small intestine, wherein the environment is basic because of the release of sodium bicarbonate from the pancreas.

I’ll be talking more about digestive enzymes in future posts:)


Mader, Sylvia S. Inquiry into Life, 11th ed. New York: McGraw-Hill, 2006.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Biology: insulin response and insulin resistance

The tutor defines insulin response and insulin resistance and explains their connection.

Recall: herein, ACV means apple cider vinegar.

In yesterday’s post I mentioned my discovery that apple cider vinegar potentially increases the effectiveness of insulin.

As carbohydrates are digested, glucose (a type of sugar) enters the blood from the digestive system. The body’s response to the rising blood sugar is to release insulin. It’s known as the insulin response. Insulin enables glucose to enter cells so they can use it for energy or fat storage.

Sometimes, body cells may become less sensitive to insulin, which is known as insulin resistance. Then, the insulin is less effective at conducting glucose from the blood into the cells; more insulin is needed to do the same as before.

Therefore, if insulin resistance increases, so must the insulin response. The fact that ACV seems to increase insulin’s effectiveness leads to the consequence that it apparently lowers the body’s insulin response.

I’ll be discussing related ideas in coming posts:)


Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Biology: nervous system: action potential

The tutor offers a summary of how a nerve impulse propagates.

The cells that carry nerve impulses are called neurons. Neurons have long conduits through which the impulses travel. A nerve impulse, as it conducts along a neuron, can be called an action potential. At the point of progress, the potential difference (aka voltage) swings from -65mV (rest potential) to +40mV (action potential) back to -65mV (rest potential).

The voltage refers to the potential difference across the cell membrane. It is managed by deployment of ions. The swing from -65mV to +40mV is accomplished by sudden controlled migration of Na+ ions into the cell. The return swing from +40mV to -65mV results from controlled departure of K+ ions. (The neuron controls when those ions can cross its membrane.)

After the action potential, the ions need to be reset so they are ready to propagate the next one. The Na+ ions are put back outside, while the K+ ions are brought back inside. This period can be referred to as the refractory period. The neuron may not be able to “fire” again until its completion.



Mader, Sylvia S. Inquiry into Life, 9th Ed. Toronto: McGraw-Hill, 2000.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Fibre: soluble, insoluble?

The tutor has wondered about fibre ever since he heard about soluble fibre.

Back in the early 90s, when I was in university so cut off from day-to-day culture (no TV, no money, no time), a few snippets still did reach me.  One was the term “soluble fibre.” I was highly skeptical; how could fibre, undigestible by definition, yet be soluble?

At an early age I was taught that fibre passes through the intestines, keeping the bowels loose and the stool easy to pass.  It can do so because it’s not digestible.  At the same time, it holds water, keeping the stool soft.  Therefore, it speeds the movement of material through the gut.  To do so, wouldn’t you expect it to be insoluble?

Well, the insoluble fibre is the kind I’ve just described above.  However, soluble fibre also exists, but serves a different function.  In contrast with insoluble fibre, soluble fibre slows food’s exit from the stomach.  Apparently, as it dissolves in water, it forms a complex with the water molecules, giving them more inertia.  Possibly, cholesterol can get stuck in the complex as well, making it less likely to be absorbed.  Anyhow, the effect is that, with the soluble fibre binding together the water molecules in which it’s dissolved, the liquified food in the stomach is more sluggish.  Therefore, it stays in the stomach longer.  One result is feeling “full” for a longer duration after eating.  The other is a slower release of glucose into the bloodstream, which may help offset – or even prevent – symptoms of diabetes.

The sources of both soluble and insoluble fibre are numerous.  A variety of fresh fruits and vegetables, plus a variety of whole grains, will likely avail plenty of both. Here’s a fun fact, though:  oat bran provides soluble fibre, while wheat bran provides insoluble.  I seem to recall, from the 90s to the early 2000s, an increased focus on oat bran rather than just bran.

Soluble and insoluble fibre: now we know:)


Web MD

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Biology: oxygen and carbon dioxide transfer through the blood

Tutoring biology 12, you cover the circulatory system.  The tutor mentions a specific issue about it.

The number one reason for the circulatory system is transport of oxygen to the cells and carbon dioxide away from them.  This is done via the blood, which is water-based.  The immediate problem might be that gases don’t necessarily dissolve very well in water.

Red blood cells contain hemoglobin (which is why they are red).  Hemoglobin attracts and holds oxygen very effectively, enabling the red blood cells to carry the oxygen through the circulatory system to the capillaries.  There, the oxygen is dropped off to the cells.

Carbon dioxide can be carried by red blood cells (as carbaminohemoglobin), but not very effectively.  In the blood, most carbon dioxide combines with water to form carbonic acid (H2CO3), next breaking into hydrogen ion H+ and bicarbonate ion HCO3. Ions travel easily in water. At the lungs, the hydrogen ion and bicarbonate ion recombine into carbonic acid, which then separates into carbon dioxide and water. The carbon dioxide is exhaled.



Mader, Sylvia S. Inquiry into Life, 11th edition. New York: McGraw-Hill, 2006.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Biology: diffusion

When you tutor biology, molecular movement and transport are topics you need to explain.  Front and centre is diffusion.

Diffusion is the tendency of particles to move from an area of high concentration to lower concentration.  It happens spontaneously, meaning it does not require an output of energy.

Moving from high concentration to lower concentration can be referred to as following the concentration gradient.  Therefore, diffusion follows the concentration gradient. The gradient can be thought of as a “slope” that the molecules “roll down” to get to lower concentration.

In everyday life, diffusion is everywhere.  Consider, for instance, a pleasant walk on a calm, dark night.  You smell steaks barbecuing.  You look around, but can’t seem them. Yet, the airborne aromatic molecules have reached you from the barbecue.  That movement of the molecules from the cooking steaks to your nose is an example of diffusion.  Note that it happens by itself; it’s spontaneous.

The human body relies on diffusion for some means of transport.  For instance, at the cell membrane, oxygen passes in and carbon dioxide leaves by diffusion.  It’s perfect: since the cell is constantly using oxygen, its concentration is always low inside.  The concentration of oxygen in the surrounding blood is much higher.  Therefore, oxygen constantly diffuses into the cell.  Carbon dioxide, on the other hand, is constantly being produced in the cell, but is much lower in the blood.  Therefore, it diffuses out of the cell into the blood, whence it is carried away.

The cell can depend on diffusion for gas exchange for two reasons:

1)  The cell membrane is permeable to oxygen and carbon dioxide.

2)  Diffusion happens fast enough, at the cellular level, to be effective.

Permeable means that it can be passed through.  The cell membrane is permeable to oxygen and carbon dioxide, allowing them to diffuse in and out.  The cell membrane is not permeable to many molecules and/or ions, however.  For briefing on that issue, check my post here about the cell membrane.

The reason that diffusion happens fast enough, at the cellular level, for effective gas exchange is that the cell is very small. Therefore, it has high efficiency. See my post here about cell efficiency.

Diffusion is only one method of transport in the body. It is spontaneous, but depends on permeability and efficiency. It is sufficient, for example, for gas exchange between the cells and the blood. However, there are many other contexts in which diffusion is not sufficient. Therefore, I’ll be discussing other transportation methods in future posts:)

Source: Mader, Sylvia S. Inquiry into Life, 11th edition. New York: McGraw-Hill, 2006.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Biology: Three kinds of respiration

Tutoring Biology 12, you cover the cardiovascular system.  The biology tutor discusses the gas exchange aspect.

People commonly associate respiration with breathing.  However, from a biology point of view, the meanings are different.  Breathing is the physical process of bringing fresh air into the lungs and then pushing out “used” air.  Respiration means gas exchange.

There are three kinds of respiration:  external, internal, and cellular.

External respiration is the one everyone thinks of:  in the lungs, the blood drops off its carbon dioxide and picks up oxygen.

Internal respiration happens in the tissues.  Blood drops off its oxygen to the tissue fluid (whence it reaches the cells), while collecting the carbon dioxide that the cells are constantly producing.

Cellular respiration happens inside the cell, in the mitochondria.  It is the chemical process of burning glucose with oxygen to produce energy, carbon dioxide, and water. (The carbon dioxide produced by cellular respiration is, of course, what you breathe out when you’re running:))

Each of these aspects of respiration needs more discussion, but this is a good starting point.  Drop in again for more about them:)

Source:  Mader, Sylvia S.  Inquiry into Life, 11th edition.  New York:  McGraw-Hill, 2006

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Urine Regulation: Aldosterone

Tutoring Biology 12, you realize that with most organ systems, the hormonal control is the most difficult to retain.  The Biology tutor continues about urine regulation with this discussion of aldosterone.

Of course, urine is produced by the kidneys.  If you missed it, you can read how a kidney works in my post here.

In my previous post I talked about ADH and how the body uses it to regulate urine volume. There is another hormone – called aldosterone – that the body uses to control how much water is reclaimed from the filtrate. (Recall that the filtrate is the mix of water, ions, and small molecules first removed from the blood by the kidneys.)

Aldosterone is released by the adrenal cortex. However, the adrenal cortex needs to be informed to do so by the presence of renin in the blood. Renin is secreted by the cells of the juxtaglomerular apparatus, which are adjacent to the glomerulus and sense the blood pressure within. Specifically, when the cells of the juxtaglomerular apparatus sense that the blood pressure is too low, they respond by secreting renin into the bloodstream.

The renin circulates through the body to the adrenal cortex. Detecting the renin, the adrenal cortex responds by secreting aldosterone.

Aldosterone targets the cells of the distal convoluted tubule, telling them to let go of more K+ (K+ means potassium ions), but reclaim more Na+ (sodium ions) in compensation. The effect is that more water is reabsorbed from the filtrate, increasing blood volume and decreasing urine volume.

Unlike ADH, aldosterone does not result in blood dilution, since more ions are reclaimed alongside the extra water that is reabsorbed. Someone might ask, “If aldosterone increases the reclamation of sodium ions, how does that mean increased water reabsorption?” The answer is that sodium ions have a powerful pull on water – more powerful than potassium ions. So if you reabsorb sodium ions instead of potassium ions, more water will be drawn back into the blood as well.

Ultimately, the kidneys release renin – which leads to the release of aldosterone – in order to defend their own function.  If blood pressure is too low, the kidneys cannot filter the blood properly.  By increasing water reabsorption and therefore blood volume, aldosterone helps maintain the necessary blood pressure for proper filtration.

Source: Biology 12, Module 4: Human Biology 2. Open School BC, 2007.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Urine regulation: ADH

Tutoring biology 12, you cover kidney function.  The biology tutor introduces ADH, which is a hormone used to regulate urine volume.

For explanation of how a kidney works, see my post here.

Today, we focus on the fine tuning of urine volume. The hypothalamus monitors the concentration of the blood. It may decide, for instance, that the blood risks dehydration. How can the hypothalamus respond to help prevent dehydration?

The hypothalamus has the option of ordering the posterior pituitary to release ADH (anti diuretic hormone). ADH acts on the cells of the distal convoluted tubule and the collecting duct, causing them to be more permeable to water. The result is that more water will be reabsorbed back into the blood. Subsequently, blood volume will stay higher, while urine volume will decrease.

Let’s imagine the other situation: the person has just drunk lots of water to flush themselves out. In such a case, the hypothalamus will detect the surplus of water in the blood, so won’t order the secretion of ADH. The cells of the distal convoluted tubule and collecting duct will allow less water to be recollected, so more will be left in the urine. Urine volume will increase, while blood volume will decrease.

At night, the hypothalamus may order the secretion of ADH to keep urine acculumation low during sleep. The benefit: the person will not have to get up as often to urinate – or maybe not at all until morning.

Another hormone – aldosterone – can also be used to influence urine volume. It will be discussed in a future post:)

Source: Biology 12, Module 4, Open School BC, 2007.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Biology: the female system, cont.

When you tutor Biology 12, which is needed for nursing, you cover the male and female reproductive systems.  Here is the continuation from the Dec 30 post.

Previously I discussed the end of the monthly female cycle: if conception does not occur, menstruation does. However, what about the other case: when conception does occur?

The fertilized egg finds lodging in the blood lining of the uterus. Immediately, the placenta starts developing. As it does, it secretes a hormone (HCG) which orders the corpus luteum to continue producing progesterone. The progesterone from the corpus luteum maintains the blood lining in the uterus temporarily. Meanwhile, the placenta develops rapidly; soon, it starts producing its own progesterone. Throughout the pregnancy, the release of progesterone from the placenta will prevent menstruation.

There are a couple of terms that might be helpful. Implantation is the lodging of the fertilized egg in the blood lining of the uterus. The endometrium is the blood lining itself.

For an exploration of the hormonal influences at birthing, stay tuned:)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.