SPI Biology · Human Physiology
Life Processes in Humans
The body digests food, breathes to release energy from it, carries everything around in the blood and throws out waste as urine.
Why this matters
Eight questions in the bank, seven of them EASY: the acid of the stomach, the enzyme found in both saliva and pancreatic juice, where gases are exchanged, lime water and exhaled air, cramps after hard exercise, the element used in clotting, the four chambers of the heart and the path of urine. Each one is a single named fact.
Concept 1 of 4: Digestion: each organ and what it adds
Food is broken down step by step as it moves along the gut. Each organ adds its own juice, and each juice has an enzyme that splits one kind of food. Learn the organ, the juice and the food it works on as one row.
Definition
- Mouth: saliva has salivary amylase, which turns starch into sugar.
- Stomach: gastric glands make hydrochloric acid (kills germs, makes the medium acidic), pepsin (starts protein digestion) and mucus (protects the stomach wall).
- Liver: makes bile, which has no enzyme. It breaks fat into small droplets (emulsifies it) and makes the food alkaline.
- Pancreas: pancreatic juice has trypsin (protein), lipase (fat) and amylase (starch).
- Small intestine: digestion ends here and the villi absorb the food into the blood.
- Large intestine: absorbs water.
| Organ | Juice or enzyme | What it acts on |
|---|---|---|
| Mouth | Salivary amylase | Starch (a carbohydrate) |
| Stomach | Hydrochloric acid | Kills germs, makes the medium acidic for pepsin |
| Stomach | Pepsin | Protein |
| Liver | Bile (no enzyme) | Fat, broken into small droplets |
| Pancreas | Trypsin | Protein |
| Pancreas | Lipase | Fat |
| Pancreas | Pancreatic amylase | Starch (a carbohydrate) Amylase is the one enzyme found in both saliva and pancreatic juice. |
| Small intestine | Villi | Absorb digested food into the blood |
Protein has two enzymes (pepsin, trypsin); starch has two places (mouth, pancreas).
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Example 1 · Human Physiology · Life Processes in Humans
Which of the following component of our food is digested by an enzyme which is present in saliva as well as in pancreatic juice?
Calling bile an enzyme
Bile digests nothing on its own. It breaks fat into small droplets so that lipase can work on it. The enzyme that digests fat is lipase.
Picking a weak acid for the stomach
The stomach makes hydrochloric acid, a strong mineral acid. Acetic acid is in vinegar and lactic acid is in curd and tired muscles; neither comes from the stomach.
Concept 2 of 4: Breathing and respiration
Breathing brings air to the lungs; respiration is what the cells do with the oxygen. Glucose is broken down to release energy, and carbon dioxide is the waste we breathe out. When a muscle runs short of oxygen, it breaks glucose down another way and makes lactic acid.
Definition
- Air path: nose, throat (pharynx), voice box (larynx), windpipe (trachea), bronchi, bronchioles, alveoli.
- Gas exchange happens only in the alveoli: tiny air sacs with thin walls and many blood capillaries. Oxygen goes into the blood; carbon dioxide comes out.
- Haemoglobin in red blood cells carries the oxygen.
- Aerobic respiration (with oxygen): glucose breaks to pyruvate, then to carbon dioxide + water + much energy.
- Anaerobic in our muscles (short of oxygen): pyruvate becomes lactic acid, which causes cramps.
- Anaerobic in yeast: pyruvate becomes ethanol + carbon dioxide.
- Lime water test: exhaled air turns lime water milky because of its carbon dioxide (calcium carbonate forms).
| Where | Oxygen | Pyruvate becomes |
|---|---|---|
| Mitochondria of most cells | Present | Carbon dioxide and water, with much energy |
| Muscle cells during hard exercise | Short | Lactic acid, with less energy Lactic acid building up in the muscle is what causes cramps. |
| Yeast | Absent | Ethanol and carbon dioxide |
Ethanol belongs to yeast; lactic acid belongs to our muscles.
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Practice questionEasy
Example 2 · Human Physiology · Life Processes in Humans
During respiration exchange of gases take place in
Exchange in the windpipe or throat
The trachea, larynx and throat only carry air. Oxygen and carbon dioxide cross into and out of the blood only in the alveoli of the lungs.
Mixing up the two kinds of anaerobic respiration
In our muscles pyruvate becomes lactic acid. Ethanol and carbon dioxide come from yeast, not from the human body.
Water vapour as the lime water gas
Exhaled air also has water vapour, but only carbon dioxide reacts with lime water to make the white calcium carbonate that turns it milky.
Concept 3 of 4: Blood and the four chambers of the heart
The heart is two pumps side by side. The right side takes used blood from the body and sends it to the lungs; the left side takes fresh blood from the lungs and sends it to the whole body. Blood itself is a liquid, plasma, carrying three kinds of cells.
Definition
- Right atrium: receives deoxygenated blood from the body.
- Right ventricle: pumps it to the lungs through the pulmonary artery.
- Left atrium: receives oxygenated blood from the lungs through the pulmonary veins.
- Left ventricle: pumps it to the body through the aorta. Its wall is the thickest.
- Arteries carry blood away from the heart; veins bring it back and have valves.
- Blood: plasma, red cells (haemoglobin, which contains iron, carries oxygen), white cells (fight germs), platelets (clotting).
- Calcium is the element needed for blood clotting.
| Chamber | Receives blood from | Sends blood to |
|---|---|---|
| Right atrium | The body (deoxygenated) | Right ventricle |
| Right ventricle | Right atrium | The lungs, by the pulmonary artery |
| Left atrium | The lungs, by the pulmonary veins (oxygenated) | Left ventricle The left atrium is the chamber that receives blood from the lungs. |
| Left ventricle | Left atrium | The whole body, by the aorta |
Right side: body to lungs. Left side: lungs to body.
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Example 3 · Human Physiology · Life Processes in Humans
The element involved with blood clotting is
Iron for clotting
Iron is in haemoglobin and helps carry oxygen. The element that blood needs to clot is calcium.
Thinking the right side of the heart sends blood to the body
The right side handles deoxygenated blood and sends it to the lungs. Only the left ventricle pumps blood to the body, which is why its wall is the thickest.
Concept 4 of 4: Excretion: the path of urine
The kidneys clean the blood. Waste filtered out of the blood becomes urine, which flows down two tubes into a bag that stores it, and leaves by one tube.
Definition
- Each kidney has about a million nephrons, the tiny filters that make urine.
- Ureters (two): carry urine from the kidneys to the bladder.
- Urinary bladder: stores urine.
- Urethra (one): carries urine out of the body.
- Urine is mostly water, with urea and salts.
| Step | Organ | Job |
|---|---|---|
| 1 | Kidneys | Filter the blood and make urine (in the nephrons) |
| 2 | Ureters | Carry urine down to the bladder |
| 3 | Urinary bladder | Stores urine |
| 4 | Urethra | Carries urine out of the body Ureter comes before the bladder; urethra comes after it. |
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The same idea in a practice question:
Practice questionEasy
Example 4 · Human Physiology · Life Processes in Humans
Choose the correct path of urine in our body
Swapping ureter and urethra
The two names sound alike. The ureters come first (kidney to bladder) and the urethra comes last (bladder to outside). A path that puts the urethra before the bladder is wrong.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (4)
Digestion: each organ and what it adds8 rows
| Organ | Juice or enzyme | What it acts on |
|---|---|---|
| Mouth | Salivary amylase | Starch (a carbohydrate) |
| Stomach | Hydrochloric acid | Kills germs, makes the medium acidic for pepsin |
| Stomach | Pepsin | Protein |
| Liver | Bile (no enzyme) | Fat, broken into small droplets |
| Pancreas | Trypsin | Protein |
| Pancreas | Lipase | Fat |
| Pancreas | Pancreatic amylase | Starch (a carbohydrate) Amylase is the one enzyme found in both saliva and pancreatic juice. |
| Small intestine | Villi | Absorb digested food into the blood |
Protein has two enzymes (pepsin, trypsin); starch has two places (mouth, pancreas).
Breathing and respiration3 rows
| Where | Oxygen | Pyruvate becomes |
|---|---|---|
| Mitochondria of most cells | Present | Carbon dioxide and water, with much energy |
| Muscle cells during hard exercise | Short | Lactic acid, with less energy Lactic acid building up in the muscle is what causes cramps. |
| Yeast | Absent | Ethanol and carbon dioxide |
Ethanol belongs to yeast; lactic acid belongs to our muscles.
Blood and the four chambers of the heart4 rows
| Chamber | Receives blood from | Sends blood to |
|---|---|---|
| Right atrium | The body (deoxygenated) | Right ventricle |
| Right ventricle | Right atrium | The lungs, by the pulmonary artery |
| Left atrium | The lungs, by the pulmonary veins (oxygenated) | Left ventricle The left atrium is the chamber that receives blood from the lungs. |
| Left ventricle | Left atrium | The whole body, by the aorta |
Right side: body to lungs. Left side: lungs to body.
Excretion: the path of urine4 rows
| Step | Organ | Job |
|---|---|---|
| 1 | Kidneys | Filter the blood and make urine (in the nephrons) |
| 2 | Ureters | Carry urine down to the bladder |
| 3 | Urinary bladder | Stores urine |
| 4 | Urethra | Carries urine out of the body Ureter comes before the bladder; urethra comes after it. |
Watch out for (8)
- Calling bile an enzyme→ Digestion: each organ and what it adds
- Picking a weak acid for the stomach→ Digestion: each organ and what it adds
- Exchange in the windpipe or throat→ Breathing and respiration
- Mixing up the two kinds of anaerobic respiration→ Breathing and respiration
- Water vapour as the lime water gas→ Breathing and respiration
- Iron for clotting→ Blood and the four chambers of the heart
- Thinking the right side of the heart sends blood to the body→ Blood and the four chambers of the heart
- Swapping ureter and urethra→ Excretion: the path of urine
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