Human Body | ICSE Class 6 Biology Notes

This note covers human organ systems, the organs and stages of digestion, digestion of carbohydrates, proteins and fats, absorption, the respiratory organs, breathing and respiration, common respiratory diseases, blood components and groups, blood vessels, circulation, heartbeat, pulse, blood pressure and healthy habits.

How do the body's organ systems work together?

An organ is a body part that performs particular functions. An organ system is a group of organs working together. The human body contains several organ systems, with different responsibilities that contribute to the functioning of the whole body.

The digestive system breaks down complex food into simpler substances that the body can absorb and use. The respiratory system brings air into the lungs and enables the exchange of gases. The circulatory system transports substances around the body through blood, the fluid that flows in tubes called blood vessels.

Why does transport matter?

Cells are the basic units of the body. They need materials for energy, growth and repair. Food entering the mouth cannot directly reach every cell. Similarly, air entering the lungs does not travel as air through all the body's organs.

Nutrients are useful components of food. Digested nutrients are absorbed from the intestine and transported in blood. Oxygen, a gas used in releasing energy from food, enters blood in the lungs. Blood carries it to the body's cells.

Carbon dioxide is a gas produced when cells release energy using oxygen. Blood carries it towards the lungs for removal. Digestion, respiration and circulation therefore have distinct roles, but they support the same living body.

Note: Breaking food into simpler substances, releasing energy from those substances and transporting materials are different processes. Understanding their connections does not make them the same process.

Which organs does food pass through during digestion?

The alimentary canal is the long passage running from the mouth to the anus. Digestion means breaking complex food components into simpler forms. Food passes along the canal while its muscular walls and digestive secretions help process it.

From the mouth to the stomach

In the mouth, teeth crush and chew food into smaller pieces. This physical breakdown is mechanical digestion. Saliva, the fluid released into the mouth by salivary glands, moistens food and begins the digestion of starch, a complex carbohydrate. Carbohydrates are food substances that include starch and sugars and supply energy.

The tongue mixes food with saliva and helps push it into the oesophagus, or food pipe, which connects the mouth region to the stomach. Waves of contraction and relaxation in its walls push food forwards. Such movements occur throughout the alimentary canal.

The stomach is a muscular organ in which food is churned and mixed with digestive secretions. Food leaving it is partly digested. It then enters the small intestine, the long, coiled part where digestion is completed and digested nutrients are absorbed.

How do the digestive organs compare?

The large intestine is wider and shorter than the small intestine. The rectum is its lower storage region. The anus is the final opening of the canal. These names identify different parts with different tasks.

The body outline shows a food pipe leading to the stomach, coiled small intestine inside the outline of the large intestine, and the rectum and anus below. The mouth, liver and pancreas are also labelled.

See Fig. 9.1 in your NCERT textbook

How are carbohydrates, proteins and fats digested?

Carbohydrates include sugars and starch and provide energy. Proteins are food components used in growth and repair. Fats are another energy-providing food component. Their complex forms need to be broken down before the body can use them.

Enzymes are substances made by living organisms that speed up chemical reactions. Digestive enzymes help break complex food substances into simpler ones. Chewing breaks food into pieces, while enzymes change the substances within those pieces.

What happens in the mouth and stomach?

Starch is a complex carbohydrate. Saliva contains salivary amylase, an enzyme that breaks starch down into sugar. This explains why chapati or boiled rice begins to taste sweet when chewed for a long time.

Stomach secretions contain digestive juice, acid and mucus, a protective, slippery substance. The protein-digesting enzyme pepsin works in the acidic conditions provided by stomach acid. The acid also kills many harmful bacteria, which are microscopic organisms.

Under normal conditions, mucus protects the stomach lining from the acid. Digestion in the stomach remains partial. The stomach does not finish the digestion of all the food components before sending food onwards.

How do the liver and pancreas help?

The liver is an organ that produces bile, a secretion that helps reduce the acidity of food arriving from the stomach and separates fats into tiny droplets. This makes it easier for fat-digesting enzymes to act.

The pancreas is an organ that releases pancreatic juice into the small intestine. This juice helps digest carbohydrates, proteins and fats. The wall of the small intestine also releases digestive juice, completing their breakdown.

1. Chewing breaks food into smaller pieces, and saliva begins the chemical digestion of starch in the mouth.
2. Food reaches the stomach, where churning mixes it with secretions and protein digestion begins.
3. Partly digested food enters the small intestine, where bile helps prepare fats for enzyme action.
4. Pancreatic and intestinal juices complete digestion, producing substances that can be absorbed and used.

Carbohydrates form simple sugars such as glucose, a sugar used by cells to release energy. Proteins form amino acids, their simpler building units. Fats form fatty acids and glycerol, the simpler substances obtained from fat digestion.

Note: Bile breaking large fat droplets into smaller droplets is different from enzymes breaking fats into fatty acids and glycerol. Both actions help fat digestion, but they do different jobs.

How are digested nutrients absorbed and undigested food removed?

Absorption is the passage of digested nutrients through the intestinal wall into the body's transport system. Most nutrients are digested and absorbed in the small intestine. Its inner lining has numerous finger-like projections called villi; one projection is a villus.

Villi increase the surface area available for absorption. Blood vessels close to their surfaces receive absorbed nutrients and transport them to other parts of the body. The small intestine therefore connects food processing with the body's transport system.

What happens after absorption?

Assimilation means the use of absorbed nutrients by the body, including building substances needed for growth and repair. Glucose can be broken down with oxygen in cells to release energy. Absorption brings nutrients inside; assimilation describes their use.

Undigested and unabsorbed material passes into the large intestine. Water and some salts are absorbed there. The remaining semi-solid waste is called faeces, or stool. It is stored in the rectum and passes out through the anus.

Egestion is the removal of undigested food material through the anus. It differs from digestion, which changes food, and absorption, which transfers digested nutrients through the intestinal wall. Keeping these three meanings separate makes the journey of food easier to follow.

Which eating habits support digestion?

Chewing food properly mixes it with saliva and makes swallowing easier. Eating meals at proper times and avoiding overeating support digestive health. Indigestion means discomfort associated with digestion; it is not the name of one particular digestive organ.

Dietary fibre, the roughage in plant foods, helps stool pass more easily. Fruits, vegetables and whole grains provide fibre. Brushing teeth, cleaning the tongue and rinsing the mouth after meals support oral hygiene, meaning cleanliness of the mouth.

Which parts make up the respiratory system?

The respiratory system provides a route for air to enter and leave the lungs. Nostrils are the external openings of the nose. Air passes through them into the nasal passages, the spaces inside the nose through which air travels.

Tiny hairs and mucus in these passages help trap dust and dirt. This filtering action does not mean that every unwanted particle is stopped. Often small infectious particles, meaning particles capable of causing infection, can still reach the lungs.

What is the route from the nose to the lungs?

The pharynx is the throat passage, part of which is shared by food and air. Air passes through the larynx, or sound box, into the trachea, also called the windpipe. The larynx helps produce sound.

The trachea divides into two main branches called bronchi; one branch is a bronchus. Each enters a lung and branches further into smaller tubes. These smaller branches include bronchioles, fine air passages within the lungs.

The lungs are the paired breathing organs in the chest. They contain tiny air sacs called alveoli; one sac is an alveolus. Thin walls and surrounding fine blood vessels allow gases to pass between the air sacs and blood.

The rib cage, the bony framework around the chest, protects the lungs. Below them lies the diaphragm, a dome-shaped muscle whose movement helps change the space inside the chest during breathing.

The drawing labels the nostrils, windpipe, right and left lungs, alveoli, rib cage and diaphragm. Branching air passages appear inside a lung, and the diaphragm is shown beneath the lungs.

See Fig. 9.8 in your NCERT textbook

How do the ribs and diaphragm bring about breathing?

Breathing is the movement of air into and out of the lungs. Taking air in is inhalation; sending air out is exhalation. Changes in the space inside the chest help produce these movements of air.

What happens during inhalation?

1. The ribs move upwards and outwards, helping the chest expand.
2. The diaphragm moves downwards below the lungs.
3. These movements increase the space inside the chest.
4. Air enters the lungs through the respiratory passages.

What happens during exhalation?

1. The ribs move downwards and inwards towards their earlier position.
2. The diaphragm moves upwards beneath the lungs.
3. The space inside the chest decreases.
4. Air is pushed out of the lungs through the respiratory passages.

To understand a breathing diagram, follow both the ribs and the diaphragm. During inhalation the ribs move up while the diaphragm moves down. These movements are in different directions but both increase the space within the chest.

During exhalation their movements reverse. The important link is between movement, chest space and airflow. Naming the moving parts alone does not explain how air enters or leaves the lungs.

Two chest drawings compare inhalation and exhalation. Arrows show air drawn in or forced out, ribs moving outwards or back, and the diaphragm moving downwards or upwards.

See Fig. 9.10 in your NCERT textbook

A bottle model can represent these changes. Two balloons represent the lungs, and a rubber sheet across the bottom represents the diaphragm. Pulling the sheet down inflates the balloons; releasing it upwards makes them deflate.

The model links a moving boundary with changing air space. Match the downward pull with inhalation and the upward movement with exhalation. The balloons change size because air moves into or out of them.

How does respiration differ from breathing?

Respiration is the process in which food substances are broken down in cells to release usable energy. Breathing supplies air to the lungs. These are connected activities, but air movement alone is not the chemical release of energy from food.

What happens to gases in the lungs?

Fresh air reaches the alveoli during breathing. Oxygen passes from the air sacs into the surrounding blood. At the same time, carbon dioxide carried from the body passes from blood into the alveoli and can leave during exhalation.

Blood then carries oxygen to the body's cells. Cells use oxygen to break down glucose, releasing energy and forming carbon dioxide and water. This is aerobic respiration, meaning respiration that uses oxygen.

In words, glucose reacts with oxygen to form carbon dioxide and water, releasing energy. The energy supports activities of the body. Digestion supplies simpler food substances, circulation transports materials, and respiration releases energy within cells.

During physical activity, breathing becomes faster to help meet the body's increased need for oxygen and energy. Breathing rate means the number of breaths taken in a minute. Count one inhalation followed by one exhalation as one complete breath.

Exhaled air contains more carbon dioxide than inhaled air. Not all the inhaled oxygen is used up. Therefore, breathing out does not mean that the lungs release pure carbon dioxide or that exhaled air contains no oxygen.

Which common diseases affect the respiratory system?

A disease disturbs the normal functioning of the body. A respiratory disease affects breathing passages or lungs. The names to recognise include asthma, bronchitis, pneumonia and tuberculosis. These names do not all describe the same condition or the same cause.

Asthma involves breathing difficulty and wheezing caused by inflammation of the bronchi and bronchioles. Inflammation is the body's response to injury or irritation, involving changes such as swelling. Wheezing means a whistling sound during breathing.

Bronchitis is inflammation of the bronchi. Pneumonia is an infection affecting the lungs, including their alveoli. Tuberculosis, abbreviated TB, is a bacterial disease that can affect the lungs. Bacterial means caused by bacteria.

Why are clean surroundings and healthy habits important?

Nasal hairs and mucus provide a useful first filtering step, but respiratory protection is not complete. Some infectious particles can pass through. Cleanliness and covering the mouth and nose when coughing or sneezing help limit the spread of respiratory infections.

Smoking is associated with bronchitis and other serious lung problems. Avoiding tobacco is therefore an important healthy habit. Regular physical activity and good food habits support health, while learning the names of diseases helps distinguish normal body functions from illness.

What are the components of blood and their functions?

Blood is the fluid that flows through blood vessels, the tubes carrying it around the body. It transports digested food from the small intestine, oxygen from the lungs and waste materials towards organs that remove them.

Plasma is the fluid part of blood in which blood cells are suspended. It provides the liquid medium for transport. Blood also contains red blood cells, white blood cells and platelets. Each component contributes a different function.

How do the blood components compare?

Red blood cells, abbreviated RBCs, contain haemoglobin, a red pigment that binds oxygen and helps carry it to cells. A pigment is a colouring substance. Haemoglobin gives blood its red appearance as well as helping oxygen transport.

White blood cells, abbreviated WBCs, fight germs that may enter the body. Germs are disease-causing microscopic agents. Their protective function differs from the oxygen-carrying function of red blood cells.

Platelets help form a blood clot, a plug that can close a cut and limit bleeding. Oxygen transport, defence and clotting are different tasks. Naming a component correctly means linking it with its own function.

Which blood groups should be recognised?

Blood groups are categories used to classify blood. Their names include A, B, AB and O. These letters are group labels, not abbreviations for organs or blood cells. A person's blood group is different from a list of blood components.

For example, plasma and platelets describe components within blood, whereas A and O identify blood groups. Keep these two kinds of classification separate when describing the circulatory system.

Blood donation means giving blood for use by people who need it. A blood bank stores donated blood with special care. Donation and storage help make blood available when patients require it.

How do arteries, veins and capillaries differ?

Blood travels through a connected network of vessels. An artery carries blood away from the heart. A vein carries blood towards the heart. These definitions depend on the direction of flow, not simply on the amount of oxygen in the blood.

Capillaries are extremely fine blood vessels connecting the smaller branches of arteries with veins. Their thin walls allow materials to pass between blood and surrounding cells. They bring circulating blood close to the places where substances are needed or produced.

How does structure suit function?

Blood leaves the heart under high pressure, so arteries have thick, elastic walls. Elastic means able to stretch and return towards the original shape. Veins have thinner walls and contain valves, structures that help blood flow towards the heart.

Capillary walls are one cell thick. This short distance allows exchange between blood and cells. The three vessel types therefore contribute different parts of one transport route: outward flow, exchange and return flow.

Why are the lung vessels important exceptions?

The pulmonary artery carries blood from the heart to the lungs. Pulmonary means relating to the lungs. This blood is rich in carbon dioxide. It is still an artery because it carries blood away from the heart.

The pulmonary vein carries oxygen-rich blood from the lungs to the heart. It is a vein because it carries blood towards the heart. These vessels show why “artery means oxygen-rich” is an unreliable definition.

Follow direction before deciding a vessel's name. Then consider whether it is carrying blood towards the lungs for gas exchange or carrying blood from the lungs after gas exchange. Direction and oxygen content are related observations, but they are not interchangeable definitions.

How does the heart keep blood circulating?

The heart is a muscular organ that acts as a pump. It lies in the chest, with its lower tip slightly tilted towards the left. It is roughly the size of a person's fist. Its pumping action maintains blood movement through the vessels.

The heart has four chambers, or internal spaces. The two upper chambers are atria; one is an atrium. The two lower chambers are ventricles. A partition separates the two halves and helps prevent oxygen-rich and carbon dioxide-rich blood from mixing.

What route does circulating blood follow?

1. Blood returning from the body reaches the right side of the heart carrying carbon dioxide from cells.
2. The right side pumps this blood towards the lungs through the pulmonary artery.
3. In the lungs, carbon dioxide passes from blood into the air sacs, while oxygen passes into blood.
4. Oxygen-rich blood returns through the pulmonary vein to the left side of the heart.
5. The left side pumps blood through arteries towards the rest of the body.
6. Blood exchanges materials near body cells and returns through veins, continuing the circulation.

Circulation means the movement of blood through the heart and vessels. The route connects the lungs with the rest of the body. The heart pumps blood, while the lungs provide the place where it exchanges gases with air.

The drawing places the lungs above the heart and a capillary network below. Arrows show flow through the pulmonary artery and vein, and through the body artery, capillaries and vein.

See Fig. 7.3 in your NCERT textbook

A schematic diagram simplifies a structure or process to show its main connections. Follow the arrows to read this one. Trace the lung route and the body route as connected parts of a repeating journey.

What do heartbeat, pulse and blood pressure tell us?

A heartbeat is the rhythmic contraction and relaxation of the heart's muscles. Contraction means tightening; relaxation means release from that tightened state. These repeated movements pump blood. Heart rate is the number of heartbeats in one minute.

A pulse is the throbbing felt in an artery as blood is pumped through it. Each heartbeat generates a pulse. Pulse rate is the number of pulse beats in a minute and indicates the rate of heartbeat.

How can a pulse be counted?

1. Place the index and middle fingers of the right hand on the inner side of the left wrist.
2. Feel for the repeated throbbing beneath the fingers.
3. Count the pulse beats for one complete minute.
4. Record the count as the pulse rate in beats per minute.

A pulse observation is a count over time, not a measurement of the force of blood against vessel walls. Record whether the observation was made at rest or after activity when comparing observations. Do not substitute an assumed count for an actual measurement.

Blood pressure describes the pressure exerted by blood against the walls of blood vessels. It is measured with a sphygmomanometer, an instrument for measuring blood pressure. A pulse count and a blood-pressure measurement describe different features of circulation.

How can good habits support the heart?

Regular exercise and good food habits help keep the heart healthy. Walking, running, cycling and outdoor play are forms of physical activity. A balanced diet supplies all essential nutrients, roughage and water in suitable amounts for growth and development.

Include fruits, vegetables and whole grains in meals. Avoid making fatty or sugary processed foods a daily habit. Enough sleep and avoiding tobacco also support health. These habits belong together with an understanding of how the digestive, respiratory and circulatory systems cooperate.

Glossary

• Organ system — A group of organs working together to carry out particular functions within the body.
• Digestion — The breakdown of complex food components into simpler forms that the body can absorb and use.
• Alimentary canal — The long digestive passage extending from the mouth to the anus through which food travels.
• Enzyme — A substance produced by living organisms that speeds up chemical reactions, including the breakdown of food.
• Absorption — The passage of digested nutrients through the intestinal wall into the body's transport system.
• Villi — Finger-like projections lining the small intestine that increase the surface area available for nutrient absorption.
• Egestion — The removal of undigested food material from the alimentary canal through the anus.
• Diaphragm — A dome-shaped muscle below the lungs whose movements help change chest space during breathing.
• Alveoli — Tiny air sacs in the lungs where gases pass between air and surrounding blood.
• Respiration — The breakdown of food substances in cells to release energy for the activities of life.
• Plasma — The fluid part of blood in which blood cells are suspended and substances are carried.
• Haemoglobin — The red pigment in red blood cells that binds oxygen and helps transport it around the body.
• Artery — A blood vessel that carries blood away from the heart towards the lungs or body organs.
• Vein — A blood vessel that carries blood from the lungs or body organs towards the heart.
• Pulse — The throbbing felt in arteries as the beating heart pumps blood through the circulatory system.

Common errors and misconceptions

• Misconception: All digestion takes place in the stomach. Correct: Digestion begins in the mouth, continues in the stomach and is completed in the small intestine.
• Misconception: Bile and digestive enzymes act on fat in the same way. Correct: Bile divides fat into tiny droplets; enzymes break fats into simpler substances.
• Misconception: Breathing and respiration are identical. Correct: Breathing moves air into and out of the lungs; cellular respiration breaks down food to release energy.
• Misconception: The diaphragm moves upwards during inhalation. Correct: It moves downwards, while the ribs move upwards and outwards, increasing the space inside the chest.
• Misconception: Every artery carries oxygen-rich blood. Correct: Arteries carry blood away from the heart. The pulmonary artery carries carbon dioxide-rich blood towards the lungs.
• Misconception: White blood cells give blood its red colour. Correct: Haemoglobin in red blood cells gives blood its red appearance; white blood cells fight germs.
• Misconception: Counting the pulse measures blood pressure. Correct: It measures pulse rate. Blood pressure concerns blood pressing against vessel walls and requires a different measurement.

Exam-style questions with model answers

Q1. State two functions of saliva when food is chewed in the human mouth. [2 marks]

1. Saliva moistens chewed food, making it soft and easier to swallow.
2. Its enzyme salivary amylase begins the digestion of starch by breaking it into sugar.

Q2. Give the end products of digestion of carbohydrates, proteins and fats, with one separate point for each food component. [3 marks]

1. Carbohydrates are broken down into simple sugars such as glucose. These simpler substances can be absorbed and used by the body.
2. Proteins are broken down into amino acids. These are simpler building units that the body can use after digestion and absorption.
3. Fats are broken down into fatty acids and glycerol. These are the products of chemical digestion, rather than merely smaller fat droplets.

Q3. Compare breathing with cellular respiration in three respects: the action involved, where it occurs and its connection with energy release. [3 marks]

1. Breathing is the physical movement of air into and out of the lungs. Cellular respiration involves chemical breakdown of food substances.
2. Breathing involves the lungs and respiratory passages, assisted by chest movements. Cellular respiration takes place within the cells of the body.
3. Breathing supplies oxygen-containing air for gas exchange. Cellular respiration releases usable energy from food; the two processes therefore have different roles.

Q4. Describe inhalation in four linked points, covering the ribs, diaphragm, space inside the chest and movement of air. [4 marks]

1. The ribs move upwards and outwards, helping the chest expand during the process of inhalation.
2. The diaphragm moves downwards beneath the lungs as part of the same breathing movement.
3. Together, these movements increase the space inside the chest, providing the change needed for inward airflow.
4. Air enters through the respiratory passages and moves into the lungs as inhalation takes place.

Q5. State one main function each of plasma, red blood cells, white blood cells and platelets. [4 marks]

1. Plasma forms the fluid part of blood, providing the medium in which blood cells and transported substances are carried.
2. Red blood cells contain haemoglobin, which binds oxygen and helps transport it from the lungs to the body's cells.
3. White blood cells fight germs that may enter the body, contributing to its protection against disease-causing agents.
4. Platelets help form blood clots at injuries, producing a plug that limits the loss of blood from a cut.

Q6. Trace blood flow from the right side of the heart through the lungs and body back towards the heart. Give five stages and include the pulmonary artery and pulmonary vein. [5 marks]

1. The right side of the heart pumps carbon dioxide-rich blood towards the lungs through the pulmonary artery, which carries blood away from the heart.
2. In the lungs, carbon dioxide moves from blood into the alveoli, while oxygen moves from the alveoli into the surrounding blood.
3. The pulmonary vein carries the oxygen-rich blood from the lungs back to the left side of the heart.
4. The left side of the heart pumps blood through arteries towards the body, where fine capillaries allow exchange with cells.
5. After supplying materials and picking up waste products such as carbon dioxide, blood returns through veins towards the right side of the heart.

Q7. Two samples of boiled rice, one unchewed and one thoroughly chewed, are tested with iodine. The unchewed sample turns blue-black; the chewed sample shows no colour change. Iodine gives a blue-black colour when starch is present. Explain these observations in five linked points about starch, chewing and saliva. [5 marks]

1. The blue-black colour of the unchewed rice shows that it contains starch, using the stated test for the presence of starch.
2. Chewing breaks the rice into smaller pieces and mixes it with saliva inside the mouth, bringing food into contact with digestive secretion.
3. Saliva contains salivary amylase, a digestive enzyme that acts on starch and breaks it down into simpler sugar.
4. The lack of colour change in the chewed sample indicates that starch is no longer present in that tested sample.
5. The two observations support the conclusion that starch digestion begins in the mouth through saliva, alongside the physical breakdown caused by chewing.

Q8. A vessel carries blood from the heart to the lungs. Identify the vessel and explain why it is an artery even though its blood is rich in carbon dioxide. [2 marks]

1. The vessel is the pulmonary artery, which carries blood from the heart towards the lungs.
2. It is an artery because it carries blood away from the heart; its name does not depend on oxygen content.

Key takeaways

• The digestive, respiratory and circulatory systems work together to supply cells with nutrients and oxygen and transport waste materials.
• Food travels along the alimentary canal, while secretions from the liver and pancreas help digestion in the small intestine.
• Carbohydrates form simple sugars, proteins form amino acids, and fats form fatty acids and glycerol during digestion.
• Villi increase the small intestine's surface area for absorption; the large intestine absorbs water and some salts from undigested material.
• Inhalation involves ribs moving upwards and outwards and the diaphragm moving downwards, increasing the space inside the chest.
• Breathing moves air, whereas cellular respiration releases energy from food; blood links gas exchange in the lungs with body cells.
• Red blood cells carry oxygen, white blood cells fight germs, platelets help clotting, and plasma provides blood's fluid medium.
• Arteries carry blood away from the heart and veins return it; regular exercise and good food habits support heart health.

Test yourself

Why can chewing chapati for a long time make it taste sweet?

Saliva begins breaking its starch into sugar while chewing mixes the food with saliva.

What is the difference between absorption and assimilation?

Absorption brings digested nutrients through the intestinal wall. Assimilation is their use within the body for activities such as growth and repair.

What are the bronchi, and where do they lead?

The bronchi are the two main branches of the trachea, with one entering each lung.

How does the diaphragm move during exhalation?

It moves upwards, helping reduce the space inside the chest as air leaves the lungs.

Where does oxygen pass from inhaled air into blood?

Oxygen passes across the thin walls of the alveoli into the blood vessels surrounding them.

Which blood component helps limit bleeding from a cut?

Platelets help form a clot that plugs the injury and limits blood loss.

Why is the pulmonary vein called a vein?

It carries blood towards the heart, even though that blood is oxygen-rich after leaving the lungs.

What is measured when pulse beats are counted for a minute?

The count gives pulse rate in beats per minute, which indicates the rate of heartbeat.