KS3Respiratory

System

© Pritesh Raichura

1 Recap of Digestive System

Do now:

1. Put the following in order of size: Tissue / Cells / Organism / Organ / Organ system

2. Match the words you have ordered to the correct definitions below:a. A group of different organs that work together to perform a particular

function.b. A group of similar specialised cells that work together to perform a

particular function.c. A group of different tissues that work together to perform a particular

function.d. A microscopic structure that is the building block of all organisms.e. An individual living thing. Many multicellular __________________ have

several organ systems working together.3. Name 2 examples of

a. Organismsb. Tissuesc. Cellsd. Organse. Organ systems

All cells need oxygen & glucose

All cells in the human body need a supply of energy to carry out their functions (do their jobs). For example, muscle cells need to contract (get shorter), allowing us to move. The muscle cells will only contract if three things happen:

1. The muscle cells receive enough oxygen2. The muscle cells receive enough glucose (a sugar), which has a store of

energy3. The muscle cells can carry out chemical reactions called respiration, which

releases the energy from the glucose, using oxygen.

In year 7 we studied the digestive system and learned how its function is to break down the nutrients in food into small enough molecules to absorb into the blood. The circulatory system then transports the nutrients, including glucose, to all of the cells of the body. The glucose then moves into the cells by a process called diffusion.

In this topic, we will learn how oxygen is taken in from the air by an organ system called the respiratory system. This will help us to understand how the oxygen from the air ultimately reaches the cells of our body, such as our muscle cells, thus allowing respiration to take place. Respiration allows the muscle cells to contract and this helps us to move. Similarly, oxygen and glucose must be delivered to the cells in our brain, so that respiration can occur to release energy for our brain cells to help us think. This applies to all of the specialised cells in our body; all require a constant supply of oxygen and glucose so that the cells can carry out respiration and allow the cells carry out their function (do their job).

Before we study the respiratory system in detail, let’s recap what we have learned about the digestive system (so that we understand how we obtain glucose), and what we have

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learned about respiration (so that we understand how our cells use glucose and oxygen to release energy for the cells to perform their functions).

Digestion

Digestion is the process in which the body breaks down food, absorbs the nutrients from the food and excretes (gets rid of) any waste. The process is carried out by the digestive system, which is an organ system that consists of: the mouth, oesophagus, stomach, liver, pancreas, small intestine, large intestine and rectum. Each of these organs has a specific role that helps digest food. Digesting (or breaking down) food is essential because the nutrients that are in the food can only be absorbed into the body if they are small enough.

Mouth

Digestion begins in the mouth, where the teeth mechanically break down the food into small pieces. This is only a start to the process of digestion, as chewed pieces of food are still too large to be absorbed by the body. Food has to be broken down chemically into really small molecules before it can be absorbed. Enzymes, which are proteins that speed up chemical reactions, are needed to break down nutrients quickly enough. In the mouth, an enzyme called amylase is released with the saliva (your spit), which breaks down carbohydrates into small sugars called glucose.

Stomach

From the mouth, the chewed food (now called ‘bolus’) travels down the oesophagus and into the stomach. The stomach has three important roles. Firstly, hydrochloric acid kills any bacteria that are in the food. This stops us from getting ill in case our food is contaminated with bacteria. Secondly, the acid environment is ideal for protease enzymes, which break down proteins into amino acids. Thirdly, the walls of the stomach are muscular, which helps to churn the food.

Small intestine

Next, the food enters the small intestine whose main job is to absorb the nutrients. Here, three different types of enzymes chemically break down the nutrients in our food into small enough molecules to be absorbed. Carbohydrase breaks down carbohydrates, protease breaks down proteins and lipase breaks down fats. Bile, a yellow liquid, is made by the liver and is released into the small intestine to help these enzymes work properly. It also helps the lipase to digest fat more quickly. Once the nutrients are broken down, the small intestine absorbs the nutrients.

Large intestine

Now that the nutrients are absorbed, the digestive system can get rid of any

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undigested food that is left. It moves into the large intestine, where most of the remaining water is absorbed. This leaves the faeces (waste or ‘poo’) to be stored in the rectum, ready to be excreted.

Comprehension questions

1. Define function.2. Use your knowledge about specialised cells to describe the function of:

a. A muscle cellb. A sperm cellc. A red blood cell

3. Explain why all cells need energy.4. State three things that need to happen for any cell to be able to carry out its

function.5. State the organ system which helps our body to obtain glucose.6. State the function of the circulatory system.7. Describe the roles of the digestive system. Use the words: ‘break down’,

‘nutrients’, ‘small’, ‘absorb’, ‘waste’ and ‘excrete’ in your answer.8. Name the organs involved in digestion.9. Define enzyme.10. Describe the role of enzymes in digestion.11. State the organ which absorbs the nutrients that have been broken down by the

digestive system into the blood.12. One of the nutrients absorbed during digestion is glucose. After glucose is

absorbed into the blood, it travels to the cells of the body. Explain what the glucose will be used for once it reaches the cells of the body.

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2 Recap of Diffusion

Do Now

1. Name the two substances that must be delivered to all cells to use to release energy.

2. Name the reaction that cells carry out to release energy.3. Write the word equation for aerobic respiration.4. State the role of the:

a. Digestive systemb. Circulatory systemc. Respiratory system

5. What is the role of the mitochondria?

Mitochondria

Last lesson we learned that all cells need energy. Cells release energy from glucose, which is a sugar obtained during digestion. The glucose reacts with oxygen during a series of chemical reactions called respiration. This lesson, we look at exactly what respiration is and where it happens. We also look at the role of diffusion.

Inside all the cells in the body, there are organelles called mitochondria. Mitochondria are known as the ‘powerhouses’ of the cell, because they perform aerobic respiration and release energy for the cell to use. Cells in multicellular organisms are specialised to perform various functions, so depending on how much energy a cell needs to carry out its job, it will have a corresponding number of mitochondria. For example, skin cells are not very active, and so typically contain only 200 mitochondria. In contrast, muscle cells require a lot of energy to carry out their function (to contract) and so have a lot more mitochondria in their cells – closer to 1700!

Diffusion

During digestion, we break down carbohydrates that are in our food into small sugars such as glucose. The glucose is absorbed into the blood by the small intestine. The heart pumps the blood around the body so the blood is constantly circulating. Once in the blood, the glucose is delivered to all of the cells in the body. The glucose in the blood diffuses into cells that need glucose. The lungs take in oxygen from the air, and it diffuses into the blood. In a similar way to glucose, all cells also rely on the circulation of the blood to receive oxygen. Just like glucose, oxygen diffuses into cells.

Diffusion is the net movement of a substance from a high concentration to a low concentration. Since your cells are constantly using up glucose during respiration, the concentration of glucose in cells gets lower and lower. When the concentration of glucose is lower than the concentration of glucose in the blood, glucose will diffuse into the cells.

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In this way, our digestive system and circulatory system make sure that all of the cells in our body receive a constant supply of glucose.

Comprehension questions

1. State the role of the mitochondria in cells.2. Explain why different cells contain different numbers of mitochondria.3. Name the process used to break down food into nutrients so they are small

enough to absorb.4. Define diffusion.5. Explain the phrase ‘net movement of a substance’?6. Sketch an cell next to a blood vessel, where:

a. There is no diffusion of glucose. (Hint: will the cell have a higher concentration of glucose, or the blood, or neither?)

b. Glucose diffuses into the cell. (Hint: will the cell have a higher concentration of glucose, or the blood, or neither?)

7. Plants also have mitochondria in their cells. Explain what this tells you about plants.

8. Ext: Is diffusion a chemical reaction or a physical process? Explain your answer.

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3 Recap of Respiration

Do now

1. Name the organ in the digestive system which absorbs glucose into the blood.2. Name the organelle in which aerobic respiration takes place.3. Diffusion is the net movement of a substance from a __________ concentration to a

__________ concentration.4. A tissue is a group of __________ working together to perform a particular function.5. State the role the circulatory system.

Respiration

Once oxygen and glucose enter the cell, they diffuse to the mitochondria. Here a series of chemical reactions called aerobic respiration take place. Overall, the word equation is:

glucose + oxygen carbon dioxide + water (+energy)

Glucose and oxygen are the reactants whose atoms rearrange during the chemical reaction. The products of respiration are carbon dioxide and water. Energy is not called a product since it is not made out of atoms. We say energy is released and not ‘made’, because energy can never be created or destroyed. The energy released from respiration can be used to carry out the functions of the specialised cell. Since energy is released during this chemical reaction, respiration is an exothermic reaction.

Importantly, respiration is not the same as breathing. Breathing includes taking air into the lungs (inhaling) and pushing air out of the lungs (exhaling). Neither inhalation nor exhalation is a chemical reaction that releases energy so neither is called respiration. In fact, it is possible for respiration to happen without any oxygen at all – anaerobic respiration. When animals suddenly need lots of energy such as during exercise, the respiring cells start to use up oxygen very quickly. If the cells use up oxygen more quickly than can be replaced, the cells will switch to using anaerobic respiration. This process releases less energy from glucose than aerobic respiration, and the product is lactic acid:

glucose lactic acid (+energy)

Summary

If we are to make links between all of the things we have learned, we can start to connect lots of ideas together (see diagram):

1. Plants photosynthesise to make glucose. (Plants also respire to release energy from the glucose).

2. Animals eat and digest plants, absorbing the plant-made glucose into the blood.

3. Animals breathe to get oxygen into the blood through a process called gas exchange. (We will learn more about this next lesson).

4. The heart pumps blood around the body to all of the cells.5. Glucose and oxygen diffuse from the blood into the body cells.6. In the mitochondria of the body cells, glucose and oxygen react to release

energy in a process called aerobic respiration.

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7. The specialised cells use the energy to perform their functions, helping the organism survive.

Comprehension questions

1. State the reactants of aerobic respiration.2. State the products of aerobic respiration.3. Explain why energy is not considered a ‘product’ of respiration.4. State what type of reaction respiration is.5. Describe the situation in which animals switch from aerobic to anaerobic

respiration.6. Maria says that ‘Breathing in and out is the same as respiring’. Explain why she is

incorrect.

Ext: ‘If you stop eating food, after a while, your cells will stop functioning.’ Explain why this statement is correct. You must link eating to cell function in your answer.

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4 Respiratory System

Do now

1. State the two main gases found in the air.2. State the percentage composition of these two gases in the air.3. Put the following in order:

a. Glucose from our diet enters our blood through our small intestine.b. The glucose and oxygen from the blood diffuses into our body cells.c. Respiration releases energy for the cell to use.d. Our body cells contain mitochondria that use glucose and oxygen to

respire.e. The cell uses this energy to carry out its function.f. The blood carries glucose and oxygen as it is pumped around our body.g. Oxygen from the air diffuses into our blood through our lungs.

4. State the two products of aerobic respiration.5. Which of these two products is a waste product that is eventually breathed out?

The organ system

To survive, living organism need materials from their environment. To achieve this, some organ systems have evolved to exchange materials with the environment, such as the digestive system and the respiratory system. The main function of the respiratory system is to allow humans to take in oxygen from the atmosphere and to give out carbon dioxide. This overall goal can be broken down into two primary functions: ventilation & gas exchange. Ventilation is inhalation and exhalation (the actual act of breathing in and breathing out). Ventilation gets air into and out of the lungs. Gas exchange is the diffusion of gases into and out of the blood that supplies the lungs.

Which organs are included in this organ system? In this lesson, we will study the anatomy of the respiratory system in depth. We will also learn the functions of the various anatomical structures that make up the respiratory system. In the next few lessons, we then study in detail how ventialtion happens and how gas exchange happens. We then study how our respiratiory system must also carry out secondary functions: to protect our lungs and body.

Structures

To understand the respiratory system, it is important to know the anatomy of the system. Anatomy is the study of the different structures that make up the body. It helps to know the some of the scientific names and the common names for some of these structures:

Throat: pharynxVoice box: larynxFood pipe: oesophagusWind pipe: trachea

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Comprehension questions

1. The respiratory system and digestive system are both examples of what?a. Cellsb. Tissuesc. Organsd. Organ systems

2. State the function that both the respiratory system and digestive system have in common. (Hint: read the first paragraph).

3. ‘The respiratory system’s main job is to carry out respiration.’ True or false?4. In one sentence, state the main function of the respiratory system.5. Define ventilation.6. Explain the difference between inhalation and exhalation.7. Explain the difference between gas exchange and ventilation.

The structures that air passes through

When we inhale (breathe in), air flows in from the nose into the nasal cavity. This is a space behind the nose. From here, the air flows down through the pharynx. When we breathe in from our mouth, the air flows directly into our pharynx.

The nose and mouth are connected. Look carefully at the diagrams to see how. Both food and air passes through our pharynx, before going into the correct pipe: the trachea carries air to the lungs, whilst the oesophagus carries food to the stomach.

Understanding this anatomy explains why you can breathe in through your mouth or your nose. It also explains, rather disgustingly, why we sometimes feel a drink coming up into our nose when we laugh or cough suddenly.

Because the pharynx can lead either to the stomach via the oesophagus or the lungs via the trachea, there must be a way to make sure food goes down the oesophagus and air goes into the lungs.

When you swallow, a special flap of cartilage tissue (the same type of stiff tissue that your ears are made out of) called the epiglottis closes the trachea and keeps the oesophagus open. This prevents food entering the trachea. During inhalation, the epiglottis lifts up, allowing air to enter the trachea. This means you cannot inhale and swallow at the same time – you can only do one or the other.

Before reaching the trachea, the air from the pharynx passes through the larynx (voice box), allowing you to make sounds when you need to. The larynx contains two bands of

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muscles called vocal cords. When you breathe in, the muscles open to let air through. But when you exhale you can contract the muscles, pulling the cords together causing them to vibrate allowing you to sing or speak. The vibrations can be heard as sounds. This explains why you can only make control your voice when you breathe out, not in.

After passing through the larynx, the air goes down the trachea, which is also made of cartilage. The trachea is a pipe that eventually splits into two branches called bronchi (singular: bronchus). The left bronchus supplies the left lung with air. It then branches again into smaller, narrower tubes called bronchioles. Each bronchiole ends in a cluster of air sacs called alveoli (singular: alveolus). The alveoli are surrounded by capillaries. Capillaries are very small and narrow blood vessels.

Comprehension questions

1. Draw a flow chart naming the different parts of the respiratory system that the air passes through after breathing in through the nose. (Hint: start at the nose and end at the alveoli; there are six parts in between).

2. Both food and air pass through the pharynx. True or false.3. Both food and air pass through the larynx. True or false.4. Describe the function of the epiglottis.5. Name the structure that vibrates when we talk.6. If we count the tubes in the lungs, we have 1 _________, 2 ________ and many

_______________.7. Alveoli are tiny air sacs and are surrounded by a capillary. True or false?

Gas exchange

Oxygen from the air diffuses through the wall of the alveolus into the capillary that surrounds it. This oxygenates the blood. Carbon dioxide from the blood diffuses out of the capillary and into the alveolus. When we exhale, we breathe out the air that now contains less oxygen and more carbon dioxide than the air we inhaled.

We will learn more about gas exchange in a future lesson.

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5 Ventilation

Do now (3 minutes)

1. Name the three states of matter.2. State the organelle in which photosynthesis takes place.3. Name the four layers of the Earth.4. Sketch the symbol for a light bulb.5. State the word equation for aerobic respiration.

Recap (3 minutes)

1. State the scientific name for the:a. Wind pipe.b. Food pipe.c. Flap that blocks the wind pipe when swallowing.

2. Ventilation is _______________ and _________________.3. The wind pipe branches into two pipes, called ____________ which go into each

lung.4. At the end of each bronchiole, there are tiny air sacs called a_______________.5. Name the organ system that has the following function:

a. Transport blood which carries oxygen, glucose (and other nutrients) around the body.

b. Carry out ventilation & gas exchange. Bring oxygen from air to the blood, and carbon dioxide out.

c. Break down food and absorb nutrients into the blood.

Ventilation

You will recall from the previous lesson that the respiratory system has two main functions: ventilation and gas exchange. Ventilation is the process of breathing in and out. This lesson, we will learn the structures involved in controlling ventilation.

The human body can be divided into three anatomical sections. At the top is your head. The top of your chest to the bottom of your lungs (where the diaphragm is) is called your thorax. The section below your diaphragm is called your abdomen. The abdomen is where most of your digestive system is.

In your thorax is the rib cage: a set of bones called ribs that join at the sternum in the centre of the chest. The rib cage has two functions: to protect the organs in the chest (lungs and heart) and to help us to breathe. The rib cage helps us to breathe in by being pushed upwards and outwards, increasing the volume of the chest. In order to move the rib cage, special muscles between the ribs called intercostal muscles contract. When we exhale, the intercostal muscles relax, allowing the ribcage to return to its normal size, reducing the volume of the chest, forcing air out of the lungs.

Below the lungs, there is a special muscle called the diaphragm. The diaphragm is a long muscle that lowers when it contracts. When the diaphragm lowers, it creates more space in the thorax, allowing the lungs to expand, causing air to rush into the lungs.

Comprehension questions

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1. Name the bones that make up the rib cage.2. State the two functions of the rib cage.3. Name the muscles that control the movement of the rib cage.4. Describe how the rib cage moves when the intercostal muscles contract.5. Describe how the volume of the thorax changes when the intercostal muscles

contract.6. Name the muscle below the lungs that separates the thorax from the abdomen.7. Describe how this muscle moves during inhalation.8. Does the movement of this muscle increase or decrease the volume of the

thorax?9. Ext : Draw a flow chart to show what happens during the first stages of

inhalation.

Pressure

Why does increasing the size of the thorax cause air to rush in? To understand this we need to understand pressure.

All particles have energy. Particles in a gas have more energy than the particles in a liquid or solid. This explains why particles of a gas are constantly moving around. When these particles are in a closed space such as the lungs, as they move around, they hit the walls of the lungs.

In the lungs, gases apply (exert) a force to the lung walls when the particles of gas hit the walls. When the thorax get bigger, the pressure decreases because the particles become more spread out. In fact, the pressure in the lungs becomes lower than the atmospheric pressure. Whenever there is a pressure difference, air will move to try to make the pressure equal. This causes air to rush into the lungs. It is similar to squeezing all of the air out of your water bottle. The pressure inside this bottle is lower than the atmosphere. When you open the lid, what happens? Air from the atmosphere rushes into the bottle to equalise the pressure.

So, when the intercostal muscles contract, the rib cage moves up and out. When the diaphragm contracts, it moves down. Both of these increase the area of the thorax. This causes the pressure in the lungs to decrease, causing air to rush into the lungs. This is what causes inhalation.

The exact opposite happens during exhalation.

Comprehension question

1. Put these in order of particles that have the highest to lowest energy: gas, solid, liquid.

2. What do we call the total forces of particles in the air hitting the walls of the lungs?

3. Does an increase or decrease in the volume of the lungs cause the pressure to decrease?

4. Explain why air rushes into the lungs when the intercostal muscles and diaphragm contract.

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5. Fill in the blanks for exhalation: When the intercostal muscles _________, the rib cage moves ______ and ______. When the diaphragm ____________, it moves _________. Both of these ___________ the area of the thorax. This causes the pressure in the lungs to __________, causing air to rush ___________ the lungs. This is _______________.

Inhalation

Exhalation

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6 Gas Exchange

Do now

1. Name the two poles of a magnet.2. State the direction of the magnetic field.3. Name the reagent you would use to test for starch.4. Describe what you would observe if starch is present.5. Name the scientist who suggested organisms adapt to their environment

through natural selection.6. Name the product of the reaction between sodium and oxygen.

Recap

1. State the two functions of the respiratory system.2. State the gas reactant needed for aerobic respiration.3. Breathing and respiration are the same thing. T or F?4. State the structures of the lungs that air passes through starting from the wind-

pipe. Hint: there are four structures.5. Name the two groups of muscles that contract when we inhale.6. Describe how the volume of the thorax changes when we inhale.

Gas exchange

Last lesson, we learned about ventilation: inhalation and exhalation of air. Once air from the atmosphere enters our lungs, the oxygen must enter our blood so that it can be carried to every respiring cell in our body. Equally, carbon dioxide, the waste product of aerobic respiration, must be removed from the blood and enter our lungs, so it can be exhaled. Both of these functions are achieved through a process called gas exchange. Gas exchange is the diffusion of oxygen from the alveoli into the blood, and the diffusion of carbon dioxide from the blood to the alveoli.

Immediately after inhalation, there is air inside the alveoli of the lungs. The composition of this air is: 78% nitrogen, 21% oxygen, 0.04% carbon dioxide and the rest is water vapour, argon and other gases. Gas exchange includes the diffusion of oxygen from the alveoli into the blood. The air we exhale contains only 16% oxygen. This means we absorb around a quarter of the oxygen we inhale. The air we breathe out contains 4% carbon dioxide. The large difference between the composition of the air we inhale and exhale is evidence that a significant amount of diffusion takes place. How are the alveoli, which are the functional unit of the lungs, adapted to maximise the rate of diffusion?

Comprehension questions

1. Define gas exchange.2. State the two functions of gas exchange.3. Describe how the percentage composition of oxygen in the air we inhale and

exhale changes.4. Explain why the percentage composition of oxygen in the air we inhale and

exhale changes.5. Describe how the percentage composition of carbon dioxide in the air we inhale

and exhale changes.

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6. Explain why the percentage composition of dioxide in the air we inhale and exhale changes.

Adaptations of alveoli

Diffusion is usually a slow process because it relies on the random (Brownian) motion of molecules. There are four factors that affect the rate of diffusion: steepness of the concentration gradient (difference in concentration between the two sides), the surface area across which diffusion is happening, the distance the molecules must travel and temperature. Our respiratory system has evolved to make each of these four factors favourable to maximise the rate at which gas exchange (by diffusion) takes place. Can you draw an image to show why each factor affects the rate of diffusion?

Each alveolus is supplied with capillary, which carries blood. The alveoli have a very good blood supply, allowing lots of diffusion to take place – an important adaptation for rapid gas exchange. This blood has a very low concentration of oxygen, because it is blood returning from the body. All of the cells of the body have used up the oxygen from the blood. The high concentration of oxygen in the alveoli and low concentration of oxygen in the blood means there is a steep concentration gradient. A steep concentration gradient ensures diffusion occurs rapidly. Oxygen diffuses across the wall of the alveolus (which is one cell thick), through the wall of the capillary (which is also one cell thick) and into the blood stream. The thin walls of the alveolus and capillary provide a short diffusion path for the oxygen, another adaptation causing diffusion to occur rapidly.

Diffusion is the key process that explains the movement of oxygen and carbon dioxide molecules. The molecules are constantly moving between the alveoli and the blood, but there is a net movement of oxygen from the alveoli into the blood, and a net movement of carbon dioxide from the blood into the alveoli.

Importantly, diffusion is happening continuously. Inhalation of fresh air occurs with each breath we take, and this increases the rate of diffusion because the concentration of oxygen inhaled is 21% again (instead of 16% after diffusion has occurred). This maintains a steep concentration gradient to allow diffusion to continue at a high rate.

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Therefore the fourth factor which makes diffusion rapid is continuous inhalation and exhalation.

Finally, when air enters our airways, it is warmed by the nasal cavity to within one degree of our body temperature. This is to prevent us from losing too much body heat – but, as an additional benefit, warmer air diffuses faster. We know this is the main reason because air that is too warm is cooled to match our body temperature too. Therefore, arguably, this is not really an adaptation to increase the rate of diffusion per say.

Comprehension questions

1. State four factors which affect the rate of diffusion.2. Describe the four main adaptations of the lungs that increase the rate of gas

exchange.3. Name the process that explains the movement of oxygen from the alveoli to the

blood.4. Name the blood vessel that supplies each alveolus.5. Explain the feature of the lungs that reduces the distance gases must diffuse

during gas exchange.6. Explain why it is important that we constantly breathe in and out. Refer to one of

the factors that affect the rate of diffusion in your answer.

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7 ExerciseDo Now

1. Name the muscles found between the ribs. 2. Name the muscle found under the lungs that lowers during inhalation. 3. Are the lungs found in the head, thorax or abdomen?4. When we breathe in, the volume of the thorax ___________.5. When we breathe out, the volume of the thorax ___________.6. Explain why every cell in our body needs oxygen. 

Exercise

In gas exchange, oxygen and carbon dioxide move between the alveoli and the blood in the lungs. Oxygen is transported to cells for aerobic respiration and carbon dioxide, a waste product of respiration, is removed from the body. Breathing (ventilation) occurs through the action of intercostal muscles and the diaphragm. What affects the rate at which we breathe? Why do we breathe more quickly and more deeply sometimes? The amount of oxygen required by cells in the body determines the rate of breathing. In other words, the more oxygen our cells need, the faster our breathing rate.

During exercise, the muscle cells in the body contract and relax more than they do at rest. To contract, muscle cells require energy transferred from respiration. This means that muscle cells respire more during exercise than they do at rest. Muscle cells require oxygen and glucose to be delivered to them more quickly during exercise and waste carbon dioxide must be removed more quickly.

Exercise affects the respiratory system by increasing the rate of breathing and the depth of breathing. Rate of breathing is how many times the lungs inhale and exhale in one minute and depth of breathing is the volume of gas inhaled each time. The circulatory system also changes during exercise by increasing the heart rate. The heart rate is the number of times the heart beats per minute and an increased heart rate increases the rate of blood flow through the lungs and around the body.

We can think of this as supply and demand: more exercise demands more energy, which demands more oxygen and glucose. To supply more oxygen, our breathing rate and depth increases. To deliver more oxygen and glucose, out heart rate increases.

The increased rate and depth of breathing during exercise increases the rate of gas exchange in the alveoli of the lungs. More oxygen is moved in to the blood from the alveoli of the lungs and more carbon dioxide is moved out of the blood to the alveoli.

To meet the increased demand for glucose, the muscles release glucose from a special storage molecule called glycogen. This can then be converted back to glucose for use during exercise with the oxygen from gas exchange in the alveoli.

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Anaerobic respiration

Not enough oxygen may reach the muscles during vigorous exercise. When this happens, muscle cells use anaerobic respiration in the cytoplasm of cells to obtain energy. Anaerobic respiration involves the incomplete breakdown of glucose. It releases around 5% of the energy released by aerobic respiration, per molecule of glucose. During anaerobic respiration the waste product in muscle cells is lactic acid rather than carbon dioxide and water:

glucose → lactic acid (+ little energy)

Much less energy is released during anaerobic respiration than during aerobic respiration. This is because the breakdown of glucose is incomplete. Anaerobic respiration produces an oxygen debt. This is the amount of oxygen needed to oxidise lactic acid to produce carbon dioxide and water. The existence of an oxygen debt explains why we continue to breathe deeply and quickly for a while after exercise.

Muscles become fatigued (tired) during long periods of vigorous activity. This means that they stop contracting efficiently and they no longer work as well. One cause of this is the build-up of lactic acid in the muscles from anaerobic respiration. The lactic acid is removed from the muscles by blood flowing through them and providing oxygen to break lactic acid down in to carbon dioxide and water.

Fitness versus health

Fit people are able to carry out physical activities more effectively than unfit people as training improves the efficiency of the respiratory and circulatory system. As people train through exercising more they can improve their breathing depth and the volume of blood pumped by the heart. Their heart rate (pulse) is likely to return to normal more quickly after exercise as gas exchange is more efficient.

But being fit is not the same as being healthy. Healthy people are free from disease and infection - they may or may not be fit as well. It is possible to be fit but unhealthy, or healthy but unfit.

Questions

1. State the word equation for aerobic respiration in humans.2. State where in the cell aerobic respiration takes place.3. State the word equation for anaerobic respiration in humans.4. State where in the cell anaerobic respiration takes place.5. Describe three differences between aerobic and anaerobic respiration.6. Describe the effect of exercise on rate and depth of breathing.7. Explain the effect of exercise on rate and depth of breathing.8. Explain why anaerobic respiration occurs during hard exercise.9. Define oxygen debt.10. Explain how the respiratory system reduces oxygen debt.11. What substance is glucose stored as in the muscles?12. Explain the cause of muscle fatigue.13. Explain why exercising more improves your fitness.14. Explain why an Olympic sprinter may be fit but could be unhealthy.

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Factors affecting the respiratory system

Do now

1. Define ventilation.2. State the function of the respiratory system.3. Name the two muscles that relax during exhalation.4. Name the cell that carries oxygen.5. Name the proteins that is found in this cell that binds oxygen.

The human respiratory system is adapted to allow air to pass in and out of the body, and for efficient gas exchange to happen. Exercise and smoking both affect the lungs and circulatory system.

Effects of smoking

Smoking can cause lung disease, heart disease and certain cancers. Nicotine is the addictive substance in tobacco which quickly reaches the brain and creates a dependency so that smokers become addicted.

Smoking affects the air passages of the respiratory system. Sticky mucus in these air passages normally traps pathogens. This mucus is normally swept out of the lungs by the cilia on the epithelial cells lining the trachea, bronchi and bronchioles. However, cigarette smoke contains harmful chemicals that damage these cilia cells, leading to a build-up of mucus and a smoker’s cough. Smoke irritates the bronchi, causing bronchitis which is where there is infection in the bronchi of the lungs.

Cigarette smoke also damages the walls of the alveoli. The alveoli walls break down and join together, forming larger air spaces than normal. This reduces the efficiency of gas exchange as there is now a smaller surface area of alveoli with a poorer blood supply. People with the lung disease emphysema (a type of COPD, or chronic obstructive pulmonary disease) carry less oxygen in their blood and find even mild exercise difficult as gas exchange in the alveoli is very inefficient.

Carbon monoxide (CO) from cigarette smoke combines irreversibly with the haemoglobin in red blood cells. This reduces the ability of the blood to carry oxygen, putting strain on the circulatory system and increasing the risk of coronary heart disease and strokes as the circulatory system becomes damaged.

Carcinogens are substances that cause cancer. Tobacco smoke contains many carcinogens, including tar. These carcinogens increase the risk of lung cancer, and cancer of the mouth, throat and oesophagus. The picture above show sections of a healthy lung and a smoker's lung, showing tar deposits.

Questions

1. Name the addictive chemical in tobacco.

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2. State the definition for a carcinogen and give an example.3. State three types of cancer where there is an increased risk for smokers.4. State three problems caused by smoking.5. Name the cells damaged by cigarette smoke and where they are found.6. Explain why smokers have “smokers cough”.7. Explain why smoking can increase risk of bronchitis.8. Describe the effect of smoking on the alveoli.9. Explain how smoking affects gas exchange in the alveoli.10. Describe the effect of carbon monoxide on the ability of blood to carry oxygen.

Asthma

Asthma affects the small airways (bronchioles) that carry air in and out of the lungs. If you have asthma your airways can become inflamed, swollen and constricted (or narrowed) and excess mucus is produced. More than 5.2 million people in the UK receive treatment for asthma - including 1.1 million children.

The symptoms of an asthma attack include wheezing, a tight chest and difficulty breathing. Symptoms can be treated using asthma relievers. Relievers are drugs that relax and open up the airways, making it easier to breathe (ventilate). Relievers are often administered using a device called an inhaler - which enables you to breathe the medicine in through your mouth, directly into your lungs were it acts to open up airways.

During an asthma attack the lining of the airways becomes inflamed, fluid builds up in the airways and the muscles around the bronchioles contract, which constricts the airways. This makes it difficult for ventilation of the lungs and therefore less gas exchange takes place.

Questions

1. State the part of the respiratory system affected by asthma.2. Explain the cause of asthma in the airways.3. Describe three symptoms of an asthma attack.4. Explain how relievers reduce the symptoms of asthma.5. Describe the change in the respiratory system during an asthma attack.6. Explain why asthma attacks are dangerous for people if not treated quickly with

a reliever.7. Suggest why people with asthma may find it difficult to undertake vigorous

exercise without a reliever.

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Respiratory System

1 Circulatory system

Heart, blood vessels & blood.Transports blood which carries oxygen, glucose (and other nutrients) around the body.

13 Rib cage Bones in chest: Ribs + sternum. Protect organs & help us breathe.

2 Respiratory system

Nose nasal cavity pharynx larynx trachea bronchi bronchioles alveoliVentilation & gas exchange.Oxygen from air diffuses from the alveoli into the blood, and carbon dioxide out.

14 Intercostal muscles

Muscles between ribs. Help us breathe.

3 Digestive system

Mouth oesophagus stomach small intestine large intestine rectum anus+ Salivary gland, liver, gall bladder, pancreas.Break down food and absorb nutrients into the blood.

15 Diaphragm Muscle below lungs. Helps us breathe.

16 Red blood cell

Specialised cell containing haemoglobin to bind oxygen in the blood. Bi-concave disc, no nucleus.

4 Nasal cavity Space behind nose.Moistens, cools & filters air.

17 Gas exchange

Diffusion of oxygen from air in alveoli to blood. Diffusion of carbon dioxide from blood to air in alveoli.

5 Pharynx Throat. Connects mouth and nasal cavity to oesophagus and trachea.

18 Inhalation Breathing in air.

6 Epiglottis Flap of cartilage. Covers trachea during swallowing, lifts during inhalation.

19 Exhalation Breathing out air.

7 Larynx Voice box. Contains vocal cords. 20 Ventilation Inhalation & exhalation.8 Trachea Wind pipe. Carries air from pharynx to

lungs.21 Breathing

rateNumber of breaths taken per minute.

9 Bronchi(s. bronchus)

Trachea splits into two bronchi, each conducting air to one lung.

22 Glycogen Polymer of glucose allowing it to be stored in tissues.

10 Bronchioles Bronchi split into many bronchioles, each 23 Carcinogen Chemical capable of causing cancer

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conducting air to a group of alveoli.11 Alveoli

(s. alveolus)Tiny air sacs in lungs. Once cell thick. Site of gas exchange.

34 Asthma Respiratory disease caused by the regular inflammation of the airways.

12 Capillary Tiny blood vessel supplying all cells. One cell thick to allow short diffusion path for substances

35 Nicotine Addictive substance in tobacco.

Knowledge Organiser – KS3 Biology – Respiratory System

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