تدريب Shadowing: GCSE Biology - The Lungs & Gas Exchange (2026/27 exams) - تعلم التحدث بالإنجليزية مع YouTube

In this video, we're learning about the human gas exchange system.

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In this video, we're learning about the human gas exchange system.

So we'll cover the structure of the gas exchange system, how alveoli carry out gas exchange, and then finally, how to calculate breathing rate as well.

start with the structure of the human gas exchange system.

Now, our body cells carry out respiration, which is how they release the energy we need for functions like thinking, feeling, and the muscle contractions we use to move as well.

Our cells need oxygen for respiration, and without oxygen they wouldn't be able to release energy, so we wouldn't survive.

We're going to follow the journey of oxygen through the human gas exchange system, which all starts when we breathe in air that contains oxygen.

It first enters through our nose or mouth, and then travels down the trachea, which is also known as the windpipe.

The air then moves into two bronchi, and each bronchus, which is what we call just one of these bronchi, leads to one of the two lungs.

These bronchi then split into smaller tubes called bronchioles, which keep getting smaller and smaller until the air reaches tiny sacs called alveoli.

These alveoli are surrounded by tiny blood vessels called capillaries.

And if we look more closely at just one alveolus, this is actually where gas exchange happens.

As oxygen moves from the air in the alveolus into the blood in the capillaries.

The oxygen enters red blood cells which contain haemoglobin, a substance that lets them carry oxygen through the bloodstream to the body cells, where it's then used for respiration.

It's important that you remember the respiration produces carbon dioxide as a waste product, and it travels in the opposite direction to the oxygen.

It moves from the body cells into the blood, which carries it to the capillaries surrounding the alveoli.

Once it's moved into the alveoli, the air containing carbon dioxide moves through the bronchioles, bronchi and trachea, and finally out through the nose or mouth and into the air when we exhale.

Next, let's look at how the alveoli carry out gas exchange.

Now the way gases move between the alveoli and the capillaries surrounding them is called diffusion.

and we use this word to describe the movement of substances from an area of high concentration to an area of low concentration.

For instance, let's say that this is the direction of blood arriving from the body cells to the capillary next to this alveolus, and this is the direction of blood leaving the lungs that will eventually be returned to the body cells.

Now at this point, the blood in the capillary doesn't have much oxygen because most of it's been used up by the body cells, but the air in the alveolus has lots of oxygen because it's just been inhaled.

So, oxygen diffuses down or along its concentration gradient, from an area of high concentration in the alveolus to an area of low concentration in the blood.

On the other hand, because it's produced by body cells during respiration, there's lots of carbon dioxide in the capillaries around the alveolus, so it's put a high concentration there.

But there's usually not much carbon dioxide in the air in the alveolus, so it's put a low concentration there.

This means carbon dioxide diffuses from the blood into the alveolus, and so it can then be exhaled out of the body.

The blood vessels leaving the lungs carry oxygen away to the body cells, and this is helpful because it keeps the oxygen concentration in the capillaries low around the alveoli, and so oxygen can keep diffusing into the blood.

This is happening all the time to keep our cells supplied with lots of oxygen.

Now, the alveoli have lots of adaptations for gas exchange that serve to make them really efficient at it.

First, if you look here on the alveolus, the walls are just one cell thick, which means there's a really short diffusion distance for gases to pass across.

Second, we have a large surface area because there are hundreds of millions of alveoli in the lungs, and this increases the rate of diffusion overall.

Third, the walls of the alveoli are moist, and this allows gases to dissolve.

This is important because it helps them to diffuse across more quickly.

Finally, let's look at how to calculate breathing rate, which is a measurement of the number of breaths you take per minute.

To calculate breathing rate we use the equation breathing rate equals the number of breaths taken divided by time,

where breathing rate is usually measured in breaths per minute and time is measured in minutes.

Let's see how this works by looking at a worked example.

On a walk, a person takes 15 breaths in 30 seconds.

What is their breathing rate?

First, we need to check our units are all correct.

We've been given our value for time in seconds instead of minutes here, so we need to take 30 seconds and divide it by 60 because there are 60 seconds in a minute.

This gives us 0.5 minutes.

Next, let's grab our equation and plug in our values, which gives us 15 divided by 0.5.

This means that the person's breathing rate is 30 breaths per minute.

Something important here though is that our breathing rate changes depending on what we're doing.

For example, it increases when we exercise more vigorously because our muscles need more oxygen, but also to get rid of carbon dioxide more quickly.

So if this same person started sprinting, they'd need to take in more oxygen, and so take more breaths in the same amount of time.

And so overall, their breathing rate would increase as a result.

If you haven't heard yet, you can find all of our videos on our website, cognito.org.

You'll also find questions, flashcards, exam-style questions, and past papers.

And we track all of your progress so that you always know what to study next.

So sign up for free by clicking here, or browse our playlist here on YouTube.

Thank you.

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