hi everyone welcome to IGCSE study buddy where you can revise biology topics from the Cambridge IGCSE syllabus if you are enjoying this video so far please don't forget to hit the like button and subscribe to my channel this video summarizes topic 11 gas exchange in humans the gas exchange system is responsible for getting oxygen into the blood and removing carbon dioxide as a person breeds in order for gas exchange to take place efficiently there are certain features of gas exchange surfaces that humans have they are large surface area thin surface good blood supply and good ventilation with air having a large surface area provides more space for diffusion to take place thereby speeding up the rate of gas exchange a thin surface reduces the distance across which the gases must diffuse thereby allowing a faster diffusion rate a good blood supply ensures that the concentration gradients are always maintained new deoxygenated blood is always arriving and oxygenated blood is constantly being carried away and good ventilation with air also ensures that the concentration gradients of carbon dioxide and oxygen are maintained now let's identify the parts of the breathing system this is the larynx the area containing the vocal cords this is the trachea or windpipe which connects the throat to the lungs these are the lungs which are the main organs in the respiratory system containing the surfaces where gas exchange takes place this is the diaphragm a flat sheet of muscle under the lungs which helps change the volume of the chest during breathing these are bronchi which are tubes that Branch out into two from the trachea carrying air from the trachea to the lungs and these are bronchioles here's a magnified diagram so these are bronchioles which are smaller tubes branched off from the bronchi leading to the alveoli which are tiny air sacs surrounded by capillaries gas exchange takes place here and these are capillaries surrounding the alveoli which are blood vessels through which blood passes these are ribs the bones that protect the lungs among other organs these are intercostal muscles found between ribs these muscles control the movement of ribs during breathing these are external intercostal muscles which are on the outside of the rib cage and these are internal intercostal muscles which are on the inside of the rib cage both these muscles are important in moving the rib cage during inhalation and exhalation what is the function of cartilage in the trachea the trachea is lined with rings of cartilage these rings of cartilage strengthen and support the trachea they keep the trachea open during breathing and prevent it from collapsing let's learn about ventilation ventilation or breathing is the act of moving air into and out of the lungs to allow gas exchange to occur let's learn what happens during inspiration also known as inhalation this is the act of breathing in the external intercostal muscles contract this means that the internal intercostal muscles relax since they are antagonistic pairs of muscles where when one muscle contracts the other muscle relaxes this pulls the rib cage upwards and outwards the diaphragm which is Dome shaped when relaxed in its normal position contracts and moves downwards flattening both of these factors lead to the volume of the thorax to increase the thorax is basically the chest area which will increase in volume like a blown up balloon when the volume of the thorax increases the air pressure inside the lungs decreases this is because the force exerted by the movement of gas molecules inside the lungs against the walls is lower since there's more space therefore pressure inside the lungs is lower in comparison to the surrounding air therefore air moves into the lungs from outside in the case of expiration or exhalation basically the opposite happens this is the act of breathing out the external intercostal muscles relax this means that internal intercostal muscles contract this lowers the rib cage downwards and inwards the diaphragm relaxes and moves back upwards to its original Dome shape both of these factors lead to the volume of the thorax to decrease when the volume of the thorax decreases the air pressure inside the lungs increases this is because the force exerted by the movement of gas molecules inside the lungs against the walls increases therefore pressure inside the lungs is higher in comparison to the outside atmosphere therefore air is forced out of the lungs to the surrounding air so once again in terms of volume and pressure during breathing in the volume increases so the pressure decreases therefore air moves into the lungs during breathing out volume decreases so pressure increases forcing the air out of the lungs next the differences in composition between inspired and expired air may be investigated using lime water as a test for carbon dioxide when we breathe in the fresh air will flow in from outside and go through boiling tube a when we breathe out the air will flow through boiling tube B lime water turns from clear to cloudy or milky in the presence of carbon dioxide the lime water in boiling tube a will remain clear whereas the lime water in boiling tube B will turn cloudy this proves that exhaled air has more carbon dioxide than inhaled air the composition of gases in inspired and expired air is different this difference is due to the gas exchange that happens at the alveoli in the lungs the table below will explain these differences in composition there is more oxygen in the air that we breathe in around 21 percent and the amount of oxygen in the air that is breathed out is 16 percent Which is less than that in inspired air the air in the atmosphere contains around 0.04 percent of carbon dioxide Which is less than that in expired air which is four percent the air that we breathe in has less water vapor than in the air that we breathe out so why are there differences in composition between expired and inspired air in the case of oxygen the inhaled oxygen diffuses through the walls of the alveoli and enters the bloodstream since the concentration of oxygen in the blood is lower the concentration of carbon dioxide in the blood surrounding the alveoli is higher than the inhaled carbon dioxide so the carbon dioxide diffuses out the body's warmth causes water from the alveoli surface to evaporate into the expired air that's why there's more water vapor when breathing out this diagram illustrates the gas exchange that takes place at the alveoli oxygen diffuses from the alveoli into the blood and carbon dioxide diffuses from the blood into the alveoli next let's learn about how physical activity affects breathing this can be investigated with a simple experiment count the number of breaths taken during one minute at rest measure how much the chest expands during each breath using a measuring tape find the average chest expansion over five breaths exercise for a fixed amount of time let's say three minutes immediately after exercise count the number of breaths taken in one minute also measure the average chest expansion over five breaths due to exercise the number of breaths per minute increases and chest expansion also increases therefore exercise increases the rate and depth of breathing so why does exercise increase the rate and depth of breathing exercise causes the body cells to respire faster to release more energy more carbon dioxide is produced so there's an increased carbon dioxide concentration in the blood this is detected by the brain which signals the body to increase the rate and depth of breathing this in turn allows gas exchange to happen more rapidly therefore carbon dioxide is removed faster from the body and also there's an increased intake of oxygen which is supplied to respiring cells faster finally let's learn how the breathing system is protected from pathogens and particles a thin layer of mucus lines the respiratory tract this mucus is produced by cells called goblet cells the respiratory tract is also lined with ciliated epithelial cells these cells have tiny hairs on them called cilia so the mucus produced by goblet cells trap pathogens and particles the Celia are constantly moving and they beat and push the mucus away from the lungs towards the throat where it can be swallowed this destroys pathogens and protects the lungs from them that concludes chapter 11 gas exchange in humans hope this video helped you thank you for watching and please don't forget to subscribe to IGCSE study buddy for more biology revision videos bye