KS 4 Biology What is Blood 1 of

KS 4 Biology • What is Blood? 1 of 40 © Boardworks Ltd 2004

Contents What is Blood? What is blood made of? Plasma Red blood cells White blood cells Platelets Summary activities 2 of 40 © Boardworks Ltd 2004

Blood and the circulatory system The circulatory system is made up of the heart, blood and blood vessels. What exactly is blood and what does it do? Blood is the fluid that flows in the circulatory system and carries substances around the body. 3 of 40 © Boardworks Ltd 2004

How much blood? How many litres of blood are there in the circulatory system of an average adult? 5. 5 litres 4 of 40 © Boardworks Ltd 2004

What is blood made of? Blood is made up of a liquid called plasma and blood cells that float in this plasma. If a test tube of blood is left to stand for a while what happens to it? The blood cells sink to the bottom of the test tube and separate from the plasma which is a clear yellow liquid. The liquid in blood is yellow! So why does blood look red? 5 of 40 plasma (55% of volume) blood cells (45% of volume) © Boardworks Ltd 2004

Different types of blood cells Blood plasma carries three types of blood cells. They have different shapes and carry out different functions. red blood cell white blood cell platelet 6 of 40 © Boardworks Ltd 2004

What’s in a drop of blood? 7 of 40 © Boardworks Ltd 2004

Contents What is Blood? What is blood made of? Plasma Red blood cells White blood cells Platelets Summary activities 8 of 40 © Boardworks Ltd 2004

What does plasma do? Blood flows around the body transporting substances from one place to another. Plasma is the blood fluid that surrounds blood cells and carries them along as it flows through the blood vessels. Plasma is mostly water and contains other substances that are dissolved in it. What useful and waste substances are dissolved in and transported by plasma? 9 of 40 © Boardworks Ltd 2004

What is dissolved in plasma? Plasma is mostly water with other substances dissolved in it. l Useful substances dissolved in plasma are digested food. This must be transported to where it is needed in the body. l Waste substances dissolved in plasma are carbon dioxide and urea. These must be transported to where they can be removed from the body. 10 of 40 © Boardworks Ltd 2004

Plasma: transporting digested food The digestive system breaks long insoluble molecules of food into small soluble molecules that the body can use. Where does soluble digested food enter the blood? digested food in blood plasma Soluble digested food diffuses from the small intestine into the bloodstream and dissolves in the plasma. The digested food is then carried to the body’s cells and used in various chemical reactions. 11 of 40 © Boardworks Ltd 2004

Plasma: transporting carbon dioxide Carbon dioxide is produced by respiration in the body’s cells. This waste product is poisonous to the body and so must be removed as quickly as possible. How does this happen? carbon dioxide in blood plasma Carbon dioxide diffuses from body cells into the blood where it dissolves in plasma. Carbon dioxide then carried from the cells to the lungs. How is this waste product finally removed from the body? 12 of 40 © Boardworks Ltd 2004

Plasma: transporting urea Urea is another waste substance that is transported by the blood. It is made in the liver. Urea is toxic to the body and must be removed as quickly as possible. urea in blood plasma Urea enters the blood in the liver and dissolves in plasma. It is then carried from the liver to the kidneys. The kidneys filter blood and remove urea from plasma. This waste product is then removed from the body in urine. 13 of 40 © Boardworks Ltd 2004

Dissolved substances in plasma 14 of 40 © Boardworks Ltd 2004

What does plasma do? 15 of 40 © Boardworks Ltd 2004

Contents What is Blood? What is blood made of? Plasma Red blood cells White blood cells Platelets Summary activities 16 of 40 © Boardworks Ltd 2004

What do red blood cells do? Red blood cells are the most common type of blood cell. The job of red blood cells is to transport oxygen from the lungs to the body’s cells, where is used in respiration. oxygen The body contains millions and millions of red blood cells. Why does it need so many? 17 of 40 © Boardworks Ltd 2004

Features of a red blood cell A red blood cell has several features that help it do its job: 18 of 40 It contains haemoglobin, a special pigment that combines with oxygen. Disc-shaped, with a dent on each side, creates a large surface area for gas exchange. It has no nucleus, so there is more space for haemoglobin and so more oxygen. A large surface area compared to volume, so oxygen is always close to the surface. © Boardworks Ltd 2004

Another feature of red blood cell Another important feature of a red blood cell is its size. The diameter of a red blood cell is slightly bigger than the average diameter of a capillary. How does this help the release of oxygen? The size of a red blood cell forces it to slow down as it passes through a capillary. The surface of the red blood cell is exposed to the surface of the capillary and so gas exchange will definitely happen. 19 of 40 © Boardworks Ltd 2004

Features of a red blood cell – activity 20 of 40 © Boardworks Ltd 2004

Red blood cells and haemoglobin Haemoglobin is the special pigment in red blood cells. At the lungs, oxygen diffuses into red blood cells and combines with haemoglobin to form oxyhaemoglobin. oxygen + oxyhaemoglobin This is how red blood cells are able to bind to oxygen and carry it in the blood. Oxyhaemoglobin makes red blood cells appear bright red. 21 of 40 © Boardworks Ltd 2004

Red blood cells and haemoglobin Red blood cells loaded with oxyhaemoglobin carry oxygen from the lungs to the body’s cells. Here, oxyhaemoglobin changes back to haemoglobin and oxygen is released. oxyhaemoglobin + oxygen Oxygen is then able to diffuse into the body’s cells. Why do red blood cells appear a dull red colour when oxygen is released? 22 of 40 © Boardworks Ltd 2004

Journey of a red blood cell Oxygen enters the body when air is inhaled into the lungs. oxygen + haemoglobin How does this oxygen enter the blood? Oxygen diffuses from the alveoli on the surface of the lungs into the bloodstream. The oxygen then diffuses into the red blood cells where it meets haemoglobin. (not to scale) 23 of 40 © Boardworks Ltd 2004

Journey of a red blood cell In the red blood cells at the lungs, oxygen combines with haemoglobin to form oxyhaemoglobin. This oxygen-rich blood travels from the lungs, through the circulatory system, to body cells. How does oxygen get from red blood cells into the body’s cells? oxygen + haemoglobin oxyhaemoglobin (not to scale) 24 of 40 © Boardworks Ltd 2004

Journey of a red blood cell When red blood cells reach the body’s cells, oxyhaemoglobin changes back to haemoglobin and oxygen is released. Oxygen then diffuses from the red blood cells across the lining of the capillary and into the body’s cells. What happens next to the red blood cells? oxygen + haemoglobin oxyhaemoglobin + oxygen (not to scale) 25 of 40 © Boardworks Ltd 2004

Journey of a red blood cell Red blood cells that have released oxygen to the body’s cells have to get back to the lungs. So this oxygen-poor blood travels from the body’s cells through the circulatory system. At the lungs, the red blood cells can pick up more oxygen and start another journey around the body. oxygen + haemoglobin oxyhaemoglobin + oxygen (not to scale) 26 of 40 © Boardworks Ltd 2004

Red blood cells in an alvelous 27 of 40 © Boardworks Ltd 2004

Red blood cells in a capillary bed 28 of 40 © Boardworks Ltd 2004

How do red blood cells carry oxygen? 29 of 40 © Boardworks Ltd 2004

Contents What is Blood? What is blood made of? Plasma Red blood cells White blood cells Platelets Summary activities 30 of 40 © Boardworks Ltd 2004

What do white blood cells do? White blood cells are the largest type of blood cell. They have a large nucleus and can change their shape. White blood cells protect the body from disease by fighting invading microbes that can cause infection. White blood cells can squeeze through the walls of capillaries. How does this help them fight against microbes? 31 of 40 © Boardworks Ltd 2004

Different types of white blood cells protect the body in different ways: Some white blood cells fight against infection by surrounding invading microbes and then digesting them! Other white blood cells produce antibodies or antitoxins to fight against infection. 32 of 40 © Boardworks Ltd 2004

White blood cell count Doctors can check the number of white blood cells in a person’s blood to find out if they are healthy or fighting off an infection. healthy white blood cell count is low unwell white blood cell number is high Why is the white blood cell count higher when a person is fighting off an infection? 33 of 40 © Boardworks Ltd 2004

Contents What is Blood? What is blood made of? Plasma Red blood cells White blood cells Platelets Summary activities 34 of 40 © Boardworks Ltd 2004

What do platelets do? Platelets are third type of blood cell. platelet They are important for blood clotting. Platelets are cell fragments that have broken off from other larger cells. They are much smaller than red and white blood cells and do not have a nucleus. 35 of 40 © Boardworks Ltd 2004

Platelets and blood clotting 1 Platelets help to make tiny fibres that form a net at the site of a cut. 2 Red blood cells are trapped in this net forming a blood clot. 36 of 40 3 The clot dries and forms a scab which protects the cut while new skin grows. Why is it important not to pick a scab? © Boardworks Ltd 2004

Contents What is Blood? What is blood made of? Plasma Red blood cells White blood cells Platelets Summary activities 37 of 40 © Boardworks Ltd 2004