Human Respiratory and Circulatory System PDF

## 2.1 Human Respiratory and Circulatory System ### Objective: - Explain that living organisms have a complex transport system for the transfer of various solids, liquids and gases across the body. ### Human Respiratory System Living things, whether they are a single cell or made up of billions...

## 2.1 Human Respiratory and Circulatory System ### Objective: - Explain that living organisms have a complex transport system for the transfer of various solids, liquids and gases across the body. ### Human Respiratory System Living things, whether they are a single cell or made up of billions of cells, need transport systems. They need to transport substances such as glucose and oxygen around the body and move them into the cells, and they need to remove waste substances such as carbon dioxide and urea. How do substances move in and out of cells? The answer is, often, by diffusion. As scientists, we know that matter is, whether solid, liquid or gas, is made up of moving particles which are too small for us to see. Diffusion takes place in gases and liquids as a result of the random movements of these tiny particles. Diffusion is the net (overall) movement of particles from an area where there are lots of them (a high concentration) to an area where there are fewer of them (a lower concentration). Understanding diffusion is important for understanding many the complex transport systems we see in many living organisms, including transport in the human respiratory system, transport in the blood, and the examples shown here. ### Diffusion in action Let's do a thought experiment. You are walking home from school. Your evening meal is cooking in the kitchen. As soon as you go into your home, you can smell the food. You probably start to feel hungry! How did the smell of the food reach your nose? Particles escape from the cooking food, where they are at a high concentration. They spread out randomly through the air by diffusion, down a concentration gradient. You breathe in some of these particles and your nose sends signals to your brain, which recognises the food. ### Diffusion in the digestive system What happens when you eat a meal? Your body cannot use the food you eat until it is broken down and carried in your blood to the cells which need it. The digested food moves into your blood from your digestive system by diffusion down a concentration gradient. ### Diffusion and Pollination All over the world people enjoy fruit, from pomegranates to bananas, and from grapes to pineapples. Lots of other animals also like eating fruit. Fruits are produced when flowers are pollinated. Lots of insects, birds and bats rely on diffusion to find the flowers they pollinate. How does this work? Many flowers produce a scent, which diffuses through the air to tell pollinators they are there. Insects like butterflies and moths pick up the scent and follow it up the concentration gradient until they reach the flower. ### Blood and sharks The oceans of the world are very large, but sharks still find their prey. If an animal is injured it will bleed. The blood spreads out through the water by diffusion. Sharks have a very good sense of smell. They smell substances such as blood in the water, even at very low concentrations. They will swim up the concentration gradient, smelling the blood until they find their prey. ### Diffusion and the lungs Later in this chapter, you are going to look at how we breathe, and how gases are exchanged in our lungs. It is important to remember what happens in diffusion. It will help you to understand how your respiratory system works, and what happens when it goes wrong. ### Diffusion: The net movement of particles in a liquid or gas down a concentration gradient, from a high concentration to a lower concentration. ### Questions: 1. Describe what matter is made of. 2. Give a definition of diffusion. 3. Describe how you can tell if there are some flowers in a dark room. 4. Describe how you think oxygen might get from the air in your lungs into your blood. ### Key points: - **Diffusion** is the net movement of particles in a fluid down a concentration gradient, from a high concentration to a lower concentration. - **Diffusion** is very important in many biological systems.