Living things have certain life processes in common. There are seven things that they need to do to count as being alive. The phrase MRS GREN is a way to remember them
MMovementAll living things move, even plants
RRespirationGetting energy from food
SSensitivityDetecting changes in the surroundings
GGrowthAll living things grow
RReproductionMaking more living things of the same type
EExcretionGetting rid of waste
NNutritionTaking in and using food
It can be easy to tell if something is living or not. A teddy bear might look like a bear, but it can't do any of the seven things it needs to be able to do to count as being alive. What about a car? A car can move, it gets energy from petrol (like nutrition), it might have a car alarm (sensitivity), and it gets rid of waste gases through its exhaust pipe (excretion). But it can't grow or make baby cars. So a car is not alive.
Respiration is a chemical reaction that happens in all living cells. It is the way that energy is released from glucose, for our cells to use to keep us functioning. Remember that respiration is not the same as breathing (which is properly called ventilation). Aerobic respiration
The glucose and oxygen react together in the cells to produce carbon dioxide and water. The reaction is called aerobic respiration because oxygen from the air is needed for it to work. Here is the word equation for aerobic respiration:
glucose + oxygen → carbon dioxide + water (+ energy)
(Energy is released in the reaction. We show it in brackets in the equation because energy is not a substance.)
Now we will look at how glucose and oxygen get to the cells so that respiration can take place and how we get rid of the carbon dioxide. Glucose from food to cells
Glucose is a type of carbohydrate, obtained through digestion of the food we eat. Digestion breaks food down into small molecules. These can be absorbed across the wall of the small intestine into the bloodstream. Glucose is carried round the body dissolved in blood plasma, the pale yellow liquid part of our blood. The dissolved glucose can diffuse into the cells of the body from the capillaries. Once in the cell glucose can be used in respiration. Oxygen from the air to cells
When we breathe in oxygen enters the small air sacs, called alveoli, in the lungs. Oxygen diffuses from there into the bloodstream.
Oxygen is not carried in the plasma, but is carried by the red blood cells. These contain a red substance called haemoglobin, which joins onto oxygen and carries it around the body in the blood, then lets it go when necessary. Like glucose, oxygen can diffuse into cells from the capillaries. Red blood cells carry oxygen around the body
Carbon dioxide from cells to the air
The carbon dioxide produced during respiration diffuses out of the cells and into the blood plasma. The blood carries it to the lungs. It then diffuses across the walls of the alveoli and into the air, ready to be exhaled.
Respiratory system and ventilation
The respiratory system
The human respiratory system contains the organs that allow us to get the oxygen we need and to remove the waste carbon dioxide we don't need. It contains these parts:
tubes leading from the lungs to the mouth and nose
various structures in the chest that allow air to move in and out of the lungs
Movements of the ribs, rib muscles and diaphragm allow air into and out of the lungs. Take care - this is called breathing or ventilation, not respiration. When we breathe in, we inhale. When we breathe out, we exhale. Air passes between the lungs and the outside of the body through the windpipe, called the trachea. The trachea divides into two bronchi, with one bronchus for each lung. Each bronchus divides further in the lungs into smaller tubes called bronchioles. At the end of each bronchiole, there is a group of tiny air sacs. These air sacs have bulges...