Life processes and control
Life processes
Trace food through the human gut and blood round the double circulation, say where each digestive juice acts, and explain how a plant moves water up and sugar down.
A sleeping dog is doing nothing you can see, and is unmistakably alive. What gives it away is not movement of the visible kind but the work going on underneath: molecules being shifted about to keep an ordered body from falling into disorder. That work costs energy, the energy comes from food, and food has to be taken in, broken down, carried to the cells that need it, and its leftovers carried away again. Those four jobs — nutrition, respiration, transportation, excretion — are the life processes.
Why a big body needs plumbing
A single-celled organism has its whole surface against the outside world, so food, gases and waste can simply diffuse across it. Grow bigger and the inner cells lose that contact. Special tissues then take in food and oxygen at one place, which creates a new problem — the rest of the body is somewhere else — and a transport system is the answer to it.
Worked example
A meal of rice and dal is swallowed. Where does each part of it finally get broken down?
In the mouth, salivary amylase starts on the starch of the rice and turns some of it to simple sugar.
Chewing makes the pieces small and of one texture; saliva wets them and starts the chemistry at the same time.
Try it together
A student runs hard for two minutes and gets a cramp in one calf.
Work out what happened inside the muscle.
1.Whatever the pathway, glucose is first broken down into a three-carbon molecule. What is that molecule called?
Have a go
Have a go on your own. Yeast is added to fruit juice in a stoppered tube and the gas coming off turns lime water milky. Which pathway is the yeast using?
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.