The processes that take place inside a living thing so that it can grow, stay alive and continue its own kind are called life processes. Taking in food, digesting it, breathing, carrying materials around the body, removing waste, and producing young are all examples. These processes are what make a living thing able to survive and to keep its kind going.
Why is there a list at all?
It is tempting to learn the six names on that wheel and stop. Do not stop, because the names on their own are nearly useless. What is worth understanding is why there are six of them, and the answer is one sentence that will carry you through this entire unit.
You are not one thing. You are a crowd of billions of cells, and every single one of them has to be kept alive separately. Each cell needs food. Each cell needs oxygen. Each cell makes waste that would poison it if it stayed. And each cell has to release its own energy, because energy cannot be posted from one cell to another. Every life process on that wheel is an answer to that one problem.
| The problem a cell has | The life process that solves it |
|---|---|
| Food has to get into the body in the first place, and be broken small enough to use | Nutrition, which includes eating and digestion |
| A cell in your toe cannot walk to the kitchen. Food and oxygen must be carried to it | Transportation |
| Food is not energy yet. It has to be broken down inside the cell to release energy | Respiration |
| Everything a cell does leaves something behind that would poison it | Excretion |
| Cells wear out, and no living thing lasts forever | Growth and reproduction |
| All of the chemical work above has to be organised and kept in balance | Metabolism, which is the name for all of it taken together |
Do plants do all of these too?
Yes, every one of them, and this is the answer to the first question the textbook asks. A plant takes in nutrition, carries materials around itself, respires, excretes, grows and reproduces. The confusion comes because a plant does not do any of it in a way you can watch. It has no mouth, no heart, no lungs and no kidneys, so it looks as though nothing is happening.
That is worth holding on to, because it is the shape of the whole unit. The processes are the same in a plant and in a cow. The machinery is completely different. Every topic that follows compares those two sets of machinery, and the reason they differ is nearly always that an animal can move and a plant cannot.
An amoeba needs no organs at all. Why do you?
Here is a question the textbook does not ask, and it is the best one in the topic. An amoeba carries out every single life process on that wheel. It feeds, it transports, it respires, it excretes, it grows and it reproduces. And it does all of it with no mouth, no blood, no lungs and no kidneys, because it has no organs of any kind. It is one cell.
So why do you need a heart, two lungs and two kidneys to do exactly the same jobs? The answer is one you already worked out in Unit 3, when you asked why a cell has to stay small. Everything a cell needs comes in through its surface. In an amoeba, every part of the animal is touching the outside world, so nothing ever has to be delivered anywhere. Food is already at the surface. Oxygen is already at the surface. Waste is already at the surface.
Your cells are not like that. A cell in the middle of your thigh is nowhere near the outside. It has never touched air and it never will. Everything it needs has to be fetched from far away and brought to it, and everything it throws out has to be carried right back across the body and dumped. Organs exist because of distance. Being big is what created the delivery problem, and every organ system in this unit is a delivery service invented to solve it.
Every time you meet a new organ in Unit 5, ask one thing: how does this help a cell in the middle get served? A xylem tube, a heart, a lung, a kidney, a stoma and a sweat gland all look completely different, and every one of them is an answer to that same question. Students who hold on to it stop memorising organs and start predicting them.
What happens if one process goes out of balance?
The textbook asks this and the usual answer is that the organism will die. That is true and it explains nothing. The useful answer is to see that these processes are not a list, they are a chain, and a chain does not care how strong most of it is.
| If this fails | What actually goes wrong |
|---|---|
| Transportation | The stomach can be full of food and the lungs full of air, and cells still starve, because nothing is reaching them. This is what happens when a blood vessel is blocked. The body has plenty. The delivery stopped. |
| Respiration | Food arrives at the cell and stays food. Nothing is released from it, so there is no energy for any other process, and all the rest stop within minutes. |
| Excretion | Nothing is missing at all. Waste simply builds up until it poisons the cells that made it. This is why a person whose kidneys have failed becomes ill even while eating and breathing normally. |
| Nutrition | There is nothing for transportation to carry and nothing for respiration to break down, so two other processes fail because of this one. |
Read the middle column again and notice the pattern. In every row the body is still doing five things correctly. That is not enough, and it is never enough, because a life process that has failed cannot be made up for by one that is working well. You cannot breathe harder to make up for a kidney.
A car takes in fuel, releases energy from it, moves, gives off waste gas and gets warm. That is four of the six, and yet nobody thinks a car is alive. So what is missing? Two things. A car cannot grow from the inside, and a car cannot make another car. Every living thing does both, and this is why growth and reproduction stay on the list even though they are not needed to survive a single day. Nutrition, transportation, respiration and excretion keep one individual alive. Growth and reproduction keep the kind alive, which is a completely different job.
The full lesson is waiting for you
Create a free account to unlock activities, practice tests, presentations and videos - and to track your progress and confidence score for every subject.
That's a peek at activity 1 of 5 - sign in for all of them, full length.
A life process is a process that happens inside a living thing so that it can grow, stay alive and continue its kind.
14 more points to remember - sign in to see the rest.
Question 1 of 10
Sign in to watch the video for this topic.
Six Names, One Problem
- Nutrition: get food into the body and break it small enough to use
- Transportation: carry it to every cell, because a cell cannot fetch its own
- Respiration: release the energy inside the cell, where it is needed
- Excretion: remove what would otherwise poison the cell that made it