The spirit of God made me, and the breath of the Almighty gave me life.”
Job 33:4, Douay-Rheims
In the last chapter, we looked at the Kingdoms of Creation, which include creatures or things that are living. How can you tell if something is living? After all, a palm tree is very different from a panda, but both are living. Fortunately, scientists have considered all the different types of living things – from tiny bacteria to enormous blue whales – and have noticed that they all do many of the same things.
To find some of them out, let’s consider what you do every day. You wake up in the morning and take a deep breath of morning air. Breathing, or respiration, is one thing that all living things do. After you make your bed, you go down for breakfast (what would you like to have?). This is how we get energy or nutrition, and all living things need to do this as well, sometimes through eating like us and other times by making their own food.
After helping to clean up from breakfast, you sit down to do your school work. You notice that the sun is in your eyes so you get up and adjust the curtains. You have found two more things common to all creatures – sensitivity to your surroundings and movement. Sensitivity means that you react to something that happens around you, like when a dog perks up her ears at a sound or a fish swims to the surface to get food. Movement is any kind of change of position, from running and jumping, to swimming and branching (even plants move – just wait to find out more!)
After a hearty lunch (and some more nutrition), you remember that you have to clean out your cat’s litter box. It might seem icky, but all living things excrete, or get rid of waste, such as the undesirable things in the litter box or what is in a baby’s diaper. Your cat had kittens a couple of weeks ago, so once your chore is done you hurry to visit them. How big they all are getting! Reproducing (having babies) and growing are the last two things that all living things do.
We can use what living things do in order to figure out if something is alive or not. Consider a hamster – is it alive? It can move and grow, it does respire (breathe) and excrete (that’s why we need to clean the cage!). It needs nutrition from food and water, is sensitive to its environment (it peeks its little head up when you open the cage door), and it can reproduce (although hopeful won’t). It can do all seven things, so a hamster is alive.
What about a river – can it do all the things that living things do? Rivers do move and they can grow over time, but they do not respire, reproduce, or excrete; they are not sensitive to their surroundings; and they do not need food. Two out of seven things? Sorry, a river is not a living thing. That does not mean, of course, that they are not important. Non-living things make up a vital portion of our world. We will see them again in a while when we visit the Commons of Creation, but for now, we will have to bid them adieu.
One other thing that all creatures have in common is that they are made of cells. Cells are the tiny building blocks that make up your body – you have somewhere in the neighborhood of 10 trillion of them (enough that if you put them end-to-end they would wrap around the Earth at least one and half times). They are very small – so small you would have to use a microscope to see them – which is good because imagine how large you would be otherwise!
Cells do all kinds of amazing things, from taking apart the nutrients that you eat to supplying the air to your cells when you breathe to telling your leg when to kick the ball. Different types of cells do these different jobs (and many more) in a wonderful, complex dance that keeps you happy and healthy. We will visit these different types of cells as we go further into the Kingdoms of Creation.