Every living thing eats

Food is essential to the survival of every living thing. What differs between one organism and the next is not whether it needs food but how it gets hold of it.

Figure to be added

Figure 2.1 — a field scene: cattle grazing on grass under a large tree, a heron standing at the edge of a pool of water, and the sun above.

Assignment 2.1

Identify the organisms shown in the figure.
Name the mode of nutrition of each of those organisms.

Working it out

You already know what a cow eats and what a heron eats, so you can say easily enough how each of them obtains its food: they depend on other organisms for it. The grass, the tree and every other green plant in the picture are the exception. Nothing in the scene feeds them.

The only things in the picture not eating something else

Count the arrows you could draw. The heron eats fish, the cow eats grass, the grass eats — nothing. Every arrow in a scene like this starts at a green plant, and the plant is the only thing with no arrow pointing into it. This chapter is about where that first arrow comes from.