8 
INTRODUCTION 
5. Organism. — Every living thing is an organism. It 
may be so small that the microscope is needed to see it. 
Nevertheless it is an organism. If it is a large tree, like a 
giant redwood, it is an organism. Elephants, horses, and 
men are organisms. 
These five expressions, cell , tissue, organ, organ system, 
and organism describe the parts of plants and animals which 
carry on the six life pro¬ 
cesses referred to above. 
We shall read more about 
them as our study of 
biology progresses. 
Classification of Living 
Things. — Our study of 
biology cannot progress 
far before we see the need 
of classifying animals 
and plants. Animals are 
generally grouped in two 
divisions : invertebrates 
(animals without back¬ 
bone) and vertebrates (an¬ 
imals with backbone). 
Plants are also divided into two groups : cryptogams (flower¬ 
less and seedless plants) and phanerogams (flowering or 
seed-bearing plants). Below is given a detailed reference 
table of these classifications. 
Figure 5. — Similar Cells United to 
Form a Tissue. 
Compare these cells with the one shown 
in Figure 4. 
I. Invertebrates. Animals without a backbone. 
1. Protozoa. 8000 different kinds, as, amoeba, paramoecium. 
2. Porifera. Sponges, 2500 different kinds. Examples, the bath 
sponge and grantia. 
3. Coelenterata. Hydra, corals, and jellyfish. 4500 different 
kinds. 
4. Echinodermata. Starfishes and sea urchins. 4000 different 
kinds. 
