1.3 The kingdoms of living organisms Animals Animals (Figure 1.4) are usually easy to recognise. Most animals can move actively, hunting for food. Under the microscope, we can see that their cells have no cell walls. Some animals have, in the past, been confused with plants. For a very long time, sea anemones were classified as plants, because they tend to stay fixed in one place, and their tentacles look rather like flower petals. Now we know that they are animals. Characteristics: ♦♦ multicellular (their bodies contain many cells) ♦♦ cells have a nucleus, but no cell walls or chloroplasts ♦♦ feed on organic substances made by other living organisms.
Centipede
Blackheaded gull
Earthworm
Figure 1.4 Some examples of animals.
Plants
Shepherd’s purse
The plants that are most familiar to us are the flowering plants, which include most kinds of trees. These plants have leaves, stems, roots and flowers (Figure 1.5). However, there are other types of plants – including ferns and mosses – that do not have flowers. What all of them have in common is the green colour, caused by a pigment called chlorophyll. This pigment absorbs energy from sunlight, and the plant can use this energy to make sugars, by the process of photosynthesis. As they do not need to move around to get their food, plants are adapted to remain in one place. They often have a spreading shape, enabling them to capture as much sunlight energy as possible. Characteristics: ♦♦ multicellular ♦♦ cells have a nucleus, cell walls made of cellulose and often contain chloroplasts ♦♦ feed by photosynthesis ♦♦ may have roots, stems and leaves. 6
Cambridge IGCSE Biology
Figure 1.5. An example of a plant. Original material © Cambridge University Press 2014
flower
fruit
leaf
root