Animals and Plants in the Water

Energy Capture

     Plants are primary producers: they create their food from carbon dioxide and water by using the energy in sunlight. They spread out their leaves (or cells with chloroplasts), and get to work. If there is not enough light or water where they are rooted, they die. However , they make lots of seeds so that a few will find places where they can prosper.

     Primary producers can use other energy sources than light. The primary producers around our deep ocean volcanic vents use heat and sulphur dioxide that are in the water. Scientists wonder if there is life under the frozen oceans on Europa or other distant moons.

     For animals, the problem of staying alive is more difficult. Animals are consumers: they must find something to eat to get energy. All animals are dependent on the food created by plants. Some animals eat plants, and some eat other animals. In order to stay alive, animals must either locate themselves where there is a steady supply of food or find ways to move to where the food is.

Mobility

     Living things need to be able to go to where they can find food. Although we think of plants as being immobile, plants grow toward the light, and can slowly lengthen their stems and turn their leaves to take advantage of the light available. They can change form by letting one side of a stem grow faster than the other. Plants never stop growing, and put out new leaves (or long streamers under water) to capture as much light as possible. The big mobility challenge for plants, however, is how to scatter their seeds over the widest possible area. No matter how suitable an environment may be for a certain kind of plant, disaster may come some day: perhaps the volcano will erupt or the flood will bury the plants with mud. Seeds may be scattered by wind and water currents, or by animals.

    A few land plants move in response to stimuli. The sensitive plant will fold its little leaves when touched, and the Venus Fly Trap will close to trap an insect.

Animals, even those who seem rooted like plants, have special structures that move. The Sea Cups at the top of this page are animals: they move their tentacles to create water currents that carry tiny food particles to their mouths. Because the ocean currents carry many small organisms, sessile animals (those who are rooted in one spot) can survive by capturing those particles if they are in a good spot to begin with. Sessile animals include anemonies, sea lilies, and corals. Shell fish, such as clams and oysters, pump the water through their bodies and strain out little bits of food.

     Most animals, however, are mobile. They swim, fly, or run using fins, wings, or legs.. This mobility, however, is costly. Movement requires energy and good coordination. Animals require nervous systems and efficient ways to breathe and nourish working cells.

Body Form

     Plants grow to fit into their environments, and they differ in the arangement and number of their branches, flowers, and leaves. Mobile animals cannot afford such structural freedom. You can see that members of every species follow a basic body pattern. This pattern is constantly being tested: energy must be used efficiently, reflexes must be very quick, the body must be well coordinated, the whole system must resist sickness and recover quickly from injury. The predator must hunt well or go hungry: the prey animals must be vigilant and quick. Staying alive is a challenge for every organism.