Differences between plants and animals
The main difference between plants and animals is the way they obtain food, i.e. their mode of nutrition.
All green plants manufacture their own food from carbon dioxide and water. Energy for this process, called photosynthesis comes from the sunlight that is trapped by chlorophyll, the green pigment present in plants. Oxygen is given out as a waste product. This mode of nutrition is known as holophytic or autotrophic nutrition.
Green plants and all organisms that exhibit this mode of nutrition are called autotrophs. Some autotrophic micro-organisms obtain the energy they need from the breakdown of certain inorganic salts)
Animals do not have the pigment chlorophyll and so cannot manufacture their own food. They feed on plants and other animals. This is known as holozoic or heterotrophic nutrition. Animals and all organisms that exhibit this mode of nutrition are known as heterotrophs.
Adaptations to these different modes of nutrition account for the following differences plants and animals.
- Most plants remain in one position since they can obtain the necessary inorganic materials for photosynthesis from the and the surrounding air. As a result, they do not have organs of locomotion. Animals move from place to place as they have to go in search for food, so they usually have well developed organs of locomotion.
Plants respond slowly to external stimuli while animals respond quickly. A quick response helps animals in their search for food and to escape from other animals that want to feed on them. In addition, to external stimuli, animals also have well-developed organs absent in plants.
Since plants are mainly stationary, they produce very little waste products. These are usually not removed but stored in certain cells as harmless substances. Animals are very active, so a lot of waste substances are produced. In addition, their heterotrophic mode of feeding also produces harmful wastes. Hence, animals have well developed excretory systems (e.g. kidneys and Malpighian tubules).
Plants have a spreading or branching body form with no definite symmetry, and a large extremal body surface which enables them to trap sunlight and absorb the inorganic substances they need for photosynthesis. Animals have compact bodies which enable them to move about quickly. Most plants show unlimited growth. They keep producing new shoots ie branches, leaves and flowers throughout their lifetime. Animals show limited growth. They have a fixed number of organs such as eyes, ears and limbs.
Growth mainly occurs at the tips of he roots and stems of plants. In animals, growth occurs equally in all parts of the body.
Plants are composed of cells that are enclosed in a rigid cell walls made of cellulose; a substance found only in plants. In many plants the cell walls usually become strengthened by the deposition of substances like lignin. The rigid cell walls give plants mechanical support.
Animals are made of cells that do not have cell wall. Hence some animals have hard body coverings (exoskeletons) which gives them mechanical support, others have a rigid frameworks (Endoskeletons) inside their bodies.
Plants store excess food in their body mainly as starch and oil. In animals, however, excess food is stored mainly as glycogen (commonly known as animal starch) and fat.
Plants and animals respire continuously. Animals take in oxygen and give out carbon dioxide. An actively photosynthesizing plant, however, takes in carbon dioxide and gives out oxygen. This is because the photosynthetic rate is faster than the respiratory rate.
Gaseous exchange between the plant and its surroundings occurs over the whole-body surface of the plant. In most animals, gaseous exchange occurs in special organs such as gills, tracheae or lungs.
What are the similarities between plants and animals
- All plants and animals are made of eukaryotic cells
- Both plants and animals respire to produce energy
- Both plants and animals reproduce younger ones
- Plants and animals respond to external stimuli. E.g., certain plants play dead when touched while in animals, their nervous system respond to pain by withdrawing the part of the animal that sensed the pain.
- They both adapt to the condition of their environment.
- Plants and animals need food and water to survive