OCR Gateway Science - Understanding Our Environment B2

Organisms are classified into large groups such as animals and plants. Animals can be further classified as invertebrates or vertebrates. The vertebrates can be classified further as fish, amphibians, reptiles, birds or mammals. Each of these classes has particular characteristics. The binomial system is used to name individual species. Some organisms can be difficult to classify.

An ecosystem is a community of animals, plants and micro-organisms, together with the habitat where they live.

Living things can be classified according to their characteristics. Many can be classified as either an animal or a plant.

Animals: do not have chloroplasts, cannot make their own food, compact shape allows them to move around easily.

Plants: have chloroplasts, can make their own food by photosynthesis, cannot move around, more spread out shape.

Some organisms cannot be classified as belonging to either the animal kingdom or the plant kingdom. For example, fungi cannot move around, and they cannot make their own food. They are classified in a separate kingdom.

Euglena is a single-celled organism that can move like an animal but contains chloroplasts like a plant. It is difficult to classify.

Organisms of the same species:

• have more characteristics in common than they do with organisms of a different species, and
• can interbreed to produce fertile offspring.

Binomial system: In the 18th century, Carl Linnaeus started the modern system of putting species of organism into certain groups and giving them scientific names. Each species is given a name using Latin words, so that the same name can be used all over the world. For example, the scientific name for human beings is Homo sapiens. The first part of the name tells you the genus, while the second part of the name tells you the particular species in that genus.

Dolphins and whales are mammals that live in the sea. They have very similar features to fish such as sharks. This is because adaptations such as fins and a streamlined shape were important if the animals were to survive in this environment.

Plants make their own food by photosynthesis. Carbon dioxide and water react together in the presence of light and chlorophyll to make glucose and oxygen. The glucose is converted into starch, fats and oils for storage. It is used to make cellulose for cell walls, and proteins for growth and repair. It is also used by the plant to release energy by respiration.

Photosynthesis is the chemical change which happens in the leaves of green plants. It is the first step towards making food, not just for plants but ultimately every animal on the planet as well. During this reaction, carbon dioxide and water are converted into glucose and oxygen. The reaction requires light energy, which is absorbed by a green substance called chlorophyll.

Glucose is soluble. It is transported in the plant as soluble sugars but stored as starch - which is insoluble, so it cannot escape from the cells. The stored starch can be turned back into glucose later and…