Form and features of living things

Living things can be described based on their features

We classify living things into groups to make sense of the world around us and to communicate about it. The classification system used by scientists today is similar to the one devised by Carolus Linnaeus in the 1700s. He grouped living things on the basis of observable external features and created a ranked hierarchical system of identification. The highest level of classification he identified is the kingdom.

Today, scientists recognise that there are more kingdoms, for example, the kingdom of fungi, the kingdom of plants and the kingdom of animals. Scientists are also working to re-classify species to reflect shared ancestry—to group things that are closely related on a molecular level (DNA) and not just things that look related.

External features of plants

The kingdom of plants is comprised of multicellular organisms that transform the energy of the Sun into chemical energy through photosynthesis. They generally have structures to capture light, for example, leaves, and structures to capture water and nutrients from the environment, for example, roots. Plants rely on external forces to move them from place to place, for example, wind, water or animals dispersing seeds.

Although they vary widely in appearance, virtually all flowering plants have three main parts: roots, a stem, and leaves.

• The root is the part of a plant usually found below ground. Roots anchor the plant in the soil and absorb the water and nutrients it needs to grow.
• The stem is the part of the plant usually found above ground. It provides structural support to lift the leaves up into the sunlight and transports nutrients between the roots and the leaves.
• Leaves are specialised for photosynthesis and are often thin and flat to maximise the amount of sunlight captured for photosynthesis, but they can be a variety of other shapes.

Flowering plants produce flowers and fruit as part of their reproductive cycle. Flowers are the reproductive organs of a plant and usually contain both male and female parts. After fertilisation, the female parts of a flower develop into seed-containing fruits.

External features of animals

The kingdom of animals is comprised of multicellular organisms that must eat other things to survive. They generally have body structures such as claws, teeth and digestive systems for catching and eating their food. All animals are able to move from place to place using internal structures, such as muscles and skeletons, at some stage in their life cycle. More detail is provided in Diverse range of living things/Diversity.

Features and behaviours can aid survival

Looking at an animal or a plant, you can identify structural features and their probable function. For example, some animals have large eyes that allow them to see in darkness and some plants have waxy leaves that help minimise water loss. These features, which are important to the survival of an animal or plant in its native environment, are called adaptations. Adaptations can also be behaviours, such as the instinct to run from danger or the unfurling of leaves when sunlight hits them.

Generally, scientific adaptations are identified at a population level; one individual with a difference is a mutant who might survive better in the environment. If the individual’s children inherit the trait and also survive better in the environment, then the mutation will gradually become ‘normal’ in the population and be considered an adaptation.

The ‘environment’ for a population is the physical habitat, for example, a desert, and also the community of other livings things in which it lives. For example, the abilities of predators determine the adaptations of prey: if a species’ main predator has eyes that primarily detect motion then the instinct to freeze when spotted is an adaptation to that ‘environment’.

Science seeks to justify with evidence and reasoning why features or behaviours can be considered adaptations to an environment. The desert environment is good for studying adaptations to survive because it is so harsh and so it is rare to find features and behaviours that don’t help a population’s survival. Many desert species are ‘specialists’ (adapted to live in the specific conditions of the desert, for example, the thorny devil) rather than generalists (adapted to live in most environments with varying degrees of success, for example, common rats).

Some plants have adaptations to deal with salinity. For example, mangroves can secrete excess salt through salt glands in their leaves. Although not a complete solution to the problem of salinity in Australia, some crossbred hybrid species of rice and wheat grow reasonably well in low levels of salty water.

More information on adaptations can be found at Diverse range of living things/Adaptations.