Characteristics of living things

The study of living things

Biology

Biology means the study of lifeand it is the science which investigates all living things. For as long as people have looked at the world around them, people have studied biology. Even in the days before recorded history, people knew and passed on information about plants and animals. Prehistoric people survived by learning which plants were good to eat and which could be used for medicine. Farming would not have developed if they had not begun to understand which animals could produce food like milk and eggs.

In the past, more than 2000 years ago, people in the Middle East understood the part that insects and pollen played in the life cycle of plants. The ancient Egyptians studied the life cycle of insects and were particularly interested in the changes they went through as they grew from larvae to adult insects. The ancient Mesopotamians even kept animals in what were the earliest zoological gardens. The ancient Greeks, too, were greatly interested in understanding the world around them. Aristotle recorded his observations of plants and animals, and his successor, Theophrastus, wrote the first books on plant life, which made a very important contribution to the study of botany.

After the fall of the Roman Empire, the centre of the scientific world moved to the Middle East. The Arab scholar Al-Jahiz wrote the Book of Animalsin the 9 ^th century. He was just one of a great number of Arabic, Persian and Turkish scientists who set out the foundations for the modern science of biology. Later still, in Europe, particularly in Germany, scholars such as Albertus Magnus discussed the properties of life. Magnus wrote seven books on plants and twenty-six on animals.

Modern biology really began in the 17^th century. At that time, Anton van Leeuwenhoek, in Holland, invented the microscope and William Harvey, in England, described the circulation of blood. The microscope allowed scientists to discover bacteria, leading to an understanding of the causes of disease, while new knowledge about now the human body works allowed others to find more effective ways of treating illnesses. All this new knowledge needed to be put into order and in the 18^th century the Swedish scientist Carl Linnaeus classified all living things into the biological families we know and use today.

In the middle of the 19^th century, unnoticed by anyone else, the Austrian monk Gregor Mendel, created his Laws of Inheritance, beginning the study of genetics that is such an important part of biology today. At the same time, while travelling around the world, Charles Darwin was formulating the central principle of modern biology - natural selection as the basis of evolution.

It is hard to believe, but the nature of viruses has become apparent only within the last half of the 20^th century and the first step on this path of discovery was taken by the Russian botanist Dmitry Ivanovsky in 1892.

In the 20^th century, biologists began to recognise how plants and animals live and pass on their genetically coded information to the next generation. Since then, partly because of developments in computer technology, there have been great advances in the field of biology; it is an area of ever-growing knowledge.

Living things

There are a vast number of living things in the world. These comprise animals, plants and microorganisms. Living things are often described as organisms.

Living things are found everywhere in the world — on land, in the air, in the sea and underground. Different organisms live in different places. The place where an organism lives is called its habitat.The habitat of a fly might be a greenhouse, a goldfish's habitat might be its tank or bowl. The Earth provides millions of different habitats — some hot, some cold, some dry, some wet. The conditions in a habitat make up the environment.

In general, living things prefer a moderate environment with warm temperatures, water and a supply of food.

The differences in physical factors, such as temperature, humidity and daylight hours, between localities are often reflected in the organisms found there. For example, animals which live in water often have streamlined bodies and those that live in very cold climates often have thick fur or layers of fat. We can sum this up by saying that many organisms are adaptedto the habitat in which they live.

Characteristics of living things

There are thousands of different chemical reactions occurring in even the smallest animals and plants. These reactions are essential for life. If they stop, the organism dies. All the chemical processes in an organism are called its metabolism.

There are seven important characteristics or life processes common to allplants and animals.

They grow.Plants grow all their lives, but animals usually stop growing once they are adult. Even when growth stops, the materials in an animal's body are being replaced by substances from its food. In an adult human being, all the chemicals in the body are replaced over a period of seven years.

They feed.Organisms must feed in order to grow. Food is needed for growth, for energy and to replace worn-out parts. Animals and plants feed in different ways.

Plants take in simple substances like carbon dioxide and water. They use these simple substances to make more complex substances which can be used as food. In order to do this, plants need energy which they get from sunlight. This process of making food is called photosynthesis.

Animals eat plants or other animals. They then break down the complex chemicals in their food into simpler substances. These simpler substances are then used for growth or energy.

They need energy.Living things need energy to grow, to replace worn-out parts and to move. They get this energy from their food. The process of breaking down food and gaining energy is called respiration.

They get rid of waste products.Organisms are like factories. Materials are constantly being taken in and used to produce other materials. Some of the products are useless, others are poisonous. The waste products of metabolism must not be allowed to collect in an organism or they will poison it. So the organism must get rid of them — this process is called excretion.

They produce offspring.Organisms must produce offspring in order for the species to survive. This process is called reproduction. Usually reproduction involves the union of a male and a female of the same species. This is called sexualreproduction. Some organisms can reproduce on their own without needing both a male and a female. This is called asexualreproduction.

They move.Animals can move parts of their body or even their whole body from one place to another. Plants cannot move themselves from one place to another, but they can move parts of their structure. For example, leaves may turn towards the sunlight and roots may grow towards moisture.

They respond to stimuli.If someone tickles you, you will probably draw back. The tickling is a stimulus,your drawing back is a response. The main stimuli to which organisms respond are heat, light, sound, touch and chemicals which have tastes and smells. In general, plants respond to stimuli much more slowly than animals.