The Characteristics Of Life

Biology is the study of life and living organisms. 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.

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 how the human body works allowed others to find more effective ways of treating illnesses. All these 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 traveling around the world, Charles Darwin was formulating the central principle of modern biology – natural selection as the bases of evolution.

It is hard to believe, but the nature of viruses has become apparent only within the last half of the 19^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 recognize 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.

During the past few hundred years biology has changed from concentrating on the structure of living organisms to looking more at how they work or function. Over this time biologists have discovered much about health and disease, about the genes which control the activities of our bodies and how humans can control the lives of other organisms. We need to understand how our activities affect the environment, how humans can take responsibility for their own health and welfare and how we must be careful to make appropriate rules for the use of our genetic information.

Nowadays biologists are making fantastic discoveries which will affect all our lives. These discoveries have given us the power to shape our own evolution and to determine the type of world we will live in. Recent advances, especially in genetic engineering, have dramatically affected agriculture, medicine, veterinary science, and industry, and our world view has been revolutionized by modern developments in ecology. There has never been a more exciting nor a more important time to study biology.

Biology is the scientific study of life. But what is life? When we see a bird on a rock it may seem obvious that the bird is alive and the rock is not, but what precisely makes the bird alive and the rock not? Throughout history, thinkers in many fields tried to define life. Although they have failed to provide a universally accepted definition, most scientists agree that all living things share certain basic characteristics:

■ Living things are made of organized structures.

■ Living things reproduce.

■ Living things grow and develop.

■ Living things feed.

■ Living things respire.

■ Living things excrete and waste.

■ Living things respond to their surroundings.

■ Living things move.

■ Living things control their internal conditions.

■ Living things are able to evolve.

Non-living systems may show some of the characteristics of living things, but life is the combination of all these characteristics.

Organization.All things are made of chemicals, but in living things the chemicals are packaged into highly organized structures. The basic structure of life is the cell. Cells themselves contain small organelles that carry out specific functions. A cell may exist on its own or in association with other cells to form tissues and organs. Because of their highly organized structure, living things as organisms.

Reproduction.Reproduction is the ability to produce other individuals of the same species. It may be sexual or asexual. Reproduction involves the replication of DNA. This chemical contains genetic information which determines the characteristics of an organism, including how it will grow and develop. The continued existence of life depends on reproduction, and this is perhaps the most characteristic feature of living things. Reproduction allows both continuity and change. Over countless generations this has allowed species to become well suited to their environment, and life to evolve gradually to more complex forms.

Growth and development.All organisms must grow and develop to reach the size and level of complexity required to complete their life cycle. Growth is a relatively permanent increase in size of an organism. It is brought about by taking in substances from the environment and incorporating them into the internal structure of the organism. Growth may be measured by increases in linear dimensions (length, height, etc.), but is best measured in terms of dry weight as this eliminates temporary changes due to intake of water which are not regarded as growth. Development involves a change in a shape and form of an organism as it matures. It is usually accompanied by an increase in complexity.

Feeding.Living things are continually transforming one form of energy into another to stay alive. Although energy is not destroyed during these transformations, heat is always formed. Heat is a form of energy which cannot be used to drive biological processes, so it is sometimes regarded as `wasted energy`.

Living things have to renew their energy stores periodically from their environment, to continue transforming energy and to replace the `wasted energy`. They also have to obtain nutrients – chemicals that make up their bodies or help them carry out their biological processes. Living things acquire energy and nutrients by feeding, either by eating other organisms, or by making their own food out of simple inorganic chemicals using energy from sunlight or from chemical reactions.

Respiration.Living things need energy to stay alive and to do work. Although food contains energy, this is not in a directly usable form. It has to be broken down.

The energy released during the breakdown is used to make ATP (adenosine triphosphate) in a process called respiration. ATP is an energy rich molecule and is the only fuel that can be used directly to drive metabolic reactions in living organisms.

Excretion.The energy transformations that take place in an organism involve chemical reactions. Chemical reactions that occur in organisms are called metabolic reactions.

Waste products are formed in these reactions, some of which are poisonous, so they must be disposed of in some way. The disposal of metabolic waste products is called excretion.

Responsiveness.All living things are sensitive to certain changes in their environments (stimuli) and respond in ways that tend to improve their chances of survival.

The degree of responsiveness depends on an organism`s complexity: a bacterium may be limited to simple responses, such as moving towards favorable stimuli or away from harmful ones; people can make highly sophisticated responses to a wide variety of stimuli which they may perceive either directly or with the aid of technological devices.

Movement.Responses usually involve some form of movement. Movement of whole organisms from one place to another is called locomotion. Plants and other organisms that are fixed in one place do not display locomotion, but they can move parts of their bodies. Movements of living things differ from those of non-living things by being active, energy-requiring processes arising from within cells.

Homeostasis.All living things are, to some extend, able to control their internal conditions so that their cells have a constant chemical and physical environment in which they can function effectively. The regulation and maintenance of a relatively constant set of conditions within an organism is called homeostasis. Homeostasis is a feature of all living systems, from a single cell to a whole biosphere (the part of Earth containing life).

Evolution.Living things are able to change into new forms of life. This evolution usually takes place gradually over successive generations in response to changes in the environment.

Fact of life:

The continued existence of life depends on reproduction, and this is perhaps the most characteristic feature of living things. Reproduction allows both continuity and change. Over countless generations this has allowed species to become well suited to their environment, and life to evolve gradually to more complex forms.

What Do Biologists Do?

Modern biology is an enormous subject that has many branches. Specialists in some branches include:

● molecular biologists and biochemists who work at the chemical level, with the aim of revealing how DNA, proteins, and other molecules are involved in biological processes;

● geneticists who study genes and their involvement in inheritance and development;

● cell biologists who study individual cells or groups of cells, often by culturing them outside organisms; thee investigate how cells interact with each other and their environment;

● physiologists who find out how organ systems work in a healthy body;

● pathologists who study diseased and dysfunctional organs;

● ecologists who study interactions between organisms and their environment. Some focus their attention on whole organisms; others study populations, individuals of the same species living together at one location.

There are also biologists who specialize in particular groups of organisms; for example, bacteriologists study bacteria, botanists study plants, and zoologists study animals.

Biologists are employed in many fields including conservation and wildlife management, industry, health care, horticulture, agriculture, zoos, museums, information science, and marine and freshwater biology. In addition, many biologists are employed as teachers, lecturers, or research workers.

Part C.A letter to students who study biology:

Dear Students,

I am writing this letter to welcome all of you who are about to begin your first year course in Biology here at the university. You might think it is a little early for me to ask you to think about what you will do when you leave here in three years` time. However, our science, like any other, has so many different areas it is impossible to study them all. The first thing you will have to think about is specializing. This letter is to offer you some suggestions to think about for your future.

As you know, there are four main areas of biology that we shall concentrate on in the coming years. Biology can be divided into zoology, the study of animal life, and botany, the study of plant life. We shall also study molecular biology, the study of how the building blocks of living things, the cells, work. Another topic of interest is genetics, how biological information is passed on from one generation to the next: that is, inheritance. You should specialize, but you will also need to know about all of these four areas of study. Plants and animals do not live separately from each other; all living things are made up of cells and one of things genetics tells us is how plants and animals adapt to the conditions around them.

So what about after the course is over and you have graduated in Biology? Can you have a career in biology? For those who choose to specialize in genetics or molecular biology there are important career opportunities in medicine. At the present time, there is a great deal of research going on in gene therapy where biologists are working with doctors and chemists to find new ways of treating diseases. Other biologists are looking at ways of changing the genetic composition of the plants we grow for food; of making them more able to fight diseases and at the same time produce more food.

We are experiencing a period of climatic change too, and this is having an effect on the way animals and plants live. The science of ecology is becoming more and more important; biologists who specialize in zoology are working in many parts of the world. Some are working to protect species like the tiger, which are seriously threatened by climate change. Others are investigating wildlife from the smallest insects to the largest mammals, trying to understand how they all live together. Botanists are looking at the effect new types of food crops have on the environment and how changes in that area can affect our general health. There is even a new area of biology called astrobiology, which is looking at the possibilities of life on other planets – but perhaps that is something for the more distant future.

Whatever you specialize in, as long as there is life on this (or any other) planet, there is work for a biologist.

Good luck and enjoy your studies!

Jean Shearer

Professor of Biology.

Part D.The scientific method:

The definition of biology states that it is a `scientific study`. This distinguishes biology from other ways of studying life. However, there is no single rigid scientific method that biologists use: there are numerous ways of studying life scientifically. Nevertheless, biological investigations usually include one or more of the following key elements:

- observing: making observations and taking measurements

- questioning: asking questions about observations and posing a problem

- hypothesizing: formulating a hypothesis, a statement that explains a problem and can be tested

- predicting: stating what would happen if the hypothesis were true

- testing: testing the hypothesis, usually by carrying out a controlled experiment aimed at producing data that will either support or contradict the hypothesis

- interpreting: interpreting the test results objectively and drawing conclusions that accept, modify, or reject the hypothesis.

A biologist may start an investigation by making observations or by using observations described by other biologists. Such observations may be obtained directly by the senses, such as listening to a bird song, or indirectly through instruments such as recording the song on a computer system. On the other hand, an investigation may start simply by a biologist having an idea that something happens in a particular way, and then the idea will be tested by making observations or carrying out experiments to see if it is valid. A hypothesis is suggested and then tested in all investigations. One essential aspect of a scientific experiment is that it can be repeated by other scientists working independently.

A typical hypothesis makes a clear link between an independent or manipulated variable and a dependent variable. Variables are conditions or factors (such as light, temperature, or time) that can vary or may be varied. In an experiment, the independent or manipulated variable is the one that is systematically changed; the dependent variable is the effect or outcome that is measured. For example, when investigating the activity of an enzyme at different temperatures, temperature is the independent variable that is manipulated by the scientist; rate of reaction is the dependent variable that is measured at each temperature. Other variables called controlled variables are kept constant or controlled at set levels.

At the end of an experiment, the results must be interpreted as objectively as possible. Sometimes they are so clear that it is obvious whether they support or contradict the hypothesis. Often, however, results are variable and need statistical analysis before conclusions can be made. The conclusions may lead to the hypothesis being accepted, modified, or rejected. Even if results support hypothesis, it is accepted only tentatively because it can never be proved completely. However, it only needs a single contrary observation to refute a hypothesis (prove it wrong or incomplete). A hypothesis is therefore only the best available explanation at any time. This makes biology a highly dynamic subject and not merely a collection of facts.

Cell Theory

Cells were discovered in 1665 by the English scientist and inventor Robert Hooke. Hooke designed his own compound light microscope to observe structures too small to be seen with the naked eye. Among the first structures he examined was a thin piece of cork (the outer surface of bark from a tree). Hooke described the cork as being made of hundreds of little boxes, giving it the appearance of a honeycomb. He called these little boxes cells. It soon became clear that virtually all living things are made of cells, and that these cells have certain features in common.

The cell theory

The concept that cells are the basic units of life became embodied in a theory called the cell theory, which embraces the following main ideas:

·cells form the building blocks of living organisms

· cells arise only by the division of existing cells

· cells contain inherited information which controls their activities

· the cell is the functioning unit of life; metabolism (the chemical reactions of life) takes place in cells

· given suitable conditions, cells are capable of independent existence.