Nature and Properties of Life. Cell Theory
In its broadest sense, biology is the study of living things—the science of life. Living things come in an astounding variety ofshapes and forms, and biologists study life in many differentways. They live with gorillas, collect fossils and listento whales. They isolate viruses, grow mushrooms and examinethe structure of fruit flies. They read the messages encoded in the long molecules of heredity and count how many times a hummingbird’s wings beat each second.
What makes something “alive”? Anyone could deduce that a galloping horse is alive and a car is not, but why? We cannot say, “If it moves, it’s alive,” because a car can move and gelatine can wiggle in a bowl. They certainly are not alive. What characteristics do define life?
All living organisms share some basic characteristics:
1. Ability to keep invariant structure. Most of organisms consist of one or more cells with highly ordered structures: atoms make up molecules, which construct cellular organelles, which are contained within cells. This hierarchical organization continues at higher levels in multicellular organisms and among organisms.
2. Ability to receive and keep information. All organisms respond to stimuli. Plants grow toward a source of light and your pupils dilate when you walk into a dark room.
3. Ability to change in time. All organisms are capable of growing and reproducing and they all possess hereditary molecules that are passed to their offspring, ensuring that the offspring are of the same species. Although crystals also “grow,” their growth does not involve hereditary molecules.
4. Ability to transform and keep the energy and matter. All organisms have regulatory mechanisms that coordinate the organism’s internal functions. These functions include supplying cells with nutrients, transporting substances through the organism and many others.
5. Homeostasis. All organisms maintain relatively constant internal conditions, different from their environment, a process called homeostasis. All living things share certain key characteristics: order, sensitivity, growth, development and reproduction, regulation and homeostasis.
Biology is a fascinating and important subject because it dramatically affects our daily lives and our futures. Many biologists are working on problems that critically affect our lives, such as the world’s rapidly expanding population and diseases like cancer and AIDS. The knowledge these biologists gain will be fundamental to our ability to manage the world’s resources in a suitable manner, to prevent or cure diseases, and to improve the quality of our lives and those of our children and grandchildren. Biology is one of the most successful of the “natural sciences” explaining what our world is like.
Origination of Life
Among the theories of origin of life are selected five main hypotheses. One of the most famous theories about the origin of life on the Earth is creationism. As for this hypothesis, the supernatural event in the past gave start of life on the planet. Some people believe that God is the creator of our Earth and all living organisms.
As alternative in ancient China and Egypt existed another hypothesis about spontaneous origin. Aristotle was the creator of this theory. He asserted that particles of substances have some “active beginning” and under normal conditions it can create a living organism. It was correct but not everything could be explained. Many scientists studied this problem. They are Van Helmont, F.Redi, Anton van Levenhook etc.
If preceeding hypotheses consider the theories about the origin of life, the theory of stationary state assures that our Earth has always existed. “That it never arised and it never vanish”.
Richter and Arenius were sure that life on the Earth originated outside our planet. They thought that the meteorites and dusts from space transferred life from the Universe to the Earth.
The theory of biochemistry evolution explains the theory of biogenesis. A few millions years ago, the Earth consisted of H, Ge, C, N, O, P, Fe, Si, Al and etc in gas state. These atoms interacted and formed the sun in the center of the Universe and other planets around the sun. Fe collected in the center of the Earth and formed kernel. Al and Si formed the Earth crust. And N, O, C formed the atmosphere around the planet. Then H and O formed water that is the basis of living organisms. Many scientists think that life originated in “broth” of atoms (H, O, N, C, Al etc).
Cells Are The Basic Units of Living Things. Cell Theory
Biology as a science has been developing for centuries. The first scientists could investigate and study only big objects. But the invention of a microscope made a great contribution to the development of biology processes and objects. Let’s consider in short the history of modern biology development:
1590 - Jansen invented the microscope;
1665 - Robert Hooke discovered cell structure of a many-celled organism;
1680 - A.Livenhook discovered one-celled organisms;
1831 - 1833 ‑ R.Brown described the cell nuclei; 1838 - 1839 - T.Schwann and M.Schleiden formulated the cell theory;
1840 - Pourqueniet established living qualities of the cytoplasm;
1858 - R.Virkhov substantiated the principle of cell heredity by the way of division;
1866 -1888 - Cell division was studied and chromosomes were described;
1930s - An electronic microscope was invented. DNA research.
All organisms reproduce, use energy, grow, respond and are made up of at least one cell. A cell is the basic unit of living matter. Thus, birds and cork trees are made up of living cells.
After the invention of a microscope, scientists were able to observe objects around them more carefully than ever before. Many hypotheses were stated. Many experiments involving living things were performed. The scientific method was truly in progress. By the end of the 19th century, the cell theory was proposed. It stated that:
1. All organisms are made of cells;
2. All cells form from other cells.
The cell theory is one of the most important theories in the study of life science and a major unifying concept in biology. The modern cell theory states that:
1. All living matter is composed of cells;
2. All cells arise from other cells;
3. All metabolic reactions of a living organism, including all energy exchanges and all biosynthetic processes, take place within cells;
4. Cells contain the hereditary information of the organisms of which they are a part and that information is passed from a parent cell to a daughter cell.
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