THEORETICAL PART OF THE CHAPTER

1.1 Description of the scientific concept (according to Wynne Harlen, 2015)

There are many different organisms, including e.g. plants and animals. They differ from non-living beings by their ability to move, multiply, and respond to certain stimuli. All these processes are based on the fact that organisms have a metabolism which maintain the body with its functions. For life they need e.g. water, air, food, a way to get rid of waste and an environment that stays within a certain temperature range. Some organisms do not appear active, but every organism will at some stage carry out the life processes of respiration, reproduction, feeding, excretion, growth and development. All organisms will eventually die.

Functions of a cell

All living organisms are made of one or more cells. Most cells can only be seen through a microscope. The basic processes of life are the results of what happens inside the cells. Cells divide for growth and multiplication or to replace old cells (see Big Idea 9). The cells need food as an energy source (see Big Idea 4) to carry out these functions. Such functions belong to the “basic program” of all cells. Some cells in multicellular organisms do other things in addition. They are specialized, for example as muscle, blood or nerve cells.

Cells work together as tissue, tissues as organs and organs as organ systems. In the human body such systems provide functions such as breathing, digestion, excretion and temperature control. The circulatory system takes material needed by the cells to all parts of the body and removes soluble wastes to the urinary system. Stem cells are cells that are not yet specialized. They can be programmed for different functions and are therefore able to repair tissues. Cells function best within certain conditions (for example, a certain temperature). Organisms have therefore developed mechanisms to stay within these frameworks. Some animals, including us humans, keep e.g. the temperature and the acidity within certain limits.

Within cells there are many molecules if different kinds which interact in carrying out the functions of the cell. In multi-cellular organisms, cells communicate with each other by passing substances from one cell to another. A membrane that surrounds each cell plays an important role. This membrane determines what can get into or leave a cell. This is how the most important components remain in the cell and required substances (for example food) are taken up.

Control of a cell

The activity of different types of cells is controlled by enzymes. Hormones, released by specialized tissues and organs, regulate activity in other organs and tissues and control the overall functioning of the organism. In humans, most hormones are transported in the blood. Many medicines operate by speeding up or slowing down the regulatory mechanisms of enzymes or hormones. Cells are also controlled by the brain and spinal cord by sending messages about nerve cells in the form of fast electrical signals.

Cell research

Cells of different organisms can also live outside the organism as long as they have everything they need to survive and grow. Scientists to investigate cell functions use these cell cultures. They have medical implications such as the production of vaccines, screening of drugs and in vitro fertilization. Plant tissue cultures are used widely in the plant science, forestry and horticulture. Cells cannot divide infinitely often; the number of these divisions is limited. Diseases caused by invading microorganisms, environmental conditions or defective cells disrupt cell function. Multicellular organisms die if their cells are incapable of further division.