Hi, in this section we will look at the characteristics of cells and viruses. Here is a brief outline on the characteristics of cells and viruses, we will begin with the characteristics of life. Then, since the smallest units that have the characteristics of life ourselves, we will study the two cell types in nature which are the prokaryotes and eukaryotes. Finally, we will study viruses, which are not considered living organisms. And we shall see later on why is that so? In order to understand the characteristics of life, we will first look at what constitutes life.

We will study the four processes of life. Consider some more aspects of life And then since all living organisms are made up of cells, we will end this lecture with the formulation of the cell theory. In order to understand the characteristics applies, we will see what constitutes life. Since microbiology focuses on the study of small living things we will need to discuss how we define life or in other words what constitutes Life Is it the organic or the inorganic compounds. You see, glucose, amino acids and urea are examples of organic compounds whereas ions such as sodium and chloride and molecules such as nitrogen and carbon dioxide are examples of inorganic compounds the general scientific thought until 18 28 was that living things were made up of organic chemicals. These organic compounds were thought to be carried only living things and were very different from the inorganic chemicals found in nonliving things.

However, this idea was put to rest in 1828 when Fredrik ruler, synthesized urea, which is an organic compound, using only inorganic reactants in his laboratory. For this purpose he used ammonium cyanide which decomposes into ammonia and cyanic acid both in organic compounds that react to form organic urea. Since then, it was known that living things contain both organic and inorganic compounds and that nonliving things contain both are ganic and inorganic compounds as well. Now comes the real question. If the organic chemicals can be made in the absence of life, then what is the difference between a living and a nonliving thing? And coming back to our basic question, What is life?

To understand what is life we can look at the four processes involved in life. Those are growth, reproduction, responsiveness, and metabolism. Growth is increased in size. In a cell, the increase in size increases the surface area and the volume. A four times increase in the surface area corresponds to an eight times increase in the volume. Nine times the increase in the surface area corresponds to a 26 Seven times increase in volume.

While growth refers to an increase in size, reproduction refers to an increase in the number of cells. reproduction cannot go by asexual or sexual means. A sexually reproduction is accomplished by a single cell. The main way that prokaryotes reproduce is by asexual reproduction by a process called binary fission. In this diagram of binary fission, the DNA of the cell replicates first, then the cytoplasmic membrane elongates and the DNA begins to separate and the cytoplasmic membrane in vaccinates making a cross wall and the cross wall forms completely separating the two daughter cells identical to the their parents Del Sol. eukaryotes use mitosis for asexual reproduction.

Sexual reproduction is accomplished when two gametes are sex cells combined. An example of this type of reproduction is Mei osis in eukaryotes. Now the last two processes of life are responsiveness and metabolism. responsiveness is the ability to change internal and our external properties in reaction to changing conditions, which can be a stimuli around or within the organism. metabolism is the ability to take nutrients from the outside and use those nutrients in chemical reactions to provide two main things those are energy and structures which are needed for the above mentioned aspects of growth. reproduction.

And responsiveness. Now, some more considerations about the processes of life. These processes need not exist all simultaneously, they can be postponed curtailed by age disease or choice. The rates of growth metabolism or responsiveness may be reduced or stopped. For example, a seed a bear that hibernates or the under sports of the anthrax bassline. These pauses may be for the sake of waiting for more suitable conditions.

Now, what about viruses, there are some but like most of the characteristics of life, as we had shall see in detail at a later lecture. In the 1800s Theater Sean and Mathias Sladen status That all living things are composed of cells. Cells are living entities surrounded by a membrane that are capable of growing, reproducing, responding and metabolizing. These are the four processes of mine that we had just discussed. The smallest living things are therefore single celled microorganisms, does the cell theory was formulated. So in summary, living organisms contain both inorganic and organic compounds.

Life processes include growth, reproduction, responsiveness, and metabolism. All living things are made up of cells. And viruses are not considered cells since they lacked most of the characteristics of life.