Medica

2.1 Cell Theory
2.1.1 Outline the cell theory.
The cell theory states that: 
 
* All living organisms are composed of cells. Multicellular organisms (example: humans) are composed of many cells while unicellular organisms (example: bacteria) are composed of only one cell. Cells are the basic unit of structure in all organisms. 
* Cells are the smallest unit of life. They are thesmallest structures capable of surviving on their own.
* Cells come from pre-exsisting cells and cannot be created from non-living material. For example, new cells arise from cell division and a zygote (the very first cell formed when an organism is produced) arises from the fusion of an egg cell and a sperm cell. 

2.1.2 Discuss the evidence for the cell theory.
When scientists started tolook at the structures of organisms under the microscope they discovered that all living organisms where made up of these small units which they proceeded to call cells. When these cells were taken from tissues they were able to survive for some period of time. Nothing smaller than the cell was able to live independently and so it was concluded that the cell was the smallest unit of life. For sometime, scientists thought that cells must arise from non-living material but it was eventually proven that this was not the case, instead they had to arise from pre-exsisting cells. An experiment to prove this can be done as follows: 
 
* Take two containers and put food in both of these
* Sterilize both of the containers so that all living organisms are killed
* Leave one of thecontainers open and seal the other closed 
What will happen is that in the open container mold will start to grow but in the container that was sealed no mold will be present. The reason for this is because in the open container, cells are able to enter the container from the external environment and start to divide and grow. However, due to the seal on the other container no cells will be ableto enter and so no mold will develop, proving that cells cannot arise from non-living material. 

2.1.3 State that unicellular organisms carry out all the functions of life.
Unicellular organisms carry out all the functions of life including metabolism, response, homeostasis, growth, reproduction and nutrition.

2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses,bacteria, organelles and cells, using the appropriate SI unit.
Remember:
1 millimeter (mm) = 10-3 meters
1 micrometer (μm) = 10-3 millimeters 
1 nanometer (nm) = 10-3 micrometers

A molecule = 1 nm
Thickness of cell membrane = 10 nm
Viruses = 100 nm
Bacteria = 1μm
Organelles = up to 10 μm
Eukaryotic cells = up to 100 μm

2.1.5 Calculate the linear magnification of drawings and the actual size ofspecimens in images of known magnification.
 
* Take a measurement of the drawing (width or length)
* Take this same measurement of the specimen  
* Remember to convert units if needed to
* Place your values into the equation
* Magnification = length of drawing / length of actual specimen
You can also calculate the length of the specimen if this is unknown: lengthof the drawing / magnification. 
Conversion of units:
1 centimeter = 10-2 meters
1 millimeter = 10-3 meters
1 micrometer = 10-6 meters
1 nanometer = 10-9 meters

2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size.
Many reactions occur within the cell. Substances need to be taken into the cell to fuel these reactions and the wast products of thereactions need to be removed. When the cell increases in size so does its chemical activity. This means that more substances need to be taken in and more need to be removed. The surface area of the cell is vital for this. Surface area affects the rate at which particles can enter and exit the cell (The amount of substances that it takes up from the environment and excretes into the environment),...