The "Cell Theory" embraces four simple ideas:
- The cell is the building block of structures in living organisms
- The cell is derived from other cells by division
- The cell contains hereditary material which contains information which is used as instructions for growth, development and functioning
- The cell is the functioning unit of life (nothing smaller that the unit of the cell can survive) the chemical reactions of life take place within cells.
2.1.2 Discuss the evidence for the cell theory
Living things are made of cells
- Observations by microscopists on the structure of unicellular and multicellular organisms especially on the structure of tissues and organs
- Discovery of viruses as particles that are 'crystalline' when outside a host cell, and that can only reproduce themselves at the expense of their host cell's metabolic machinery
- Biochemical investigations of organelles showing their ability to function outside of a cell, under labouratory-controlled conditions, for a limited time
- Pasteur observations on the origin of microbes in fermenter vessels and related discoveries that cases of apparent 'spontaneous generations' of microorganisms in pond or puddle water were due to the presence of (unnoticed) pre-existing cells
- Observations on the behaviour of cells at division and during reproduction
- Observations on the behaviour of chromosomes and the establishment of the nature and role of genes/DNA in the day-to-day control of cells and in the process of heredity
- Discovery of enzymes and the enzymes machinery of cellular processes such as cell aerobic respiration and fermentation
- Discovery of biochemical events in cells, such as the formation of proteins from amino acids
- Discovery of cell ultra-structure of the presence of discrete organelles and of the biochemical events located in particular organelles.
Exceptions for cell theory:
In a muscle fibre there are more than one nucleus per cell. This is different to the rest because there are more than one control center for a cell. However, it still doesn't explain the existence of first cell.
2.1.3 State that unicellular organism carry out all the functions of life.
Unicellular organisms consist of only one cell. This cell therefore has to carry out all the functions of life.
The functions of life are things that all organisms must do to ensure survival
- Nutrition - Obtaining food, to provide energy and the materials needed for growth
- Metabolism - Chemical reactions inside the cell, including cell respiration to release energy
- Growth - An irreversible increase in size
- Sensitivity - Perceiving and responding to changes in the environment
- Homeostasis - keeping conditions inside the organism within tolerable limits
- Reproduction - Producing offspring either sexually or asexually
2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells using the appropriate SI units.
This is the table for the SI units for meter
In 1 meter, there are 1000 millimeter. (mm)
In 1 millimeter, there are 1000 micrometer (µm)
In 1 micrometer, there are 1000 nanometer (nm)
These three are the only 3 SI units required.
Comparing sizes
Molecules are around 1 nm
Thickness of membrane are around 10 nm
Viruses are around 100 nm
Bacterium are around 1000 nm or 1µm
Organelles are around 10 µm
Cells are around 100 µm
Note: There is a difference between magnification and resolution. Magnification simply makes it bigger. Resolution is the distance between two objects such that they can be seen as two objects.
2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification.
Image size = Magnification x Specimen size
Use the triangle to assist in figuring out the actual size.
This is a great example of using magnification http://www.youtube.com/watch?v=L1d-02yRsRE&list=PLD84FB4ECF83A6062
2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size.
As the volume increases the surface area increases at a slower rate. This means the surface area to volume ratio gradually decreases.
The metabolism of a cell is linked to its mass:volume ratio, whereas it is the surface area that provides the exchange surface for heat and substances.
The more cytoplasm the more heat and waste products generated, and the greater the demand for oxygen and nutrients. However the models above show that the relative surface area increases at a slower rate than the organism. Thus organisms and cells develop different methods to cope with this problem.
2.1.7 State that multicellular organisms show emergent properties.
Life as an emergent property
Emergent property are those that arise from the interaction of component parts. The whole is greater than the sum of its parts. This means to become different and therefore specialise in a particular function. Cells in a multicellular organism are produced by mitosis. Hence have all the chromosomes and all the genes. Most of these genes will be switched off as they will code for functions that the cell does not do.
2.1.8 Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.
Multicellular organisms have cells which are highly specialised to perform particular functions. Specialized cells occur organised into tissues and organs. A tissue is a group of similar cells specialized to perform a particular function, such as heat muscle tissue of a mammal. An organ is a collection of different tissues which performs a specialized function such as the heart of a mammal. So the tissues and organs of multicellular organisms consists of specialized cells.
2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways.
Stems cells are defined as cells that have the capacity to self-renew by cell division and to differentiate. They have considerable powers of regeneration and repair. There has also been a great interest in stem cells because of their potential for tissue repair and for treating a variety of degenerative conditions.
2.1.10 Outline one therapeutic use of stem cells
Bone marrow transplants are one of the many therapeutic use of stem cells. Stem cells found in bone marrow give rise to red blood cells, white blood cells and platelets in the body. These stem cells can be used in bone marrow transplants to treat people who have certain types of cancer.
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