The appearance, ultrastructure and function of lysosomes.

Lysosomes are sacs containing digestive enzymes. They are created by the golgi apparatus.

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The enzymes in the lysosomes have many important functions

• Digest material that phagocytic cells engulf: commonly this would mean digesting a pathogen that had been engulfed by a white blood cell.
• Digest old organelles (if left to build up they can be toxic)
• Digest old cells (autolysis)
• Release enzymes outside the cell so they can digest things externally (exocytosis)
• Digesting food that is delivered to the cell into useful components

When a lysosome has digested something, including waste products like old organelles, and useful chemicals are absorbed into the cytoplasm to be used again by the cell.

The appearance, ultrastructure and function of mitochondria.

Mitochondrion are the organelles where aerobic respiration takes place.

The stages of respiration that take place there require enzymes, so there is DNA that allows the cell to manufacture its own proteins (enzymes.) This DNA is held in the matrix; a material that also contains proteins and lipids.

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A mitochondria has a double membrane: the two both control the movement of substances in and out of the cell. The inner membrane provides the surface area for the reactions in respiration: it is folded many times into cristae to create a large surface area. This area is covered in the enzymes needed for respiration.

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The appearance, ultrastructure and function of the cell surface membrane.

The cell surface membrane is an example of a plasma membrane (click for more detail on plasma membranes) and has several jobs to perform:

• Separates the cell content from the surrounding environment
• Controls the movement of substances into and out of the cell
• Allows for the conditions inside the cell to differ from those outside

  

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The structure of an epithelial cell from the small intestine as seen with an optical microscope.

Epithelial cells make up a lot of tissue in the human body- including that of the small intestine. They are eukaryotic cells (nucleus and a variety of organelles) which specialise in absorption and secretion.

With a light (optical) microscope the following can be seen:

Extra reading: http://www.bio.davidson.edu/people/kabernd/BerndCV/Lab/EpithelialInfoWeb/

Analyse and interpret data associated with specific risk factors and the incidence of disease • recognise correlations and causal relationships.

The graph below compares the incidence (number of cases) of lung cancer to the risk factor of smoking.

cancerresearchuk

The age at which smoking was stopped has a direct correlation to the incidence.

This would appear to show that smoking causes cancer; but there could be other factors linking the two data which are actually the cause. To understand this imagine that people smoke because they are stressed and that stress is the cause of cancer- this would mean that as stress went up so did smoking and cancer (so there was a correlation), but that smoking was not the cause of cancer.

A casual relationship is the term for a direct link that shows one thing has caused another. In this case scientists analysed the affect of tar on cells and found that it altered the DNA causing cancerous mutations: they found a casual relationship between smoking and cancer.

Lifestyle can affect human health. Specific risk factors are associated with cancer and coronary heart disease. Changes in lifestyle may also be associated with a reduced risk of contracting these conditions.

Risk can be described as a probability of getting a disease due to an action. For example smoking is a risk factor associated with getting lung cancer because you are 15 times more likely to develop lung cancer if you smoke.

Risk factors of cancer:

• Smoking
• Bad diet/obesity
• Lack of exercise
• Exposure to UV rays

Risk factors of coronary heart disease:

• Smoking
• Bad diet/obesity
• High blood pressure (e.g. from stress)
• Blood cholesterol

By changing your lifestyle so that you are not doing the things that put you at risk of the disease, the risk of getting the disease is lowered. However, diseases cannot be eliminated by changing lifestyle because factors like age and genes can increase the risk.

Pathogens include bacteria, viruses and fungi. Disease can result from pathogenic microorganisms penetrating any of an organism’s interfaces with the environment. These interfaces include the digestive and gas-exchange systems. Pathogens cause disease by damaging the cells of the host and by producing toxins.

Micro-organisms are ones so small they cannot be seen without a microscope. Harmful micro-organisms are called pathogens and bacteria, fungi and viruses are all examples.

These organisms can infect the body by penetrating it interfaces with the environment- this means entering the body by a surface that links the inside with the outside, for example the digestive system and the gas exchange system.

When inside the body pathogens causes disease in two ways:

• They damage cells of the host (body) so they can't function properly
• They produce toxins which can alter the workings of the infected organism.