A Study On Cells And DNA Biology Essay


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Double-helix structure is the most familiar information about DNA and today, we are going to go into details at looking at a DNA structure for an animal and a plant cell together with the effects of amount of ethanol. DNA is found in the nucleus of living cell and almost all living cells have it except for red blood cell, which does not have a nucleus; whereas it is floating freely as a long coil in the cytoplasm for prokaryotes. When a chromosome is uncoiled, it forms a long thread, which consists of one DNA molecule and proteins. The genetic material of a chromosome is stored in the DNA and the protein plays no role in inheritance. However, these proteins and enzymes may obscure seeing the DNA and therefore, it must be removed for clear vision. Furthermore, cell wall and cell membrane have to be broken in order to release the DNA, which has been kept in them.


To investigate an effective way to compare the DNA extraction techniques of an animal and a plant cell and to investigate the effects of different concentration of ethanol has on the amount of DNA precipitated.

Research Questions:

How does the concentration of ethanol affect the amount of DNA precipitated?

Are the extraction methods for both animal and plant cells similar?


If lesser concentration of ethanol were used then the amount of DNA precipitated will be lower or less obvious

If animal cell is used for experiment then there is no need for heating but to grind it.

If plant cell is used for experiment then there is no need for grinding but to heat it.


Constant variables:

The types of detergent used (The same bottle of detergent should be used throughout the experiment and the dropper should be the same to avoid mixing other solutions together with the detergent) , the types of salt solution used (The same dropper should be used throughout the whole experiment to avoid mixing of substances in the salt solution.)

Manipulated variables:

The types of cell [Different test tubes, beakers and droppers should be used for each types of cell to avoid mixing them together.] (plant or animal), the concentration of ethanol used (Labels on the bottle should be carefully looked at first before using it.)

Responding variables:

The amount of precipitation formed, the visibility of precipitation

Apparatus/ Materials:

Safety gloves and mask

500ml beaker

250ml beaker

A mortar and pestle

6 test tubes

Cold water

Salt solution

30%, 75% and 95% ethanol concentration

Bunsen burner, tripod stand and wire gauze

Droppers for each solution and sample

Test tube rack

Label stickers


Measuring cylinder

Chicken liver

Wheat germ


Data Analysis


Different cell require different methods of extraction due to their different cell structure; mainly about the presence of cell wall or not. Furthermore, different concentration of ethanol has altered the result of the precipitation.

Cell wall is a rigid outer layer, which surrounds the plasma membrane of the plant cell, like wheat germ. It is composed of cellulose, a tough and fibrous carbohydrate and can only be broken using heat. Therefore, heat is supplied to break the cell wall and cell membrane in order to exposed the DNA for easier extraction. 50 ÌŠ C- 60 ÌŠ C will be enough and more than that will damage the DNA.

Detergent is added to remove lipids and protein from the cell. The cell membrane has 2 layers of lipids molecules and proteins going through them.

When detergent gets into contact with the cell, it will capture the lipids and proteins, leaving DNA in the solution. Next, salt solution has the ability as the detergent too. Lastly, ethanol is added. DNA is soluble in water but not in ethanol. Therefore, ethanol is added (cool condition is the most favorable one) into the test tube at 45 degree (to avoid homogenous the solution) to precipitate the DNA for easier extraction later. The higher the concentration of ethanol, the more the amount of DNA precipitated. After that cool water bath is used to speed up the precipitating process. For chicken liver, only cell membrane, protein and lipids have to be removed and so heating is not required but grinding is necessary to break the cell membrane.

Further analysis

DNA, which is negatively charged and can be neutralized by salt solution that carries positive charge. Next, ethanol, which is neutral, can repel all the charges, separating water from DNA. Water must be removed because DNA is soluble in water but we should not remove all the water because by doing so, DNA will be invisible under naked eyes and therefore, 100% concentration of ethanol should not be used. When ethanol is added into the test tube, its less dense properties make it float above protein and fats. After some time, DNA will float in ethanol too. Cold water, which has the ability to slow down the reaction of enzymes that can break down the double-helix structure of DNA into stringy-like substance. Therefore, the higher the concentration of ethanol, the more the amount of DNA precipitated but 100% ethanol should never be used.

What is the most effective way to extract DNA from cells?

I have researched online regarding the methods of extracting DNA from cells before doing this experiment. Those methods involved adding meat tenderizer solution, which contains papain, pineapple juice or contact lens solution to break down protein molecules in the cells, sodium acetate or ammonia is also added to precipitate protein and centrifuging is needed to mix ethanol with the sample for faster precipitation. Amongst all, extracting DNA by heating wheat germ (grinding chicken liver), mixing with salt solution, detergent and ethanol then cool the sample in cold bath is the easiest and most convenient way. Furthermore, adding high concentration of ethanol and cold water bath are the most effective way to extract DNA from cells because the higher the concentration of ethanol, the easier and quicker the DNA will be precipitated because DNA is insoluble in ethanol. Next, cooling effect also quickened the reaction because DNA is most insoluble in cold condition, just like blood, which dissolves in hot water but not in cold water. The theory is the same and these conditions make extraction of DNA fast, effective and less troublesome.

There is a trend in the experiment, which is when the higher the concentration of ethanol is used, the more the amount of DNA precipitated and the easier to be seen with naked eyes. Next, the data collected can be said as reliable and valid because I have made comparison with other groups and researched about it online, we probably get the similar result.

Error analysis

Estimation error:

We did not measure exactly 4ml for 3 sample solutions because there was only 1 measuring cylinder available. Therefore, we were forced to estimate the amount by comparing it to a 4ml solution.

Next, for the first 3 samples, we have added too much salt solution and too little alcohol because guidance was given after we have done three-sample solution. However, we followed the guidance given for the rest of our samples.

Procedural error:

The droppers for each solution (salt solution, ethanol-30%, 75%, 95%) have been mixed up as so many groups were using it. Impurities may contain in it, which alter the final result.

Suggestions for improvements

Measuring cylinder should be used next time for more accurate measurement as the amount of ethanol; salt solution, detergent and sample solutions must be in a right proportion in order to get a reliable and an accurate result.

Instruction must be asked before conducting an experiment especially regarding volume to improve the accuracy and reliability of the result.

Label must be put on each dropper to indicate which dropper is for which solution in order to prevent solution from being contaminated and avoid using the wrong dropper, which may alter the result.


My results do support my hypothesis, which are:

How does the concentration of ethanol affect the amount of DNA precipitated?

Are the extraction methods for both animal and plant cells similar?

Results have supported that the higher the concentration of ethanol, the more the amount of DNA precipitation formed. Next, the extraction method for both animal and plant cells are slightly different due to the presence of cell wall in wheat germ.

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