To test the hypothesis that respiration uses stored food - Biology Essay Example

1 - To test the hypothesis that respiration uses stored food introduction. The dry mass and not the wet mass of the beans was measured because water would add to the weight and would distort the results. As water is created during respiration, getting rid of the water will show if the water is used.

2. You would find the dry mass of a bean seedling by, after removing the bean from the cotton wool, drying it. By placing it in the oven it will not burn it to a crisp but merely dry out. After it has been done once and weighed, it must be done again and again until two successive results are the same.

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3. If the seeds had been kept in the light rather than in the dark, they would have germinated, and that would have affected the results, as the seedlings would have grown.

4. The results of the experiment show that the longer that the bean is kept in the cupboard, the more of it is respired. This therefore supports the hypothesis, as it shows that the stored food (the beans) has respired, as there is less of it afterwards.

Investigation 2:What happens to sugars when they are used in respiration?

5. In the control experiment, the control rat is fed only glucose, with no additives.

6. The air that the rats exhaled was bubbled through limewater because limewater absorbs carbon dioxide, a waste product of respiration, and that can therefore be tested for its radioactivity at the end of the experiment.

7. The radioactivity count for those rats that were not fed radioactive glucose is not zero because all substances contain a certain amount of radioactivity, and so therefore there was bound to be some come out the other end with the control rats.

8. From this experiment, we can draw the conclusion that, as the radioactivity count of the experimental rat compared to that of the control rat is so much higher, that glucose must be almost entirely broken down and used in respiration.

Investigation 3:Investigating the gases used and produced in respiration

9. The purpose of the water bath in this experiment is to keep the two test tubes at the same temperature, to keep the experiment fair.

10. The rise in the liquid level in the capillary tube connected to the germinating seedlings, compared to no change in the tube connected to the glass beads, is because oxygen has come out and filled up the tube. This is because the carbon dioxide has been absorbed by the limewater, and so the only gas that can come through is the oxygen.

11. For this experiment, a better control than glass beads would be to take some seedlings which had been killed. Then, there would be no way of respiration, as the seeds would be dead, and they would be very similar to the things used in the experiment, making it fairer.

Investigation 4:Is energy transferred in respiration?

12. If I were doing this experiment, to kill one set of seeds, I would heat them until they had stopped living. They would still be the same size as the live seeds, just dead, and so making it definite that they would not respire.

13. Cottonwool was used to plug the flasks rather than rubber bungs or corks because the cottonwool would not heat up and affect the thermometer, whereas the rubber could quite easily have, which would have distorted the results.

14. The difference in the to results, that the live seeds gave off more heat than the dead seeds, I think, shows that the process of respiration, as well as giving off carbon dioxide and oxygen, also gives off energy, which can create heat.

Making final conclusions

In the first experiment, we saw that respiration uses stored food to happen (ie. the beans) and that after it has happened there is actually less of the food left than there was before, showing how it actually uses it up.

In the second experiment, we saw how glucose is almost entirely broken down by the body for respiration, due to the amount of radioactivity in the carbon dioxide that the rats breathed out.

In the third experiment, we saw how not only carbon dioxide is created in respiration, but also another gas. Due to the soda lime absorbing the CO2, there must have been another gas which pushed the coloured liquid up the tube. These are likely to be hydrogen and oxygen, which is water, and could have gone through and pushed up the level of liquid.

In the fourth experiment, we saw how the seeds also gave off energy, which created the heat, Therefore, the word equation is:

Glucose + oxygen = carbon dioxide + water + energy

C6H1202 + 602 = 6CO2 + 6H20 + 2880kJ

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