As the temperature increases to above 40ºc the enzyme and substrate molecules move even faster. A consequence of this faster movement means that the structure of the enzyme molecule vibrates so energetically that the hydrogen bonds that form the active site in the tertiary structure break. The enzyme would loose its globular shape and prevent the substrate from actually fitting into the active site. It is at this point that the enzyme is said to be denatured.
If the temperature is reduced near or below freezing, enzymes remain inactive and will become active once again when a higher temperature is restored
Null hypothesis – varying temperature does not have a significant effect on seed germination.
Plan
Take 18 clean petri dishes; add to each of the dishes a cotton wool pad making sure that it’s the same in each petri dish. Next take 10ml of water using a pipette and uniformly wet the cotton wool pad. Count out 20 mustard seeds (Brassica nigra) and place them equally spaced in one of the petri dishes and then repeat for the rest of the 17 dishes that are left. Cover the dishes with a non sealed petri dish lid so that the water doesn’t dry out and so that the oxygen is able to get to the seed. Next place 3 petri dishes in each of the locations shown below
- 0°c – Freezer
- 5°c – Refrigerator
- 20°c – Room Temperature
- 30°c – Incubator
- 40°c – Incubator
- 50°c – Incubator
Diagram of apparatus
Petri dish with seeds
Throughout the experiment I will change the temperature that the seeds are in to see if the temperature does affect germination. The things that will be kept the same throughout the experiment will be the amount of water the seed are given, the amount of cotton wool in the petri dish, the amount of time seeds have to germinate and the quantity of seeds. I will also use a new packet of seeds and choose the seeds out of the same packet.
When the seeds are kept in the freezer, refrigerator and incubator they will be kept in the dark. So when the seeds are at room temperature the seeds will be covered by a box, so that they have the same conditions as the other seeds as to get a fair test.
I will leave the seeds for 7 days before I will look at them to see if they have germinated. This should give enough time for the seeds to germinate if they are going to. I will know when the seeds have germinated because they will look like the diagram below.
Results
Analysis of results – the Chi-squared test
Chi-squared = X ² = ∑ (d²/x) X2 = Chi-squared
∑ = The sum of
d = Difference between observed
and expected values
x = Expected value
X2 = 20.5 + 8.89 + 72.3 + 61.48 + 18.55 + 20.5 = 202.22
From the graph the germination of seeds greatly increased from 0°c to 20°c, with no seeds germinating at 0ºc and 20 seeds germinating at 20ºc. At the temperature of 20°c and 30ºc the number of seeds that germinated is similar but not the same. After 30ºc the germination of seeds greatly decreased until it reached 50ºc where no seed germinated. From the graph you could suggest an optimum temperature for the biggest yield of mustard seeds; this would be between 20ºc and 30ºc.
At the temperature 0°c no seeds germinated. This is because there is not heat energy so enzymes remain inactive and will become active once again when a higher temperature is restored. Also because there is no heat energy then there is little movement so the chance of random collisions between the substrate and active site of the enzyme are low. This would mean that there would be few or no enzyme-substrate complexes. This would cause no activation of enzymes so therefore there would be no germination.
As temperature rose from 0ºc to 20ºc there was an increase germination rate. The increased temperature increases the rate of enzyme reaction. This increase in the heat energy will increase the kinetic energy. Both enzyme molecules and substrate molecules move faster and increase the number of random collisions between the substrate and the active site of the enzyme. Due to these collisions more enzyme substrate complexes form and produce many products causing germination to take place.
In the temperatures 20°c and 30°c nearly all of the seeds germinated this would suggest that the conditions were at there optimum and the seeds if they didn’t germinate could be accounted for the fact that maybe there were sterile seeds in the pack of seed.
At the start of germination water will enter through the micropyle and at temperatures 20ºc to 30ºc the water successfully activates the inactive enzymes. This is due to the increased heat energy which will increase the kinetic energy. Both enzyme molecules and substrate molecules will move faster inside the seed and increase the number of random collisions between the substrate and the active site of the enzyme. Due to these collisions more enzyme substrate complexes form.
When these enzymes are activated it causes insoluble food stores to be converted to soluble food. It turns the starch into glucose and protein into amino acids. The conversion of insoluble foods to soluble foods causes tissues to swell so that the testa is split open. Now the testa is split open water and oxygen can enter through the gaps. Oxygen along with the glucose enables aerobic respiration to occur which releases energy. This energy along with raw materials enables the embryo in the seed to grow.
As the temperature increases to above 40ºc the enzyme and substrate molecules move even faster. A consequence of this faster movement means that the structure of the enzyme molecule vibrates so energetically that the hydrogen bonds that form the active site in the tertiary structure break. The enzyme would loose its globular shape and prevent the substrate from actually fitting into the active site. It is at this point that the enzyme is said to be denatured.
In the hypothesis it said that temperature has no significant effect on the germination of seeds but at looking at the results gained in this investigation and the Chi-squared table it shows that the assumption was wrong. In this investigation we have 6 classes and looking at the Chi-squared table this result shows that there is less than 0.1% (0.001) chance that the results gained in the investigation are due to chance. This means that the deviation shown is significant and that the results are not purely to chance but must be affected by other factors for example temperature.
From the results gained from this investigation it shows that the temperature does have significant effect germination.
We disproved the initial hypothesis which we said germination isn’t affected by temperature. It therefore shows us that enzymes are in seeds and so germination is controlled by temperature.
The carrying out of this practical went well with few problems. In this investigation there were some anomalies. This was found in dish 1 at the temperature 20°c. You would expect all the seeds to germinate but not all of them did. This may be because there were sterile seeds in the packet of seeds in this investigation.
In any investigation there may be errors which have occurred that we could improve on if we were doing this investigation again. The possible errors that could have occurred would have been that the cotton wool wasn’t uniformly wet this would mean that some of the seeds would get more water than the rest and also not creating the experiment a fair one. Also a possible error may have occurred in making sure that a constant temperature was maintained in the locations that the seeds were kept.
Improvements to this investigation that could be made would be trying the seeds in different temperatures. For example start from 0°c and graduate up in 5°c intervals. There would be no need to do any temperatures below 0°c because in this investigation no seeds germinated at this temperature. This is also true for trying any temperatures above 50°c.
To further investigate what affects germination in seeds there are many investigations that could be carried out. For example does the amount of water affect the rate of germination? Does the amount of oxygen affect germination within a seed? Is germination dependent the intensity of light? Does the amount of space that the seed has affect its rate of growth?
Different seeds may have different optimum temperatures because of different conditions that they are used to. Another investigation that could be explored could be to find the optimum germination temperatures are of different seeds and compare them and the conditions you would normally find them in.
We disproved the initial hypothesis which we said germination isn’t affected by temperature. It therefore shows us that enzymes are in seeds and so germination is controlled by temperature.
The carrying out of this practical went well with few problems. In this investigation there were some anomalies. This was found in dish 1 at the temperature 20°c. You would expect all the seeds to germinate but not all of them did. This may be because there were sterile seeds in the packet of seeds in this investigation.
In any investigation there may be errors which have occurred that we could improve on if we were doing this investigation again. The possible errors that could have occurred would have been that the cotton wool wasn’t uniformly wet this would mean that some of the seeds would get more water than the rest and also not creating the experiment a fair one.
Improvements to this investigation that could be made would be trying the seeds in different temperatures. For example start from 0°c and graduate up in 5°c intervals. There would be no need to do any temperatures below 0°c because in this investigation no seeds germinated at this temperature. This is also true for trying any temperatures above 50°c.
To further investigate what affects germination in seeds there are many investigations that could be carried out. For example does the amount of water affect the rate of germination? Does the amount of oxygen affect germination within a seed? Is germination dependent the intensity of light? Does the amount of space that the seed has affect its rate of growth?
Different seeds may have different optimum temperatures because of different conditions that they are used to. Another investigation that could be explored could be to find the optimum germination temperatures are of different seeds and compare them and the conditions you would normally find them in.
