Investigation to examine the effects of varying tomato juice concentration on the germination of seeds
Investigation to examine the effects of varying tomato juice concentration on the germination of seeds
I plan to investigate the effects of varying tomato juice concentration on the germination of seeds. To do this, I am going to put cotton wool soaked in a constant volume of varying concentration tomato juice in photo film pots with a constant number of cress seeds. I will check the seeds every 24 hours to see how many have germinated.
Preliminary Work
Before doing the main experiment, I investigated the conditions in which I should carry it out. I investigated whether I should use fungicide, and if so, how should I apply it, whether tomato juice inhibits germination, how much liquid and cotton wool I should use and whether I would do the experiment in light or dark conditions. I needed to know if it would change the experiment too much by using fungicide. I knew that the spores in the air might have reacted with the tomato juice to produce fungus that would make it harder to count the germinated seeds, and so would hinder the experiment. The results showed that fungicide did not hinder the experiment too much:
Number of seeds germinated:
As the results show, the fungicide did not have an adverse effect on the experiment because the pattern of results was the same for those sprayed with fungicide, and those not sprayed. There seemed to be less fungal growth in those cases sprayed with fungicide. For this reason, I will continue using fungicide in my main experiment.
The results also showed that tomato juice did in fact inhibit germination, and so must contain germination inhibitors. Therefore, I think that it would be interesting to see how powerful these inhibitors are. I shall use various dilutions of tomato juice to investigate whether only small variations of quantities will significantly affect germination.
I also saw that the seeds grew at different speeds after germination, as they had different shoot lengths. I thought that it would be interesting to see how well the seeds grew early after germination in different conditions.
Although there was more of a change of the amount of seeds germinated between days in light, I have decided to carry out my experiment without light. I have decided this because there will be less fungus as the juice will not come into contact with the spores in the air as much. This is because the cotton wool will be acting as a semi-permeable barrier. Therefore, the seeds will be seen and examined more clearly.
What I think will happen
I think that the higher the concentration of tomato juice, the fewer seeds that germinate.
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Although there was more of a change of the amount of seeds germinated between days in light, I have decided to carry out my experiment without light. I have decided this because there will be less fungus as the juice will not come into contact with the spores in the air as much. This is because the cotton wool will be acting as a semi-permeable barrier. Therefore, the seeds will be seen and examined more clearly.
What I think will happen
I think that the higher the concentration of tomato juice, the fewer seeds that germinate.
Why I think this will happen
Certain environmental conditions like the availability of water, warmth and oxygen must be present for an embryo of a seed to grow. When plants shed their seeds in autumn or summer, these requirements are already present. But in many cases, the seeds do not germinate until the next spring. These seeds are dormant and an internal control mechanism prevents premature germination, even if the external conditions are suitable. The advantage of a dormant time is that germination is delayed until unsuitable conditions like snow, frost and freezing conditions are past.
Seed dormancy and germination are controlled by the levels of abscisic acid and gibberellins in the seed, or around the seed in the fruit sap. Abscisic acid is produced by a maturing seed and causes a reduction in the water from about 85% to 10% of its fresh mass. The continued presence of abscisic acid in or around the seeds inhibits their development. These seeds will not germinate until the concentration of abscisic acid has fallen. As its concentration of abscisic acid falls, a seed absorbs water and its concentration of gibberellins increases. The presence of gibberellins causes breakdown of stored food within the seed, enabling the embryo to grow.
Because fruit juice contains germination inhibitors, the seeds will not germinate as much as they could with water, for example, which does not contain germination inhibitors. If the fruit juice is diluted with water, then the amount of germination inhibitors will decrease. This will mean that it is easier for the seeds to germinate, and so more will germinate.
As the concentration of tomato juice drops, the amount of germination inhibitors will also fall. This means that when the tomato juice is at a lower concentration, more seeds will germinate than if the concentration of tomato juice was higher.
A list of the apparatus I plan to use
2 x 10ml Measuring cylinders
sheet of Cotton wool
10 ml Tomato juice
10 ml Water
220 Cress seeds
Forceps
22 Photo film cases
Lab coat
Which factors affect how the investigation will work?
Volume of tomato juice solution
Concentration of tomato juice
Light intensity
Temperature
Amount of cotton wool
Space around seeds
Water availability
Oxygen availability
The volume of tomato juice solution will have an effect on how the investigation will work because it determines how much liquid is in the photo film case. It is important because the seeds could be submerged, so not being able to get oxygen, or may not have enough liquid, so drying out.
The concentration of tomato juice will have an effect on how the investigation works because it will determine how much germination inhibitor is present.
The amount of light may have an effect on how the investigation will work because some seeds need light to germinate; some only germinate in the dark. If the amount of light was very low, then the seeds will have little chance of germinating so the experiment would not work so well.
The temperature of the conditions around the seeds will have an effect on how the investigation will work because seeds need to be at a certain temperature for them to germinate. If the temperature is too low, germination will be slowed, if the temperature is too high, germination may be grossly accelerated.
The amount of cotton wool will affect how the investigation will work because if there is not enough cotton wool, the seeds could be submerged in tomato juice solution, but if there is too much then the liquid will not soak into the cotton wool and the seeds will not be in contact with enough liquid.
The space around the seeds will affect how the investigation will work because if there is not enough space, the seeds will not be able to germinate and grow.
Oxygen availability will affect how the investigation will work because seeds need oxygen to germinate. It is required for aerobic respiration and so is needed for the seeds to live.
This would affect the experiment because seeds need a certain amount of water to germinate. Water is required to activate the biological process associated with germination, because these take place in aqueous solution. The seeds need to have sufficient water but, at the same time, not so much that they are submerged.
What will I keep the same?
Volume of tomato juice solution
Light intensity
Temperature
Amount of cotton wool
Space around seeds
Water availability
Oxygen availability
The light intensity and temperature will be kept the same for each result because the photo film cases used in the experiment will all be stored together in the laboratory. Each seed will be subjected to the same variations of light and temperature to avoid some seeds having an unfair advantage of germination because of non-ideal conditions.
The oxygen availability will depend on the amount of cotton wool used which affects how much free liquid there is. The amount of cotton will be kept constant and be measured.
The volume of tomato juice solution will be kept constant because the solution will be measured in a measuring cylinder.
The space around the seeds will be kept constant because the same amount of seeds will be put in each of the film cases and the film cases will all be the same size.
What will I change?
The concentration of tomato juice. I will do this as by varying the concentration of tomato juice, I will also be varying the amount of germination inhibitors and the purpose of my experiment is to see how much of an effect the germination inhibitors have on the germination of seeds.
What will I measure?
I will measure the amount of seeds that germinate.
Detailed plan
Before beginning the experiment, I will wear a lab coat and goggles for safety reasons.
I will obtain twenty-two photo film cases and cut out forty, two centimetre squared, pieces of cotton wool. I will place a piece of cotton wool in the bottom of each film case. I will then take a 10ml measuring cylinder and put the required amount of tomato juice in it. I will then fill the measuring cylinder up with water to the 10ml mark. I will vary the concentrations as follows:
I will repeat the experiment one more time for each tomato juice concentration.
Having poured the correct amount into the film case, soaking the cotton wool, I will place 10 cress seeds on top of the cotton wool, which are as evenly spaced as is in the bounds of experimental error. I will then spray the seeds in each of the film cases five times with fungicide. I will then place another piece of two centimetres squared cotton wool on the top of the seeds.
I will check the seeds every 24 hours for 4 days. I will remove the top layer of cotton wool with forceps and count the amount of seeds that have germinated in each film case for each concentration, measure the length of shoots and record the results.
When measuring the shoot lengths, I will push a thin ruler into the cases. When recording the results, I will take an average of the shoot lengths in each case.
