Oxygen is needed for respiration to take place in the plant. In this process energy is created by the breakdown of the sugars that are made during photosynthesis. Oxygen combines with hydrogen to form water. Water makes up a large proportion of the mass of any plant. Water is used to transport minerals and sugars produced during photosynthesis.
Magnesium – is essential for many of the functions inside of the plant. It is an essential element of the chlorophyll molecule. It is an enzyme activator and constituent of many of the enzymes in a plant. Magnesium deficiency symptoms in tomato (Epstein and Bloom 2004). Leaves are often a pale green colour (due to the effect on chlorophyll). Some of the leaf margins will curl upwards or turn red-brown to a purple colour.
Manganese –The leaves will show a light interveinal chlorosis developed under a limited supply of Mn. The early stages of the chlorosis induced by manganese deficiency are somewhat similar to iron deficiency. Manganese deficiency symptoms in tomato (Epstein and Bloom 2004)
Nitrogen – deficiency will affect the rate at which the plant will grow. The older leaves at the bottom of the plant will first turn a yellow-greenish colour, then yellow, red or even purple. The newer leaves at the top of the plant will turn slightly yellowish-green. The colour change is due to the destruction of chloroplasts.
Phosphorus deficient plants are often stunted and short in stature. The stalks that develop are weak and thin and appear spindly. Purple veins may appear on the leaves or the leaves may turn purplish. Older leaves may appear bluish-green.
Sulphur deficiency resembles that of Nitrogen, but it appears first in younger leaves with them pale-yellow or light green.
Iron deficient leaves show strong chlorosis at the top of the plant and then moves down to the bottom. Leaves turn a yellow colour but keep there green veins.
Potassium deficient leaves show marginal tip burn. As the deficiency progresses death occurs in the interveinal spaces between the main veins along with interveinal chlorosis.
Biological Aim
The aim of this experiment is to determine what effect the lack on minerals has on the growth of a plant.
Hypothesis
As fertiliser contains all of the necessary minerals that a plant will need to grow, the duckweed grown in fertiliser will produce the most leaflets. As tap water contains some minerals (chloride etc), duckweed will grow better in this than in distilled water that contains no minerals.
Null Hypothesis
The duckweed will not be affected by the absence of minerals and therefore there will be no difference between the number of leaflets in the three experiments.
Equipment
The equipment used was a described in the NEC handout
Method
The method was conducted as described in the NEC handout
Variables
Independent variable = the conditions in which the duckweed is grown
Constant variables
Need to make sure that the volume of liquid added to each of the containers is the same amount. This ensures that any effect of growth rate is not as a result of the amount of water added.
The duckweed is taken from the same area of the pond this should ensure that the pond weed has gown in the same nutrients and environmental conditions.
The duckweed taken from the pond is of a proportionate size. That the samples have the same amount of leaflets.
Risk assessment
There is a risk of infectious diseases such as weil’s disease from contaminated water supplies. It is therefore essential that precautions are taken when placing hands into the water. All open wounds on the hands should be covered and vinyl gloves warn when coming into contact. Also care must be taken when around ponds, ensure that no risks are taken to get hold of the duckweed.
Results
Table 1 shows the number of leaflets on each duckweed plant grown under different conditions
Graph 1 shows the effect of minerals on the growth of leaflets on Duckweed
The plants grown in distilled water show very little difference in the amount of leaflets that grew on the duckweed plant. It also showed the smallest amount of growth in overall size. The growth of the duckweed is due to the minerals held in the plant, those minerals absorbed from the pond. As the duckweed ages the minerals are used up, there are no new minerals being replaced and the plant starts to show deficiencies in many of the minerals by the loss of chlorophyll and turn yellow.
The duckweed grown in the tap water like the one grown in the distilled water retains minerals from the pond. There are some minerals in the tap water that aid grow this is shown by more leaflets growing in the later stages of the experiment. However if this experiment was elongated the amount of new leaflets would decrease that the plant would plateau as in the distilled water. This is due toany nutrients in the tap water being used up by the plant. The plant would also begin to exhibit phenotypic symptoms of nutrient deficieny such as yellow leaves.
Plants grown in the fertiliser have the greatest rate of growth. The rate at which new leaves is not slowing and all leaves are a healthy green colour. This is because the nutrients that were in the plants from the pond are being replaced by excess minerals in the fertilisers. The longer the experiment proceeds the greater the rate of leaflet growth. This is shown by an increase in the gradient of the graph.
With a p value of <0.01 we can reject the null hypothesis and accept the hypothesis with a confidence of 99%. This means that there is a significant difference in the growth of leaflets in plants grown in different mediums. It suggests that minerals have a significant difference in the growth of plants.
Evaluation
Although this experiment shows the effect that minerals and the lack of minerals have on plant growth. This is all that it tells use. It makes no advancement to our knowledge of the effect of individual minerals to plants. This would have been overcome by the use of Sachs solutions which are specifically designed to have a single nutrient deficiency. This would then show how the effect of removing one nutrient would have on the phenotype of a plants growth.
There was also a problem with water loss from the containers probably due to evaporation from the container and the leaves of the plant. No attempt was made to replace the loss fluid. This could then have had an effect on the growth of the plants. Before the experiment started I should have marked the meniscus of the water and then topped up the volume with distilled water.
The health of the duckweed plants used was not investigated at the beginning of the experiment. Even though the duckweed was taken from the same area of the pond, some of the samples could have been diseased. If I would have had time I could of investigated this by growing all of the duckweed in nutrient rich water for a few weeks before replacing them in the new mediums. This would have meant all of the samples would have been healthy and disease free.
I also noticed that to the end of the experiment algae was growing in the tap water and fertiliser samples. This could have some effect on the rate of plant growth. To prevent this, the water could have been boiled and cooled before adding in the plant.