This document is for my NCEA level 3 internal, where we must do our own biological investigation for the 3.1.
Aluminium can inhibit plant growth, and so we did this for our investigation, I got one of the best in the class.
The effect of Aluminium in
Pisum Sativum
Biology AS91601 BIO 3.1
Introduction: When growing your own plants for the first time, things may seem daunting, take the
Pisum Sativum (P. Sativum), the average garden pea for example, we may not consider the elements
inside our soil and how it may effect our plants growth rates. Inside the soil there is an abundance of
nutrients and elements, however, we are particularly interested in Aluminium, and how this may
effect plant growth for the P. Sativum. It has been thought that Aluminium inside soil may inhibit the
plants growth rates due to phytotoxicity, pH change and a lowering in uptake of vital nutrients such as
nitrogen. So we assume that there is a correlation between the amount of aluminium in the soil to the
plants growth rates, hence an investigation was carried out.
Purpose: The goal of this investigation is to find the overall relationship between the growth of the P.
Sativum roots and the concentration of Aluminium that is inside the soil of each plant.
Hypothesis: I believe that there will be a direct relationship between the amount of aluminium inside
the soil that the P. Sativum is growing in and the growth rates of the plant. I believe that the more
aluminium the soil contains, the slower the growth rates of the roots will be.
I hypothesize this because when there is an abundance or excess amounts of aluminium present in
acidic types of soil, aluminium toxicity may occur. From prior knowledge, I know aluminium toxicity
can result in much slower rates of cell division, and cell extension as well as transportation, this
ultimately will affect the roots overall health and hence the length of the roots of the P. Sativum.
Independent Variable: My independent variable will be the concentration/amount/mass of
Aluminium Nitrate mineral additives. The ranges I have used for this investigation is 1%, 0.75%,
0.5%, 0.25%, and 0%. The percentage shows the percentage of Al(NO 3)3 (s) I will add in the potting
mix, where each will be determined by the ratio of Al(NO3)3 (s) to soil in grams (g) ie: 1% of 22.5g of
soil is 0.225g of Al nitrate. By having a constant (0%), I am able to make a comparison of the results
of a chemically treated plant to a natural, untreated plant, to see how the mineral actually affects
growth rates, and subsequently, will prove or disprove my hypothesis.
Dependent Variable: This shall be the longest root length of the P. Sativum after 11 days of
germination and growth. I planted the seeds on the 6th of May and harvested on the 17th of May. To
measure the length of the longest root, rinse the roots of the harvested seed in distilled water, then
using a string, place the string on the seed and follow the length of longest root and mark it on the
string, then using that string, measure the string from the end to the marked length. By using a string,
we can wrap around the roots and get an accurate measurement, because the roots are twisted and
tangled, so using a string, we can get the most accurate measurement.
Controlled variables:
To ensure the validity and reliability of the results in this investigation, certain variables must be held
constant to ensure no sample is advantageous to another or vice versa. By having these controlled
variables, we can ensure internal validity.
One of the variables I controlled is the potting mix I used, this is by having the same bag of potting
mix, this mix came from the same bag and manufacturer. This is essential to keep constant as varying
the potting mix may vary the amount of nutrients that each sample receives and may skew the results
in favour of a more nutrient rich soil, results could have easily been thrown off if this measure had not
been upheld.
, Another confounding variable that must be held the same is the amount of water given to the
seedlings. Too much or too little can cause harm to the new plant by either drowning it or having it
deprived of water, hence cannot grow properly because of extreme conditions and add unaccounted
stress on the plant. This again, is very vital to keep constant, as we do not want to kill our plants
during their growth or inhibit their growth by an external factor, hence skewing the results. Again, this
could easily manipulate the results given if this measure had not been taken, hence we give each plant
the same amount of water.
To add onto the previously mentioned variable, the type of water is also very important to keep the
same. I used distilled water rather than tap water when watering my plants. If one plant were to
receive distilled water, and another tap water, then the plants will get different nutrients and minerals.
This is because tap water is not as refined and pure as distilled water, and may give the plants extra
minerals, hence possibly giving them an advantage or disadvantage regarding growth. To go further,
tap water consists of many different minerals and organisms, such as magnesium, calcium, zinc which
all benefit plant growth, but also contains sulphate and chlorine, which are more harmful to plants.
But on the other hand, distilled water is more refined, by boiling the water, and condensing the water
vapours, thereby ridding the water of minerals, hence being roughly 99% less contaminated than tap
water. By taking this extra precaution, we limit the number of external factors affecting plant growth,
and the aluminium nitrate, this helps keep the focus of the investigation on Al(NO 3)3 (s) meaning only
one variable is affecting plant growth.
Continuing on, one vital aspect to plant growth is temperature, and this must be controlled. This is
held controlled by having the plants grow inside the same propagating tray within close proximity of
each other and in the same surrounding environment. This is essential to keep constant, as different
plants may respond to temperature differently, and if it is too cold, it will slow down vital life
processes and slow down intercellular chemical reactions such as respiration. Or if it gets too high in
temperature, then enzymes will denature, and no longer have a perfect induced fit into substrates,
thereby slowing chemical reactions due to the lack of functioning enzymes. Both can hinder cell
functions, and consequently the root growth rates of the P. Sativum, hence why it is important to keep
a constant.
Each plant should grow for the same amount of time, obviously, by leaving plants in longer than
others will create unfair results, because some get more growth time than others. Plants left to grow
for longer are very likely to grow longer when compared to one that has been taken out beforehand,
giving an unfair advantage, hence giving us unreliable and inaccurate results that are invalid. To avoid
this, plant the seeds as fast as possible to restrict the time difference, and also to harvest the plants in
the same manner for similar reasons.
Lastly, the light exposure each sample receives must be kept the same. One that receives more may
have an advantage over another because more light exposure allows them to perform higher levels of
photosynthesis. This could skew the data in favour of a sample receiving more sunlight. This is
controlled by placing the pots of the seed in close proximity within each other in a place with a fair
amount of sunlight exposure, so the light exposure will be the same for all samples ensuring validity
and removing bias.
Equipment: 5x8 propagating tray (each cell approx. 4cm*4cm*4.4cm, L*W*H) (with plastic lid and
bottom tray), 2mL pipette, measuring cylinder, spatula, distilled water, ruler, potting mix (Kings Plant
Barn Ready to Use Potting Mix), 40 Tasty pea (Pisum Sativum) seedling, mineral additive aluminium
nitrate, 250mL beaker, electric scale, latex gloves, mask, labels, sharpie, string, plastic scoop, 2L ice
cream tub
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