12 Biology Task 1 (PART B)
By Joel Power
Teacher: Mrs J. Duncan
Title:
The effect of pH on Genetic Barley’s Phenotype.
Aim:
To investigate the effect of pH on genetic barley’s phenotype.
Hypothesis:
If the pH is from 5.5-6.5 then the genetic barley’s growth will be optimal,
however, if the pH is more acidic or alkaline than this, then growth will be
unfavourable and therefore cause varying phenotypes.
Materials:
Risk
Assessment:
Method:
-
42 x genetic barley seeds
3 x sheets of cotton wool
3 x large plastic petri dishes
3 x water spray dispensers
250mL beaker
forceps
data logger
pH probe
glass stirring rod
0.1M hydrochloric acid bottle
0.1M sodium hydroxide bottle
Identification of Risk
Assess
Precaution
Hydrochloric acid
causing eye, lung or
skin irritation.
Low
Avoid skin contact and
wash hands after use.
Avoid inhalation of
vapours.
Sodium hydroxide
causing eye or skin
irritation.
Low
Avoid skin contact and
wash hands after use.
Glassware breaking
causing cuts or
wounds.
Low
Carry with care and a
firm grip. Do not leave
near bench edges.
1. A sheet of cotton wool was laid inside a large plastic petri dish and
sprayed generously with water until the cotton wool was damp.
2. Forceps were used to arrange fourteen barley seeds on the cotton
wool so that they were evenly spaced about 1cm apart.
3. Steps 1-2 were repeated two more times.
4. The seeds were sprayed with normal tap water generously and
evenly daily to ensure that they did not dry out and all received the
same amount of water.
5. The petri dishes’ cover was put on and they were left on a bench in
stable conditions where generous shade and some sunlight was
evenly available to all seeds.
6. The 250mL beaker was filled with 250mL of tap water.
7. The data logger and the pH probe were used to detect the pH of the
water. While stirring the water with the glass stirring rod, drops of
0.1M hydrochloric acid were placed in the water to lower the pH and
drops of 0.1M sodium hydroxide were used to heighten the pH until a
pH of 5 was reached.
8. The solution was poured into a water spray dispenser.
9. The 250mL beaker, the pH probe and the glass stirring rod were
rinsed.
10. Steps 6-9 were repeated to reach a pH of 6 and then repeated again
to reach a pH 7.
11. After six days, once the seedlings had properly germinated and
started growing, the mean height for each set of seedlings was
calculated and recorded. This was also completed every two days
following (excluding weekends).
12. From this time, the three water spray dispensers, each with a
particular pH, were then used to water a particular set of 14 seedlings
in each petri dish daily, instead of the normal tap water.
13. After eight days, the growth range (end result - initial result) of each
pH level’s seedlings was calculated and recorded.
Independent Variable:​ pH of water.
Dependent Variable: ​Phenotype of genetic barley.
Control Variables:​ Water type/availability, sunlight availability, nutrient
availability and seed type to ensure even nutrient availability. Growth range
as a substitute for final height to eliminate possible bias in final height
because of differences in initial height.
Results:
Table 1: Mean Height and Growth Range of Genetic Barley Depending
on pH Level
Date
pH 5 Height
(cm)
pH 6 Height
(cm)
pH 7 Height
(cm)
03/12/18
8.2
7.1
6.9
05/12/18
8.9
8.9
6.9
07/12/18
9.4
11
7.1
10/12/18
10.5
11.8
7.2
Growth Range
2.3
4.7
0.3
Graph 1: Mean Growth Range of Genetic Barley Depending on pH Level
Image 1: Seedling appearance according to their pH Levels
Table 2: Final Qualitative Observations
pH
Observations
6
Thick, standing straight
5
Medium thickness, sagging
7
Thin, laying down
Discussion:
The most effective growth occurred as a result of a pH of 6, characterised by
the seedling’s phenotype being thick, having straight posture, and a growth
range of 4.7cm. Whereas a pH of 5 gave inferior growth, shown by the
genetic barley’s phenotype of medium thickness, sagging posture, and a
growth range of 2.3cm. A pH of 7 gave the poorest growth as their phenotype
was thin, laying down, and showed a growth range of only 0.3cm. These
results supported my hypothesis, that if the pH is from 5.5-6.5 then growth
will be optimal, however, if the pH is more acidic or alkaline than this, then
growth will be inhibited and therefore cause varying phenotypes.
As demonstrated, genetic barley has a pH which is optimal for their growth
and straying from this level has been shown to impair their growth. This is
caused by numerous factors.
Firstly, an environment that is either too alkaline or too acidic causes a lack in
the availability of nutrients and inhibits the plant’s ability to absorb nutrients.
A deficiency of the essential nutrients carbon, hydrogen, oxygen, nitrogen,
phosphorous, and potassium causes ill growth as they are vital elements in
promoting growth.
Many different functions within plants are carried out by the proteins they
contain. Proteins are made up of polypeptide chains which come from
synthesised amino acids whose structure includes an amine group, carboxyl
group, and a variable R group. The polypeptide chains are organised into
specific shapes that are essential to the correct functioning of a protein.
However, a pH that is too high or too low disrupts the tertiary structure of a
protein as it alters the interplay between the R groups of various amino acids
and breaks the bonds between them. This changes the protein's shape,
causing it to become denatured which obstructs the functionality of the
protein and therefore impedes the plant’s ability to grow. Proteins are critical
for functions such as the biosynthesis of membrane channels and pumps,
hormones, and enzymes. Enzymes have a significant role in photosynthesis
which is a process responsible for the production of glucose. Consequently,
without enzyme activity, glucose production would be inhibited and glucose is
a substance that significantly aids plant growth. Further, hormones such as
auxins are responsible for stem elongation which work with cytokinins to
promote cell division. Additionally, membrane channels and pumps are
responsible for transporting materials that are vital for plant growth in and out
of the cell. Therefore, It would be detrimental to plant growth if extreme pH
levels were to denature proteins that are responsible for the biosynthesis of
membrane channels and pumps, hormones, and enzymes.
The design of this experiment gave highly valid results. The effect that pH
has on genetic barley’s phenotype was successfully investigated due to the
suitability of the equipment and method utilised. A widely used scientific pH
probe and data logger were used which precisely (to 2 decimal places)
distinguished between three different pH levels in order to observe their
varying effects on the genetic barleys phenotype. Additionally, the method
included the control of numerous variables. This included keeping consistent
and equal water type and availability among seeds, equal sunlight availability
among seeds and using cotton as a neutral medium which all ensured equal
nutrient availability to all seedlings. Further, growth range acted as a
substitute for the effect pH had on height. Differences in initial height that
could possibly skew final height results were eliminated by comparing the
various pH level’s growth range instead of final height.
The design of this experiment did not give reliable results. Even though
random errors were reduced by observing differences and calculating the
mean growth range of 13 seedlings per pH level, the consistency of the
growth range between each individual seedling was not observed. Further,
the experiment was not repeated and therefore results received could not be
enforced by consistency.
The design of this experiment gave highly accurate results. The method and
equipment used, including the use of the precise scientific pH probe and data
logger helped give rise to our results supporting the accepted pH range for
optimum growth in genetic barley. Out of a pH of 5, 6, and 7, we discovered
that optimum growth occurs from a pH of 6 which supports the accepted
optimum pH range of 5.5-6.5 as it is precisely in the middle of the range.
During this experiment, there were problems that were encountered. While
the seedlings were growing, there was a high level of heat which would
dehydrate them. To overcome this, plenty of water and shade was given,
particularly over weekends when they could not be accessed. Further, the
petri dishes’ lid was put on during germination so the water could not escape.
Additionally, towards the end of the experiment, the three water types with
their specific pH levels started to run out. To overcome this, the seedlings
were watered less to conserve water. We did not want to make more solution
in concern of affecting the experiment negatively. However, this was not
optimal so an amendment to make to this investigation in future would be to
make a bigger volume of each solution initially.
Potential areas for further investigation include the adaptation of a different
environmental factor such as water/sunlight availability or soil type to see
their effect on phenotype.
Conclusion:
The aim of this investigation, to investigate the impact of pH on genetic
barleys phenotype was successfully achieved. A pH of 6 showed optimal
growth, giving a phenotype of a higher growth range, thick width, and straight
posture. A pH of 5 and 6 showed poorer growth as their phenotypes were a
lower growth range, thinner and sagging more. This supports my hypothesis,
that if the pH is from 5.5-6.5 then the genetic barley’s growth will be optimal,
however, if the pH is more acidic or alkaline than this, then growth will be
unfavourable and therefore cause varying phenotypes. This occurs as pH
levels that are too acidic or too alkaline cause a lack in nutrient availability,
impeded ability to absorb nutrients and the denaturation of proteins that are
responsible for functions vital to a plants growth.
Bibliography
Armstrong, Z., Deeker, W., Madden, A., & Mcmahon, K. (2019). ​Pearson Biology 12: NSW
student book​. Melbourne, Victoria: Pearson Australia.
Banas, T. (2017, April 24). ​The Effect of PH on the Rate of Photosynthesis.​ Retrieved January
05, 2019, from https://sciencing.com/effect-ph-rate-photosynthesis-5892500.html
Grey, M. (2017, September 21). ​The Effects of Water pH on Plant Growth.​ Retrieved January
04, 2019, from https://www.gardenguides.com/85878-effects-water-ph-plant-growth.html
Shmoop Editorial Team. (2008, November 11). ​Biology Plant Hormones - Shmoop Biology.
Retrieved February 01, 2019, from
https://www.shmoop.com/plant-biology/plant-hormones.html
Soil pH.​ (n.d.). Retrieved from https://www.cropnutrition.com/efu-soil-ph