This is a distinction standard work of a unit 6 assignment, marked by an excellent tutor and written with great depth and passion. This assignment Is based on the first learning aim (A) and is about how different colours of light affect plant growth. This assignment was chosen based on what I was a...
Azim Uddin 13M Unit 6A: Investigative project Submission date: 19/12/2019
Assignment Title: Project research
Introduction:
The project proposal will investigate photosynthesis. The process of photosynthesis is important for
all living things. We require plants to photosynthesise [6C0 2 + 6H2O –> C6H12O6 + 6O2] in order to
produce oxygen and remove carbon dioxide (CO 2) from the atmosphere as plants absorb CO 2. As we
face an ordeal with climate change; more CO 2 is being emitted through production of fossil fuels
which harms the environment. United Nation states that ‘global net human-caused emissions of
carbon dioxide (CO2) would need to fall by about 45 percent from 2010 levels by 2030, reaching ‘net
zero’ around 2050.’ (UN, 2019). This means that any remaining emissions would need to be balanced
by removing CO2 from the air. As plants absorb CO 2; helping the environment, the purpose of certain
light growing plants much faster will help improve climate change, enabling a better, sustained
future. This is because growing more plants will fix climate change as it will decrease CO 2 emissions.
In addition, plants provide us with fruits and a place for animals to live. Without plants our global
food chain system would break down and endanger the cycle.
In addition, this proposal will improve farming thus, benefitting farmers to take advantage of plant
growth. This will allow them to increase their yield crops and lead to more profit. The investigation
will provide information to greenhouses to improve their understanding of how different light
colours are effective in various ways leading to improvements in their greenhouse. Less economically
developed countries (LEDC’s) will benefit from this investigation to sustain and protect their
environment. Choi et al., 2015 stated plants under light emitting diode (LED) with colours such as
blue yielded much higher production of fruits then those with no light. (Choi et al, 2015). However,
LEDs have an initial price that is expensive and if they are overheated during winter as they depend
on the environments temperature it will lead to the device failing leading to repurchase and more
costs. (LEDs Magazine, 2019). Yet, the article by Choi et al., 2015 suggested that light does effect
plants and it encourages them to grow. Therefore, this will benefit those who are interested in plant
growth.
Lin et al., 2013 stated specifically that a combination of lights is the most effective for plant growth.
White light (sunlight) drives plant growth. Plants grown under red, blue and white LED were proven
to have better growth, nutrition, development, appearance and edible quality. (Lin et al., 2013). The
strength of his investigation was he compared plant growth; where red and blue light was combined
and red, blue and white light was mixed. This gives an insight on the effect of combined lights when
combined with white light, implying that white light has the most effect on plant growth. In
comparison, to Kim et al., 2006 investigation; he suggested that a higher amount of green photons
resulted in reduced plant growth. However, he also stated that when green light was combined with
red and blue light; they all enhanced plant growth. (Kim et al., 2006). This shows us that green light
is the least effective for plant growth and is important and relevant when preparing for the proposed
investigation as it provides information about the least effective colour for plant growth. However,
both scientists ascertained that when lights are combined together with their short and long
wavelengths, that they have the most effect on plant growth. This is because plants will absorb any
energy from light. This will be essential when partaking the planned investigation as it insights how
to prepare. Both studies showed us that plants react to the spectrum of lights, most specifically
when combined.
Background research:
There are two stages of photosynthesis: Light dependent and light independent reactions.
Stage 1 - Light dependent reaction:
1
, Azim Uddin 13M Unit 6A: Investigative project Submission date: 19/12/2019
Assignment Title: Project research
Firstly, the light dependent reaction occurs in the thylakoids of the grana in chloroplasts. Light
energy results in the excitation of electrons in the chlorophyll placed in the thylakoid membrane.
These electrons are then passed along a series of electron acceptors (photoionisation) in the
thylakoid membranes, collectively known as the electron carrier system. Energy from excited
electrons funds the production of ATP (adenosine triphosphate). 4 protons make one ATP molecule.
Electron loss from chlorophyll causes the splitting of water (photolysis). [H 2O –> 2H+ + 2e- + ½ O2].
Light splits water into protons (H+ ions), electrons and oxygen (waste). The protons are pumped
across the membrane using the ATP. The final electron acceptor forms NADP +. Oxygen is produced,
water to re-used, and electrons stream back to replace those lost in the chlorophyll. Hydrogen ions
(H+) from photolysis, together with NADP + forms NADPH2. (Hocking, Sochacki and Winterbottom,
2015). (A Level Biology, 2019).
Stage 2 - Light independent reaction:
There are two useful substances that are produced by the light-dependent stage, ATP and NADPH 2.
These are needed to drive the light-independent stage. They react with glycerate 3-phosphate (GP)
to produce a triose sugar – triose phosphate. Triose phosphate is used either to produce a 6C sugar
or to form ribulose bisphosphate (RuBP). The conversion of triose phosphate (3C) to RuBP begins
Calvin’s cycle and utilises ATP, which supplies the energy required. A RuBP molecule (5C) together
with a carbon dioxide molecule (1C) forms two GP molecules (2 3C) to complete Calvin’s cycle. The
GP is then available to react with ATP and NADPH2 to synthesise more triose sugar or RuBP.
(Hocking, Sochacki and Winterbottom, 2015). (A Level Biology, 2019).
Furthermore, plants use photosynthesis to generate food and energy for growth and cellular
respiration. Photosynthesis uses sunlight to grow. Light is absorbed by a pigment called chlorophyll
embedded in the thylakoids membrane. This occurs during the light dependant stage. Whilst
photosynthesis occurs, chlorophyll absorbs blue and red light to grow and reflects green light. The
sun allows plants to produce its own organic molecules such as glucose. Plants absorb water,
sunlight and carbon dioxide to produce their own nutrients. Where the synthesis is occurring it is the
light independent stage. As plants absorb the food it leads to plant growth. (Hocking, Sochacki and
Winterbottom, 2015).
Figure 1:
Figure 1 shows
the stages of
photosynthesis.
(Hocking,
Sochacki and
Winterbottom,
2015).
2
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