This is my learning aim A part of the unit 6 module in my Applied science course. In this assignment, I investigated the factors affecting photosynthesis and carried out the experiment of how light intensity affects the rate. Even if you chose to investigate a different topic you can use this assig...
Unit 6: Investigative Projects
Learning aim, A: Undertake a literature search and review to produce an investigative projects
proposal.
Assignment title: Project research
Literacy review for photosynthesis
What is photosynthesis?
Photosynthesis is a type of chemical reaction that plants need in order to respire, grow and reproduce
[1]. Plants can make their own food via the process of photosynthesis. It takes place inside the leaves
of the plant cell that contains chloroplasts which are small structures that contain chlorophyll [1]. The
components needed for photosynthesis to take place are carbon dioxide, water and light [1].
Chemical process for photosynthesis
Carbon dioxide + water -----> glucose + oxygen
6CO2 + 6H2O ----> C6H12O6 + 6O2
How does photosynthesis take place in the leaves?
The leaves are adapted for photosynthesis via its properties and structure. The leaves are green due to
the chlorophyll they contain. The chlorophyll allows the leaf to absorb sunlight. Leaves also have a
large surface area which like the chlorophyll absorbs sunlight [1]. The structure of leaves is thin and
because of this, gases get diffused in and out of the leaf easily [1]. Another structural feature leaves
have is that they have veins known as xylem and phloem which allow the transport if water, mineral
ions and glucose [1].
Factors affecting photosynthesis
1. Light intensity
As light intensity increases so does the rate of
photosynthesis. After a certain point in which the
photosynthesis rate is at its fastest, the rate of
photosynthesis cannot go any faster and eventually the
curve flattens showing that even if light intensity
increases the rate of photosynthesis stays stationary at
its fastest rate [3]. At point A and B light is a limiting
factor as light shown onto plant has an effect on the rate
of photosynthesis and between B and C it is not a
limiting factor because the light shone has no effect on
rate of photosynthesis [3].
2. Carbon dioxide concentration
As carbon dioxide concentration increases so does the rate
of photosynthesis, however likewise to light intensity after a
certain CO2 concentration the increase stops being obvious
and the curve eventually flattens [3]. Carbon dioxide
concentration increasing does not affect the rate of
photosynthesis after this point. At points A to B the carbon
dioxide concentration is a limiting factor as the change in
concentration of carbon dioxide has an effect on the rate of
photosynthesis. However, from points B to C the carbon
dioxide concentration is no longer a limiting factor and
, Unit 6: Investigative Projects
Learning aim, A: Undertake a literature search and review to produce an investigative projects
proposal.
therefore the rate of photosynthesis does not change even if the concentration of carbon dioxide
changes.
3. Temperature
As temperature increases so does the rate of photosynthesis
however after a certain point the increase in temperature
results in the rate of photosynthesis to decrease [3]. At points
A to B the increase in temperature causes the rate of
photosynthesis to increase. Point B is the highest rate the
photosynthesis process could be. From points B to C, the
increase in temperature causes the rate of photosynthesis trend
to have a negative correlation corresponding to the beginning
in which the graph had a positive correlation.
There are different ways in which we can measure the rate of
photosynthesis. We can measure rate of photosynthesis by
measuring the uptake of carbon dioxide, production of oxygen,
production of carbohydrates or the increase in dry mass [7].
Uptake of carbon dioxide could be measured in three ways: using immobilised algae, using IRGA or
using a carbon dioxide monitor [7]. Immobilised algae are easy and gives accurate results and is
carried out using an algal balls technique in which immobilised algae are in hydrogen carbonate
indicator solution. The IRGA method is the use of infra-red gas analyser which allows the carbon
dioxide passing inside a chamber to be compared to carbon dioxide concentration leaving the chamber
surrounding the leaf [7]. Measuring production of carbohydrates is a longer way of measuring a rate
of photosynthesis due to it involving drying and weighting leaf with weeks in between each weighting
in order to compare the amount of carbohydrates [7]. More the leaf weights, the more carbohydrates it
contains. This is not an ideal method as it is complex, time consuming and not very reliable. Another
way we can measure the rate of photosynthesis is by observing the increase in dry mass which can
also be known as serial harvests [7]. This is also a time-consuming method because it involves the
harvesting of several plants [7]. Due to there being several, measurements should be replicated in
order to have a fair experiment in which you must find the average and standard deviation [7]. This
could lead to inaccuracy in the results and therefore is not preferred.
In my experiment I will be measuring the production of oxygen by counting the oxygen bubbles
produced due to the light intensity.
Project proposal
Hypothesis:
The factor I will be investigating will be the light intensity and how it affects the rate of
photosynthesis. My hypothesis is that as the light intensity increases so will the rate of photosynthesis
however, once the rate of photosynthesis of the pondweed reaches its peak it will stay the same and
not increase any further.
Variables:
The independent variable in the project is the light intensity and how close the light will be from the
pondweed. The dependent variable is what I will measure/observe, and that will be the amount of
oxygen bubbles which shows the rate of photosynthesis. My controlled variable will be the size of the
pondweed, the volume of water and temperature of water. The controlled variables are important as
they will help me ensure that my experiment will be a fair practical.
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