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Factor affecting photosynthesis

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Factors Affecting Photosynthesis
Low light intensity lowers the rate of photosynthesis. As the intensity is increased the rate also increases. However, after reaching an intensity of 10,000 lux (lux is the unit for measuring light intensity) there is no effect on the rate. Very high intensity may, in fact, slow down the rate as it bleaches the chlorophyll. Normal sunlight (usually with an intensity of about 100,000 lux) is quite sufficient for a normal rate of photosynthesis.

Open and Closed Stomata
Sub Topics

1. Carbon Dioxide Concentration
2. Temperature
3. Chlorophyll Concentration
4. Water
5. Pollution
6. Application
7. Compensation Point Carbon Dioxide Concentration
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In the atmosphere, the concentration of carbon dioxide ranges from .03 to .04 %. However, it is found that 0.1% of carbon dioxide in the atmosphere increases the rate of photosynthesis significantly. This is achieved in the greenhouses which are enclosed chambers where plants are grown under controlled conditions. The concentration is increased by installing gas burners which liberate carbon dioxide as the gas burns. Crops like tomatoes, lettuce are successfully grown in the greenhouses. These greenhouse crops are found to be bigger and better-yielding than their counterparts growing in natural conditions.
The following graph shows how different concentrations affect the rate of photosynthesis.

Light Intensity
Temperature
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An optimum temperature ranging from 25oC to 35oC is required for a good rate. At temperatures around 0oC the enzymes stop working and at very high temperatures the enzymes are denatured. Since both the stages of photosynthesis require enzyme activity, the temperature has an affect on the rate of photosynthesis.

Graph Showing Effect of Temperature on Rate of Photosynthesis
Chlorophyll Concentration
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The concentration of chlorophyll affects the rate of reaction as they absorb the light energy without which the reactions cannot proceed. Lack of chlorophyll or deficiency of chlorophyll results in chlorosis or yellowing of leaves. It can occur due to disease, mineral deficiency or the natural process of aging (senescence). Lack of iron, magnesium, nitrogen and light affect the formation of chlorophyll and thereby causes chlorosis.
Water
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Water is an essential factor in photosynthesis. The effect of water can be understood by studying the yield of crops which is the direct result of photosynthetic activity. It is found that even slight deficiency of water results in significant reduction in the crop yield. The lack of water not only limits the amount of water but also the quantity of carbon dioxide. This is because in response to drying the leaves close their stomata in order to conserve water being lost as water vapour through them.
Pollution
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Pollution of the atmosphere with industrial gases has been found to result in as much as 15% loss. Soot can block stomata and reduce the transparency of the leaves. Some of the other pollutants are ozone and sulphur dioxide. In fact, lichens are very sensitive to sulphur dioxide in the atmosphere. Pollution of water affects the hydrophytes. The capacity of water to dissolve gases like carbon dioxide and oxygen is greatly affected.
Application
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Study of photosynthesis and the factors affecting it helps us understand the most important biochemical life sustaining processes. All plants and animals are dependent on the sun for energy. This energy is made available to them by the process of photosynthesis. Man, like other animals, is dependent on the plants for his food. Scientists are constantly working towards developing new varieties of crops which give better yield of crops. With the population explosion and resulting pressure on land resources, the percentage of land available for cultivation is reducing at an alarming rate. This means that in the restricted space, the crops have to yield more. All this has been possible so far with the understanding of the photosynthesis. Greenhouse plants and crops in unfriendly freezing conditions have been possible due to the study of the factors affecting photosynthesis.
Studies have shown that there are a group of plants called the C4 plants which are more efficient in harnessing carbon dioxide from the atmosphere. Since the atmospheric level of the gas is only 0.3 to 0.4% and maximum crop yield is reported at 1% level, these plants are ideal for cultivation as they can draw maximum carbon dioxide from the atmosphere, greatly increasing the yield. One of the areas of current focus is the better understanding of the mechanism of C4 plants.
Compensation Point
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The rate of photosynthesis is not constant throughout the day. It's rate is affected by the intensity of light. The actual requirement of the light intensity for maximum photosynthesis in a plant depends on the type of plant and also on its habitat. Generally, average sunlight intensity is sufficient for photosynthesis except on rainy or cloudy days. The rate of photosynthesis increases with increasing intensity of light and decreases with decreasing intensity of light. During early morning or late evenings when the rate of photosynthesis becomes equal to the rate of respiration, there will not be any net exchange of gases (CO2 and O2) between the plant and the surrounding environment. The light intensity, at which the photosynthetic intake of carbon dioxide is equal to the respiratory output of carbon dioxide is called the compensation point.
‘’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’……………………………………………….

Introduction

In this course work, I will be discussing how the concentration of carbon dioxide affects the rate of photosynthesis. To find this out I will do an experiment to find out how much oxygen a piece of Elodea
(Canadian pondweed) produces over a set period under controlled supervision. Back Ground Knowledge

All plants photosynthesise, They do this in order to create their own food by converting sunlight, carbon dioxide and water into glucose and oxygen, which is a by-product (6Co + 6H O à C H O + 6O ) Plants have a part in their cell called chloroplast which contain chlorophyll the diagram below explains:

[IMAGE]

What are the limiting factors of photosynthesis?

Although the diagram shows you what you need for photosynthesis it does not tell you what the limiting factors are. The limiting factors in photosynthesis are carbon dioxide, water, light and chlorophyll.
This is because up to a point the more of each factor that is available to the plant will result in an increase in the photosynthesizing rate.

Why did I use pondweed?

I used pondweed so I could measure the amount of oxygen it produced accurately. I can do this by catching the oxygen bubbles under water, because of this choosing an aquatic plant was the best choice. I will use 5cm of elodea because it is a big enough piece to get a measurable result. I will know how quickly the elodea has photosynthesised by taking readings of how much solution was left in the burette after 24 hours and again after 48 hours.

Why use the sodium bicarbonate?

I used sodium bicarbonate solution in the experiment because it reacts with water to make carbon dioxide, which meant I could control the amount of carbon dioxide available to the pondweed. However, because of the time limitations I got my results by sharing the class results, this meant that I had to use the following concentrations of sodium bicarbonate: 0% 1.25% 0.5% 1% 5%. I used these percentages so that I had a good range of percentages but this didn’t give very good results because I made a big jump from 1% to 5%. If I did the experiment, again I would use these percentages: 0% 0.5% 1% 2% 3% 4%and 5% so that it had a steady increase.

How will I control the variables other than the Co concentration?

To control the other variables (water, light and chlorophyll). I will be using a set amount of water, I will be using the same lamps at the same voltage and I will be using a set amount of pondweed so that the amount of chlorophyll level should be the same. They will all have the same window letting in natural light and the temperature will be the same because they are in the same room.

Plan

I plan to set up an experiment using pondweed to see how much oxygen is produced over 24 hours and 48 hours. I will then put my results in tables and graphs to help me answer my main question.

Preliminary

In my preliminary experiment, I tested the concentrations I had chosen to check that the Elodea photosynthesised. I used a plastic funnel and a ray box, after using these in the preliminary I decided to replace them with a glass funnel that was transparent so that more light could get through. I also decided that a ray box was not giving out enough light because the elodea was not photosynthesising well and so I decided to change it to a desk lamp to give it a more directed and stronger light source.

Here is a diagram of my preliminary experiment:-

Here is a diagram of the experiment I used to get my results:-

Method:

1. set up the equipment in the apparatus list as the diagram above.

2. Record the volume of solution at the start of the experiment

3. turn the light source on

4. record the volume of solution after 24 hours of the first recorded volume

5. record the volume of solution after 24 hours of the second recorded volume

Accuracy

To make my results accurate I will be measuring the water level from the bottom of the meniscus. I will do this by taking the results with my eyes level to the bottom of the meniscus. I will repeat the experiment twice so that including the average I have three sets of results, which I will then plot on a graph. If the results do not turn out how I am expecting I will look back at my work to check any problems I may have had.

I will be leaving my elodea for 2 days and taking readings after 24 hours and 48 hours. This is because it will give it a reasonable amount of time to photosynthesise. I will find out how much oxygen the plant has produced over that time by taking my original reading for O in the burette and deducting my readings at 24h and again at 48h.

Prediction

What do I expect to happen?

I expect that as the sodium bicarbonate concentration increases that the rate of photosynthesis will increase until it hits its maximum rate of photosynthesis. I can tell this because as the sodium bicarbonate reacts with the water it will produce carbon dioxide, which will increase the rate of photosynthesis.

What I expect my graph to look like:

[IMAGE]

[IMAGE]

Why I expect this to happen:

I expect this to happen because this is the normal graph you would expect for a plant photosynthesising.

Results

Conc. Of sodium bicarbonate

(%)

Amount of NaHCO before

(ml)

Expt 1 Expt 2

Amount of NaHCO after 24h

(ml)

Expt 1 Expt 2

Amount of NaHCO after 48h

(ml)

Expt 1 Expt 2

Average oxygen produced over 24h

Expt 1 Expt 2

Average oxygen produced over second 24h

Expt 1 Expt 2

0

0

42.80

46.45

42.60

45.45

42.50

45.45

0.20

1.00

0.10

0.00

0.25

0.25

46.00

41.00

---

40.30

---

39.75

0.70

---

---

0.55

0.5

0.5

45.00

39.30

43.90

33.80

43.80

29.30

1.10

5.50

0.10

4.50

1

1

45.85

46.10

40.80

45.70

37.80

---

5.05

0.40

3.00

---

5

5

46.75

44.80

43.10

42.35

43.00

41.85

3.65

2.45

0.10

0.50

As you can see, from the results I have some missing results this is because while doing the investigation some burettes were knocked which meant that the liquid fell to the bottom of it. My group did 0.5% experiment. The result in red is highlighted because I did not use this result to get the average. This is because the pondweed must have died because it did not produce any oxygen.

Concentration of NaHCO (%)

Sum used to calculate average amount of O

Average amount of oxygen produced in a 24hour period (ml)

0.00

0.10 + 0.20 + 1.00

3

0.43

0.25

0.70 + 0.55

2

0.63

0.50

1.10 + 0.10 + 5.50 + 4.50

4

2.80

1.00

5.05 + 3.00 + 0.40

3

2.82

5.00

3.65 + 0.10 + 2.45 + 0.50

4

1.68

Analysis

My graph shows that when I increased the concentration of sodium bicarbonate from 0% to 1% the rate of photosynthesis increased. At first, it increased quite quickly but then it slowed down until eventually when we did 5% it decreased rapidly the only problem with my graph is there are not enough results between 1% and 5% so I cannot be sure how the rate of photosynthesis drops.

My graph starts similarly to my prediction however then it drops when my prediction says it should hit its optimum and stay there but instead it drops. I think this happened because when I increased the percentage of sodium bicarbonate the alkalinity of the solution goes up and disrupts the plants enzymes. A way to find out if this was happening would be to test the alkalinity of the solution. A way you could do this would be to use an electronic device that measures the
PH in the water. If the alkalinity was different in each concentration then it would be an unfair test of how the concentration of carbon dioxide effects the rate of photosynthesis because the PH would also be a variable and I wouldn’t know which variable, the carbon dioxide or the PH was effecting the plant and its rate of photosynthesis.

Evaluation

From my investigation, I can conclude that to a point an increase in sodium bicarbonate concentration the rate of photosynthesis will increase. However because I did not use any concentrations between 1% and 5% I don’t know how the rate of photosynthesis decreases but by the time it had gotten to 5% it had dropped to 1.7ml of oxygen produced by photosynthesising. There are two possible reasons for this happening, it could be an anomaly or it could just be a drop at that point. To find this out I would have to redo the investigation to include experiments with 2, 3 and 4 percent concentration of NaHCO .
The results from the concentrations are not very close but the 0.50 and 1.00 were very similar with only 0.02ml difference but the same jump from the 0.25 to 0.50 had the difference of 2.17ml. This suggests that because the spread of results were so different that the evidence may not by trustworthy.

To improve my experiments I could have used a different light source that did not heat up the solution so much. I also would use more pondweed so that I would get a clearer set of results. I would also have to find a different way to supply the carbon dioxide so that the
PH was not a variable.

Factors affecting the rate of photosynthesis
The rate of photosynthesis is affected by a number of factorsincluding light levels, temperature, availability of water, andavailability of nutrients. If the conditions that the plant needs areimproved the rate of photosynthesis should increase.The maximum rate of photosynthesis will be constrained by a limitingfactor. This factor will prevent the rate of photosynthesis from risingabove a certain level even if other conditions needed for photosynthesis are improved. This limiting factor will control themaximum possible rate of the photosynthetic reaction.For instance, increasing the temperature from 10ºC to 20ºC coulddouble the rate of photosynthesis as the plant's enzymes will becloser to their optimum working temperature. As the temperature isincreased, molecules in the cells will be moving at a faster rate due tokinetic theory. If the temperature is raised above a certain level, therate of photosynthesis will drop as the plant's enzymes aredenatured. They will therefore be more likely to join onto the enzymesand react.The amount of water available to the plant will affect the rate of photosynthesis. If the plant does not have enough water, the plant'sstomata will shut and the plant will be deprived of CO². It is difficult innormal lab conditions to prove that water directly affectsphotosynthesis unless a heavy isotope is used to trace the path of water.Chlorophyll is needed for photosynthesis. This can be proved bystudying a variegated leaf. It is however very difficult to study howdifferent levels of chlorophyll in the plant will affect it's photosynthesis

rate. This is because in a variegated leaf the cells either containchlorophyll or they don't.Carbon dioxide concentration will directly affect the rate of photosynthesis as it is used in the photosynthesis reaction. It is alsoeasy to change the amount of carbon dioxide that the plant receives.Light is also directly used in the photosynthesis reaction and is easyto change in normal lab conditions. Carbon Dioxide and Light are thefactors that I will change in the experiment as they are easy tochange and measureIt can be affected by many things, including:1)
Sunlight
- its Intensity & wavelength.2)
Temperature
3)
CO
2 and O
2
- availability4)Any factor that influences the production of chlorophyll,enzymes, or energy carriers(ATP and NADPH)
.The rate of photosynthesis will always corrospond to that factor whichis in least supply. Its rate will only increae when its supply isincreated.
Sunlight
Generally the more light there is, the more photosynthesis occurs.This is true up to a point, where the plant has reached maximumphotosynthesis levels, and so any increase in light intensity will notaffect the plant further.
Temperature
Generally higher temperatures are better than cold temperatures for photosynthesis. However if it is humid, and the air is saturated withwater vapour, photosynthesis is limited. This is because the water vapour being expelled cannot leave and go into the air, as there isn'ta concernation difference for it to diffuse across. So the water vapour sits in the leaf, stopping photosynthesis.
CO
2
Basically the more CO
2
in the air, the better the rate of photosynthesis. Of course CO
2
is taken in during the daytime, and if its content was less that normal, photosynthesis couldn't happennormally. Fertilisers increase the number of soil fungi and bacteria,thus increasing the levels of CO
2
from their respiration anddecomposition processes. So fertilisers are good news for plants.
HOW does light affect the rate of photosynthesis?
The rate of photosynthsis in a plant depends on the supply of carbondioxide, supply of light, supply of water, temperature and variousother factors like the amount of chlorophyll.At any one time, the rate is limited by the factor which is in shortestsupply. If the plant is in dim light, but has plenty of CO
2
, H
2
O and iswarm enough, then it will be light which is limiting the rate of thewhole process. If this is the case, then increasing the light willincrease the rate of photosynthesis.On a dull day in winter in a greenhouse in UK, it is probably lightwhich is limiting photosynthsis. However, in the tropics, with plenty of light and warmth, photosynthesis is normally limited by carbondioxide concentration in the air. Some greenhouse owners (even inUK) increase the concentration of CO
2
in their greenhouse to speedup the rate of photosynthesis in summer when there is plenty of light.
How Carbon Dioxide Concentration Affects Photosynthetic Rate As carbon dioxide concentration increases, the rate of photosynthesisincreases. At high concentrations, the rate of photosynthesis beginsto level out due to factors not related to carbon dioxide concentration.One reason might be that some of the enzymes of photosynthesis areworking at their maximum rate.1In general, carbon dioxide is found in low concentration in theatmosphere, and so atmospheric carbon dioxide levels may be amajor limiting factor on photosynthesis when at low levels.

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