Team J

Photosynthesis and Respiration at the Christchurch School Dock

John Radcliffe, Katherine Johnson, Jonathan Bennett, and James Conway

GREAT JOURNEYS BEGIN AT THE RIVER!

Christchurch School is dedicated to using its great location on the river to help bring the Rappahannock River to the classroom. To help bring this about, much of the curriculum is dedicated to using the water to bring about further education, for students and teachers alike. Hopefully, our school will be able to have a positive impact on the River, in the same way that it impacts us. As just one example of furthering our own knowledge through the River with minimal to no impact, the Honors College Biology class will be using the Rappahannock River and data collected from it using the system described below to help learn about teaching a lesson in a dynamic, interesting way, about making use of technology that will become ever increasingly prevalent in the classroom, and finally, about the biological processes in our environment - the Rappahannock River.

This is a video about the system Dr. Carrillo set up to record data at the Christchurch dock. It updates every fifteen minutes. There are six main components - the weather measuring device, the instrument that reads sunlight, the water data collector, a camera, a data logger, and a radio transmitter. The Weather Measuring device is called a Vaisala Weather Transmitter WXT510, and it measures and records the air temperature, wind speed, wind direction, barometric pressure, rainfall, and relative humidity. To measure the sunlight in the air, a Li-COR LI200X Silicon Pyranometer (.pdf file) is used. To collect data like water depth, water temperature, salinity, oxygen concentrations, pH and turbidity, a YSI 6600V2-4 S Multi-Parameter Water Quality Logger is used. A Campbell Scientific CC640 camera records a picture of the area around the Christchurch Dock with every set of measurements. To store all collected data, a Campbell Scientific CR1000 data logger is used, and to protect it from the elements, it is enclosed in a NEMA enclosure. Finally, a Campbell Scientific RF450 Spread Spectrum radio receiver (.pdf file) transmits and receives data to its receiver located on campus.

To monitor the data we collect, please visit this site. It will update every fifteen minutes, when new data is sent to it from the system at the water front. For an explanation of the data page, click on the below screen cast.

Explanation of our internet data page

Team J is going to teach the reader about the photosynthesis and respiration cycles. First, we will start basic - we will explain what happens in each reaction and why it happens.

Secondly, we will show these two cycles in action at Christchurch. We will explain how each cycle is dependent on the other, and how both are interrelated and necessary for the continued existence of life on our Earth. We will use graphs to show the correlation between photosynthesis and respiration throughout days, weeks, and finally the year. Hopefully, we will achieve our goal of educating the reader on how these reactions work and be able to show the cycles as they occur in everyday life.

Photosynthesis and Respiration

What is Photosynthesis?

6 CO₂ + 6 H₂O – C₆ H₁₂ O₆ + 6 O₂

Photosynthesis is the process in which plants transform energy from light into sugars which are used as energy. Photosynthesis occurs in the chloroplasts, small organelles that absorb light easily. Light-dependent reactions called photophosphorylation use sunlight's energy to turn ADP (a form of energy) into ATP ( a more useful form of energy, one used by almost every living thing) and create NADPH, an oxidizing agent, in the first part of photosynthesis (called photosystems I and II). The photosystems are all about the absorption of light. Light and water are necessary for these systems to work properly. The second part of the process is the use of ATP and NADPH to create the beginnings of glucose (used in respiration as energy) in the Calvin Cycle. The Calvin Cycle does not rely on light, although it is only possible through the light dependent photosystems I and II. The Calvin Cycle creates the precursors to glucose through the use of CO₂ (or O₂ in the case of photorespiration) rubisco, and ribulose bisphosphate (RUBP). Rubisco is a particularly important enzyme in that it makes the Calvin Cycle work - thus making Photosynthesis and Respiration occur. It makes up 50% of protein in chloroplasts becuase of its' slow nature - it catalzyes very few molecules a second compared to other enzymes. Photorespiration is when there isn't enough CO₂ to keep the plants alive so they resort to desperate measures and take the O2 from photosystem II and use it to generate CO₂. While this is critical for their long term survival, the plant is basically eating itself. A crucial byproduct of photosynthesis is oxygen, which is used in respiration.

Link to a video explanation of photosynthesis

What is Photosystem II?

Photosystem II is the part of photosynthesis that replenishes photosystem I. It does this by using water to return an electron to the non-cyclic portion of photosystem I which is lost when forming NADPH. Photosystem II also has a proton pump in order to fuel the ATP synthase.

Link to a video explanation of photosystem II

What is Respiration?

C₆ H₁₂ O₆ + 6 O₂ – 6 CO₂ + 6 H₂O + ATP

Respiration is the process of extracting energy from glucose by breaking the bonds of glucose and transferring the energy to ATP bonds instead. What this really means is that a plant or organism is creating energy for it to grow and survive and disposing of waste through the breakdown of glucose. Essentially, plants and animals respire, meaning that they take in oxygen to create ATP and push out carbon dioxide. Respiration begins in the cytosol with the process of glycolysis which takes a 6 carbon glucose atom and breaks it into two 3 carbon pyruvates. Glycolysis meaning glyco- sugar, lysis- chop, and you can see this as the glucose molecule is chopped apart. The breakdown of sugar begins here. These 3 carbon pyruvates are then oxidized into Acetyl CoA in the mitochondria, small cells, and each lose a carbon that goes towards the production of NADH and ATP. The Acetyl CoA molecule moves into the Citric Acid Cycle (also known as the Krebs Cycle) which, with the use of oxaloacetate, generates NADH, another oxidizing agent. The Krebs Cycle is a process of breaking the remaining carbon bonds into separate carbon atoms which then combine with oxygen to form carbon dioxide. The Krebs Cycle is responsible for the most ATP created during respiration. The NADH then moves into the electron transportation system which turns ADP into ATP. This process is aerobic respiration which means that it takes place in organisms that require oxygen - however there is another form of respiration called anaerobic respiration. Anaerobic respiration is a process that is similar to fermentation in that it uses a different energy source other than oxygen, like Nitrate, Carbonate, or Sulfate to oxidize its cycles. A crucial byproduct of respiration is carbon dioxide, which is used in photosynthesis.

Link to a video explanation of respiration and the electron transport chain

Photosynthesis and Respiration at Christchurch School

The Buffering Capacity of Seawater

Any change in Carbon Dioxide in a body of water also changes the pH. This means that CO₂ controls pH.

H₂CO₃ = HCO₃ = CO₃

This equation is called the Dissolved CO₂ in seawater model.

When CO₂ is dissolved in seawater, carbonic acid (H₂CO₃) is produced. The carbonic acid drives down the acidity of the water, making pH drop. Therefore, when carbon dioxide levels increase in water, pH drops.When CO₂ is used up in the water and the amount decreases, carbonate (CO₃) takes its place. The carbonate is more basic than carbonic acid, so this makes the pH increase. A fall in carbon dioxide levels correlate with an increase of pH, and likewise, an increase in carbon dioxide correlates with decline of pH.

For a a more in depth explanation of Buffering Capacity, visit Wikipedia or watch a lecture about it from UC Berkley.

Below is a chart showing the relationship between pH and carbon dioxide.

Oxygen Levels in Water

There are two main ways to control oxygen – by biology or by temperature. Biology consists of living animals and plants, but plants have a much larger effect on oxygen levels. Plants affect the oxygen levels through photosynthesis and respiration. In photosynthesis, carbon dioxide and water react in the plant to produce glucose and oxygen, as well as ATP. Sunlight is also necessary for photosynthesis to occur and is a key factor. In respiration, glucose and oxygen react and produce carbon dioxide and water. This is the exact opposite of photosynthesis, and neither will work without the other. If photosynthesis does not produce much glucose or oxygen, the bacteria will not be able to produce as much carbon dioxide. Without the carbon dioxide, the plants will not survive, and the cycle would not continue. Temperature controls oxygen simply - when the water is hot, there is less oxygen, and when it is cold, there is more oxygen.

Biology is controlling the photosynthesis/respiration rates at the Christchurch dock. If the water temperature was controlling the rates, there should be less oxygen when the water is warmest and higher amounts of oxygen when the water is coldest. This is not the case. The graph below shows this - when the water is warm, oxygen levels peak, and when the water is cold, oxygen levels are at their lowest points. This means that biology is controlling the rates of photosynthesis and respiration.

The oxygen levels peak when the water is warmest – during the day. The water and air temperature do have an effect on photosynthesis however. When the water is warmer, plants are more active and more likely to photosynthesize. At night, when the temperature is colder, the plants are the least active. This is also when the least amount of oxygen is produced. Biology is controlling the rates because of the effect sunlight had on the oxygen levels. When the sun was shining brightly, photosynthesis occurred and the oxygen level increased accordingly. When it was not shining and it was cloudy during a storm on September 6th, the oxygen levels were much lower because less photosynthesis could take place.

Day/Night Cycles

Oxygen levels at Christchurch School fluctuate during the full twenty-four day because of the photosynthesis and respiration cycle. From dawn to sundown, photosynthesis is the major reaction taking place. Respiration still takes place, but not at the same rate as at night. When the sun rises at dawn, the algae and other plants ‘awaken’ and the sunlight begins to jumpstart photosynthesis. Oxygen is produced and carbon dioxide, which was made during the night, is consumed. As the water temperature warms, animals are more active in the water, and give off more carbon dioxide for plants to use to produce even more oxygen. Oxygen is not as abundant in warm water, but the warmer temperatures also make the biology more active, which makes up for the slightly lower oxygen levels. Once the sun goes down, photosynthesis stops taking place because it no longer has all the necessary reactants. The cooler temperatures of both the water and air also keep biology from being as active, and consequently, biology produces less oxygen. The bacteria start respiring once photosynthesis stops. They use the glucose and oxygen that was produced during the day to create carbon dioxide and water.

(To see the correlation between CO₂ and pH, refer back to the Buffering Capacity of seawater. As pH increases towards 14, the amount of carbon dioxide in the water is decreasing. As pH decreases towards 0, carbon dioxide levels are increasing. This will be inversely proportional to the amount of oxygen in the water - when CO₂ is high, the O₂ is low, and vice versa.)

These graphs shows the correlation between Dissolved Oxygen and pH on a random day in each season of the year. The data is almost a direct correlation, meaning that as one increases the other also increases and as one decreases the other also decreases - in this case, oxygen increases at about the same rate pH does. The correlation shown is a direct example of photosynthesis and respiration. Photosynthesis is occurring when oxygen and pH are increasing, while respiration is occurring while pH and oxygen are decreasing. As you can see from the time stamps on the x axis, photosynthesis occurs mostly during the day when there is the most sunlight, while respiration occurs mostly at night.

Weekly Cycles

The weekly cycles at Christchurch school are very similar to the daily cycles. There are peaks throughout each day and night of each system, and these peaks are also seen overall through the week. In every one of the weeks we picked, there was one day where the amount of dissolved oxygen crested and then never got to the same levels as it was previously. This is especially evident in the Fall and Winter weeks. This can be explained in two ways – the death of the biomass or a change in weather. When the biomass that is photosynthesizing gets too big, it will die off because it cannot continue to support itself. This will result in much less O₂ production, and subsequently, less CO₂ in the water. A change in weather could also result in a change in the levels of photosynthesis and respiration taking place. A cloudy day lacking in sunlight, rain, and different temperatures could all be contributing factors.

In every one of the graphs, pH and the oxygen levels in the water mirror each other closely- in other words, they directly correlate. Remember that pH inversely correlates with Carbon Dioxide – when one is high, the other is low, and vice versa. Because of this, we can say that the carbon dioxide and oxygen levels are related. This further reinforces the data from the single days and shows the relationship over a week’s time.

Monthly/Yearly Cycles

(We do not have enough accurate data from previous years at the Christchurch dock, so we will assume that these patterns will stay consistent over years of data. We will also assume that each month is representative for the entire season.)

Photosynthesis and respiration occur more than the other at specific times during the year. Photosynthesis is most active during the summer and respiration is most active during the winter. During the summer months, the sun is shining the longest and so plants can photosynthesize longer. The warmer temperatures also make biology more active and they produce more oxygen. Respiration still occurs during the summer, but it has less time to do so. As a result, the net gain of oxygen is higher. Sometimes in the summer, there are sharp drops in oxygen levels. This is because the plants that make up the biomass cannot sustain themselves. The number of plants cannot keep growing, eventually they have to die. The plants that are producing oxygen die, and the bacteria take over from them. This makes the oxygen levels down and carbon dioxide levels go up. Since the carbon dioxide is necessary for plants, this helps them start to grow again. As you can see from the graphs below, the amount of Dissolved Oxygen in the water is significantly higher than in the winter - about 120 percent saturation in the summer to about 100 percent saturation in the winter.

In the fall, the days start to shorten and the temperature drops. Since the sun shines less and less as fall progresses, photosynthesis has increasingly smaller amounts of time to react. The falling water and air temperature makes biology less active, so less oxygen is produced. This gives respiration fewer reactants to use, but overall, it starts to take over from photosynthesis. During the coldest part of the year, biology is the least active. Also, this is when the days are the shortest, so photosynthesis has the least time to react. This is when temperature starts to control the oxygen levels the most. Since there is more oxygen in cold water, and the water is the coldest during the winter, oxygen is still present.

After the winter equinox, the sun starts to shine longer and the temperature of the water and air starts to warm. Biology starts to come alive again after the winter, and starts to exhibit more control over the oxygen levels. The plants are more active and start growing again. This makes the biomass go up, which leads to more photosynthesis. Respiration also will increase since it has more glucose and oxygen to use, but photosynthesis keeps going up into the summer. Photosynthesis is the leading reaction in the spring and summer and respiration is the leading reaction during the fall and winter in the Rappahannock.

Conclusion

Christchurch's new motto is," Great Journeys Begin at the River". With this new motto came a need for a new plan, and thus the idea for Christchurch's Great Journeys plan was born. This blueprint for success is a way for students to gather new experiences along with broadening their horizons. This new strategy is observable throughout the campus - from extra curricular activities, to chapel, to academic work. This project is one of those ways to improve students' connection with the River and to teach them to better use technology. Another of the main purposes for this project was for students to work together, and create a combined project that would best explain, and describe a scientific topic.

Our website first explains the technology used to monitor the River down at the Christchurch waterfront, and how it gives us vital information we need to learn about our environment - the Rappahannock. Our site goes on to explain photosynthesis and respiration, and how they correlate. Finally, it explains how photosynthesis and respiration cycle across days, weeks, and months/years. We hope that we have successfully explained this interesting, and sometimes confusing cycle adequately. If you have any questions or suggestions on how we could improve our site, you can email any of us at our school email accounts.