Introduction: Elodea is a species of aquatic plant often called waterweed. Like other plants, Elodea absorbs carbon dioxide and releases oxygen during photosynthesis. In this lab, an Elodea specimen is submerged in water under a lamp with a filter that can change the color of the light. We will measure Elodea’s rate of photosynthesis by measuring the amount of oxygen it produces. We will investigate the effects of light color and light intensity on Elodea’s rate of oxygen production. Baking soda (sodium bicarbonate, Na HCO3) breaks down to release CO2 when mixed with water, so adding it to the water increases the availability of CO2.By placing the Elodea plant into water containing varying levels of baking soda, we can also investigate the effect of carbon dioxide availability on the rate of photosynthesis. Hypothesis & Prediction: A hypothesis is a testable statement that explains what will happen with a reason. A prediction is what you think will happen.
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1. Make a prediction about which light color (red, blue, green, or colorless) will result in the highest photosynthesis rate.
Red and blue colour light will result in the highest photosynthesis rate. The graph below shows the rate of photosynthesis versus wavelength of light incident.
The graphshow that most of the photosynthesis takes place in the blue and red regions of the spectrum
2. Predict whether the rate of the photosynthesis will be highest at: A. low intensity of light
B. medium intensity of light
C. high intensity of light
The rate of photosynthesis will be highest at high intensity of light.
The plateau indicates that after a steady increase the rate is unaffected because the chlorophyll molecules lose their excitability. 3. Based on what you already know about photosynthesis, write a testable hypothesis to explain the influence of an increase in light intensity on the photosynthetic rate in tomato leaves. An increase in the intensity of light increases the photosynthetic rate in tomato leaves.
To test the hypothesis
The plant is exposed to different intensities of light and rate of photosynthesis is measured.
4. Based on what you already know about photosynthesis, write a testable hypothesis to explain the influence of an increase in carbon dioxide on the photosynthetic rate in tomato leaves. An increase in carbon di oxide concentration increases the photosynthetic rate in tomato leaves.
To test the hypothesis
The plant is supplied with increasing CO2 levels and rate of photosynthesis is measured.
a. Write the generalized CHEMICAL reaction of photosynthesis. 6 CO2 + 6H2O Sunlight and chlorophyll C6H12O6 + 6O2 b. Explain how the light-dependent and light-independent reactions are interdependent. The products of the light dependent reactions, ATP and NADPH, are used to drive the synthesis of sugars which occurs through the light independent reactions.
c. Summarize the light-dependent reactions of photosynthesis, being sure to indicate where the reactions occur and the products of the reactions. PROCESS
Light-dependent reaction of photosynthesis
light energy is absorbed by the pigments present in the antenna, and funnelled to special chlorophyll a molecules called reaction centre chlorophylls. There are two photosystems, PS I and PS II. PS I has a 700 nm absorbing chlorophyll a P700 molecule at its reaction centre, while PS II has a P680 reaction centre that absorbs red light at 680 nm. After absorbing light, electrons are excited and transferred through PS II and PS I and finally to NAD forming NADH. During this process a proton gradient is created across the membrane of the thylakoid. The breakdown of the protons gradient due to movement through the ATPase enzyme releases enough energy for synthesis of ATP. Splitting of water molecules is associated with PS II resulting in the release of O2, protons and transfer of electrons to PS II.
Thylakoid of chloplasts
d. Summarize the light-independent reactions of photosynthesis, being sure to indicate where the reactions occur and the products of the reactions.
Light-independent reaction of photosynthesis (Calvin cycle) In the light independent raections, CO2 is added by the enzyme, RuBisCO, to a 5-carbon compound Ribulose Bi phosphate( RuBP) that is converted to 2 molecules of 3-carbon Phosphoglyceraldehyde. This is then converted to sugar by the Calvin cycle, and the RuBP is regenerated. During this process ATP and NADPH synthesised in the light reaction are utilised.
Stroma of chloroplasts
ADP + Pi