Photosynthesis Lab Patterns and Net Primary Production in

Ecosystem

Plants Transform Energy and Exchange Matter

• Plants are open systems

• Light → chemical potential C6H12O6 → heat

• Roots absorb H2O (H used in building C6H12O6) and nutrients like N & P needed for building proteins & phospholipids

• Leaves absorb CO2 (used in building C6H12O6) and release O2

• Plants perform both photo. & cell. resp.

Please read & annotate P. 4

1. How was air removed from leaf air-spaces and replaced by solution?

2. What effect did this have on the leaf-disks?

3. What caused leaf disks to float again? How does this processes allow us to compare photosynthetic rates?

4. What was the reason for adding sodium bicarbonate (baking soda) to the solution?

How can we measure the rate of photosynthesis?

Measure the production of O2

Baking soda (bicarbonate) provides the CO2

Evidence of O2

production = when leaf-disks float

Enzymes

Baking soda (bicarbonate) provides the CO2

Evidence of O2

production = when leaf-disks float

Enzymes

Use syringe-method to create vacuum & fill air-spaces with solution

O2 production during photosynthesis will displace solution, cause disks to float

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1. What is ET50?2. What is the ET50 for this data set?3. Complete this sentence: The lower the ET50,

the _____ the rate of photosynthesis

There are three measures of central tendency: mean, median and mode.

Because some disks may be damaged by the procedure and may not float again, the medianis the best measure of central tendency in this investigation.

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The ET50 is the time it takes for 50% (half) of the disks to float, which is about 12 – 13 min.

1. Describe and explain the relationship shown in graph (A):

2. Graph (A) shows ET50

as the dependent variable, what is the dependent variable for graph (B)?

3. Describe how this change affects the pattern shown in graph (B) and explain this change:

A

B

What is the effect of light intensity on the rate of photosynthesis?

Light Intensity (FT-C)

ET50

200 20

400 17

600 15

800 12

200 400 600 800

What is the effect of light intensity on the rate of photosynthesis?

Light Intensity

(FT-C)

ET50 1/ET50

200 20 0.05

400 17 0.06

600 15 0.07

800 12 0.08

200 400 600 800

Independent variables to explore:

Variable Method

Temperature Use ice and microwave to cool/heat solution

pH Add pH buffers to adjust pH of solution

[CO2] Adjust concentration of bicarbonate

Light intensity Use differing number of window screens

*When you have chosen your variable, feel free to see me for a suggested range to test

The Effect of Light Intensity on the Rate of Photosynthesis

The Effect of pH on the Rate of Photosynthesis

The Effect of the Wavelength of Light on the Rate of Photosynthesis

The Effect of Temperature on the Rate of Photosynthesis

The Effect of CO2 Concentration on the Rate of Photosynthesis

Light is limiting:Photosynthesis rate ↑ with light level

Light is not limiting (saturation):

Photosynthesis is occurring at physiologically maximum rate

Lowest rate at green because chlorophyll pigment does not absorb green (that is why leaves appear green – the green light is reflected)

Highest rate at violet and red because these are the wavelengths the pigment chlorophyll absorbs

CO2 is limiting reagent:↑ in photo. Rate w. ↑ in [CO2]

CO2 is not a limiting reagent:

Enzymes related to the carbon-fixation part of photosynthesis are saturated – operating at physiologically maximum capacity

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Since photosynthesis is a series of chemical reactions catalyzed by enzymes, it is sensitive to whether the enzymes are partially or fully denatured.

Fully denatured

Fully denatured

Partially denatured

Partially denatured

Optimal enzyme quaternary structure (3-D shape)

Molecular motion ↑ with ↑ temp.

Enzymes collide with substrate more frequently

Optimal temperature for enzymes driving photosynthesis

↑ temp. past optimal shuts down photosynthesis (off-line); excessive heat will cause denaturation

Global Annual Net Primary Production1. What is the pattern shown in the oceans?2. What is the pattern shown on the continents?

Low High

1. What are the three most productive biomes per m2?2. Which biome produces the greatest % of the Earth’s net

primary production?3. Why the discrepancy for your answer to 1 and 2?

Terrestrial Primary Productivity• Photosynthesis is an enzyme-catalyzed reaction• Optimal temperature depends on plant species

(enzyme adaptations)• Rate of photosynthesis increases with temperature up

to the optimum

Aquatic Primary Productivity

• Cold water can hold more dissolved O2 and CO2

• CO2 is needed for photosynthesis• O2 is needed for respiration• Plants perform both photo. and resp.

Terrestrial & Aquatic Primary Productivity

• Increasing light increases photo. rate up to a point• Light intensity rapidly decreases with water depth

• Water is needed as a reactant in photosynthesis• Plants also lose water via open stomata

(transpiration) as they perform photosynthesis

Terrestrial Plants: Water and Primary Production

Nitrogen (N) and Phosphorous (P)

N and P are the most important nutrients that plants take up via the soil. In most environments one or both limit plant growth.

List 2 biological molecules that plants need N for:

List 2 biological molecules that plants need P for:

• DNA & RNA (nitrogenous bases: A, T, C & G)• Protein (amino group of each amino acid)

• Phospholipids that make up membranes• DNA and RNA (sugar-phosphate backbone)• ATP (adenosine triphosphate – cell energy)

Terrestrial & Aquatic Primary Productivity

Which nutrient limits marine phytoplankton production? Cite evidence from the graph to justify your answer:

Nutrient Addition Experiment in the Ocean

Nutrient Addition Experiment in a Salt Marsh1. Describe the effect of adding Phosphorus (P) only:2. Describe the effect of adding Nitrogen (N) only:3. Which nutrient most limits growth in this ecosystem?4. Which treatment boosted growth the most?

1. Which nutrient appears limiting for fresh-water algae?

2. How does this relate to the use of phosphate-based detergents?

Fresh-WaterSalt-Water

P – tends to be limitingN – tends to be limiting

• Curve C for grass only – stimulated by grazing but harmed by overgrazing

• Curve A for most other terrestrial and marine autotrophs