Lab 8: Photosynthesis

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Lab 8 Photosynthesis
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Introduction to Photosynthesis

• Autotrophs self producers chloroplasts
  capture light energy from the sun, CO2 and water
  to create chemical energy in the form of Glucose.
  

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Introduction to Photosynthesis

• Whereas Respiration (O2 in, CO2 out) in plants
  takes place 24 hours per day, Photosynthesis (CO2
  in, O2 out) occurs only in the light of day.

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Introduction to Photosynthesis

• Measure Photosynthetic Rate by measuring
• 1. O2 produced OR 2. CO2 consumed
• We will be measuring O2 produced.

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Introduction to Photosynthesis
Thylakoid site of light reactions
Grana
Stroma site of dark reactions
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Introduction to Photosynthesis

• Light Dependent Reaction

Light energy is absorbed by chlorophyll in
thylakoids

• Water molecules split

Products

• Some oxygen is released into the atmosphere
• Some oxygen is used by the cells in respiration

Thylakoid
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Introduction to Photosynthesis

• Dark (Light Independent) Reaction

2 high energy substances (produced in light
reaction)
From atmosphere
Products
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Introduction to Photosynthesis

• IMPORTANT
• At Night, there is NO light energy from the sun.
• No O2 , ATP, or NADPH is produced.
• No energy for Dark reactions, the DARK REACTIONS
  STOP!
• No O2 produced.
• AT NIGHT, plants must obtain their O2 for
  cellular respiration from the atmosphere.

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I. Rate of O2 consumption of a spinach leaf in
the dark (Respiration Rate)

• EXPERIMENT I.
• Determine the rate of O2 consumed by a spinach
  leaf in the dark.
• Create a 20 degree water bath.
• Add 2 ml of saturated sodium bicarbonate (WHY?
  it is the source of CO2 for the dark reactions).
• Set microcentrifuge tube in test tube.
• Fill the microcentrifuge tube ¾ full of water.
• Calculate the Spinach Leaf Surface Area.
• Place Leaf, stem down, in the microcentrifuge
  tube.
• Proceed with directions on page 7

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III. Effect of Wavelength on Net Photosynthetic
Rate of a Spinach Leaf

• EXPERIMENT II.
• Measure photosynthetic rate of a spinach leaf at
  different light intensities.
• Test this by moving the light source to different
  distances from the spinach leaf, and measuring
  the O2 consumed or produced.

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III. Effect of Wavelength on Net Photosynthetic
Rate of a Spinach Leaf

• Light Energy (Electromagnetic Radiation) travels
  in waves.
• Shorter wavelengths (Violet and Blue) have more
  energy than longer wavelengths (Red) which have
  less energy.

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III. Effect of Wavelength on Net Photosynthetic
Rate of a Spinach Leaf

• Objects contain pigments that selectively absorb
  some wavelengths of visible light, while
  reflecting other wavelengths.

A green leaf absorbs all wavelengths of visible
light EXCEPT green, which the leaf reflects.
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III. Effect of Wavelength on Net Photosynthetic
Rate of a Spinach Leaf

• Chlorophyll A (the primary pigment in spinach)
  is
• embedded in the thylakoids,
• participates in the light dependent reaction of
  photosynthesis,
• absorbs certain wavelengths of light energy from
  the sun,
• is blue-green in color.

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III. Effect of Wavelength on Net Photosynthetic
Rate of a Spinach Leaf

• Chlorophyll B and the carotenoids carotene and
  xanthophyll (accessory pigments in spinach)
• absorb different wavelengths of light,
• transmit that energy to chlorophyll A for the
  light reactions,
• broaden spectrum of colors (wavelengths) of light
  which can drive photosynthesis.

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D. Why do leaves change color in autumn?
1. as temps decrease, trees stop prod.
chlorophylls a b
2. chlorophyll breaks down rapidly due to
cool temps short day length
3. as result, carotenoid pigments are
unmasked
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Why do leaves change color in autumn?

• Temperatures decrease, trees stop producing
  chlorophylls A B.
• Chlorophyll breaks down rapidly due to cool
  temperatures short day length.
• Result -gt carotenoid pigments are unmasked.

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III. Effect of Wavelength on Net Photosynthetic
Rate of a Spinach Leaf

• EXPERIMENT III.
• Determine if all wavelengths (colors) of light
  are equally effective in driving photosynthetic
  reactions in spinach leaves.
• Test this by measuring the O2 produced when
  illuminating the leaf with blue, red, and green
  light of the same intensity.

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III. Effect of Wavelength on Net Photosynthetic
Rate of a Spinach Leaf

• Hypothesis Formulation When exposed to
  different wavelengths (colors) of light (blue,
  red, green), which set up will have the fastest
  and which will have the slowest rates of
  photosynthesis (O2 produced)?

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IV. Separation and Identification of Pigments

• Use the Thin Layer Chromatography (TLC) method
  to identify pigments contained in the spinach
  leaf.

• Burst Chloroplasts by rolling a coin across the
  surface of a spinach leaf.
• The different pigments are dissolved in the
  solvent provided.
• Depending on the polarity of the different
  pigment molecules, they will either stay in place
  on the TLC strip (most polar, xanthophylls) OR
  the dissolved pigments will climb high on the TLC
  strip (less polar, carotene).