Chapter 8 biology

Seite 1

8.1 Q/A

1) What is the overall “purpose” of photosynthesis? Its purpose is to convert light energy into chemical energy by synthesizing glucose.

2) Where do the reactions of photosynthesis take place? Photosynthesis takes place in the chloroplast of a cell ( if they have it). In plants, this is in leaves.

3) Describe the structure of a chloroplast, listing all membranes and compartments.

Outer membrane: A membrane that surrounds the whole organelle

Intermembrane space: Space in between the two membranes.

Inner membrane: A secondary membrane surrounding the additional parts of the chloroplast.

Thylakoid: A piece of a stacked structure that uses light energy in photosynthesis.

Thylakoid space: Space inside a Thylakoid that uses water, light, and chlorophyll.

Granum: a stack of Thylakoids.

Stroma: supportive fluid surrounding Granum.

4) Write the summary equation for photosynthesis.

6 CO2 + 6 H2O ---- Light &Chlorophyll ---> C6H12O6 + 6O2

5) In general terms, explain the role of redox reactions in photosynthesis.

Water is oxidized and Carbon Dioxide is reduced during photosynthesis.

6) Describe the two main stages of photosynthesis in general terms.

The light reactions- conversion of light energy into the chemical energy of ATP and NADPH (a chemical that carries electrons) Water is used as a source of electrons, thus forming oxygen. Takes place in the ETC of the Thylakoid.

Calvin Cycle- separate series of reactions that do not require light energy directly. (AKA light-independent or dark reactions), however, they still depend on the products of the light reactions. This uses ATP, NADPH, and Carbon Dioxide to produce glucose. This occurs in the stroma.

Seite 2

8.2 Q/A

1) Describe the relationship between an action spectrum and an absorption spectrum.

Absorption spectrum plots a pigments light absorption vs wavelength.

Action spectrum graphs the relative effectiveness of different wavelengths of light based on recording a certain "action" during photosynthesis.

2) List the wavelengths of light that are most effective for photosynthesis.

The wavelengths of light that appear to be most effective are ones in the 400-500 wavelength or 650-700 wavelength light.

3) Explain what happens when a solution of chlorophyll-a absorbs photons. Explain what happens when chlorophyll-a in an intact chloroplast absorbs photons.

In a solution, the chlorophyll-a becomes excited and has more potential energy.

In an intact chloroplast, certain wavelengths of light are absorbed and photosynthesis begins with the energized electron being taken by an electron acceptor.

4) Provide a summary of the light reactions of photosynthesis. Where specifically do these reactions take place?

Light-harvesting complexes

Reaction-center complex

5) List the components of the photosystem and explain the function of each component.

Light-harvesting complexes are primarily pigments bound to proteins. These pigments absorb light energy and pass the energy to the reaction center complex. (Light-harvesting complexes surround the reaction center)

Reaction-center complex: A protein complex that contains a pair of chlorophyll-a molecules and a primary electron acceptor molecule. When chlorophyll-a molecules absorb energy, their excited electrons get transferred to a primary electron acceptor molecule. Chlorophyll-a becomes oxidized.

chlorophyll-a-take in energy, become oxidized.

pigment molecules-transfer energy.

Primary electron acceptor- takes the electron from the chlorophyll-a

6) What are the two types of photosystems?

photosystem II (or P680) - This photosystem is responsible for producing ATP.

photosystem I (or P700) - This photosystem is responsible for producing NADPH.

7) Trace the movement of electrons in linear electron flow.

We start with photosystem II (with a reaction center of P680). Light photons strike a pigment molecule in a light-harvesting complex, and its energy is passed around eventually making its way to the pair of Chlorophyll-a molecules in the reaction center complex. When the pair of Chlorophyll-a molecules' electrons are excited, the excited electrons are transferred to the primary electron acceptor. The electrons will then be transferred from the primary electron acceptor molecule through a series of redox reactions that we refer to as the electron transport chain.

During these reactions, hydrogen ions will move from the stroma to the thylakoid space creating a hydrogen ion concentration. This concentration will drive ATP synthase to form ATP in the stroma.

Light photons strike a pigment molecule in a light-harvesting complex, and its energy is passed around eventually making its way to the pair of Chlorophyll-a molecules in the reaction center complex. When the pair of Chlorophyll-a molecules' electrons are excited, the excited electrons are transferred to the primary electron acceptor. The electrons will then be transferred from the primary electron acceptor molecule through a series of redox reactions that we refer to as the electron transport chain. The final electron acceptor at the end of the chain is NADP+. NADP+ is reduced to NADPH, which is formed in the stroma.

The electrons lost by the pair of Chlorophyll-a molecules in the reaction center complex of PSI (on P700) are replaced with electrons passed down the electron transport chain from PSII (from P680)

8) Describe the similarities and differences in chemiosmosis between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts.

photophosphorylation produces less ATP & NADPH & O2. It takes in H20.

Oxidative phosphorylation uses O2 & NADH & FADH2 to produce more ATP and Water.

Seite 3

8.3 Q/A

1) State the function of each of the three phases of the Calvin cycle. Where do the reactions of the Calvin cycle take place?

Carbon Fixation- Uses RubisCO for "fixing" carbon dioxide out of the atmosphere. Makes CO2(gas) & enzyme Rubisco turn into 3 carbon-phosphoglycerate(solid).

Reduction- reduces the 3 carbon molecule (PGA) forming glyceraldehyde-3-phosphate (G3P). G3P can be converted into Carbs, Fatty acids, or amino acids. There is a net gain of 1 G3P.

Regeneration of the carbon dioxide acceptor (RuBP)- Remaining G3P molecules are rearranged to regenerate RuBP, which is needed as a starting material for RubisCO to "fix" carbon dioxide.

This all takes place in the stroma of the chloroplasts.

2) Describe the role of ATP and NADPH in the Calvin cycle.

ATP provides energy for the chemical reactions and NADPH provides a way to reduce the chemicals used.

3) List the possible fates of photosynthetic products.

energy, RUBP for the propagation of the Calvin cycle, building blocks for the cell, use in cellular respiration.

4) Describe what rubisco does when the O2 concentration is much higher than the CO2 concentration.

photorespiration- when C3 plants use O2 and produce CO2 instead of glucose.

5) Describe the major consequences of photorespiration in C3 plants.

It decreases photosynthesis efficiency and crop yields.

6) Describe two important photosynthetic adaptations that minimize photorespiration.

C4 plants - separate the reactions using two different types of cells. Carbon fixation takes place in one cell type, while the Calvin cycle takes place in a different cell type. They also use PEP carboxylase instead of RubisCO to "fix" carbon dioxide. Makes a C4 molecule.

CAM plants-same cell type, but have these reactions take place at different times. Carbon fixation occurs at night, while the Calvin cycle occurs during the day. Only open their stomata at night or after a large rainstorm to minimize water loss. Makes a C4 molecule as well.