Chapter 8 - Photosynthesis6CO2 + 6H2O + light C6H12O6 + 6O2

The capture and conversion of solar energy to chemical bond energy

Photosynthesis occurs in…

Plants, algae, some bacteria

Not all plants are photosynthetic

Some parasitic plants are not photosynthetic

Photosynthesis occurs in chloroplasts

Photosynthetic products are utilized in respiration

Chlorophyll is the primary photosynthetic pigment

Chlorophyll absorbs specific wavelengths of visible light

1883 – T.W. Englemann

Red and blue light most effective for producing oxygen during photosynthesis

Wavelength and photosynthesis

Accessory pigments

Chlorophyll in photosystems absorb light energy and

release electrons

What happens when light is

absorbed by a molecule?

“Free” electrons are a source of kinetic energy

Z-scheme & energy flow

Chemiosmosis drives ATP synthesis

Photolysis and chemiosmosis

• Photolysis replaces electrons removed from chlorophyll

• Electron flow “pumps” H+ ions through membrane

Light reactions animation

Chemiosmosis animation

ATP synthase phosphorylates ADP (photophosphorylation)

H+ ions

Chlorophyll

1. Is the organelle in which photosynthesis takes place

2. Absorbs green wavelengths of light3. Is the primary photosynthetic

pigment4. All of these5. Both 1 and 2

When light energy is absorbed by chlorophyll

1. Chlorophyll produces oxygen2. Chlorophyll becomes an accessory

pigment3. Chlorophyll is destroyed4. Chlorophyll becomes radioactive5. Chlorophyll releases an electorn

Active transport of hydrogen ions into the thylakoid space

1. Occurs during chemiosmosis2. Involves the electron transport chain

of photosystem II3. Occurs by the process of photolysis4. Involves the electron transport chain

of photosystem I

Photolysis1. Occurs when light energy splits a

chlorophyll molecule in half2. Is when light splits open a chloroplast to

release sugars3. Splits water molecules to resupply

chlorophyll with electrons 4. Is the production of ATP utilizing a

hydrogen ion gradient5. Occurs when absorbed light causes an

electron to be removed from a chlorophyll molecule

The hydrogen ion gradient inside the thylakoid membrane forms as

a result of

1. Photosystem II2. Photolysis3. Chemiosmosis4. Photophosphorylation5. Both 1 and 2

Dr. Calvin, Nobel prize in chemistry, 1961

Calvin’s experiment (see Fig. 8.9)

Calvin’s results

The Calvin cycle produces G3P

Occurs in the stroma

Several enzyme-catalyzed steps

Requires energy Produces sugars

Calvin Cycle Animation

Summary of photosynthesis

Photosynthesis animation

Rate of photosynthesis varies with environmental conditions

What is meant by the “rate of photosynthesis”?

What environmental conditions affect the rate of photosynthesis?

Factors influencing the rate of photosynthesis

Carbon dioxide concentration Water availability Light intensity Temperature

Variations of photosynthesis

85% of plants use “C3” photosynthesis– C3 cycle = Calvin cycle

C4 photosynthesis– C4 plants include many tropical

monocots, other grasses (0.4% of plants) Crassulacean Acid Metabolism (CAM)

– CAM plants – cacti, orchids, bromeliads, succulents (~10% of plants)

C4 photosynthesis is more efficient than C3 under certain

conditions

Photorespiration and rubisco

Rubisco – Ribulose 1,5-bisphosphate carboxylase/oxygenase– Most abundant protein on earth

(25-40% of total plant protein)– Activity depends on carbon dioxide

concentration in the leaf

Rubisco activity and CO2 concentration

When would photorespiration occur and why?

When are CO2 concentrations low?

–When stomata close•Hot days•Moisture stress

C4 vs. CAM

Crassulacean Acid Metabolism Evolved in areas of high light intensity,

little precipitation Stomata closed during the day, open at

night

Which of the following are true of the Calvin cycle?

1. Occurs in the cytoplasm2. RUBP reacts with oxygen to form

Rubisco3. RUBP reacts with CO2 to form

Rubisco4. All of these are true5. None of these are true

The Calvin cycle occurs

1. In C3 plants but not C4 or CAM plants

2. In the mesophyll of all plants3. In the bundle sheath of C4

plants4. In C4 and CAM plants, but not

C3 plants

Photorespiration is most likely to occur

1. On cool, cloudy days2. In plants adapted to desert

habitats3. In C3 plants4. In C4 plants and CAM plants5. Both 2 & 4

During photorespiration1. Plants react O2 with glucose to make

ATP2. Plants react O2 with ATP to make

glucose3. Plants use the energy of light to

make ATP4. RUBP reacts with CO2 to make sugars

5. RUBP reacts with O2 to make CO2

CAM plants 1. Use their bundle sheath cells to run

the Calvin cycle at night2. Use their bundle sheath cells to run

the Calvin cycle during the day3. Absorb CO2 during the day, and make

sugars during the night4. Absorb CO2 during the night, and

make sugars during the day5. Both 1 and 3

Photosynthesis research

Why study photosynthesis?

Photosynthesis Center at Arizona State