Chapter 8 - Photosynthesis 6CO 2 + 6H 2 O + light  C 6 H 12 O 6 + 6O 2 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 light 3. Is the primary photosynthetic pigment 4. All of these 5. Both 1 and 2

When light energy is absorbed by chlorophyll 1. Chlorophyll produces oxygen 2. Chlorophyll becomes an accessory pigment 3. Chlorophyll is destroyed 4. Chlorophyll becomes radioactive 5. Chlorophyll releases an electorn

Active transport of hydrogen ions into the thylakoid space 1. Occurs during chemiosmosis 2. Involves the electron transport chain of photosystem II 3. Occurs by the process of photolysis 4. Involves the electron transport chain of photosystem I

Photolysis 1. Occurs when light energy splits a chlorophyll molecule in half 2. Is when light splits open a chloroplast to release sugars 3. Splits water molecules to resupply chlorophyll with electrons 4. Is the production of ATP utilizing a hydrogen ion gradient 5. 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 II 2. Photolysis 3. Chemiosmosis 4. Photophosphorylation 5. 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 “C 3 ” photosynthesis –C 3 cycle = Calvin cycle  C 4 photosynthesis –C 4 plants include many tropical monocots, other grasses (0.4% of plants)  Crassulacean Acid Metabolism (CAM) –CAM plants – cacti, orchids, bromeliads, succulents (~10% of plants)

C 4 photosynthesis is more efficient than C 3 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 CO 2 concentration

When would photorespiration occur and why?  When are CO 2 concentrations low? –When stomata close Hot days Moisture stress

C 4 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 cytoplasm 2. RUBP reacts with oxygen to form Rubisco 3. RUBP reacts with CO2 to form Rubisco 4. All of these are true 5. 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 plants 3. In the bundle sheath of C4 plants 4. In C4 and CAM plants, but not C3 plants

Photorespiration is most likely to occur 1. On cool, cloudy days 2. In plants adapted to desert habitats 3. In C3 plants 4. In C4 plants and CAM plants 5. Both 2 & 4

During photorespiration 1. Plants react O 2 with glucose to make ATP 2. Plants react O 2 with ATP to make glucose 3. Plants use the energy of light to make ATP 4. RUBP reacts with CO 2 to make sugars 5. RUBP reacts with O 2 to make CO 2

CAM plants 1. Use their bundle sheath cells to run the Calvin cycle at night 2. Use their bundle sheath cells to run the Calvin cycle during the day 3. Absorb CO 2 during the day, and make sugars during the night 4. Absorb CO 2 during the night, and make sugars during the day 5. Both 1 and 3

Photosynthesis research  Why study photosynthesis?  Photosynthesis Center at Arizona State Photosynthesis Center at Arizona State