Chapter 6 Photosynthesis6.1

• Autotrophs- make their own energy

• Heterotrophs – have to consume energy

• Cells use stored chemical energy

– ATP – adenosine triphosphate• Adenine – nitrogen, Ribose – 5 C sugar, 3

Phosphates• Full Battery

– ADP – adenosine diphosphate – 2 phosphates

- Half full battery

6CO2 + 6H2O C6H12O6 + 6O2

carbon dioxide + water sugar + oxygen

• Chlorophyll – main pigment in plants,

– Green – chlorophyll a and b, Red – anthocyanins, Orange and Yellow – carotenoids.

– Absorbs light very well in the blue and red regions of the visible light spectrum, NOT in the green light.

– Chlorophyll reflects green, that is why see it.

– In fall, when deciduous trees shed leaves to conserve energy, they stop photosynthesizing and true underlying colors, yellow, orange, red, are present.

Absorbtion diagram

Reactions of Photosynthesis

• All processes of photosynthesis take place in the chloroplast.

pg 114• 2 phases of photosynthesis:

– 1. light-dependent rxn – 2. light-independent rxn (Calvin Cycle)

Chloroplast

Water

O2

Sugars

CO2

Light-Dependent Reactions

CalvinCycle

NADPH

ATP

ADP + PNADP+Chloroplast

Section 8-3

Figure 8-7 Photosynthesis: An Overview

Light Dependent Rxn• Requires light• Within the thylakoid membrane• Steps

– Photosystem II - Sunlight excites e- in the chlorophyll. 2 e- come from water molecule.

– They split the water. Make H ions.– e- move through the e- transport chain to photosystem

I.– These high energy e- use active transport to move H+

ions from stroma to inner thylakoid. – Chlorophyll in photosystem I reenergizes the e- and

NADP+ carries the 2 electrons and one H+ ion making it NADPH. (Note 2 NADPH are formed)

– inner thylakoid become more positive and outside the membrane more negative, therefore creating and gradient to function the protein ATP Synthase. (chemiosmosis)

– This energy is now used to send a H+ atom to the ADP to make ATP.

– Both ADP and NADP+ are incomplete, to be full force, need light to convert to ATP and NADPH which are main energy carriers.

Figure 8-10 Note: Reactions move from left to right on the figure, from photsystem II through the electron transport

chain to photosystem I.

Questions:

1. Where are these light dependent reactions occurring?

2. Where is water broken down?

3. Where are two places that chlorophyll absorbs the energy of sunlight?

4. Where and how is ATP produced in the process?

5. How is NADPH produced in the process?

Answers:

• Within the thylakoid membrane of a chloroplast.• Water is broken down on the inner surface of the

thylakoid membrane.• In photosystem II and photosystem I.• ATP is produced as H+ ions pass thought ATP

synthase, as shown to the right of photosystem I.• NADPH is produced when NADP+ picks up high-

energy electrons from photosystem I at the outer surface of the thylakoid membrane.

Light Independent Rxnor Calvin Cycle

• Requires no light• Occurs within the stroma (space outside the grana)

–Starts with 6 CO2 from atmo. Making 3-PGA

–ATP and NADPH convert 3- PGA into higher energy sources. (once used, ATP and NADPH are now back to their weak states (ADP & NADP+)

–3-PGA converted into G3P–Two of G3P separated from the pack forming 6-

carbon chains (Glucose).–More ATP is used to convert back to RuBP, ready

to pick up more CO2.

Final products– Calvin cycle uses 6 CO2 to produce a single

6-carbon sugar molecule. (glucose)

• ATP and NADPH are quick energy. Made in the light dependent rxn, but then fed into the Calvin Cycle and used to turn into higher energy for the cell to use. (Sugars and glucose)

Figure 8- 11 pg 120

Questions:

1. Where does the Calvin cycle take place?

2. What enters the Calvin cycle from the atmosphere?

3. Where do the ATP and NADPH come from?

4. What is the product of this cycle?

5. What happens next to the 3-carbon molecules?

6. How is the cycle complete?

Answers

1. It take place in the stroma, outside the grana.2. Six CO2 molecules.3. Both STP and NADPH come from the light-

dependent reactions.

4. Two 3-carbon molecules5. They are used to form one 6 carbon sugar.6. The cycle is complete when the remaining 3-carbon

molecules are converted back into 5-carbon molecules, which are ready to combine with new carbon dioxide molecules to begin the cycle again.

Factors that Effect Photosynthesis

1. Drought2. Temperature (cold weather can damage

enzymes)3. Intensity of light

• More light, more photosynthesis. • Once the intensity reaches a certain level, it plains

off.

4. CO2 Levels – more CO2, simulates more photo. Eventually it will level off.

Alternative Pathways

• Stomata – small openings on leaves. – Gas exchange and water

Open Book page 120

• Carbon Fixation is Calvin Cycle1. Each CO2 binds with RuBP (ribulose

biphosphate)

2. 3-PGA (3-phosphoglycerate)

3. G3P – (glyceraldehyde 3 phosphate)1. Makes the glucose

4. Returns to RuBP

C4 Pathway – hot days, can close their stomata

corn, sugar cane, grab grass.

this is an adaptation

Fix C into a 4 Carbon compound not 3.

CAM Pathway

• Crassulacean acid metabolism.– Open stomata at night, close during the day.