Unit 3 – Chapter 7

How Do Cells Acquire Energy?

I. Sunlight and SurvivalA. Autotrophs = self-nourishing

B. Photoautotrophs = sunlight captured to drive metabolic reactions

• Photosynthesis

• Light Energy Chemical Energy

C. Heterotrophs = other organisms as source of energy

D. Chemosynthesis = energy from inorganic molecules

• Hydrothermal Vents

Light energy Chemical energyPhotosynthesis

E. Light Energy- has characteristics of both waves and bundles (photons)

- Waves – the electromagnetic spectrum

II. Photosynthesis Overview

A. Chloroplast structure 20 to 100/photosynthetic plant cell

1. Inner and outer membranes2. Intermembrane space3. Stroma4. Granum (grana is plural) = stack of

membrane bound sacs called thylakoidsa. Thylakoids - Thylakoid membrane - Thylakoid space

B. Three major steps of photosynthesis

1. Absorb light energy (photosynthetic pigments)2. Convert light energy to unstable chemical bonds (ATP and NADPH)

3. Convert unstable chemical bonds to stable chemical bonds (G3P and glucose) (Calvin Cycle)

These are light dependent reactions that take place in the thylakoids

These are the light independent reactions that take place in the stroma

C. Key Concepts: Photosynthesis is the pathway by which

carbon and energy enter the web of life

In plants, photosynthesis takes place in

chloroplasts

Photosynthesis is summarized this way

12H20 + 6CO2 ---> 602 + C6H12O6 + 6H2O

ATP supplies energy for reactions which synthesize glucose from CO2 and water

D. Photosynthetic pigments1. Absorption spectrum vs. Action spectrum (absorbed wavelengths) (performance)

2. Chlorophyll aWhy green?

3. Englemann’s Observational Test Oxygen-requiring bacteria congregated

where oxygen was being produced by algae

4. Accessory pigments Purpose = to transfer energy to chlorophyll a

1. Chlorophyll b 3. Phycobilins2. Carotenoids 4. Anthocyanins

5. Chlorophyll structurea. Porphyrin ring with Mg++ at center

-absorbs light energyb. Hydrocarbon chain tail

-anchors molecules in thylakoid membrane

6. Role of chlorophyll a

Chl a

Chl* Chl+

Excited state

Ground state

Charged state

light energy

electrons to NADP+

H2O electrons

2 H+

½ O2

III. Noncyclic Photophosphorylation(Light Dependent Reactions)

Photolysis

Non – Cyclic

Video Clip

IV. Cyclic Photophosphorylation(variation of Light Dependent Reactions)

V. Calvin-Benson Cycle Occurs in the stroma Called “light-independent reactions” Called “carbon fixation” Forms stable bonds from energy in

NADPH and ATP

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IX. Other forms of carbon fixationA. Photorespiration

1. Under hot,dry conditions stomata close to prevent dehydration

2. In C3 plants the CO2 levels drop, causing rubisco to use O2

3. No ATP produced, 2-carbon compounds wasted

B. C4 plants have a way to overcome photorespiration1. Calvin cycle in bundle-sheath cells

2. CO2 pumped into bundle-sheath cells from mesophyll cells at a cost of ATP3. Corn, sugarcane, crab grass

C. CAM plants1. Plants living in arid conditions (desert)2. Stomata are closed during day to prevent water loss3. Therefore during the night, CO2 is taken in and used to make organic acids, malate (R-COOH)4. During day CO2 is released from organic acid to supply Calvin cycle for carbon fixation5. Cactus, pineapple

1) PHOTOSYNTHESIS ESSAY

Membranes are important structural features of cells. (a) Describe how membrane structure is related to the

transport of materials across a membrane. (b) Describe the role of membranes in the synthesis of ATP in

either respiration or photosynthesis.

Or

2) ENZYME QUESTION

Enzymes are biological catalysts.a. Relate the chemical structure of an enzyme to its

specificity and catalytic activity.b. Design a quantitative experiment to investigate the

influence of pH or temperature on the activity of an enzyme.

c. Describe what information concerning the structure of an enzyme could be inferred from your experiment.