Unit 3 – Chapter 7 How Do Cells Acquire Energy?

I. Sunlight and Survival A.Autotrophs = self-nourishing B.Photoautotrophs = sunlight captured to drive metabolic reactions Photosynthesis Light Energy  Chemical EnergyLight Energy  Chemical Energy C.Heterotrophs = other organisms as source of energy D.Chemosynthesis = energy from inorganic molecules Hydrothermal Vents

Light energy Chemical energy Photosynthesis

E.Light Energy - has characteristics of both waves and bundles (photons) - Waves – the electromagnetic spectrum

II. Photosynthesis Overview

A.Chloroplast structureChloroplast structure 20 to 100/photosynthetic plant cell 1. Inner and outer membranes 2. Intermembrane space 3. Stroma 4. Granum (grana is plural) = stack of membrane bound sacs called thylakoids a. 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 12H CO 2 ---> C 6 H 12 O 6 + 6H 2 O ATP supplies energy for reactions which synthesize glucose from CO 2 and water

D.Photosynthetic pigments 1. Absorption spectrum vs. Action spectrum (absorbed wavelengths) (performance)

2. Chlorophyll a Why green?

3. Englemann’s Observational TestEnglemann’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. Phycobilins 2. Carotenoids4. Anthocyanins

5. Chlorophyll structure a. Porphyrin ring with Mg ++ at center -absorbs light energy b. 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 + H 2 O electrons 2 H + ½ O 2

III. Noncyclic Photophosphorylation (Light Dependent Reactions)

Photolysis

Non – Cyclic Video Clip

IV. Cyclic Photophosphorylation (variation of Light Dependent Reactions)

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

IX. Other forms of carbon fixation A. Photorespiration 1. Under hot,dry conditions stomata close to prevent dehydration 2. In C 3 plants the CO 2 levels drop, causing rubisco to use O 2 3. No ATP produced, 2-carbon compounds wasted B.C 4 plants have a way to overcome photorespiration 1.Calvin cycle in bundle-sheath cells 2.CO 2 pumped into bundle-sheath cells from mesophyll cells at a cost of ATP 3. Corn, sugarcane, crab grass

C. CAM plants 1.Plants living in arid conditions (desert) 2.Stomata are closed during day to prevent water loss 3. Therefore during the night, CO 2 is taken in and used to make organic acids, malate (R-COOH) 4.During day CO 2 is released from organic acid to supply Calvin cycle for carbon fixation 5.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.