Autotrophs & Photosynthesis

Collecting Energy From the Nonliving Environment

Remember: autotrophs (aka producers) use energy from the sun along with carbon dioxide and water to make organic molecules (aka – food). This is called photosynthesis.

The ability of autotrophs to do this is vital to the survival of all other organisms. WE ALL depend on autotrophs for our food.

Remember: we use that food to create the energy molecule ATP in our cells to survive.

My Expectations

• That you know (i.e. have memorized) a few basic things about photosynthesis for you to be an informed citizen of the world

• That you be able to given passages, diagrams, charts, graphs be able to draw information about the specific steps – I.e. that you develop the skills necessary to

draw information from resources– USE YOUR WRIING PROMPTS TO REVIEW

The reaction

• Sunlight + Water + CO2 Glucose + O2

Purpose of Each reactant

• Sunlight provides energy

• Water provides electrons and

H atoms

• CO2 provides carbon atoms

The Two Phases

I. Overview of Photosynthesis

A.) Photosynthesis depends on the absorption of light energy – how does this occur?

1.) pigment molecules inside a chloroplast called chlorophyll a & b and carotenoids capture the photons.

2.) The main pigment

(chlorophyll a) reflects green

light thus leaves look green.

a) when a leaf dies you can see the other pigments (ie. fall)

Organization levels of a leaf from large to small.A chloroplast is an organelle in a cell.

3.) Structure of chloroplasts:a) Chlorophyll

molecules are found in membranes called thylakoids.

b) These membranes are arranged in stacks & are surrounded by a fluid called the stroma.

II. The Specifics of Photosynthesis

A.) The Light Reactions

Purpose: To use light energy to make the molecules ATP and NADPH which are required to make sugar in the second step of photosynthesis.

1.) Chlorophyll molecules cluster together in the thylakoids to form photosystems. There are two types – photosystem I (PSI) and photosystem II (PSII)

2.) The chlorophyll molecules in each photosystem (PSI & PSII) absorb light energy.

The energy causes a particular chlorophyll molecule in each photosystem to lose an electron.

a.) The lost electron from PSI combines with H+ and the carrier molecule NADP+ to form NADPH.

-NADPH carries* & donates* electrons & H+ during the second step of photosynthesis, the Calvin cycle.

*JUST LIKE NAD+ & FADH do in Cellular respiration! To Calvin Cycle!!!

b.) The lost electron from PSII, is passed to a series of molecules called an electron transport chain (similar to Cellular Respiration) that connect it to PSI. This electron will replace the one lost by the chlorophyll in PSI!

i.)The energy of the passing electron allows ATP to be made! This goes to the Calvin cycle.

*NOT TO CELL METABOLISM

ATP

c.) PSII replaces its lost electron by breaking down a water molecules (with enzymes)

i.) The process of splitting water also releases hydrogen and oxygen!!!

ii) This is the source of much of the oxygen we have in our atmosphere.

iii) So, you depend on plants not only for food but for oxygen too!

LOOK! Both ATP & NADPH are produced by the light reaction & both go to the Calvin Cycle – the second set of reaction in photosynthesis.

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• Review light reaction:

• IN= light & water

• OUT= NADPH & ATP

• PURPOSE: capture energy & take it to Calvin Cycle!

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120072/bio13.swf::Photosynthetic%20Electron%20Transport%20and%20ATP%20Synthesis

B.) The Calvin Cycle (takes place in the stroma of the chloroplast)

Purpose: Uses NADPH & ATP from the light reactions AND carbon dioxide to build sugar molecules.

1.) carbon dioxide (from atmosphere) enters plant cell & chloroplast and reacts with a series of molecules and enzymes.

2.) NADPH from the light reactions provides electrons and hydrogen ions to the reacting molecules and ATP provides the energy to build the sugar molecules.

a.) The Calvin cycle reactions break down ATP and NADPH into ADP, PHOSPHATE & NADP+. These molecules will be recycled by the light reactions and turned back into ATP and NADPH - these will then go back to the Calvin cycle…and so on…

3.) The product of the Calvin cycle is the sugar molecule glucose!

a.) This initial product can be used by the plant to make many carbon containing molecules required for growth and can be stored for later energy needs.

1. Carbon dioxide must be present to start the “cycle” of reactions.

2. After that, different enzymes and molecules react forming many intermediate molecules.

3. These reactions require the energy transferred from NADPH and ATP from the light reactions.

4. The product that leaves the Calvin cycle is a sugar molecule

Simplified Calvin cycle

• Review Calvin Cycle

• IN= ATP, NADPH, CO2

• OUT= SUGAR (C6H12O6)

• PURPOSE: to take captured energy and store it in the bonds of macromolecules.

• QUESTION:

• Do plants go through Cellular respiration?