Chapter 8 Photosynthesis

I./2. Some organisms are producers and others are consumers.

a)a) AutotrophsAutotrophs make their own energy from inorganic sources through the process of photosynthesis or chemosynthesis

a)a) HeterotrophsHeterotrophs are organisms that consume organic compounds in their food

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Why is Photosynthesis Important?Why is Photosynthesis Important?Energy Flow through an ecosystem: Almost all of the biochemical Energy Flow through an ecosystem: Almost all of the biochemical

energy on Earth comes directly or indirectly from the sunenergy on Earth comes directly or indirectly from the sun

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Photosynthesis Photosynthesis is the production of carbohydrates (glucose) from CO2 and H2O, with

the help of sunlight.

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6CO2 + 6H2O --------------> C6H12O6 + 6O2 sunlight

carbon dioxide water glucose oxygen

Chemical energy out (sugar)

Light energy inInorganic molecules

Photosynthesis Location

• Takes place in the organelle called the Chloroplast• Chloroplasts contain Chlorophyll, a pigment that

captures light energy to make glucose

A Closer Look at Chloroplasts

-Inside the chloroplasts are disk shaped sacs, called the thylakoid.

- This is where the light dependent reactions occur

-The thylakoids are arranged in stacks called Granum

-The thylakoids are bathed in a thick fluid called stroma. This is where the calvin cycle takes place

-Chlorophyll is the green pigment embedded in the thylakoid

Structure of the Leaf •Chloroplasts are in the middle layer of leaves called the mesophyll

• On the underside of the leaf, the stomata allows gases (CO2 and O2) to enter and exit the leaf

• Guard Cells regulate the stomata • Veins called xylem and phloem carry water, glucose

and nutrients

Light

• Photon = a discrete packet of light energy. • Light is either absorbed, transmitted or reflected

Light Used in Photosynthesis• Chlorophyll pigments can absorb only some

wavelengths of the visible light from the electromagnetic spectrum.

• Chloroplasts absorb mainly blue-violet and red-orange lights. This absorbed light energy is converted to chemical energy.

• Green light is reflected and transmitted by green plants – hence, they appear green.

Paper Chromatography: method for separating and identifying mixtures

Rf value:

Distance pigment traveled Distance solvent traveled

Photosynthesis Overview

6CO2 + 6H2O --------------> C6H12O6 + 6O2

1. What is the color of this pigment?

2. What are the inputs/reactants of the light dependent reaction?

3. What are the products of the light dependent reaction?

Two Stages of Photosynthesis• Photosynthesis occurs in two stages.

– Light reactions – Calvin Cycle

The two stages are linked together by NADPH and ATP.

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Stored Energy in Chemical Bonds

Energy Released for Cellular Work (By breaking chemical

bonds)

- ATP and NADpH store energy in chemical bonds - Energy is released when bonds are broken

Light Reaction• When: Dependent on light and occurs only during

the day • Where: thylakoid membrane of the chloroplast.• Purpose: Create energy carriers for Calvin Cycle

• Inputs: Light Energy + H20• Outputs: Oxygen +ATP+ NADPH

• Destination of outputs:– Oxygen released from stomata– ATP and NADPH fuel Calvin cycle

Calvin Cycle • Outcome: Creates G3P which is used to make Sugars • Takes place in the Stroma• Inputs: C02 , ATP , NADPH

• Outputs: Sugar, ADP+ P, NADP +

• Destination of outputs:– Sugar used in the plant– NADP+ and ADP are recycled to light dependent cycle

8.2 Light Dependent Reactions

Light Reactions Involves: Step 1: chlorophyll uses solar energy to split

H2O into H + O2

Step 2: O2 escapes as a waste product Step 3: Conversion of light into chemical energy

Electrons and hydrogen are used to make NADPH, an energy rich molecule and

ATP (chemical energy)• Both ATP and NADPH store energy in their bonds

• They will be used in the Calvin Cycle (light independent reactions)

Photosystem II Photosystem I

Light Dependent Reaction1. Clusters of pigments are embedded in the

thylakoids. (Photosystems I and II)(Photosystems I and II)

2. Energy from the sun causes electrons in the pigments to become “excited” jump to a higher energy level (Photosystem II loses an electron)

3. Photosystem II then “steals” an electron from H2O by splitting the molecule into H+H+O

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Oxygen production

4. The Oxygen from two water molecules fuse to form OO22 gas, which is released as waste into the air.

5. Hydrogen molecules are released as free protons (H+)

6. Electrons travel down the an electron transport chain. This process pumps H+ ions across the membrane into the thylakoid (The electron Transport chain)

- this creates a high concentration of H+ inside the thylakoid

The Electron Transport Chain produces energy storage Compound ATP and NADPH

7. Excited electrons from Photosystem I travel through an ETC and help produce NADPHNADPH.

a) H+ is added to NADP+ to create NADPH (stored energy)

b) These electron will be replaced by electrons from Photosystem II.

8. H+ floods back out through an enzymeenzyme channel called ATP ATP synthasesynthase.

9. Each H9. Each H++ that is transported aids in the production of one ATPone ATP molecule.

10. NADPH and ATP will be used to fuel the Calvin Cycle in the Stroma

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How are the following reactants used in the light

dependent stage of photosynthesis?

- Sunlight - Water

How are the following products created during

the process of photosynthesis?

- Oxygen

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Light Independent Reaction: Calvin Cycle

• Overview: use CO2 and Energy rich molecules (ATP and NADPH) to create sugar

Light Dependent Reaction/ Calvin Cycle

• independent of light and occurs during the day and the night: Relies on light dependent products

• Where: stroma of the chloroplast.• IN: ATP, NADPH, CO2• OUT: G3P which will be used to make glucose,

ADP + P, NADP+(Both will be energized again in light dependent reactions)

• Calvin Cycle involves the production of ‘food’ as glucose, by using CO2, ATP energy and NADPH.

6H20 6CO2 Light C6H12O6 6 O2

In what reaction is this used/ made

Describe Specifically how this is used/made

Calvin Cycle Steps: 1. CO2 enters the stroma2. It combines with a 5-C sugar RuBP using the enzyme Rubisco

to form a 3-C acid (carbon fixation)3. Using energy from ATP & NADPH high

energy sugars (G3P) are made for the plant- ATP donates a phosphate group and NADPH donates electrons and Hydrogen molecules

4. ADP & NADP+ go back to the thylakoid to be “recharged”

BIG PICTURE: - In the end, 6 carbon dioxide molecules enter

the cycle to make one six-carbon glucose.

- The energy required to do this came from the NADPH and ATP that was formed with the help of the sun’s energy.

Fate of Atoms in Photosynthesis• CO2 becomes part of glucose (C6H12O6)

• H2O is split into H and O; O2 is released as a gas; H’s become part of glucose.