Chapter 5 2 Photosynthesis Photosynthesis Photosynthesis The process

Chapter 5. 2 Photosynthesis

Photosynthesis § Photosynthesis – The process that plants use to make energy from the sun. § The process by which plants and some other organisms convert light energy to useable chemical energy. § The Student of the Day will be able to answer this question. § § § What element is Organic Chem. centered around? What is a molecule made of 6 Carbons? A plant makes sugar molecules which store energy and allow the plant to grow and reproduce.

How does a plant get energy? § Plants need supplies in order to make sugar. § Where do you think the Carbon comes from? § Where do you think the Hydrogen comes from? § A plant will take in three things in order to make a sugar molecule; Carbon Dioxide, Water and Sunlight.

What else does a plant make? § Along with the 1 sugar molecule that a plant will make during photosynthesis a plant makes Oxygen molecules as a waste product. § What does a plant do with the Oxygen molecules that it makes? CO 2 + H 2 O + sunlight C 6 H 12 O 6 + O 2 +

Think about it! CO 2 + H 2 O + sunlight C 6 H 12 O 6 + O 2 • How many Carbons are in the sugar molecule? Hydrogen? Oxygen? • How many Carbons are in the reactant? Hydrogen? Oxygen? • This molecular equation is not balanced. • 6 CO 2 + 6 H 2 O + sunlight C 6 H 12 O 6 + 6 O 2 • The equation now has the same number of atoms in the product as it does in the reactant.

Where does this process take place? § What are the leaves of a plant made of? § The organelle inside a plant cell where photosynthesis takes place is the chloroplast. § Inside a chloroplast are tiny discs that look like a stack of nickels called thylakoids. § Inside thylakoid are pigments. § The pigment inside thylakoid will absorb light from the sun.

Chloroplast

Visible Light Spectrum § The sun produces many different sized waves. A small percentage of these waves we can see or hear. The rest of the waves our brains cannot comprehend.

More about light waves § Certain light waves that come down from the sun are absorbed while others are reflected. § For example your shirt is absorbing and/or reflecting all types of color. § If you are wearing a white shirt, it is reflecting all of the colors back to your eye. § Those that are wearing black shirt are absorbing all of the waves of color. § Story time: Very Stupid criminal!

Pigments § There are four types of pigment in the thylakoid that we will learn about. 1. Chlorophyll A – absorbs all spectrums of light except for green and blues 2. Chlorophyll B - absorbs all spectrums of light except for yellows, greens and some blues. 3. Carotenoids - absorbs all spectrums of light except for reds, oranges and yellows. 4. Xanthophyll - absorbs all spectrums of light except for yellow.

Absorption Spectra of photosynthesis pigments.

Sample Paper Chromatography

Stages of Photosynthesis § There are three important stages of photosynthesis. § Light Dependant Reaction – needs light in order to function. § There are two steps in the Light Dependant Rxn. - Light Absorption - Electron Transport § Light Independent – Does not mean that it has to be dark to work. It can work both at night & at daytime. - Calvin Cycle

3 Stages of Photosynthesis

Stage 1: Light Absorption § Step 1: Light hits the thylakoid in the plant cell and the pigment absorbs the energy. § Step 2: When the light hits the thylakoid it excites an electron in the pigment. The ejumps to a higher energy level and moves to a molecule near the thylakoid. § Step 3: An enzyme takes water into the cell and breaks it into 2 H atoms and an O atom. The H atoms are stripped of their electron which replace the electron that has just been bumped up. What do you think happens to the Oxygen?

Here’s how light absorption works.

Stage 2: Electron Transport § Electron Transport Chain – Series of molecules through which excited e-s are passed along the thylakoid membrane. § Step 1 – The excited e-s is passed through a series of molecules. § Step 2 – The energy lost by the electron causes more Hydrogen to move into the thylakoid. Where do the Hydrogen come from? This causes a concentration gradient. § If you need to move against a concentration gradient what do you need?

Stage 2: Electron Transport Cont. § One pump places a phosphate onto ADP making ATP. § Another pump takes the leftover Hydrogen and puts it onto a molecule called NADP which turns it into NADPH. § NADPH is an e- carrier that provides the high energy electron needed to make Carbon. Hydrogen bonds in the next Stage (The Calvin Cycle.

Photosystems § Photosystem II § Photosystem I see overhead

Light Independent Reaction § So far we have talked about water and light energy. What part of photosynthesis haven’t we talked about? § Carbon Dioxide Fixation – The transfer of CO 2 to organic compounds. The process of making C 6 H 12 O 6. § The most common Carbon Dioxide Fixation reaction that occurs in photosynthesis is the Calvin Cycle.

Calvin Cycle 1. 3 CO 2 molecules are added to 3 5 -Carbon compounds. 2. The 3 6 -Carbon compounds split into 6 3 Cabon compounds.

Calvin Cycle Continued § A phosphate from ATP & an e- from NADPH turn the 3 Carbon Compounds into 3 Carbon sugars. 3. One 3 Carbon sugar is used to make carbohydrates for energy storage. 4. The other 5 3 -Carbon sugars turn into 3 5 Carbon compounds used to continue the cycle. § Factors that would affect photosynthesis: Light, CO 2 and temp. (enzyme activity)