Chapter 5 Section 2 Photosynthesis photo= light Synthesis= to make

100 atomic bombs worth of energy strike the earth every day Plants, algae and some bacteria capture about 1% Light energy is converted into chemical energy 1 st law of thermodynamics OK not creating but changing form

3 Stages of Photosynthesis 1.Light energy captured 2. Light energy converted into chemical energy (ATP and NADPH)‏ 3. ATP and NADPH used to form organic compounds from CO 2

6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Yes…..You need to know this But……….. It does not tell you how it happens, which you will also have to know!!!!!! 

Plants contain 2 types of chlorophyll (a &b)‏ Absorb at both the blue and red ends of the spectrum thus reflecting green Many also contain accessory pigments called carotenoids that absorb in the violet to green end These are the cause of the fall leaf colors

Chloroplast Structure  Pigments are found in the thylakoid membrane (lipid bilayer)‏  A stack of thylakoids is called a granum which are interconnected by membranes  chloroplasts are plant cell organelles

Stage 2 Energy Conversion When pigments absorb light they gain energy and electrons become “excited” the added energy moves them to a higher energy level The excited electron is then passed to a series of proteins in the thylakoid membrane Called the Electron Transport Chain

At the end of the chain is a proton pump (H + ) The energy in the electron is used to pump H + into the thylakoid membrane Creates a proton gradient!!!!!! Water is split to replace the lost electron in the pigment The H turned into H + and electron 2 Oxygen combine to form O 2

Within the thylakoid membrane there is another photosystem At the end of this chain two high energy electrons are passed to NADP + to form NADPH The H represents the high energy electrons The pigment’s electron is replaced by the electron from the other photosystem. Stage 1 and Stage 2 are often referred to as the Light Reactions as they need light to proceed

E.T.C. Excited e -

ATP Production A proton gradient has been established across the thylakoid membrane –H + are more concentrated inside than outside –H + want to move to the outside of the thylakoid due to diffusion –They cannot diffuse directly due to charge Protons pass through an enzyme called ATP synthase –The force generated is used to convert ADP into ATP

Stage 3: Storage of Energy The ATP and the NADPH from the first two stages are used in the production of organic materials such as sugars –ATP provides energy and NADPH supplies H Called the Dark Reactions because they don’t require light energy –Also referred to as carbon dioxide fixation –Also called the Calvin Cycle after Melvin Calvin (whose mother obviously hated him)‏

Back to light reactions

Rate of Photosynthesis Affected by light intensity up to the saturation point Affected by CO 2 concentration to a maximum point As with most chemical reactions photosynthesis is also affected by temperature as enzymes have an optimal temperature in which to function