1 Photosynthesis Making food (glucose) using light

2 Contents Introduction Balanced equation The equation – oversimplified Role of Photosynthesis Factors necessary The Biochemistry of photosynthesis The Light Stage The Dark Stage ATP and NADP Summary Chart

3 Introduction The sun is the ultimate source of energy for earth. Plants are autotrophs i.e. they make their own food – they are producers. Most plants are green (chlorophyll) – make their food (glucose) by photosynthesis.

4 Balanced equation LIGHT ENERGY 6CO 2 + 6H 2 O > C 6 H 12 O 6 + 6O 2 CHLOROPHYLL A suitable temperature is also needed

5 The equation - oversimplified LIGHT C O 2 + H 2 O > CHLOROPHYLL CHO + O

6 Role of photosynthesis Plants use it to make food Animals get their food from plants Provides the oxygen needed for respiration by most living things Provided us with fossil fuels

7 Factors necessary 1.Carbon dioxide - CO 2 supplies the carbon (C) and oxygen (O) from which glucose is made. 2.Water - H 2 O supplies the H which combines with CO 2 to form glucose. 3.Light - supplies the energy necessary to convert H 2 O and CO 2 into glucose. 4.Chlorophyll - green pigment - contains the element magnesium (Mg) - formed in chloroplasts 5.Suitable temperature - photosynthesis is an enzyme controlled reaction and temperature affects the rate of enzyme action.

8 THE BIOCHEMISTRY OF PHOTOSYNTHESIS Oxidation: Addition of Oxygen OR removal of Hydrogen OR loss of electrons (OIL) Reduction: Addition of Hydrogen OR removal of Oxygen OR gain of electrons (RIG)

9 Photosynthesis takes place within the chloroplasts of plant cells. It is a two stage process: - 1.Light-dependent Stage 2.Dark Stage or Light-independent Stage

10 THE LIGHT STAGE Sunlight causes two events to happen in the chloroplast. 1.Its shining on a chlorophyll molecule causes a high-energy electron (~e - ) to be released. chlorophyll  chlorophyll + + ~e - 2.It splits water (photolysis) into, protons (H + ) electrons and oxygen. H 2 O  2H + + 2e - + O See Chart

11 THE LIGHT STAGE What happens to these products? From the water a)The electrons are passed to chlorophyll. b)The protons (H + ) are released to a general pool of protons, for use later. c)The oxygen is either released to the air or used within the cell (in respiration). See Chart

12 THE LIGHT STAGE From the chlorophyll The e ~ is either used to make ATP (from ADP and P), or picked up by NADP to form NADP _ The NADP _ combines with a proton (H + ) to form NADPH (Note: this H is made up of a proton and an electron) See Chart

13 THE DARK STAGE The protons (H + ) from the pool of protons and electrons (i.e. the H from NADPH) together with the ATP and CO 2 from the air combine to form a simple sugar C x (H 2 O) y or carbohydrate. See Chart

14 ATP and NADP (1/2) ATP (adenosine triphosphate) is the energy currency in a cell i.e. any metabolic activity that requires energy uses ATP. Adenine – Ribose ~ P ~ P ~ P When ATP is used a phosphate is removed and it is converted into ADP (adenosine diphosphate) Adenine – Ribose ~ P ~ P + P See Chart

15 ATP and NADP (2/2) The ADP and P produced in the Dark Stage is returned to the Light Stage and used to regenerate ATP. Similarly the NADP produced in the Dark Stage is returned to the Light Stage to gather more protons (H + ) from the pool of protons and electrons to form NADPH which can be used again. See Chart

16 Chlorophyll + ~ e _ Carrier ADP + PATP NADP NADP _ H2OH2O Photolysis 2e _ + O H+H+ Pool NADPH CO 2 ATPADP + P C 6 H 12 O 6 Given off or used in Respiration ~ e _ e _ Go to Slide

17 Photosynthesis Summary Chart Chlorophyll + ~ e _ Carrier ADP + P ATP NADP NADP _ H2OH2O Photolysis ~2e _ + O 2H + Pool NADPH CO 2 ATP ADP + P C 6 H 12 O 6 Given off or used in Respiration ~ e _ e _ Electron Carrier System