Objectives: 4(B) Investigate and explain cellular processes, including homeostasis, energy conversions, transport of molecules, and synthesis of new molecules 9(B) Compare the reactants and products of photosynthesis and cellular respiration in terms of energy and matter

 Photosynthesis is a process of converting light energy into chemical energy.

 Photosynthesis occurs in two phases:  Light-dependent phases – light energy is converted into chemical energy.  Light-independent – chemical energy is used to synthesize glucose.

 The absorption of light is the first step in photosynthesis.  Once light energy is captured, it can be stored as ATP and NADPH.

Chloroplasts  Organelles that capture light energy  Contain two main compartments  Thylakoids – flattened saclike membranes. ▪ Stack of thylakoids are called grana.  The fluid filled space outside the grana is called the stroma.

Pigments  Light-absorbing colored molecules called pigments are found in the thylakoid membranes.  Different pigments absorb specific wavelengths of light.  Most common pigment in plants is chlorophyll.  Plants also have accessory pigments.

Electron Transport  Thylakoid has a large surface area   space for a large number of electron transporting molecules and two protein complexes called photosystems.  Photosystems have light-capturing pigments.

1. Light energy excites electrons in photosystem II (PSII) releasing them down the electron transport system (ETS) This energy also causes a water molecule to split providing replacement electrons for PSII and leaving two protons in the thylakoid space.

2. Energized electrons move from PSII to an acceptor molecule in the thylakoid membrane. 3. The electron acceptor molecule transfers the electrons along a series of electron carriers to photosystem I (PSI).

4. With an added boost from light, PSI transfers the electrons to a final electron acceptor called ferrodoxin. 5. Ferrodoxin transfers the electrons to the electron carrier NADP+, forming the energy storage molecule NADPH.

Chemiosmosis  The process of splitting water and electron transport causes a buildup of protons (H+) in the thylakoid space  The H+ moves down its concentration gradient through a transport protein called ATP synthase.  This energy is used to convert ADP to ATP.

 In the second phase of photosynthesis, called the Calvin cycle, carbon dioxide (CO 2 ) and energy from ATP and NADPH are used to make sugars.

Steps in Calvin Cycle  Step 1: Carbon Fixation  CO 2 molecules combine with 5-carbond molecules to form 3-phosphoglycerate (3-PGA)  Step 2  Chemical energy stored in ATP and NADPH is transferred to 3-PGA to form glyceraldehyde 3- phosphate (G3P).

 Step 3  Some G3P molecules leave the cycle to be used for the production of glucose and other organic compounds  Step 4  An enzyme called rubisco converts the remaining G3P molecules into 5-carbon molecules called ribulose 1,5-bisphosphate (RuBP).  These molecules combine with new CO 2 and continue the cycle.

C 4 Plants  The C 4 pathway allows plants to maintain photosynthesis while reducing water loss.  Called C 4 because they fix carbon into four carbon compounds instead of three-carbon molecules.  Significant structural modification in the arrangement of cells within the leaves – separate CO 2 uptake from location of Calvin cycle.

CAM plants  Crassulacean acid metabolism (CAM) is found in desert plants such as cacti.  Collect CO 2 at night and store it in organic compounds.  During the day, release CO 2 from organic compounds and enters the Calvin cycle..