Photosynthesis (8.1 and 8.2)

Chemical Energy and ATP Energy is the ability to do work Organisms must be able to obtain and use energy Adenosine triphosphate ATP – composition Adenine, ribose (5-C sugar) 3 phosphate groups ADP Has 2 phosphate groups

Storing and Releasing Energy Storing energy Storing small amounts of energy can be done by adding the 3rd phosphate group to ADP to make ATP ADP is like a rechargeable battery that powers the cell Releasing Energy Breaking the chemical bonds in ATP can release energy ATP can easily store and release energy by breaking and re-forming the bonds between the phosphate groups – very useful and efficient energy source for cells

Using Biochemical Energy Carry out active transport Sodium (Na+) –potassium (K+) pumps Energy for muscle cell contractions and movement Movement of cilia and flagella Synthesis of proteins Responses to chemical signals on cellular surfaces Produce light (fireflies) Glucose is a better energy storage molecule than ATP

Heterotrophs and Autotrophs Cannot make their own food Consume other organisms to obtain nutrients used for energy Autotrophs Make their own food by capturing the energy from the sun Energy is stored in food molecules produced Photosynthesis – capturing the sun’s energy to produce high-energy carbohydrates (sugars and starches)

Chlorophyll and Chloroplasts Light White light is actually a mixture of different wavelengths (colors) Visible spectrum: ROYGBIV Pigments Light-absorbing molecules Photosynthetic organisms use pigments to capture the sun’s energy Chlorophyll a and b Absorb well in the blue-violet and red regions of the spectrum but not green Green light is reflected to plants appear green

Chloroplasts The organelle where photosynthesis takes place Thylakoids – saclike photosynthetic membranes Chlorophyll is located here Grana - interconnected thylakoids arranged in stacks Stroma Fluid portion, outside the thylakoids

Energy Collection Chlorophyll is a special pigment It absorbs the light energy from the sun A large fraction of the energy absorbed is transferred directly to electrons in the chlorophyll molecule itself The energy levels of the electrons are raised allowing a steady supply of high-energy electrons allowing photosynthesis to proceed

High-Energy Electrons Highly reactive and require a special “carrier” molecule An electron “carrier” is a compound that can accept a pair of high-energy electrons and transfer them, along with their energy, to another molecule

Carrier Molecules NADP+ Nicotinamide adenine dinucleotide phosphate Holds two high-energy electrons along with a hydrogen ion (H+) NADP+ converted to NADPH which allows some of the energy from the sun to be trapped in chemical form Can also carry energy to other parts of the cell Helps to build high0energy molecules such as glucose

Overview of Photosynthesis Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen

Light Reactions Light-Dependent Reactions Require direct involvement of light and light-absorbing pigments Use energy from sunlight to produce energy-rich compounds like ATP In the thylakoid membranes of the chloroplasts Oxygen is released as a byproduct

Light Reactions Light-Independent Reactions ATP and NADPH produced from the light-dependent reactions are used to produce high-energy sugars from CO2 No light is needed Takes place outside of the thylakoids in the stroma

Photosynthesis – Both Rxns

Factors Affecting Photosynthesis Light - intensity Water/CO2 Concentration - concentration Temperature – optimal range