Chapter 4 Cells and Energy ATP and Photosynthesis

Work Is done when anything is moved Life processes rearrange molecules, ions, and atoms Requires energy

Energy Is the ability to do work Comes from food Food is broken down into small molecules that can enter cells Cells break down molecules to release the energy

Energy from molecules Is not all used at one time Used to balance supply and demand Energy not used right away is stored in a molecule called ATP ATP releases the energy when the cell needs it Cells die without ATP

ATP Adenosine triphosphate Sugar (ribose) Adenine 3 phosphate groups Energy is stored in the phosphate-phosphate bonds When a phosphate is removed, energy is released to the cell ADP is left

ADP Adenosine diphosphate Sugar (ribose) Adenine 2 phosphate groups Is recycled by adding another phosphate to store energy Putting another phosphate on ADP converts it back to ATP

ATP / ADP Cycle

Energy cycle ADP + P + energy = ATP ATP Energy available for work is free energy Energy stored in molecules is potential energy ATP is the energy link between energy-using and energy-releasing reactions

Autotrophs Trap energy from sunlight for photosynthesis Most plants are green because of chlorophyll (green pigment) Chlorophyll reflects green light Energy from sun is trapped inside thylakoid membrane of chloroplast

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Photosynthesis 2 groups of reactions: light reactions and Calvin cycle (dark reactions) Light reactions Light converted to chemical energy Photo part Split water and give hydrogen to Calvin cycle Calvin cycle Forms sugar from CO2 and H (from water) Synthesis part

Light reactions Electrons in chlorophyll absorb light energy Electrons leave chlorophyll and are passed through electron transport chain Extra energy is stored as ATP Water is split into O2 and H+ (photolysis) H + electron picked up by NADP+ (electron carrier) O2 given off as waste

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Calvin Cycle Enzyme adds C from CO2 to a 5-carbon molecule C is not fixed to an organic molecule (carbon fixation-coverts gaseous CO2 to a useable form for living things: sugars, starch, cellulose) Called dark reactions because light does not have to be available for fixation

Section 9.2 Summary – pages 225-230 (CO2) (CO2) The Calvin Cycle (Unstable intermediate) (RuPB) ADP + ATP ATP ADP + NADPH NADP+ (PGAL) (PGAL) (PGAL) (Sugars and other carbohydrates) Section 9.2 Summary – pages 225-230

Life without light Some organisms are chemosynthetic (bacteria) Obtain energy by converting inorganic compounds into useable forms Usually final participants in decomposition processes