Autotrophs – make their own food Plants and some other types of organisms are able to use light energy from the sun to produce their own food. Autotrophs – make their own food Heterotrophs – obtain energy from the foods they consume or absorb. All organisms must release the energy in sugars and other compounds. Address misconceptions: Ask: Do cells “think” about the life processes they carry out? Cells have no thoughts. Often speak of how a cells “uses” energy or of how a cell can “add” a phosphate group, these words should not suggest that cells decide when or how to act.

Adenine Ribose 3 Phosphate groups ATP Ribose 3 Phosphate groups Energy comes in many forms, including light, heat, and electricity. Energy can be stored in chemical compounds. ATP is one of the principle compound that organisms use to store and release energy.

ADP ATP Energy Energy Adenosine triphosphate (ATP) Fully Partially Section 8-1 Energy Energy Adenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP) Partially charged battery Fully charged battery ADP looks almost like ATP, except it has 2 phosphate groups instead of 3. This difference is the key to the way in which living things store energy. When a cell has energy available, it can store small amounts of it by adding a phosphate group to ADP molecules, producing ATP. ATP is like a fully charged battery, ready to power the machinery of the cell. What happens when a phosphate groups is removed from ATP? Energy that is stored in ATP is released by breaking the chemical bond between the second and third phosphates. Energy is released.

ADP ATP Energy Energy Adenosine triphosphate (ATP) Fully Partially Section 8-1 Energy Energy Adenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP) Partially charged battery Fully charged battery ADP looks almost like ATP, except it has 2 phosphate groups instead of 3. This difference is the key to the way in which living things store energy. When a cell has energy available, it can store small amounts of it by adding a phosphate group to ADP molecules, producing ATP. ATP is like a fully charged battery, ready to power the machinery of the cell. What happens when a phosphate groups is removed from ATP? Energy that is stored in ATP is released by breaking the chemical bond between the second and third phosphates. Energy is released.

If ATP is such a useful source of energy, why do most cells have only enough ATP to last them for a few seconds of activity? ATP is a great molecule for transferring energy; it is not a good molecule for storing large amounts of energy over the long term. A single molecule of glucose stores more than 90 times the chemical energy of a molecule of ATP. It is more efficient for cells to keep only a small supply of ATP on hand. Cells regenerate ATP from ADP as needed by using the energy in glucose.

Light and Pigments In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts. Sunlight is a mixture of different wavelengths of light. Plants gather the sun’s energy with light-absorbing molecules called pigments. Chlorophyll is the plants’ principle pigment (chlorophyll a and chlorophyll b). Chlorophyll absorbs light in the blue-violet and red regions of the visible spectrum. Green light is reflected by leaves. When chlorophyll absorbs light, the energy from the sun is transferred to the electrons of the chlorophyll molecule.

Chlorophyll a and Chlorophyll b Figure 8-5 Chlorophyll Light Absorption Section 8-2 Absorption of Light by Chlorophyll a and Chlorophyll b Chlorophyll b Chlorophyll a V B G Y O R

Photosynthesis: Reactants and Products Section 8-2 Light Energy Chloroplast CO2 + H2O Sugars + O2

Figure 8-7 Photosynthesis: An Overview Section 8-3 Chloroplast H2O O2 Sugars CO2 Light Chloroplast NADP+ ADP + P Light- Dependent Reactions Calvin Cycle ATP NADPH

Light-Dependent Reactions Figure 8-10 Light-Dependent Reactions Light-Dependent Reactions Section 8-3 Hydrogen Ion Movement Photosystem II Chloroplast ATP synthase Inner Thylakoid Space Thylakoid Membrane Stroma Electron Transport Chain Photosystem I ATP Formation

Calvin Cycle Figure 8-11 Calvin Cycle Section 8-3 CO2 Enters the Cycle Energy Input ChloropIast 5-Carbon Molecules Regenerated 6-Carbon Sugar Produced Sugars and other compounds

Factors that affect the rate of photosynthesis: Availability of water Light intensity Temperature

Concept Map Photosynthesis CO2 H2O Light- dependent reactions Section 8-3 Photosynthesis includes Light- dependent reactions Calvin cycle CO2 H2O takes place in uses use take place in Thylakoid membranes Stroma NADPH ATP Energy from sunlight to produce of to produce ATP NADPH O2 Chloroplasts High-energy sugars