chapter iCh. 4: This chapter is all about cells make and use energy.
 4.4 – A chapter about cellular energy is really about the unit of energy that cells use: Adenine tri-phosphate (ATP). This molecules is really similar in makeup to a nucleotide. Figure 4-8 shows how ATP can be used over and over again. All of the energy is stored in on phosphate chemical bond, so you break it off to get the energy and put it back on again to store energy.
Technical terms to know: ATP, ADP.
 4.5-4.10 – All about photosynthesis. This process is all done in chloroplasts. The bottom of Figure 4-11 shows the most crucial information, what goes in and what comes out. Figure 4-16 shows where the process really starts, with the sun. The other sections before that show why the pigment part of the chloroplast, chlorophyll, absorbs light. You just need to know that chlorophyll is like a solar-powered version of ATP. It can absorb sunlight and use the sun’s energy to give off high-energy electrons. Incidentally, this is why plants need water, to replace the electrons that chlorophyll loses in the process. The plant uses the energy in those electrons to power photosynthesis. Photosynthesis is split into two parts:
1. the parts that use light (light reactions, the book calls these “photo” reactions). These are all in figure 4-20.
2. The parts that don’t need light (dark reactions, the book calls these the synthesis reactions). These parts take the stuff from the first part and use it to make carbohydrates. This is in figure 4-21.
Let’s start with part 1. The crucial part that makes the light reactions work is the electron transport chain (labeled as 2 in figure 4-20). Here the cell uses the power taken from chlorophyll to do active transport of hydrogen atoms. It pumps them all into one compartment, and then lets them all