1. CHAPTER 4 CELLS AND ENERGY

2. The chemical energy used for most cell processes is carried by ATP.
Carbohydrates and lipids are the most important energy sources in food.
All carbon based molecules in food store chemical energy.

3. ATP (adenosine triphosphate) is a molecule that transfers energy from the breakdown of food molecules to cell processes.
The energy carried by ATP is released when one of the phosphate groups is released form the molecules. ATP is converted to ADP (adenosine diphosphate).

4. ADP can be converted back to ATP if a phosphate group is added to ADP
ADP can be converted back to ATP if a phosphate group is added to ADP. This is not a simple process. A large complex group of proteins is needed to do it.

5. Organisms break down carbon-based molecules to produce ATP.
Once food is broken down into smaller molecules, ATP production can begin.
Calorie is a measure of energy. Different foods have different calories.

6. Lipid molecules can produce the largest amount of ATP.
Plant cells use ATP as well. Plant cells produce ATP via sugar production in photosynthesis.

7. A few organisms do not need sunlight and photosynthesis as a source of energy.
Chemosynthesis is a process by which some organisms use chemical energy instead of light energy to make energy storing carbon-based molecules.

8. 4.2 Overview of Photosynthesis

9. Photosynthetic organisms are producers.
Photosynthesis is a process that captures energy from sunlight to make sugars that store chemical energy. Therefore, directly or indirectly, the energy for almost all organisms begins as sunlight.

10. Chlorophyll is a molecule in chloroplasts that absorbs some of the energy in visible light. Plants have two types of chlorophyll, chlorophyll a and chlorophyll b. These two types of chlorophyll mainly absorb energy from red and blue light. Green light is not absorbed as much by chlorophyll. Plants have other molecules for that. Plants are green, however, because they reflect green wavelengths by chloroplasts.

11. Chloroplasts are the membrane bound organelles where plant photosynthesis occurs.
Two main parts of the chloroplasts are the grana and stroma. The grana are stacks of enclosed compartments called thylakoids. The membranes of thylakoids contain chlorophyll, other light absorbing molecules and proteins. The stroma is the fluid that surrounds the grana inside a chloroplast.

12. Photosynthesis occurs in two phases: The light dependant reaction and light independent reaction.
The light dependent reaction captures energy from sunlight. These reactions take place in membranes within and across the thylakoids. Water and sunlight are needed for this stage of photosynthesis.

13. 1. Chlorophyll absorbs energy from sunlight
1. Chlorophyll absorbs energy from sunlight. Energy is transferred along the thylakoid membrane. Water molecules are broken down and oxygen is released.
2. Energy is transferred to molecules such as ATP.
The light independent reaction uses energy from the light dependent reactions to make sugars.. This occurs in the stroma of chloroplasts. Carbon dioxide is needed for this stage of photosynthesis.

14. 3. Carbon dioxide is added to a cycle of chemical reactions to build larger molecules. Energy from the light- dependent reactions is used in the reactions.
4. A molecule of a simple sugar is formed. The sugar, usually glucose (C6H12O6), stores some of the energy that was captured from sunlight

15. Chemical equation for photosynthesis
6CO2 + 6H2O  C6H12O6 + 6O2
carbon dioxide plus water via light enzymes produces a sugar and oxygen