Chapter 9: Energy in a Cell



Chapter 9: Energy in a Cell

Section 9.1 The Need for Energy

I. Cell Energy

1. Energy is essential to life, all living organisms must be able to obtain energy from the environment.

2. Plants are able to trap light energy and use it.

3. Other organisms must eat food to obtain energy.

A. Work and the need for energy.

1. Many cellular processes require energy.

Ex. Active transport, cell division, locomotion of cell, are some

examples.

2. ATP (adenosine triphosphate) is a molecule in your cells that is the source of energy.

3. This energy is stored in the chemical bonds of ATP.

4. ATP is composed of:

a. one adenosine molecule (which is the sugar ribose connected to an adenine molecule)

b. three phosphate groups

II. Forming and Breaking Down ATP

1. The energy of ATP becomes available to a cell when the molecule is broken down.

2. When ATP is broken down energy is released and the resulting molecule is ADP (adenosine diphosphate)

3. ATP is broken down into ADP when the chemical bond between the second and third phosphate group in ATP is broken.

4. At this point ADP can form ATP again by bonding with another phosphate group.

5. This process creates a renewable cycle. (fig. 9.2)

*As long as phosphate groups are available, a cell can create

ATP whenever it needs to.

A. How cells tap into the energy stored in ATP

1. When ATP is broken down and the energy is released, it must be captured and used or it is wasted and given off as heat.

2. ATP ( ADP + P + Energy

3. To access the energy locked up inside an ATP molecule it usually binds to a protein (or enzyme). There is a specific binding site where ATP fits into and the protein will aide in the removal of the third phosphate group. (pg. 223, fig. 9.2 b)

III. Uses of Cell Energy

1. Making new molecules

2. Maintaining homeostasis

3. Eliminating wastes

Section 9.2 Photosynthesis: Trapping the Sun’s Energy

I. Trapping Energy from Sunlight

1. Plants use energy in the form of ATP as well. Since sunlight is not

available all the time they must harvest the suns energy and store

it for later use.

2. Photosynthesis = the process that uses the sun’s energy to make

simple sugars.

1. These simple sugars are then converted into complex

carbohydrates, such as starches, which store energy.

3. Photosynthesis happens in two phases

1. Light-dependent reactions – convert light energy into chemical energy (ATP molecules)

2. Light-independent reactions- produce simple sugars (like glucose)

**General Equation for photosynthesis**

6CO2 + 6H2O + sunlight ( C6H12O6 + 6O2

4. The Chloroplasts and Pigments

1. Chloroplast = organelle where photosynthesis occurs

2. Inside the chloroplast, the thylakoid membranes contain pigments that absorb

sunlight.

3. Chlorophyll = the green pigment that absorbs sunlight.

II. Light- Dependent Reactions

1. First phase of photosynthesis requires sunlight (dependent on sunlight)

2. Light Dependent reactions electron carriers (NADP+) to combine with energized electrons and H+ to Produce NADPH. NADPH acts as a storage container for electrons that will be used in the light dependent reactions.

3. Reactants: Chlorophyll (in the chloroplast), light energy from the sun, excited electrons, NADP+

4. Products: ATP and NADPH

III. Light – Independent Reactions

1. This is also known at the Calvin Cycle

2. Calvin Cycle – a series of reactions that use carbon dioxide to from sugars.

3. Takes place in the stroma of the chloroplast

4. The Calvin Cycle will transform 1 molecule of carbon dioxide, ATP, and NADPH and turn it into simple sugars (AKA glucose)

Section 9.3 Getting Energy to Make ATP

(Please note: some info. has been omitted from section 9.3)

I. Cellular Respiration

1. Plants and animals both do the process of cellular respiration.

2. Cellular Respiration = process by which mitochondria break down

food molecules to produce ATP.

3. Cellular respiration equation:

C6H12O6 + O2 ( CO2 + H2O + ATP

4. There are three stages of cellular respiration:

a. glycolysis

b. citric acid cycle

c. electron transport chain

d.

A. Glycolysis

1. Glycolysis= series of chemical reactions in the cytoplasm of a cell

that breaks down glucose into two molecules of pyruvic acid.

2. As glucose is broken down, 4 ATP molecules will have been created

(which the cell can use immediately) and also some additional

energy carriers as well, which will move on to the electron

transport chain to be used later on to make additional ATP

molecules.

3. The two pyruvic acid molecules now move into the mitochondrion

and enter the citric acid cycle to be further broken down and to

release more energy.

B. The Citric Acid Cycle

1. This cycle takes place in the matrix of the mitochondrion.

2. This cycle produces two ATP molecules, four CO2 molecules and some additional energy carriers.

3. The CO2 is released out of the cell, the ATP is ready to be used, and the energy carriers move on to the electron transport chain to create more ATP molecules.

C. The Electron Transport Chain

1. This process takes place in the inner membrane of the mitochondrion.

2. It uses oxygen and the energy carriers produced by glycolysis and the citric acid cycle to produce 32 ATP’s.

** From the breakdown of just one glucose molecule, your cell gains 36 to

38 ATP molecules! **

II. Fermentation (pg. 235)

*There are times, such as heavy exercise, when your cells are without

oxygen for a short period of time.

*When this happens, fermentation takes place instead of cellular

respiration.

*There are two types of fermentation:

a. Lactic acid fermentation

b. Alcoholic fermentation

A. Lactic Acid Fermentation

1. This is an anaerobic process which occurs in the cytoplasm of cells

of animals.

2. Process of what happens:

Glucose ( Glycolysis (pyruvic acid) ( Lactic acid + 2 ATP’s

B. Alcoholic Fermentation

1. This is an anaerobic process which occurs in the cytoplasm of cells

of plants, yeast cells, and some bacteria.

2. Process of what happens:

Glucose ( Glycolysis (pyruvic acid) ( CO2 + Alcohol + 2 ATP

III. Comparing Photosynthesis and Cellular Respiration (pg. 237)

What do you notice???

Photosynthesis: CO2 + H2O sunlight ( C6H12O6 + O2

Cellular Respiration: C6H12O6 + O2 ( CO2 + H2O + ATP

|Photosynthesis |Cellular Respiration |

|1. Food synthesized (made). |1. Food broken down. |

|2. Energy from sun stored in glucose. |2. Energy of glucose released. |

|3. CO2 taken in. |3. CO2 given off. |

|4. Oxygen given off. |4. Oxygen taken in. |

|5. Produces simple sugars. |5. Produces CO2 and H2O. |

|6. Requires light. |6. Does not require light. |

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