The Need for energyCell Energy

Energy is essential to life. All living organisms must be able to obtain energy from the environment in which they live.

Plants and other green organisms are able to trap the light energy in sunlight and store it in the bonds of certain molecules for later use.

Work and the need for energy

• Several processes that require energy.

Active transport, cell division, movement of flagella or cilia, and the production, transport, and storage of proteins.

Energy is stored in the chemical bonds of that molecule and can be used quickly and easily by cells.

• The name of this energy molecule is adenosine triphosphate, or ATP for short.

• ATP is composed of an adenosine molecule with 3 phosphate groups attached.

Forming and breaking down ATP

• Adenosine with 1 phosphate = AMP

• Adenosine with 2 phosphate= ADP

• Adenosine with 3 phosphate = ATP

Adding phosphate require energy needing the least and 3 the most.

Energy is stored in the bonds.

When this bond is broken energy is released.

• When the chemical bond between the second and third phosphate groups in ATP is broken, energy is released and the resulting molecule is ADP.

• ADP can form ATP again by bonding with another phosphate group.

• ADP can be used as energy also but will not give off as much energy as ATP.

Photosynthesis: Trapping the sun’s energy

• The cells of green organisms must trap light energy and store it in a manner that is readily usable by cell organelles- in the chemical bonds of ATP.

• The process that uses the sunlight to make simple sugar is called photosynthesis. These simple sugars are then converted into complex carbohydrates, such as starches, which store energy.

Photosynthesis happens in two phases

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

2. Light-independent reactions- use the ATP to produce simple sugars.

Equation for photosynthesis

6CO2 + 6H2O C6H12O6 + 6O2

productsreactants

Chloroplast and pigments

• Photosynthesis takes place in the membranes of the thylakoid discs in chloroplasts.

• To trap the energy in the sun’s light, the thylakoid membranes contain pigments, molecules that absorb specific wavelengths of the sunlight.

• Most common pigment is chlorophyll which absorbs most wavelengths of light except green.

• Since it chlorophyll can not absorb the wavelength for green it is reflected, giving leaves a green appearance.

• In the fall the, trees stop producing chlorophyll in their leaves. Other pigments become visible, giving leaves a wide variety of colors.

Light-dependent reactions

• The first phase of photosynthesis requires sunlight.

1. Sunlight strikes chlorophyll molecules in the thylakoid membrane, the energy in the light is transferred to electrons. (electrons become excited or highly energized)

2. Electrons are passed from chlorophyll to an electron transport chain, a series of proteins embedded in the thylakoid membrane.

Light-dependent reactions

• capture energy in sunlight and transfer it

• - take place in thylakoid membrane of a chloroplast

• - chlorophyll absorbs energy from sunlight

• - water is broken down (into H+ ions, electrons, and oxygen)

Light-dependent reactions

• - oxygen is released as a waste product

• - NADPH is formed (functions like ATP = energy) when electrons are added to NADP+

• - energy is transferred to make ATP (when H+ ions diffuse)

• - overall, oxygen is given off as a waste product, NADPH and ATP are formed

Light-Independent reactions

The second phase of photosynthesis does not require light. It is called the Calvin Cycle, which is a series of reactions that use carbon dioxide to form sugars.

Calvin cycle is named after Melvin Calvin.

Light-Independent reaction

• energy (NADPH and ATP) from light reactions make sugars

• - occurs in stroma of chloroplast

• - does not need sunlight

• - carbon dioxide is needed

• - a simple sugar, glucose, is formed from carbon dioxide and energy from ATP and NADPH

Light independent reactions

• - overall, glucose, NADP+, and ADP are created.

• NADP+ and ADP go back to the light dependent reactions

Light-Independent