Photosynthesis and Cellular Energy: ATP, Autotrophs, and Light Reactions

adenosine triphosphate (ATP)

one of the most important compounds that cells use to store and release energy

heterotroph

Organisms that obtain food by consuming other living things

autotroph

Organisms that make their own food

photosynthesis

The process by which autotrophs use the energy of sunlight to produce high-energy carbohydrates—sugars and starches—that can be used as food

What is ATP made up of?

ATP consists of adenine, a 5-carbon sugar called ribose, and three phosphate groups

Adenosine diphosphate (ADP)

looks almost like ATP, except that it has two phosphate groups instead of three. Contains some energy, but not as much as ATP. When a cell has energy available, it can store small amounts of it by adding phosphate groups to ADP, producing ATP.

ADP Example

Like a rechargeable battery that powers the machinery of the cell

Releasing Energy

Cells can release the energy stored in ATP by breaking the bonds between the second and third phosphate groups

Efficient energy storage

Because a cell can add or subtract these phosphate groups, it has an efficient way of storing and releasing energy as needed

Using Biochemical Energy

One way cells use the energy provided by ATP is to carry out active transport

Sodium-Potassium pumps

ATP provides the energy that keeps these pumps working, maintaining a balance of ions on both sides of the cell membrane (3 sodium out, 2 potassium in)

ATP and muscle movement

ATP powers movement, providing the energy for motor proteins that contract muscles and the power of the movement of cilia and flagella

ATP and protein synthesis

Energy from ATP powers the synthesis of proteins and responses to chemical signals at the cell surface

ATP storage efficiency

ATP is not a good molecule for storing large amounts of energy over the long term

ATP supply

It is more efficient for cells to keep only a small supply of ATP on hand

Regenerating ATP

Cells can regenerate ATP from ADP as needed by using the energy in foods like glucose

Pigment

Light-absorbing molecules in plants that gather the sun's energy

Chlorophyll

The plants' principal pigment

thylakoid

saclike photosynthetic membranes that chloroplasts contain an abundance of

stroma

the fluid portion of the chloroplast outside of the thylakoids

NADP+

(Nicotinamide adenine dinucleotide phosphate) carrier molecules that accept and hold 2 high-energy electrons along with hydrogen ions

Light-dependent reactions

the first set of reactions that require the direct involvement of light and light-absorbing pigments

Light-independent reactions

During these reactions, ATP and NADPH produced in the light-dependent reactions are used to produce high-energy sugars from carbon dioxide. No light is required to power the light-independent reactions.

Light

Energy from the sun travels to Earth in the form of light. Sunlight is a mixture of different wavelengths, many of which are visible to our eyes and make up the visible spectrum.

Visible spectrum

Our eyes see the different wavelengths of the visible spectrum as different colors: red, orange, yellow, green, blue, indigo, and violet.

Chlorophyll A

A type of chlorophyll found in plants, characterized by a lighter green - blue-green color.

Chlorophyll B

A type of chlorophyll found in plants, characterized by a darker green - yellow green color.

Leaves

Reflect green light, which is why plants look green.

Carotene

An organic pigment that absorbs light in other regions of the spectrum, contributing to the red and orange colors seen when chlorophyll breaks down.

Chloroplasts

where photosynthesis takes place inside organelles

Energy Collection

Because light is a form of energy, any compound that absorbs light absorbs energy (pigment). Chlorophyll absorbs visible light especially well.

High-Energy Electrons

Electrons produced by chlorophyll that are highly reactive and require a special carrier to transport them.

Electron carrier molecules

A compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to make another molecule.

Reactants

Starting material in photosynthesis, which includes water and carbon dioxide.

Products

End result of photosynthesis, which includes high-energy sugars and oxygen.