Chapter 4: Cells and Energy pt. 1

1. Chemical Energy and ATP

All cells need chemical energy

The chemical energy used for most cell processes is carried by ATP.

• ATP: A molecule that transfers energy so that cells can use it.
  • ATP uses energy from the breakdown of molecules.
• ADP: Molecule that can be converted into ATP by adding a phosphate group.

Organisms break down carbon-based molecules to produce ATP.

• Foods must be broken down into carbon-based molecules in order to create ATP for energy.
  • The type of food can affect how much ATP is produced.

A few types of organisms do not need sunlight and photosynthesis as a source of energy.

• Organisms like plants rely on sunlight to produce energy through photosynthesis
  • Organisms like animals rely on sunlight indirectly through eating plants.
• Certain organisms do not require sunlight and find other energy sources.
• Chemosynthesis: The process by which some organisms use chemical energy instead of light energy to make carbon-based molecules.
• Chemosynthetic organisms make their own food like plants.

2. Overview of Photosynthesis

The overall process of photosynthesis produces sugars that store chemical energy

Photosynthetic organisms are producers.

• Producers are organisms that create a source of chemical energy for themselves and other organisms.
  • Plants are producers because the energy they create through photosynthesis is used when other organisms consume the plants.
• Photosynthesis: A process that captures energy from sunlight to make sugars that store chemical energy.
  • The food chain usually begins with sunlight being the direct energy source for plants.
  • Plants absorb visible light for photosynthesis.
• Chlorophyll: A molecule that absorbs energy in visible light.
  • Found in chloroplasts, an organelle in plant cells.

Photosynthesis in plants occurs in chloroplasts

• Chloroplasts need the grana and the stroma for photosynthesis.
• Grana are stacks of thylakoids.
• Thylakoids: Compartments in chloroplasts that contain chlorophyll and light-absorbing proteins.
• The stroma is the fluid outside the thylakoids.
• Light-dependent reactions: Reactions that capture energy from sunlight in or near the thylakoids.
  • Water and sunlight are needed for this.
• Light-independent reactions: Reactions that use energy from the light-dependent reactions to make sugars.
  • Occur in the stroma of chloroplasts.
  • CO2 is needed for this.
  • Sugars that are formed from these reactions store the light energy that was captured.

Photosynthesis equation:

6CO2 + 6H2O → C6H12O6 + 6O2

3. Photosynthesis in Detail

Photosynthesis requires a series of chemical reactions.

The first stage of photosynthesis captures and transfers energy.

• Photosystems: Molecules that transfer captured energy.
  • Used during light-dependent reactions.

Overview of the Light-Dependent Reactions

• During light-dependent reactions, energy is captured and transferred to electrons.
• Energy from electrons is used to make energy carriers (ATP and NADPH)

Photosystem II and Electron Transport

• In photosystem II energy is absorbed from sunlight.
  • The energy is transferred to electrons.
• Electron transport chain: Transports electrons after they leave the chlorophyll.
  • Electrons from broken down water molecules replace the electrons that left the chlorophyll.
  • Within the chain, the electrons’ energy is used to push hydrogen ions into the thylakoid.

Photosystem I and Energy-Carrying Molecules.

• In photosystem I , energy is absorbed from sunlight as well.
  • The energy is added to electrons which may be from photosystem II.
  • NADPH is produced with the new energy from the electrons
  • NADPH can be used to transfer energy for light-independent reactions.

ATP Production

• ATP is produced with the hydrogen ions building in the thylakoid with the electrons’ help.
• ATP synthase: An enzyme that completes the production of ATP
  • ATP synthase adds phosphate groups to ADP to make ATP.

Summary of the Light-Dependent Reactions

• Energy is captured from sunlight and produced into oxygen, NADPH, and ATP.
  • Energy from ATP and NADPH can be used to make sugars.

The second stage of photosynthesis uses energy from the first stage to make sugars.

• Light-independent reactions do not need sunlight but need energy from ATP and NADPH.

The Calvin Cycle

• Calvin Cycle: Cycle that uses carbon dioxide and energy from ATP and NADPH to make simple sugars.
  • When carbon dioxide is added to the cycle, carbon molecules are formed and bonded into sugars.

Summary of the Light-Independent Reactions

• Energy from ATP and NADPH and carbon dioxide enter the Calvin cycle.
• Sugars are formed from carbon molecules and leftover products are recycled to be used again.

Functions of Photosynthesis

• Photosynthesis is important for plants’ growth and development, for regulating the environment with oxygen, and for producing food for other organisms.

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