1.3. How Organisms Acquire Carbon and Energy

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What do organisms use carbon and energy for?

Carbon

  • Build up cells
  • Example: Cell division

Energy

  • Perform energy-consuming reactions
  • Examples: Movement, cell division

ATP – The cell’s energy currency

Model of an ATP molecule. Carbon atoms are black, hydrogen white, nitrogen blue, oxygen red, and phosphorus yellow.Model of an ATP molecule. Carbon atoms are black, hydrogen white, nitrogen blue, oxygen red, and phosphorus yellow.

An ATP molecule may be cleaved into Pi and ADP.An ATP molecule may be cleaved into Pi and ADP.When an ATP molecule is cleaved into ADP + Pi, energy is released.

  • The cell uses this energy to perform energy-consuming reactions.

What's an “energy currency”? The ATP cycle.

  • The cell “pays” in ATP as soon as an energy-consuming reaction needs to take place.
  • The cell “gets paid” in ATP by breaking down e.g. fat and sugar.

The ATP cycle.The ATP cycle.

From where do organisms get their energy?

Chemotrophs

Get energy through cellular respiration

  • Oxidation of sugar (glucose)

Cellular respiration

Glucose + oxygen → carbon dioxide + water + energy

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

The energy released is converted into ATP.

Phototrophs

Get energy from sunlight (photosynthesis)

  • Synthesize glucose

Photosynthesis

Water + carbon dioxide + energy → glucose + oxygen

6H2O + 6CO2 + hν → C6H12O6 + 6O2

The energy in light (denoted "hν") is used to assimilate carbon dioxide and synthesize glucose.

From where do organisms get their carbon?

Autotrophs

Autotrophs use carbon dioxide as their primary carbon source while heterotrophs use organic molecules.Autotrophs use carbon dioxide as their primary carbon source while heterotrophs use organic molecules.Make their own “food” from CO2.

  • Example: photosynthesis

Heterotrophs

Eat other organisms

  • Examples: humans, fungi, most bacteria …

Different types of organisms

Organisms may be classified according to their primary energy and carbon sources:

 

Auto­trophs

Hetero­trophs

Type of organism

Photo­auto­troph

Chemo­auto­troph

Photo­hetero­troph

Chemo­hetero­troph

Energy source

Light

In­organic com­pounds

Light

Organic com­pounds

Carbon source

CO2

CO2

Organic com­pounds

Organic com­pounds