Photosynthesis and respiration

Photosynthesis and respiration

The Photosynthesis is the biological process where solar energy is used to transform carbon dioxide and water into carbohydrates and oxygen. The cellular respiration is the biological process by which carbohydrates and oxygen are transformed to produce energy in form of ATP.

DefinitionLight-driven process of organic compound formation.Process of using organic compounds to obtain chemical energy.
Where is it done?Chloroplasts (plants and algae)

Plasma membrane (cyanobacteria)

Cytoplasm and mitochondria (eukaryotes)

Plasma membrane (bacteria, archaea)

Who do it?Photoautotrophic organisms:
  • Plants
  • Algae
  • Cyanobacteria
Most living organisms:
  • Plants
  • Animals
  • Mushrooms
  • Protozoa
  • Bacteria
What does it produce?
  • Glucose (C 6 H 12 O 6 )
  • Oxygen O 2
  • Carbon dioxide (CO 2 )
  • Water (H 2 O)
  • ATP
  • Light dependent
  • Independent of Light
  • Glycolysis
  • Krebs cycle
  • Oxidative phosphorylation
Electron transport chainPhotosystems I and IIComplexes I, II, III and IV
  • C3 photosynthesis
  • C4 photosynthesis
  • CAM photosynthesis
  • Aerobic respiration
  • Anaerobic respiration
  • Production of carbohydrates.
  • Release of oxygen.
  • Transformation of light energy into chemical energy.
  • Obtaining energy from carbohydrates.
  • Release of carbon dioxide for the greenhouse effect.
Equation6CO 2 + 6H 2 O + light → C 6 H 12 O 6 + 6O 26 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + ATP

What is photosynthesis?

Photosynthesis is the process of transforming carbon dioxide and water to form sugars and oxygen. In this process the energy of light is transformed into chemical energy.

The organisms that carry out photosynthesis are photoautotrophs: plants, algae, and cyanobacteria. In plants, photosynthesis takes place in the leaves, where chloroplasts are found. In cyanobacteria, the photosynthetic machinery is found in the plasma membrane.

The general chemical reaction of photosynthesis is summarized in the following equation:

6CO 2 + 6H 2 O + light → C 6 H 12 O 6 + 6O 2

where from carbon dioxide, water and light energy glucose and oxygen are obtained that is released into the atmosphere.

Phases of photosynthesis

Photosynthesis reactions are classified into two phases:

  • Light-dependent phase : energy derived from sunlight activates an electron in chlorophyll, which enters the chloroplast’s electron transport chain and produces ATP, oxygen, and reducing agents.
  • Light independent phase (or dark phase): carbon fixation reactions are carried out, where ATP and reducing agents produced in the light phase to convert carbon dioxide into sugar.

Types of photosynthesis

Plants can be differentiated by the type of photosynthesis they carry out:

  • Photosynthesis C3 : in most plants carbon dioxide binds the three-carbon molecule phosphoglyceric acid.
  • C4 photosynthesis : in corn and sugar cane, carbon dioxide binds to the four-carbon molecule oxaloacetic acid.
  • CAM Photosynthesis – Found in succulent plants.

What is cellular respiration?

The breath is the cellular process that allows to use the energy stored in carbohydrates using oxygen. The products are carbon dioxide, ATP and water . ATP is used for metabolic reactions while CO 2 leaves the cell and is then eliminated.

Most living organisms carry out cellular respiration:

  • in plants, animals, fungi and protozoa it is carried out in the mitochondria and the cytoplasm.
  • In some bacteria and archaea it is carried out on the plasma membrane.

The general chemical reaction of respiration is summarized in the following equation:

6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O

where glucose reacts with oxygen resulting in ATP, carbon dioxide, and water.

Phases of cellular respiration

Cellular respiration reactions can be classified into three phases:

  • Glycolysis : it is the first route of decomposition of glucose to obtain energy, pyruvate and reducing agents.
  • Krebs cycle or citric acid cycle : Pyruvate enters a cycle of enzymatic reactions to break down into carbon dioxide and produce ATP and reducing agents.
  • Oxidative phosphorylation : it is the metabolic pathway that captures electrons and reducing agents to produce more ATP.

Types of cellular respiration

Respiration can be of two types depending on the compound that accepts electrons:

  • Aerobic respiration : oxygen O 2 is the molecule that accepts electrons to transform into water (H 2 O).
  • Anaerobic respiration : in environments where O 2 is not present , some microorganisms (bacteria and archaea) use other molecules as electron acceptors, for example sulfate and nitrate.

Relationship between photosynthesis and cellular respiration

Photosynthesis and respiration are complementary processes:

  • Photosynthesis uses solar energy to produce organic compounds; respiration uses organic compounds to obtain chemical energy.
  • The organic compounds of photosynthesis serve as food for organisms that are not photosynthetic.
  • Carbon dioxide is transformed into organic compounds by photosynthesis; organic compounds are transformed into carbon dioxide by respiration.
  • In photosynthesis, oxygen is released that is then used in respiration.
  • Photosynthesis and respiration are part of the life cycle of carbon.
  • Both processes use chains of electron transporters to capture the energy needed for other reactions.


Written by RockedBuzz

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