Photosynthesis and Cell Respiration

Alejandra Macias


PHOTOSYNTHESIS : Is the process by which light energy in converted to chemical energy.

  • Photosynthesis happens in the chloroplast.

  • Reactants
  1. Sunlight
  2. Water (H20)
  3. Carbon Dioxide (CO2)

  • Products
  1. ATP
  2. Oxygen (O2)
  3. Glucose (C6H12O6)

Stage 1: Energy is captured from the sunlight , and an electron gets excited and leaves the chlorophyll. Then is used to produce ATP.

Stage 2: Electron Travels along the electron transport chains. The movement of the electron passing through the electron transport chain provides energy needed to make ATP.

Stage 3: The dark reaction : Carbon Dioxide (CO2) is used to make compounds in which energy is stored.

The Calvin Cycle: A series of enzymes assisted chemical reactions that produces a three carbon sugar.

The Calvin Cycle :

Stage 1. A molecule of carbon dioxide is added to a five carbon compound.

Stage 2. The resulting 6-carbon splits into 2 three-carbon compounds.

- Phosphate groups from ATP and electrons from NADPH are added to form three-carbon sugars.

Stage 3. One of the sugars is used to make organic compounds for energy to be stored.

Stage 4. The other sugar is used to regenerate the initial five compound, used to restart the cycle.

They Might Be Giants - Photosynthesis

Cellular Respiration

Cellular Respiration: Is the process cells use to harvest the energy in organic compounds to make ATP. (Oxygen makes this process more efficient but it can be done without oxygen.)

  • Reactants:
  1. Glucose
  2. Oxygen

  • Products
  1. Carbon Dioxide
  2. Water
  3. ATP

Aerobic- Metabolic processes that requires oxygen.

Anaerobic- Metabolism process that do not require oxygen.

Stage 1: Glucose is converted to pyruvate producing ATP and NADPH (In small amounts).

Stage 2: When oxygen is present, pyruvate and NADPH are used to make a large amount of ATP. This is known as Aerobic Respiration.

-When oxygen is not present, pyruvate is converted to either lactate and carbon dioxide.

- Aerobic Respiration occurs in the mitochondria in eukaryotic cells, and in the cell membrane of the prokaryotic cell.

Stage 1: Glucose is broken down in the cytoplasm.

Breaking down of Glycolysis:

  • Step 1: In a series of 3 reactions, phosphate groups from 2 ATP molecules are transferred to glucose molecule.

  • Step 2: In 2 reactions, the 6 carbon compound is broken down to 2 three-carbon compounds, each with a phosphate.

  • Step 3: 2 NADH molecules are produced, and 1 more phosphate groups is transferred to each 3-carbon compound.

  • Stage 4: In 4 reactions, each 3-carbon pyruvate compound is converted to a 3-carbon pyruvate, producing 4 ATP molecules in the process.

Stage 2: Producing of ATP, when oxygen is present , pyruvate produced in glycolysis enters a mitochondrion and is converted to a 2- carbon compound.

Krebs Cycle

Step 1: Acetyl-CoA combines with a 4-carbon compound.

Step 2: Carbon dioxide is released from the 6-carbon compound, forming a 5- carbon compound. Electrons are transferred to NAD+, making a molecule of NADH.

Step 3: Carbon dioxide is released from 5-carbon compound, resulting in a 4-carbon compound. A molecule of ATP is made, and a molecule of NADH is also produced.

Step 4: The existing 4-carbon compound is converted to a new 4-carbon compound. Electrons are transferred to an electron acceptor called FAD, making a molecule of FADH2.

Step 5: The 4- Carbon compound is converted to the 4-carbon that started the cycle and another NADH is produced.

Fermentation is the absence of oxygen.

when oxygen is not present Aerobic Respiration cannot occur.

-The electrons are not transferred from NADH so NAD+ cannot be recycled.

Instead Fermentation allows the recycling of NAD+ using an organic hydrogen acceptor.

Two Types of Fermentation

  • Lactic Acid Fermentation

- Can be used in the production of foods such as yogurt and some cheeses.

During exercise pyruvate in muscles is converted to lactate when the cells loos oxygen.

  • Alcohol Fermentation.

- Pyruvate is broken down to ethanol Carbon Dioxide is released throught the process.

Pyruvate is first converted to a 2-carbon compound, releasing carbon dioxide.

Cell respiration

Differences and Similarities Between Cellular Respiration and Photosynthesis.

Photosynthesis (Reactants)
  1. Carbon Dioxide
  2. Water

Photosynthesis (Products)
  1. Glucose
  2. Oxygen

Cellular Respiration (Reactants)

  1. Glucose
  2. Oxygen

Cellular Respiration (Products)

  1. Carbon Dioxide
  2. Water


  • The reactants of Photosynthesis are the products of Cellular Respiration.
  • The products of Photosynthesis are the reactants of Cellular Respiration.
  • Cellular Respiration has fermentation and photosynthesis does not.
  • Photosynthesis used radiant energy (Sunlight)
  • Cellular Respiration release of chemical energy (ATP)


  • ATP is a key molecule in each
  • They both pass through the Electron Transport Chain to produce ATP.
  • They both pass through a certain amount of cycles.
  • Glycolysis is generated in both (cell respiration) and in Calvin Cycle (Photosynthesis)
  • Can observe emergent properties via multiple steps in both processes.