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Energy of Living Things. The process by which light energy is converted to chemical energy is called photosynthesis. Organisms that use energy from sunlight or inorganic substances to make organic compounds are called autotrophs.

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energy of living things
Energy of Living Things
  • The process by which light energy is converted to chemical energy is called photosynthesis.
  • Organisms that use energy from sunlight or inorganic substances to make organic compounds are called autotrophs.
  • Most autotrophs, especially plants, are photosynthetic organisms.
  • Some autotrophs, including certain bacteria, use inorganic substances to make organic compounds.
  • Organisms that must get energy from food instead of directly from sunlight or inorganic substances are called heterotrophs.
  • Heterotrophs, including humans and other animals, get energy from food through the process of cellular respiration.

1. The prefix photo- means “light.” The root word synthesis comes from a Greek word that means “putting together.” How could knowledge of these word parts help you define the word photosynthesis?

2. The prefix auto- means “self.” The root word troph comes from a Greek word that means “to feed.” How could knowledge of these word parts help you define the word autotroph?

3. The prefix hetero- comes from a Greek word that means “other.” How could knowledge of this prefix and the root word troph help you define the word heterotroph?

4. An analogy is a comparison. Complete the analogy: Heterotrophs are to humans as autotrophs are to . What relationship forms the basis of this analogy?

5. How does cellular respiration help your body perform its life functions?

food chain
Food Chain
  • Sunlight
  • Autotroph
  • 1st trophic level
  • 1% of energy from sun
  • Heterotroph
  • 2nd trophic level
  • 10% of energy from plant
  • Herbivore
  • Heterotroph
  • 3rd trophic level
  • 10% of energy from cow
  • Carnivore/omnivore
where does the energy come from
Where does the energy come from?
  • Scientists estimate that only 10 percent of the energy present at each level of the food chain is available to the next level.
  • Scientists also estimate that only 1 percent of the light energy from the sun that reaches photosynthetic organisms is converted to chemical energy during photosynthesis.
  • Assume that 1 million kilocalories (kcal) of energy from the sun is available to the autotrophs in the food chains above. Determine the amount of energy that will be available at every level of each food chain.
  • Explain why most food chains consist of no more than three or four levels. What happens to the stored energy that does not advance from one level of the food chain to the next?
  • A 55 kg person at rest requires an average of 54 kcal/hour. The same person engaged in activity requires an average of 87.5 kcal/hour. What is the percent increase in required kcal/hour between rest and activity?
  • Which would be a more efficient diet for an active person, plant foods or meat? Explain
  • Earth’s population is increasing at a rate that may outpace our ability to produce enough food. Why are some people promoting vegetarianism as an answer to this dilemma?


The process by which plant cells, some bacteria and some protists use solar energy to produce ATP. The conversion of unusable sunlight energy into usable chemical energy, with the help of pigments such as chlorophyll and carotenoids.

The process includes two separate phases:

Light-dependent Reaction

Light-independent Reaction (Dark reaction)


Phase1:Light Reaction or photophosphorylation depends on sunlight to make products required in phase 2.

Phase2:Dark Reaction or Calvin Cycle occurs without the need of light, using products from phase 1 and recycling molecules to be reused in phase 1.

6co 2 6h 2 o c 6 h 12 o 6 6o 2
6CO2 + 6H2O  C6H12O6 + 6O2
  • The general equation for photosynthesis is above. Carbon dioxide combines with water to form glucose and oxygen with the use of sunlight for energy.
  • Glucose is the organic molecule used to make energy in living organism.
  • This process occurs in the chloroplasts of plant cells
photosynthesis occurs in the thylakoid disc within the chloroplast of the plant cell
Photosynthesis occurs in the thylakoid disc within the chloroplast of the plant cell.
  • Tree  leaf  cell  chloroplast  Thylakoid
light reaction
Light Reaction.
  • Requires light
  • Chlorophyll molecules are embedded in the membrane of the thylakoid disc
    • Light strikes the chlorophyll causing a chain reaction that converts light energy into chemical energy required by phase 2.
    • ATP & NADPH are made which are two high energy molecules
Light hits a chlorophyll which excites an electron
  • The electron then jumps to another protein, leaving the chlorophyll with 1 less electron
    • The electron continues down a series of proteins producing NADPH
  • A water molecule splits to donate an electron to the chlorophyll and releases O2 and H+ making the chlorophyll ready for another round
    • Oxygen is released into the atmosphere and H+ builds up in the thylakoid disc
    • The H+ is pumped out through diffusion to make ATP with the help of an enzyme
the final products
The final products
  • Each CO2 requires 3 ATP & 2 NADPH in the Calvin Cycle
  • 6 CO2 are required for each C6H12O6 molecule to be made
  • A total of 18 ATP & 12 NADPH are needed
review questions
Review Questions:
  • What are the reactants of photosynthesis?
  • What are the products of photosynthesis?
  • What is the electron donor to the chlorophyll?
  • Why does the chlorophyll need a new electron?
  • How does the electron leave the chlorophyll?
  • What happens to the electron that leaves the chlorophyll?
  • Where does the light reaction occur?
  • What happens to the electron donor?
  • How does hydrogen make ATP?
  • What are the final products of the light reaction? And where are these products going to be used?
  • What does photophosphorylation mean?
phase 2 calvin cycle
Phase 2: Calvin Cycle
  • Dark Reaction of CO2 Fixation
  • The second stage of photosynthesis, which takes place in the stroma (between the thylakoid disc and the chloroplast membrane) of the chloroplast, can occur without the presence of sunlight. In this stage, known as the Calvin Cycle, carbon molecules from CO2 are fixed into glucose (C6H12O6). The reactions of the Calvin Cycle is as follows:
1. A five-carbon sugar molecule called ribulose bisphosphate, or RuBP, is the acceptor that binds CO2.
  • This process, called CO2 fixation, by the enzyme, forming an unstable six-carbon molecule, breaking down to give two molecules of the three-carbon called phosphoglyceric acid (PGA).
2. The two 3PG molecules are converted into phosphoglyceraldehyde (PGAL) molecules, a three-carbon sugar phosphate, by adding a high-energy phosphate group from ATP, then breaking the phosphate bond and adding hydrogen from NADPH + H+.
3.Three turns of the cycle, using three molecules of CO2, produces six molecules of G3P. However, only one of the six molecules exits the cycle as an output, while the remaining five enter a complex process that regenerates more RuBP to continue the cycle. Two molecules of G3P, produced by a total of six turns of the cycle, combine to form one molecule of glucose.
overview of dark rxn
Overview of Dark Rxn
  • The Calvin Cycle needs to go around 6 times using 6 CO2 to make one glucose molecule.
  • Each time around the cycle 3 ATP are used. A total of 18ATP for one C6H12O6.
  • 18 ATP 18 ADP + 18 Pi
  • Each time around the cycle 2 NADPH are used. A total of 12 NADPH for one C6H12O6.
  • 12 NADPH  12 NADP+ + H +
  • The ADP, Pi, and NADP + go back to light reaction to be reused
questions on dark rxn
Questions on Dark Rxn.
  • What happens to the CO2 in the Calvin Cycle?
  • Where does the energy for this cycle come from?
  • Where do the used molecules, ADP, Pi, & NADP+, go?
  • How many turns of the cycle have to occur to form one glucose molecule?
  • How many CO2 molecules are needed?
  • How many ATP and NADPH molecules are needed?
  • Where do the molecules in the cycle come from?
  • Where does the glucose molecule go?
  • Are the water molecules and CO2 molecules used in the same reaction?