Photosynthesis (Chloroplast) and Cellular Respiration (Mitochondria)
Reading Guide
Photosynthesis and cellular respiration are the two main processes performed by most living
organisms to obtain usable energy from nature. While photosynthesis is performed by most
plants who can prepare their own food, most animals fulfill their energy requirements through
cellular respiration.
Photosynthesis is the process used by plant cells
to convert light energy from the sun into
chemical energy, so as to create energy-rich
carbohydrate molecules like glucose (C6H12O6).
Photosynthesis takes place in the cells of plant
leaves in structures called chloroplasts, which
contain chlorophyll. The plant cells absorb light
from the sun through the chlorophyll pigment, and using water and carbon dioxide obtained
from the environment, undergo a series of chemical reactions to produce carbohydrate
molecules
Photosynthesis Equations:
Carbon Dioxide + Water + Sunlight → Glucose + Oxygen
6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2
Cellular respiration is the process of breaking down food molecules to obtain energy and store
it in the form of adenosine triphosphate (ATP) molecules.
Plant cells, after creating sugar molecules through photosynthesis, undergo cellular respiration
to create ATP molecules.
Animals obtain food molecules from plants and other organisms, and then undergo cellular
respiration to obtain ATP molecules. All living organisms utilize these stored ATP molecules to
carry out their metabolic processes.
The process of photosynthesis involves two stages of
chemical reactions:
Light-dependent Reactions
This is the first stage of the photosynthetic process.
These reactions take place in the presence of sunlight, and use light energy from the sun to
produce ATP molecules and other molecules known as NADPH. These molecules are used as the
energy source to carry out the reactions in the next stage of photosynthesis.
Light-independent Reactions (Calvin Cycle)
In this stage, energy-containing sugar molecules are synthesized. The ATP and NADPH
produced in stage I are used to fuel the reactions in this stage. Here, CO2 molecules are
broken down and converted into sugars and other compounds. The Calvin Cycle is repeated
twice in order to yield one molecule of glucose
Cellular Respiration
Cellular respiration begins at this stage in the cytoplasm of
the cells, and yields 2 carbon-based molecules called
pyruvate, and 2 molecules of ATP. Oxygen plays no part
during this stage, so it is called anaerobic respiration.
Anaerobic Respiration
There are two types of anaerobic respiration: Lactic
Acid Fermentation and Alcoholic Fermentation. In lactic
acid fermentation, pyruvic acid is converted to lactic acid.
This causes muscle soreness. In alcoholic fermentation, pyruvic acid is converted to ethanol.
This is method used to make “moon shine”. Fermentation is important because it allows ATP to
be made even when oxygen is not available. However, this process is less efficient than creating
ATP when oxygen is present
Aerobic Respiration
This process takes place in specialized structures within the cell called mitochondria, and uses
the products of glycolysis, the pyruvate molecules, to release energy, along with CO2 and water
as the by-products of the reaction. The energy released is stored in the form of ATP molecules.
Usually, a total of 38 ATP molecules are produced.
Cellular Respiration Equations
Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP)
C6H12O6 + 6O2 → 6CO2 + 6H2O + 2900 KJ
Discussion Questions
1. Explain the difference between photosynthesis and cellular respiration.
2. What are products of photosynthesis? _______________________
3. Explain why the end product of photosynthesis is the beginning reaction of cellular
respiration.
4. What are the reactants of cellular respiration? _________________________
5. What type of respiration is used in prokaryotic cells _____________________
6. What type of respiration is used in eukaryotic cells_______________________
7. How much energy is produced after aerobic respiration?____________
8. REAL WORLD EXPERIENCE: Lactic Acid Fermentation vs. Alcoholic Fermentation. When
does fermentation occur normally (process/events)?
9. Photosynthesis takes place in____________(organelle) so cellular respiration takes
place in the ____________________ (organelle).
10. Define ATP:
Matching
a. Fermentation
e. 36ATP
b. Glucose and carbon dioxide
f. 38 ATP
c. Lactic Acid Fermentation
g. ATP and carbon dioxide h. Alcoholic Fermentation
_______
end product or aerobic respiration
_______
produces soreness
_______
(#)production of ATP in aerobic respiration
_______
production of ATP without oxygen
d. 2 ATP
“Either/Or”
Mark an “X” on the correct description.
utilizes sunlight to produce food molecules.
occurs only in plants and some bacteria
utilizes glucose molecules to obtain energy-storing ATP
molecules.
takes place in the cytoplasm and mitochondria of the cell.
uses glucose molecules and oxygen to produce ATP molecules and
CO2 as the by-product
involves using that chemical energy and breaking it down to
release energy.
occurs at all times
uses water, sunlight, and CO2 from the atmosphere to create
glucose molecules, and releases oxygen as a by-product.
using that chemical energy and breaking it down to release
energy.
takes place in all types of living organisms.
involves conversion of one type of energy into another: light
energy into chemical energy
takes place only when there is sunlight
takes place in two stages of light reactions and dark reactions.
takes place in plant leaves containing the chlorophyll pigment.
Photosynthesis
Cellular
Respiration