Cell Energy
Main Topics
• Photosynthesis
• Cellular Respiration
Objectives
• Know the roles of photosynthesis and cell
respiration in the ecosystem
• Describe reactants and products in both
photosynthesis and cellular respiration
• Compare and contrast systems in plants and
animals for nutrient absorption, hormone
response, and gas exchange
Vocab
•
•
•
•
•
•
Photosynthesis
Cellular Respiration
Autotroph
Heterotroph
Aerobic
Anaerobic
How do organisms obtain and use
energy?
All cells use chemical energy carried by
ATP
• Autotroph- can make their own food
– Ex: plants, algae
• Heterotroph- cannot make their own food
– Must eat others for food
– Ex: animals, humans
Photosynthesis
• A process that captures energy from sunlight
to make sugars that store chemical energy.
• Sun’s energy >>> Chemical energy (sugar)
• Takes place in the chloroplast
Note: energy for almost all organisms begins as
sunlight.
Photosynthesis
Factors that affect photosynthesis
• Water
• Temperature
• Light intensity
Chlorophyll
• A molecule in chloroplasts that absorbs some
of the energy in visible light
• Two main types of chlorophyll (a and b)
– Absorb mostly red and blue wavelengths of light
– Reflect green wavelength of light
Chloroplast
Chloroplast overview
• Two main parts of the chloroplast needed for
photosynthesis are the grana and the stroma.
• Grana (granum)- stacks of coin-shaped
compartments called thylakoids.
• Stroma- fluid that surrounds the grana inside a
chloroplast.
• Thylakoids- membranes of thylakoids contain
chlorophyll.
Photosynthesis in detail
• Light-dependent reactions
– Capture energy from sunlight
– Take place in membrane of thylakoids
– Water and sunlight needed
• Light-independent reactions
– Also called the Calvin Cycle
– Uses energy from light-dependent reactions to
make sugars
– Take place in the stroma
– Carbon dioxide needed
Light-dependent reactions
• Water molecules are broken down
• Oxygen molecules are released
• Energy carried along thylakoid is transferred to ATP
Light-independent reactions
Calvin cycle
• Carbon dioxide is added
• Energy from light-dependent reactions is used
• Sugar is formed (usually glucose)
• Photosynthesis video
Plant anatomy (nutrient absorption)
Plant anatomy (gas exchange)
Cellular Respiration
• Process that releases chemical energy from
sugars and other carbon-based molecules to
make ATP when oxygen is present.
• Aerobic process- it requires oxygen
• Takes place in the mitochondria
Mitochondria
3 steps of cell respiration
1. Glycolysis
2. Krebs Cycle
3. Electron Transport
Glycolysis
• Splits glucose into two three-carbon
molecules and makes two molecules of ATP
• Anaerobic process- does not require oxygen
• Takes place in the cell’s cytoplasm (not in the
mitochondria)
Krebs cycle
• Takes place in the interior space, or matrix, of
the mitochondrion
• Uses the three-carbon molecules from
glycolysis
• Small number of ATP molecules are made
• Carbon dioxide given off as waste
• Energy is transferred to the electron transport
chain
Electron transport
• Takes place in the inner membrane of the
mitochondrion
• Energy from the Krebs cycle is transferred to
the inner membrane
• Oxygen enters the process
• Large number of ATP molecules are made
• Water and heat are given off as waste
Cellular Respiration
• Up to 38 ATP molecules are made from the
breakdown of 1 glucose molecule
• Used when oxygen is present
Fermentation
• Does not make ATP, but it allows glycolysis to
continue
• Used when oxygen is not present
• Produces lactic acid, which causes your
muscles to burn during hard exercise
• Crash Course: Cell Respiration