Download Photosynthesis - Mercer Island School District

Photosynthesis
From Sunlight to Sugar
What is Photosynthesis?
Photosynthesis is a process that captures
energy from sunlight to make sugars used
as food for producers. The light energy is
stored as chemical energy in the sugars.
What is Photosynthesis?
• Autotrophs
(producers) use
sunlight energy to
build carbohydrates.
Organisms that can
perform photosynthesis:
Plants, Algae and some
Bacteria
Where does it occur in the cell?
Occurs in the
Chloroplast of a cell
Grana
The Chloroplast
• Contains Chlorophyll, a green pigment that absorbs
and traps light energy from the sun.
• Grana: within the chloroplast. Stacks of thylakoids.
• Thylakoid: Membrane “sacs” that contain the
chlorophyll.
• Stroma: Fluid filled space that surrounds the grana.
Chlorophyll
Membranes of the thylakoids contain chlorophyll.
Absorbs most light; reflects green (and yellow) light (this is why
we see it as green).
Plants have other photosynthetic pigments: Carotenoids
These are not green so they absorb and reflect other spectrums
of light. They are less abundant so they get masked by
chlorophyll making leaves look green.
Xanthophyll
Carotene
Chlorophyll
Green (and yellow) light are
Reflected.
What is the overall Photosynthesis
Reaction?
(light)
6 H2O + 6 CO2
(Water + Carbon Dioxide)
(chlorophyll)
C6H12O6 + 6 O2
(Glucose + Oxygen)
Some released into
The atmosphere
Taken into the leave
Absorbed by the roots
Transferred to all
Parts of the plant
http://www.youtube.com/watch?v=mYbMPwmwx88
Steps of Photosynthesis
• STEP 1 is the LIGHT
REACTION
– The “Photo” part;
Light is required
– Occurs in the
Thylakoid of a
chloroplast.
– Chlorophyll traps light
energy
Steps of Photosynthesis
STEP 2: CALVIN CYCLE
• The light Independent Reaction or “Dark Reaction”.
• The “Synthesis” part of photosynthesis; Glucose is
made.
• Occurs in the stroma of the chloroplast.
Stroma
Step 1: Light Reaction Detail
• Light energy causes chlorophyll electrons to get
excited and gain energy.
• the excited electrons lose energy which is used to
perform the following:
Split water: 2 H2O  2H+ + O2
Trapped as ATP: ADP + P + energy from the ePicked up by NADP (an electron carrying molecule):
e- + 2H+ + NADP  NADPH + H+ (The electron carrier)
Step 1: Light Reaction
Split water releasing e-
ATP formed
NADPH picking up e-
http://www.youtube.com/watch?v=BK_cjd6Evcw
Step 1: Light Reaction
Overview:
• Used:
– H2O
– Light Energy
• Produced:
– NADPH from NADP picking up free Hydrogen Ions
– O2 from split H2O
– ATP from energy given off by excited chlorophyll
electrons
Sunlight + H2O
ATP + NADPH + O2
Step 2: Calvin Cycle Detail
• From the Light Reaction comes hydrogen
ions (from NADPH), electrons, and ATP.
• Calvin Cycle: CO2 and H+ are cycled
through a series of reactions with the help
from ATP producing glucose (C6H12O6)
which is used as food for the plant and has
chemical energy stored in it.
Step 2: Calvin Cycle
ADP + P
Carbon
Molecule
Complex
Continues
Cycle
To the
Light
Reaction
Glucose
NADP Back
Step 2: Calvin Cycle
• ATP from the Light Reaction provides
energy to drive the cycle.
• Energy from ATP is stored in newly
formed Carbon bonds of glucose.
Step 2: Calvin Cycle
Overview
• No light needed
• Used:
– H+ carried by NADPH
– ATP
– CO2
• Produced:
– C6H12O6 (Glucose)
– ADP + P (Back to Light Reaction)
– NADP+ (Back to Light reaction)
ATP + NADPH + CO2
C6H12O6
Reactants diffused
into the chloroplast
Products leaving
Chloroplast
Steps of Photosynthesis
(light/energy)
6 H2O + 6 CO2
(chlorophyll)
C6H12O6 + 6 O2
Step 1: Light Reaction:
Sunlight + H2O
ATP + NADPH + O2
Step 2: Calvin Cycle (Dark Reaction):
ATP + NADPH + CO2
C6H12O6
Review
• What is the purpose of photosynthesis?
• Write the overall balanced equation and
circle the main product. Underline the
waste product.
Review
• What is the purpose of photosynthesis?
To trap light energy in sugars which are used
as food for the plant.
• Write the overall balanced equation and
circle the main product. Underline the
waste product.
(light/energy)
6 H2O + 6 CO2
(chlorophyll)
C6H12O6 + 6 O2
Review
• What is the purpose of the light reaction?
• What is the purpose of the Calvin Cycle?
• What is transferred from the Light
Reaction to the Calvin Cycle?
Review
• What is the purpose of the light reaction?
To absorb light energy
• What is the purpose of the Calvin Cycle?
To produce simple sugar (glucose)
• What is transferred from the Light Reaction to the
Calvin Cycle?
ATP and NADPH
Review
• If you put a plant in green light and blue light,
what would you expect in terms of its growth?
• A) Both plants will not grow since white light is
necessary.
• B) Plant in green would grow, plant in blue light
would not.
• C) Plant in green would not grow, plant in blue
would grow.
• D) Both would grow
Review
• If you put a plant in green light and blue light,
what would you expect in terms of its growth?
• A) Both plants will not grow since white light is
necessary.
• B) Plant in green would grow, plant in blue light
would not.
• C) Plant in green would not grow, plant in blue
would grow.
• D) Both would grow