Photosynthesis
Chapter 8 in the Textbook
Chemical Energy and ATP
• What type of organic macromolecule is
shown in the diagram.
• The in the diagram label the following:
– Phosphate groups
– Sugar
– Nitrogenous Base
Chemical Energy and ATP
ATP (adenosine triphosphate) is the most important
molecule cells use to store and release energy
Energy: the ability to do work
Energy comes in many different forms:
• Light energy
• Mechanical Energy
• Chemical Energy
Chemical Energy and ATP
• When an organism uses the energy from ATP, the ATP is
converted into ADP
– ADP (Adenosine Diphosphate ) has only 2 phosphate groups.
– Cells can add a phosphate to ADP to make ATP to store
energy. (This requires energy)
– Where do YOUR cells get
the energy to convert
ADP into ATP?
– How is ATP and ADP
similar to rechargeable
batteries?
What do seeds need to grow?
Using scissors punch a hole in the bottom of each cup.
Cup 1 (No water): Add soil and seeds. Cover the cup with
plastic wrap so water cannot enter.
Cup 2 (No soil): Add cotton, water and seeds. Leave the cup
uncovered.
Cup 3 (No Light): Add soil, water and seeds, then cover with foil
to block out all light.
Cup 4 (Control): Add soil, water and seeds. Leave the cup
uncovered.
Chemical Energy and ATP
The mitochondria and the chloroplast are the most
important organelles in energy transformations.
• Chloroplast
– Uses the energy in sunlight to create glucose
– Found in the cells of plants and protists
• Mitochondria
– Uses the energy in
glucose to convert ADP
into ATP
– Found in the cells of all
eukaroytic organisms
(including plants!!!)
Chemical Energy and ATP
NADPH is a molecule that has a
similar function to ATP
• NADPH contains chemical
energy.
• When the cell uses the energy,
NADPH is converted into NADP+
• Energy from sunlight is
necessary to convert NADP+
back into NADPH
Chemical Energy and ATP
How could a small seed gain
enough energy to grow into
seed a giant tree?
Autotroph – uses energy
from the sun to produce food
Heterotroph – obtains energy
from food it consumes
Chemical Energy and ATP
Light and Pigments
Overall Photosynthesis Equation
6CO2 + 6H2O
Carbon
Dioxide
Water
LIGHT
C6H12O6 + 6O2
Glucose
Oxygen
Photosynthesis: the process where plants convert energy
from the sun into chemical energy stored in the bonds of
carbohydrates.
Light and Pigments
Light Speed, c = 2.9979 x 108 m/s
Or 670.6 million mph
How are the two types of
light different? How are
they similar?
Light and Pigments
Electromagnetic Spectrum
Wave length and energy are
inversely proportional
The smaller the wave length,
the more energy
Which type of light has more
energy, the blue or the red?
Explain.
Light and Pigments
• What colors of light
are being absorbed?
• What colors of light
are being reflected?
• What color would
the object appear if
there was no blue
light?
• Why are plants
usually green?
Light and Pigments
• Pigments – light
absorbing molecules
• Chlorophyll – the
most abundant
pigment in plants,
that absorbs blue
and red light.
Photosynthesis: An Overview
• Photosynthesis takes place in the
chloroplast
– Thylakoids – saclike photosynthetic
membrane in the chloroplast
– Stroma - the region outside of the
thylakoid membranes
Photosynthesis: An Overview
Photosynthesis is a complex process that can be broken
down into 2 steps:
The Light Reaction
(The light dependent Reaction)
Step 1: Photosystem II
• Photosystem: a cluster or chlorophyll and proteins
found in the thylakoids.
• Light is absorbed by photosystem II which creates high
energy electrons.
• A water molecule is split to provide more electrons and
hydrogen ions and oxygen is released.
Step 2: Electron Transport Chain
• The electrons from photosysem II move to the electron
transport chain.
• Electrons move from molecule to molecule to pump H+
ions from the stroma into the thylakoid space.
• What type of transport is used to move the H+ ions?
Explain
Step 3: Photosystem I
• Since the electrons used some energy pumping H+ ions
they need to be renergized.
• Light collected at photosystem I renergizes electrons.
• The electrons along with H+ ion combine with NADP+ to
from NADPH
Step 4: ATP Formation
• A high concentration of H+ have been pumped into the
thylakoid.
• The H+ “want” to move into the stroma. Why?
• The only way to get to the stroma is to go through a
protein called ATP Synthase.
• When H+ move through ATP Synthase a ADP molecule is
converted into ATP
The Dark Reaction
(The light independent Reaction)
• The NADH and ATP from
the light reaction move to
the stroma.
• The leaf absorbs CO2
from the atmosphere.
• The energy from the
NADH and ATP is used to
convert CO2 into
carbohydrates.
• What is the main function
of carbohydrates?
The Dark Reaction
(The light independent
Reaction)
• Each molecule of glucose
contains enough energy to
produce 36 ATP’s.
• Plants produce starch when
they need to store energy.
• Starch is a long chain of glucose.
Factors affecting Photosynthesis
Water
• Plants need water for photosynthesis
– In the light reaction a water molecule is
split apart in electrons and H+.
– Electrons and H+ are needed to create
NADPH and ATP
• If there is not enough water
– The plant will wilt because a lack or
turgor pressure
– The plant will stop photosynthesizing to
conserve water
• Can too much water harm a plant?
Factors affecting Photosynthesis
Temperature
• The chemical reactions that occur
during the light reactions and the
dark reactions are all controlled by
enzymes.
– Too cold: photosynthesis occurs
slowly because enzymes and
substrate move slower.
– Too hot: photosynthesis occurs
slowly because enzymes begin to
denature.
Factors affecting Photosynthesis
Light
• Light intensity determines the
rate of photosynthesis
– The more intense the light, the
faster the rate of photosynthesis.
• The pigments in plant can only
absorb certain wavelengths of
light.
– Green light is mostly reflected by
chlorophyll and will not affect the
rate of photosynthesis.
Photosynthesis and Cell Respiration
• Cell Respiration is the opposite of
photosynthesis.
– What is the equation for
photosynthesis?
– What is the equation for
respiration.
– Respiration breaks down
carbohydrates into ATP.
Photosynthesis and Cell Respiration
• Plants perform both
photosynthesis and respiration.
– Think: It would pointless to
make carbohydrates if you did
not break them down into
energy.