The Structure of the Leaf
and the Process of
Photosynthesis
Unit 4- Part 2
Mrs. Stahl
Leaves
• Major site of photosynthesis / food production.
• Minimize water loss by collecting water and
transpiration.
• Take in carbon dioxide and produce oxygen
through the stomata.
• Stomas are tiny pores in the leaf.
• Protects stems and roots with shade and shelter.
Basic Structure
• Blade- usually broad and flat; collects the
sunlight
• Petiole- stem that holds the leaf blade up.
4 Types of Plant Tissues
• 1. Ground Tissue- most common
• 2. Dermal Tissue
• 3. Vascular Tissue
• 4. Meristematic Tissue- division
of new cells.
Covers the outside.
Has a waxy cuticle to limit
water loss.
Bark= dead cells
Makes up much of the
inside.
Provides support and stores
materials in roots and stems.
Packed with chloroplasts.
Transport water, mineral
nutrients, and organic
compounds to all parts of
the plant. Xylem and
phloem.
Meristematic Tissue
•
•
•
•
Growth tissue
Where cell division occurs
Turns into ground, dermal, or vascular
Apical Meristems- tips of roots and stems->
primary growth occurs here.
• Lateral Meristems- secondary growth. Increase
the thickness of roots and stems.
The Importance of Guard Cells and
Stomata
• The stomata is the site of transpiration and gas
exchange.
• Guard cells surround each stomata, and open and
close by changing shape.
• Day- stoma is open, allowing the carbon dioxide to
enter and water to evaporate.
• Night- close
Factors that cause the guard cells to
open and close
• Temperature, humidity, hormones, and the
amount of carbon dioxide in the leaves tells
the guard cells to open and close.
Physiological Process of
Transpiration,
Photosynthesis, and
Cellular Respiration
Transpiration
• Evaporation of water from leaves
• Water is pushed up through the xylem by root
pressure created from water moving up the soil to
the plants root system and into the xylem-> results
in dew drops on grass
• Water is also pulled up through cohesion through
the xylem tissue-> creates a negative pressure or
tension from roots to leaves.
Rate of Transpiration
•
•
•
•
Slows in high humidity
Accelerates or speeds up in low humidity
Increases with wind
Increases with intense light= increased
photosynthesis and water vapor
Photosynthesis
• Defined as the process that captures
energy from sunlight to make sugars that
store chemical energy.
• Location- Chloroplast of plant cells.
Photosynthesis
• Chloro= Green
• Phyll= Leaf
• Plast = Molded
chloroplast
leaf cell
leaf
Two Processes
• Light dependent reactions= NEED SUNLIGHT
• Light independent reactions= DO NOT NEED
SUNLIGHT
Equation
Chloroplast- refer to your
foldable
• Three main parts are:
–Grana- stacks of coined shaped
membranes.
Thylakoid
– Inside the grana and they are the little disks.
They contain chlorophyll and other light
absorbing pigments.
– Photosystems- light collecting units. They are
proteins that organize chlorophyll and other
pigments into clusters.
Add this onto
your foldable.
Stroma
– Fluid that surrounds the grana inside the
chloroplast.
• Chlorophyll- the molecule in the
chloroplast that absorbs the energy from
the sunlight. There are two main types,
chlorophyll a and b, that absorb mostly
red and blue light. Other pigments absorb
the green.
• Green color in plants comes from the
reflection of the green wavelengths by
chlorophyll.
You do not
have to put
this in your
notes!!!
Just a little
fun fact!
Carotenoids are yellow-orange
pigments which absorb light in violet,
blue, and green regions.
When chlorophyll breaks down in fall,
the yellow-orange pigments in leaves
show through.
Fall Foliage
So let’s begin
• The sunlight hits the leaves and
CO2 is let in through the stomata
(little pores) while H2O is let in
through the roots.
1st
Light Dependent
Reactions or Light
Reactions
– Requires sunlight
– Take place in the thylakoids
– Water and sunlight are needed
– Chlorophyll absorbs energy
– Energy is transferred along the thylakoid
membrane, and then to light-independent
reactions
– Oxygen is released as a waste product
2nd
Light Independent Reactions
• Uses the energy transferred from the light
dependent reactions to make sugars.
• Reactions occur in the stroma
• Calvin Cycle- metabolic pathway found in the
stroma of the chloroplast; where carbon enters
in the form of CO2, and leaves in the form of
glucose.
• ATP is produced as a final step. The enzyme ATP
synthase is responsible for making ATP by adding
phosphate groups to ADP.
Now that we have a brief overview
let’s look at it in a little more detail.
NADPH
• Electron carrier
• Transports high energy electrons around
during photosynthesis
• Like a school bus – picks up at point A, drops
off at point B
Light Dependent Rxn
• Light E converted to chemical E
• Light E causes an electron (e-) to leave
chlorophyll in photosystem II
• Light splits water - photolysis
– ½ O2 is a waste product
– Electrons given to chlorophyll to replace lost
electron
– H+ used later
Photosystem II captures and transfers
energy.
Light Dependent Rxn
• e- from PS II passes down an electron
transport chain
– Energy is released to help pump H+ into inner
thylakoid space
• Creates a H+ gradient to be used later
• e- “lands” in PS I
– More light = more energy to e– e- jumps off PS I into NADP+ with H+ from water
Light Dependent Rxn
• H+ inside thylakoid space exits through a
protein called ATP synthase
– Energy stored in H+ gradient makes ATP
• NADPH and ATP go to light independent
rxn/Calvin cycle
Photosystem I captures energy and
produces energy-carrying molecules.
Light Independent / Calvin Cycle
• Chemical E is converted to glucose
• Carbon fixation: when carbon from the atmosphere is
“fixed” into an organic carbon molecule
• Rubisco is the enzyme used fix carbon in the first step.
– Most abundant enzyme on Earth!
1. CO2 enters cycle
2. Energy Input from LDR
Each cycle creates
one 3C molecule.
Two cycles = 1
glucose
4. 5C molecules
regenerated
3. 6C glucose produced
Chloroplast
Sunlight entering
Thylakoid
Chlorophyll
Energy is
transferred to
electrons
Oxygen
Energy carrying molecules
ATP & NADPH
transferred to the LIR
H2 O
Glucose
CO2 from the
atmosphere
Calvin Cycle in the
stroma
Questions to review
• 1. Where do the light dependent reactions
occur?
• 2. Where do the light independent reactions
occur?
• 3. What two reactants are shown entering the
chloroplast?
• 4. What two products are shown leaving the
chloroplast?
• 5. What does the Calvin Cycle produce?
Answers
•
•
•
•
•
1. Thylakoid membrane
2. Stroma
3. Water and carbon dioxide
4. Oxygen and sugar
5. Glucose
Videos
https://vimeo.com/7316737
http://www.mhhe.com/biosci/bio_animations/02_MH_Photosynthesis_Web/
http://www.youtube.com/watch?v=lDwUVpOEoE4
Let’s Summarize- Bellwork
Write the Equation for Photosynthesis
Process
Light Dependent
Reactions
Light Independent
Reactions/Calvin Cycle
Location
Reactants
Ending Products
Let’s Summarize
6CO2 + 6H2O → C6H12O6 + 6O2
Process
Location
Reactants
Ending Products
Light Dependent
Reactions
Thylakoid Membrane
Sunlight
H2O
ATP
NADPH
O2
ATP
NADPH
CO2
Glucose
Light Independent
Stroma
Reactions/Calvin Cycle