Transcript PhotosynthesisStructure

Photosynthesis
Chloroplast Structure
&
Reactants  Products
Plant Cells Contain Chloroplast – the organelles
that carry on photosynthesis converting light
energy into sugar!
Gas Released
Gas Used
Light
energy
6 CO2 + 6
H2O
Carbon dioxide Water
C6H12O6
Photosynthesis
+ 6
O2
Glucose Oxygen gas
Raw Materials
Simple Sugar
Photosynthesis
• Chloroplasts are
concentrated in
mesophyll, the green
tissue in the interior of
a leaf
• Membranes in the
chloroplast form the
framework where many
of the reactions of
photosynthesis occur
Fig. 7-2a
Leaf Cross Section
Leaf
Mesophyll
Vein
CO2 O2 Stoma
Mesophyll Cell
Chloroplast
The Chloroplast
• A chloroplast contains two membranes (as do
mitochondria)
• A thick fluid called the stroma fills the inner
compartment of the chloroplast
• Suspended in the stroma are the thylakoids, a
system of interconnected individual
membranous sacs, which enclose another
compartment known as the thylakoid space
• The thylakoids are arranged in stacks called
grana
Chloroplast
Outer and inner
membranes
Thylakoid
Stroma
Granum
Thylakoid
space
Intermembrane
space
The Chloroplast
• Built into the thylakoid membranes are the
chlorophyll molecules that capture light
energy
• Photosynthesis occurs throughout a plant (all
the green parts), but is concentrated in the
leaves
• A plant will invest much of its energy into the
production of its leaves in order to capture as
much light energy as possible
Make like a tree and…
• Leaves are designed to capture light and
increase the absorption of carbon dioxide
• Carbon dioxide enters the leaf (and oxygen
exits the leaf) via the stomata, tiny pores
protected by guard cells
• Water is supplied to the tree via its roots, but
may exit the leaves when the stomata are
open (a catch 22!); why stomata open at night
in many plants
Pigments
• Pigments are light-absorbing molecules built
into the thylakoid membranes
• Pigments absorb some wavelengths of light,
but reflect others
• We do not see the absorbed wavelengths
(because their energy has been absorbed by
the pigment molecules); we see the
wavelengths that the pigment reflects!
Pigments
• A leaf is green because chlorophyll absorbs
colors other than green; absorbs light most
strongly in the blue and red, but poorly in the
green
• Different pigments absorb different
wavelengths
• Chloroplasts contain different types of
pigments
Pigments
• Chlorophyll A
(a type of
chlorophyll
pigment)
absorbs light
mainly in the
blue-violet (high
energy) and
Chlorophyll B
red (low energy)
wavelengths
Light
Chloroplast
Thylakoid
Reflected
light
Absorbed
light
Transmitted
light
•In addition to
chlorophyll,
other
pigments,
known as
accessory
pigments are
present in
plants; these
include
carotene, and
cyanins, colors
like orange &
brown.
Pigments
Light
Chloroplast
Reflected
light
Absorbed
light
Transmitted
light
Autumn color change
• Autumn leaf color is a phenomenon that
affects the normally green leaves of deciduous
trees and shrubs, changing to reds and yellows
(and various shades in between)
• In late summer, the veins
that carry fluids into and
out of the leaf are
gradually closed off, and
chlorophyll decreases
Autumn color change
• When chlorophyll concentrations decrease at
the end of summer, some of these other
pigments – which are usually masked by
chlorophyll – reveal their colors
• Carotene, for example, is especially longlasting variations of orange color
http://ohad.me/?showimage=53
The Chloroplast Structure Cont.
Fig. 7-2b
Chloroplast
Outer and inner
membranes
Thylakoid
Stroma
Granum
Thylakoid
space
Intermembrane
space
Fig. 7-2a
Leaf Cross Section
Leaf
Mesophyll
Vein
CO2 O2 Stoma
Mesophyll Cell
Chloroplast
Fig. 7-6b
Light
Reflected
light
Chloroplast
Absorbed
light
Thylakoid
Transmitted
light
Fig. 7-0c
Light
energy
6 CO2 + 6
H2O
Carbon dioxide Water
C6H12O6
Photosynthesis
+ 6
O2
Glucose Oxygen gas