Chapter 3
Photosynthesis
Where does all that
glucose come from?
How does it do that?
radiant energy
What is it?
Photosynthesis uses radiant energy from the
sun to fix carbon dioxide into carbohydrates
CO2
CO2
Photosynthesis
glucose
CO2
CO2
CO2
CO2
The captured radiant energy is stored within
the bonds of the carbohydrate as chemical
energy
Photosynthesis is used by many autotrophs
to make their own food
 egs. vascular plants, algae, cyanobacteria
http://www.smhi.se/weather/baws_ext/info/2004/Baltic_algae_2004_en.htm
Overall (Net) Equation
Photosynthesis
glucose + O
CO2 + H2O + energy
Energy  glucose
2
H+
CO2
H+
H2O
O2
Overall (Net) Equation
Cellular Respiration
Photosynthesis
glucose + O2  Energy
CO2 + H2Oglucose
+ energy
H+
CO2
H+
H2O
O2
Photosynthesis and Cellular Respiration
appear to be reverse processes, but they
use very different mechanisms
Similarities
Both cellular respiration and Photosynthesis
are similar in that both use:
1. electron transport chains
2. dissolved enzymes
3. membrane-enclosed space for chemiosmosis
Plant Tissues
Plants are made of various types
of tissues
 egs. Stem, leaves, roots,
reproductive organs
The main site of photosynthesis
is the leaves, although
chloroplasts are found in all
green plant parts
Leaves
Vascular
Epidermis
Mesophyll
Bundles
cuticle
epidermis
palisade mesophyll
spongy mesophyll
vascular bundle
stomate
Leaves
cuticle
epidermis
palisade mesophyll
spongy mesophyll
vascular bundle
stomate
 Leaves have 3 main types of tissues:
1. Epidermis


Usually one cell thick and secrets a waxy
cuticle to prevent water loss
Pores called stomata found in lower
epidermis
Leaves
cuticle
epidermis
palisade mesophyll
spongy mesophyll
vascular bundle
stomate
2. Mesophyll


Most photosynthesis occurs here
Two layers of parenchyma cells
•
Palisade layer
◦
•
Cell arrangement maximizes exposure to light
Spongy layer
◦
Loose arrangement of cells leaving air spaces for gas exchange
Leaves
cuticle
epidermis
palisade mesophyll
spongy mesophyll
vascular bundle
stomate
3. Vascular Bundles


Transport system of the plants
Contains xylem (water transport) and
phloem (sugar transport)
Opening/Closing Stomata
The guard cells (stomata) can be opened and
closed to regulate gas exchange and minimize
water loss in leaves
Chloroplast
Pore
OPEN
CLOSED
Guard Cells
Opening Stomata
Cell is now hypertonic to surroundings
K+
To open the stomata:
K+
ATP
K+
ATP
H+
K+
H+
H2O
ATP
ATP
K+
ATP
H2O
H+
H+
ATP
K+
CLOSED
OPEN
 Potassium ions (K+) are
actively pumped into the
guard cells (uses ATP)
 This causes the GCs to
become hypertonic to their
surroundings
 Water is drawn into the
GCs, increasing turgor
pressure
Closing Stomata
ATP
ATP
ATP
K+
K+
K+
ATP
K+
K+
K+
OPEN
ATP
ATP
To close the stomata:
 K+ pumps deactivated
allowing ions to diffuse out
 Water drawn back out of the
GC with the K+ ions
 Decrease in turgor
pressure makes GCs go
limp (flacid)
Closing Stomata
Cell is now hypotonic to surroundings
K+
To close the stomata:
K+
H2O
H2O
H+
H+
K+
K+
K+
K+
OPEN
H+
H+
 K+ pumps deactivated
allowing ions to diffuse out
 Water drawn back out of the
GC with the K+ ions
 Decrease in turgor
pressure makes GCs go
limp (flacid)
Closing Stomata
To close the stomata:
H2O
H2O
H+
H+
H+
CLOSED
OPEN
H+
 K+ pumps deactivated
allowing ions to diffuse out
 Water drawn back out of the
GC with the K+ ions
 Decrease in turgor
pressure makes GCs go
limp (flacid)