Plants
Anatomy, Physiology &
Photosynthesis
Plant anatomy
• Aerial portion
– absorb light energy
– gas exchange of O2,
CO2 & H2O
– stomata (holes)
– Structural support
• Terrestrial portion
– anchorage
– H2O absorption
– nutrient uptake
Leaf epidermal peel
Stomata regulate uptake and
release of gases not by
pressure but by simple
diffusion.
In order to exchange gases
stomata must remain open
and lose large amounts of
water.
Is this a good strategy?
Leaf cross section
Cohesion and
adhesion of water!
Water moves due to a
concentration
gradient and negative
pressure!
Typical Ranges for Components of Xylem and Phloem Saps in Higher
Plants
Concentrations (μg mL-1)
Substance
Sugars
Amino acids
P
K
Ca
Mg
Mn
Zn
Cu
B
NO3NH4+
Xylem
Phloem
Absent
200-1,000
70-80
200-800
150-200
30-200
0.2-6.0
1.5-7.0
0.1-2.5
3.0-6.0
1,500-2,000
7-60
140,000-210,000
900-10,000
300-550
2,800-4,400
80-150
100-400
0.9-3.4
8-23
1.0-5.0
9-11
Absent
45-846
What is photosynthesis?
• The conversion of electromagnetic energy
to chemical energy
• Light photons supply the energy to remove the
carbon from carbon dioxide and link them together
to form a compound of glucose.
light
6 CO2 + 6 H2O
C6H12O6 + 6 O2
Recall I mentioned that you learned 1 of the 2 most important
chemical equations, well this is the other!
1st Law of thermodynamics
• Energy can not be created or destroyed; it
can only undergo conversion from one
form to another
• Therefore photosynthesis does not create
energy
Photosynthesis
• Process of converting light energy to
chemical energy that is useful for
biological systems.
• Almost all energy on this planet uses
energy originally derived through the
process of photosynthesis.
The Overall Equation for
Photosynthesis
• The reactants and products of the reaction
Light
energy
Carbon
dioxide
Water
Photosynthesis
Glucose
Oxygen
gas
Unnumbered Figure 7.1
How plants capture electromagnetic energy
•
Plant pigments absorb light energy
– chlorophyll a, chlorophyll b, carotenoids
Chlorophyll a
Where are the pigments located
within a plant cell?
•
chlorophyll within the thylakoid
membrane
chemical equation for photosynthesis
light
6 CO2 + 6 H2O
C6H12O6 + 6 O2
Light dependent reactions:
2H2O + 2ADP +2Pi +2NADP+ Æ O2 + 2ATP + 2NADPH + 2H+
Energy from 4 photons of light
No CO2 used
O2 produced as a waste product
H Æ H+ and NADPH, electrons from H end up in NADPH
NADPH is 2 times greater in energy than ATP
Light independent reactions
6CO2 Æ C6H12O6 + 6 O2 used in other reactions
Energy and 12H
Heat
Heat
Energy
12NADPH Æ 12 NADP+
and
18 ATPÆ 18ADP + 18Pi
Light dependent reactions + light independent reactions
6CO2 + 12NADPH +18ATP + 12H2O + 12H+ Æ C6H12O6 + 12NADP+ +18PiH2O + 18ADP
Summary equation again:
6 CO2 + 6 H2O
C6H12O6 + 6 O2
Three phases of photosynthesis
• Sunlight energy captured
• Using sunlight energy to synthesize ATP (adenosine
triphosphate)
• Using ATP to synthesize organic compounds from
carbon dioxide
(fixation of inorganic carbon)
Bottom line: we went from light energy to electrical energy
and then from electrical energy to chemical bond energy.
Why a carbohydrate?
• If a plant can produce an energetic
molecule, like ATP, why bother
synthesizing glucose then later convert it
back to ATP? PORTABILITY
• ATP and NADPH are fairly unstable
compounds. Imagine trying to send these
compounds around without losing energy
as they go.
Summary of Photosynthesis
cellular respiration
cellulose
starch
other organic compounds
Respiration vs. Photosynthesis?
• Respiration takes energy stored in the
chemical bonds of glucose and converts it
to ATP.
• Photosynthesis takes energy from light
and converts it into glucose.
Photosynthesis
6 CO2 + 6 H2O Æ C6H12O6 + 6 O2
Respiration:
C6H12O6 + 6O2 Æ 6CO2 +6H2O
C6H12O6+ 6O2
Photosynthesis
Respiration
Light
Energy
6H2O + 6CO2
Heat
Energy
You should be able to:
•
•
•
•
Identify the main regions of a plant (roots, stems and leaves) identify their
main functions, the structures within each region that help them carry out
those functions, and the physical factors that affect each.
Explain how the physical environment, particularly water and light
availability, can affect plant growth form.
Identify the main purpose of photosynthesis.
For both the light dependent and light independent reactions be able to
identify:
– The source of energy driving each set of reactions, and where it ends up.
– The important molecules needed by each set of reactions.
– The products of each set of reactions.
•
•
•
•
Explain why glucose is a better way of transporting energy than ATP or
NADPH
Explain the importance of the polarity of water to the process of getting
water from the roots to the leaves.
Explain the importance of the products of photosynthesis to the process of
respiration and vice-versa.
Explain the energetic relationship between photosynthesis and respiration.