Plants

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Plants

• Anatomy, Physiology Photosynthesis

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Plant anatomy

• Aerial portion
• absorb light energy
• gas exchange of O2, CO2 H2O
• stomata (holes)
• Structural support
• Terrestrial portion
• anchorage
• H2O absorption
• nutrient uptake

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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
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Cohesion and adhesion of water!
Water moves due to a concentration gradient and
negative pressure!
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Typical Ranges for Components of Xylem and Phloem
Saps in Higher Plants
Concentrations (?g mL-1)
Substance Xylem Phloem
Sugars Absent 140,000-210,000 Amino acids
200-1,000 900-10,000 P 70-80
300-550 K 200-800
2,800-4,400 Ca 150-200
80-150 Mg 30-200 100-400 Mn
0.2-6.0 0.9-3.4 Zn
1.5-7.0 8-23 Cu
0.1-2.5 1.0-5.0 B 3.0-6.0
9-11
NO3- 1,500-2,000 Absent NH4
7-60 45-846
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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!
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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

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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.

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The Overall Equation for Photosynthesis

• The reactants and products of the reaction

Light energy
Photo-synthesis
Glucose
Oxygen gas
Carbon dioxide
Water
Unnumbered Figure 7.1
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How plants capture electromagnetic energy

• Plant pigments absorb light energy
• chlorophyll a, chlorophyll b, carotenoids

Chlorophyll a
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Where are the pigments located within a plant
cell?

• chlorophyll within the thylakoid membrane

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chemical equation for photosynthesis
light
6 CO2 6 H2O C6H12O6 6 O2
Light dependent reactions
2H2O 2ADP 2Pi 2NADP ? O2 2ATP 2NADPH
2H
Energy from 4 photons of light
O2 produced as a waste product
No CO2 used
H ? H and NADPH, electrons from H end up in
NADPH NADPH is 2 times greater in energy than ATP
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Light independent reactions
6CO2 ? C6H12O6 6 O2 used in other reactions
Energy and 12H
Heat
Energy
Heat
12NADPH ? 12 NADP and
18 ATP? 18ADP 18Pi
Light dependent reactions light independent
reactions
6CO2 12NADPH 18ATP 12H2O 12H
? C6H12O6 12NADP 18PiH2O 18ADP
Summary equation again
6 CO2 6 H2O C6H12O6 6 O2
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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.

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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.

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Summary of Photosynthesis
cellular respiration cellulose starch other
organic compounds
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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.

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Photosynthesis
6 CO2 6 H2O ? C6H12O6 6 O2
Respiration
C6H12O6 6O2 ? 6CO2 6H2O
C6H12O6 6O2
Respiration
Photosynthesis
Light Energy
Heat Energy
6H2O 6CO2
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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.