chapter 8 photosynthesisflanneryscience.weebly.com/uploads/2/5/3/1/25316760/...a photosynthesis road...
TRANSCRIPT
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Chapter 8 Photosynthesis
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THE BASICS OF PHOTOSYNTHESIS
• Photosynthesis
– is used by plants, algae (protists), and some bacteria
– uses the energyfrom sunlight to convert water and carbon dioxide into high-energy carbohydrates(glucose and starch)
– oxygen is a waste product!!!
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The Simplified Equation for Photosynthesis
6 O2
6 H2O C6H12O6 6 O2
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A Photosynthesis Road Map
• The initial incorporation of carbon from the atmosphere into organic compounds is called carbon fixation.
– This lowers the concentration of carbon dioxide in the atmosphere.
– Deforestation reduces the ability of the biosphere to absorb carbon by reducing the amount of photosynthetic plant life.
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Chloroplasts: Sites of Photosynthesis
• Chloroplasts are
– the site of photosynthesis
– found mostly in the interior cells of leaves.
• Inside chloroplasts are interconnected, membranous sacs called thylakoids, which are suspended in a thick fluid called stroma.
• Thylakoids are concentrated in stacks called grana.
• Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits.
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Light and Pigments
How do plants capture the energy from sunlight?
• They use light absorbing molecules called pigments found in chloroplasts.
• the main pigment of plants is chlorophyll, and it is found in the thylakoid membrane of a chloroplast.
• when these pigments absorb light they also absorb the light’s energy which raises the energy level of the electrons in the chlorophyll molecules
• these high energy electrons then go on to “power” photosynthesis.
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A Photosynthesis Road Map
• Photosynthesis occurs in two multistep stages:
1. the light reactionsconvert solar energy to chemical energy
2. the Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide.
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A Photosynthesis Road Map
Light Reactions
Chlorophyll absorbs solar energy and is
then converted to ATP from ADP and NADPH
from NADP+ and gives off O2 gas as a
by-product.
WAIT!!!! BUT, WHAT IS NADP+ and NADPH??????
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NADP+ (Light Reactions)
• NADP+ (nicotinamide adenine dinucleotide phosphate) is an electron carrier molecule.
• When sunlight excites electrons in the chlorophyll, the electrons gain a lot of energy!!!
• These electrons then require a special electron carrier molecule which is NADP+.
– Think of theses electrons as hot coals from a campfire, you wouldn’t pick them up with your hands to move them from one place to the next, instead you would use a pan, or a carrier to transport them.
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NADP+ (Light Reactions)
• This electron carrier molecule accepts a pair (2) high energy electrons and transfers them along with most of their energy to another molecule.
• This process is called electron transport.
• NADP+ is a carrier molecule that can carry 2 high energy electrons plus a hydrogen ion (H+) to form NADPH!!!
NADP+ 2e- + H+ NADPH
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Figure 7.3-1
Light
H2O
O2
Chloroplast
Lightreactions
NADPH
ATP
– –
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The Calvin Cycle
Welcome to the Dark Side……
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A Photosynthesis Road Map
Calvin Cycle
• Uses the products of the light reactions (ATP and NADPH) to power the production of sugar from CO2.
• Enzymes that drive the CC are in the stroma.
• DOES NOT REQUIRE LIGHT directly!!!
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Figure 7.3-2
Calvincycle
CO2
NADP+
ADPP
Sugar
Light
H2O
O2
Chloroplast
Lightreactions
NADPH
ATP
– –
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3 Factors That Affect the Rate of Photosynthesis
• Water Supply
• Shortage of water can slow or stop photosynthesis
• Temperature
• Photosynthesis depends on enzymes that function best between 0°C and 35°C
• Light Intensity
• Increasing light intensity increases the rate at which photosynthesis occurs, to a point.
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Post Lecture Questions!
In plants, photosynthesis takes place inside the
a) thylakoids.
b) chloroplasts.
c) photosystems.
d) chlorophyll.
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Post Lecture Questions!
NADPH is produced in light-dependent reactions and carries energy in the form of
a) ATP
b) high-energy electrons
c) low-energy electrons
d) ADP
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Post Lecture Questions!
What is another name for the Calvin cycle?
a) light-dependent reactions
b) light-independent reactions
c) electron transport chain
d) photosynthesis
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Post Lecture Questions!
Which of the following factors does NOT directly affect photosynthesis?
a) wind
b) water supply
c) temperature
d) light intensity