Photosynthesis Capturing Solar Energy
Jan 04, 2016
Photosynthesis
Capturing Solar Energy
Overview of Photosynthesis
(glucose)• Occurs in some bacteria or chloroplast of plants and
protists • Carbon dioxide (CO2) is reduced to produce glucose
• Energy required is captured from the sun by chlorophyll
• Photosynthesis has a Light reaction and a Dark reaction
Fig. 7.2
A more colorful photosynthesis Fig 6-7
What is chlorophyll?Chloroplasts contain several pigments:
– Chlorophyll a– Chlorophyll b– Carotenoids
Chlorophyll absorbs Red and Blue light from the visible spectrum but reflects Green light.
Fig. 6-3
Light absorption in photosynthetic bacteria (7.5)
Light-Dependant Reaction• Occurs on thylakoid membranes of the
chloroplast• Only occurs in the presence of light• Two parts: Photosystems and Electron
Transport Chains (E.T.C.)• Transfers light energy to energy molecules –
ATP and NADPH
Light Reaction (7.10)
Photosystem II• Water loses 2 electrons and releases O2 .
• Light energizes the 2 electrons • e- passes through E.T.C. which produces ATP• ATP is carried over to the Calvin cycle
Photosystem I• Electrons are energized again • Energized electrons bond with a proton and
NADP+ to form NADPH• NADPH is carried over to the Calvin Cycle.
Light Reaction (7.14)
Light Independent (Dark) Reaction• Doesn't require light.• Occurs in stroma of the chloroplast
Calvin Cycle1. 6 CO2(1C) bonds with 6 RuBP(5C) and splits
to form 12 PGA (3C)2. ATP and NADPH (From Light Reaction)
reduces 12 PGA to 12 PGAL(3C)3. 2 PGAL forms Glucose (6C) (or other sugars)
remaining 10 form 6 RuP(5C)4. More ATP turns 6 RuP into 6 RuBP
Dark Reaction
Regulation of Photosynthesis
• Require CO2, H2O and Light
• Plants need to regulate the absorption of CO2 and H2O
• Stomata – openings allow CO2 in, O2 & H2O out.
Stomata – open and close with the help of guard cells (NIB)
Gas exchange (7.2)
Some plants are specialized to survive in dry climates.
Types of Plants
• C3 plants:– Use CO2 directly from the air
– Are very common and widely distributed
• C4 plants:– Close their stomata to save water during hot and
dry weather – Can still carry out photosynthesis
• CAM plants:– Are adapted to very dry climates – Open their stomata only at night to conserve water
C4 and CAM (7.14)
How much photosynthesis? (Do not copy)
• Photosynthetic organisms absorb more energy than humans consumes in a year
• In all, photosynthetic organisms convert around 104,900,000,000,000 Kg of carbon into organic compounds each year
• Bacteria have higher SA/V and consequently more efficient at absorbing light and producing glucose
Photosynthesis Again