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Chapter 8: Energy and
Photosynthesis
Energy and Photosynthesis
• Energy is necessary for all life
–Plants and green organisms:
• Trap light energy in the form of sunlight and store it for later use
–All other organisms:
• Eat green plants to obtain energy
Adenosine Triphosphate (ATP)
• Energy molecule• Composed of:
– Adenosine molecule– Ribose sugar– 3 phosphate groups
• ATP becomes available for a cell to use when the bonds between the phosphate groups are broken– Releases energy when a phosphate group is removed– Bond breaks between the 2nd and 3rd phosphate
groups• Results in adenosine diphosphate (ADP)
• ATP is a small molecule– Stored energy (ex: a battery)
• Cells use energy to maintain homeostasis
Photosynthesis• Photo-: means light
• Synthesis: to put together
• Process that uses the sun’s energy to make simple sugars
• 2 phases
– Light-dependent reactions
– Light-independent reactions
History• Van Helmont (1600’s)
– Planted seedling in pot of soil, watering it regularly
– Concluded plant mass comes from the water
• Priestley (1700’s)– Candle with glass jar cover flame died– Mint sprig and candle with glass jar cover
flame burned– Conclusion: plants release oxygen
• Ingenhous– Supported Priestley will occur only when
mint plant is exposed to light
Photosynthesis Requirements
• Light (sun)• Carbon Dioxide (from the air)
– Taken in to plants through little openings in the leaves called stomata
• Water (from the ground)– Taken in through the roots of plants
• Chlorophyll and enzymes in the plant• Rate of photosynthesis depends on:
– The availability of sunlight, CO2, and H2O– The intensity (brightness) of light– Temperature (20-35º C is optimal)
• White light mixture of different wavelengths of light– Visible spectrum ROYGBIV
• Pigments: molecules that absorb specific wavelengths of sunlight– Ex: Chlorophyll (in chloroplasts): a and b
• Absorbs well in blue and red light• Absorbs most wavelengths except green (reflects
green light)• Makes plants appear green
– Other plant pigments:• Xanthophyll: yellow pigment• Carotene: orange pigment
• Equation: 6CO2 + 6H2O + light C6H12O6 + 6O2
Carbon Dioxide + Water Sugar + Oxygen gas• Chloroplast: cell organelle where
photosynthesis occurs– Light-dependent reactions take place in the
thylakoid membrane (contains pigments)
• Picture of a chloroplast:– Grana: stack of thylakoids– Stroma: outside of the thylakoids– Photosystem: clusters of pigment and protein
that absorb light energy (found in thylakoids)
Review:
1. Match the scientist with the appropriate experiment or conclusion:
Priestley van Helmont Ingenhousz_____ Plants need sunlight to produce oxygen
_____ Plants gain most of their mass by taking in water
_____ Using a candle and a jar, he observed that plants produce a substance that kept the candle burning
_____ He measured the mass of the soil in which a plant grew
_____ He observed plants exposed to light
Light-Dependent Reactions
• 1st phase• Requires light• Converts light energy into
chemical energy• ATP produced fuels light-
independent reactions• NADP+: electron carrier
– Holds 2 high-energy electrons and H+
– Converts NADP+ to NADPH
• Light reactions use trapped light energy to convert ADP to ATP and NADPH
– Occurs in the grana of chloroplasts
– Splits water (photolysis)• H: needed to make glucose• O: released as a waste product into the
atmosphere
Light
Light reactions
Dark reactions
ATP
H+
C6H12O6 (glucose)
(in grana) (in stroma)H2O as waste
O2 as waste
H2O in CO2 in
Light-Independent Reactions
• Does not require light
• Called dark reactions or the Calvin cycle
• Process of actually making glucose (uses CO2 to make simple sugars/starches)
– Uses energy from ATP and NADPH
• Can occur in the light or the dark
• Requires enzymes
• Occurs in the stroma of chloroplasts
• Any glucose not used immediately can be stored as starch or sugars
• Chemosynthesis
– Process of making food from inorganic compounds
– Does not use sunlight
• Uses Sulfur in deep sea vents
• Methanogens use Carbon Dioxide and Hydrogen
Autotrophs• Use photosynthesis
or chemosynthesis
– Make their own food
Bell Ringer:
1. The light-dependent reactions take place within the __________ membranes.
2. The light-independent reactions are also known as the ________.
3. In the light-dependent reactions, the gas ____ is produced.
4. High-energy sugars are produced during the _______ reactions.
5. The light-independent reactions take place in the ________.