Honors Biology Chapter 7 PHOTOSYNTHESIS Uses energy from
Honors Biology Chapter 7 PHOTOSYNTHESIS Uses energy from sunlight Converts water and carbon dioxide from the environment into organic food molecules and oxygen gas
Photosynthetic organisms many kinds, terrestrial and aquatic Grasslands Oceans Freshwaters
Two Sets of Reactions 1. Light-dependent (light) Reactions In thylakoid membranes - chlorophyll absorbs sunlight - makes energy molecules ATP - Makes O2 gas - reduces electron carrier NADP+ 2. Light-independent reactions
Calvin cycle (dark reactions) Uses energy molecules from light reactions Fixes carbon dioxide Changes inorganic CO2 into a compound plants can use Oxidizes NADPH
Makes glucose 6 CO2 + 6 H2O C6H12O6 + O2 Visible light drives the light reactions <> Sunlight is white light, containing all colors
Colors of light Depends on wavelength () -Shorter wavelength - blue-violet end of spectrum higher energy -Longer wavelength -red-orange end of spectrum
lower energy Visible light: small part of Electromagnetic spectrum travels as a wave ---- behaves as a particle (photon) Shorter wavelength Longer wavelength
Higher energy Lower energy Absorption of Light Energy Plants absorb blue and red light best Photosynthetic pigments
Plants have multiple pigments to absorb as much sun energy as possible Chlorophyll a is the primary pigment starts the chain of reactions Chlorophyll b, carotenes, xanthophylls and others are accessory pigments. They absorb wavelengths that chlorophyll a cannot absorb use more of sunlight
Accessory Pigments Action Spectrum for Elodea Chromatography Separates a liquid mixture by solubility Colors of light absorbed by a chloroplast
Colors NOT absorbed are reflected or transmitted -- the colors we SEE Absorbed light energy is transferred to electrons in pigment -- energized electrons
Chlorophyll absorbs mostly from the red and blue ends of the spectrum - reflects green. Parts of a chloroplast Thylakoid membranes - have chlorophyll - absorb sunlight - site for 1st set of reactions
Grana stack of thylakoid sacs Stroma fluid surrounding thylakoids - site for 2nd set of reactions Parts of a Leaf What is a Photosystem? A cluster of pigments and other molecules in thylakoid membranes
Capture light energy Energized electrons begin reaction chain that makes ATP or NADPH Light reactions are a series of
oxidation and reduction reactions Oxidation lose energy Lose an electron (alone or on atoms) Lose a hydrogen atom (H+ + e-)
Lose a phosphate group (PO4) Be broken apart (decomposed, hydrolyzed) Reduction gain energy Gain electrons (alone or on atoms) Form more chemical bonds (synthesized) Electron carriers Coenzymes help in a reaction but are not
the catalyst Take electrons (and often H+) from one molecule in a chain of reactions and give them up in a later reaction a. Electrons transfer energy b. In photosynthesis, electron transfers help make energy molecules ATP and NADPH What is NADP?
NADP accepts electrons and H+ ions from water in 1st set of reactions NADP + H NADPH Gives them to CO2 in 2nd set of reactions NADPH - H NADP CO2 + H + e- glucose NADP is an electron and hydrogen
acceptor It carries e- and H+ ions until a later reaction NADP + H NADPH NADPH H NADP Light-Dependent Reactions
1. Photosystems absorb sunlight a. electrons from chlorophyll go to Electron Transport Chain b. Make ATP 2. Light splits water: a) H2O 2 H+ + 2 e- + O b) H+ reduce NADP NADPH c) Oxygen O2 gas d) Electrons - replace electrons lost from chlorophyll
Light Splits Water H2O 2 H+ + 2 e- + O Hydrogens (H+) reduce NADP NADPH Oxygen (need 2 water molecules) O2 Electrons - replace electrons lost from chlorophyll
Light Reactions reactant products 1. Water Also need -Sunlight -chlorophyll
1. ATP 2. NADPH 3. Oxygen gas How does light make ATP? Energizes electrons Electrons enter an
Electron Transport Chain Series of membrane proteins transfer electrons Electrons power ATP synthesis Chain of oxidation-reduction reactions Energy from electrons concentrates H+ ions forms a proton(H+) gradient in thylakoid space
Chemiosmosis ATP Synthase - enzyme in thylakoid membranes H+ ions diffuse through synthase enzyme
Phosphorylates ADP (ADP + P) Makes ATP ADP + P ATP Chemiosmosis Photosystem II makes ATP
Electrons from PS II go to PS I Photosystem I makes NADPH Light-Dependent Reactions Summary of Light reactions 1. Capture light energy, make ATP 2. Split water (H2O) into 2 H+ + O + 2e1) Electrons replace those lost from chlorophyll
2) O makes oxygen gas 3. Add H+ and e- to NADP NADPH 1) Later they become part of glucose molecule Light Reactions make: ATP
NADPH O2 2 1 3 See oxygen gas made by an aquatic plant
Melvin Calvin 1911-1997, chemist at Berkeley Used C-14* to trace path of carbon in photosynthesis Found cycle of reactions Nobel in Chemistry 1961 Light-Independent Reactions Calvin Cycle Dark reactions
In stroma of chloroplast Uses ATP made in light reactions Fixes CO2 from air Adds H+ from water Adds e- from ETC Makes GLUCOSE What is carbon fixing?
CO2 from air becomes part of organic compound These combine to make glucose Calvin Cycle in stroma
#2) Carbon is fixed 6-C compound, splits Start: 5-carbon cpd in stroma (RuBP) #3) (2) 3-C cpds
End: Remaining carbon RuBP #4) ATP and NADPH are used #5) (2) 3-C compounds 1 glucose How is sugar made?
carbon fixation rubisco enzyme 6-carbon compound 1) RUBP (5-C) bonds to CO2
makes a 6-C compound 2) This splits makes 2 (3-C) PGA RuBP 5 carbons PGA + H 3 carbons
3) PGA gets H from NADPH PGAL (G3P) 4) 2 G3P/PGAL 1 glucose Remaining G3P RuBP G3P3
2 G3P 5) Energy needed to build G3P from CO2 comes from ATP made in the light reactions glucose
6)Remaining G3P RUBP carbons Overview of Photosynthesis LE 7-5 Photosynthesis uses light energy to make food molecules
H2O Chloroplast CO2 Light Fixes carbon
NADP ADP Absorbs light energy Makes energy molecules ATP, NADPH
(CO2 becomes part of organic molecule) P
LIGHT REACTIONS (in thylakoids) Light splits water -makes O2 El ec
tro CALVIN CYCLE (in stroma) ATP ns
Uses energy molecules made in light NADPH Makes sugar O2
Starch Sugar Lipids proteins cellulose Factors Affecting Photosynthesis 1. Light bright sun, more energy
a. Long days (summer), more light absorbed b. Wavelength cannot absorb green light 2. Temperature warm, but not too hot a. Hot days stomata close to save water 3. Water soil must be moist a. Water comes up through xylem in veins b. Exits through open stomata
c. Water low? stomata close Environmental Factors affecting Photosynthesis How amount of light affects rate of photosynthesis plateau
At high light intensity, rate stays constant because all photosystems are being used At low light intensity, rate increases as light increases How CO2 concentration affects rate of photosynthesis
plateau At high CO2 concentration, rate is constant because all coenzymes are being used At low CO2 concentration, rate increases as CO2 increases
How temperature affects rate of photosynthesis Rate increases with increasing temp (energy) - To optimum Rate drops above
optimum temp -stomata close to save water -enzymes denature C3 plants in hot weather In hot, dry weather, most** plants close stomata to save water No more CO2 comes in
Photorespiration occurs intermediate products used for food no glucose made **C3 plants: CO2 is fixed into a 3-carbon compound in Calvin cycle Guard cells open/close stomata Close when [CO2]
or water is low Closed Open C-4 Plants C-4 plants fix and store CO2 in a 4-carbon compound while stomata are open
- use stored carbon when stomata close in hot weather can still make sugar Corn crabgrass Sugar Cane C-4 Pathway
Store carbon as a 4-carbon compound in special cells around veins called bundle sheath cells After stomata close, cells change stored carbon back to CO2 for Calvin cycle CAM Plants
Succulents pineapples cacti Fix CO2 during the night, when it is cool enough for open stomata - Do photosynthesis during the day, using the
stored carbon Carnivorous Plants Eat insects to get nitrogen Live where decomposition is slow, low N in soil Pitcher plant Venus Fly Trap
Hinged leaves with trigger hairs Insect walking on leaves touches hairs - Leaves close, insect digested Pitcher plant
Sweet nectar at bottom of tube - Insects stuck in nectar, digested Sundew eats insects Sugary dew attracts insects Insects get stuck -Leaves enclose and digest
-Absorb nutrients from insect Parasitic plants Supplement nutrition by taking from other organisms Dodder Plant Pure parasite cannot photosynthesize - Special roots tap into veins of host plant
Mistletoe supplements photosynthesis taps into host cell veins drains sap Indian Pipe Cannot photosynthesize Carotenes in nature
Where can we see carotenes, xanthophylls, and other pigments besides in autumn leaves? END Chapter 8
Photosynthesis reduces atmospheric CO2
Excess greenhouse gases: - from human activity -burning fossil fuels - deforestation - increases global warming - photosynthesis removes CO2 and helps moderate warming Greenhouse - Traps heat
indoors TALKING ABOUT SCIENCE 7.14 Mario Molina talks about earths protective ozone layer Nobel Prize winner Mario Molina has studied how pollutants are affecting Earth's ozone layer Solar radiation converts O2 high
in the atmosphere to ozone (O3) The ozone layer shields organisms on Earth's surface from damaging UV radiation CFCs have caused dangerous thinning of the ozone layer International restrictions on CFC use are allowing a slow recovery
LE 7-14b The ozone layer Southern tip of South America Antarctica
Pond Mud and its Bacteria (Winogradsky Column) Anaerobic Phototrophs - purple bacteria - green sulfur bacteria TRANSPORT IN A LEAF Water enters a leaf through the veins; xylem carries water up from
the soil. Water then diffuses from the veins into the mesophyll cells. -Carbon dioxide diffuses into the leaf through small openings on the surface called stomates -Phloem carries the newly synthesized glucose to other parts of the plant where it can be used
for energy or stored. The Light Reactions of Photosynthesis one (of two) electron transport chains Photosystem cluster of chlorophyll, other pigments, proteins and other molecules that all
work together to harvest light energy and package it in ATP and NADPH Chlorophyll absorbs sunlight -Energized electrons in chlorophyll go to E.T.C -ETC makes ATP (ADP + P) - Water is split; electrons from water replace the electrons lost from chlorophyll
-Another chlorophyll also absorbs sunlight -This pathway makes NADPH (NADP + H) ATP synthesis As in cell respiration, electron transport chain powers production of ATP by chemiosmosis through enzyme ATP synthase
The Dark (Light-Independent) Reactions of Photosynthesis Calvin Cycle -Uses energy molecules made in light reactions -ATP, NADPH -a 5-carbon compound in the stroma is used in the reactions and then recycled
-CO2 combines with hydrogen (from NADPH) to make 3-carbon PGAL -2 PGAL combine to make one glucose
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