Unit 3 - Ch 9 - Photosynthesis Flashcards
Simplified equation for photosynthesis
6CO2 + 6H2O → C6H12O6 + 6O2
light and chlorophyll power the reaction
CO2 and H2O are the reactants
Requirements for photosynthesis
- CO2
– from the atmosphere
- enters the leaf via stomata
- .04% concentration of CO2 in the atmosphere - diffusion - H2O
– from soil via roots
- source of e- - Chlorophyll
– pigment that absorbs light energy - Light
- energy source, overall photosynthesis is an endergonic process
Biological Importance of Photosynthesis
Trophic Webs
- photosynthesis supports virtually all trophic webs on earth - Ps organisms are producers in the ecosystem
Removes Atmospheric CO2
- Ps is a primary regulator of the carbon cycle
- carbon sequestration - carbon sink
Produces O2
- Aerobic Respiration - vs. anaerobic
- Ozone - O3 in the upper atmosphere - protects from UV radiation
A leafs flat, thin shape:
– maximizes surface area for light absorption
- leads to water loss from leaf (transpiration)
Leaf cuticle
– waxy layer on both leaf surfaces - minimizes transpiration
- vary by species (thicker in desert species)
Leaf epidermis
Upper and lower, beneath the cuticle
Mesophyll
- middle portion of the leaf (means middle leaf)
1. Palisade - elongated cells packed with chloroplasts
- Spongy - more open / gas exchange layer
- CO2 diffuses into, O2 diffuses out
Vascular Tissue
- Leaf veins
1. Xylem - conducts water from roots to leaf
2. Phloem - conducts carbohydrate from leaf to roots - girdling
Stomata
leaf opening for gas exchange
Guard Cells
- two guard cells form a stoma
- osmotically regulated to open and close the stoma
- open = turgor pressure
- closed = not turgid
Photochemical Reaction
- Location -
- Energy Input -
also called Light Phase of photosynthesis
Location - occurs within the thylakoid
Energy Input - photons of light
Role of Pigments in Photochemical Reaction
- Chlorophyll (a and b) - absorb primarily red and blue wavelengths of visible light
- Accessory Pigments - transfer light energy to chlorophyll
a. Carotenes - orange in color
b. Xanthophylls - yellow
Photosynthetic Units
pigment arrays in the thylakoid membrane - energy is transfered onto a reaction center via a “light funnel”
- Photosystem I (P700) – maximum absorption at 700 nm
- Photosystem II (P680) - maximum absorption at 680 nm
Major Photochemical Steps (3)
- Photolysis
- Photoreduction
- Photophosphorylation
Photolysis
splitting apart water to produce e- for photosystem II
- produces O2
- H+ for production of NADPH
Photoreduction
producing NADPH (endergonic)
Photophosphorylation (2 types)
Produces ATP from ADP using light energy (endergonic)
a. Noncyclic
- involves both photosystems
- “ z scheme”
- photoreduction occurs (NADPH)
- photollysis occurs (recharge Photosystem II) - one way flow of e-
b. Cyclic
- only involve photosystem I
- no photoreduction or photolysis
- accumulates ATP when CO2 levels are low
Thermochemical Reaction
- location -
- energy input -
also called “Dark Phase” and Calvin Cycle
Location
– occurs within the stroma
Energy Input
– ATP and NADPH from photochemical
- light independent
Excess PGALs in Thermochemical Reaction
- form glucose-phosphate (6C)
- proteins and lipids are synthesized from carbohydrates in the metabolic pool
- require nitrogen from the environment to form proteins
Relationship Between Respiration and Photosynthesis
- Photosynthesis creates organic compounds and O2, products which serve as reactants for cellular respiration
- cellular respiration creates CO2 and H2O, products which serve as reactants for photosynthesis
How does the relationship between cellular respiration and photosynthesis relate to tropical deforestation, fossil fuel combustion and global warming?
Combustion of fossil fuels (coal, oil, nat. gas) and decomposition of organic compounds mimic cell respiration
= increase CO2
Deforestation decreases photosynthesis
= CO2 increases in the atmosphere
