photosynthesis Flashcards
(20 cards)
Reaction
6 CO2 + 6 H2O > light > C6H12O6 + 6 O2
Photosynthetic Pigments
Pigment - substance that absorbs light of particular wavelengths
•color of an object depends on the wavelength reflected
•photosynthetic pigments absorbed & convert light energy to chemical energy
Important pigments : chlorophyll A&B
Accessory pigments : increase amount of light usable by plant
Carotenoids : carrotenes (orange) & xanthophylls (yellow)
Reason for many chloroplast in a leaf
Contain chlorophyll and carotenoids
Reason for leafs thin flat shape
Maximum surface area
Cuticle
Waxy covering preventing water loss
Epidermis
Protective covering
Palisade layer (mesophyll)
Expose maximum number of chloroplast to light
Spongy layer (mesophyll)
Air spaces allow for gas exchange between cells and environment
Stomata
Allow gases (CO2, O2, H2O) to enter and exit a leaf
Guard cells
Regulate the opening and closing of the stomata
Veins (xylem & phloem)
Transport materials (xylem : water, phloem : nutrients)
Chemistry of photosynthesis
CO2 is taken from the air and used to form carbohydrates and other organic compounds
•Made from the transfer of hydrogen atoms and electrons
•hydrogen atoms and electrons are extracted from water molecules
•leftover oxygen atoms O2
Photosynthesis is endergonic (process)
•Bonds in the reactants are broken, atoms are rearranged, and bonds in the products (glucose and oxygen) are formed
• Energy required to break the bonds in the reactants is greater than energy released during the formation of bonds in the products
• this energy difference is stored as a chemical energy in carbohydrate molecules
Stages of Photosynthesis
1) Capturing light energy
A) • light energy is captured by photosynthetic pigments
•arranged in molecule clusters (photosystems) which are embedded in the thylakoid membrane
•when light strikes the photosystems, electrons within the chlorophyll are boosted to higher energy levels
B) •excited electrons from chlorophyll molecules within the reaction center is transformed to a protein molecule within the reaction center
C) • lost electrons must be replaced
•plants obtain electrons by splitting water in a process called photolysis
• chlorophyll takes the electrons from the hydrogen atoms, leaving hydrogen ions behind
• remaining oxygen atoms combine to oxygen gas
Stages of Photosynthesis
2) using light energy to make ATP & NADPH
•excited electrons from photosystem 2 get passed to nearby proteins, transferring energy in the process
•series of proteins are called the electron transport chain
• the energy transferred through ETC is used to form ATP by the process of chemiosmosis
•photosystem 1 uses light energy to convert NADP + to NADPH
NADPH
Electron carrier
Stages of Photosynthesis
3) Building carbohydrates : Calvin Cycle
Step 1) CO2 from the atmosphere combined with 5-carbon sugar called RuBP
•resulting molecules are two 3-carbon molecules
Step 2) Reduction
•ATP & NADPH help to convert the two 3-carbon molecules into two molecules of G3P (aka PGAL)
Step 3) Regeneration of RuBP
• 3 turns of the cycle (using 3 CO2) molecules) produces 6 molecules of G3P
• only 1 G3P exits the cycle and goes on to make glucose
• the other 5 molecules regenerate RuBP & continue the cycle
Photorespiration
C3 Plants - on hot & dry days, these plants close their stomata to conserve water
•reduces amount of CO2 available
• increase of O2 in air space
• process doesn’t produce sugar or ATP
Alternate mechanisms of carbon fixation
C4 plants - fix CO2 into a 4-carbon compound that provides CO2 to the Calvin cycle (corn, sugar cane)
CAM plants - open stomata at night producing a 4-carbon compound that provides CO2 during the day (cacti, pineapples)
Factors affecting photosynthesis
Temperature - increase in temp will increase rate of photosynthesis to a point
Carbon Dioxide Level - increasing CO2 levels can increase a rate of photosynthesis to a point
Water - lack of water will cause the rate of photosynthesis to decrease
Minerals - a lack of certain minerals can decrease the rate of photosynthesis
