biology week 8

photosynthesis

the transformation of sunlight into energy

autotrophs

“self-feeders” that do not eat other living beings

heterotrophs

“Other-feeders” that eat other organisms

mesophyll

tissues of a plant’s interior leaf

stomata

pores in plant leaves that allow for the entrance of CO₂ and the exit of O₂

chlorophyll

the pigment that makes plants look green

general formula for photosynthesis

6CO₂ + 6H₂O + light energy —> C₆H₁₂O₆ + 6O₂

light reactions

the first stage of photosynthesis. Converts solar energy into ATP and NADPH while releasing O₂

Calvin cycle

the second stage of photosynthesis. Fixates and reduces atmospheric CO₂ into glucose

NADP⁺

nicotinamide adenine dinucleotide phosphate. An electron carrier molecule in plants

NADPH

the reduced form of NADP⁺

photophosphorylation

the use of light reactions in plants to create ATP by adding a phosphate group to ADP through chemiosmosis

carbon fixation

3 CO₂ molecules are bound to the 5-carbon sugar RuBP in a reaction catalyzed by the rubisco enzyme. This molecule splits in half for a total of 5 molecules of 3-phosphoglycerate

wavelength

the distance between crests of electromagnetic waves

electromagnetic spectrum

the entire range of radiation wavelengths

visible light

radiation between 340nm and 740 nm

photons

particles of light with discrete quantities of energy

spectrophotometer

an instrument that measures the wavelengths that a substance absorbs

absorption spectrum

a wavelength vs absorption graph of a substance

chlorophyll a

the main light-capturing pigment in chloroplasts

chlorophyll b

the accessory pigment in chloroplasts

action spectrum

a graph that profiles the effectiveness of different wavelengths for a certain species

carotenoids

orange-yellow pigments in chloroplasts that absorb violet or blue-green light

photosystem

a reaction-center complex surrounded by multiple light harvesting complexes

reaction-center complex

proteins holding a special pair of chloroplasts a molecules and a primary electron acceptor

light-harvesting complex

protein-bound pigment molecules that absorb photons to transfer to the reaction-center complex

primary electron acceptor

an electron carrier molecule in the reaction-center complexes of chloroplasts

photosystem II (PSII)

the photosystem that reacts first in light reactions. Captures 680nm wavelengths the best.

photosystem I (PSI)

the photosystem that acts second in light reactions. Captures 700nm wavelengths the best

linear electron flow

the flow of energy through both photosystems during light reactions in photosynthesis

cyclic electron flow

when photoexcited electrons use PSI but not PSII to create ATP but no NADPH or oxygen

glyceraldehyde 3-phosphate (G3P)

the 3-carbon sugar formed after 3 turns of the Calvin cycle

rubisco

an enzyme that catalyzes the bond between CO₂ and a 5-carbon sugar RuBP during the carbon fixation step of the Calvin cycle

reduction phase of the Calvin cycle

ATP gives each 3-phosphoglycerate an extra phosphate group, forming six 1,3-phosphoglycerate molecules. Each 1,3-phosphoglycerate molecule is reduced by NADPH, forming 6 molecules of G3P. Only one G3P molecule exits the cycle.

RUBP regeneration

3 molecules of ATP are spent to rearrange the remaining 5 G3P molecules into 3 RuBP molecules

formula for the Calvin cycle

9ATP + 6NADH —> G3P

C₃ plants

plants that use rubisco to fix CO₂ to RuBP

photorespiration

when C₃ plants consume O₂ and CO₂ is released. Uses ATP and does not create sugar. Caused by heat.

C₄ plants

plants that form a 4-carbon compound as the first product of the Calvin Cycle.

bundle-sheath cells

cells that perform the Calvin Cycle in C₄ plants

PEP Carboxylase

The enzyme that bonds CO₂ to oxaloacetate in C₄ photosynthesis.

crassulacean acid metabolism

the process that desert plants use to collect and store CO₂ during the night by incorporating them into organic acids.