Photosynthesis: Chp 10 Flashcards
autotrophs
“self feeders”; they sustain themselves without eating anything derived from other organisms. Ultimate source of organic compounds. AKA producers
Heterotrophs
live on compounds produced by other organisms. AKA consumers. Dependent on the process of photosynthesis for both food and oxygen
chloroplasts
specific sites of photosynthesis in plant cells
mesophyll
tissue found in the interior of the leaf where chloroplasts are mostly located
stroma
dense fluid-filled area of the plant
chlorophyll
located in the thylakoid membranes and is the light-absorbing pigment that drives photosynthesis and gives plants their green color
stomata
tiny pores i the exterior of the lower epidermis of a leaf where carbon dioxide enters and oxygen and water vapor exits the leaf
photosynthesis equation
6CO2+6H2O+Light Energy—>C6H12O6+6O2
what are the two stages of photosynthesis
light reactions and calvin cycle
light reactions
occur in the thylakoid membranes where solar energy is converted to chemical energy. Net products are NADPH, ATP, and oxygen. STEPS:
1: light is absorbed by chlorophyll and drives the transfer of electrons from water to NADP+, forming NADPH
2: water is split during these reactions, and O2 is released
3: ATP is generated, using chemiosmosis to power the addition of a phosphate group to ADP, a process called photophosphorylation
calvin cylce
occurs in the stroma, where CO2 from the air is incorporated into organic molecules in carbon fixation. the calvin cycle uses the fixed carbon plus NADPH and ATP from the light reactions in the formation of new sugars
light
electromagnetic energy that is important for photosynthesis
photons
discrete particles that make up light. they have a fixed quantity of energy
pigments
substances that absorb light
absorption spectrum
a graph plotting a pigment’s light absorption versus wavelength
action spectrum
graphs the effectiveness of different wavelengths of light in driving the process of photosynthesis
photosystems
photons of light that are absorbed by certain groups of pigment molecules in the thylakoid membrane of chloroplasts. Consists of two parts: the light-harvesting complex and a reaction center
the light-harvesting complex
is made up of many chlorophyll and carotenoid molecules that allows the complex to gather light effectively. when chlorophyll absorbs light energy in the form of photons, one of the molecule’s electrons is raised to an orbital of higher potential energy. The chlorophyll is said to be in an excited state
reaction center
consists of two chlorophyll a molecules, which donate the electrons to the second member of the reaction center, the primary electron acceptor.
light reactions liner electron flow
1: photosystem 2 absorbs light energy, allowing P680 reaction center of two chlorophyll a molecules to donate an electron to the primary electron acceptor. the reaction-center chlorophyll is oxidized and now required an electron
2: an enzyme splits a water molecule into two hydrogen ions, two electrons, and an oxygen atom. the electrons are supplied to the P680 chlorophyll a molecules. the oxygen combines with another oxygen molecule, forming O2 that will be released into the atmosphere
3: the original excited electron passes from the primary electron acceptor of ps 2 to phs 1 through an electron transport chain.
4: the energy from the transfer of electrons down the electron transport chain is used to pup protons, creating a gradient that is used in chemiosmosis to phosphorylate ADP to ATP. ATP will be used as energy in the formation of carbohydrates in the calvin cycle.
5: meanwhile, light energy has also activated PS1, resulting in the donation of an electron to its primary electron acceptor. the electrons just donated by PS1 ar replaced by the electrons from PS2
6: the primary electron acceptor of ps 1 passes the excited electron along to another electron transport chain, which transmits them to NADP+, which is reduced to NADPH. the high energy electrons of NADPH are used in the calvin cycle
cyclic electron flow
alternative to linear electron flow. uses PS1 and not PS2. cyclic electron flow uses a short circuit of linear electron flow by cycling the excited electrons back to their original stating point in PS1. cyclic electron flow produces ATP by chemiosmosis, but no NADPH and no O2 is released
calvin cycle three major steps
1: three CO2 molecules are attached to three molecules of the five-carbon sugar ribulose biphosphate (RuBP). these reactions are catalyzed by the enzyme rubisco and produce an unstable product that immediately splits into two three-carbon compounds called 3-phosphoglycerate.
2: the 3-phosphoglycerate molecules are phosphorylated to become 1, 3-biphosphoglycerate
3: 6 NADPH reduce the six 1, 3-bisphosphoglycerate molecules to six glyceraldehyde 3 phosphate (G3P)
4: one G3P leaves the cycle to be used by the plant cell. two G3P molecules can combine to form glucose, which is generally listed as the final profuct of photosynthesis
5: FInally, RuBP is regenerated as the 5G3P are reqorked into three of the starting molecules, with the expenditure of 3 ATP molecules
photorespiration
a metabolic process that causes en enzyme rubisco to bind O2 in place of CO2 causing oxidation/breakdown of RuBP
C4 plants
adapted plants that reduce photorespiration. they have 2 kinds of photosynthetic cells: bundle-sheath cells and mesophyll cells.
CAM plants
adapted plants that reduce photorespiration by keeping their stomata closed during the day to prevent excessive water loss
