bio ch 7 photosynthesis Flashcards
what is an autotroph
self feeders; make their own food and sustain themselves without consuming organic molecules derived from any other organisms
what are photoautotrophs
use the energy of light to make energy and sustain themselves
what is photosynthesis
process by which plants convert CO2 and H2O to their own organic molecules and release O2 as a byproduct
what are the ultimate source of organic molecules for almost all other organisms
photoautotrophs; referred to as producers of the biosphere because they produce its food supply
what are chemoautotrophs
prokaryotes that use inorganic chemicals as their energy source and are the producers in deep-sea vent communities
what are heterotrophs
consume other plants or animals or decompose organic material
where does photosynthesis occur
chloroplasts
what is chlorophyll
gives leaves their green color; light-absorbing pigment in chloroplasts that plays a central role in converting solar energy into chemical energy
what is the mesophyll
where chloroplasts are concentrated; green tissue in the interior of the leaf
what are stomata
tiny pores on the leaf’s surface where CO2 enters and O2 exits
how does water reach the leaves of a plant
it is absorbed by the roots and delivered to the leaves in veins
how many chloroplasts does a typical mesophyll cell have
30-40
how many membranes are on a chloroplast
2 (inner and outer)
what do the 2 membranes of the chloroplast enclose
an inner compartment filled with a thick fluid called stroma
what is stroma
the thick fluid that fills chloroplasts and holds thykaloids
what are thylakoids
a system of interconnected membranous sacs suspended in the stroma that enclose another internal compartment called the thykaloid space
what are grana
stacks of thylakoids
what are the functions of the thylakoid membranes
- hold the chlorophyll molecules that capture light energy
- house much of the machinery that converts light energy to chemical energy
what is the equation for photosynthesis
6CO2 + 6H2O = C6H12O6 + 6O2
where does the O2 produced during photosynthesis come from
water
what reactant of photosynthesis becomes reduced
CO2; reduced into sugar
what reactant of photosynthesis becomes oxidized
H2O; oxidized into O2
is photosynthesis an energy producing process or an energy releasing process
energy producing
does photosynthesis require energy
yes
is photosynthesis endergonic or exergonic
endergonic
what are the two stages of photosynthesis
light reactions and the Calvin Cycle
where do the light reactions occur
the thykaloid membranes
what occurs in the light reactions
water is split, which gives a source of electrons and gives off O2 as a byproduct
electrons are transferred to the electron acceptor, NADP+, making it NADPH, which temporarily stores electrons and hydrogen ions
generates ATP
summarize what happens in the light reactions
solar energy is absorbed and converted to chemical energy that is stored in ATP and NADPH
where does the Calvin cycle occur
the stroma of the chloroplasts
what does the calvin cycle ultimately do
assembles sugar molecules using CO2 and the energy rich products of the light reactions
what is carbon fixation
the incorporation of carbon from CO2 into organic compounds
where do the electrons come from that are used for reducing carbon in the calvin cycle
NADPH from the light reactions
where does the chemical energy come from that powers several of the steps of the calvin cycle
ATP from the light reactions
why is the calvin cycle sometimes referred to as the dark reactions or light independent reactions
bc none of the steps requires light directly
what happens when a pigment molecule absorbs a photon of light
one of the electrons jumps to an energy level farther from the nucleus where it has more potential energy. It is unstable and usually drop back down to their ground state, releasing their excess energy as heat
what is special about chlorophyll as a pigment
it emits light as well as heat after absorbing photons
how does chlorophyll behave in the thylakoid membrane
they transfer the energy to other pigment molecules and eventually to a special pair of chlorophyll molecules; this pair passes off an excited electron before it has a chance to drop back to its ground state
what is a photosystem
consists of a number of light-harvesting complexes surround a reaction-center complex
what happens in the light harvesting complexes in photosystems
they contain various pigment molecules bound to proteins; the pigments absorb photons and pass the energy from molecule to molecule until it reaches the reaction center
what happens in the reaction center complex of a photosystem
contains the pair of special chlorophyll a molecules and a molecule called the primary electron receptor, which accepts electrons and becomes reduced; the electron is transferred from the reaction center chlorophyll a to the primary electron receptor
what is the chlorophyll a in the photosystem II called
P680 bc thats the wavelength of light it absorbs
what is the chlorophyll a in the photosystem I called
P700 bc thats the wavelength go light it absorbs
what is the main result of the light reactions
light energy is transformed into the chemical energy of ATP and NADPH
how is light energy transformed into the chemical energy of ATP and NADPH
electrons removed from water pass from photosystem II to photosystem I to NADP+. between the two photosystems the electrons move down an electron transport chain and provide energy for the synthesis of ATP
what does photosystem II do with its electrons
passes them through an ATP mill; provides energy for synthesis of ATP; also replaces the lost electrons in p700
what does photosystem I do with its electrons
hands its electrons off to reduce NADP+
what replaces the lost electrons in P680
the splitting of water
what replaces the lost electrons in P700
the electron that reaches the bottom of the electron transport chain from photosystem II
what are the products of light reactions
O2, ATP, NADPH
what is a photon
a discrete pack of energy of light; has a fixed quantity of energy, and the shorter the wavelength of light, the greater the energy of its photons
what are carotenoids
pigments that are various shades of yellow and orange; responsible for fall foliage
what are the two important functions of carotenoids
- may broaden the spectrum of colors that can drive photosynthesis
- photoprotection: some absorb and dissipate excessive light energy that would otherwise damage chlorophyll or interact with oxygen to form reactive oxidative molecules that could damage cell molecules
what powers ATP synthesis in the light reactions
chemiosmosis
what happens in chemiosmosis
the potential energy of a concentration gradient of H+ ions across a membrane powers ATP synthesis. This gradient is created when an electron transport chain uses the energy released as it passes electrons down the chain to pump H+ across a membrane
how is a concentration gradient created across the membrane
H+ ions are pumped across the membrane from the stroma into the thylakoid space
how does the H+ get back across the membrane
the energy of the concentration gradient drives the H= back across the membrane through ATP synthase, which completes the flow of H+ to the phosphorylation of ADP
what is photophosphorylation
the chemiosmotic production of ATP in photosynthesis
why is the chemiosmotic production of ATP in photosynthesis called photophosphorylation
because the initial energy input is light
what are the inputs to the calvin cycle
CO2 (from the air) and NADPH and ATP (from the light reactions)
what are the 4 steps of the calvin cycle
Carbon fixation
Reduction
Release of one molecule of G3P
Regeneration of RuBP
what happens in carbon fixation
Rubisco, an enzyme, combines CO2 with a 5 carbon sugar called RuBP. It is unstable and splits into two molecules of 3PGA. When 3 CO2 enter, 6 3PGA result
what happens in reduction
NADPH reduces 3PGA to G3P using the energy of ATP; energy is consumed from 6 molecules of ATP and oxidize 6 molecules of NADPH. 6 molecules of 3PGA are reduced, making 6 molecules of G3P
what happens in release of one molecule of G3P
Five of the G3Ps remain in the cycle. One G3P leaves as the net product of photosynthesis. G3P is used to make glucose and other organic compounds
what happens in regeneration of RuBP
energy from ATP rearrange the atoms in the 5 G3P molecules to form 3 RuBP molecules, which can start another turn of the cycle
what are C3 plants
first product of carbon fixation is a 3 carbon compound
what are examples of c3 plants
soybeans, oats, wheat, rice
what is one problem farmers face in growing c3 crops
they can close their stomata on a hot dry day and prevent CO2 from entering the leaf, which results in photorespiration (water and CO2 are the products instead of glucose)
what is photorespiration
occurs in the light and consumes O2 and releases CO2; uses ATP, yields no sugar, can drain away 50% of carbon fixed by the calvin cycle
what are C4 plants
first product of carbon fixation is a 4 carbon compound; close their stomata in hot dry weather but can continue making sugars and going through the calvin cycle because it has an enzyme that can fix carbon even when the co2 concentration on the leaf is low
what are examples of c4 plants
corn and sugarcane
what are CAM plants
adapted to very dry climates; opens its stomata and admits CO2 only at night; CO2 is fixed into a 4 carbon compound that banks CO2 at night and releases it during the day so the calvin cycle can still operate even with the stomata closed during the day
where do plants store excess food
roots, tubers, seeds, and fruits
what are greenhouse gases
gases in the atmosphere that absorb heat radiation
what does the ozone layer do
shields the earth from uv radiation
