photosynthesis Flashcards
what are autotrophs and what do they produce?
producers of the biosphere, that sustain themselves without eating anything from organisms, produce organic molecules from CO2, H2O, inorganic molecules and sunlight
what are heterotrophs and examples?
consumers of the biosphere, obtain their organic material through other organisms, humans depend on photo autotrophs for food and O2
examples of autotrophs?
almost all plants are photo autotrophs, bacteria, and archae
where is the major location for photosynthesis?
leaves
what is stomata?
CO2 enters and O2 exits the leaf through microscopic pores
what is mesophyll?
this is where chloroplasts are found and each mesophyll contains 30-40 chloroplasts
what is the stroma?
the envelope of two membranes surrounding a dense fluid around a chloroplast
what are thylakoids?
sacs in the chloroplast which compose of third membrane system, may be stacked in columns called grana
what are grana?
location of chlorophyll and they are stacked sacs
is chloroplast DNA maternal?
yes, like mitochondria circular DNA is bact
what is the formula for photosynthesis?
6CO2 + 6H2O + solar energy -> C6H1206 + 6O2
What is the difference of the reaction between photosynthesis and cellular respiration?
photosynthesis is the reverse of cellular respiration, photosynthesis is endergonic and cellular respiration is exergonic
what happens in the photosynthesis reaction?
its a redox reaction, and H2O is oxidized and CO2 is reduced
what is the process of photosynthesis redox reaction?
reverses the direction of electron flow and an endergonic process (energy boost is provided by light)
what are the two stages of photosynthesis?
light reactions (photo-part) and Calvin cycle (synthesis part/ light independent/C3/dark)
what happens during the light reactions stage?
covert solar energy to the chemical energy of ATP and NADPH
how does the light reaction convert solar energy to chemical energy?
light splits H2O into hydrogen and oxygen, releases O2, reduces the electron acceptor NADP+ to NADPH, generate ATP from ADP by photophosphorylation
what happens during the calvin cycle?
forms sugar from CO2 using ATP, NADPH from light reaction, begins with carbon fixation, incorporating CO2 into organic molecules
what are the products of light reactions?
O2, ATP, NADPH
what are the products of the calvin cycle?
glucose, NADP, ADP
what is the nature of sunlight?
form of electromagnetic energy, travels in rhythmic waves
what is a wavelength?
the distance between the crests of two adjacent waves and it determines the type of electromagnetic energy
what is the electromagnetic spectrum?
entire range of electromagnetic energy from very short gamma rays to very long radio waves
what is visible light?
the fraction of the spectrum that our eyes see as different colors
what is sunlight?
discrete packets of energy called photons
what happens when sunlight shines on a pigment
certain wavelengths are absorbed
what is an absorption spectrum?
graph plotting a pigments light absorption versus wavelength
what is an active spectrum?
profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis
what colors work best for photosynthesis?
violet-blue and red
what are photosynthetic pigments?
the light receptors that absorb visible light, 10 different pigment in plants, different pigments absorb different wavelengths
what happens to wavelengths that aren’t absorbed?
reflected or transmitted
why do leaves appear green?
chlorophyll reflects and transmits green light
what are carotenoids?
an accessory pigment that works in conjunction with chlorophyll, cannot transfer light energy directly to photosynthetic pathway, they must pass their absorbed energy to chlorophylls
what is chlorophyll A?
absorbs most in blue-violet (430nm) and red (662nm), only pigment that makes up reaction center, does not absorb green
what is chlorophyll b?
absorbs most blue (450nm) and red (640nm), does not absorb green, plants in shade have more of chl b
what is the ratio of chl A and B?
6:1
what happens during the excited state?
its highly unstable so excited electrons lose their energy and fall back to the ground state releasing energy in the form of heat or light or fluorescence
what is photoexcitation?
when a pigment absorbs light, one of the pigments electrons gain energy, goes from a ground state to an excited state
what is photosystem 2?
best at absorbing a wavelength of 680nm, the reaction center chlorophyll A is called P680
what is photosystem 1?
best at absorbing a wavelength of 700nm, the reaction center chlorophyll a is called P700
what are the two routes for electron flow in light reactions?
linear and cyclic
what is the linear electron flow?
the primary pathway, involves both photosystems 1 and 2, produces ATP, NADPH and O2 using light energy
what is the cyclic flow?
involve mainly PSl, produces ATP using proton gradient,, no NADPH, no oxygen, occurs when high levels of NADPH are present, balances ATP/NADPH energy budget, protects PS 2
first step of linear electron flow?
in photosystem 2 chlorophyll absorbs light and causes electron excitation which gets passed from chlorophyll to chlorophyll
what happens when ATP drops?
plant shifts to cyclic electron flow and NADPH rises, calvin cycle drops
how does the cyclic electron flow produce ATP?
electrons cycle back from Fr to the cytochrome complex back to the PS1 reaction center called cyclic photophosphorylation, no NADPH, no oxygen
difference between noncyclic photophosphorylation and cyclic photophosphorylation?
NCP - formation of ATP & NADPH
– electrons flow from H2O to PSII to PSI to NADPH
– Make O2 from splitting H2O
– Make ATP from H+ gradient
• CP – Use only PS I, not PSII
• Small amt ATP is produced.
• No NADPH or O2 made
• No splitting of water
• Electrons come only from light harvest
what is the cyclic electron flow steps?
- generates atp using protein gradient
- does not produce NADPH or O2
- occurs when high levels of NADPH are present
- Balance ATP/NADPH energy budget
- protects PS2 against photoinhibition
what does the linear electron flow produce?
ATP, NADPH, O2, using light energy
Why is cyclic electron flow primitive?
Some organisms such as purple sulfur bacteria have PS I
but not PS II.
• Thus Cyclic electron flow is thought to have evolved before
linear electron flow.
• Cyclic electron advantage:– more ATP can be produced without
producing NADPH
• Glycolysis is primitive
Comparison of chemiosmosis in chloroplasts &
mitochondria?
In mitochondria, protons are pumped to the intermembrane space & drive ATP synthesis as they diffuse back into the mitochondrial
matrix
* In chloroplasts, protons are pumped into the thylakoid space &
drive ATP synthesis as they diffuse back into the stroma
How does The Calvin cycle use the chemical energy of ATP &
NADPH to reduce CO2 to sugar?
The cycle builds sugar from smaller molecules by using ATP & the
reducing power of electrons carried by NADPH, Carbon enters the cycle as CO2 & leaves as a sugar named
glyceraldehyde 3-phospate (G3P).
What are the three phases of the Calvin cycle.?
Carbon fixation
Catalyzed by rubisco, ribulose bisphosphate carboxylase,
the most abundant enzyme on earth
2. Reduction
Formation of G3P (glyceraldehyde 3 phosphate)
3. Regeneration of the CO2 acceptor RuBP
(RuBP = ribulose bisphosphate)
Why is the Calvin cycle a sugar factory?
Calvin cycle constructs an energy-rich sugar molecule called
glyceraldehyde-3-phosphate,
what produces glyceraldehyde 3 phosphate and what is it?
For every 3 molecules of CO2 that enter the cycle,
the net output is 1 G3P
G3P is = raw material (monomer) for making glucose, cellulose, starch.
Most of the remaining G3P to used to regenerate RuBP
How many turns of the Calvin cycle to make 1 Glucose?
2 molecules of G3P are required to make 1 glucose.
6 turns of Calvin Cycle → 2 G3P molecules →
1 Glucose
Calvin cycle uses 18ATP & 12NADH to produce 1 Glucose
A problem for C3 plants?
Excessive Loss of water & CO2 through stomata on hot days, In hot areas, C3 plants cannot grow well as rubisco acts as an
oxygenase, instead of carboxylase
What is rubisco?
Rubisco acts as a carboxylase & CO2 is first fixed into a compound with 3 carbons (3 phosphoglycerate). Rubisco fixes oxygen instead of CO2 (photorespiration).
Pros and cons of photo respiration?
Disadvantage: PR lowers production of sugars – limits plant
growth.
• On a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle.
• Advantage: PR reduces buildup of O2 without opening stomata.
Problem with photorespiration (PR)?
Photorespiration consumes O2 & releases CO2 without
producing ATP or sugar.
• In Photosynthesis CO2 is taken in & sugar is produced.
• These 2 processes work against each other!!
What are C4 plants?
C4 plants minimize the cost of photorespiration by incorporating
CO2 into 4-carbon compounds.
• There are 2 distinct types of cells in the leaves of C4 plants:
– Bundle-sheath cells are arranged in tightly packed sheaths
around the veins of the leaf.
– Mesophyll cells are loosely packed between the bundle sheath
& the leaf surface.
What happens in the bundle sheaths?
These 4-carbon compounds are exported to bundle-
sheath cells.
Within the bundle-sheath cells, the 4-C
compounds release CO2 that is then used in the
Calvin cycle
What is crassulacean acid metabolism?
Some plants, including succulents, use crassulacean
acid metabolism (CAM) to fix carbon
How do CAM Plants – adapt to arid environments?
Some plants, including succulents, use crassulacean
acid metabolism (CAM) to fix carbon
how many G3P molecules are needed to make 1 glucose?
2 molecules of G3P are required to make 1 glucse.
what happens to CAM plants during the day vs the night?
Night - CAM plants open their stomata, incorporating
CO2 into organic acids
* Day - CO2 is released from organic acids & used in the
Calvin cycle.
