Chapter 6 Flashcards
Photosynthesis
process that converts solar energy into chemical energy that is used by biological systems
3 major events photosynthesis has
- Sunlight is converted into chemical energy
- water is split into oxygen
- carbon dioxide is fixed into sugars
photosynthesis reaction
Inputs: six CO2 molecules and 12 h2o molecules and sunlight
outputs: 1 sugar glucose molecule and 6 oxygen molecules
Photosynthesis is carried out by
plants, algae, cyanobacteria, phytoplankton
- known as photoautotrophs or producers
plants as photosynthesizers
green portions carry on photosynthesis
carbon dioxide enters leaves through stomata
roots absorb water
CO2 and H2O diffuse into mesophyll cells then into chloroplasts
Chloroplasts
are a plastid or plant cell organelle
full of round flattened discs called thylakoids
where photosynthesis occurs
thylakoids
found in chloroplasts
stack of thylakoids is called granum
main pigment of photosynthesis
stroma
space inside chloroplasts
where calvin cycle takes place
light reactions
light dependent reactions
capture light energy to power photosynthesis
occur during the day time
take place in thylakoids
dark reactions
light independent reactions
do not need light energy to power their reactions and can occur day or night
also called the Calvin cycle
take place in the stroma of chloroplasts
fix carbon dioxide into glucose
process of light reactions
Photosystem II happens before Photosystem I
energy absorbed by the chlorophyll is used to power photosystem 2 that breaks the bond of water absorbed through the plant’s roots.
o2 is released through the stomata
protons cross thylakoid membrane and power protein complex ATP synthase to make ATP.
NADP+ is powered up by photosystem I to make NADPH to be used in dark reactions
finish with charged NADPH, ATP, and released O2.
stomata
little pores in leaves that open and close to let oxygen out and carbon dioxide in
Wavelengths
red color has the least amt of energy but the greatest wavelength
violet has the most amt of energy but smallest wavelength
photosynthetic pigments
chlorophyll a and b absorb violet, blue, and red wavelengths better than others - reflect green so leaves appear green
cartenoids appear yellow or orange because they reflect those colors - they absorb light in the violet-blue-green range
Electron transport chain
located in thylakoid membrane
promotes efficient transfer of electrons
atp synthase complex also here
ATP production - thylakoid space is a reservoir for H+
establishes H+ gradient = large amt of potential energy
H+ gradient is used to produce ATP.
NADP+ is a coenzyme that accepts electrons and a H+ to become NADPH.
Calvin cycle - making sugars
powered by ATP and NADPH generated by light reactions
occurs in stroma of chloroplasts
end product is glucose
three steps
1. Carbon dioxide fixation
2. Carbon dioxide reduction
3. regeneration of first substrate (RuBP)
Process of calvin cycle
- starts with RuBP molecules and carbon dioxide molecules
- enzyme called Rubisco combines them into an unstable intermediate
- this quickly splits in half and forms 2 molecules of 3 PGA which are stable
RuBP start and end product of calvin cycle - atp and NADPH from light reactions provide energy to convert the two molecules of 3-PGA into their final form
- 2 G3P are joined to make a glucose molecule
8Regeneration of RuBP
1 G3P can be made into glucose or other organic molecules
5 G3P used to reform RuBP
utilizes ATP from light reactions
fate of G3P
plants and algae can make any molecule they need from G3P
Form amino acids, fatty acid, and glycerol
form glucose for energy needs
form sucrose for transport through plant
form starch for storage
form cellulose for cell walls
C3 plants
light and rainfall are moderate
has mesophyll cells arranged in parallel rows
carry out both reactions in mesophyll cells
C4 plants
weather is hot and dry
where a C4 compound is formed first after CO2 fixation
layered arrangement around leaf veins
chloroplasts in mesophyll cells fix Co2 cells only, shield bundle sheath cells from buildup of O2
c4 plants partition reactions - allows stomata to stay closed while avoiding oxygen exposure to rubisco
CAM Photosynthesis
crassulacean acid metabolism
most succulents in a desert environment, driest plants
partitioning in time
during the night, CAM plants open stomata when it is cooler
use c3 molecules to fix C4 molecules
release stored co2 when NADPH and ATP avaliable from light reaction
CAM plants compete well with C3 or C4 when the environment is extremely arid
