Chapter 7 Flashcards
photosynthesis
reduction of CO2 to a carbohydrate using light energy
photosynthesis equation
6H2O + 6CO2 + energy (photons) –> C6H12O6 +6O2
photosynthesis is carried out by
some bacteria
algae (mostly single celled)
plants (multi celled)
what causes algae blooms?
1) nutrients -(usually phosphorus) sewage, farm run off
2) temp- production of toxic compounds
- oxygen consumption by algae and bacteria feeding on dead algae
photosynthesis organisms live
in association with some animals
in eukaryotes photosynthesis takes place in
the chloroplast
stroma
area between the inner membrane and the thylakoids
in prokaryotes photosynthesis takes place on
an internally folded membrane
light is a type
of photon
particles of energy
photons
photons vary in
their energy level
photos have properties that are
wave like
each photon has a defined
energy level and wavelength
light is defined as
photons we can see
light sources usually have many different types of
photons all which can be potentially be used for photosynthesis
interactions between photons and atoms
- atoms can absorb the energy of photons
- atoms can give off photons
- only certain atoms or molecules absorb certain types (wavelength) of photons
pigments
molecules that absorb visible light
absorption of photons by molecules
electron takes on a higher energy state
the electron is unstable at the higher energy state
in most molecules the electron returns to its original state and emits
1. photons
2. heat (movement of the molecule)
pigments involved in photosynthesis
chlorophylls and accessory pigments
chlorophylls
main photosynthetic pigment absorbs blue and red light
electrons held loosely by nucleus
light absorbtion by pigments
accessory pigments allow photons chlorophyll can’t absorb
pigments used in photosynthesis are
organized into photosystems 1 and 2
groups of chlorophyll and accessory pigments
found on the thylakoid membrane
how is light energy converted to potential energy
chlorophyll removed from cholroplast
green photons are reflected. other colors are
absorbed
immediately after light is removed
red photons released as electrons return to lower energy state
chlorophyll in a chloroplast
electrons that absorb photons are passed to an electron transport chain
two stages in photosynthesis
- light reactions: light energy transferred to electrons: used to make ATP and high energy electron source for:
- dark reactions: CO2 reduced to a carbohydrate
photosystem 1
electrons excited by photon energy can take one of two paths
photosystem two paths:
cylic path
non cyclic path
cyclic path
electrons travel through an electron transport chain back to photosystem 1
the process produces ATP by chemiosmosis
non cyclic path
electrons passed to an electron carrier
light reactions
energy from photons are directed towards chlorophyll
energy level of chlorophyll electrons is increased and
causes them to be lost from the chlorophyll molecule
photosystem 2
electrons lost from the chloroohyll are replaced by electrons from H2O
electrons are passed down an electron trasnport chain
H+ is actively transported from the stroma into thyacoid compartment
photosystem 2 continued
H+ passes back into the stoma through ATP synthase, producing ATP
at the end of the electron transport chain the electrons are passed to photosystem 1
photosystem 2 is only involved in ATP production
summary of light reactions
inputs: products: photons O2 H2O ATP ADP NADPH P NADP+
dark reactions (calvin cycle) 3 phases
- carbon fixation
- reduction
- regeneration
- carbon fixation
Co2 combines with 5 carbon sugar
(RuBP) and splits into 2 molecules
- reduction
electrons are donated to 3 carbon molecules from NADPH
energy from ATP is required
one of the 3 carbon products used to produce glucose
- regeneration
one of the 3 carbon compounds used to make new RuBP
requires ATP
summary of dark reactions
inputs: outputs:
CO2 G3P ( 3 carbon molecule)
NADPH
ATP energy ADP
P
NADP+
carbs
carbohydrates made in photosynthesis provide the carbon source and energy for all other organic molecules
photosynthesis resulted in a rapid increase in O2 about 2 billion years ago
light vs dark
light formed under aerobic conditions
dark formed under anaerobic conditions
dark is temp sensitive
light is not
photostasis
balance between light and dark reactions
if reactions centers remain reduced, they will be damaged
organisms build photosynthetic systems to balance light and dark reactions
as temp drop some organisms produce protective pigments, others reduce their chlorophyll levels
plant lose
water when they take in CO2
stomata
regulate gas exchange in leaves and prevent water loss
plants may
not photosynthesize to prevent water loss
