chapter 8: photosynthesis Flashcards
what is photosynthesis?
the process that converts solar energy into chemical energy (high energy compounds - ex. glucose)
what organisms do photosynthesis?
plants, algae, protists, and some prokaryotes
what are the two types of organisms?
autotrophs and heterotrophs
what are autotrophs?
organisms that sustain themselves without eating anything derived from other organisms. they are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules.
what do organisms with limited access to sunlight use?
chemosynthesis - use a certain type of chemical to create glucose, it’s used for energy
what are heterotrophs?
organisms obtain their organic material from other organisms. heterotrophs are the consumers of the biosphere. almost all heterotrophs, including humans, depend on photoautotrophs for food and O2
what are photoautotrophs?
use energy of sunlight to make organic molecules - ex. plants
why do we need glucose?
as a source of carbon and high energy
why do we need O2?
as a final e- acceptor
what is the structure of photosynthetic cells?
enzymes and other molecules grouped together in a membrane
why is the structure of photosynthetic cells beneficial?
this organization allows for chemical reactions of photosynthesis to proceed efficiently
what did chloroplasts most likely evolve from? why?
from photosynthetic cells as the structure is similar
what is the major location for photosynthesis?
leaves
what are choloroplasts?
little organelles that contain chlorophyll. chloroplasts are mainly in cells of the mesophyll
what is chlorophyll?
green pigment
what is the mesophyll?
the interior tissue of the leaf
how many chloroplasts does one mesophyll cell have?
30-40
does every cell have chloroplasts?
no
does the waxy cover have chloroplasts?
no
where do CO2 molecules enter and O2 molecules leave from?
microscopic pores called stomata. stomata are opening which are regulated by guard cells
what is chlorophyll in?
the membrane of thylakoids - connected sacs in the chloroplast (little disks)
what are multiple thylakoids stacked together called?
grana
what is stroma?
a dense interior fluid
what is the chemical equation for photosynthesis?
6CO2 + 6H2O + light energy –> C6H12O6 + 6O2
what happens to the e- in photosynthesis compared to respiration?
the direction of e- flow is reversed
is photosynthesis a redox process?
yes
what is reduced in photosynthesis?
6CO2 and C6H12O6
what is oxidized in photosynthesis?
6H2O and 6O2
is photosynthesis endergonic or exergonic?
endergonic; the energy boost is provided by light
what are the two parts of photosynthesis?
the light reactions (photo part) and the calvin cycle (synthesis part)
where do the light reactions happen?
in the thylakoids
does the calvin cycle require light?
no
where does the calvin cycle happen?
in the stroma
what are chloroplasts similar to?
solar-powered chemical factories
what are thylakoids?
membranes within the chloroplasts
what do the thylakoids do?
transform light energy into the chemical energy of ATP and NADPH
what is light a form of?
electromagnetic energy, also called electromagnetic radiation
how does light travel?
in rhythmic waves
what is a wavelength?
the distance between crests and waves
what does wavelength determine?
the type of electromagnetic energy
what happens to the waves as we move to the left on the spectrum?
wavelengths get smaller and energy gets higher
what does visible light consist of?
wavelengths (including those that drive photosynthesis) that produce colours we can see
how does light behave?
as though it consists of discrete particles called photons
what is a photon?
a bundle of energy
what are pigments?
substances that absorb visible light; different pigments absorb different wavelengths
what happens to wavelengths that are not absorbed?
they are reflected or transmitted
why do leaves appear green?
because chlorophyll reflects and transmits green light
what is a spectrophotometer?
measures a pigment’s ability to absorb various wavelengths (in %)
what does a spectrophotometer do?
this machine sends light through pigments and measure the fraction of light transmitted at each wavelength.
what happens when a pigment absorbs light?
it goes from a ground state to an excited state - capture energy from excited e-
what is an absorption spectrum?
a graph plotting a pigments light absorption vs. wavelength
what is the main photosynthetic pigment?
chlorophyll a
what do carotenoids do?
they are accessory proteins that absorb excessive light that would damage chlorophyll
what happens when the excited e- in a pigment falls (general)?
photons are given and an afterglow called fluorescence is given off
what does a photosystem consist of?
a reaction-centre complex ( a type of protein complex) surrounded by light-harvesting complexes
what is the light harvesting complex? what do they do?
pigment molecules bound to proteins. transfer the energy of photons to the reaction centre
what happens to the primary e- acceptor in the reaction centre?
accepts the excited e- and is reduced as a result
what are the two photosystems in the thylakoid membrane?
photosystem II and photosystem I - in order
what is photosystem II best at absorbing?
best at absorbing a wavelength of 680 nm. the reaction centre of chlorophyll a of PSII is called P680
what is photosystem I best at absorbing?
best at absorbing a wavelength of 700 nm. the reaction-centre chlorophyll a of PS I is called P700
what is the linear e- flow in photosynthesis?
involves the flow of e- through both photosystems to produce ATP and NADPH using light energy
explain the steps of the light reactions.
notes
compare chloroplasts and mitochondria.
chloroplasts and mitochondria both generate energy by chemiosmosis but use different sources of energy. the mitochondria transfers chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP (used as carrier). in the mitochondria, protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix. in chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma.
where are ATP and NADPH produced?
on the side facing the stroma, where the Calvin cycle takes place
how do light reactions increase potential energy?
light reactions increase the potential energy of electrons by moving them from H2O to NADPH
what does the calvin cycle do?
regenerate its starting material after molecules enter and leave the cycle
is the calvin cycle anabolic or catabolic? explain.
anabolic. it builds sugar from smaller molecules by using ATP and the reducing power of e- carried by NADPH
how does carbon enter the calvin cycle?
as CO2
how does carbon leave the calvin cycle?
as glyceraldehyde (G3P)
how many times does the calvin cycle happen?
3 times
what are the phases of the calvin cycle?
1) carbon fixation
2) reduction
3) regeneration of the CO2 acceptor
what happens in phase one - carbon fixation?
involves the incorporation of CO2 molecules into the ribulose biphosphate (RuBP) using the enzyme rubisco
what happens in phase two - reduction?
involves the reduction and phosphorylation of 3-phosphoglycerate to G3P
what happens in phase three - regeneration?
involves the rearrangement of G3P to regenerate the initial CO2 receptor, RuBP
where does G3P go?
into the cytoplasm
what are C4 plants?
C4 plants minimize the cost of photorespiration by incorporating CO2 into a 4-carbon compound
what are CAM plants?
some plants (ex. succulents) use crassulacean acid metabolism (CAM) to fix carbon. CAM plants open their stomata at night, incorporating CO2 into organic acids. stomata close during the day, and CO2 is released from organic acids and used in the calvin cycle
