BIOL 189 Photosynthesis
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Photosynthesis What is photosynthesis, in words, and the general equation?
Is the production of glucose and water from carbon water and sunlight.
Photosynthesis 6 CO2 + 6 H2O + light -> C6H12O6 + 6 O2
What is the difference between a producer and consumer, autotroph and heterotroph?
autotroph- plants and protist make their own food without consuming organic molecules for energy or carbon
heterotrophy- organisms that must consume organic molecules for energy, carbon, or both to survive
Where are stomata, and what do they allow in and out of the leaf?
Stomata (many stoma)– pores that allow gas exchange (CO2 in, O2 out) with the environment
Located inner membrane of chloroplast.
What are the compartments of a chloroplast, and what separates them?
Outer membrane \inner membrane\inner membrane space
Two covering membranes, inner membrane contains the stroma, a thick fluid. Membranous stacks of disks called grana made up of thylakoids in the stroma. The thylakoid membranes contain chlorophyll and many enzymes needed for photosynthesis.
What are the two stages of photosynthesis and where do they occur in the chloroplast?
- Light reaction-Light reactions –
- occurs in the thylakoid membrane
- H2O + light + ADP + NADP+ -> O2 + ATP + NADPH
- (ATP and NADPH are the ‘charged’
- energy molecules)
- H2O- electron source Light- energy
- source O2- waste product from splitting water NADPH- electron shuttle to the
- dark reactions ATP- energy source to the dark reactions
- Calvin cycle-“synthesis” phase
- Calvin Cycle or Dark reactions (no light required) – in stroma of
- CO2 + ATP + NADPH -> sugar (+ ADP +
- CO2 – Carbon source for sugar
- (C6H12O6) ATP – Energy source NADPH – electron source Sugar- High energy
- Carbon fixation – incorporation of
- carbon from an inorganic form (usually gaseous CO2) into solid organic
What are the inputs and outputs of these two stages, where
does each go, and what function does each input and output serve?
- Input: CO2 and ATP, NADPH from light
- Output: glyceraldehyde-3-phosphate
- (G3P, GA3P, or PGAL), a sugar used to make glucose or other molecule
Which stage of photosynthesis produces oxygen, and which produces sugars?
Oxygen- light reaction
Surgars- calvin cycle
What does it mean that carbon is ‘fixed’?
- Rubisco in the calvin cycle fixes
- the unstable carbon
Which enzyme does this job in a C3 plant?
- C3 plants: CO2 is used directly from
- the air into the Calvin Cycle (soybeans, oats, rice- most common) Stomata must
- close when air is dry; no CO2 in! Rubisco (RUBP carboxylase/oxygenase)
- incorporates O2, not CO2 - results in
- photorespiration, where no sugar or ATP are produced (and RuBP not easily
- recycled) Rubisco incorporates more O2 in warmer conditions or when O2
- concentrations rise
Why does chlorophyll appear green, and carotenoids
yellow-orange to us?
- Green light is reflected, and
- carotenoids appear when tree is in a dormate state and the production of green
- has slowed down.
- Chlorophyll absorbs light energy in
- the “violet-blue” and “red” areas, and reflects “green” areas. Carotenoids
- absorb in other areas of the spectrum to harvest more energy or protect
Where are the other colors of light going?
- Lights that are not absorbed are
What happens to light that strikes an object?
- When light energy (photon- a fixed
- quantity of energy) is absorbed by a pigment, an electron is excited to a
- higher energy state.
- When the electron goes back to its
- original energy state, energy is released.
- Forms energy can take: Heat Light (fluorescence)
- Energy passed to neighbors
What is the function of photosynthetic pigments?
What are PSI and PSII? Where are they? What do they do?
- Ps2- The primary electron acceptor
- from PSII (electrons from splitting water, O2 produced as waste) initiates an
- ETC, which stores energy to produce ATP using a proton gradient and ATP
- Ps1- The primary electron acceptor
- from PSI (electrons from PSII ETC) initiates a separate ETC which culminates in
- reducing NADP+, with 2 electrons and H+ to NADPH.
- They are in the thylokoid part of
- light reaction
- they make CO2 and ATP, NADPH from
- light reactions for the calvin cycle.
What is a reaction
is ATP generated during the light reactions?
- ETC builds up proton (H+) gradient
- inside grana; ATP synthase makes ATP from the energy
How is NADP+ reduced during the light reactions?
- The primary electron acceptor from
- PSI (electrons from PSII ETC) initiates a separate ETC which culminates in
- reducing NADP+, with 2 electrons and H+ to NADPH
How do C4 and CAM plants solve problems associated with
desiccation in a terrestrial environment while gaining enough carbon dioxide to
- O2 C3 cam
- Day absorb (-) nothing (0)
- Night gives off (+) absorb (-)
question: Even though the overall
equations of cellular respiration and photosynthesis look like one process is
the reverse of the other, the details of each process illustrate that the two
are separate and distinct. Provide and briefly explain two similarities and two
differences between cellular respiration and photosynthesis. Think about where
they take place, and the ways in which ATP is produced in each, as a starting
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