Unit 4: Lecture 15

Define autotroph.

An organism that obtains organic food molecules without eating other organisms or substances from other organisms.

Define photoautotrophs.

An organism that uses light energy to synthesize organic compounds from carbon dioxide.

What is the most important chemical transformation on earth?

Photosynthesis- process that converts solar energy into chemical energy

What is the formula for photosynthesis?

6CO2 + 6H2O -\> C6H12O6 + 6O2

What is light?

Electromagnetic energy AKA electromagnetic radiation

How does light travel?

Rhythmic waves

Define electromagnetic spectrum.

The entire range of radiation

Define visible light.

Wavelengths that produce colors the human eye can see; includes the wavelengths that drive photosynthesis

What does electromagnetic radiation have?

Particle-like (photons) and wave-like characteristics

What length of wavelength has more potential energy?

Shorter wavelengths

What makes the distance of a wavelength?

The distance between its peaks

What is the range of wavelength lengths?

10^-5 to 10^13 nm

Do long wavelengths damage tissue?

No, only short wavelengths do

Why is the sky blue?

Waves of sun of all different wavelengths hit particles of the atmosphere; some are absorbed, some are reflected; blue\= the reflected light waves of the lower end of the spectrum

Why are leaves green?

Green light gets reflected, other wavelengths are likely absorbed

Wavelengths that are not absorbed are ______________.

Reflected

How do chloroplasts capture energy?

Plant pigments: substances that absorb visible light (e.g. chlorophyll, carotenoids)

What do carotenoids do?

Prevent too much light from damaging chlorophyll (protective)

Why do fruits vary in so much color?

Plants have over a thousand different pigments

What are the two most common chlorophyll?

Chlorophyll a and b: absorb violets, blues and reds, but reflect or transmit greens and yellows

Why are chlorophyll a and b, and carotenoids mostly at the lower wavelengths?

They are absorbing the higher energy so it doesn't destroy the plant tissue

What is a photon?

An entity that carries energy from the sun, but has zero mass (not an atom or particle)

What are the 3 stages of electron excitation?

1. Energetic photon hits electron
2. Electron moves to higher energy level
3. Electron falls back to previous energy level, releasing the energy as heat

What happens when the sun hits the chlorophyll?

1. Photons hit the atoms in the chlorophyll
2. Electrons absorb the energy (excited state) and jump to an outer energy level
3. Electrons spontaneously falls down to its initial state (ground state) with some of the energy lost as heat and fluorescence (afterglow)

The further away from the nucleus, the \_____________.

More energy the electron carries

What do electrons normally occupy?

The lowest energy level possible (ground state)

What happens when an electron in the pigment absorbs light?

It moves to an unstable excited state

What is the net change in energy of an electron after a photon hits it?

Energy loss (as unrecoverable energy\=heat)

What is the primary location of photosynthesis?

Leaves

Where are chloroplasts found?

Mesophyll cells (the interior tissue of the leaf)

How many chloroplasts does each mesophyll cell contain?

30-40 chloroplasts

What is the stroma?

Fluid within membranes (sight of Calvin Cycle)

What is the thylakoid?

Flattened sac: Membrane-bound compartment; location of chlorophyll

What is a thylakoid space?

Proton (H+) storage

What are the number of membranes in a chloroplasts?

Three membranes: Inner membrane, outer membrane, and granum stack

What is a granum/ grana?

Stack of thylakoids

What is the stoma/stomata?

Pores that allow gas exchange through opening and closing (regulated by guard cells)

What are guard cells?

Change shape depending on the amount of water and K+ present; water-filled \= open stomata

What are the similarities and differences between photosynthesis and cellular respiration?

Similar: Redox reactions Different: Electron carriers

Why does photosynthesis use a different electron carrier?

NADPH; allows independent control, shutting down NADPH will not affect cellular respiration

What does 6CO2 and 12H2O become in photosynthesis?

C6H12O6 + 6H2O + 6O2-\> 6CO2 becomes C6, O6, and O; 12H2O becomes H12, H2, and O2

What are photo reactions?

Light reactions (light-dependent): capture solar energy as chemical energy in the thylakoids

What are synthesis reactions?

Light-independent reactions: in the stroma

What is contained in the thylakoid membrane?

Two photosystems: PS II works to create ATP-\> electron transport chain-\> PS I reduces NADP+ to NADPH-\> electron transport chain-\> ATP Synthase

What is a photosystem composed of?

Light-harvesting complexes (pigment molecules bound to proteins) that transfer the energy of photons to the reaction center, a protein complex it surrounds

How does photosystem II harvest light?

1. Photon hits an outermost chlorophyll/carotenoid/plant pigment molecule in the light-harvesting complexes and excites its electron
2. An electron jumps to a higher energy level by absorbing the photon and falls to ground state
3. The neighboring pigment's electron gets excited from the release of energy from the previous electron
4. Energy transfer continues to occur until it excites a special pair of chlorophyll a molecules (P680) in the reaction center
5. P680 transfers an electron to the primary acceptor (P680->P680+)
6. Primary acceptor sends electron down an electron transport chain to open up transmembrane proteins (creating a proton gradient that makes ATP)
7. Photosystem I

What happens in photosystem I?

1. Same energy transfer from photon to electron occurs until it excites the special chlorophyll in PSI (P700)
2. P700 transfers its electron to PSI's primary acceptor (P700->P700+)
3. Electron (from PSII) funnels through P700+
4. PSI's primary acceptor sends an electron down an ETC where NADP+ is reduced to NADPH

How are the light-harvesting pigments arranged around the reaction center?

In an antenna around rxn center

Why is it called P680?

It is best at absorbing 680 nm light

What is the strongest oxidizing agent?

P680+

What does P680+ take an electron from?

2 electrons from water (hydrogen atom) by water-splitting (by enzymes) to reduce P680+; Oxygen will form an oxygen gas (by-product)

What is the noncylcic or linear electron flow?

NADP+ is reduced to NADPH by the electron of PSI's ETC

What is cyclic flow?

Uses only PSI; electrons cycle back from ETC to the PSI rxn center generating a surplus of ATP, but no NADPH or O2 produced; exclusively used in bacteria (e.g. purple sulfur bacteria)

Why is cyclical useful to an organism?

Too much photons-\>NADPH-\>will shut everything down/kill the plant; Cyclical flow will turn photons to ATP

How do chemiosmosis in mitochondria vs. chloroplasts differ?

Oxidative phosphorylation and Photophosphorylation

What is the common goal of different membrane usage between mitochondria and chloroplasts?

Production of ATP

What is the primary carbon acceptor of the calvin cycle?

Ribulose bisphosphate (RuBP)

What are the three phases of the Calvin cycle?

1. Carbon Fixation
2. Reduction
3. Regeneration of RuBP

What is the first phase of the Calvin cycle?

Carbon fixation: taking carbon from an inorganic source (3 CO2) by catalyzing it using rubisco to turn it into an organic product (G3P- glyceraldehyde-3-phosphate)

What is the second phase of the Calvin cycle?

Reduction: Hydrogens from NADPH are taken to help form sugar (builds a 1:2:1 sugar ratio)

What is the third phase of the Calvin cycle?

Regeneration of RuBP by using 3 ATP

What is the final product of the Calvin cycle?

1 G3P (a 3 carbon molecule)

What happens when a plant becomes dehydrated?

Guard cells close the stomata to conserve H2O, CO2 and O2 are locked in (gas exchange stops)

What happens when the stomata closes?

Photorespiration- rubisco add O2 instead of CO2 in the Calvin cycle leading to a release of CO2 without producing ATP or sugar (provides protection from the build up of the light rxn products); Kills photosynthesis potential (carbon fixation) by 50%

What are most plants?

C3 (e.g. wheat, beans)- the initial fixation of CO2, via rubisco, forms a three-carbon compound

What are C4 plants?

\-Four-carbon compounds (e.g. corn, sugarcane, mostly grasses but some shrubs)

\-different leaf anatomy (bundle-sheath cell under the mesophyll cell)

\-minimize photorespiration by PEP carboxylase incorporating CO2 into four-carbon compounds in mesophyll cells

What is unique with PEP carboxylase?

Does not bind to O2 like rubisco; has a higher affinity for CO2 than rubisco does

Where does the Calvin cycle occur in C4 plants?

The bundle-sheath cell

What are CAM plants?

\-Crassulacean acid metabolism

\-use PEP carboxylase

\-only opens stomata at night, incorporating CO2 into four-carbon molecule (stored in vacuoles for use in the day when ATP and NADPH are abundant)

C4 plants vs CAM plants

\+C4- Spatial separation (mesophyll cell and bundle-sheath cell)

\+CAM plants- Temporal separation (night and day)