Photosynthesis Review - EG

Do fermentation and anaerobic respiration require oxygen?

NO → both produce ATP w/o oxygen

What produces most ATP in cellular respiration?

oxidative phosphorylation

What happens to the electron transport chain w/o oxygen?

it stops functioning completely

2 ways cells make ATP w/o oxygen

1. fermentation

2. anaerobic respiration

What do fermentation and anaerobic respiration begin with?

glycolysis

Which process uses an electron transport chain → fermentation or anaerobic?

anaerobic respiration

What replaces oxygen in anaerobic respiration?

another electronegative molecule

• ex. sulfate ; SO₄^2-

How does fermentation allow ATP production to continue?

by regenerating NAD+ for glycolysis

2 common types of fermentation

1. alcohol fermentation

2. lactic acid fermentation

What is the purpose of fermentation?

to regenerate NAD+ so that glycolysis is able to continue

What does pyruvate become in alcohol fermentation?

ethanol

What is released during alcohol fermentation?

CO2

What intermediate is formed before ethanol?

acetaldehyde

What happens to NADH in alcohol fermentation?

it is oxidized to NAD+

What organisms use alcohol fermentation?

yeast

• brewing

• baking

• winemaking

What does pyruvate become in lactic acid fermentation?

lactate

Is CO2 produced in lactic acid fermentation?

NO → CO2 is NOT produced

What happens to NADH in lactic acid fermentation?

it is oxidized to NAD+

When O2 is scarce, how do humans benefit from lactic acid fermentation?

they use lactic acid fermentation to generate ATP

• ex. during intense exercise

What foods are made using lactic acid fermentation?

cheese + yogurt

What is fermentation used for in food production?

• bread

• alcohol

• chocolate flavor development

Photosynthesis

conversion of light energy into chemical energy

Where does photosynthesis occur?

chloroplasts

Who performs photosynthesis?

• plants

• algae

• some protist

• some prokaryotes

• any organisms WITH CHLOROPLASTS

Why is photosynthesis important?

feeds almost all life and produces oxygen

Autotrophs

• “self-feeders”

• get energy and carbon directly from nonliving sources

Heterotrophs

obtain energy and carbon from the organic material derived from other organisms

• depend directly or indirectly on photoautotrophs for food and oxygen

Consumers

eat other organisms

Decomposers

break down and sorbs energy and nutrients from nonliving remains or wastes of other organisms

Stomata

the microscopic pores where CO2 and O2 exit the leaf

Where are chloroplasts mainly found?

in the cells of the mesophyll → the interior tissue of the leaf

How many chloroplasts does each cell contain?

30-40

Direct product of photosynthesis

NOT GLUCOSE → it is the 3-carbon sugar used to make glucose (G3P)

What is oxidized in photosynthesis?

H2O

What is reduced in photosynthesis?

CO2

Is photosynthesis endergonic or exergonic?

endergonic

• redox process

What occurs when chloroplasts split H2O into hydrogen and oxygen?

the electrons of hydrogen are incorporated into sugar molecules and oxygen is released as a by-product

What provides the energy in photosynthesis?

LIGHT

2 stages of photosynthesis

1. light reactions (the photo part)

2. calvin cycle (the synthesis part)

Where do the light reactions occur in photosynthesis?

thylakoid membranes

Where does the calvin cycle occur?

the stroma

What do light reactions produce?

• ATp

• NADPH

• O2

What molecule is split in light reactions?

water

What happens to NADP+

reduced to NADPH

Photophosphorylation

ATP is generated by adding a phosphate group to ADP in this process

Chloroplasts are…

solar-powered chemical factories

What does the Calvin cycle produce?

G3P (sugar precursor)

• with the help of NADPH and ATP produced by the light reactions

3 phases of the calvin cycle?

1. carbon fixation

2. reduction

3. regeneration

What do ATP and NADPH each provide in the calvin cycle?

• ATP → the necessary chemical energy

• NADPH → electrons needed to reduce CO2

What enzyme fixes CO2?

rubisco

How many CO2 molecules are needed to make one G3P?

3

What type of energy is light?

electromagnetic radiation

What is a photon?

a particle of light energy

Why do leaves appear green?

chlorophyll reflects green light

What is the main photosynthetic pigment?

chlorophyll a

Pigment

substances that absorb visible light

• different pigments absorb different wavelengths

Wavelength

the distance between crests of electromagnetic waves

Electromagnetic spectrum

the entire range of wavelengths of electromagnetic radiation

Wavelengths in visible light (human eye)

380-750 nm

Photon relationship to wavelength of light

inversely proportional

• photons have a FIXED quantity of energy

Benefit of accessory pigments (chlorophyll b)

broaden the light spectrum used for photosynthesis

Carotenoids

absorb excessive light that would damage chlorophyll

What does a photosystem consist of?

a reaction center complex surrounded by light harvesting complexes

Where are photosystems located?

thylakoid membranes

What are the 2 photosystems?

1. photosystem II (P680)

2. photosystem I (P700)

What is the final electron acceptor in photosynthesis?

NADP+

Reaction center complex

an association of proteins holding a special pair of chlorophyll a molecules and a primary electron acceptor

What occurs in the reaction center?

chlorophyll a transfers an excited electron to the primary electron acceptor

• one of the first steps of the light reaction

What powers ATP production in chloroplasts?

proton gradient (chemiosmosis)

Photosystem II

functions FIRST ; is best at absorbing light at wavelength of 680 nm

• P680

Photosystem I

best at absorbing a wavelength of 700 nm (P700)

Difference between PS I and PS II

association w/ different proteins results in different light absorbing properties

What is photorespiration?

rubisco uses O2 instead of CO2, wasting energy

When does photorespiration occur?

hot, dry conditions (stomata closed)

Linear electron flow

involves the flow of electrons through both photosystems and other molecules embedded in the thylakoid membrane to produce ATP and NADPH using light energy

Similarities in chemiosmosis in chloroplasts and mitochondria

• generate ATP by the same general mechanism (chemiosmosis)

• use energy generated by an electron transport chain to create a proton gradient across a membrane

• rely on diffusion of protons through ATP synthase to drive ATP synthesis

Light reactions and calvin cycle function together to produce…

sugar

Is the calvin cycle anabolic or catabolic?

ANABOLIC → uses energy from ATP and the reducing power of NADPH to build sugar from smaller molecules

How do C4 plants reduce photorespiration?

separate CO2 fixation and calvin cycle in different cells

How do CAM plants reduce water loss?

open stomata at night

What happens to sugars made in photosynthesis?

used for energy, transported or stored as starch

Why is photosynthesis essential for life?

produces food and oxygen

What does carbon fixation form?

a 6-carbon molecule

How does carbon fixation work?

by combining CO2 and the 5-carbon sugar, ribulose biphosphate (RuBP)

Reduction

involves the phosphorylation of 3-phosphoglycerate

• ONLY 1 MOLECULE OF G3P EXITS THE CYCLE FOR USE BY THE CELL

Regeneration

involves rearrangement of 5 remaining molecules of G3P, to regenerate the initial CO2 acceptor (RuBP)

• 3 EXTRA ATP are required for this step

What is glucose NOT directly generated by?

the light reactions OR calvin cycle

How many molecules of G3P does it take to make 1 glucose?

2

What occurs in photorespiration?

rubisco fixes O2 instead of CO2 → produces a 2-carbon compound

What does photorespiration consume and release?

• consumes → ATP, O2 and organic fuel from calvin cycle

• releases → CO2 w/o producing any ATP or sugar

Benefit of photorespiration

provides protection against damaging products of light reactions that build up when calvin cycle slows due to low CO2

Calvin cycle in C4 plants

CO2 is fixed in mesophyll cells

• calvin cycle runs in separate bundle-sheath cells

Why are scientists concerned about the different responses by C3 and C4 plants?

they’re concerned that their different responses might alter their relative abundance

CAM plants

another photosynthetic adaptation to arid conditions that has evolved in certain succulents

How do CAM plants incorporate CO2 into organic acids?

they open their stomata at night

• they’re close during the hot, dry hours of the day

How are C4 and CAM pathways similar?

they both incorporate CO2 into organic intermediates before entering the calvin cycle

Difference between C4 and CAM plants

• C4 → carbon fixation and calvin cycle occur in different cells

• CAM → processes occur in same cells, different times of day