Photosynthesis in Higher Plants

Photochemical phase

Carbon fixation phase

Oxidative phase

Regenerative phase

Photosynthesis increases linearly

Breakdown of chlorophyll and decrease in photosynthesis

Stomata open wider

$CO_{2}$ fixation stops immediately

Carbon dioxide

Oxygen

Nitrogen

Hydrogen

By altering the wavelength of light

By affecting the speed of enzymatic reactions in the stroma

By changing the color of pigments

By increasing the amount of water in the soil

They are $O_2$ and $H_2O$; they act as the initial inorganic substrates that are reduced by solar energy in the stroma.

They are $ADP$ and $NADP^+$; they act as enzymes that facilitate the diffusion of $CO_2$ from the atmosphere into the chloroplast.

They are $ATP$ and $NADPH$; they provide the chemical energy and reducing power required to convert $CO_2$ into carbohydrates.

They are $Chlorophyll$ $a$ and $b$; they serve as the mobile energy carriers that transport light energy directly to the $CO_2$ molecule.

The source of oxygen in photosynthesis

The first action spectrum of photosynthesis

The importance of $CO_2$ in sugar synthesis

The storage form of glucose in plants

A graph showing the rate of photosynthesis at different wavelengths

A graph plotting the amount of light energy absorbed by a pigment at different wavelengths

A graph showing the movement of pigments on a chromatogram

A graph showing the concentration of $CO_2$ inside a leaf

1 electron and 1 proton

2 electrons and 1 proton

2 electrons and 2 protons

1 electron and 2 protons

To provide carbon skeletons for sucrose synthesis

To prevent the inhibition of Calvin cycle enzymes by starch accumulation

To maintain the phosphate balance in the chloroplast stroma

All of the above

ATP hydrolysis

$NADPH$ oxidation

It does not require external energy as the reaction is highly exergonic

Photon energy directly captured by the enzyme

$5-10 \mu m$ in length

$1-2 \mu m$ in length

$20-40 \mu m$ in length

$0.5-1 \mu m$ in length

Stroma, Grana

Grana, Stroma

Grana, Lumen

Lumen, Grana

Outer membrane

Stroma

Thylakoids/Grana

Inter-membrane space

DNA and Ribosomes

Only DNA

Only Ribosomes

Only proteins

$0.5-1.0 \mu m$

$2-4 \mu m$

$10-20 \mu m$

$100 \mu m$

Ribosomes

The internal membrane system

The circular DNA

The lipid droplets

The enzymes are destroyed in the dark

The stroma dries out in the dark

The supply of ATP and $NADPH$ is exhausted

Carbon dioxide cannot enter the leaf in the dark

The lipid bilayer of the envelope

The thylakoid membrane (specifically the PSII complex and OEC)

The stromal DNA

The outer membrane porins

Presence of circular DNA

Presence of starch granules

Site of light-independent reactions

High concentration of Cytochrome $f$

Light absorption will stop

The reduction of $NADP^+$ will stop

ATP synthesis will stop, but electron transport may continue

Water splitting will stop immediately

1

2

3

4

Chlorophyll a

Chlorophyll b

Xanthophyll

Carotene

Collagen

RuBisCO

Insulin

Hemoglobin

Oxygen and ATP

$CO_2$ and a 3-carbon molecule

Glucose and water

RuBP and $CO_2$

Photosystem I on the stroma side

Photosystem II on the lumen side

ATP synthase on the stroma side

Cytochrome complex in the middle

Green alga Cladophora and aerobic bacteria

Chlorella and radioactive carbon

Cyanobacteria and anaerobic bacteria

Purple and green sulfur bacteria

18

24

30

36

Electron transfer

Resonance energy transfer (Exciton transfer)

Bioluminescence

Active transport

$C_{3}$ plants have a higher optimum temperature than $C_{4}$ plants

$C_{4}$ plants have a higher optimum temperature than $C_{3}$ plants

Both have the same optimum temperature

Temperature has no effect on the biosynthetic phase

It contains the catalytic site for $ATP$ synthesis

It forms a transmembrane channel for proton diffusion

It binds $NADP^{+}$ for reduction

It absorbs light energy to drive phosphorylation

PS I $\rightarrow$ PS II $\rightarrow$ $NADP^+$

Water $\rightarrow$ PS II $\rightarrow$ PS I $\rightarrow$ $NADP^+$

PS I $\rightarrow$ Water $\rightarrow$ PS II $\rightarrow$ ATP

PS II $\rightarrow$ $NADP^+$ $\rightarrow$ PS I $\rightarrow$ ATP

Calvin

Arnon

Priestley

Engelman

Zero

Once

Twice

Many times

Plastocyanin

Ferredoxin

Pheophytin

Water

Photosystem I

Cytochrome $b_6f$ complex

Photosystem II

ATP synthase

1

2

4

3

It uses water as an alternative source

It only requires PS I and its associated electron transport chain

It does not require light energy

It occurs in the stroma where PS II is absent anyway

Non-photochemical quenching (NPQ) via the xanthophyll cycle

Increased rate of non-cyclic electron flow

Activation of Rubisco

Shutdown of cyclic photophosphorylation

Chlorophyll $b$

Chlorophyll $a$

Xanthophyll

Beta-carotene

About 0.5 units

About 1.0 units

About 3.0 units

About 7.0 units

18

24

30

38

Smaller with no grana

Larger with no grana

Smaller with many grana

Absent

$C_4$ pathway

$C_3$ pathway

$C_2$ pathway

Glyoxylate cycle

1

3

6

12

18 ATP and 12 NADPH

30 ATP and 12 NADPH

30 ATP and 18 NADPH

12 ATP and 12 NADPH

Kranz anatomy

The presence of the Calvin cycle

The initial $\text{CO}_2$ acceptor is PEP

RuBisCO is present in mesophyll cells

The release of $\text{CO}_2$ from organic acids

The addition of $\text{CO}_2$ to a stable organic intermediate

The reduction of $\text{CO}_2$ using NADPH

The splitting of water to release $\text{CO}_2$

Oxaloacetate

Malate

Pyruvate

Phosphoenolpyruvate

2 times

10-100 times

500 times

1.5 times

RuBisCO

Fructose-1,6-bisphosphatase

PEP carboxylase

Carbonic anhydrase

They start using oxygen for photosynthesis

Current atmospheric $CO_2$ levels are limiting for them

Higher $CO_2$ prevents them from ever wilting

Enriched $CO_2$ makes the temperature cooler

Only the most abundant factor

The factor that is at its most optimal level

The factor that is currently limiting the process

The age of the plant only

Because dark reactions occur at night

Because dark reactions are enzymatic and enzymes are temperature sensitive

Because light reactions do not involve any movement of electrons

Because chlorophyll only works in the cold

Green and Yellow

Blue and Red

Infrared

Ultraviolet

Continuous increase in growth rate

The rate of photosynthesis may decline due to damage

The plant will switch to anaerobic respiration

The plant will stop taking up water

Larger leaf area generally allows for higher rates of total photosynthesis

Fewer leaves increase the efficiency of each individual leaf

Small leaves are always more efficient than large leaves

The size of the leaf has no impact on photosynthesis

The amount of water it consumes

The habitat to which it is adapted

The color of its flowers

The length of its roots

They have a higher density of chlorophyll $a$ in their bundle sheath cells.

They efficiently avoid the oxygenase activity of RuBisCO, allowing them to utilize more $ATP$ and $NADPH$ produced at high light.

They absorb green and yellow light more efficiently than $C_{3}$ plants.

Their stomata stay open wider at high light intensities compared to $C_{3}$ plants.

Photorespiration only occurs in the dark and is inhibited by light.

As light intensity increases, the temperature of the leaf often increases, which in turn increases the rate of photorespiration.

Photorespiration is independent of light intensity but depends on $N_{2}$ levels.

High light intensity inhibits photorespiration by saturating RuBisCO with $CO_{2}$.

Stage 1 involves physical photon capture, while Stage 2 is a series of enzyme-catalyzed biochemical reactions.

Stage 1 occurs in the stroma, whereas Stage 2 occurs on the thylakoid membranes.

Stage 2 requires the photolysis of water, which is a highly endothermic reaction.

Stage 1 is limited by $CO_{2}$ concentration, while Stage 2 is limited by light.

Respiration

Photosynthesis

Transpiration

Absorption

17th

18th

19th

20th

Julius von Sachs

T.W. Engelmann

Joseph Priestley

Jan Ingenhousz

Sachs

Van Niel's hypothesis (proven later by others)

Priestley

Ingenhousz

They were all performed in the 20th century

They relied heavily on the use of electron microscopes

They established that photosynthesis is a multi-step process involving light

They proved that plants do not need water

Bacteria are photosynthetic

Oxygen is evolved only in the presence of light

Bacteria prefer darkness

Light kills the bacteria in other regions

It acts as a chemical reactant

It provides the energy required to split the hydrogen donor

It converts $CH_2O$ into starch

It increases the temperature for enzyme activity

Increased bacterial growth

No bacterial congregation and potential damage to the alga

Bacterial congregation similar to the blue region

The alga would produce more starch

Mint grows faster than trees

A mint plant fits easily under a bell jar used in the experiment

Mint is the only plant that produces oxygen

Mint does not require sunlight

Tissue culture

Hydroponics

Hybridization

Genetic engineering

Green light is highly absorbed

Blue and red light are mostly absorbed

Only yellow light is absorbed

All wavelengths are absorbed equally

Lipid-linked

Water-soluble

Protein-only

Mineral-free

Stroma

Carotenoids

Water

Oxygen

Chlorophyll a only

Accessory pigments

Water molecules

Carbon dioxide

Yellow

Yellow-orange

Blue-green

Orange-red

Blue light ($430-470 nm$)

Green light ($500-550 nm$)

Red light ($660-680 nm$)

Both Blue and Red light

It becomes reduced.

It becomes electronically excited.

It breaks down into smaller components.

It moves from the thylakoid to the stroma.

Methane ($-CH=$) bridges

Ether ($-O-$) bridges

Sulfide ($-S-$) bridges

Peptide bonds

Beta-carotene

Lutein

Chlorophyll $a$

Zeaxanthin

It decreases significantly because chlorophyll absorption is lowest in the green region

It increases because green light has more energy than red light

It remains the same because the plant can adapt to any wavelength

It stops completely because green light is toxic to pigments

Glucose

Oxygen

NADPH

FADH2

Break down ATP

Synthesize ATP

Release protons

Absorb light

To let protons leak freely

To maintain the proton gradient

To absorb more light

To prevent water splitting

Outer mitochondrial membrane

Thylakoid membrane

Nuclear envelope

Plasma membrane

To pump protons into the lumen

To split water molecules

To provide a channel and catalyze ATP formation

To carry electrons from PS II to PS I

To absorb light energy

To provide a physical barrier to maintain a proton gradient

To catalyze the Dark reaction

To synthesize glucose directly

Solar photons

High energy phosphate bonds

Proton-motive force

Oxidation of glucose

The stroma becomes acidic relative to the lumen

The lumen becomes basic relative to the stroma

The lumen becomes acidic relative to the stroma

There is no change in pH; only electrical charge changes

Appressed regions of the grana thylakoids

Non-appressed regions (stroma lamellae and margins of grana)

Uniformly distributed throughout all thylakoid surfaces

Only in the inner chloroplast membrane

Heat energy in the stroma

Electrical energy in the form of an electrochemical proton gradient

Kinetic energy of the $RuBisCO$ enzyme

Potential energy of the glucose molecule

Chloroplast

Peroxisome

Mitochondrion

Cytoplasm

RuBisCO

PEP carboxylase

Hexokinase

ATPase

RuBisCO

PEP carboxylase

Carbonic anhydrase

DNA polymerase

It increases

It decreases

It stops completely

It has no effect

10

5

2.5

2

Pyruvate dehydrogenase

Glycolate oxidase

Glycerate kinase

Serine hydroxymethyltransferase

To recover some of the carbon lost when RuBisCO acts as an oxygenase

To produce glucose independently of the Calvin cycle

To generate ATP for the cell

To store $CO_{2}$ in the form of organic acids

Hydroxypyruvate

Glycerate

Glycolate

Phosphoglycolate

It is excreted through the stomata

It is converted into urea

It is reassimilated in the chloroplast by the action of Glutamine Synthetase

It is used to synthesize nucleic acids in the nucleus

Glycine

Serine

Glutamate

Aspartate