Plants & Plants & PhotosynthesisPhotosynthesis

Plant TissuesPlant Tissues GroundGround tissue –tissue –

ParenchymaParenchyma – thin walled, used – thin walled, used for storage, photosynthesis, or for storage, photosynthesis, or secretion.secretion.

Collenchyma Collenchyma – thick, flexible – thick, flexible walls, used for supportwalls, used for support

SclerenchymaSclerenchyma – thickest walls, – thickest walls, used for support.used for support.

Dermal -Dermal -•Guard cellsGuard cells – – surround stomata, surround stomata, turgor controls openingturgor controls opening

•EpidermisEpidermis – thin protective layer, – thin protective layer, waxy cuticle secretionwaxy cuticle secretion

•Specialized cells & Cuticle – Specialized cells & Cuticle – secretive, defensivesecretive, defensive

Vascular –Vascular –•XylemXylem – – conduction of water and conduction of water and minerals; may have both primary & minerals; may have both primary & secondary walls which lends itself to secondary walls which lends itself to secondary function as support. Dead secondary function as support. Dead at maturity.at maturity.

•TracheidsTracheids – long,tapered, have – long,tapered, have openings at ends called pits (2openings at ends called pits (2◦◦ wall wall absent).absent).•Vessel elements – shorter & wider; Vessel elements – shorter & wider; openings at ends openings at ends have no walls.have no walls.

•PhloemPhloem – conduction of sugars.– conduction of sugars.Sieve tube elements Sieve tube elements

sieve tubessieve tubes. Lack nuclei & . Lack nuclei & ribosomes,but are living. ribosomes,but are living. Openings on end form Openings on end form sieve sieve platesplates - allows contact between - allows contact between cells.cells.

Companion cellsCompanion cells – – connected by plasmodesmata; connected by plasmodesmata; provide provide physiological support.physiological support.

Leaf AnatomyLeaf Anatomy

Leaf AnatomyLeaf Anatomy

Epidermis w/cuticleEpidermis w/cuticle Guard cells - stomataGuard cells - stomata Mesophyll – palisade layer, Mesophyll – palisade layer,

spongy layer, air spacesspongy layer, air spaces Vascular bundles – xylem, Vascular bundles – xylem,

phloemphloem

Control of StomataControl of Stomata Surrounded by 2 guard cells Surrounded by 2 guard cells

which swell w/water. Uneven which swell w/water. Uneven construction of cell wall causes construction of cell wall causes the cells to bulge outward, the cells to bulge outward, creating opening.creating opening.

A diffusion of KA diffusion of K++ ions creates a ions creates a gradient for the movement of gradient for the movement of water, which leads to swelling.water, which leads to swelling.

Control of StomataControl of Stomata

Temperature, inner COTemperature, inner CO22 levels levels influence opening.influence opening.

Most plants close stomata at Most plants close stomata at night, probably due to high COnight, probably due to high CO22 levels.levels.

Water loss, or Water loss, or transpirationtranspiration is is minimized when stomata are minimized when stomata are closed.closed.

PhotosynthesisPhotosynthesis

Light energy + 6HLight energy + 6H22O + 6COO + 6CO22 C C66HH1212OO66 + 6O + 6O22

OverviewOverview

The process begins with light-The process begins with light-absorbing pigments which are absorbing pigments which are able to absorb the energy from able to absorb the energy from light. In a series of reactions, this light. In a series of reactions, this energy is eventually used to energy is eventually used to produce a molecule of glucose.produce a molecule of glucose.

ChloroplastsChloroplasts Similar to the mitochondria, Similar to the mitochondria,

chloroplasts are composed of an chloroplasts are composed of an outer phospholipid membrane outer phospholipid membrane encasing a fluid interior (in this encasing a fluid interior (in this case case stromastroma). ).

Pancakelike membranes called Pancakelike membranes called thylakoidsthylakoids are arranged in stacks are arranged in stacks called called granagrana (granum, singular) (granum, singular)

The thylakoids contain the light-The thylakoids contain the light-absorbing pigments, such as absorbing pigments, such as chlorophyll a and bchlorophyll a and b, and , and carotenoidscarotenoids and various and various enzymes.enzymes.

The fluid stroma contains several The fluid stroma contains several enzymes involved in enzymes involved in carbohydrate synthesis.carbohydrate synthesis.

Chemical reactions of Chemical reactions of photosynthesisphotosynthesis

The process of photosynthesis The process of photosynthesis can be divided into two major can be divided into two major series of reactions:series of reactions:

Light-dependent reactionsLight-dependent reactions Light-independent or dark Light-independent or dark

reactions reactions

Light – dependent Light – dependent reactionsreactions

HH22O + ADP + PO + ADP + Pii + NADP + NADP++ + light + light

ATP + NADPH + OATP + NADPH + O22 + H + H++

This equation sums up what occurs This equation sums up what occurs in this process. in this process.

Notice a Notice a photophotophosphorylation phosphorylation occurs, making ATP from ADP & Poccurs, making ATP from ADP & P ii

The details of LDRThe details of LDR Noncyclic photophosphorylation Noncyclic photophosphorylation

occurs in two pigment clusters occurs in two pigment clusters called called Photosystems I and IIPhotosystems I and II..

Different pigments absorb Different pigments absorb different ranges of light different ranges of light wavelengths. wavelengths.

The absorbed light “excites” The absorbed light “excites” electrons.electrons.

These energized electrons are These energized electrons are unstable and immediately re-emit unstable and immediately re-emit the absorbed energy. the absorbed energy.

The energy is then reabsorbed by The energy is then reabsorbed by neighboring pigment molecules in neighboring pigment molecules in a chainlike fashion, eventually a chainlike fashion, eventually being absorbed into a special being absorbed into a special chlorophyll a molecule called chlorophyll a molecule called PP680680. . (max. amt. of light absorbed nm)(max. amt. of light absorbed nm)

This is actually This is actually photosystem IIphotosystem II, , beginning the energy transfer beginning the energy transfer process.process.

A A primary electron acceptorprimary electron acceptor than than accepts and passes two accepts and passes two energized electrons through an energized electrons through an electron transport chain of electron transport chain of proteins, including proteins, including ferredoxinferredoxin and and cytochrome.cytochrome.

As the electrons move “down” As the electrons move “down” the chain, losing energy, the the chain, losing energy, the “lost” energy is used to “lost” energy is used to phosphorylate ATP. phosphorylate ATP. (For every 2 (For every 2 electrons through the system, an average electrons through the system, an average of 1.5 ATP molecules are made.)of 1.5 ATP molecules are made.)

The pigment cluster, The pigment cluster, Photosystem I,Photosystem I, is the final is the final recipient of the electrons, which recipient of the electrons, which are again energized by sunlight.are again energized by sunlight.

Energized electrons are passed Energized electrons are passed off to off to PP700 700 and then another and then another

primary electron acceptor.primary electron acceptor. Another, shorter, ETC, passes Another, shorter, ETC, passes

electrons along, terminating in electrons along, terminating in the energy-rich coenzyme the energy-rich coenzyme NADPHNADPH. (NADP. (NADP++ and H and H+ + are are combined by the absorption of combined by the absorption of the electrons)the electrons)

This entire process causes the This entire process causes the removal of two electrons from removal of two electrons from

PS II.PS II. These electrons are replaced by These electrons are replaced by

splitting water in a process called splitting water in a process called photolysis.photolysis.

HH22O O 2H+ + ½ O 2H+ + ½ O22 + electrons + electrons

Cyclic photophosphorylationCyclic photophosphorylation involves PS I and occurs involves PS I and occurs simultaneously with noncyclic. simultaneously with noncyclic.

Energized electrons from PS I join Energized electrons from PS I join with protein carriers and generate with protein carriers and generate ATP.ATP.

Since electrons are not passed off to Since electrons are not passed off to NADPH, they can be recycled.NADPH, they can be recycled.

Concentrations of ATP and NADPH Concentrations of ATP and NADPH probably influence whether or not probably influence whether or not the pathway is cyclic or noncyclic.the pathway is cyclic or noncyclic.

Light Dependent Light Dependent ReactionsReactions

What are the three main What are the three main processes that make up LDR?processes that make up LDR?

What’s needed?What’s needed? What’s produced?What’s produced? Where does it occur?Where does it occur?

Light-independent Light-independent reactions: Calvin-Benson reactions: Calvin-Benson cyclecycle ““Fixes” COFixes” CO2 2 organic molecule organic molecule

Uses energy in ATP and NADPHUses energy in ATP and NADPH Six turns of the cycle are needed Six turns of the cycle are needed

to generate 1 glucose molecule, to generate 1 glucose molecule, however, glucose is NOT the however, glucose is NOT the DIRECT result of this cycle.DIRECT result of this cycle.

Calvin-Benson Cycle: Calvin-Benson Cycle: A Closer LookA Closer Look

Carbon FixationCarbon Fixation – CO – CO2 2 attaches attaches

to a to a 5C5C sugar, sugar, RuBPRuBP (ribulose (ribulose biphosphate) via the enzyme biphosphate) via the enzyme rubisco. rubisco.

The 6C intermediary is unstable The 6C intermediary is unstable and quickly splits to form two and quickly splits to form two

3C PGA3C PGA (3-phosphoglycerate) (3-phosphoglycerate)

ReductionReduction – Each PGA receives – Each PGA receives an additional phosphate group an additional phosphate group from ATP and electrons from from ATP and electrons from NADPH reducing it to NADPH reducing it to G3P aka G3P aka PGAL PGAL (also an intermediate of (also an intermediate of glycolysis).glycolysis).

Several turns of the cycle are Several turns of the cycle are needed to continue……needed to continue……

Regeneration Regeneration – Once three turns – Once three turns of the cycle are achieved, the gain of the cycle are achieved, the gain of 6 G3P is used to regenerate 3 of 6 G3P is used to regenerate 3 molecules of RuBP, leaving one molecules of RuBP, leaving one extra G3P to be used by the plant extra G3P to be used by the plant to make glucose. to make glucose.

Carbohydrate synthesisCarbohydrate synthesis – Once – Once six turns are achieved, there are six turns are achieved, there are enough molecules of G3P to enough molecules of G3P to make glucose.make glucose.

PhotorespirationPhotorespiration The enzyme rubisco is capable of “fixing” The enzyme rubisco is capable of “fixing”

oxygen as well as carbon dioxide, thus it oxygen as well as carbon dioxide, thus it can be very inefficient.can be very inefficient.

The products made when oxygen is The products made when oxygen is “fixed” to RuBP are not useful to make “fixed” to RuBP are not useful to make glucose.glucose.

This reduces the amount of carbon This reduces the amount of carbon dioxide that is “fixed”, thus reducing dioxide that is “fixed”, thus reducing glucose production and growth.glucose production and growth.

CC44 & Cam Photosynthesis & Cam Photosynthesis

Certain plants have evolved a means of Certain plants have evolved a means of reducing the amount of photorespiration reducing the amount of photorespiration that can occur.that can occur.

CC4 4 plants – carbon dioxide “fixes” to PEP plants – carbon dioxide “fixes” to PEP

(phosphoenolpyruvate) with the help of (phosphoenolpyruvate) with the help of the enzyme PEP carboxylase to form the enzyme PEP carboxylase to form OAA (oxaloacetate), a 4 C compound.OAA (oxaloacetate), a 4 C compound.

CC44 & Cam Photosynthesis & Cam Photosynthesis

OAA is then converted to malate and OAA is then converted to malate and shuttled to special cells within the leaf shuttled to special cells within the leaf which are not in direct contact with which are not in direct contact with oxygen. oxygen.

The malate then breaks down, forming The malate then breaks down, forming carbon dioxide (& pyruvate) and the carbon dioxide (& pyruvate) and the carbon fixation begins. carbon fixation begins.

CC44 & Cam Photosynthesis & Cam Photosynthesis

Not only does this increase Not only does this increase photosynthesis efficiency it also helps photosynthesis efficiency it also helps these plants conserve water because these plants conserve water because they do not need to have their stomata they do not need to have their stomata open as much to take in carbon dioxide.open as much to take in carbon dioxide.

These plants are often found thriving in These plants are often found thriving in hot, dry climates.hot, dry climates.

CC44 & Cam Photosynthesis & Cam Photosynthesis

Crassulacean acid metabolism –Crassulacean acid metabolism – Very similar to CVery similar to C4 4 but for a few but for a few

differences.differences. Malic acid is made rather than malate.Malic acid is made rather than malate. Malic acid is shuttled to Malic acid is shuttled to vacuolevacuole of cells. of cells. Stomata are open at night and closed Stomata are open at night and closed

during the day to reduce water loss.during the day to reduce water loss.