BIO 154: Plant Form and Function Flashcards

Comprehensive practice flashcards covering plant anatomy, water transport mechanisms, photosynthetic light/dark reactions, photorespiration, C4/CAM metabolism, and plant physiology.

What dome-shaped mass of cells protects the root apical meristem as the root grows through soil?

The root cap.

Which specific cells inside the root cap are responsible for sensing gravity and directing root growth downward?

Gravity-responsive cells.

What is the primary anatomical function of root hairs in plant mineral and water uptake?

They increase the surface area available for absorption.

What exact path do water and minerals follow from the soil into the vascular tissue of the root?

Soil $\rightarrow$ root hairs $\rightarrow$ cortex $\rightarrow$ endodermis $\rightarrow$ vascular tissue.

Which anatomical structure carries the leaf blade in eudicots and allows it to be oriented for light interception?

The petiole.

Which stem meristem tissue gives rise to new xylem and phloem elements during growth?

The cambium.

Where are axillary buds located in the repeating component structure of the shoot system?

In the angle between the leaf and the stem.

What are the three fundamental types of ground tissue found across plant organs?

Parenchyma, collenchyma, and sclerenchyma.

Why do sclerenchyma cells typically die upon reaching functional maturity?

Lignification of their thick secondary walls prevents nutrient and gas exchange.

How does the spatial arrangement of vascular bundles in a dicot stem differ from that in a dicot root?

Dicot stems have vascular bundles arranged in a concentric ring, whereas dicot roots have a central vascular stele.

What hydrophobic structural feature in the endodermis forces water to cross a plasma membrane for filtration?

The Casparian strip.

Which plant group's domestication provided the primary caloric foundation that facilitated early human urbanization?

Wild grasses.

What is the general equation for total water potential ($\Psi_W$) in a plant cell?

$$\Psi_W = \Psi_S + \Psi_P + \Psi_M$$

What is the standard water potential ($\Psi$) value of pure water under standard temperature and atmospheric pressure?

$$\Psi = 0$$

If a leaf cell has a solute potential ($\Psi_S$) of $-0.8\, \text{MPa}$ and a pressure potential ($\Psi_P$) of $+0.5\, \text{MPa}$, what is its total water potential ($\Psi_W$)?

$$-0.3\, \text{MPa}$$

How do solute potential ($\Psi_S$) and pressure potential ($\Psi_P$) differ regarding possible mathematical signs?

Solute potential ($\Psi_S$) can be $0$ or negative (never positive), whereas pressure potential ($\Psi_P$) can be negative, zero, or positive.

Which water potential component ($\Psi_M$) results from water interacting with charged surface particles like clay and seeds?

Matric potential ($\Psi_M$).

Which fraction of soil water forms a thin film around soil particles, is held tightly, and cannot be absorbed by roots?

Hygroscopic water.

Which soil water component is held in spaces between soil particles and serves as the main usable source for plants?

Capillary water.

How do diffusion, osmosis, and bulk flow differ in their physical driving forces?

Diffusion is particle movement driven by concentration gradients; osmosis is water diffusion across a selectively permeable membrane; bulk flow is mass movement driven by a pressure gradient.

According to course comparisons, how long does water diffusion take across a $50\, \mu\text{m}$ cell versus a $10\, \text{cm}$ maize leaf?

About $1\, \text{second}$ across a $50\, \mu\text{m}$ cell, versus about $48\, \text{days}$ across a $10\, \text{cm}$ leaf.

What four phenomena comprise the TACT mechanism of upward water transport in xylem?

Transpiration, Adhesion, Cohesion, and Tension.

In the TACT theory, what is the functional difference between cohesion and adhesion?

Cohesion is the binding of water molecules to each other via hydrogen bonds, while adhesion is water sticking to charged cell wall surfaces.

What energy source powers the continuous transpiration pull driving water through the plant continuum?

Solar energy (evaporation powered by sunlight).

What hydrostatic pressure value can occur inside the xylem conduits near the top of a $100\, \text{m}$ tree?

Approximately $-5\, \text{MPa}$.

What structural traits distinguish tracheids from vessel elements in xylem tissue?

Tracheids (gymnosperms) are narrow with complex pit membranes; vessel elements (angiosperms) are wider, shorter, have simple pit membranes, and open/perforated end walls.

What ion shifts occur when blue light triggers guard-cell ATP-driven proton pumps?

$H^+$ is pumped out, prompting $K^+$ uptake through channels and $Cl^-$ uptake via a $Cl^-/H^+$ symporter.

How does solute accumulation inside guard cells cause stomatal pores to open?

It lowers guard-cell water potential, drawing water in by osmosis, increasing turgor pressure, and causing guard cells to bend outward.

Which osmotically active organic solutes assist potassium ions ($K^+$) in maintaining daytime stomatal aperture?

Sucrose and malate.

What chemical transformation occurs to sucrose in guard cells late in the day to bring about stomatal closure?

As light levels fall, sucrose is converted into osmotically inactive starch.

What hypothesis, proposed in 1926, explains long-distance phloem translocation driven by pressure gradients?

The Münch Pressure (Mass) Flow Hypothesis.

Which cell types constitute the living functional conducting system of phloem tissue?

Sieve-tube elements, sieve plates, and companion cells.

What is the primary difference between symplastic and apoplastic phloem loading at source tissue?

Symplastic loading moves sugars through plasmodesmata, while apoplastic loading requires ATP and active transport into companion cells.

How do directionality and cellular state compare between xylem and phloem transport?

Xylem conducts water/minerals strictly upward through dead conduits; phloem transports sugars bidirectionally through living cells.

What is the overall chemical equation for oxygenic photosynthesis?

$$6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$$

What wavelength range defines Photosynthetically Active Radiation (PAR) absorbed by photosynthetic pigments?

$$400\text{--}700\, \text{nm}$$

Which visible light color carries the highest amount of energy per photon?

Violet light.

Which central metallic ion is contained within the porphyrin ring of a chlorophyll molecule?

Magnesium ($\text{Mg}$).

What are the specific reaction center absorption peaks for Photosystem II (PSII) and Photosystem I (PSI)?

P680 for Photosystem II and P700 for Photosystem I.

What occurs during energy transfer within the light-harvesting antenna complex of a photosystem?

Excitation energy is transferred between pigment molecules via resonance without electron transport until reaching the reaction center.

In non-cyclic electron transport, what molecule serves as the initial electron donor to replace electrons lost by P680?

Water ($\text{H}_2\text{O}$).

What three final chemical products are generated by non-cyclic electron transport?

$\text{O}_2$, ATP, and NADPH.

What three primary mobile electron carriers transport electrons between PSII, the cytochrome complex, and PSI?

Plastoquinone, plastocyanin, and ferredoxin.

How does the pathway of electron flow in cyclic electron transport differ from non-cyclic transport?

Electrons from ferredoxin return to the cytochrome complex and plastocyanin back to P700 instead of reducing $\text{NADP}^+$.

What is the primary physiological function of cyclic electron transport in chloroplasts?

To generate additional ATP via chemiosmosis without producing NADPH or $\text{O}_2$.

What biochemical process powers ATP synthesis using a proton ($H^+$) gradient across the thylakoid membrane?

Chemiosmosis.

Why did aerotactic bacteria accumulate near blue and red light regions in Theodor Engelmann's 1883 Spirogyra experiment?

Blue and red light drove the highest rate of photosynthesis, releasing the most oxygen.

At what specific wavelength regions do chlorophyll $a$ and chlorophyll $b$ show maximum absorption peaks?

Approximately $400\text{--}450\, \text{nm}$ (blue) and $650\text{--}700\, \text{nm}$ (red).

Why was the green algal species Spirogyra chosen for Theodor Engelmann's action spectrum experiment?

It features long, continuous filamentous strands with large spiral chloroplasts suitable for direct microscopic observation.

Which Nobel Prize winning chemist drew a cartoon while piecing together the sequential steps of photosynthesis?

Richard Walker.

In which compartment of the chloroplast do the light-independent reactions (Calvin cycle) take place?

In the stroma.

Who received the Nobel Prize in Chemistry in 1961 for elucidating the carbon fixation pathway?

Melvin Calvin.

What are the three main stages of the Calvin cycle in order?

1) Carbon fixation (carboxylation), 2) Reduction, and 3) Regeneration of RuBP.

What chemical reaction takes place during Stage 1 (Carbon fixation) of the Calvin cycle?

$\text{CO}_2$ combines with RuBP to form two 3-PGA molecules, catalyzed by Rubisco.

What high-energy triose sugar is generated during Stage 2 (Reduction) using ATP and NADPH?

Glyceraldehyde-3-phosphate (G3P).

Which enzymatic step during RuBP regeneration requires ATP consumption?

The phosphorylation of ribulose-5-phosphate.

What is the full enzyme name abbreviated as Rubisco?

Ribulose-1,5-bisphosphate carboxylase/oxygenase.

Why is Rubisco characterized in lecture slides as a 'promiscuous' enzyme?

It can catalyze reactions with both $\text{CO}_2$ (carboxylase activity) and $\text{O}_2$ (oxygenase activity).

What fraction of total plant protein can Rubisco represent, and what is its total estimated global mass?

Up to $50\%$ of total plant protein, with an estimated global mass of about $50\,\text{million tons}$.

How much carbon dioxide ($\text{CO}_2$) does Rubisco fix globally every year?

Approximately $100\,\text{billion tons}$.

What balanced chemical equation summarizes the total inputs and outputs of the Calvin cycle for constructing one hexose sugar?

$$6\text{CO}_2 + 12\text{NADPH} + 18\text{ATP} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 12\text{NADP}^+ + 18\text{ADP} + 18\text{P}_i$$

Out of $12$ G3P molecules produced from $6$ turns of the Calvin cycle, how many are recycled and how many are exported?

$10$ G3P molecules are recycled to regenerate RuBP, while $2$ G3P molecules are exported for sugar synthesis.

Which molecules are produced from surplus G3P for short-distance vascular transport and long-term energy storage, respectively?

Sucrose for translocation and starch for long-term storage.

What long-standing evolutionary view of Rubisco was updated by recent studies such as Bouvier et al. (2024)?

The belief that Rubisco was permanently stuck in an 'evolutionary rut'.

What primary products form when Rubisco binds $\text{O}_2$ instead of $\text{CO}_2$ during the oxygenase reaction?

One molecule of 3-phosphoglycerate (3-PGA) and one molecule of 2-phosphoglycolate (2-PG).

How many carbons remain directly usable in carboxylation/oxygenase products when Rubisco acts as an oxygenase versus a carboxylase?

Only $5$ carbons ($1 \times \text{3-PGA} + 1 \times \text{2-PG}$) instead of $6$ carbons ($2 \times \text{3-PGA}$).

Which salvage pathway recovers carbon from 2-phosphoglycolate (2-PG) generated by Rubisco oxygenase activity?

The C2 glycolate pathway.

What is the sequence of intermediate metabolites in the C2 glycolate salvage pathway?

Phosphoglycolate $\rightarrow$ glycolate $\rightarrow$ glycerate $\rightarrow$ 3-phosphoglycerate.

What percentage of carbon is successfully recovered when two 2-PG molecules ($4\text{C}$) are converted into one 3-PGA molecule ($3\text{C}$)?

$75\%$ carbon recovery.

What energy cost is incurred by the plant to run the Rubisco oxygenase reaction and glycolate salvage pathway?

$3.5\,\text{ATP} + 2\,\text{NADPH}$.

Why does photorespiration lower net photosynthetic efficiency in C3 plants?

It consumes energy ($3.5\,\text{ATP} + 2\,\text{NADPH}$) and releases previously fixed carbon without producing sugars or ATP.

Which primary enzyme performs initial carbon fixation into a 4-carbon organic acid in the mesophyll of C4 plants?

Phosphoenolpyruvate carboxylase (PEPC).

What distinct anatomical structure, featuring bundle sheath cells surrounding leaf vascular bundles, is characteristic of C4 plants?

Kranz anatomy.

How does C4 metabolism achieve spatial separation of carbon fixation steps?

Initial fixation by PEPC occurs in mesophyll cells, whereas Rubisco and the C3 cycle operate inside bundle sheath cells.

What three economically important crop plants utilize C4 photosynthesis?

Maize/corn (Zea mays), sugar cane (Saccharum spp.), and sorghum (Sorghum bicolor).

How do C4 and CAM plants differ in their operational separation of initial carbon fixation and the C3 cycle?

C4 plants use spatial separation (mesophyll vs. bundle sheath cells), whereas CAM plants use temporal separation (night vs. day).

Which 4-carbon organic acid accumulates in the vacuoles of CAM plants overnight?

Malic acid (malate).

At what time of day does a CAM plant reach its lowest cellular pH?

At sunrise (approx $06:00$), following overnight accumulation of malic acid.

What happens to stored malate in CAM plants during daylight hours when stomata are closed?

Malate is decarboxylated into pyruvate and $\text{CO}_2$, supplying internal $\text{CO}_2$ to Rubisco for the C3 cycle.

What diurnal pattern do cellular starch levels exhibit in CAM plants over a 24-hour cycle?

Starch levels decrease overnight as starch is converted to PEP, and increase during the day as Calvin cycle products rebuild starch stores.