Photosynthesis and Plant Transport

Comprehensive vocabulary flashcards covering the stages of photosynthesis, chloroplast anatomy, Calvin cycle intermediates, plant cell turgor pressure, stomatal mechanics, xylem/phloem transport mechanisms, and ecological adaptations in C3, C4, and CAM plants.

Chlorophyll

The green pigment in plant cells that absorbs light energy, capturing primarily red and blue light while reflecting green light.

Chloroplasts

The specialized organelles in plant cells where both stages of photosynthesis occur, consisting of thylakoids, thylakoid membranes, thylakoid space, and stroma.

Thylakoids

Flattened membrane sacs situated inside chloroplasts that organize the machinery for the light reactions.

Thylakoid Membrane

The lipid bilayer inside chloroplasts that embeds chlorophyll, photosystems, the electron transport chain, and ATP synthase.

Thylakoid Space

The internal lumen of a thylakoid where hydrogen ions ($\text{H}^+$) accumulate to establish a proton gradient.

Stroma

The fluid-filled space surrounding the thylakoid stacks in a chloroplast where the Calvin cycle synthesizes sugars.

Light Reactions

Stage 1 of photosynthesis occurring in the thylakoid membrane that requires light to split water, release $\text{O}_2$, and produce $\text{ATP}$ and $\text{NADPH}$.

Calvin Cycle

Stage 2 of photosynthesis occurring in the stroma that uses $\text{CO}_2$, $\text{ATP}$, and $\text{NADPH}$ to synthesize the sugar precursor $\text{G3P}$.

Photosystem II

The photosystem that functions first in the light reactions, splitting water to release oxygen and passing energized electrons to the electron transport chain.

Photosystem I

The photosystem that re-energizes electrons coming from the electron transport chain so they can be transferred to make $\text{NADPH}$.

Electron Transport Chain (ETC)

A series of membrane-bound proteins that shuttle electrons and harness their energy to pump $\text{H}^+$ ions into the thylakoid space.

Chemiosmosis

The mechanism wherein $\text{H}^+$ ions diffuse down their electrochemical gradient across a membrane through ATP synthase to generate $\text{ATP}$.

ATP Synthase

An enzyme embedded in the membrane that produces $\text{ATP}$ as $\text{H}^+$ ions flow down their concentration gradient through its channel.

Photophosphorylation

The production of $\text{ATP}$ from $\text{ADP}$ and inorganic phosphate driven by light-dependent photosynthetic processes.

NADPH

An electron carrier produced during the light reactions that transfers high-energy electrons and hydrogen to the Calvin cycle.

RuBP (Ribulose 1,5-Bisphosphate)

A five-carbon sugar molecule that serves as the carbon dioxide acceptor during the initial carbon fixation step of the Calvin cycle.

Rubisco

The enzyme that catalyzes carbon fixation by joining incoming $\text{CO}_2$ to the five-carbon acceptor RuBP.

G3P (Glyceraldehyde-3-phosphate)

A three-carbon sugar yielded by the Calvin cycle that serves as the basic building block for glucose and is recycled to regenerate RuBP.

Endergonic

A non-spontaneous chemical process requiring a net input of energy, such as photosynthesis using light to build carbohydrates.

Exergonic

A chemical reaction that overall releases free energy, exemplified by cellular respiration breaking down glucose to make $\text{ATP}$.

Chlorophyll Absorption Spectrum

A plotted profile showing the percentage of light absorbed by chlorophyll a and chlorophyll b across different wavelengths, with prominent absorption in blue and red.

Stomata

Microscopic pores located predominantly on leaf surfaces that open and close to allow gas exchange of $\text{CO}_2$, $\text{O}_2$, and water vapor.

Guard Cells

Specialized paired epidermal cells bordering a stoma that regulate its opening and closing in response to osmotic shifts driven by $\text{K}^+$ uptake or loss.

Turgid

The firm, swollen condition of a plant cell caused by internal turgor pressure when water enters under hypotonic conditions.

Flaccid

The limp, soft state of a plant cell that occurs when water is lost and turgor pressure drops, potentially leading to wilting.

Xylem

Vascular tissue in plants responsible for the unidirectional, upward transport of water and dissolved minerals from roots to stems and leaves.

Phloem

Vascular tissue in plants responsible for transporting sugars and other organic nutrients bidirectionally from source tissues to sink tissues.

Transpiration

The evaporative loss of water vapor from plant leaves through open stomata that generates negative pressure pulling water upward.

Cohesion-Tension Theory

The model of xylem transport stating that evaporation generates tension pulling a continuous, cohesive column of water upward through the plant.

Root Pressure

Positive hydrostatic pressure created in the root xylem by active mineral ion accumulation and subsequent osmotic water influx.

Source (Plant Transport)

A plant organ or tissue where sugar is synthesized or released from storage, such as a mature photosynthesizing leaf.

Sink (Plant Transport)

A plant organ or tissue where sugar is consumed or stored, such as growing roots, developing fruits, or emerging leaves.

Companion Cells

Specialized cells adjacent to phloem sieve elements that actively load sugars into the phloem and supply metabolic support.

Pressure Flow Hypothesis

The mechanism explaining phloem sap transport where active loading of sugars at a source draws water in from xylem, creating hydrostatic pressure that pushes sap toward a sink.

C3 Plants

Plants that fix carbon directly into a 3-carbon intermediate via Rubisco in mesophyll cells, which are vulnerable to photorespiration in hot and dry climates.

C4 Plants

Plants adapted to hot, sunny conditions that spatially separate initial 4-carbon fixation in mesophyll cells from the Calvin cycle in bundle sheath cells to minimize photorespiration.

CAM Plants

Plants adapted to arid environments that open stomata at night to fix $\text{CO}_2$ into organic acids and release that carbon to the Calvin cycle during the day.

Bundle Sheath Cells

Cells arranged in tight rings around leaf veins in C4 plants that contain Rubisco and carry out the Calvin cycle in a high-$\text{CO}_2$ environment.

Photorespiration

An energetic pathway where Rubisco fixes oxygen instead of carbon dioxide, consuming energy and releasing fixed carbon without sugar production.