General Biology Prelab 4: Light Absorption, Photosynthesis, and Electron Transport

Vocabulary flashcards on light absorption, plant leaf anatomy, photosynthetic reactions, paper chromatography, and spectrophotometry based on Prelab 4.

Autotroph

An organism that manufactures its own food, typically through photosynthesis by trapping sunlight and converting it into potential chemical energy.

Heterotroph

An organism that must find and consume food from external sources rather than manufacturing its own.

Oxidation

A chemical reaction that occurs when electrons are lost, chemical bonds are broken, and large molecules break down into smaller molecules.

Reduction

A chemical reaction that occurs when electrons are gained, chemical bonds are created, and small molecules are assembled into larger molecules.

Redox Reactions

Inseparable coupled chemical reactions in which one molecule loses an electron (oxidation) while another molecule gains an electron (reduction).

Chloroplast Structure

A double-membrane-bounded plant and algal organelle consisting of an outer and inner membrane, a fluid-filled matrix called stroma, and grana stacks composed of thylakoids.

Stroma

The liquid matrix located inside the inner membrane of a chloroplast that surrounds the thylakoid stacks.

Thylakoid

A disk-shaped, membrane-enclosed sac within the chloroplast stroma containing photosynthetic pigments such as chlorophyll and carotenoids.

Granum

A stack of disk-shaped thylakoids inside the chloroplast that provides a large surface area for light-absorbing reactions.

Julius von Sachs

The scientist who discovered chloroplasts in $1864$ and demonstrated that starch production in leaves requires exposure to sunlight.

Jan Ingenhousz

The scientist who proved in $1779$ that photosynthesis is driven by sunlight and that plants absorb $\text{CO}_2$ while releasing $\text{O}_2$.

Henri J. Dutrochet

The scientist who discovered that chlorophyll is essential for photosynthesis and identified stomata as the site of gas exchange in $1837$.

Peter Dennis Mitchell

The scientist who discovered in $1978$ that an electron transport chain in chloroplasts uses a proton gradient to create energy in the form of ATP and NADPH.

Cuticle

A thin waxy layer covering the upper and lower epidermis of a leaf that reduces water loss.

Leaf Cross-Section

Anatomy of a leaf showing outer epidermal layers, inner vascular tissue (xylem and phloem) surrounded by bundle sheath cells, upper palisade mesophyll, and lower spongy mesophyll.

Xylem

The water-conducting tissue located within the vascular bundles of a leaf.

Phloem

The food-conducting tissue located within the vascular bundles of a leaf.

Palisade Mesophyll

Columnar cells densely packed with chloroplasts located near the upper surface of most photosynthetic leaves.

Spongy Mesophyll

Loosely packed photosynthetic cells near the lower surface of a leaf surrounded by air spaces where most gas exchange occurs.

Stoma

A small epidermal pore on leaves through which gas exchange occurs ($\text{CO}_2$ in, $\text{O}_2$ out).

Guard Cells

A pair of specialized epidermal cells surrounding each stoma that regulate its opening and closing.

Photon

A particle of light traveling from the sun in waves that can be absorbed or reflected by photosynthetic pigments.

Chlorophyll

The primary green photosynthetic pigment group in plants that reflects green wavelengths while absorbing red and blue light.

Carotenoids

A group of accessory pigments in plants that reflect yellow, orange, and red wavelengths of light.

Cyclic Electron Flow

A light-dependent photosynthetic reaction where energized P700 chlorophyll molecules lose electrons to an electron transport chain to generate ATP without generating NADPH or splitting water.

Noncyclic Electron Flow

A light-dependent pathway involving Photosystem II and Photosystem I where excited chlorophyll loses two electrons, splits $\text{H}_2\text{O}$, and yields ATP, NADPH, and $\text{O}_2$.

Calvin Cycle

The light-independent reactions occurring in the stroma where $\text{CO}_2$ is fixed and reduced using ATP and NADPH to form glucose ($\text{C}_6\text{H}_{12}\text{O}_6$).

Chemiosmosis

The process where protons ($\text{H}^+$) move down their concentration gradient through ATP synthase, causing its turbine-like base to rotate and phosphorylate ADP into ATP.

Paper Chromatography

A laboratory technique used to separate a mixture into its component solute parts based on their differential migration rates through paper as a solvent moves.

Solvent Front ($S_f$)

The total distance traveled by the migrating liquid solvent on a chromatography paper strip.

Relative Front ($R_f$)

The constant ratio of solute distance traveled to solvent distance traveled in chromatography, calculated as $R_f = \frac{\text{distance traveled by pigment}}{S_f}$.

Absorption Spectrophotometry

A method using a spectrophotometer to measure the amount of light absorbed by pigment solutions across a spectrum of wavelengths.