Photosynthesis and Plant Biology

This set of vocabulary flashcards covers the complex biochemical pathways of photosynthesis, including pigments, leaf anatomy, and the specific stages of light-dependent and light-independent reactions.

Photosynthesis

The process by which plants, some bacteria, and some protistans use sunlight energy to produce glucose from carbon dioxide and water.

Chlorophyll a

The primary green pigment present in all photosynthetic organisms that absorbs energy from violet-blue and reddish orange-red wavelengths.

Accessory pigments

Pigments including chlorophyll b, c, d, e, xanthophylls, and carotenoids (such as beta-carotene) that absorb wavelengths of light not captured by chlorophyll a.

Chlorophyll tail

A lipid-soluble hydrocarbon tail with the chemical formula $\text{C}_{20}\text{H}_{39} -$.

Chlorophyll head

A flat hydrophilic structure with a magnesium ion at its centre, linked to the hydrocarbon tail by an ester bond.

Xylem vessels

Specialized plant cells through which water is transported from the roots up to the leaves.

Stomata

Specialized structures flanked by two guard cells that allow gases to enter and leave the leaf while regulating water loss.

Cuticle

A protective waxy layer covering the leaf that prevents carbon dioxide from passing through directly.

Thylakoid

The structural unit of photosynthesis consisting of flattened sacs or vesicles containing photosynthetic chemicals.

Grana

Stacks of thylakoids arranged collectively like pancakes within a chloroplast.

Stroma

The fluid-filled areas between the grana where light-independent reactions occur.

Photoactivation

The process occurring when chlorophyll a absorbs light, resulting in the splitting of water molecules and energy transfer to ATP and NADP.

Phosphorylation

The chemical addition of a phosphate group to an organic compound.

Light-dependent reactions

A series of reactions in the grana that require light to make energy-carrier molecules (ATP and NADPH).

Photophosphorylation

The process of using light energy trapped by chlorophyll to synthesize ATP.

Photolysis

The light-driven splitting of water into oxygen, hydrogen ions, and free electrons: $2\text{H}_2\text{O} \rightarrow 4\text{H}^+ + \text{O}_2 + 4\text{e}^-$.

NADPH

The reduced state of nicotinamide adenine dinucleotide phosphate, formed via: $\text{NADP}^+ + 2\text{e}^- + 2\text{H}^+ \rightarrow \text{NADPH} + \text{H}^+$.

Light-independent reactions

Reactions in the stroma that use ATP and NADPH to reduce carbon dioxide and produce carbohydrates.

Photoionisation

The process by which sufficient light energy ionises a chlorophyll molecule, freeing an electron and leaving a positively charged ion.

Photosystem

A functional unit making up the core of photosynthetic activity, consisting of a chlorophyll molecule, an electron acceptor, and an electron donor.

Photosystem II (PSII)

Also known as P680, this photosystem occurs first in the electron transfer sequence despite its name.

Photosystem I (PSI)

Also known as P700, this photosystem absorbs energy most efficiently at $700\,nm$.

Z scheme

The name given to the electron transfer process due to the Z shape formed by energy changes accompanying the reactions.

Non-cyclic phosphorylation

A process found in thylakoid membranes that produces both ATP and NADPH through the combined action of PSII and PSI.

Chemiosmosis

The production of ATP driven by H+ ions diffusing down an electrochemical gradient from the thylakoid compartment to the stroma.

Cyclic phosphorylation

A process involving only Photosystem I that generates extra ATP by transferring electrons back to the transport chain rather than to NADP+.

Carbon fixation

The process of incorporating atmospheric or aquatic carbon dioxide into organic compounds.

Ribulose 1,5-biphosphate (RuBP)

A five-carbon sugar that combines with carbon dioxide at the start of the dark reaction.

Glycerate 3-phosphate (GP)

A molecule formed when the unstable six-carbon sugar created from RuBP and $\text{CO}_2$ breaks down.

Glyceraldehyde 3-phosphate (GALP)

The molecule formed by the reduction of glycerate diphosphate by NADPH; it serves as a precursor to glucose and other organics.

Calvin Cycle

The sequence of light-independent steps where the first stable product is the 3-C chemical phosphoglycerate (PGA).

Limiting factors

The main factors affecting the rate of photosynthesis: light intensity, carbon dioxide concentration, and temperature.