Plant Physiology: Photosynthesis in Higher Plants

Comprehensive vocabulary flashcards covering the biological and chemical processes of photosynthesis in higher plants, including key scientists, reaction pathways, and limiting factors.

Autotrophs

Green plants that synthesise the food they need through photosynthesis and upon which all other organisms depend.

Photosynthesis

A physico-chemical process by which green plants use light energy to drive the synthesis of organic compounds.

Joseph Priestley

Scientist who in 1770 performed experiments revealing the essential role of air in plant growth and discovered oxygen in 1774.

Jan Ingenhousz

Researcher who showed that sunlight is essential for plants to purify air and that only green parts of plants release oxygen bubbles.

Julius von Sachs

Provided evidence in 1854 that plant growth produce glucose, usually stored as starch, and identified chlorophyll in chloroplasts.

T.W. Engelmann

Used a prism to describe the first action spectrum of photosynthesis by observing bacteria accumulation in blue and red light regions near illuminated alga.

Cornelius van Niel

Microbiologist who demonstrated that photosynthesis is a light-dependent reaction where hydrogen from an oxidisable compound reduces $CO_2$ to carbohydrates.

Light Reactions (Photochemical reactions)

Membrane-bound reactions in the chloroplast involving light absorption, water splitting, oxygen release, and the formation of $ATP$ and $NADPH$.

Dark Reactions (Carbon reactions)

Phases of photosynthesis in the stroma that are not directly light-driven but use $ATP$ and $NADPH$ to synthesise sugars.

Grana and Stroma Lamellae

The membrane system within the chloroplast responsible for trapping light energy and synthesising $ATP$ and $NADPH$.

Chlorophyll a

The chief pigment associated with photosynthesis, showing maximum absorption and higher rates of photosynthesis in blue and red regions.

Accessory Pigments

Pigments such as chlorophyll b, xanthophylls, and carotenoids that absorb light, transfer energy to chlorophyll a, and protect it from photo-oxidation.

Photosystem I (PS I)

A light-harvesting complex containing a reaction centre chlorophyll a with an absorption peak at $700\,nm$, called $P700$.

Photosystem II (PS II)

A light-harvesting complex featuring a reaction centre chlorophyll a with an absorption maxima at $680\,nm$, called $P680$.

Z scheme

The full transfer scheme of electrons from $PS\ II$ uphill to an acceptor, down the transport chain to $PS\ I$, and finally to $NADP^+$.

Splitting of Water

The process associated with $PS\ II$ that provides electrons to replace those moved from the photosystem, expressed as $2H_2O \rightarrow 4H^+ + O_2 + 4e^-$.

Photophosphorylation

The synthesis of $ATP$ from $ADP$ and inorganic phosphate in the membranes of chloroplasts in the presence of light.

Chemiosmotic Hypothesis

The theory explaining $ATP$ synthesis as linked to the development of a proton gradient across the thylakoid membranes.

ATP Synthase

An enzyme consisting of a transmembrane channel ($CF_0$) and a protruding headpiece ($CF_1$) that synthesises $ATP$ as protons diffuse across the membrane.

3-phosphoglyceric acid (PGA)

A 3-carbon organic acid identified by Melvin Calvin as the first stable product of $CO_2$ fixation in the $C_3$ pathway.

Ribulose bisphosphate (RuBP)

A 5-carbon ketose sugar that serves as the primary acceptor of $CO_2$ in the Calvin cycle.

RuBisCO

Ribulose bisphosphate carboxylase-oxygenase; the world's most abundant enzyme that catalyses the initial carboxylation of $RuBP$.

Calvin Cycle

A three-stage pathway (carboxylation, reduction, regeneration) occurring in all photosynthetic plants to produce glucose.

Kranz Anatomy

A special leaf structure in $C_4$ plants where large bundle sheath cells form a wreath-like arrangement around vascular bundles.

Phosphoenol pyruvate (PEP)

The primary 3-carbon $CO_2$ acceptor molecule present in the mesophyll cells of $C_4$ plants.

Oxaloacetic acid (OAA)

The first 4-carbon stable product formed in the mesophyll cells of plants following the $C_4$ pathway.

Photorespiration

A wasteful process in $C_3$ plants where $RuBisCO$ binds $O_2$ instead of $CO_2$, leading to the release of $CO_2$ with the utilisation of $ATP$.

Blackman’s Law of Limiting Factors (1905)

States that if a chemical process is affected by more than one factor, its rate is determined by the factor nearest to its minimal value.