Photosynthesis and Plant Biology

These vocabulary flashcards cover the process of photosynthesis, including the structure of chlorophyll and chloroplasts, the mechanics of light-dependent and light-independent reactions, and the factors affecting the photosynthetic rate.

Photosynthesis

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

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 (like beta-carotene) that absorb light energy wavelengths not captured by chlorophyll a.

Chlorophyll Structure

Consists of a lipid-soluble hydrocarbon tail ($C_{20}H_{39}-$) and a flat hydrophilic head with a magnesium ion at its centre, linked 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 like carbon dioxide and oxygen to enter and leave the leaf.

Cuticle

A protective waxy layer covering the leaf that carbon dioxide cannot pass through.

Thylakoid

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

Grana

The collective term for thylakoids that are stacked like pancakes within the chloroplast.

Stroma

The areas between the grana in a chloroplast where light-independent reactions occur.

Photoactivation

The process where chlorophyll a absorbs light energy, causing an electron to become 'excited' and transferred to a primary electron acceptor.

Photophosphorylation

The use of light energy trapped by chlorophyll to synthesize ATP from ADP and phosphate.

Photolysis

The light-dependent splitting of water into oxygen, hydrogen ions, and free electrons, summarized by the equation: $2H_2O \rightarrow 4H^+ + O_2 + 4e^-$.

Light-independent reactions

Series of reactions in the stroma that use ATP and NADPH to make carbohydrates from carbon dioxide reduction.

Photoionisation

The process where a chlorophyll molecule is ionized by light energy, freeing an electron and leaving a positively charged chlorophyll ion.

Photosystem core

A complex consisting of a chlorophyll molecule, an electron acceptor, and an electron donor.

PSII (P680)

Photosystem II; the second photosystem discovered but the first to occur in the electron transfer process, absorbing efficiently at $680\,nm$.

PSI (P700)

Photosystem I; a photosystem that absorbs light energy most efficiently at $700\,nm$.

Z scheme

The Z-shaped pattern of energy changes that occur during the electron transfer process between PSII and PSI.

Non-cyclic phosphorylation

A process occurring in the thylakoid membranes involving both photosystems that produces both ATP and NADPH.

Chemiosmosis

The process where the diffusion of $H^+$ ions across an electrochemical gradient from the thylakoid compartment to the stroma drives ATP production.

Cyclic phosphorylation

A process involving only Photosystem I that generates additional ATP for light-independent reactions without forming NADPH.

Carbon fixation

The incorporation of atmospheric carbon dioxide into organic compounds.

RuBP

Ribulose 1,5-biphosphate; a five-carbon sugar that combines with carbon dioxide at the start of the Calvin Cycle.

GP

Glycerate 3-phosphate; a 3-carbon molecule formed when the unstable six-carbon sugar produced by carbon fixation breaks down.

GALP (PGAL)

Glyceraldehyde 3-phosphate; a 3-carbon molecule formed by the reduction of phosphorylated GP using NADPH.

PGA

Phosphoglycerate; identified as the first stable 3-C product of the Calvin Cycle.

Limiting factors

The main environmental factors that restrict the rate of photosynthesis, specifically light intensity, carbon dioxide concentration, and temperature.