Photosynthesis and Chloroplast Function

This set of vocabulary flashcards covers the fundamental concepts of photosynthesis, including the structure of pigments and chloroplasts, the specific steps of the light-dependent and light-independent reactions, and the factors that influence photosynthetic rates.

Photosynthesis

The process by which plants, some bacteria, and some protistans use sunlight energy to produce glucose from $CO_2$ and water, yielding oxygen as a byproduct.

Chlorophyll a

The primary pigment found in all photosynthetic organisms; it absorbs energy from violet-blue and reddish orange-red wavelengths.

Accessory pigments

Pigments such as chlorophyll b, c, d, and e, xanthophylls, and carotenoids (like beta-carotene) that absorb energy wavelengths not absorbed 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 that transport water from the roots up to the leaves.

Stomata

Specialized structures flanked by two guard cells that allow carbon dioxide to enter and oxygen and water vapor to leave the leaf.

Thylakoid

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

Grana

Stacks of thylakoids arranged like pancakes within the chloroplast.

Stroma

The fluid-filled areas between the grana within 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.

Phosphorylation

The chemical addition of a phosphate group to an organic compound, such as the synthesis of ATP from ADP.

Photolysis

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

Light-dependent reactions

A series of reactions occurring in the grana that require direct light energy to produce ATP and reduced NADP (NADPH).

Light-independent reactions

Reactions occurring in the stroma where ATP and NADPH are used to reduce carbon dioxide into carbohydrates like glucose.

Photoionisation

The process where sufficient light energy ionises a chlorophyll molecule by freeing an electron, leaving the molecule positively charged.

Photosystem

A functional unit composed of a chlorophyll molecule associated with an electron acceptor and an electron donor.

Z scheme

The pattern of energy changes that occurs during the electron transfer process involving Photosystem II and Photosystem I.

Chemiosmosis

The process where an electrochemical gradient of $H^+$ ions across the thylakoid membrane drives the production of ATP.

Cyclic phosphorylation

A process involving only Photosystem I that generates excited electrons to produce extra ATP without forming NADPH.

Carbon fixation

The process of incorporating carbon dioxide from the atmosphere 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 three-carbon molecule formed when the unstable six-carbon product of carbon fixation breaks down.

GALP / PGAL

Glyceraldehyde 3-phosphate (also known as phosphoglyceraldehyde); a 3-C molecule produced when GP is phosphorylated by ATP and reduced by NADPH.

Limiting factors

Environmental factors such as light intensity, carbon dioxide concentration, and temperature that can restrict the rate of photosynthesis.

P680 and P700

The specific wavelengths at which Photosystem II (P680) and Photosystem I (P700) absorb energy most efficiently.