BIOl212 Ch10

Vocabulary flashcards covering the key terms, structural components, and metabolic pathways of photosynthesis in Campbell Biology (12th Edition), Chapter 10.

Photosynthesis

The process that converts solar energy into chemical energy within chloroplasts, directly or indirectly nourishing almost the entire living world.

Autotrophs

"Self-feeders" that sustain themselves without eating anything derived from other organisms; they act as the producers of the biosphere by producing organic molecules from $CO_2$ and other inorganic molecules.

Heterotrophs

Organisms that obtain organic material from other organisms and serve as the consumers of the biosphere, including decomposers that consume dead organic material or feces.

Mesophyll

The interior tissue of the leaf where chloroplasts are mainly located and where most photosynthesis occurs.

Stomata

Microscopic pores in the leaf through which $CO_2$ enters and $O_2$ exits.

Stroma

The dense fluid enclosed within the envelope of two membranes of a chloroplast, surrounding the thylakoid membranes.

Thylakoids

Connected sacs in the chloroplast that constitute a third membrane system and segregate the stroma from the thylakoid space.

Grana

Columns or stacks of thylakoid sacs located within the chloroplast.

Chlorophyll

The green photosynthetic pigment residing in the thylakoid membranes that absorbs violet-blue and red light while reflecting and transmitting green light.

Wavelength

The measure of the distance between crests of electromagnetic waves, ranging from less than a nanometer for gamma rays to more than a kilometer for radio waves.

Electromagnetic spectrum

The entire range of electromagnetic radiation, in which visible light spans wavelengths from $380\,\text{nm}$ to $740\,\text{nm}$.

Photons

Discrete particles of light, each carrying a fixed quantity of energy that is inversely related to the wavelength of light.

Carotenoids

Yellow or orange accessory pigments that absorb violet and blue-green light, broaden the spectrum for photosynthesis, and function in photoprotection by dissipating excessive light energy.

Photosystem

A light-capturing unit located in the thylakoid membrane consisting of a reaction-center complex surrounded by light-harvesting complexes.

Reaction-center complex

A protein complex in a photosystem that contains a special pair of chlorophyll a molecules and a primary electron acceptor.

Light-harvesting complex

An association of pigment molecules bound to proteins that captures photon energy and transfers it to the chlorophyll a molecules in the reaction-center complex.

Primary electron acceptor

A molecule in the reaction center that accepts high-energy electrons from the excited chlorophyll a special pair and is reduced as a result.

Photosystem II (PS II)

One of the two light-capturing units in the thylakoid membrane; features a reaction-center chlorophyll a called P680 because its absorption optimum is at $680\,\text{nm}$.

Photosystem I (PS I)

One of the two light-capturing units in the thylakoid membrane; features a reaction-center chlorophyll a called P700 because its absorption optimum is at $700\,\text{nm}$.

Linear electron flow

The primary pathway of the light reactions that involves both photosystems (PS II and PS I) and produces ATP and NADPH using light energy while splitting water and releasing $O_2$.

Cyclic electron flow

A light-driven pathway using only photosystem I, where photoexcited electrons cycle from ferredoxin (Fd) back to the cytochrome complex via plastocyanin (Pc), yielding ATP but no NADPH or oxygen.

Calvin cycle

The anabolic stage of photosynthesis occurring in the stroma that uses ATP and NADPH to reduce $CO_2$ to sugar through carbon fixation, reduction, and RuBP regeneration.

Rubisco

RuBP carboxylase-oxygenase; the enzyme that catalyzes the attachment of $CO_2$ to the five-carbon sugar ribulose bisphosphate (RuBP) during carbon fixation.

Glyceraldehyde 3-phosphate (G3P)

The three-carbon carbohydrate produced directly by the Calvin cycle; for net synthesis of one G3P molecule, the cycle must fix three molecules of $CO_2$, consuming $9\,\text{ATP}$ and $6\,\text{NADPH}$.

Photorespiration

A metabolic pathway where rubisco binds $O_2$ instead of $CO_2$, consuming organic fuel without generating ATP or sugar; it drains up to 50% of the carbon fixed in many $C_3$ plants.

$C_4$ plants

Plants that minimize photorespiration by fixing $CO_2$ into a four-carbon compound in mesophyll cells before releasing it to bundle-sheath cells for the Calvin cycle.

PEP carboxylase

An enzyme in the mesophyll cells of $C_4$ plants that fixes $CO_2$ to phosphoenolpyruvate (PEP) to form oxaloacetate; it has a higher affinity for $CO_2$ than rubisco and functions at low $CO_2$ concentrations.

Bundle-sheath cells

Tightly packed photosynthetic cells arranged around leaf veins in $C_4$ plants where $CO_2$ is released from four-carbon compounds and fixed by rubisco in the Calvin cycle.

CAM plants

Plants that use crassulacean acid metabolism to conserve water by opening stomata at night to store $CO_2$ in organic acids within vacuoles, then closing stomata during the day while releasing $CO_2$ for the Calvin cycle.