Photosynthesis and Cellular Energy

Vocabulary practice flashcards covering the concepts, structures, biochemical pathways, and adaptations of photosynthesis and cellular respiration from Chapter 9.

Photosynthesis

The biological process by which autotrophs convert light energy from the sun into chemical energy stored in organic compounds such as carbohydrates, utilizing carbon dioxide ($CO_2$) and water ($H_2O$).

Cellular Respiration

The process in cells by which organic compounds are broken down and combined with oxygen ($O_2$) to produce $ATP$, yielding carbon dioxide ($CO_2$) and water ($H_2O$) as waste products.

Adenosine Triphosphate ($ATP$)

The primary energy storage molecule used by all living cells, composed of an adenine base, a ribose sugar, and three phosphate groups, which releases usable energy when transformed into $ADP$.

Adenosine Diphosphate ($ADP$)

A lower-energy compound composed of adenine, ribose, and two phosphate groups that functions like a partially charged battery and is recharged into $ATP$ when energy and a phosphate group are added.

Heterotrophs

Organisms that obtain their chemical energy ($ATP$) by consuming other organisms or organic matter.

Autotrophs

Organisms capable of producing their own food and organic matter using light energy through photosynthesis or chemical energy through chemosynthesis.

Chemosynthesis

The biological process of producing organic matter using chemical energy rather than light energy.

White Light

A mixture of many different wavelengths and colors of light across the visible spectrum, ranging from $400\,\text{nm}$ to $700\,\text{nm}$.

Pigments

Light-absorbing chemical compounds that impart visible color to an object by absorbing specific wavelengths while reflecting others.

Chlorophyll a

A primary photosynthetic pigment located in chloroplasts that absorbs more red light and directly participates in the light reactions.

Chlorophyll b

An accessory photosynthetic pigment in chloroplasts that absorbs more green light and aids chlorophyll a in capturing light energy.

Carotenoids

Accessory pigments in chloroplasts that absorb alternative light wavelengths and are frequently masked by the presence of chlorophylls.

Thylakoid

A flattened, sac-like inner membrane compartment inside chloroplasts where the light-dependent reactions of photosynthesis occur.

Grana

Dense, organized stacks of thylakoid membranes located inside the chloroplast (singular: granum).

Stroma

The liquid solution surrounding the thylakoid stacks inside the chloroplast where the Calvin cycle takes place.

Light Reaction

The initial set of reactions in photosynthesis occurring in the thylakoid membrane that begins with the absorption of light, excites electrons, splits water, and produces $ATP$ and $NADPH$.

ATP Synthase

A membrane protein and enzyme that harnesses the potential energy of a proton ($H^+$) concentration gradient across the thylakoid membrane to synthesize $ATP$ from $ADP$ and phosphate.

Calvin Cycle

The second stage of photosynthesis occurring in the stroma that utilizes the chemical energy stored in $ATP$ and $NADPH$ during the light reactions to produce organic compounds.

Carbon Fixation

The incorporation of inorganic carbon from carbon dioxide ($CO_2$) into organic compounds during the Calvin cycle.

RuBP

A five-carbon carbohydrate located in the stroma that combines with carbon dioxide ($CO_2$) during Step 1 of the Calvin cycle.

PGA

A three-carbon molecule produced when the unstable six-carbon compound formed from RuBP and $CO_2$ splits in the Calvin cycle.

PGAL

A three-carbon compound synthesized from PGA using energy from $ATP$ and $NADPH$; some molecules leave the cycle to form organic compounds while the rest regenerate RuBP.

$C_3$ Plants

Plants that fix carbon exclusively through the standard Calvin cycle, forming three-carbon PGA molecules as their initial stable intermediate.

$C_4$ Pathway

An alternative photosynthetic carbon fixation pathway in plants like corn, sugar cane, and crabgrass that fixes carbon dioxide into a four-carbon compound and consumes roughly half as much water as $C_3$ plants.

CAM Pathway

A water-conserving carbon-fixing pathway used by desert plants such as cactuses that open their stomata to take in carbon dioxide ($CO_2$) exclusively at night.

Stoma

A microscopic pore on a plant leaf surrounded by guard cells that opens and closes to control the exchange of gases ($CO_2$ and $O_2$) and the loss of water vapor.