Cycles in Nature: Photosynthesis & Cellular Respiration

Vocabulary flashcards covering key terms related to photosynthesis, factors affecting it, cellular respiration, and associated structures and molecules.

Photosynthesis

Process by which green plants convert light energy, water, and carbon dioxide into glucose and oxygen inside chloroplasts.

Cellular Respiration

Process by which cells break down glucose, using oxygen to produce ATP, carbon dioxide, and water inside mitochondria.

Chlorophyll

Green pigment in chloroplast thylakoid membranes that absorbs light energy for photosynthesis.

Chloroplast

Plant-cell organelle where photosynthesis occurs; contains thylakoids, grana, and stroma.

Stomata

Minute openings in a plant epidermis that allow gas exchange; regulated by guard cells.

Guard Cell

Crescent-shaped epidermal cell that opens and closes a stoma to control gas and water exchange.

Mesophyll

Middle leaf layer (palisade + spongy cells) where most photosynthesis takes place.

Palisade Mesophyll Cell

Column-shaped leaf cell rich in chloroplasts, specialized for capturing light.

Cuticle

Waxy coating on the upper leaf surface that protects against dehydration.

Upper Epidermis

Protective outer leaf layer lacking chloroplasts and covered by cuticle.

Xylem

Plant vascular tissue that transports water and dissolved minerals from roots upward.

Phloem

Plant vascular tissue that moves sugars produced in photosynthesis to other plant parts.

Light-Dependent Reaction

First stage of photosynthesis in thylakoid membranes; converts light energy and water into ATP, NADPH, and O₂.

Light-Independent Reaction (Calvin Cycle)

Second stage of photosynthesis in stroma; uses ATP, NADPH, and CO₂ to synthesize glucose.

ATP (Adenosine Triphosphate)

Primary cellular energy currency produced in photosynthesis and respiration.

NADPH

High-energy electron carrier produced in light reactions and consumed in the Calvin cycle.

RuBisCO

Calvin-cycle enzyme that fixes atmospheric CO₂ to RuBP during carbon fixation.

Thylakoid

Flattened sac inside chloroplast where light reactions and photosystems reside.

Granum

Stack of thylakoids within a chloroplast.

Stroma

Fluid interior of chloroplast surrounding thylakoids; site of the Calvin cycle.

Photon

Packet of light energy absorbed by pigments to initiate photosynthesis.

Photorespiration

Light-dependent process where O₂ is taken up and CO₂ released due to glycolate oxidation.

Carbon Dioxide (CO₂)

Gas taken in by plants for photosynthesis and released by organisms during respiration.

Oxygen (O₂)

Gas released by photosynthesis and required as final electron acceptor in aerobic respiration.

Glucose (C₆H₁₂O₆)

Energy-rich sugar produced by photosynthesis and broken down in respiration.

Limiting Factor

Environmental variable (light, CO₂, temperature, water) that controls the rate of photosynthesis.

Light Intensity

Amount of light energy; higher levels generally increase photosynthetic rate until saturation.

Temperature (Photosynthesis)

Environmental heat level; optimum 25–35 °C for maximal enzyme activity in photosynthesis.

Water Supply

Essential reactant; deficiency causes stomatal closure, lowering CO₂ intake and photosynthesis rate.

Glycolysis

Anaerobic breakdown of glucose in cytoplasm into pyruvate with a net gain of 2 ATP.

Krebs Cycle (Citric Acid Cycle)

Aerobic pathway in mitochondrial matrix that oxidizes acetyl-CoA, releasing CO₂ and forming NADH, FADH₂, and ATP.

Electron Transport Chain (ETC)

Series of membrane proteins in inner mitochondrial membrane that use electrons from NADH/FADH₂ to generate 32–34 ATP and water.

Aerobic Respiration

Cellular respiration that requires oxygen and fully oxidizes glucose to CO₂ and H₂O.

Anaerobic Respiration

Energy-producing process without oxygen, yielding less ATP and products like lactic acid or ethanol.

Fermentation

Anaerobic pathway converting pyruvate into lactic acid or ethanol and CO₂ while regenerating NAD⁺.

Autotroph

Organism (e.g., green plant) that produces its own food via photosynthesis.

Heterotroph

Organism that consumes organic compounds and converts them to CO₂ and energy.

NADH

High-energy electron carrier produced during glycolysis and Krebs cycle, feeding electrons into ETC.

FADH₂

Electron carrier generated in Krebs cycle and used in the electron transport chain.

Carbon Dioxide Concentration

Amount of CO₂ in air; higher levels (up to ~0.1 %) can increase photosynthesis until another factor limits.

Water (H₂O)

Molecule split in light reactions to provide electrons and protons; also product of respiration.

Pigments

Molecules such as chlorophyll a, chlorophyll b, carotenoids, and xanthophylls that absorb specific light wavelengths.

Chlorophyll a

Primary photosynthetic pigment directly involved in light reactions.

Chlorophyll b

Accessory pigment that broadens light absorption spectrum and transfers energy to chlorophyll a.

Photo System I

Pigment-protein complex in thylakoids producing NADPH during light reactions.

Photo System II

Thylakoid complex that splits water and initiates electron transport, generating ATP.