Biology Unit 6 Photosynthesis

Nucleotide

The basic building block of nucleic acids (DNA and RNA), consisting of a sugar, phosphate group, and nitrogenous base.

ATP (Adenosine Triphosphate)

The cell's main energy-carrying molecule that stores energy in phosphate bonds.

ADP (Adenosine Diphosphate)

A lower-energy molecule formed when ATP loses a phosphate group.

Chloroplast

The organelle in plant cells where photosynthesis takes place.

Stoma

A single pore in a leaf that allows gas exchange.

Grana

Stacks of thylakoids inside a chloroplast.

Thylakoid

Flattened membrane sacs in chloroplasts where light-dependent reactions occur.

Stroma

The fluid-filled space inside a chloroplast surrounding the thylakoids; location of the Calvin Cycle.

Light-Independent Reaction (Calvin Cycle)

Photosynthetic reactions in the stroma that use ATP and NADPH to convert CO₂ into sugars.

Light-Dependent Reaction

Photosynthetic reactions in the thylakoid membranes that use light energy to produce ATP, NADPH, and O₂.

NADP⁺

An electron carrier that accepts high-energy electrons during photosynthesis.

NADPH

The energized form of NADP⁺ that carries electrons and hydrogen to the Calvin Cycle.

Cuticle

A waxy layer covering leaves that helps reduce water loss.

Palisade Mesophyll

A layer of tightly packed cells rich in chloroplasts where most photosynthesis occurs.

Spongy Mesophyll

A layer of loosely packed cells with air spaces that facilitate gas exchange.

Epidermis

The outer protective layer of cells covering a leaf.

Stomata

Small openings in leaves that regulate gas exchange and water loss.

Vascular Bundle

A plant vein containing xylem and phloem tissues.

Xylem

Vascular tissue that transports water and dissolved minerals from roots to the rest of the plant.

Lignin

A strong, waterproof substance that strengthens xylem cell walls.

Vessel Elements

Wide, tube-like xylem cells that form continuous pathways for water transport.

Tracheids

Long, narrow xylem cells that conduct water and provide support.

Cohesion-Tension Theory

The explanation for how water moves upward through xylem due to transpiration and the cohesion of water molecules.

Transpiration

The evaporation of water from plant leaves through stomata.

Phloem

Vascular tissue that transports sugars and other organic nutrients throughout the plant.

Sieve Element

A specialized phloem cell that transports sugars through sieve tubes.

Companion Cell

A phloem cell that supports sieve elements and helps load and unload sugars.

Plasmodesmata

Microscopic channels connecting neighboring plant cells, allowing transport and communication.

Pressure Flow Theory

The explanation for how sugars move through phloem from sources to sinks.

Translocation

The movement of sugars and other organic substances through phloem.

Source

A plant region that produces or releases sugars, such as mature leaves.

Sink

A plant region that uses or stores sugars, such as roots, fruits, or growing tissues.

Chlorophyll a

The primary photosynthetic pigment that directly participates in the light reactions.

Chlorophyll b

An accessory pigment that helps absorb additional wavelengths of light.

Photon

A packet of light energy.

Pigment

A molecule that absorbs specific wavelengths of light.

Tissue

A group of similar cells that work together to perform a specific function.