Water Transports (Xylem)
Water enters root hairs by this process.
Osmosis.
Loss of water from a plant, mainly through leaf stomata.
Transpiration
Main sugar transported through phloem.
Sucrose.
Model explaining water movement through xylem.
Cohesion-tension model.
Location where sugar is produced or stored.
Source
Pressure created as water enters roots.
Root pressure
Cells that control the opening and closing of stomata.
Guard cells
Location where sugar is used or stored.
sink.
Model explaining sugar movement through phloem.
Pressure-flow model.
Aphids feed from this vascular tissue.
Phloem.
Force that keeps water molecules connected in one column.
Cohesion.
Pressure that causes guard cells to swell.
Turgor pressure.
Sugar is actively transported into these phloem cells at the source.
Sieve-tube members
Water enters phloem at the source because of this process.
Osmosis.
Sweet waste produced by aphids.
Honeydew
Attraction between water molecules and xylem walls.
Adhesion.
What happens to stomata when guard cells lose water?
They close.
What creates the positive pressure that moves sugar through phloem?
Water entering the sieve tubes by osmosis
Explain how transpiration pulls water upward through xylem.
Water evaporates from leaves, creating tension that pulls a continuous column of water upward through xylem because of cohesion and adhesion.
What do ants gain from aphids?
Honeydew (sucrose-rich droplets)
Explain the cohesion-tension model step-by-step.
Water enters roots by osmosis → creates root pressure → water fills xylem → transpiration from leaves creates tension → cohesion keeps water molecules connected → adhesion keeps water attached to xylem walls → water is pulled upward from roots to leaves.
Explain why photosynthesis stops when stomata close.
Closing stomata prevents CO₂ from entering the leaf, so photosynthesis cannot continue even though water loss is reduced.
Explain the pressure-flow model step-by-step.
Sugar is loaded into sieve tubes at the source → water enters by osmosis → positive pressure develops → sugar solution flows toward the sink → sugar is unloaded → water leaves and returns to xylem.
Compare xylem transport and phloem transport.
Xylem: transports water/minerals upward by the cohesion-tension model.
Phloem: transports sucrose from source to sink by the pressure-flow model.
Describe the mutualism between ants and aphids.
Aphids tap into phloem and excrete honeydew. Ants drink the honeydew and protect the aphids from predators.