Xylem and Phloem

Function of Xylem

carries water and dissolved minerals

Function of Phloem

carries dissolved sugars (photosynthesis), plant hormones, and amino acids

Is the xylem dead at maturity?

Dead at maturity (leaves a hollow tube behind)

Is the phloem dead at maturity?

Alive but have lost their nucleus and most cytoplasm, creating a hollow tube

What is the flow direction of xylem?

Upwards from roots to leaves (transpiration pull)

What is the flow direction of phloem?

Both directions (from source to sink)

2 cells that make up the xylem

vessel elements and tracheids

2 cells that make up the phloem

sieve tubes and companion cells

Sieve cells

have rigid cells walls; have perforations at the top and bottom that allow for unimpeded flow of phloem sap

Companion cells

load and unload sugars into the sieve tubes using active transport; keeps sieve tubes alive by performing metabolic activities

What type of transport is required for xylem?

Passive transport (osmosis) into the xylem

→ transpirational pull

→ perforations (openings) allow for movement of water between cells

What type of transport is required for phloem?

Loading and unloading: active transport

Moving sugar within: bulk flow

What strengthens the xylem?

A spiral of lignin protein

What strengthens the phloem?

rigid cell walls (made of cellulose)

Be able to recognize the xylem (lignin protein) and the phloem (sieve plate, sieve tube, companion cell)

Lignin protein; looks like a spiral

Sieve plate: looks like a shower drain

Sieve tube: cylindrical shape

Companion cell: have a nucleus

What type of movement process is used in the xylem and its definition?

Transpiration: movement of water vapor out of the stomata (leaves and stems)

What type of movement process is used in the phloem and its definition?

Translocation: movement of sugar solution up or down the phloem tissue

Source cell

cell with higher concentration of sugar

Sink cell

cell with lower concentration of sugar