Xylem vessels:

Consist of dead hollow

Transport water

Waterproof (thanks to LIGNIN)

Provide support

Tracheids:

Similar to vessels but with narrower lumens

Connected by pits

Parenchyma:

Living cells with thin cellulose walls.

Store water (therefore they are turgid)

Provide support through turgidity

Fibres:

Provide strength because their walls are lignified (and therefore, dead).

Xylem Cells

Sieve tube elements:

Living, tubular cells that are connected end to end

End cell walls - have perforations in them to make sieve plates

Cytoplasm - present but in small amounts and in a layer next to the cell wall

Lack of nucleus and most organelles

Cell walls - made of cellulose

Next to each sieve tube element is a companion cell

Companion cell:

Since the sieve tube element lacks organelles, the companion cell with its nucleus, mitochondria, ribosomes, enzymes etc.,

controls the movement of solutes

provides ATP for active transport in the sieve tube element

Strands of cytoplasm called plasmodesmata connect the sieve tube element and companion cell

Parenchyma:

Provides support through turgidity

Fibres:

Provides support for the sieve tube elements

Phloem Cells

Two main types of plant tissue are used in transport - xylem and phloem.

Xylem transports water and minerals.

Phloem transports organic molecules such as the products of photosynthesis.

Translocation

• Survival of plant

• Enables sucrose to be stored or converted

Transpiration

• aborption and transport of water & mineral ions

• cooling effect

• metabolic process

• supply water

• maintain cell turgidity

The importance of transport of plants

light stimulates photosynthesis in the guard cells

guard cells accumulate K+ through active transport

guard cells become hypertonic

water enters guard cells by osmosis

guard cells become turgid

stoma opens

(because thinner outer wall stretches more than thicker inner wall)

The mechanisms of the opening of a stoma

Cool day Hot day

Condition Firm, upright Floppy leaves

Plant cell Turgid Flaccid

Rate of transpiration Low High

How herbaceous plant adapt

Surface area exposed to sunlight Increase Reduce

Stomata Open Closed

Stomata open Stomata close

Light intensity ↑ ↓

Levels of carbon hydroxide ↓ ↑

The movement of water from soil to leaves

Root pressure – osmosis ……>osmotic pressure ……>root pressure

Capillary action – adhesive(water-wall), cohesive (water-water)

Transpirational pull