Everything Life Sciences Grade 10

Structure Function

Long cells Form effective conducting tubes for

water and minerals

Dead cells: no cytoplasm No obstruction to water transport

Thick, lignified walls Support the plant and are strong enough

to resist the suction force of transpiration

pull, so they don’t collapse

Pits in cell walls Allow lateral water transport to

neighbouring cells

Tracheids have tapered ends Improved flexibility of the stem in wind

Vessels elements have open ends Water is transported directly to the next

cell

No intercellular spaces Added support for the stem

Living parenchyma cells in between

xylem

Form vascular rays for water transport to

the cortex of the stem

Patterns of secondary wall thickening Improve flexibility of the stem in wind

and allow the stem to stretch as it

lengthens

Activity: Observing the patterned secondary walls in the xylem of fresh plant tissue

Aim:

To observe the patterned secondary walls in the xylem of fresh plant tissue

Materials:

• celery stalk, rhubarb stalks or pumpkin stems(macerated - chop them across and boil
  them in water for 3 minutes, then add an equal amount of glycerine. Cool before
  using. It can be stored for a few months in the refrigerator.)


• microscopes and slides


• dissecting needles


• petri dishes or watch glasses


• eosin solution

Instructions:

1. Lift a small piece of celery / any other tissue chosen from the dish and transfer it to a
   watch glass or petri dish.


2. Use the dissecting needle and a pencil toteasethe tissue apart (separate the thread-
   like, thicker cells away from each other). Try to get the long cells away from each other,
   otherwise bundles will be too thick to allow you to see individual cells. Ignore the thin
   walled parenchyma cells around them.


3. Transfer the plant tissue to a microscope slide and add eosin solution. Separate a bit
   more if necessary.


4. Examine under low power, focusing on the bundles of xylem vessels. Look for long
   bundles of fairly wide cells withthickening in the form of rings or spirals. Do not
   confuse xylem vessels with the more common and much narrower sclerenchyma fibres

128 5.3. Plant tissues