Plant Biology
Physiology: Translocation

 THE WATER PATHWAY

 

• In this lab you are going to follow the path of water (and soil nutrients) from the soil, through the plant and out to the air. 
• Make a series of diagrams of the cells and tissues at important stages along the path.
• Then try to produce a "cartoon diagram" of the whole path showing one or two cells of each type connected together and the path(s) of water through them.

  Fresh roots of radish or RCB

  Root hairs are delicate and do not show up on sections, so we need to look at fresh material. Cut a root tip from a seedling and handle it carefully as you make a wet mount. Try to find a good view of root hairs under high power.

  If you have been really careful you can see cytoplasmic streaming in the hairs. What could this be doing?

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  Would water have to go into the cytoplasm of a root hair in order to get into the root, how else could it enter?

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  You cannot see how the root hairs relate to epidermal cells, so this part will have to be imagined for your cartoon figure.

  Transverse section of Ranunculus root

  What kind of cells occupy most of this section?

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  How is water going to move across these cells? _________________________________________________________________

  What kind of cells are just inside the cortex and what is different about their cell walls.

  Where is the water going to go when it reaches these cells?

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  Inside this layer is the pericycle which is where lateral root meristems arise. How many cells thick is the pericycle?

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  Where is the xylem and how is it arranged?

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  Make a diagram of a slice of root that shows some representative cells of each region. Helianthus (sunflower) stem (prepared section)

  Use a low power objective to get a general view of the sections on each slide.

  Choose segment of a stem, including a vascular bundle on the older (larger) section that is in a good state. Draw a wedge of stem in outline showing the tissue systems present and some representative cells from each. Without looking at the text, see if you can label:

  epidermis	cortex	schlerenchyma
  bundle sheath	sieve elements	companion cells
  vessel elements	pith

• Zea (corn stem) (prepared slide)

  Look at the section under low power:

  What is the most conspicuous difference between this and the Helianthus section?

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  Select a well-developed vascular bundle. Make an outline drawing, showing some representative details. Without looking at the text, see if you can label the following:

  sclerenchyma	sieve tubes	companion cells
  parenchyma	vessel elements

  Do you think you can see any cambium on this section?

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  In the stem, the water will move mainly in one kind of cell. Where else might some of it go and how would it get there?

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  Syringa (lilac) leaf cross section, prepared slide

  Find a region on the slide that shows a midvein. You are now ready to follow the path of water out to the atmosphere. Most of it has been in one kind of cell all the way from the root. But how is it going to get out?

  Make an outline diagram to show the following regions and a few representative cells to show the following:

  upper epidermis	lower epidermis	palisade tissue
  spongy mesophyll	xylem	phloem
  collenchyma	bundle sheath	guard cells

  Where are the stomata on this leaf?

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  What are the cells you can occasionally see running parallel to the leaf surface in the mesophyll?

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  On your diagram draw in the path of the water from the xylem to the stomata.

  

  Use another color, preferably blue to show the path that water takes through or round these cells. (There may be more than one path sometimes)

  Acetate peels from water loss lab

  If you have not already done so, be sure to count open and closed stomata on the two acetate peels you made and enter the data on the record sheet for the class.

  Mount the peels dry, using scotch tape to hold a cover slip in place.

  Find a good area on low power and then count stomata in one field with the 40X objective. There should be about 30 stomata in a field. They may all look closed at first glance -- open ones are more rounded with a fuzzy line across the inside.