Lesson 5 WATER NEEDS

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Lesson 5WATER NEEDS

• Very important chemical
• Many plants contain up to
• 95 water.

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How would you describe a leaf?
The leaf is where photosynthesis n takes place.
It is well adapted for this function.

• Flat?
• Thin?
• Green?

• Leaves have a large surface area to absorb
  sunlight rays
• A thin shape- so gases can diffuse in and out
  easily
• Green chlorophyll to absorb light
• Veins to support the leaf surface and to carry
  substances to and from all the cells in the leaf.

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Look closely at your leaf

• Is the upper surface shiny? Why is this?
• Which surface is the darker green? Does most
  light get to this surface?

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Functions of a leaf of a typical dicotyledonous
plant

• Increase surface area for photosynthesis for
  the absorption of light leaf blade
• Gas exchange - thin shape
• Site of translocation, evaporation of water help
  s pull water up form roots
• Green chlorophyll for absorption of light
• Veins support leaf surface and carry substances
  to and from leaf

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Inside a leaf
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Internal structure of a leaf
Cuticle waxy prevents evaporation
Upper epidermis
Cell wall
Palisade cells with many chloroplasts
Vacuole
Chloroplast
Nucleus
Spongy layer of cells with air spaces and fewer
chloroplasts
Cytoplasm
Lower epidermis
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Where is most water lost from a leaf?

• Investigation 1
• Put a small piece of cobalt chloride paper on a)
  upper surface of leaf. b) on the lower surface
  of leaf. c) on the table
• Watch for paper to change colour
• Cobalt Chloride paper is blue when dry and pink
  when wet.
• 3 Q. Which side turns the cobalt chloride paper
  pink first?
• 4 Q. Does this side have more or less stomata?

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Another way to prove water loss
(Roberts investigation 5 page 245)Q. Does a
plant lose more water from the lower surface or
upper surface of a leaf ?
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What I hope you will see
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Slide showing a stoma
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Closed stoma
Guard cells
pore closed
chloroplast
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Open stoma
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hGuard cells control the stomata
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How water leaves a plant

• 1. Water evaporates from spongy mesophyll cells
  into spaces
• 2. Air spaces fill with water vapour
• 3. Water diffuses through stomata into air
• 4. Water is lost from spongy cells is replaced

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Work to do

• Label internal parts of a leaf diagram
• Draw table to parts and functions of a leaf
• Answer Osmosis questions/assignments
• Draw graph to show osmosis and answer questions
  (top groups only)
• Homework
• Answer 2 exam questions