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Structure - Leaves

 

What are typical differences in structure between monocot and dicot leaves?

  • Monocots often have narrow leaves with parallel veins which may branch but do not come back together to make a net.
  • Dicots often have broader leaves with net-like venantion (never truly parallel).

What kinds of plants have stomata on the upper surface of their leaves?

water plants with floating leaves

What is the major photosynthetic tissue in most dicot leaves?

spongy mesophyll

Which is the first part of the leaf to mature and how does this show up in the development of veins?

tip; veins develop from here towards the leaf base

Why do grass leaves grow again after we mow?

the leaves retain the intercalary meristem

Can you relate the anatomical differences between sun and shade leaves to their use of light?

  • Shade leaves broad and thin, spread out to capture what light there is.
  • Sun leaves narrow to cut down evaporative surface and thicken to absorb high proportion of light.

What happens to cells and cell walls during leaf abscission; in which cells do these changes occur?

parenchyma cells separate through breakdown of middle lamella.

xylem breaks.

What kind of structure (stem or leaf) gave rise to these modifications: cladophylls, spines, thorns, stolon, rhizome, tuber, bulb, corm, succulents?

Cladophylls, thorns, stolons, rhizomes, tubeers and corms are mostly stem.

Succulents are leaves or stem.

What is the function of these modifications for the plant and in what way do they help it adapt to the environment?

  • cladophylls -photosynthetic
  • spines and thorns - protective
  • stolon - vegetative reproduction
  • rhizome, tuber, bulb, corm - perennation and vegetative propagation
  • succulents often adapted to low soil water potential (including saline soils)

In comparison with shade leaves, the leaves exposed to the sun on a maple tree would be likely to have more:

  1. stomata
  2. spongy mesophyll
  3. palisade cells

  1. This doesn't seem to make much sense; they would be at greater risk of dessication in the sun than in the shade.

     

  2. The amount of spongy mesophyll is rather constant within a species.

     

  3. Many plants have the ability to increase the depth of palisade parenchyma to take advantage of high light intensities.

Stomata work to achieve a balance between:

  1. respiration and photosynthesis
  2. transpiration and photosynthesis
  3. respiration and transpiration

  1. The balance between respiration and photosynthesis is deterined by light intensity. Above the light compensation point photosynthesis exceeds respiration and stomata have little influence over this.

     

  2. Plants are always having to balance the risk of water loss with the opportunity for photosynthesis. Stomata help them do this.

     

  3. There is little connection between respiration and transpiration; both are "necessary evils"

CO2 fixation into malate in one part of the leaf and release in another part for fixation by Rubisco is a feature of:

  1. warm season grasses
  2. Kentucky bluegrass
  3. cacti and other succulents

  1. Warm season grasses like corn, sugar cane, and many prairie grasses are C4 plants and have the ability to fix CO2 in the mesophyll so that it can be released at a higher concentration in the bundle sheath cells.

     

  2. Kentucky bluegrass is a C3 plant and does nothing like that.

     

  3. Cacti and many succulents are CAM plants that make malate in the night and release CO2 in the day.

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