Leaves

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Leaves

• Tissues of leaves and their function

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• Palisade mesophyll consists of densely packed
  cylindrical cells with many chloroplast. This is
  the main photosynthetic tissue and is positioned
  near the upper surface where the light intensity
  is highest

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• Upper epidermis a continuous layer of cells
  covered by a thick waxy cuticle. Prevents water
  loss from the upper surface even when heated by
  sunlight. Lower epidermis is in a cooler
  position and has a less thick waxy covering

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• Note stomata on epidermis. The stomata is a pore
  that allow carbon dioxide for photosynthesis to
  diffuse in and oxygen out

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• Xylem brings water to replace losses due to
  transpiration

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• Phloem transports products of photosynthesis
  out of leaf.
• Both xylem and phloem are called the vascular
  system of plants. The vein is centrally located
  to be close to all cells.

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phloem
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Transport in phloem

• Phloem is located inside leaves. Used to
  transport sugars, amino acids, and other organic
  compounds from photosynthesis.
• Structures called sieve tubes do the
  transporting.
• This is an active process requiring ATP
• High concentration in sieve tubes of solute cause
  water to move in by osmosis

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• This creates a high enough pressure for movement
  where ever the plant needs these products.
• The transport of any biochemical (includes
  sprayed on chemicals) in phloem is called
  translocation.
• Sugar Transport in Plants

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Transpiration

• Flow of water from the roots, through the stems
  to the leaves of plants (transpiration)
• Starts with evaporation of water from the cell
  walls of spongy mesophyll.
• Water is replaced with water from the xylem

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Xylem and transport of water

• Google Image Result for http//www.phschool.com/sc
  ience/biology_place/labbench/lab9/images/xylem.gif
  

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Structure of xylem
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Factors which affect transpiration

• Light closed guard cells in stomata in darkness
• Temperature high temp increase rate of diffusion
  through air spaces in spongy mesophyll
• Humidity movement by osmosis requires water
  potential gradient. Low humidity increases
  transpiration
• Wind blows saturated air away from leaf thus
  increasing transpiration

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Food storage in plants

• The excess products of photosynthesis may be
  stored in storage area called tubers.

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Roots
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• Roots absorb mineral ions and water from the soil
• Anchor the plant and are sometimes used for food
  storage
• Plants Transport and Nutrition - Water Movement

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Mineral uptake by roots

• Plants absorb potassium, nitrate and other
  mineral ions
• Concentration is lower than inside roots
• active transport
• Root hairs provide surface area for ion uptake

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