Chapter 25: Nutrition in the flowering plant

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Chapter 25 Nutrition in the flowering plant

• Leaving Certificate Biology
• Higher Level

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Transport in Flowering Plants

• Plants make their own food by photosynthesis
  therefore they are called autotrophs
• The substrates necessary for photosynthesis and
  the products of photosynthesis have to be
  transported around the plant
• Transport in plants is carried out by vascular
  tissue xylem and phloem

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Uptake and Transport of Water Through Flowering
Plant

• Water moves into the root hairs by osmosis and
  diffuses through the root cortex, cell by cell
  into the vascular xylem tissue
• Xylem vessels form a continuous tube from the
  root tip up to the leaf
• Two mechanisms combine to cause the transport of
  water up to the leaves from the roots
• Root pressure
• Transpiration

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Root Pressure

• Water builds up in the xylem vessels of the roots
  after it moves in from the root hairs and cortex
• This build up of water it produces a water
  pressure within the xylem tissue called root
  pressure
• Root pressure is not enough to send water up to
  leaves of very tall trees

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Transpiration

• Transpiration is the loss of water vapour from
  the foliage of plants
• Transpiration occurs from the stomata on leaves
  and lenticels on woody stems

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Control of Transpiration

• Transpiration can be controlled by opening and
  closing stomata
• The stomata are mostly located on the underside
  of the leaf and are composed of the opening
  (stoma) and two guard cells that are capable of
  causing the stoma to open or close
• High CO2 concentrations cause stomata to close
  (i.e. at night)
• Low CO2 concentrations cause stomata to open
  (i.e. during light)

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Mineral Transport

• As all minerals are soluble in water they are
  transported along with water through the root
  hairs, root cortex and into xylem tissue
• It then follows the same route as water except
  that minerals are used within the plant cells,
  whereas water evaporates (transpiration)
• Examples of minerals transported through plants
  are Ca2, Mg2, Zn2, Na, K, Fe3, Mn2, Cu2

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Carbon Dioxide

• Carbon dioxide is a gas produced from respiration
  (C6H12O6 6O2 ? ENERGY 6CO2 6H2O)
• Carbon dioxide is present within the airspaces of
  the leaves and comes from two sources
• Respiration within the leaf cells
• Atmosphere and enters through stomata
• Carbon dioxide is then used up in photosynthesis
  (6CO2 6H2O SUNLIGHT ? C6H12O6 6O2)

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Food Transport

• Food (glucose) is transported around the plant by
  phloem sieve tube elements (see chapter 24)
• Glucose formed during photosynthesis is
  transported to areas of the plant where it will
  be converted to starch and stored until needed

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Food Storage

• Food is stored in various storage organs
  depending on the plant species
• Modified root
• Carrot (tap root swells with starch)
• Modified stem
• Potato (base of stem that is underground swells
  with starch)
• Modified leaf
• Onion (fleshy leaves surround the apical and
  lateral buds and fill with starch as they grow)
• Modified petiole
• Celery (petiole swells with starch)

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Cohesion-Tension Transport Model

• Water is sometimes transported up to great
  heights in very tall trees (gt100m)
• Osmosis and root pressure cannot possibly account
  for this as water will only travel a few metres
  by root pressure
• Other factors that contribute to the height water
  can travels up xylem tissue are
• Transpiration from the foliage of the plant
• Cohesion of the water molecules (hydrogen
  bonding)
• Adhesion of the water molecules to the sides of
  the xylem vessels and tracheids