Chapter 25: Nutrition in the
flowering plant
Leaving Certificate Biology
Higher Level
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
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
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
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
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)
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+
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
1. Respiration within the leaf cells
2. Atmosphere and enters through stomata
• Carbon dioxide is then used up in
photosynthesis (6CO2 + 6H2O + SUNLIGHT →
C6H12O6 + 6O2)
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
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)
Cohesion-Tension Transport
Model
• Water is sometimes transported up to great
heights in very tall trees (>100m)
• 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