Chapter 25: Nutrition in the Chapter 25: Nutrition in the flowering plantflowering plant

Leaving Certificate BiologyLeaving Certificate Biology

Higher LevelHigher Level

Transport in Flowering PlantsTransport 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 Uptake and Transport of Water Through Flowering PlantThrough 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 PressureRoot 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

TranspirationTranspiration

• 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 TranspirationControl 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 TransportMineral 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 DioxideCarbon 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 TransportFood 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 StorageFood 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 Cohesion-Tension Transport ModelModel

• 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