2 Assessment Statements Outline how the root system provides a large surface area for mineral ion and water uptake by means of branching and root hairs.List ways in which mineral ions in the soil move to the root.Explain the process of mineral ion absorption from the soil into roots by active transport.State that terrestrial plants support themselves by means of thickened cellulose, cell turgor and lignified xylem.Define transpiration.Explain how water is carried by the transpiration stream, including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation.State that guard cells can regulate transpiration by opening and closing stomata.State that the plant hormone abscisic acid causes the closing of stomata.Explain how the abiotic factors light, temperature, wind and humidity, affect the rate of transpiration in a typical terrestrial plant.Outline four adaptations of xerophytes that help to reduce transpiration.Outline the role of phloem in active translocation of sugars (sucrose) and amino acids from source (photosynthetic tissue and storage organs) to sink (fruits, seeds, roots).
3 Transport in angiospermophytes Transport in flowering plants occurs on three levels:the uptake and loss of water and solutes by individual cellsshort-distance transport of substances from cell to cell at the level of tissues or organslong-distance transport of sap within xylem and phloem at the level of the whole plant
4 Variety of physical processes involved in the different types of transport
8 How the root system provides a large surface area for mineral ion and water uptake the root system of a plant must supply sufficient water & mineral ionsfor this reason, it has developed a large surface area due to;branchingpresence of root hairs near the tip
9 Ways in which mineral ions in the soil move to the root mineral ions are absorbed by root hairs on the epidermisroot hairs increase the surface area for absorptionmineral ions enter the root hairs trough active transport which uses energy in form of ATPactive transport uses of proteins pumps to move ions across membraneagainst concentration gradient i.e. from low concentration in the soil into the root cells where they are in high concentrationthe rate of absorption of mineral ions is limited by the rate at which the ions move through the soil to the rootsthere are three ways in which the ions move to the root:through facilitated diffusionthrough mass flow of water containing dissolved ionsthrough mutualistic fungal hyphae growing around the root
10 Adaptations of plant roots for absorption of mineral ions from the soil mineral ions are absorbed by active transportlarge surface area is requiredbranching of the root & presence of root hairs increases surface arearoot hair cells have carrier protein (ion pumps) in their plasma membranemany mitochondria are present in root hair cells to provide ATP for active transportconnections with fungi in the soil (fungal hyphae)
11 How terrestrial plants support themselves terrestrial plants support their tissues through:thickening of the cellulose cell walllignified xylem vesselscell turgidity, turgor pressure provide mechanical support to the plant tissue
12 Define transpirationtranspiration is water loss from plant by evaporationexcess water loss may harm the planttranspiration is the driving force that pulls water up from the roots to the leaves to supply photosynthesizing tissuethus, transpiration is a necessary evil
14 How water is carried by the transpiration stream transpiration is water loss from plant by evaporationflow of water through xylem from roots to leaves is the transpiration streamwater enters roots through the root hairs by osmosisroot hairs provide an extended surface area for active transport & osmosisactive transport of ions from soil into the roots enhances osmotic pressureosmotic pressure moves water into the xylemwater is carried in a transpiration stream in the xylemadhesion of water to the inside of the xylem helps move water upcohesion of water to itself enhances water movement up the xylemwater vapour diffuses into air spaces in spongy mesophyll of leavesit passes out through the stomata by evaporation i.e. transpirationevaporation of water vapour sets up a transpiration pull that keeps the water movingguard cells control the rate of transpiration pull by controlling evaporationxylem vessels are tubes with helical rings to enhance water movement by resisting low pressure
15 How guard cells regulate transpiration stomata are pores usually in the lower epidermiseach stomata is formed by two specialised guard Cellsthe epidermis & its waxy cuticle is impermeable to carbon dioxide & waterduring the day the pore opens to allow carbon dioxide to enter for photosynthesishowever, the plant will experience water loss, if the water loss is too severe the stoma will closedehydration, low water potential, of the mesophyll cell causes them to release the hormone abscisic acidabscisic acid stimulates the stoma to closeduring the night plants cannot photosynthesis, so the plant closes the pores thereby conserving waterguard cells gain water & openstoma is large, rate of transpiration is highguard cells lose water & closestoma is small, rate of transpiration is low
16 Hormone abscisic acid causes the closing of stomata guard cells gain water & openstoma is large, rate of transpiration is highguard cells lose water & closestoma is small, rate of transpiration is low
17 How the abiotic factors affect the rate of transpiration in terrestrial plant transpiration is loss of water vapour from the stomata of leaves & stems of plantstemperature, humidity, light intensity & wind all affect rate of transpirationhumidity, less transpiration as atmospheric humidity rises due to smaller concentration gradient of water vapourrelatively high temperatures, more transpiration as temperature rises due to faster diffusion as a result of more kinetic energy of water moleculesfaster evaporation due to more latent heat availablewindy conditions, more transpiration as wind speed increases as water vapour blown away from the leafincreasing the concentration gradient of water vapourhigh light intensity, more transpiration in the light due to light causing stomata to openwider opening of stomata with brighter light hence more transpirationCAM plants opposite, narrower stomata with high carbon dioxide concentration hence less transpirationlow air pressure, low levels of carbon dioxide
18 Adaptations of xerophytes that help to reduce transpiration xerophytes are plants that live in dry conditionsxerophytes are adapted in the following ways to reduce water loss:reduced leaves (spines or needle like) to reduce the surface area for transpirationrolled leaves with stomata on the inside to prevent water loss by transpirationsunken stomata allows layer of humidity to build up reducing water loss by evaporationthick waxy cuticle on leaves epidermis to prevent water loss by transpirationhairs allow water vapour to be retainedreduced stomata / stomata on under side of the leaf to prevent water loss by transpirationspecial water storage tissue,wide-spreading network of shallow roots obtain more waterdeep roots to absorb water from deep sourcesvertical stems to avoid mid-day sunreversed stomata rhythm, take in carbon dioxide at night to prevent water loss during the day
19 Role of phloem in active translocation of sugars (sucrose) & amino acids phloem is a living tissue composed of companion cells & sieve tube membranescompanion cells involved in ATP productionassimilate products of photosynthesis, sucrose & amino acids transported in phloemtranslocation is a bi-directional transportfrom the source; leaves to the sinks; fruits, roots, the storage organs such as stem tubers, rootspressure flow hypothesis;- movement of water into phloem causes transport
20 1. Loading of sugar (green dots) into the sieve tube at the source reduces water potential inside thesieve-tube members. This causes the tube to take up water by osmosis.2. This uptake of water generates a positive pressure that forces the sap to flow alongthe tube.3. The pressure is relieved by the unloading of sugar and the consequent loss of water from the tube at the sink.4. In the case of leaf-to-roottranslocation, xylem recycles water from sinkto source.
21 How glucose is transported & stored glucose transformed to sucrosesucrose is translocation of sugars by phloemtranslocation is an active process which requires energyit occurs from source to sinkthe source is photosynthetic tissue in the leavessink is fruits, seeds, roots & other storage organssucrose is converted to starch & stored in storage organs such as roots, tubers, stem etc.
23 Revision QuestionsOutline the adaptations of plant roots for absorption of mineral ions from the soil Describe the process of mineral ion uptake into roots Describe how water is carried by the transpiration stream. [7 ]Explain how abiotic factors affect the rate of transpiration in a terrestrial plant List four abiotic factors which affect the rate of transpiration in a typical mesophytic plant Explain how wind affects the rate of transpiration from a leaf Outline adaptations of xerophytes that help to reduce transpiration Outline the role of the phloem in the active translocation of biochemicals