9.2 Transport in angiospermophytes

Assessment Statements 9.2.1 Outline how the root system provides a large surface area for

mineral ion and water uptake by means of branching and root hairs. 9.2.2 List ways in which mineral ions in the soil move to the root. 9.2.3 Explain the process of mineral ion absorption from the soil into

roots by active transport. 9.2.4 State that terrestrial plants support themselves by means of

thickened cellulose, cell turgor and lignified xylem. 9.2.5 Define transpiration. 9.2.6 Explain how water is carried by the transpiration stream,

including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation.

9.2.7 State that guard cells can regulate transpiration by opening and closing stomata.

9.2.8 State that the plant hormone abscisic acid causes the closing of stomata.

9.2.9 Explain how the abiotic factors light, temperature, wind and humidity, affect the rate of transpiration in a typical terrestrial plant.

9.2.10 Outline four adaptations of xerophytes that help to reduce transpiration.

9.2.11 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).

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 organs

long-distance transport of sap within xylem and phloem at the level of the whole plant

Variety of physical processes involved in the different types of transport

Root system Functions of

roots;absorb waterabsorb

minerals ionssupport and

anchorsometimes

used for food storage

Tap root Fibrous roots

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 ions

for this reason, it has developed a large surface area due to;branchingpresence of root

hairs near the tip

Ways in which mineral ions in the soil move to the rootmineral 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 ATP

active transport uses of proteins pumps to move ions across membrane

against concentration gradient i.e. from low concentration in the soil into the root cells where they are in high concentration

the rate of absorption of mineral ions is limited by the rate at which the ions move through the soil to the roots

there are three ways in which the ions move to the root:through facilitated

diffusionthrough mass flow of

water containing dissolved ions

through mutualistic fungal hyphae growing around the root

Adaptations of plant roots for absorption of mineral ions from the soil

mineral ions are absorbed by active transport

large surface area is requiredbranching of the root &

presence of root hairs increases surface area

root hair cells have carrier protein (ion pumps) in their plasma membrane

many mitochondria are present in root hair cells to provide ATP for active transport

connections with fungi in the soil (fungal hyphae)

How terrestrial plants support themselvesterrestrial plants

support their tissues through:thickening of the

cellulose cell walllignified xylem

vesselscell turgidity, turgor

pressure provide mechanical support to the plant tissue

Define transpirationtranspiration is water

loss from plant by evaporation

excess water loss may harm the plant

transpiration is the driving force that pulls water up from the roots to the leaves to supply photosynthesizing tissue

thus, transpiration is a necessary evil

How water is carried by the transpiration stream

transpiration is water loss from plant by evaporation

flow of water through xylem from roots to leaves is the transpiration stream

water enters roots through the root hairs by osmosis

root hairs provide an extended surface area for active transport & osmosis

active transport of ions from soil into the roots enhances osmotic pressure

osmotic pressure moves water into the xylem

water is carried in a transpiration stream in the xylem

adhesion of water to the inside of the xylem helps move water up

cohesion of water to itself enhances water movement up the xylem

water vapour diffuses into air spaces in spongy mesophyll of leaves

it passes out through the stomata by evaporation i.e. transpiration

evaporation of water vapour sets up a transpiration pull that keeps the water moving

guard cells control the rate of transpiration pull by controlling evaporation

xylem vessels are tubes with helical rings to enhance water movement by resisting low pressure

How guard cells regulate transpiration stomata are pores usually in the

lower epidermis each stomata is formed by two

specialised guard Cells the epidermis & its waxy cuticle is

impermeable to carbon dioxide & water

during the day the pore opens to allow carbon dioxide to enter for photosynthesis

however, the plant will experience water loss, if the water loss is too severe the stoma will close

dehydration, low water potential, of the mesophyll cell causes them to release the hormone abscisic acid

abscisic acid stimulates the stoma to close

during the night plants cannot photosynthesis, so the plant closes the pores thereby conserving water

guard cells gain water & openstoma is large, rate of transpiration is highguard cells lose water & closestoma is small, rate of transpiration is low

Hormone abscisic acid causes the closing of stomata

guard cells gain water & openstoma is large, rate of transpiration is high

guard cells lose water & closestoma is small, rate of transpiration is low

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 plants

temperature, humidity, light intensity & wind all affect rate of transpiration

humidity, less transpiration as atmospheric humidity rises due to smaller concentration gradient of water vapour

relatively high temperatures, more transpiration as temperature rises due to faster diffusion as a result of more kinetic energy of water molecules

faster evaporation due to more latent heat available

windy conditions, more transpiration as wind speed increases as water vapour blown away from the leaf

increasing the concentration gradient of water vapour

high light intensity, more transpiration in the light due to light causing stomata to open

wider opening of stomata with brighter light hence more transpiration

CAM plants opposite, narrower stomata with high carbon dioxide concentration hence less transpiration

low air pressure, low levels of carbon dioxide

Adaptations of xerophytes that help to reduce transpiration xerophytes are plants that live in dry

conditions xerophytes are adapted in the following

ways to reduce water loss: reduced leaves (spines or needle

like) to reduce the surface area for transpiration

rolled leaves with stomata on the inside to prevent water loss by transpiration

sunken stomata allows layer of humidity to build up reducing water loss by evaporation

thick waxy cuticle on leaves epidermis to prevent water loss by transpiration

hairs allow water vapour to be retained

reduced stomata / stomata on under side of the leaf to prevent water loss by transpiration

special water storage tissue, wide-spreading network of shallow

roots obtain more water deep roots to absorb water from

deep sources vertical stems to avoid mid-day sun reversed stomata rhythm, take in

carbon dioxide at night to prevent water loss during the day

Role of phloem in active translocation of sugars (sucrose) & amino acids

phloem is a living tissue composed of companion cells & sieve tube membranes

companion cells involved in ATP production

assimilate products of photosynthesis, sucrose & amino acids transported in phloem

translocation is a bi-directional transport

from the source; leaves to the sinks; fruits, roots, the storage organs such as stem tubers, roots

pressure flow hypothesis;- movement of water into phloem causes transport

1. Loading of sugar (green dots) into the sieve tube at the source reduces water potential inside the sieve-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 along the tube.3. The pressure is relieved by the unloading of sugar and the consequent loss of water from the tubeat the sink.4. In the case of leaf-to-roottranslocation, xylem recycles water from sinkto source.

How glucose is transported & storedglucose transformed to

sucrosesucrose is translocation of

sugars by phloemtranslocation is an active

process which requires energy

it 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.

Revision QuestionsOutline the adaptations of

plant roots for absorption of mineral ions from the soil. [5]

Describe the process of mineral ion uptake into roots. [5]

Describe how water is carried by the transpiration stream. [7 ]

Explain how abiotic factors affect the rate of transpiration in a terrestrial plant. [8]

List four abiotic factors which affect the rate of transpiration in a typical mesophytic plant. [4]

Explain how wind affects the rate of transpiration from a leaf. [5]

Outline adaptations of xerophytes that help to reduce transpiration [8]

Outline the role of the phloem in the active translocation of biochemicals. [5]