1. 9.2 Transport in angiospermophytes

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 cells
short-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

4. Variety of physical processes involved in the different types of transport

6. Root system Functions of roots; absorb water absorb minerals ions
support and anchor
sometimes used for food storage
Tap root
Fibrous roots

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 ions
for this reason, it has developed a large surface area due to;
branching
presence 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 epidermis
root hairs increase the surface area for absorption
mineral 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 diffusion
through mass flow of water containing dissolved ions
through 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 transport
large surface area is required
branching 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)

11. How terrestrial plants support themselves
terrestrial plants support their tissues through:
thickening of the cellulose cell wall
lignified xylem vessels
cell turgidity, turgor pressure provide mechanical support to the plant tissue

12. Define transpiration
transpiration 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

14. 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

15. 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 & open
stoma is large, rate of transpiration is high
guard cells lose water & close
stoma is small, rate of transpiration is low

16. Hormone abscisic acid causes the closing of stomata
guard cells gain water & open
stoma is large, rate of transpiration is high
guard cells lose water & close
stoma 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 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

18. 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

19. 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

20. 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 tube at the sink.
4. In the case of leaf-to-root
translocation, xylem recycles water from sink
to source.

21. How glucose is transported & stored
glucose transformed to sucrose
sucrose is translocation of sugars by phloem
translocation is an active process which requires energy
it occurs from source to sink
the source is photosynthetic tissue in the leaves
sink is fruits, seeds, roots & other storage organs
sucrose is converted to starch & stored in storage organs such as roots, tubers, stem etc.

23. Revision Questions
Outline 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]