Topic 9.2 Transport in Angiospermophytes

1. Topic 9.2 Transport in Angiospermophytes

2. Root Systems • Functions • Absorb water • Absorb minerals ions • Support and anchor • Sometimes used for food storage • Roots have shallow sections that absorb rain water near soil surface and deeper, larger roots (tap roots) access deeper soil water

3. Increased surface area • Surface area for absorption is increased in 2 ways • Multiple branching of roots both lateral and horizontal • Formation of fine roots hairs

4. Mineral Uptake • Water and mineral ions can be absorbed through the cell wall of root epidermis • Root hairs are extensions of the cell wall which increases the roots ability to absorb • Plants absorb potassium, phosphate, nitrate and other minerals are usually in lower concentration outside the root, so they must be taken in by active transport

5. Passive transport (diffusion and osmosis) happen naturally without the use of energy • Solute moves from area of high concentration to the area of low concentration across a semi-permeable membrane • Active transport is moving solute particles from low concentration to high • This goes against the cell’s nature and requires energy (ATP) to be accomplished • Once inside, minerals are dissolved in water and moved to rest of plant by capillary action through vascular tissue

6. Water movement into roots • Mineral concentrations are usually higher inside the root than in the soil. • Water will move into the root by osmosis • Osmosis is the movement of water from an area of low solute concentration to the area of high solute concentration (the opposite direction of diffusion) without the input of energy

7. Terrestrial Plant Support • Support comes in 3 ways 1. Thickened cellulose in the cells just inside the epidermis 2. Extra thickened walls of xylem tissue. Acts like rebar in concrete 3. Cell turgor. (relys on ability of plant to keep uptake of water)

8. Transpiration • Transpiration – the loss of water vapor from the leaves and stems of a plant • As sunlight strikes the large surface area of the leaf, it increases the temp. inside it • Water in the spongy mesophyll is chaged to water vapor • 100% saturation of water in the leaf, compared to low % outside the leaf • When stomata open, water vapor leaves according to concentration gradient

9. To replace the water lost during this evaporation the transpiration stream sets into action • Spongy mesophyll pulls water from the xylem tissue to replace what is lost by evaporation • H2O molecules are weakly attracted to one another via cohesion, and the pull of H2O from the xylem creates suction effect along the length of the tube (transpiration pull)

10. There is also adhesion of the H2O molecules to the sides of the xylem • The forces of cohesion and adhesion maintain a constant water column from leaf to the root

11. Xylem Structure • Xylem originates from the cambium tissue • When xylem cells mature, they lose their plasma membranes so water can move in and out freely and forms continuous pipe • Helical or ring shaped thickenings of the cell wall are re-enforced with lignin to make the xylem tough • Pores in the xylem allow the water to leave xylem and go out into the plant

12. Stomatal Control of Transpiration • In the lower epidermis, guard cells come in pairs • There is an asymmetrical thickening of their cell walls • When they become turgid, they swell and curve. This opens the stomatal pore • In most plants, the stomata is open during the day • Abscisic acid (plant hormone) causes the closing of stomata

13. Factors that affect transpiration

14. Xerophytes Adaptations • Xerophytes – plants that are adapted to grow in very dry habitats (desert, sand dunes, high altitudes) • Spines or needles instead of leaves. Prevents water loss from transpiration • Vertical stems. Absorb sunlight for photosynthesis during morning and night, but avoid a most intense sunlight at midday

15. 3. Thick, waxy cuticle on upper and lower epidermis prevents water loss 4. Widespread shallow root system that is able to soak up infrequent rains at the surface

16. 5. Rolled leaves. Cuticle and upper epidermis extends all the way around leaf for protection. - Stomata are protected from wind and to slow transpiration. - Rolled leaf helps direct rain water directly towards roots

17. 6. CAM physiology (crasssulacean acid metabolism) • Keep stomata closed during day to prevent too much water and gas loss • Stomata open at night to absorb CO2 • CO2 is converted to a C4 molecule until it is needed during the day for photosynthesis

18. Transport in Phloem • Sugars, amino acids & other organic compounds produced in leaves are transported by phloem to rest of plant • The tubes that make up the phloem are called sieve tubes • Sieve tubes form by the nuclei and cytoplasm breaking down in the cells of the tube • Large pores in the end cell wall form for movement of sap

19. The plasma membranes remain • They pump organic molecules made in the leaf into their cells by active transport (use ATP) • High solute concentration is created in the sieve tubes which then draws water by osmosis • Resulting pressure pumps can pump the sap to rest of plant

20. Phloem can also transport some chemical sprays absorbed by leaf • Transport of any chemical in phloem, even if not produced by plant, is called translocation

21. Food Storage • Perennial plants last for three or more seasons • They reduce leaves/stems during dormant period & require a source of organic molecules for the start of the next growing season • Potatoes store these organic molecules in tubers (stem swelling) • Each tuber contains an embryonic plant that will use the stored food to create new leaves and stem