1. TRANSPORT MECHANISMS WITHIN VASCULAR PLANTS
PLANTS – DAY 2
TRANSPORT MECHANISMS WITHIN VASCULAR PLANTS

2. MATERIAL DISTRIBUTION IN A VASCULAR PLANT
WATER
GLUCOSE

3. CELLS IN THE LEAF
During photosynthesis, the leaf must have a constant supply of carbon dioxide and release oxygen it produces; this exchange of gases with the environment is regulated by tiny pores called stomata, found in epidermis of leaves or sometimes stems

4. TRANSPIRATION
Stomata also allow water vapour to escape the leaf. Loss of water vapour in plants is called TRANSPIRATION – water diffuses and evaporates into the air spaces of the leaves and out to the atmosphere through stomata
Stomata are accompanied by guard cells: these cells regulate the opening and closing of each stoma (singular of stomata) because when stomata are open, the plant can get all carbon dioxide it wants BUT it also loses water
When stomata are closed, water is conserved but no carbon dioxide goes in; it’s a trade-off

5. CELLS IN THE LEAF
Between the upper and lower surfaces of a leaf is a photosynthetic region called mesophyll, consists of parenchyma cells containing lots of chloroplasts
Palisade mesophyll occurs under upper epidermis, cells shaped like bricks and tightly packed in one or two layers; have many chloroplasts and are MAIN site for PS
Spongy mesophyll lies between palisade meosphyll and lower epidermis; fewer chloroplasts, are irregular in shape, are randomly arranged with large air spaces among them; air spaces promote rapid diffusion of carbon dioxide into cells and oxygen gas out of them

6. GAS EXCHANGE IN PLANTS
Gas exchange in the leaf done via diffusion: the movement of molecules (liquid or gas) from an area of higher concentration to an area of lower concentration
Movement from an area of higher concentration to one of lower concentration is known as moving along the concentration gradient
Creates a PRESSURE GRADIENT – a difference in pressure across a given distance
Pressure gradient results in a NET FORCE that is directed from high to low pressure and the force is called ‘Pressure Gradient Force”

7. DIFFUSION OF CARBON DIOXIDE
LOW CONCENTRATION OF CARBON DIOXIDE (INSIDE MESOPHYLL CELLS)
WHY????
CHLOROPLASTS
ITS WHERE PS OCCURS!
HIGHER CONCENTRAION OF CARBON DIOXIDE (IN AIR SPACES)
HIGHEST CONCENTRATION OF CARBON DIOXIDE (IN AIR)

8. ROOTS IN PLANTS
ROOTS
Extremely important; often larger than its shoot system; absorb water and minerals from soil, physically support and anchor plants and store carbohydrates
Water and minerals enter from roots and are transported through vascular tissue to stem, leaves and flowers; carbs produced in shoot system are transported down to roots for storage
Each root has protective root cap at its tip to cover the apical meristems and behind the cap, the epidermal cells have fine microscopic root hairs that increase the roots surface area for absorption of water and minerals
Center of each root is the vascular cylinder which contains the vascular tissues, xylem and phloem and some ground tissue

9. OSMOSIS: WATER TRANSPORT IN ROOTS
Osmosis: passage of a solvent, such as water, from the dilute side to the concentrated side of a membrane, filter, or other semipermeable border. Without added pressure, a solution divided in this way will undergo osmosis, in order to equalize the concentration of the two sides
Solute: substance that can be dissolved in a liquid (ie – sugar)
Solvent: a liquid that dissolves a solute (ie – water)

10. OSMOSIS
hypotonic solution: a solution where the concentration of solutes outside a cell is lower than that found inside the cell. Where does water move to?
hypertonic solution: a solution where the concentration of solutes outside a cell is higher than that found inside the cell. Where does water move to?
Visualization: /school/bio_pix/osmosis.gif OR
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11. OSMOSIS – ROOT TRANSPORT IN PLANTS
Root hairs absorb minerals from soil by active transport (requires energy) and move minerals moved to center of root
Root hairs increase surface area for roots to take up more water and minerals from ground
Minerals are the solute , water is the solvent
Lots of minerals inside the root, so water will diffuse across a semipermiable membrane (in this case, the root hairs) and move INTO the root of the plant
So, this xylem sap is hypertonic relative to soil water outside root

12. PUTTING IT TOGETHER
Water evaporates from internal leaf cells through the stomata = called Transpiration Water passes from xylem to leaf cells Water enters xylem from root tissue to replace water that moved upwards Water enters root hair cells by osmosis to replace water which has entered the xylem

13. STEMS
Support the plant and serve as a transport link to and from leaves, roots and reproductive parts
Stems have vascular bundles (xylem and phloem tubes) arranged together
Vascular cambrium is the name for lateral meristem tissues in the stems – helps stems to grow in diameter
Phloem produced to the outside and xylem produced to the inside in stems

14. TRANSLOCATION
Translocation: process of moving the products of photosynthesis throughout the plant body through phloem
Precise mechanism of this food transport is not known
Carbohydrates/glucose made by photosynthesis are moved from leaf cells to other plant parts via phloem tissue
Phloem, like xylem tissue, forms a continuous pipeline between leaves and roots
Most accepted explanation of translocation is called the pressure-flow theory where fluids will low from an area of higher pressure towards an area of lower pressure
Carbs will flow from their source (where they are made) which has a higher pressure, to where they are stored or used (sink) which has a lower pressure; the driving force is a positive pressure gradient from source to sink

15. PRESSURE-FLOW THEORY (TRANSLOCATION)
Active transport of sugar (carbohydrates) into phloem. Active transport is the movement of molecules across a membrane against a concentration gradient; requires energy.
Water follows by osmosis
Pressure gradient moves fluid down phloem
Active or passive transport of sugar into root cell