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

MATERIAL DISTRIBUTION IN A VASCULAR PLANT WATER GLUCOSE

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

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

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

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”

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)

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

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)

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: http://www.stjohn.ac.th/Department /school/bio_pix/osmosis.gif OR http://www.youtube.com/watch?v=s diJtDRJQEc

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

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

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

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

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