Describe the movement of water and minerals through the plant.

Distinguish between diffusion and osmosis to include: gaseous and liquid diffusion, transpiration, and water uptake. Identify examples of diffusion in plants, to include: transpiration and gaseous exchange.

MOLECULE

MOLECULAR CONCENTRATION

DIFFUSION The movement of gas or solute molecules from a region of higher, to a region of lower concentration until equilibrium is achieved.

GAS

GASEOUS EXCHANGE Water evaporates from the xylem in the leaf into the air pockets between the cells (100% relative humidity ) then diffuse out from the stomata in the epidermis of the leaf, into the outside air which is at a lower relative humidity (propagation). This movement produces transpirational pull Gases such as oxygen/carbon dioxide entering and leaving the plant via stomata of leaves or lenticels on stems.

TRANSPIRATION “The passage of water through the plant”, from the root hair to its exit, from the plant via the stomata on the leaf.

“Water loss from the plant by evaporation”; Transpiration is the process of water movement through a plant and its evaporation from aerial parts such as from leaves but also from stems and flowers.
Leaf surfaces are dotted with pores which are called stomata and in most plants they are more numerous on the undersides of the foliage.

The natural cohesion of the water molecule (mini magnets joining) and the adhesion of water (attraction of water to other surfaces) to the sides of the xylem allows the water column to be drawn up the stem by transpirational pull. As the top water molecule evaporates into the atmosphere of the leaf it pulls the next molecule up.

TRANSPIRATIONAL PULL Transpiration pull or the suction force is the force which aids in drawing the water upward from roots to leaves. In leaves, some amount of water is used for photosynthesis and excess water is released into atmosphere through openings called as stomata.

Identify examples of osmosis in plants, to include: water uptake into cells, turgor, and cell expansion.

OSMOSIS The diffusion of water where water molecules move from an area of high water concentration to an area of lower water concentration through a differentially (semi) permeable membrane.

Soil water (high concentration)/water in cell sap (low concentration).

Water uptake into cells (from soil to root hair/from cell to cell). As water enters a cell it increases the water concentration to the cell next to it and so water will pass on into the next cell:

CELL TURGOR Water entering a cell increases the water pressure in the cell so putting pressure onto the cell wall, creating cell turgor or turgidity.

TURGOR Water entering a cell increases the water pressure in the cell so putting pressure onto the cell wall, creating cell turgor or turgidity.

CELL EXPANSION Seeds are dehydrated and the first stage of germination is the imbibition/ absorption of water causing the cells to rehydrate causing cell expansion. Often seeds are soaked before being sown (seeds are seen to swell quickly). Also the new cells in the growing tips expand “Zone of Elongation” – cell expansion by water uptake.

Describe the pathway of water movement from the soil through the plant into the atmosphere - soil water: pathway across the root (root hairs, osmosis across root cells, flow through root cell walls, endodermis); transport through xylem of stem (transpiration pull): pathway across leaf, (xylem in veins, osmosis across leaf cells, flow through leaf cell walls, evaporation from leaf cell walls into mesophyll spaces); diffusion through stomata of leaf.

PATHWAY (PHYSIOLOGY) The natural cohesion of the water molecule (mini magnets joining) and the adhesion of water (attraction of water to other surfaces) to the sides of the xylem allows the water column to be drawn up the stem by transpirational pull. As the top water molecule evaporates into the atmosphere of the leaf it pulls the next molecule up.

Water from the xylem passes on into the cells of the spongy mesophyll, then into the intercellular air spaces as water vapour, then by diffusion it moves out of the leaf via the stomata into the outside air.

DIAGRAM OF PATHWAY REQUIRED.

State what is meant by the term ‘transpiration’. List the factors that affect the rate of transpiration: relative humidity, temperature, wind speed.

TRANSPIRATION RATE

“the factors that affect the rate of transpiration.

Relative Humidity: The drier the relative humidity outside the leaf the greater the potential gradient, so the quicker the water will move out of the leaf.

Temperature: Temperature rise will increase the rate of evaporation of the water within the leaf so increasing the rate of transpiration.

Wind Speed: The greater the wind speed over the leaf, the quicker the water is taken away from the stomata, reducing the relative humidity close to the leaf, so increasing the rate of transpiration. “

RELATIVE HUMIDITY

WIND SPEED

EVAPORATION

EVAPOTRANSPIRATION Available water (capillary-water) in soils is lost via a combination of evaporation and plant transpiration

Describe how the plant may limit water loss, to include: stomatal closure and leaf adaptations (hairs, thick cuticle, needles). ONE named plant example should be known for EACH adaptation.

LEAF STOMATA Stomata Closure: Stomata are mostly found on the under surface of leaves and are the main exit point of water from the plant (gases: oxygen/carbon dioxide both in and out). They control water loss by closing at night (open during the day) also if the leaf wilts the stomata loses its turgidity and so will close (extreme mid-day heat can cause stomata to close).

LEAF GUARD CELL

LEAF ADAPTATION

Storage/perennation by bulbs (Narcissus and Lilium):

Water storage (Sedum) – thick, waxy, cuticle cells store water in the leaf.

Sedum spectabile “Autumn Joy”.

Leaf Adaptations Limiting Water Loss: Common in plants from warm or windy climate, RHS – Thick waxy cuticle to reduce evaporation, e.g., Echeveria elegans;

RHS – Reduced leaf surface area, conifer needles; Pinus sylvestris RHS – Leaves covered in hairs to keep humidity close to the area of the stomata; Salvia argentea

Having fewer stomata; Having deep or extensive root systems; Having light, silver/grey foliage to reflect heat; Sunken stomata;Leaves that roll with the stomata on the inside, some grasses, e.g., Festuca glauca; Structural adaptations, e.g., Spartium junceum (Spanish broom) has very small leaves but the stem is dark green and photosynthesises; Spines, e.g., Opuntia polyacantha.

Protection by leaf spine (Berberis):

Climbing by tendrils (Lathyrus odoratus):

Twisting petioles (Clematis):

MISSING EXAMPLES GIVE_EXAMPLES (CONTEXT:WATER-LOSS REDUCTION BY HAIRS): leaf-adaptation

MISSING EXAMPLES GIVE_EXAMPLES (CONTEXT:WATER-LOSS REDUCTION BY THICK CUTICLE): leaf-adaptation

MISSING EXAMPLES GIVE_EXAMPLES (CONTEXT:WATER-LOSS REDUCTION BY NEEDLES): leaf-adaptation

Describe the uptake and distribution of mineral nutrients in the plant: nutrients from soil solution active uptake against concentration gradient into root cells, transport through the plant in xylem, distribution through phloem.

NUTRIENT UPTAKE Nutrient from soil solution, active uptake against a concentration gradient into root cells; Distribution through the phloem;

Uptake of ions across membranes is accomplished by 3 mechanisms: Simple diffusion – normal diffusion between cells; Facilitated diffusion – ions combine with a membrane protein which then facilitates its uptake across the cell membrane; (In both of the above, the partials move down a concentration gradient); Active transport requiring energy to be exerted (respiration): Where the mineral needs to move up a concentration gradient, the ion will combine with a membrane protein referred to as a carrier. The carrier will transport the partial across the membrane. (Most of this activity takes place via the root hairs).

Minerals: Ions – once dissolved in the plant cell sap (water) are transported through the plant in the xylem (up the plant).

Distribution Through the Phloem: Minerals ions once dissolved in the plant cell sap (water) are transported through the plant in the phloem (around the plant); See hand out.

ION

CATION

CARRIER (MINERAL UPTAKE)

MINERAL ION ABSORBTION

PARTIAL

CONCENTRATION GRADIENT The process of particles, which are sometimes called solutes, moving through a solution or gas from an area with a higher number of particles to an area with a lower number of particles. The areas are typically separated by a membrane.

SOLUTE

SIMPLE DIFFUSION Simple diffusion – normal diffusion between cells

FACILITATED DIFFUSION Facilitated diffusion – ions combine with a membrane protein which then facilitates its uptake across the cell membrane;

ACTIVE TRANSPORT Plants require mineral salts such as nitrates for growth. The concentration of nitrates is higher on plant root cell than it is in the soil solution surrounding it. The plant cannot rely on diffusion as the nitrates would diffuse out of root cell into the soil. For an organism to function, substances must move into and out of cells. Three processes contribute to this movement – diffusion, osmosis and active transport. Substances are transported passively down concentration gradients. Often, substances have to be moved from a low to a high concentration - against a concentration gradient.

Active transport is a process that is required to move molecules against a concentration gradient.The process requires energy.

Active transport in plants For plants to take up mineral ions, ions are moved into root hairs, where they are in a higher concentration than in the dilute solutions in the soil. Active transport then occurs across the root so that the plant takes in the ions it needs from the soil around it.