Why are plants important? PhotosynthesisCellular Respiration

9.1 Transport in the xylem of plants

The Leaf has evolved to:

Basic leaf structure Water, in the form of a gas, is lost through the stomata.

Major structures of a generalized leaf

Leaf structure Cuticle – protects against water loss Epidermis – protection if no cuticle Xylem – transports water Phloem – carries products of photosynthesis Palisade mesophyll – densely packed, large # of chloroplasts Spongy mesophyll – loosely packed, provides gas exchange surfaces Stomata- bottom surface, allow 0 2 & CO 2 exchange Guard cells – open & close stomata

The dermal tissue system covers and protects the plants surfaces

The epidermis covers the primary plant body

The periderm replaces the epidermis when roots and stems increase in diameter and become woody

Importance of tissue functions Palisade mesophyll – upper portion where light will hit Veins – distributed throughout the leaf for transport Spongy mesophyll – superior to stomata to allow for continuous gas exchange Stomata – on underside so temperature is lower & minimized water loss

Understandings Transpiration is the inevitable consequence of gas exchange in the leaf.

Plant Water & Mineral Movement Transpired water must be replaced Steady stream of water provides minerals as well as water Water loss cools sun-drenched leaves and stems Xylem supports the plant as well as conducting water

The root system usually grows below ground

Plant organs are composed of three tissue systems: Vascular Tissue Dermal Tissue Ground Tissue

The vascular tissue distributes water and solutes through the plant body

Understandings: The cohesive property of water & the structure of the xylem vessels allow transport under tension. The adhesive property of water & evaporation generate tension forces in leaf cell walls.

Understandings: The uptake of minerals in the roots causes absorption of water by osmosis.

Composed of 2 cell types

tapered Pits allow water to move laterally

Attached end to end to form columns Connect to one another to form columns

Virtual lab time

Stomata & Guard Cells Can only be closed a short time – why? Open & close because of turgor pressure

Why do guard cells gain & lose water? Due to transport of potassium ions Light from blue region of light spectrum triggers the ATP powered proton pumps Potassium enters the guard cells Higher solute = inward movement of water

Plant hormone Why do potassium ions exit the cell? Abscisic acid causes exit of ions = closure of stomata Abscisic acid is produced in the roots during water deficiency

Other causes of closure Carbon dioxide levelsCircadian rhythms

Understandings: Plants transport water from the roots to the leaves to replace losses from transpiration.

The cohesion-tension theory of plant fluid movement

Roots & fluid movement in plants

Cell Membrane & Transport

Root Anatomy Three Regions – Meristematic – new growth (M phase) – Elongation – enlarging (G 1 phase) – Maturation – cells are a functional part of the plant

Root Hairs & branching Root hairs & branching greatly increase the surface area which water and dissolved minerals can be absorbed. An adult rye plant was found with 14 million branches totaling 630 kilometers (380 miles)

Uptake of ions by the roots – HOW? Root interception – Root grows & intercepts ions – Example: Ca Simple diffusion – Ions move down their concentration gradient – No energy expense by plant – Example: Zn, K, Fe, P Mass flow – Bulk flow of water into the root “carries” ions to root – Delivers N, Ca, Mg, S Active transport – Ions move against their concentration gradient – Requires a specific protein “pump” in the cell membrane – Energy expense by plant

Hyphae????? Fungal symbiotic relationship = greater surface area (mutalistic)

Lab time Microscope plant lab

Adaptations for H 2 O conservation Speeds up transpiration by warming the leaf & opening stoma Light Decreasing humidity increases transpiration due to difference in water concentration Humidity Increases the rate of transpiration because humidk air near the stomata is carried away Wind

Adaptations for H 2 O conservation Increasing temperature causes greater transpiration because more water evaporates Temperature If intake of water at root does not keep up with transpiration, turgor loss occurs & the stomata close, transpiration decreases Soil water High carbon dioxide levels in the air around the plant usually cause the guard cells to lose turgor pressure & the stomata close Carbon dioxide

Xerophytes Survive in Adapted for arid climates – Deserts

Halophytes Adapted to grow in water with high levels of salinity Studied for biofuels

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Halophytes Store water = becoming succulent May secrete salt through salt glands = mangrove Some can compartmentalize Na + and Cl - in the vacuoles of their cells Sunken stomata on thickened leaves reduce water loss by creating a higher humidity near the stomata Surface area of leaves is reduced

Lab time! Measuring transpiration rates using potometers

Lab Design Skill: Design an experiment to test hypothesis about the effect of temperature or humidity on transpiration rates. (think IA)

9.2 Transport in the phloem of plants

Understanding: Plants transport organic compounds from sources to sinks

Lacks nucleus & cytoplasm Have nucleus & cytoplasm

Sieve plates connect sieve tubes

Moving from source to sink What’s a source? – Producer of sugar (photosynthesis or hydrolysis of starch) Leaves primary What’s a sink? – Plant part that uses or stores sugar Roots, buds, stems, seeds, and fruit Potatoes can be both depending on the time of year

Phloem Sap Movement of organic molecules = translocation What makes up phloem sap? – Sugar (sucrose) – Amino acids – Plant hormones – Small RNA molecules

Understanding: Incompressibility of water allows transport along hydrostatic pressure gradients Active transport is used to load organic compounds into phloem sieve tubes at the source High concentrations of solutes in the phloem at the source lead to water uptake by osmosis Raised hydrostatic pressure caused the contents of the phloem to flow toward sinks

The pressure-flow hypothesis Phloem sap can move 1 m/hr Measured by – Aphid stylets – Radioactively labeled carbon dioxide

Nature of Science Aphid stylets Aphids feed on by inserting stylist “mouth” into a sieve tube Pressure in sieve tube forces the contents into the stylet and insect’s gut Anaesthetize the insect and cut off the gut Analyse the sap Radioactive carbon dioxide Use radioactive form of carbon so that the location of carbon dioxide-fixing reactions of photosynthesis can be determined Autoradiography can then be used to track the flow of the carbohydrate, usually sucrose, through the plant

Pressure-flow hypothesis 1.Load sugar into the sieve tube at the source reducing the relative water concentration in the sieve tube members causing osmosis 2.The uptake of water causes a positive pressure (hydrostatic) in the sieve tube which results in bulk flow of the phloem sap

Pressure-flow hypothesis 3.Hydrostatic pressure is reduced when sucrose inters the sink (sugar changed to starch which is insoluble = no osmosis) 4.Xylem recycles the relatively pure water by carrying it from the sink back to the source Active transport passive

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