Plant cell requirements Makes it Roots Organic nutrients e.g. sugars for respiration Inorganic ions & water Plant cell requirements Carbon dioxide for photosynthesis Oxygen for respiration Stomata Stomata

Mammals – have faster chemical reactions happening in cells. E.g. they Have a faster rates of respiration and As result need more O2 & glucose. Plants – have slower rates of respiration They will have very different transport systems

Plant transport systems XYLEM VESSELS PHLOEM TISSUE Moves products of P Moves water from roots upwards Process is called TRANSLOCATION Process is called TRANSPIRATION

SOIL AREA of HIGH Ψ ROOT HAIR CELLS ROOTS XYLEM LEAVES AREA of LOW Ψ ATMOSPHERE

The structure of a root If water is to pass through to the xylem in the stem, it must move through several types of cell/structures. Endodermis Tough epidermis Cortex Stele Root hairs Casparian strip

The structure of a root ROOT HAIR EPIDERMIS ENDODERMIS XYLEM STELE PERICYCLE PHLOEM CORTEX

How water enters a plant RESULT: water enters the root hair Soil particle Water particle Gas AREA of LOW Ψ Root hair: with dissolved materials of cell AREA of HIGH Ψ RESULT: water enters the root hair Water with inorganic ions

How water enters a plant Osmosis AREA of HIGH Ψ AREA of LOW Ψ

How water enters a plant Osmosis AREA of HIGH Ψ AREA of LOW Ψ

How water enters a plant Osmosis AREA of HIGH Ψ AREA of LOW Ψ

How water enters a plant Osmosis AREA of HIGH Ψ AREA of LOW Ψ Xylem

The previous slide is simplistic……… Before water gets to into the xylem, it must travel through the cortex and into the central structure – the stele. ROOT HAIR EPIDERMIS ENDODERMIS XYLEM STELE PERICYCLE PHLOEM CORTEX

Water moves through roots in two ways: 1.APOPLAST PATHWAY 2.SYMPLAST PATHWAY

Water moves through roots in two ways: APOPLAST PATHWAY SYMPLAST PATHWAY

APOPLAST PATHWAY SYMPLAST PATHWAY Both are routes for water through the cortex to the stele Water moves from cell to cell by passing along cell walls Water moves into cell through vacuole/cytoplasm and into next cell via plasmadesmata This route stops at the ENDODERMIS This route continues into the stele and supplies the xylem

This stops water moving The Endodermis has a ring called the CASPRIAN STRIP This is made of a wax called SUBERIN This stops water moving thu. the APway

Invovled in water transport Vessel elements Tracheids Xylem tissue Fibres elongated, lignified dead, act as support Parenchyma cells Normal plant cells No P role Isodiametric

There are 4 types of xylem vessels Xylem vessels are made up of dead cells with thickened cell walls - LIGNIN There is no movement between vessels – hole are filled with cellulose

Remains of old cell walls Vessel element Remains of old cell walls Lignified cell walls Lumen

XYLEM VESSELS TRACHEIDS Both are tubes through which water moves up a plant Open ends Tapered ends Dominant method of water movement in modern plants Dominant method of water movement in PRIMITIVE plants

Structure of a leaf Upper Epidermis Cuticle Palisade cells Spongy Mesophyll cells Air spaces Lower Epidermis Guard cell (stomata) Vascular tissue

Stomata Guard cell Upper Epidermis Palisade cells Spongy mesophyll cells Vascular tissue

Water moves up the xylem vessel Water leaves the xylem vessel thru a pit Water moves from cell to cell via osmosis Water leaves SMcells, entering the air space Water vapour diffuses out of stomata

gradient btwn the cells and the atmosphere Often there is a water potential gradient btwn the cells and the atmosphere This ensures rapid water loss from stomata This loss is called TRANSPIRATION

Environmental factors that increase the rate of transpiration Warm/hot Windy Dry There is a high water potential gradient between the environment and the spongy mesophyll

Environmental factors that decrease the rate of transpiration Cold Wet Still There is a low water potential gradient between the environment and the spongy mesophyll

If there is a large loss of Low hydrostatic pressure Water gets sucked up due to the h’static differences If there is a large loss of water from the SMcells into the atmosphere, this will reduce the hydrostatic pressure from the top of the xylem High hydrostatic pressure

COHESION: water molecules are attracted to each other Section of a xylem vessel COHESION: water molecules are attracted to each other ADHESION: water molecules are attracted to the lignin in the xylem vessels ADHESION & COHESION ensures there is a constant stream of water running through the xylem vessels AKA MASS FLOW

ROOT PRESSURE This is done by pumping solutes into the xylem in the root Some plants help transpiration by increasing the water pressure At the base of xylem vessel ROOT PRESSURE This is not a dominant force in transpiration This is done via ACTIVE TRANSPORT This increases the rate at which water Flows into the xylem via osmosis

Water follows down the WP gradient Active pumping of solutes into the xylem

MEASURING THE RATE OF TRANSPIRATION Plant cutting Air tight seal Tube with a scale Water filled tube MEASURING THE RATE OF TRANSPIRATION USING A POTOMETER

Results can be graphed as follows; rate of water transpired Select plant to be used in the experiment. Results can be graphed as follows; rate of water transpired (µm3 per second) against time. Underwater, make a cut an angular cut (33o), separating the main plant from the cutting you are using. We are assuming, that the rate of water uptake = the rate of transpiration. The plant can now be exposed to different environmental conditions and the rate of water uptake can be measured. Keep the cutting beneath the water level, this ensures the column of water in the xylem is not broken. Then place the whole Potometer under water, and carefully insert the top of the cutting into the top of the potometer – it is vital all this is done underwater. Fill the potometer with water, being sure to introduce an air bubble into the capillary tube.

XEROPHYTES – plants adapted to low water conditions E.G. Marram grass Ammophila arenaria

All are structural adaptations to lowering the rate of transpiration Rolled leaf Leaf hairs Waxy cuticle Sunken stomata All are structural adaptations to lowering the rate of transpiration

What other adaptations have the following species evolved to cope with water stress? Opuntia Sitka spruce Phlomis italica Euphorbia canariensis See page 139