Structure and Function in Land plants ORGANS of

Structure and Function in Land plants ORGANS of Flowering plants • • • Leaves Stems Roots Flowers Fruits

Various Inputs and Outputs Water and mineral ions Some need to be moved around the plant

Plants are photosynthetic Autotrophs

PLANT REQUIREMENTS • GASES: – CARBON DIOXIDE: for photosynthesis – OXYGEN: for respiration • WATER: – As a reactant in photosynthesis – For support (turgor pressure) • MINERAL IONS – For making compounds required by the plant e. g amino acids, chlorophyll

• Most photosynthesis occurs in the leaves

Leaf Cross Section: Anatomy of a leaf cuticle Upper epidermis palisade mesophyll Vascular bundle Xylem Phloem spongy mesophyll Air space Lower epidermis Guard cells cuticle stoma

Gaining CO 2 for Photosynthesis During the day ……. Rate of photosynthesis > rate of respiration • CO 2 is being used up in Photosynthesis by mesophyll cells, lowering its concentration here • CO 2 diffuses from environment via open stomata into airspace above the stoma then into mesophyll cells • Movement is PASSSIVE; along a CO 2 concentration gradient

During the day • Water is constantly used in photosynthesis • Water is constantly evaporating from moist cell walls of leaf cells(transpiration) • This creates a high water vapour concentration in the airspaces in the leaf • Water (as a gas) diffuses out of the leaf via open stomata along a water concentration gradient • The rate of diffusion depends of the size of the gradient.

Day time exchange from the leaf of a plant Xylem cuticle Upper epidermis Palisade cells chloroplasts Spongy cells stoma lower epidermis stoma Guard cell phloem Liquid water Water vapour Carbon dioxide oxygen

Stomata • Opening in the epidermis • Formed by two guard cells • Mainly on lower surface of leaf

Guard Cells are Special • They have chloroplast (unlike the other cells in the epidermis) • They change shape when turgid to become sausage shaped • When turgid, a pore (the stomatal pore) forms between two guard cells • This is the opening through which gas exchange occurs

Opening and Closing of Stoma 1. Solute uptake(mostly K+) into guard cells: 1. Solute loss from guard cells (mostly K+): 2. Water follows by osmosis 3. Guard cells expand, become turgid and bend 4. Stoma OPENS 3. Guard cells become flaccid and change shape 4 Stoma CLOSES H 2 O K+ H 2 O H 2 O

Stomata • Usually open in morning • Usually close at night • Also close to limit water loss

Guard cells: located in the epidermis

Some plant species have adaptation to arid conditions • Thick waxy cuticle: reduces evaporation of water across leaf surface

Some plant species have adaptation to arid conditions • Sunken stomata(stomata in pits) or “hairy” leaves: Both strategies trap water vapour close to the leaf surface and reduce water vapour gradient

Some plant species have adaptation to arid conditions • Inverted stomatal rhythm: – stomata that open at night and close during the day – They are closed when it is hottest – This reduces evaporative water loss in the hottest parts of the day

Some plant species have adaptation to arid conditions • Thick Succulent leaves that can store water; also have a relatively small surface area over which transpiration can occur

Gas Exchange in non woody stems • Diffusion from environment via stomata

Gas Exchange in Woody Stems • Gas exchange occurs through Lenticels • Lenticels are spongy areas in corky surface of woody stems that allow gas exchange

Gas exchange in Roots • Oxygen diffuses from air spaces in the soil into root hair cells and root cells • Carbon dioxide diffuses out in the opposite direction

Uptake of water and mineral ions • Taken up via roots • Uptake of water by osmosis • Mostly active uptake of Mineral ions some by facilitated diffusion • This creates a water concentration gradient that maintains uptake of water

Root hairs • Greatly increase the surface area for absorption of water and mineral ions

Uptake by Roots Water moves through the cortex of root into the centre for transport.

Epidermis Root hair Cortex Phloem Xylem Casparian strip Endodermis EXTRACELLULAR ROUTE, via cell walls; stopped by Casparian strip Xylem Root hair INTRACELLULAR ROUTE, via cell interiors; through plasmodesmata Epidermis Cortex Endodermis Figure 32. 2 B

Emerging Seedling Primary root Root hairs Root tip Cotyledon

Additional functions of Roots • As well as absorption of Water and mineral ions root are also responsible for • Support & Anchor of plant • Storage of organic compounds – Starch – Sucrose – protein

Water and Sugars need to be transported

Water and Sucrose Transported in Vascular Tissue • Vascular tissue Usually is located in vascular bundles • Composed of two main types of tissues: xylem and phloem • XYLEM and TRACHEIDS: transports water and mineral ions • PHLOEM: transports sucrose and minerals

XYLEM Xylem vessels and Tracheids

Xylem • • • Dead Elongated Lignified walls Pitts in sides Larger diameter than phloem

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Xylem is Supporting Tissue • Wood: composed of Xylem tissue • Main form of support for most large plants

Transpiration • Evaporation of water from the surface of a plant • Most water lost from leaves • Mostly lost via open stomata • Leaf cuticle reduces water loss across the leaf surface

The Transpiration Stream

Factors assisting water movement through plant: 1. Transpiration: evaporation of water from plant surface water is drawn up to replace water lost 2. Root pressure: force from water entering roots by osmosis 3. Cohesion of water molecules: attraction of water molecules to each other 4. Adhesion/capillarity: attraction of water molecules to cellulose in xylem wall

Adhesion and capillarity • Xylem vessels are very narrow • This maximizes contact between water in xylem and the walls of the xylem vessels • This maximises the adhesion between water molecules and the molecules in the xylem walls.

OVERVIEW • The next few slides provide a RECAP

Key: path of water Section of Leaf Section of Root Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 3/15/2018 41

Key: path of water Section of Leaf xylem The sap in the root hair cell has higher solute concentration than the soil solution. Section of Root Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. Water enters the root hair by osmosis and dissolved mineral salts enter by active transport. 3/15/2018 42

Key: path of water Section of Leaf Section of Root Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. Water and dissolved mineral salts move up the root 3/15/2018 43

Key: path of water Section of Leaf xylem vessels Thick lignified walls prevent collapse of xylem vessels. Xylem conducts water and mineral salts upwards, from roots to leaves. Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 3/15/2018 44

Key: path of water vapour Section of Leaf intercellular air space Xylem conducts water and mineral salts upwards, from roots to leaves. Thick lignified walls prevent collapse of xylem vessels. Phloem translocates sucrose and amino acids from leaves to other parts of the plant, including the roots. Water evaporates from surface of mesophyll cells into the intercellular air space. Water flows across cortex down a water potential gradient. Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 3/15/2018 45

Key: path of water vapour Section of Leaf intercellular air space Xylem conducts water and mineral salts upwards, from roots to leaves. Thick lignified walls prevent collapse of xylem vessels. Phloem translocates sucrose and amino acids from leaves to other parts of the plant, including the roots. Water vapour diffuses out of leaf through stomata Water flows across cortex down a water potential gradient. Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. 3/15/2018 46

Key: path of water vapour Section of Leaf intercellular air space Xylem conducts water and mineral salts upwards, from roots to leaves. Thick lignified walls prevent collapse of xylem vessels. Phloem translocates sucrose and amino acids from leaves to other parts of the plant, including the roots. Water flows across cortex down a water potential gradient. Copyright © 2006 -2011 Marshall Cavendish International (Singapore) Pte. Ltd. Water vapour diffuses out of leaf through stomata Transpiration cools the plant creates transpirational pull excessive transpiration causes wilting 3/15/2018 47

Transpiration is Important • It ensures that water is drawn up from the soil solution to the leaves so that it can be used: – As a reactant in photosynthesis – As a solvent – To maintain turgid state of cell and provide hydrostatic support • It also keep the plant tissue cool

ain. Factors affecting rate of transpirati Factor Rate Reason Temperature INCREASES as temperature increases Wind INCREASES as wind increases Humidity DECREASES as the humidity of the air increases • Molecules move fast as temperature increases • As temperature increases the rate of evaporation increases • Higher temperature increases the capacity of the air to hold water • Wind moves the humid air from the region near the leaf, and replaces it with drier air • This increases the water vapour concentration gradient • As humidity increases the water vapour concentration gradient b/w the inside and outside of the leaf decreases • thus the rate of evaporation will be slower.

Factor Rate Reason Water in the soil DECREASES as the soil dries Less water available to replace water that is lost. Stomata likely to close decreasing transpiration Light usually INCREASES as light Stomata usually open in light and intensity increases the size of the aperture is related to the rate of photosynthesis, which is largely determined by the light intensity. Nature of plant Some plants have more leaves that others; some leaves have more stomata etc.

Companion Cell P H L O E M Sieve Cell

Phloem • Cells are living • Sieve tube cells lack a nucleus but companion cells have a prominent nucleus and control sieve tube cells activities • Move sucrose (amino acids and mineral ions)up, down and sideways • Transport is active

What is Transported

Phloem transport: Source to sink • Source: – Any exporting region that produces sugar (or has stores of sugars) above and beyond that of its own needs • Sink: – any non-photosynthetic organ organ that does not produce enough p/s product to meets its own needs

Transport Mechanism of Phloem transports food molecules(sucrose) made by photosynthesis by a pressure-flow mechanism 1)Sucrose is loaded into a phloem tube at the sugar source, raising the solute concentration inside the tube

Transport Mechanism of Phloem 2) Water is drawn into the tube by osmosis, raising the pressure in the tube Sucrose is moved along in the phloem to where pressure is lower(the sink) 3) Sugar 4) and water leave the tube at the sugar sink

The trouble with phloem • Phloem tissue is living tissue, unlike xylem. • When scientists studying how it works cut into it, the plants responded by plugging up the phloem.

Aphid helpers • Aphids can pierce phloem tissue and suck out sap without any problem. • Scientists used aphids to study the flow of sap in phloem. • These studies have supported the pressure-flow model

Ringbarking (girdling) • Removal of a strip of bark around the circumference of a branch or trunk of a tree • Mainly removes cork cambium and PHLOEM THINK • Why would ring barking kill a plant?

• Cut or damaged trees can sometimes produce new shoots that will send sucrose down to the roots to sustain them as the new shoot system develops • A similar thing occurs with plants adapted to bush fire when they become burnt • With ring barking this generally does not occur

Overview (DICOT)

Monocotyledons Vs Dicotyledons Differ in: • Leaf venation • Root types: Fibrous vs tap • Petal, sepal numbers • Arrangement of vascular tissue in Root and stems

Vascular Bundles in a stem • Location different in moncots and dicots – Monocots: scattered – Dicots: ring • Bundle = – Xylem – Phloem – cambium

Example of a tissue drawing use grey lead though!

Zea Maise Stem T. S

Labelled vascular Bundle

Zea Maise Root epidermis phloem xylem pith cortex

Ranunculus Stem

Ranunculus Root T. S

Ranunculus Root T. S vascular Bundle

Vascular cambium

Ground tissue • All the internal cells of a plant except transport tissue • Consists of a variety of different cell types specialised for: • Storage • support • photosynthesis Eg. fleshy portions of apples, potatoes & carrots