Presentation on theme: "Chapter : Transport in Plants"— Presentation transcript:
1 Chapter : Transport in Plants state the functions of xylem and phloem.identify the positions of xylem and phloem tissues as seen in transverse section of roots, stems and leaves.investigate, using a suitable stain, the pathway of water in a cut stem.
2 How is water transported against gravity from the roots, up the xylem and to the leaves?
3 Think Like a ScientistScientists use ‘thought experiments’ to help them solve problems.3
4 I wonder where trees get water from? Well, obviously from the ground.What are the processes involved?
5 How does water move through the transport system of a plant IF it does not have a heart to act as a pump?How is water lifted against gravity from the ground to the leaves through this transport system?Are the products of photosynthesis also carried in a set of vessels from the leaves to the roots?PAUSE toPONDER5
6 How do nitrate ions get into plants? Are they directly absorbed from the air?No. Even though the air has 79% of nitrogen, it is highly unreactive.PAUSE toPONDERHow are ions transported around in plants?
7 Transport in PlantsPlants need a transport system so that cells deep within the plants tissues can receive the nutrients they need for cell processesThe problem in plants is that roots can obtain water, but not sugar, and leaves can produce sugar, but can’t get water from the air
8 What substances need to be moved? The transport system in plants is called vascular tissueXylem tissue transports water and soluble mineralsPhloem tissue transports sugars
9 Structure of XylemUsed to transport water and minerals from roots to leavesConsists of tubes for water, fibres for support and living parenchyma cells
10 Xylem vessels Obvious in dicotyledonous plants Long cells with thick walls containing ligninLignin waterproofs walls of cells and strengthens themCells die and ends decay forming a long tubeLignin forms spiral, annular rings or broken rings (reticulate)Some lignification is not complete and pores are left called pits or bordered pits, allowing water to move between vessels or into living parts
12 Adaptations of Xylem to Function Xylem can carry water and minerals from roots to shoot tips because:Made of dead cells forming continuous columnTubes are narrow so capillary action is effectivePits allow water to move sidewaysLignin is strong and allows for stretchingFlow of water is not impeded as: there are no end walls, no cell contents, no nucleus, lignin prevents tubes collapsing
14 Structure of PhloemFunction to transport sugars from one part to anotherMade of sieve tube elements and companion cells
15 Sieve TubesSieve tube elements not true cells as they have little cytoplasmLined up end to end to form a tubeSucrose is dissolved in water to form a sapTubes (known as sieve tubes) have a few walls across the lumen of the tube with pores (sieve plates)
17 Companion cells In between sieve tubes Large nucleus, dense cytoplasm Many mitochondria to load sucrose into sieve tubesMany gaps in cell walls between companion cells and sieve tubes for flow of minerals
19 The Vascular TissuesXylem and phloem are found together in vascular bundles, that sometimes contain other tissues that support and strengthen them
20 Vascular bundles: xylem & phloem Xylem transports water & dissolved minerals from roots to leaves.Phloem transports food (sugar) made in leaves to all other parts of the plant.
21 Stem The vascular bundles are found near the outer edge of the stem The xylem is found towards the inside of each vascular bundle, the phloem is found towards the outsideIn between the xylem and phloem is a layer of cambiumCambium is a layer of meristem cells that divide to make new xylem and phloem
24 Root The vascular bundle is found in the centre There is a large central core of xylem- often in an x-shapeThis arrangement provides strength to withstand the pulling forces to which roots are exposedAround the vascular bundle are cells called the endodermis which help to get water into the xylem vesselsJust inside the endodermis is the periycle which contains meristem cells that can divide (for growth)
25 Distribution of vascular bundles in roots xylemphloemDistribution of vascular bundles in rootsxylemphloem
27 LeafThe vascular bundles (xylem and phloem) form the midrib and veins of the leafA dicotyledon leaf has a branching network of veins that get smaller as they branch away from the midribWithin each vein, the xylem can be seen on top of the phloem
28 Distribution of vascular bundles in leaves. xylemphloemDistribution of vascular bundles in leaves.
29 Diagram showing a section through a leaf. xylemphloem
33 Chapter : Transport in Flowering Plants describe the structure and functions of root hair cells in relation to their surface area, and to water and ion uptake.define transpiration.describe how factors (e.g humidity, temperature, light intensity) affect the rate of transpiration.describe how wilting occurs.
37 How does the root maintain a concentration gradient? Root PressureOsmotic pressure that build up within the root cells which forces water up the root xylemRecap on OsmosisHow does the root maintain a concentration gradient?
38 Root Pressure Uptake of water by the root hair by Osmosis Uptake of dissolved minerals through active transportCell sap within the root hairs becomes more concentrated than the water in the soil
39 Root PressureOccurs when the soil moisture level is high either at night or when transpiration is low during the dayCan only raise the water in some plants up to 20cmNot the main force
41 Water transport in STEM You have learnt that water is transported from the root to the stem and the leaf.How does the plant transport water upwards against gravity??
42 Transpiration Evaporation of water from the plant Loss of water vapor through the stomata on the underside of the leavesThe mesophyll cells in the leaves are covered with a thin layer of moistureEssential for efficient gas exchange to occurSome of this moisture evaporates into the intercellular spaces which diffuses through the stomata into the ‘drier’ airWater is pulled upwards through osmosis (Transpiration Pull)The waterway in which the water moves from a higher water potential to a lower water potentialTranspiration Stream
44 Light intensity During the day, stomata of the leaves open. Why? Photosynthesis!!Gases exchange (CO2 & O2)Water vapor also evaporates (Transpiration)
45 At 30ºC, a leaf may transpire 3 times as fast as it does at 20ºC TemperatureThe higher the temperature, the higher the air water capacity to hold moistureAt 30ºC, a leaf may transpire 3 times as fast as it does at 20ºC
47 PotometerThe rate at which plants take up water depends on the rate of transpiration- the faster a plant transpires, the faster it takes up water.
48 Capillary ActionThe attractive force between the molecules of a particular liquid is known as CohesionWater coheres to each other via chemical bonds called hydrogen bonds (holds the droplets of water together)The attractive force between two unlike materials is known as AdhesionAdhesion causes water to stick to the inside of the glassWhen water passes up the thin xylem vessels, it adheres to the surface of the vessels, while the force of osmosis gently ‘pushes’ the water molecules, which cohere to each other, upwards
51 Forces that promotes uptake of water Root PressurePromotes uptake of water in the rootTranspiration pullMain force to ‘suck’ up the waterCapillary ActionPushes the water upwards due to the adhesion between the walls of the xylem vessels and water molecules as well as the cohesion between the water molecules
53 Transport of Food in plant Food substances (sugar & amino acids) are manufactured in the green leaves through the process called photosynthesisTranslocation is the process of transporting food substances downwards from the leaves to all other parts of the plant, through the phloem
55 How would you show phloem transports food substances?
56 3 experiments to show phloem transport food substances Using AphidsAphid penetrates the stem into the phloem using its mouthpart called stylet and sucks the plant sapA feeding aphid can be anaesthetized and the stylet cut offThe phloem sap flows out through the stylet and can be analysed. It is found to contain sugars and other organic substances
61 WiltTemporary or permanent loss of turgor pressure due to excessive transpiration of the leaves & shootResult in flaccid appearances of leaves & shootCharacterized by drooping & shriveling of soft tissue
62 Is wilting necessary a disadvantage to the plants? Why? b. Wilting reduces loss of water in leaves. How does it affect intake of water for photosynthesis?c. How is it the prolong process of wilting cause harm to plants?d. What other conditions may cause plants to wilt?
63 Advantage of wiltingRate of transpiration reduces as the leaves folds up, reducing surface that is exposed to sunlight.This will cause guard cells to become flaccid and the stomata will close to conserve water in the plant.Disadvantage of wiltingRate of photosynthesis will be reduced due to the following reasons:Water becomes a limiting factor now.The amount of sunlight that can be absorbed becomes a limiting factor as leaves shriveled up.The amount of carbon dioxide becomes a limiting factor as the stomata are closed.
64 Things to ponder What time of the day should you water your plant? Too much water, is it good for your plant?
65 People often give potted houseplants more fertilizer than they need People often give potted houseplants more fertilizer than they need. As a result, the plants begin to wilt and eventually die instead of getting larger and healthier. What could be the reason for this result?
66 “Girdling” or ring-barking is a term referring to the bark of the tree in a complete ring around the trunk or a branch. Predict the effect that girdling will have on a tree. Explain. Beneficial or Destructive to plants?