Chapter 18 Transport in the Flowering Plant

1. Chapter 18 Transport in the Flowering Plant

3. Plants are Autotrophic, they make their own food during Photosynthesis in the leaves.

4. Why do plants need a transport system? To provide the materials needed for various plant metabolic processes including Photosynthesis, Respiration , Growth and Reproduction

5. What materials are transported in plants • Water • Carbon dioxide • Minerals • Carbohydrates produced in photosynthesis • Plant growth regulators

6. Water uptake • Root epidermal cells absorb water by osmosis. • Adaptations for absorption: • Root hairs give a large surface area • Have thin walls • Don’t have a waxy cuticle • The cell sap has a lower water concentration than soil water

8. Water uptake Root Hair Ground tissue Xylem Xylem form continuous hollow pipes from roots to leaf Water

9. Water movement through the root Water moves from the epidermal cells across the ground tissue of the cortex and into the xylem vessels.

10. Giant Redwoods The largest and oldest trees in the world A single mature giant redwood can draw 650,000 litres of water up through it in one season! How is this possible?

12. Upward movement of water Two mechanisms combine to cause upward movement of water through the stem in the xylem. They form a continuous hollow pipeline from the roots to the leaves.

13. Root pressure – When water is drawn into roots by osmosis the extra volume causes pressure to build up. This pressure pushes water up through the xylem Root Pressure

14. Transpiration - the loss of water vapour from the plant.As water evaporates from the leaf, more water is pulled upwards through the xylem into the leaf. Transpiration

15. Role of Transpiration Water evaporates from the leaf cells during transpiration – 99%. The cells become less turgid. The evaporation of water from the leaf cells causes more water to be pulled upwards as a contionus column to replace it through the xylem vessels. Animation of Transpiration stream

16. Water_movement

17. Learning check 1 Define Autotroph. Why do plants need a transport system? What materials are transported in plants? How are root hairs are adapted to the process of absorbing water? Outline the pathway taken by water into the plant. Name the two mechanisms combined to cause the upward movement of water through the stem in the xylem

18. The control of Transpiration Leaves need to replace the water they lose in transpiration or they may wilt and die. To prevent wilting plants need to control how much water they lose in transpiration.

19. Plasmolysis of plant cell

20. Presence or absence of a cuticle Leaves have a waxy cuticle through which water cannot pass – this is mainly on the upper side of a leaf as this side is more exposed and more water can evaporate here.

21. 2. Opening and closing of the stomata Openings on the lower epidermis of leaves for gas exchange. Guard cells control the opening - increases water loss and the closing - reduces water loss of the Stomata.

23. Structure and working of Stomata

25. Summary of Transpiration

26. When are stomata open and closed? • Stomata open during the day when photosynthesis is taking placeto allow water vapour out and CO2 in. • Stomata close at night reducing water loss and CO2 intake as photosynthesis is not occurring. Animations showing movement of water during transpiration

28. Conditions when stomata close at day Two reasons stomata may close during the day: • If the plant has lost too much water • If temperatures are too high By closing stomata the plant reduces water loss. In dry conditions stomata remain closed for long periods, photosynthesis cannot occur and food crops are reduced.

29. Learning Check 2 • What is Transpiration? • Explain the role of Transpiration in water transport. • What controls Transpiration? • What controls the loss of water from leaf? • 3 Methods of controlling transpiration are? • When are stomata open and closed? • Explain the role of Root pressure in water transport.

30. Cohesion-Tension Model of Xylem Transport

31. Need to Know How plants move water up to great heights against the force of gravity Know the contribution of Irish scientists Dixon and Joly to plant biology Understand the terms transpiration, cohesion, adhesion, tension, osmosis and use them to explain water movement up through xylem

32. Cohesion-Tension Model of Xylem Transport: explains how water is transported in plants to extreme heights against the force of gravity. Cohesion-Tension Model of Xylem Transport

33. Theory proposed by two Irish scientists Henry Dixon John Joly Working in Trinity College 1894

34. The cohesion-tension model of water transport in xylem • Two Irish Scientists working in Trinity College Henry Dixon and John Joly put forward this model in 1894 • Cohesion – the sticking of similar molecules to each other, water molecules stick to each other • Adhesion – when different molecules stick together, water adheres to the walls of xylem but this force is not as great as the cohesive forces of water

35. H H H H O O O O H H H H Cohesion Similar molecules sticking together e.g. water sticking to water Attraction between molecules

36. Cohesion • Animation showing Cohesion by hydrogen bonding in water

37. H O H Adhesion Different molecules sticking together e.g. water sticking to xylem walls Attraction

38. The Cohesion – Tension model 1. Cohesion between water molecules in the narrow xylem tubes causes the water to form into a continuous column or stream in the xylem H2O H2O H2O H2O H2O

39. H2O H2O H2O H2O H2O H2O H2O H2O H2O • 2. Water molecules evaporate due to transpiration at the leaf. • Cohesion between the water molecules replaces the water by pulling the next water molecule up the xylem. • As the column of water is hard to break this pull is felt down the entire column of water to the root.

40. As each water molecule is “pulled” from the xylem another water molecule is “pulled” up from the root. • This pulling force is passed from water molecule to water molecule all the way down the plant. • This is how water is pulled up through the plant by transpiration. • Animations of Cohesion-tension

41. 3. Transpiration from the leaf • Puts the column of water under tension • Tension can pull a column of water to great heights in plants • Tension causes the column of water to be stretched • But the cohesive forces between the water molecules are strong enough to prevent the column breaking • The strong lignin prevents xylem vessels collapsing inward

42. View An Animation of sugar and water moving through xylem and phloem

43. Outline of cohesion tension model

45. Summary points • Water evaporates from the leaf, as each water molecule evaporates another is pulled up through the thin xylem column • This pulling of water molecules puts all the water in the xylem vessels under tension • This tension is great enough to pull water to a height of 150m

46. Summary points • Stomata open in daylight and transpiration occurs causing xylem vessels to become narrow, stems therefore are narrower at day • The strong lignin prevents xylem vessels collapsing inward • When transpiration stops (at night) the tension is released and xylem vessels return to their normal width

47. Learning Check 3 Explain the terms Cohesion, Adhesion, Transpiration, Tension, Osmosis Name the Irish scientists who proposed the tension cohesion model of water movement. Explain how plants move water to great heights against the force of gravity.

48. Mineral uptake and transport Examples Calcium …… Helps make cell walls Magnesium ….. Part of chlorophyll Are absorbed by active transport which requires energy Potassium Nitrates Are transported from the roots in the xylem, dissolved in water Phosphates