1. Transport in the Flowering Plant
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
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
Transpiration.swf

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

18. 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

19. 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.

20. Plasmolysis of plant cell

21. 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.
Plant cuticles are a protective waxy covering produced only by the epidermal cells [1] of leaves, young shoots and all other aerial plant organs without periderm. The cuticle tends to be thicker on the top of the leaf, but is not always thicker in xerophytic plants living in dry climates than in mesophytic plants from wetter climates, despite a persistent myth to that effect. The cuticle is composed of an insoluble cuticular membrane impregnated by and covered with soluble waxes.

22. 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.

24. Structure and working of Stomata

26. Summary of Transpiration

27. Adaptation
How it works
Example
thick cuticle
stops uncontrolled evaporation through leaf cells
most dicots
small leaf surface area
less area for evaporation
conifer needles, cactus spines
low stomata density
fewer gaps in leaves
stomata on lower surface of leaf only
more humid air on lower surface, so less evaporation
shedding leaves in dry/cold season
reduce water loss at certain times of year
deciduous plants

28. sunken stomata
maintains humid air around stomata
marram grass, pine
stomatal hairs
marram grass, couch grass
folded leaves
marram grass,
succulent leaves and stem
stores water
cacti
extensive roots
maximise water uptake

29. When are stomata open and closed?
Stomata open during the day when photosynthesis is taking place to 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

31. 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.

32. 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.

33. Cohesion-Tension Model of Xylem Transport

34. 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

35. 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

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

37. 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

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

39. Cohesion
Animation showing Cohesion by hydrogen bonding in water

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

41. 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

42. 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.
H2O

43. 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

44. 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

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

46. Outline of cohesion tension model

48. 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

49. 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

50. 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.

51. 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

58. Uptake & transport of Carbon dioxide
Most of the Carbon dioxide comes in through the stomata from the atmosphere
It diffuses into the air spaces and then into the photosynthesising cells in the ground tissue

59. Carbon Dioxide Sources
Produced in the leaf during respiration
Diffuses from the air in though the stomata
CO2

60. Photosynthesis Products
Glucose
Glucose is converted to starch
Starch and glucose are transported in the Phloem
Oxygen
Some diffuses into air spaces in the leaf and out through stomata into the atmosphere
some of the oxygen produced is needed for respiration

61. Glucose is the carbohydrate made in photosynthesis
This may be used immediately for energy for the plant in respiration or it may be stored as starch
Some of this starch is stored in the spongy mesophyll cells in leaves
Starch stored in leaves is important in the diet of leaf eating animals such as horses and cattle

62. Trans-section of a leaf

63. Glucose converted to sucrose
When glucose get converted to sucrose it enters phloem sieve tubes and is transported through the plant
This sugary water is called phloem sap
An insect extracting sugary phloem sap from a plant

64. Food transport
Phloem carries food to all parts of the plant, some food is sent to growth areas such as buds, flowers and roots.
Food is used to form new plant structures, for respiration or it is stored as starch.

65. Learning Check 4 Name 4 Minerals taken up by the plant.
How are they transported?
Describe the uptake and transport of Carbon dioxide.
List the Products of Photosynthesis & state their use
What is the function of the phloem?

66. Food storage organs in plants
Some parts of plants may become swollen and fleshy with stored food
This food will be used by the plant to produce flowers, seeds and fruits

67. Modified Root
E.g. Tap roots of Carrots, turnips, sugar beet

68. Modified stem Potato plants develop an underground stem system
The tips become swollen with stored starch
These swollen tips are called stem tubers
In nature a potato tuber would remain dormant in the soil over winter and in spring the buds on the tuber (better known to us as the “eye”) would grow into new plants

69. Modified Leaves
E.g. onion bulbs , daffodils bulbs and tulips bulbs

70. A bulb contains a tiny underground stem which have swollen fleshy leaves attached
This stem has an apical bud and lateral buds can be seen where the leaves meet the reduced stem
The entire bulb is protected by dry scaly leaves
Some bulbs are edible (onion, garlic) while others are poisonous (daffodil, tulip) this prevents organisms in the soil from eating them!

72. Modified Petioles
Celery and Rhubarb are modified petioles

73. Learning Check 5 Name 4 food storage organs in plants.
What is the function of the stored food?
What are Potato plants?
Describe the structure of a bulb.

74. Websites on storage organs in plants & Transpiration
book/Dictionary/Dictionary_S/dictionary_storage_organ.htm
Told in storybook fashion, this short film narrates the struggle of one water droplet, Vladimir, who faces the bourgeoisie-promoted process of transpiration.