1. Transport in Plants

2. Key Terms to Know ■ Xylem ■ Phloem ■ Stem ■ Roots ■ Leaves ■ Angiosperms ■ Monocots ■ Dicots ■ Plan Diagram ■ High Power Drawing ■ Epidermis ■ Stomata ■ Root Hairs ■ Guard Cells ■ Parenchyma Cells ■ Collenchyma Cells ■ Endodermis ■ Mesophyll ■ Palisade Mesophyll ■ Spongy Mesophyll ■ Pericycle ■ Vascular Tissue ■ Xylem Vessel Elements ■ Sieve Tube Elements ■ Transpiration ■ Vascular Bundle ■ Xerophytes ■ Tracheid ■ Sclerenchyma Fibers ■ Lignin ■ Lumen ■ Xylem vessel ■ Cohesion ■ Adhesion ■ Root pressure ■ Apoplastic ■ Symplastic ■ Casparian strip ■ Passage cells ■ Mycorrihaze ■ Trasnlocatoipn ■ Companion cells ■ Sieve tube ■ Phloem sap ■ Mass flow ■ Source ■ Sink ■ cotransport

3. Transport Need of Plants ■ Plants need transport systems because they need to take substances from their environment and return waste to their environment. ■ Every cell of a multicellular organisms needs a regular supply of water and nutrients. ■ Cells close to the edge of the organism( epithelium ) can gain this by simple diffusion but there are many cells inside the plant further from the supply that cannot gain the oxygen and nutrients they need by simple diffusion. ■ This is because larger plants have a small SA:V ratio. ■ Diffusion is not adequate to meet the demands

4. Transport Need of Plants ■ What substances need to be moved? ■ Water- from soil, to roots then to the rest of the plant. ■ Minerals-from soil, to roots and then to the rest of the plant. ■ Sugars- from leaves to rest of plant. ■ Why is water important? ■ Keeping cells turgid therefore supporting the plant. ■ Required in photosynthesis. ■ absorption of substances dissolved in the soil. ■ cooling effect on the surface of leaves in hot climates (xerophytes)

5. Transport Need of Plants ■ Therefore, multicellular plants need specialised exchange surfaces and mass flow transport systems to obtain essential materials from the environment and transport them to the cells. ■ Waste also needs to be transported from the cells for excretion into the external environment ■ Plants are autotrophic (“self feeding”). ■ Plant cells need to obtain carbon dioxide and water from the external environment for photosynthesis, in order to make glucose, and need to remove the waste products of metabolism (namely oxygen) into the external environment ■ Carbon dioxide + water → Glucose + oxygen

6. Transport Need of Plants ■ Carbon dioxide (from the air) diffuses down a concentration gradient through stomata (pores) in the leaf, and, water from the soil by osmosis (through roots), in order to make glucose by photosynthesis in the chloroplasts of plant cells. ■ Some of the oxygen produced is used for respiration, and the rest excreted. ■ During the night, photosynthesis stops but respiration continues – oxygen diffuses into the leaf through the stomata down a concentration gradient ■ Minerals are obtained from the water in the soil (by diffusion and active transport) Photosynthesis (chloroplasts) – daylight Light energy 6H 2 O + 6CO 2 C 6 H 12 O 6 + 6O 2 Chlorophyll Glucose Respiration (mitochondria) – day and night C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ENERGY(ATP)

7. Transport in Plants ■ Exam Tip: Plants also need carbon dioxide, but this enters at the leaves (where it is needed).

8. Transport in Plants 1. State the four things that plants need from their environment to survive. [4] 2. Complete the following sentences: a. Plants photosynthesize in their ______________________________. That’s where they have______________________________ which can use the sun’s energy to fix ______________________________. b. Photosynthesis requires ______________________________ to stay alive, plants need to carry______________________________ and ______________________________ from the soil all the way up to the leaves. 3. Name two types of simple plants that absorb water and nutrients by diffusion and must therefore inhabit moist environments.

9. Two Systems of Transport: Xylem & Phloem ■ The transport system in a plant which does this moves substances around the plant in special tissue called vascular tissue. ■ There is xylem tissue which transports water and soluble minerals upwards, and there is phloem tissue which transports sugars upwards and downwards. ■ Phloem and xylem tissues are found together in vascular bundles. ■ These bundles may often contain some other tissue types e.g. sclerenchyma and collenchyma to give the plant extra support.

10. Two Systems of Transport: Xylem & Phloem

11. Flowering plants are divided into monocots (or monocotyledons) and dicots (or dicotyledons). This comparison examines the morphological differences in the leaves, stems, flowers and fruits of monocots and dicots. ReviewReview Watch

12. What we need to know! The structure and function of the leaves, stem and roots. Plant Organs: Stems, Roots, & Leaves

13. Tissue system and its functions Component tissues Location of tissue systems Dermal Tissue System protection prevention of water loss Epidermis Periderm (in older stems and roots) Ground Tissue System photosynthesis food storage regeneration support protection Parenchyma tissue Collenchyma tissue Sclerenchyma tissue Vascular Tissue System transport of water and minerals transport of food Xylem tissue Phloem tissue Plant Organs: Stems, Roots, & Leaves

14. ■ Roots ■ Hold plant in position ■ Absorb water and minerals from the soil ■ Have specialised cells to increase surface area for water intake

15. Carrots are one giant root!! Plant Organs: Stems, Roots, & Leaves

16. Radish Plant Root hairs Plant Organs: Stems, Roots, & Leaves ■ Fragile parts of cells that grow from the main root ■ They massively increase the surface area for absorption

17. 1.Root Hairs: increase surface area for water & mineral absorption 1.Meristem: region where new cells are produced 1.Root Cap: protects tip of growing root Plant Organs: Stems, Roots, & Leaves Root Hairs Meristem Root Cap Xylem Phloem

18. So what role to roots play in photosynthesis?? 2 mins to discuss! Plant Organs: Stems, Roots, & Leaves

19. ■ Epidermis: A single layer of cells often with long extensions called root hairs, which increase the surface area enormously. A single plant may have 1010 root hairs. ■ Cortex A thick layer of packing cells often containing stored starch. Cortex ■ Endodermis.: A single layer of tightly-packed cells containing a waterproof layer called the casparian strip. Endodermis ■ This prevents the movement of water between the cells. ■ Pericycle: A layer of undifferentiated meristematic (growing) cells.

20. Plant Organs: Stems, Roots, & Leaves ■ The xylem is found towards the inside of each vascular bundle (see the diagram), and the phloem towards the outside. ■ In between the xylem and the phloem vessels there is a layer of cambium. ■ Cambium: This is a layer of meristem cells which can divide to produce more phloem or xylem. Dicot: In the root, the xylem, are arranged in a star or cross-shape. ■ Monocot: a fleshy pith in the center of the root, instead of xylem ■ Exam Tip: Given either a diagram or a microscope you must be able to identify monocot & dicot, and label the parts

21. Plant Organs: Stems, Roots, & Leaves ■ Stem ■ 3 Main Functions! ■ Provides support for the plant ■ Transports water from the roots to the leaves and rest of plant ■ Transports glucose from the leaves to the parts of the plant that need it.

22. So… Xylem and Phloem make up the transportation system of the plant. They are like the circulatory system of the plant Plant Organs: Stems, Roots, & Leaves

23. The xylem of a plant is the system of tubes and transport cells that circulates water and dissolved minerals. Plant Organs: Stems, Roots, & Leaves

24. As a plant, you have roots to help you absorb water. If your leaves need water and they are 100 feet above the ground, it is time to put the xylem into action! A one way system - root to leaves XYLEM Plant Organs: Stems, Roots, & Leaves

25. ■ Epidermis: One cell thick. In young plants the epidermis cells may secrete a waterproof cuticle, and in older plants the epidermis may be absent, replaced by bark. ■ Cortex: Composed of various “packing” cells, to give young plants strength and flexibility, and are the source of plant fibres such as sisal and hemp. ■ Pith: The central region of a stem, used for food storage in young plants. It may be absent in older plants (i.e. they’re hollow). ■ In stems, the xylem, phloem and cambium are arranged in vascular bundles. In stems, ■ The xylem is found towards the inside of each vascular bundle (see the diagram), and the phloem towards the outside.

26. Plant Organs: Stems, Roots, & Leaves ■ In between the xylem and the phloem vessels there is a layer of cambium. ■ This is a layer of meristem cells which can divide to produce more phloem or xylem. ■ Monocot: vascular tissue arranged in scattered bundles throughout the stem (as opposed to rings) ■ Dicots: vascular tissue arranged in rings ■ Exam Tip: Given either a diagram or a microscope you must be able to identify monocot & dicot, and label the parts

27. So how does the stem have a role in photosynthesis?? 2 Minutes to discuss with person next to you Plant Organs: Stems, Roots, & Leaves

28. ■ Main photosynthetic organ ■ Broad, flat surface increases surface area for light absorption ■ Have systems to prevent water loss ■ Stomata open in day but close at night or when hot to conserve water ■ waxy cuticle on surface ■ System of gas exchange ■ Allow CO2 in and O2 out of leaf Main Functions of Leaf

29. Greener on top CO 2 gets in here Leaf Structure Plant Organs: Stems, Roots, & Leaves

30. Most of the chlorophyll CO 2 Plant Organs: Stems, Roots, & Leaves

31. Position? Upper surface of leaf Features? Box shape Chloroplasts Function? Photosynthesis Leaf cell - palisade

32. Plant Organs: Stems, Roots, & Leaves ■ Gas Exchange ■ Leaves are designed to allow carbon dioxide to get to the main chlorophyll layer at the top of the leaf ■ They have small holes called stomata on the under surface ■ Each hole is open & closed by 2 guard cells

33. Its size is controlled by 2 guard cells closed open Stoma is a small hole Plant Organs: Stems, Roots, & Leaves

34. Carbon dioxide oxygen Guard cell Provided plant is photosynthesising Stoma function is for gas exchange in the leaf Plant Organs: Stems, Roots, & Leaves

35. ■ Stomata open and close at different times of the day ■ When it is light the plant needs CO 2 for photosynthesis so the stoma open ■ At night (darkness) they close

36. So we’ve said the stoma allows for gas exhange i.e. CO2 in and O2 out.. How does this happen?? Plant Organs: Stems, Roots, & Leaves

37. What is diffusion??? Plant Organs: Stems, Roots, & Leaves

38. So thinking about photosynthesis.. How does CO2 enter the leaf by diffusion and how does O2 leave by diffusion?? Plant Organs: Stems, Roots, & Leaves

39. ■ In a leaf the vascular bundles form the midrib and veins of the leaf.leaf the vascular bundles ■ Usually, the pattern tends to be veins branching away from the midrib, forming a network which gradually gets smaller and thinner with distance from the midrib. ■ Within each vein, the xylem can be seen on top of the phloem. Within each vein, the xylem can be seen on top of the phloem ■ Exam Tip: Given either a diagram or a microscope you must be able to identify monocot & dicot, and label the parts Monocot Top Dicot Bottom

40. Plant Organs: Stems, Roots, & Leaves ■ Complete the table below to identify xylem and phloem from the tissues labelled E to I.

41. Plant Organs: Stems, Roots, & Leaves Plant Organs

42. Plant Tissue ■ Meristematic ■ The main function of meristematic tissue is mitosis. The cells are small, thin-walled, with no central vacuole and no specialized features. ■ Meristematic tissue is located in ■ the apical meristems at the growing points of roots and stems. ■ the secondary meristems (lateral buds) at the nodes of stems (where branching occurs, and in some plants, ■ meristematic tissue, called the cambium, that is found within mature stems and roots.

43. Plant Tissue ■ Protective ■ Protective tissue covers the surface of leaves and the living cells of roots and stems. Its cells are flattened with their top and bottom surfaces parallel. ■ The upper and lower epidermis of the leaf are examples of protective tissue

44. Plant Tissue ■ Parenchyma ■ The cells of parenchyma are large, thin-walled, and usually have a large central vacuole. ■ They are often partially separated from each other and are usually stuffed with plastids. ■ In areas not exposed to light, colorless plastids predominate and food storage is the main function. ■ The cells of the white potato are parenchyma cells. ■ Where light is present, e.g., in leaves, chloroplasts predominate and photosynthesis is the main function

45. Plant Tissue ■ Sclerenchyma ■ The walls of these cells are very thick and built up in a uniform layer around the entire margin of the cell. ■ Often, the cell dies after its cell wall is fully formed. ■ Sclerenchyma cells are usually found associated with other cells types and give them mechanical support. ■ Sclerenchyma is found in stems and also in leaf veins. ■ Sclerenchyma also makes up the hard outer covering of seeds and nuts.

46. Plant Tissue ■ Collenchyma ■ Collenchyma cells have thick walls that are especially thick at their corners. ■ These cells provide mechanical support for the plant. ■ They are most often found in areas that are growing rapidly and need to be strengthened. ■ The petiole ("stalk") of leaves is usually reinforced with collenchyma

47. Plant Tissue

48. Xylem is made of vessels that are connected end to end for the maximum speed to move water around. They also have a secondary function of support. When someone cuts an old tree down, they reveal a set of rings. Those rings are the remains of old xylem tissue, one ring for every year the tree was alive Plant Tissue

49. ■ Xylem conducts water and dissolved minerals from the roots to all the other parts of the plant. ■ These are thick-walled tubes that can extend vertically through several feet of xylem tissue. ■ Their diameter may be as large as 0.7 mm ■ Their walls are thickened with secondary deposits of cellulose and are usually further strengthened by impregnation with lignin. ■ The secondary walls of the xylem vessels are deposited in spirals and rings and are usually perforated by pits. ■ Xylem vessels arise from individual cylindrical cells oriented end to end. ■ At maturity the end walls of these cells dissolve away, and the cytoplasmic contents die. ■ The result is the xylem vessel, a continuous nonliving duct. ■ Xylem also contains tracheids. ■ These are individual cells tapered at each end so the tapered end of one cell overlaps that of the adjacent cell ■. Like xylem vessels, they have thick, lignified walls and, at maturity, no cytoplasm. ■ Their walls are perforated so that water can flow from one tracheid to the next. ■ The xylem of ferns and conifers contains only tracheids. ■ In woody plants, the older xylem ceases to participate in water transport and simply serves to give strength to the trunk. Wood is xylem. When counting the annual rings of a tree, one is counting rings of xylem

50. Plant Tissue ■ Adaptations of Xylem to Function ■ Xylem can carry water and minerals from roots to shoot tips because: ■ Made of dead cells forming continuous column ■ Tubes are narrow so capillary action is effective ■ Pits allow water to move sideways ■ Lignin is strong and allows for stretching ■ Flow of water is not impeded as: there are no end walls, no cell contents, no nucleus, lignin prevents tubes collapsing ■ Exam Tip: Remember to write the lignin supports the xylem walls not the whole plant

51. Enter phloem. The phloem cells are laid out end- to-end throughout the entire plant, transporting the sugars and other molecules created by the plant. Phloem is always alive. PHLOEM FUN!! What is the best way to think about phloem? Think about sap coming out of a tree. That dripping sap usually comes from the phloem. Plant Tissue

52. Phloem 2 way process! Roots to shoots to leaves and back again Plant Tissue

53. ■ The main components of phloem are ■ sieve elements and ■ companion cells. ■ Sieve elements are so-named because their end walls are perforated. ■ This allows cytoplasmic connections between vertically-stacked cells. ■ The result is a sieve tube that conducts the products of photosynthesis — sugars and amino acids — from the place where they are manufactured (a "source"), e.g., leaves, to the places ("sinks") where they are consumed or stored; such as ■ Roots ■ growing tips of stems and leaves ■ Flowers ■ fruits, tubers, corms, etc. ■ Sieve elements have no nucleus and only a sparse collection of other organelles. They depend on the adjacent companion cells for many functions. ■ Companion cells move sugars, amino acids and a variety of macromolecules into and out of the sieve elements. In "source" tissue, such as a leaf, the companion cells use transmembrane proteins to take up — by active transport — sugars and other organic molecules from the cells manufacturing them. ■ Water follows by osmosis. ■ These materials then move into adjacent sieve elements through plasmodesmata. ■ The pressure created by osmosis drives the flow of materials through the sieve tubes. ■ In "sink" tissue, the sugars and other organic molecules leave the sieve elements through plasmodesmata connecting the sieve elements to their companion cells and then pass on to the cells of their destination. Again, water follows by osmosis where it may ■ leave the plant by transpiration or ■ increase the volume of the cells or ■ move into the xylem for recycling through the plant.

54. Plant Tissue ■ Exam Tip: Phloem tissue also transports small amounts of amino acids, certain ions and plant hormones- but mainly sugars (the sugars transported are dissolved). ■ Exam Tip: The active transport of sugars require energy

55. Plant Tissue

56. Transpiration ■ Transpiration is the evaporation of water from the surfaces of the mesophyll cells in leaves followed by the loss of water vapour (diffusion) through the stomata into the atmosphere.

57. Transpiration Although it may seem bad for plants, transpiration actually moves water from the roots to the top of the plant, without using energy. how does this work? Water always moves from an area of high concentration to an area of low concentration. This movement of water is a type of diffusion called osmosis. Transpiration is the loss of water by evaporation from plants.Transpiration Air around the plant usually contains less water than the cells of the plant, so water evaporates into the air.

58. The diffusion of gases occurs in the leaves. They are adapted for this function in the following ways: ●Leaves are thin. This decreases the distance gases have to travel between the air and cells. ●There are air spaces between cells. This increases the speed of diffusion from the air to the cells inside the leaf. ●There are lots of stomata (pores) on the undersides of leaves. These let gases in and out. Transpiration

59. The amount of water vapour in the air. Columns of living cells in the stem that transport sugars up and down the stem. Columns of dead cells (thick and strengthened cellulose cell wall with a hollow lumen) which transport water from the roots to the shoot and leaves. Movement of food substances (sugars) up and down stems to growing and storage tissues. Random movement of particles from a high to low concentration. Pores on the leaves of plants which allow gas exchange with the environment. They can open or close depending on conditions. When a liquid is turned into a gas. This is how water leaves the plant via the stomata in the leaves. Movement of water and minerals from the roots to the shoot and leaves.

60. Transpiration ■ The absorption of water by roots The absorption of water by roots ■ Root hair cells absorb water and mineral ions from the soil. They have fine extensions that stick out into the soil which greatly increases the surface area for absorption. ■ Minerals absorbed by active transport using ATP ■ Minerals reduce the water potential in the cell cytoplasm (more negative) so water is taken up by osmosis Exam Tip: Water moves into the root hair cells by osmosis.

61. Transpiration ■ Active process occurring at the endodermis (layer of cells surrounding the xylem, some containing waterproof strip called casparian strip) ■ Casparian strip blocks the apoplast pathway (between cells) forcing water into the symplast pathway (through the cytoplasm) ■ The endodermis cells move minerals by active transport from the cortex into the xylem, decreasing the water potential (more negative), thus water moves from the cortex through the endodermal cells to the xylem by osmosis ■ A water potential gradient exists across the whole cortex, so water is moved along the symplast pathway (through cytoplasm) from the root hair cells across the cortex and into the xylem Movement across the root

62. Transpiration ■ The Apoplast pathway. ■ Water moves though the fluid filled space of the cellulose cell wall. Dissolved minerals are carried with the water. ■ The cell walls are quite thick and very open, so water can easily diffuse through cell walls without having to cross any cell membranes by osmosis. ■ However the apoplast pathway stops at the endodermis because of the waterproof casparian strip, which seals the cell walls. At this point water has to cross the cell membrane by osmosis and enter the symplast pathway. ■ This allows the plant to have some control over the uptake of water into the xylem.

63. Transpiration ■ The Symplast pathway. ■ Water travels though the cytoplasm of cells. ■ The cytoplasm's of all the cells in the root are connected by plasmodesmata through holes in the cell walls. ■ The plasmodesmata are composed of a thin layer of cytoplasm

64. Transpiration Exam Tip: If you are asked to identify the endodermis from a diagram, look for which layer of cell has casparian strip

65. Transpiration ■ Caspian Strip ■ Blocks the apoplast pathway (cell walls) ■ Water and dissolved nitrate ions have to pass into the cell cytoplasm through cell membranes ■ There are transporter proteins in the cell membranes that actively transport nitrate ions into the xylem lowering the water potential (more negative) ■ Water enters xylem down concentration gradient and cannot pass back

66. Transpiration ■ The diagram shows some cells from the tissues in a root. 1. Name the tissues labelled W and X. 2. Explain why water moves from the apoplast pathway to the symplast pathway when it reaches the tissue labelled W. 3. ATP is used at a high rate in the phloem tissue of roots. Explain what ATP is used for in phloem tissue.

67. Transpiration How does water move up the stem?

68. Transpiration ■ Water Movement Up the stem ■ Root pressure: minerals move into xylem by active transport, forcing water into xylem and pushes it up the stem ■ Transpiration Pull: loss of water at leaves replaced by water moving up xylem. Cohesion- tension theory- cohesion between water molecules and tension in the column of water (which is why xylem is strengthened with lignin) means the whole column of water is pulled up in one chain ■ Capillary action: adhesion of water to xylem vessels as they are narrow

69. ■ Transpiration pull Transpiration pull ■ Cohesive force of water forms a long column of water. ■ As water is lost at the top via transpiration, the column is drawn up through the xylem. ■ Also called the cohesion tension theory as the presence of lignin allows xylem vessels to withstand the tension. ■ If a column is broken, water can flow into adjacent xylem vessels via the pits.

70. Transpiration How water leaves the leaf?

71. Transpiration ■ How water leaves the leaf? ■ Through stomata ■ Tiny amount through the waxy cuticle ■ Water evaporates from the cells lining the cavity between the guard cells, lowering water potential and meaning that water enters them by osmosis from neighbouring cells, which is replaced by further neighbouring cells and so on Exam Tip: Don’t call Stomata Pores Exam Tip: Don’t be put off by the term mesophyll cells – they are just a type of leaf cell

72. Transpiration ■ Water Flows Trough Leaves ■ Loss of water vapour from upper parts of the plant ■ Water enters leaf from xylem and passes to mesophyll cells by osmosis ■ Water evaporates from surface of mesophyll cells to form water vapour (air spaces allow water vapour to diffuse through leaf tissue) ■ Water vapour potential rises in air spaces, so water molecules diffuse out of the leaf through open stomata Exam Tip: Don’t call Stomata Pores Exam Tip: Don’t be put off by the term mesophyll cells – they are just a type of leaf cell

73. Transpiration ■ Transpiration in Leaf (3 process) Transpiration ■ Osmosis from xylem to mesophyll cells ■ Evaporation from surface of mesophyll cells into intercellular spaces ■ Diffusion of water vapour from intercellular spaces out through stomata Exam Tip: Water passes from the xylem into the leaf cells by osmosis (down the water potential gradient).

74. Transpiration ■ If a plant is losing more water than it can replace, it will begin to wilt. ■ This will reduce the amount of water lost as the surface area is reduced. ■ Tip: Air Bubbles can from in xylem, which block the column of water, preventing it from reaching the cells. The cells can become flaccid

75. Measuring Transpiration ■ You can measure water loss by using a potometer

76. Measuring Transpiration ■ A potometer is a device that measures the rate at which a plant draws up water. ■ Since the plant draws up water as it loses it by transpiration, you are able to measure the rate of transpiration. ■ The basic elements of a potometer are: ■ A plant cutting ■ A calibrated pipette to measure water loss ■ A length of clear plastic tubing ■ An air-tight seal between the plant and the water-filled tubing

77. Measuring Transpiration Transpiration can be measured using a potometer. A cut plant stem is sealed into the potometer using a rubber bung. This gives an indirect measurement of the rate of transpiration. An air bubble is introduced to the capillary tube. The distance the bubble travels shows how much water the stem has taken up.

78. Measuring Transpiration ■ Number of leaves ■ More leaves = more transpiration ■ Number, size and position of stomata ■ Many stomata = more transpiration ■ large stomata = more transpiration ■ Stomata on upper epidermis = more transpiration ■ Waxy cuticle ■ Thinner waxy cuticles = more transpiration ■ Environmental factors which affect transpiration rate ■ Amount of light ■ More light = stomata open = more transpiration ■ Relative humidity ■ Greater the humidity gradient = more transpiration ■ Temperature ■ Warm air can hold more water = greater gradient ■ Increased evaporation from mesophyll cells ■ Water vapour has more kinetic energy = more movement through the stomata ■ Wind ■ More wind = less barrier = more transpiration ■ Water availability at roots ■ More water available = more water up the xylem

79. Measuring Transpiration Exam Tip: You can use a photometer to test the effect of different factors on transpiration Fan to increase air (wind) Lamp to increase light (light) Mister to increase humidity (humidity) When estimating the rate of transpiration by measuring water uptake, you need to carry out repeats to increase the reliability of your data and help identify anomalies.

80. Measuring transpiration ■ Jo is investigating the effect of some factors on transpiration in plants. Look at the diagram. It shows the apparatus she uses. ■ Jo records the mass of each tube and its contents. She leaves the apparatus for 5 days in the same room. She then records the mass again. The table shows Jo’s results. ■ Compare the effects of increasing air movement and increasing humidity on the rate of transpiration in Jo’s plants. Use information from the table, as well as your own calculations, to help you answer. ■ In Jo’s experiment, water moves from the tubes to the leaves through transport vessels. Write down the name of these vessels. Exam Tip: Don’t forget to round to significant figures

81. Xerophytes ■ Xerophytes are plants that are able to exist in conditions where water is scarce. Cacti are xerophytes that survive in hot, dry and desert regions. Cacti reduce water loss and conserve water in the following ways: Leaves: ■ Leaves reduced to spines- reduces surface area of leaf in water loss. ■ Thick waxy cuticle covers plant’s surfaces- reduces transpiration.

82. Xerophytes Exam Tip: Stomata are sunk in, layers of ‘hair’ on the epidermis and curled leaves reduce transpiration by reducing the water potential gradient between their air spaces in the lead and the air outside the leaf. Exam Tip: Remember water is lost from a leaf as water vapor.

83. HYDROPHYTES ■ Hydrophytes – these are plants which grow submerged or partially submerged in water. ■ Buoyed (lifted) up by water and with no need for water transport, floating plants saves energy since they produce little or no xylem.

84. HYDROPHYTES ■ Root: I. If present- for anchorage. II. If there is no need for roots to absorb water or mineral ions, there are no root hairs. ■ Leaves and stems: ■ Little or no cuticle- no need to conserve water.

85. HYDROPHYTES ■ Other adaptations: Extensive system of air spaces in stems and leaves: ■ Gases diffuse quickly ■ Provide buoyancy to keep the plants close to the light and are a reservoir of O 2 and CO 2.

86. TRANSLOCATION ■ Food is made in the leaves by photosynthesis. The soluble products include sucrose, amino acids and fatty acids. These are carried to all parts of the plant in solution in the phloem. ■ This transport is called translocation which means ‘from place to place’. Exam Tip: Assimilates are substance that become incorporated into plant tissue.

87. Translocation Phloem The individual sieve tube elements that make up the phloem are alive, although they have no nucleus, very few organelles and only strands of cytoplasm. Unlike in xylem vessels, the end cell walls do not disappear, but instead form structures called sieve plates, through which these strands of cytoplasm can pass. Because of their greatly reduced contents, sieve tube elements cannot keep themselves alive and have to be aided by companion cells which respire, excrete, etc. on the elements’ behalf. The cytoplasm of the companion cells and their sieve tube elements is joined through pores in the side walls.

88. TRANSLOCATION Translocation may be defined as an energy consuming process by which nutrients such as sucrose and amino acids are transported from their region of production or storage (source) to their regions of utilisation (sink) for respiration or growth. ■ EE

89. The transport of soluble organic substances (sometimes called assimilates) within a plant is known as translocation. The solutes are transported in sieve tube elements. The “Mass Flow Hypothesis” is the theory by which we think solute transport occurs in plants. Any area where sucrose is produced in a plant is known as a source, and any area where it is taken out (usually, used in respiration) is known as a sink. Sucrose is actively transported into the sieve tubes of the phloem at the source (e.g. root or leaf), lowering the water potential inside the sieve and so water enters the tubes via osmosis, creating a higher pressure inside the sieve tubes at the source. At the sink, sugars leave the phloem to be used up, increasing the water potential inside the sieve tubes, so water leaves via osmosis, lowering the pressure inside the sieve tubes. The result is a pressure gradient from source to sink, pushing sugars to where they're needed.source sink Translocation

90. Simple sugars are converted to sucrose and transported to parts of plant where storage occur to provide energy. Sucrose is: ■ Broken down by enzyme to give simple sugars that are used to respiration ■ Changed to starch for storage in the root cortex and in seeds ■ Used to make cellulose for new cell walls at the growing root tip and shoot tip ■ Stored in some fruits to make them sweet and attract animals How is Sucrose Used Up?

91. Translocation ■ Pesticides and insecticides are the chemicals that are used by the plant growers to kill the pests and insects. ■ In plants, pesticides and insecticides are translocated through the phloem tubes along with the phloem sap. ■ Depending on the mode of action, pesticides can be classified into two main groups: contact pesticides and systemic pesticides. TRANSLOCATION OF APPLIED CHEMICALS

92. Translocation ■ Contact pesticides: ■ These are the chemicals to be sprayed directly on to the pest. ■ The application of these pesticides may not be very effective as many insects and other pests may be missed when these pesticides are sprayed, as they may be hidden underneath the leaves. ■ Systemic pesticides: ■ Systemic pesticides when applied to the soil or to the leaf, they will be absorbed along with the water and translocated to the phloem to all parts of the plant. ■ Therefore, they are more easily reached the body of the pests as they feed on the plant. ■ Hence they have a much better chance of killing all the pests on the plant than contact pesticides.

93. Translocation ■ In plant transport, the part of the plant where a substance begins its journey is called a source. ■ The part where it ends its journey is a sink. Where do the journeys begin and end?

94. Translocation ■ Make sure you learn the term source & sink. ■ Mass Flow Hypothesis has 3 parts ■ Source: Active transport loads the assimilates into the sieve tubes of the phloem. Lower water potential so water enter sieve tubes by osmosis. Creates high pressure in sieve tubes at source end ■ Sink: Assimilates are removed from the phloem to be used up. Increase water potential inside sieve causes water to leave by osmosis. Lower pressure in sieve tube at sink. ■ Flow: The difference in pressure between source and sink causes assimilates to move along sieve tubes. ■ Companion Cells contain many mitochondria, which means they can make lots of ATP. ATP is needed to actively load the assimilates into the phloem sources. ■ There is more sieve plates than companion cells ■ Practice Spelling the words phloem, assimilates, and translocation you can earn extra marks for spelling. Exam Tips

95. Translocation ■ Source: water and mineral ions absorbed by the roots ■ Sink: leaves, flowers and fruits ■ Xylem vessels being dead and empty, movement of water is a passive process. ■ It relies upon the evaporation of water vapour from the leaves producing a tension in the xylem. ■ This pulls up water from the roots to give the transpiration stream and is greatest on hot, dry and windy days. In Transpiration………

96. Translocation ■ Source: leaves ■ Sink: respiring plant tissues, root and shoot tips, regions of storage such as cortex and seeds. ■ It is an active process which occurs in the phloem. ■ Phloem tubes are living cells that contain cytoplasm. ■ Movement in phloem requires active transport of sucrose at the source. ■ Water enters the phloem tubes to build up a head of pressure that forces phloem saps to the sinks. ■ It is most active on sunny,warmy days when plants are producing increased levels of sugars. In translocation…….

97. Translocation Compare & Contrast Transpiration & Translocation TranspirationTranslocation Source Sink Vascular Tissue Vascular Cells Type of Energy Source Alternate Name