TRANSPIRATION
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TRANSPIRATION

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TRANSPIRATION. What is Transpiration?. An evaporation of water in the form of water vapour from the surface of the plant to the atmosphere Where does transpiration take place? . Transpiration. Transpiration mainly takes place through openings on leaves STOMATAIf the stomata is opened, then water vapour will be lost into the atmosphereIn some cases, transpiration also takes place through the lenticels and cuticles.
TRANSPIRATION

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2. TRANSPIRATION

3. What is Transpiration? An evaporation of water in the form of water vapour from the surface of the plant to the atmosphere Where does transpiration take place?

4. Transpiration Transpiration mainly takes place through openings on leaves ? STOMATA If the stomata is opened, then water vapour will be lost into the atmosphere In some cases, transpiration also takes place through the lenticels and cuticles

5. Transpiration A thin film of water covers each mesophyll cell

7. Transpiration A thin film of water covers each mesophyll cell There are numerous air spaces between the mesophyll cells

9. Transpiration A thin film of water covers each mesophyll cell There are numerous air spaces between the mesophyll cells Water evaporates from the film of water surrounding the mesophyll cells into the air spaces (and eventually diffuses out of the stomata into the atmosphere)

11. Transpiration 4) As water diffuses out of the cell, the water potential within the cell will decrease. Due to OSMOSIS, water from adjacent cells will be drawn into the cell to replace the water loss These adjacent cells will in turn draw water from other neighboring cells

13. Transpiration 5) Water is drawn from the XYLEM vessels (in the veins) into the neighboring mesophyll cells There will be a water potential difference between the xylem vessels and the mesophyll cells. As water is drawn from the xylem vessels, a suction pressure will develop and this pressure will pull water up the xylem vessels from the roots to the leaves

15. Transpiration The pressure that allows water to be pulled from the roots to the leaves in the xylem vessels is called TRANSPIRATION PULL It allows the transportation of water and minerals in plants

16. Investigation #1: Studying the loss of water by a plant into the atmosphere

17. Procedure

18. Discussions

19. Discussions

20. Discussions

21. Discussions

22. Discussions

24. Adaptations to Prevent Water Loss 1) Waxy layer of cuticle on the leaf?s outer surface of the epidermis

26. Adaptations to Prevent Water Loss A waxy layer of cuticle covers the outer surface of the epidermis More stomata are present in the lower epidermis than the upper epidermis Guard cells control the closing and opening of stomata

27. Stomata Stomata are pores in the epidermis where gaseous exchange takes place during photosynthesis (or respiration)

30. Each stoma is surrounded by two guard cells which contain chloroplasts It is kidney-shaped The inner wall is thicker than the outer wall

33. How Guard Cells Control the Size of Stoma Guard cells contain chloroplasts that carry out photosynthesis in the presence of light. Carbohydrates are formed and thus lower the water potential of the cell Water enters the guard cells from adjacent cells by osmosis and guard cells become turgid

34. How Guard Cells Control the Size of Stoma The inner wall is thicker than the outer wall, so the cell stretches to the outer side and stoma is opened At night, there is no photosynthesis. Guard cells become flaccid and so they return to the original shape and stoma is closed

36. Distribution of Stomata in Leaves

37. Distribution of Stomata in Leaves 1) Normal Plants - Mainly on the lower surface of plants 2) Floating plants - Mainly on the upper surface of plants - Leaves may also have air sacs to keep them afloat. These sacs can be used in gaseous exchange

38. Distribution of Stomata in Leaves 3) Submerged Aquatic Plants - No stomata (not required since gaseous exchange can be carried out by diffusion though the leave surface) - No cuticle (the primary function of cuticle is to prevent excess water transpiration which is not present in aquatic plants)

39. Distribution of Stomata in Leaves 4) Plants in dry and hot conditions - usually have much less stomata to reduce the amount of water loss

40. Investigation #2: Investigating stomatal distribution in a leaf by using cobalt chloride paper

42. Investigation #3: Comparing the abundance of stomata on the upper and lower surfaces of a leaf

43. Introduction to Investigation This investigation allows us to compare the amount of stomata present on the upper and lower surfaces of a leaf by putting the leaf in hot water and observing the amount of bubbles appeared

44. Procedure

45. Discussions

46. Discussions

47. Discussions

48. Investigation #4: Comparing the abundance of stomata on the upper and lower surfaces of leaves by weighing

49. Introduction to Investigation As water is lost by evaporation, the weight of a detached leaf will decrease with time. In this investigation, leaves will be treated differently (with vaseline) and the loss in weight will then be compared among the leaves.

50. Procedure

51. Discussions

52. Discussions

53. Discussions

54. Xerophytes

55. Adaptations of Xerophytes They have numerous epidermal hair - trap moisture

57. Adaptations of Xerophytes They have numerous epidermal hair - trap moisture Some have sunken stomata - also trap moisture

59. Adaptations of Xerophytes They have numerous epidermal hair - trap moisture Some have sunken stomata - also trap moisture Some have rolling leaves which enclose the stomata ? reduce contact between stomata and the environment

61. Adaptations of Xerophytes They have numerous epidermal hair - trap moisture Some have sunken stomata - also trap moisture Some have rolling leaves which enclose the stomata - reduce contact between stomata and the environment Some have small, needle-like or spiny leaves, which have a small surface area

63. Adaptations of Xerophytes They have numerous epidermal hair Some have sunken stomata Some have rolling leaves which enclose the stomata Some have small, needle-like or spiny leaves, which have a small surface area Some have fleshy stems or leaves to help store water

65. Adaptations of Xerophytes Some trees also shed their leaves during dry seasons (e.g. autumn) in order to reduce the rate of transpiration

66. Investigation #5: Comparing the rates of transpiration of a leafy shoot under different environmental conditions using a bubble potometer

67. Introduction to Investigation Bubble potometer can be used for estimating the rate of water uptake by a plant. That is, it can be used as an indirect method in measuring the rate of transpiration. In this investigation, the transpiration rates of a plant under different conditions will be compared

68. Procedure

69. Results Table

70. Discussions

71. Discussions

72. Discussions

73. Under Sunlight The plant has faster transpiration rate when it is placed under sunlight. Stomata open wider when the plant is placed under sunlight. Therefore the diffusion rate of water vapour to the atmosphere, and thus the transpiration rate, increases. High light intensity also increases the atmospheric temperature which in turn increases the rate of transpiration

74. Near a Fan The plant has faster transpiration rate when it is placed near a fan. Greater air movement carries water vapour away from the surface of the leaf at a faster rate. This keeps the concentration of water vapour around the stomata at a low level. Hence, water vapour diffuses out of the leaf faster and the rate of transpiration is increased

75. Covered with Plastic Bag The plant has a slower transpiration rate when it is covered with a plastic bag. High humidity in the surrounding air decreases the concentration gradient of water vapour between the leaf inside and that of the atmosphere. Hence, water vapour diffuses out of the leaf more slowly and the rate of transpiration is decreased

76. Limitations The potometer can only measure the rate of water uptake by the leafy shoot but cannot directly measure the rate of transpiration. If a dehydrated plant is used, the rate of water absorption is higher than the transpiration rate. Under dry condition, the transpiration rate of the plant may exceed its rate of water absorption. Therefore, when using a bubble potometer, assume that the rate of water absorption by the plant is equivalent to the rate of transpiration

77. Investigation #6: Comparing the rates of transpiration of a leafy shoot under different environmental conditions using a weight potometer

78. Introduction to Investigation Another way to measure the a plant?s rate of transpiration is to measure its loss in weight using an electrical balance. This is called a weight potometer. In this investigation, the transpiration rates of a plant under different conditions will be compared

79. Procedure

80. Discussions

81. Discussions

82. Discussions

83. Discussions

84. Environmental Factors Affecting the Rate of Transpiration There are FIVE environmental factors which affect the rate of transpiration. They are:

85. Light Intensity More stomata open wider in light, so plants can get enough carbon dioxide from atmosphere for carrying out photosynthesis Light will increase temperature Rate of diffusion/evaporation of water vapour through stomata will increase Rate of transpiration increases

86. Effect of Light Intensity on Rate of Transpiration

88. Effect of Temperature on Rate of Transpiration

90. Effect of Relative Humidity on Rate of Transpiration

92. Effect of Wind Speed on Rate of Transpiration

93. Availability of Water

94. Wilting ? the leaves and stems become flaccid due to dehydration

95. Enrichment Reading 9.1 Daily Changes in Transpiration Rate

96. Plant Tissues Plant tissues fall into 3 fundamental categories: Dermal tissues Ground tissues Vascular tissues *These tissues can be found in roots, stems and leaves

98. Dermal Tissues Provides a protective layer around the plant Exists as a single layer of cells called the epidermis No chloroplasts

99. Dermal Tissues In the shoot system the epidermis secretes a waxy layer called the cuticle (a protective barrier to retard water loss and to prevent infection) Stomata are found on the epidermis to allow gas exchange to occur Guard cells control the closing and opening of stomata Guard cells are the only cells in epidermis that contain chloroplasts

101. Ground Tissues Make up the bulk of the plant Ground tissues are needed for storage, mechanical support and energy production They can be classified into four broad categories ? parenchyma, chlorenchyma, collenchyma and sclerenchyma

102. Parenchyma Cells The most abundant ground tissues Loosely arranged with intracellular spaces Have thin walls and large vacuoles Metabolically active Perform a variety of functions, such as photosynthesis, repair, food storage and secretion

103. Parenchyma Cells

105. Vascular Tissues Continuous throughout the plant Usually embedded in ground tissues Composed of two complex conducting tissues which form the vascular bundles Xylem + Phloem = Vascular bundles

107. Xylem Conduct water and minerals (one way only: from roots to shoot) Provide support to plant The cell walls of xylem cells derive most of their strength from lignin, a chemical compound produced only by plants It is composed of tracheids, vessel elements, fibers, and parenchyma cells

108. Xylem 1) Tracheids ? long, thin cells with closed ends and are dead at maturity. Contain numerous pits through which water moves 2) Vessel elements ? similar to tracheids but contain holes at each end and are joined end-to-end forming vessels. They are thick-walled and non-living (no cytoplasm and no nuclei)

112. Phloem Transport organic materials (glucose) synthesized by the plant from leaves to the rest of the plant It is composed of sieve tube members, companion cells, fibers and parenchyma cells

113. Phloem 1) Sieve tube members - a sieve tube, like xylem vessels, is a series of cells (sieve elements) joined end to end. The cross walls between successive sieve elements are perforated, forming sieve plates. The cell walls are thin. Although the cells are living, they lack a nucleus. Unlike xylem vessels, the cells walls are not thickened by lignin

114. Phloem 2) Companion cells ? specialized parenchyma cells that develop alongside a sieve tube member. They are elongated, thin-walled and possess a nucleus. Companion cells are linked with the sieve tubes by small canals filled with cytoplasm, which are smaller than pits. Companion cells help to regulate the metabolic activities of sieve tube elements, and help to load and unload the food for transport

117. Different Parts of a Dicot Plant Let?s examine the distribution of different tissues in various parts of a dicotyledonous plant: Root Stem Leaf

121. Cambium Layer of thin-walled cells between xylem and phloem The cambium produces new layers of phloem on the outside and new layers of xylem on the inside, thus increasing the diameter of the stem

123. Outermost layer: epidermis ? no cuticle Cortex ? thin walled parenchyma allow movement of water and minerals Vascular tissues in centre of root Tip: root cap Structure of Dicot Root

124. Root Cap A protective layer at the very tip of root To protect the delicate cells of root from being damaged as the root grows down through the soil Growing point is behind root cap ? by active cell division

125. Functions of Roots 1) Water and minerals absorption 2) Anchorage

126. Adaptations for Absorption of Water and Minerals Extensive branching system ? what is advantage? Outermost layer consists of epidermal cells that lack cuticle ? what is advantage? Some epidermal cells near the root tip have root hairs ? what is advantage?

127. Adsorption of Soil Water by Root Hairs Soil water is a dilute solution of salts ? it is more dilute than the cell sap and cytoplasm of root hair Water will pass by OSMOSIS into root hair through cell wall and cell membrane

129. Absorption of Minerals by Root Hairs Concentration of minerals in soil is usually lower than that inside the root epidermal cells Can minerals be taken up by osmosis???

130. Water and Minerals Transportation Can you design an experiment to show that water and minerals are transported along the xylem vessels only?

131. Capillary Action Adhesion Cohesion Against gravity

132. Root Pressure Minerals are actively transported from root to xylem If transpiration rate is low, salts accumulate in xylem and thus water potential is lowered Therefore, water enters xylem by osmosis Pressure builds up, pushing the content in the xylem upwards If stem is cut, water can be seen gushing out (?stem-bleeding?)

133. Transportation of Organic Substances Mesophyll cells in leaves (high [ ] of carbohydrates) -> sieve tubes of phloem (low [ ] of carbohydrates) -> active growing areas (e.g. root tips) /storage areas (e.g. fruits)

134. Why do plants need a support system?

135. Why do plants need a support system? Prevent leaves from shaded by other plants Allow leaves to receive maximum amount of sunlight for photosynthesis Display flowers as to facilitate dispersal of pollen or seeds

136. Support in Young Dicot Plants Support in young plants or non-woody parts of plants is contributed mainly by turgidity of the thin-walled cells (parenchyma) in the cortex and pith

137. Support in Young Dicot Plants Thin-walled cells in cortex and pith with large central vacuole Water enters the cell vacuole by osmosis Pressure exerted on the tough epidermis Stem becomes hard and upright

138. Support in Young Dicot Plants

139. Support in Young Dicot Plants Xylem vessels contain cells walls with lignin ? thick and rigid Vascular bundles arranged in a ring near the epidermis ? prevent bending In roots ? vascular bundles in centre to give roots more penetrating power and more resistance to stretching (prevent uprooting)

140. Support in Old Dicot Plants Majority of xylem is thick-walled cells (e.g. xylem vessels) ? make stem rigid Plant no longer rely on turgidity for support Support is now contributed mainly be rigidity of the lignified cells in xylem

141. Support in Old Dicot Plants Thin-walled cells, cambium, found between xylem and phloem As plant matures, cambium cells divide to form new cells -- inner side -> new xylem -- outer side -> new phloem Accumulation of xylem tissues -> stem becomes woody and increases in diameter

142. Support in Old Dicot Plants


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