Transpiration

1. Transpiration • Transpiration is the major mechanism that drives the movement of water through a plant. In the first section of this laboratory you will investigate factors that influence the rate of transpiration. In the second section you will study plant anatomy as it relates to transport. • To do this laboratory, you should understand the basic concepts of water potential. You can review these by looking back at Lab 1. Diffusion and Osmosis.

2. Movement of Water Up Xylem Vessels • When water enters the roots, hydrogen bonds link each water molecule to the next so the molecules of water are pulled up the thin xylem vessels like beads on a string. The water moves up the plant, enters the leaves, moves into air spaces in the leaf, and then evaporates (transpires) through the stomata (singular, stoma).

3. Hydrogen Bonding • Recall that a hydrogen bond is a weak interaction between a hydrogen atom of one molecule and, in this case, the oxygen of another molecule. • Water is a polar molecule, with the region around the oxygen atom having a slight negative charge and the regions around the hydrogen atoms having a slight positive charge. In water, the negative regions on one molecule are attracted to the positive regions on another, and the molecules form hydrogen bonds.

4. The Process of Transpiration • There are hundreds of stomata in the epidermis of a leaf. Most are located in the lower epidermis. This reduces water loss because the lower surface receives less solar radiation than the upper surface. Each stoma allows the carbon dioxide necessary for photosynthesis to enter, while water evaporates through each one in transpiration. • Now that you have been introduced to the concept of transpiration, the questions on the following page will help you understand how the properties of water and water potential are important to this process.

5. Test Yourself • 1. What property of water accounts for the fact that molecules of water "grab" the walls of the thin xylem vessels? • 2. Water molecules pull each other like beads on a string; as one molecule is evaporated through a stoma, another is pulled up. What property of water is demonstrated here? • 3. Place the following in order (list the letters), from highest water potential to lowest water potential, under normal conditions. a. Mesophyll of leavesb. Outside air around leafc. Spaces around rootsd. Inside the xylem vessels

6. How Do Guard Cells Function? • Guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata. To understand how they function, study the following figures. As you look at the figures, keep in mind that an increase in solute concentration lowers the water potential of the solution, and that water moves from a region with higher water potential to a region of lower water potential.

7. Stomatal closing 1.Potassium ions move out of the vacuole and out of the cells. 2.Water moves out of the vacuoles, following potassium ions. 3.The guard cells shrink in size. 4.The stoma closes. Stomatal opening 1.Potassium ions move into the vacuoles. 2.Water moves into the vacuoles, following potassium ions. 3.The guard cells expand. 4.The stoma opens. Guard Cell Function

8. Equation for photosynthesis • By now you should have the basic equation for photosynthesis fixed in your memory! • Write it Here:

9. Balance • A leaf needs carbon dioxide and water for photosynthesis. For carbon dioxide to enter, the stomata on the surface of the leaf must be open. As you have seen, transpiration draws water from the roots into the leaf mesophyll. However, the plant must not lose so much water during transpiration that it wilts. The plant must strike a balance between conserving water and bringing in sufficient amounts of CO2 for photosynthesis.

10. Factors That Affect the Rate of Transpiration • Transpiration is affected by various conditions in the plant's environment. The following exercises help you think about some of these effects before you test them in your laboratory experiment. • 1. Which condition would result in the higher rate of transpiration light or dark? Explain • 2. Which condition would result in the higher rate of transpiration humid environment or dry environment? • 3. Which condition would result in the higher rate of transpiration breezy conditions or still air? • 4. Which condition would result in the higher rate of transpiration hot environment or warm environment?

11. Design of the Experiment • 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 tubingYour instructor will show you how to assemble your potometer.

12. An Overview of the Experiment

13. How to Calculate Leaf Surface Area • The rate of transpiration is measured as the amount of water lost/ square meter/ minute. Because water evaporates through the many stomata on the leaf surface, the rate of transpiration is directly related to the surface area. To arrive at the rate of transpiration, therefore, you must calculate the leaf surface area of each plant: Because most stomata are found in the lower epidermis, you will determine that surface area. • •Lay the leaves to be measured on a 1-cm grid and trace their outlines.•Count the number of square centimeters. Estimate the area of the partial squares. (Here's a simple method for this estimate: Count a partial square if it is at least half covered by the leaf; do not count partial squares that are less than half covered.)•Do not include the area of the stem (petiole) in your calculations.

14. 1. If guard cells in a plant were deficient in K+, which of the following would be most likely to occur?a.Wilting would become more likely.b.Photosynthesis would decrease.c.Transpiration would increase.d.Food transport would decrease.

15. Match the letter and number • a.phloemb.mesophyllc.epidermisd.xylem

16. 3. Which line indicates a guard cell? 4. Which type of cells are indicated by label line 2? • a.parenchymab.xylemc.phloemd.epidermis

17. 5. Several factors account for the movement of water up xylem vessels. Which single factor is most important in pulling water toward the top of a tall tree? a.Evaporation of water through stomatab.Osmosis in the rootc.Capillary actiond.Atmospheric pressure • 6. All of the following enhance water transport in terrestrial plants EXCEPT:a.Hydrogen bonds linking water moleculesb.Capillary action due to adhesion of water molecules to the walls of xylemc.Evaporation of water from the leavesd.K+ being transported out of the guard cells

18. 7. Under conditions of bright light, in which part of a transpiring plant would water potential be lowest?a.Xylem vessels in the leavesb.Xylem vessels in the rootsc.Root hairsd. Spongy mesophyll of the leaves • 8. What type of environment would result in the greatest rate of transpiration? A. Cloudy, humid conditionsb.Warm, humid conditionsc.Warm, light-breezy conditionsd.Cool, humid conditions

19. In your own laboratory, you will examine slices of a plant stem under the microscope and identify the different types of tissue and their functions. You've already seen a dicot. The following exercise will give you practice in identifying plant tissues in a monocot. • Identify each of the structures in the micrograph of a monocot stem above by answering the following questions using the appropriate choices from the list. When you are finished, check your answers. • Choices for Tissue Type: xylem, phloem, parenchyma, epidermis • Choices for Function: food transport, water transport, food storage, protection

22. Help Wanted! • Different parts of plants do different jobs. Read the classified advertisements and help each of the plants parts listed below to find the right job. • Cambium, guard cells, phloem, root cap, sepals,cuticle,petals,stamen,pistil,chloroplasts, tap root, xylem  • Advertizing Executive Colorful personality needed to advertise availability of pollen and nectar. Must have experience working with bees. Door AttendantFull-time positions available at entrance to stomates Waiters/Waitresses Deliver food to hungry plant cells. Work in busy roots, stems and leaves. AnchorpersonInterested in holding a plant in place? If you have experience digging deep in search of water, we're looking for you. No branching necessary. Egg FarmerFemale needed to manage egg production and receive pollen Chemist Person needed who can convert carbon dioxide and water into glucose. Must wear a green uniform to work and enjoy working in the sun. Bodyguard Help needed to protect buds. Apply before spring HardhatsConstruction workers. Drill for water. Protect other members of water-search team will drilling. Apply at root tip Pollen ProductionAssistant Help needed to produce pollen. Seasonal work only in the spring. Conductor Individual needed to carry water. Rapid advancement. Start at the roots and work up to the top! Outdoor WorkProtect and cover upper and lower leaf surfaces. Must be able to prevent water loss and seepage. Apply at the leaf. Plumber Vascular specialist needed to lay new plumbing each growing season. Experience making new xylem and phloem necessary. Potential for Advertising Executive_______________________ • Anchorperson ______________________________ • Egg Farmer_______________________Chemist ______________________________ • Bodyguard_______________________ • Hardhats______________________________Pollen Production Assistant _______________________ • Conductor______________________________Outdoor Work_______________________ • Plumber ______________________________DoorAttendant________________________ • Waiter/Waitress _______________________________ 

23. Flower Anatomy • Flower Structure and Reproduction Flowers are the plant's reproductive structures. Angiosperms are types of plants that bear fruits and flowers. Flowers are usually both male and female, and are brightly colored to attract insects to help them carry pollen used for sexual reproduction. Not all flowers are colorful, though. These flowers usually use the wind for pollination. • Parts of the Flower • The receptacle is the part of the branch on which a flower forms. Color the receptacle (B) brown. Sepals are leaf like structures that surround and protect the flower before it blooms. Color the sepals (C) green. Petals are the colorful part of the flower that attracts insects and even other small animals, such as mice, birds, and bats. Color the petals (D) a bright color of your choice. All flowering plants have flowers, but some are not brightly colored. The petals of these flowers are reduced or absent and the plant relies on the wind or water for pollination. • The flower has both male and female reproductive parts. The female reproductive structures are called carpels. In most flowers, the carpels are fused together to form a pistil. Color the pistil (P) pink. The pistil has three parts, which can be seen, in the box labeled "pistil". The stigma at the top is often sticky and is where the pollen attaches. Color the stigma (J) purple. The style is the long tube that attaches the stigma to the ovary. Sperm from the pollen will travel down this tube to the ovules. The ovules, or eggs, are stored in the ovary until they are fertilized. Plants can only fertilize eggs of the same species. Special chemicals prevent sperm from fertilizing the eggs of flowers that are not the same kind. Color the style (K) red, and the ovary (L) pink. Color the ovules (O) black. • The male reproductive structures are called the stamens. Color the stamens (H) blue. Each stamen consists of an anther (A), which produces pollen, and a filament (F), which supports the anther. In the box labeled "stamen" color the anther dark blue, and the filament light blue. Pollen produced by the anther is carried by insects or other animals to the pistil of another flower where it may fertilize the eggs. • The other flowers in the picture follow the same plan, although they come in many different colors and styles. Color each of the flowers according to the colors above (blue for stamen, pink for pistil, bright colors for the petals. etc.). Note that in some of the flowers, not all the structures are visible. • Plant Reproduction • Sexual reproduction in plants occurs when the pollen from an anther is transferred to the stigma. Plants can fertilize themselves: called self-fertilization. Self-fertilization occurs when the pollen from an anther fertilizes the eggs on the same flower. Cross-fertilization occurs when the pollen is transferred to the stigma of an entirely different plant. • When the ovules are fertilized, they will develop into seeds. The petals of the flower fall off leaving only the ovary behind, which will develop into a fruit. There are many different kinds of fruits, including apples and oranges and peaches. A fruit is any structure that encloses and protects a seed, so fruits are also "helicopters" and acorns, and bean pods. When you eat a fruit, you are actually eating the ovary of the flower.

24. 1. What is an angiosperm? • 2. The flower attaches to what part of the plant? • 3. Why are flowers brightly colored? • 4. Name two mammals that might pollinate a plant. • 5. If the petals of a flower are reduced or absent, how is the plant pollinated? • 6. The female reproductive structures are called the: • 7. Name the three parts of the pistil: • 8. Where are the ovules stored? • 9. Name the two parts of the stamen: • 10. Describe sexual reproduction in plants. • 11. The ovary develops into what structure? • 12. Define fruit. • 13. Some flowers are not brightly colored at all, but have a very pungent odor that smells like rotting meat. How do you think these flowers are pollinated? • 14. In many flowers, the pistils and stamens reach maturity at different times. Considering what you know about pollination, why would this be an advantage to the plant?

25. Label The Parts of a Flower

26. LEAF ANATOMY • The leaf is the primary photosynthetic organ of the plant. It consists of a flattened portion, called the blade, that is attached to the plant by a structure called the petiole. Sometimes leaves are divided into two or more sections called leaflets. Leaves with a single undivided blade are called simple, those with two or more leaflets are called compound. • The outer surface of the leaf has a thin waxy covering called the cuticle (A), this layer's primary function is to prevent water loss within the leaf. (Plants that leave entirely within water do not have a cuticle). Directly underneath the cuticle is a layer of cells called the epidermis (B). The vascular tissue, xylem and phloem are found within the veins of the leaf. Veins are actually extensions that run from to tips of the roots all the way up to the edges of the leaves. The outer layer of the vein is made of cells called bundle sheath cells (C), and they create a circle around the xylem and the phloem. One the picture, xylem is the upper layer of cells (D) and is shaded a little lighter than the lower layer of cells - phloem (E). Recall that xylem transports water and phloem transports sugar (food). • Within the leaf, there is a layer of cells called the mesophyll. The word mesophyll is greek and means "middle" (meso) "leaf" (phyllon). Mesophyll can then be divided into two layers, the palisade layer (F) and the spongy layer (G). Palisade cells are more column-like, and lie just under the epidermis, the spongy cells are more loosely packed and lie between the palisade layer and the lower epidermis. The air spaces between the spongy cells allow for gas exchange. Mesophyll cells (both palisade and spongy) are packed with chloroplasts, and this is where photosynthesis actually occurs. • Epidermis also lines the lower area of the leaf (as does the cuticle). The leaf also has tiny holes within the epidermis called stomata (H). Specialized cells, called guard cells (I) surround the stomata and are shaped like two cupped hands. Changes within water pressure cause the stoma (singular of stomata) to open or close. If the guard cells are full of water, they swell up and bend away from each other which opens the stoma. During dry times, the guard cells close.

27. Cuticle (light blue) Epidermis (yellow) Guard cells (pink) Palisade Mesophyll (dark green) Phloem (purple)   Xylem (orange)   Spongy Mesophyll (light green) Bundle Sheath (dark blue)  

28. Leaf questions • 1. What two tissues are found within a vein? • 2. What does the word "mesophyll" mean? • 3. What two layers of the plant contain chloroplasts? • 4. The outermost layer of cells: _________________________ • 5. The waxy covering of the leaf.: _______________________ • 6. These cells function to open and close stomata. _____________________ • 7. Outer layer of the vein: ________________________ • 8. Column like cells that lie just under the epidermis. ___________________ • 9. Openings that allow for gas exchange. _________________________ • 10. The stalk that connects the leaf to the stem. ______________________