WATER REQUIREMENTS: Teacher Demonstration

Transcription

1 WATER REQUIREMENTS: Teacher Demonstration Objective Students will be able to describe the role of water in seed germination. : two cups of lima beans milk carton (one pint) water. Questions for the Students to Consider 1. What conditions trigger seed germination? 2. What happens to a seed when the conditions for germination are met? Does its appearance change? If so, how? 3. How is it that weeds and other wild seeds can lay dormant for so long before beginning the germination process? 1. Ask students to predict what will happen when a one pint milk carton is filled with lima beans and water, then sealed. 2. Fill the milk carton to the top with lima beans. (Leave enough room to close the top and seal it.) 3. Add water to the milk carton and lima beans until it is full. 4. Allow the carton to sit undisturbed over night. Observe the results the following day. Background Information In order for germination to begin seeds must absorb an adequate amount of water known as imbibition. In order to do this some seeds must first have their seed coats removed or scuffed up, not all seeds germinate just in the presence of water. For example, saguaro cactus seeds must pass through the digestive track of a bird before water can activate the germination process. After absorption of water, germination continues and the plant s need for water stabilizes. Follow-up Student should notice that the lima beans have swollen and begun to bulge the sides of the carton. Ask students what they think has happened to the beans, the water, and the carton. Focus the discussion on the questions written above. Brainstorming ideas is one way to approach these questions. Students ideas should be posted and saved for tomorrow. The seeds can be used for a quick dissection so students can see the plant embryo or they can be placed on a moist paper towel and allowed to continue germinating.

2 WATCHING GERMINATION Objective Students will be able to observe and describe the germination of seeds and the development of first roots, stems and leaves in the laboratory. petri dish (or a small zipper bag) filter paper (coffee filter or paper towel) 5 to 10 seeds (radish seed work well) forceps and hand lens one sheet of centimeter graph paper. Questions for the Students to Consider 1. What is germination? 2. Where do the parts of the plant come from? 3. How is a seed able to develop into a complete, living plant? 1. Discuss with students how they think a seed grows into a plant. Brainstorm student ideas and then discuss how each of their ideas could be tested in the laboratory. 2. Assign students to groups and have all groups set up their petri dishes according to the protocol below or to the protocol that was developed during the discussion. 3. Students should cut graph paper and filter paper to fit inside the petri dish. 4. Students should place the graph paper behind the filter paper, place both inside the petri dish and moisten them with water. 5. Students can then put 5 to 10 seeds across one of the lines of the graph paper using forceps or fingers. Petri Dish Graph Paper Filter Paper Seeds Students should write a prediction that addresses how they think germination will proceed. What appears first, second, and third? Groups of two to three will work best and allow for some groups to change the variable in their set-up. If the graph paper is not visible through the filter paper or paper towel, students may have to make the lines on the graph paper darker using a water proof pen. Reservoir Water Level 6. Student should then replace the bottom half of the petri dish and place it, seeds at the top, in a reservoir of water. Water should cover several centimeters, but not up to the seeds. 7. Students can then begin observing seed germination, noting any changes in

3 the seed s appearance. 8. Students should record on what day the radicle appeared, on what day the hypocotyl appeared, on what day the cotyledons appeared and on what day secondary roots appeared. If a zipper bag is used to replace a petri dish, the open end of the bag should be put into the water to allow the water to filter up to the seeds. Additionally, a cardboard or plastic stiffener can be inserted behind the graph paper to aid in the support of the bag. Group Variations Several groups can change one of the variables in the existing protocol in order to test the conditions necessary for seed germination. For example: one group may want to grow their seeds in a dark environment to test the effects of light on seed germination several groups may want to grow their seeds in varying temperatures to test the effects of temperature on seed germination one group may want to test the necessity of oxygen on seed germination you may want to set up one dish with no water to show that water is necessary in seed germination, and one dish with all of the correct variables to use as the control It is important, however, that measures be taken so that only one variable is altered. Students should do their best to set all of the other conditions equal to the testing group s (or your) protocol. Background Information Germination begins when the seed s dormancy period has ended. Germination can happen when all of the appropriate factors are present, including water, oxygen, and the correct temperature. Water absorption triggers the seed embryo to begin metabolizing. Oxygen is required for respiration, a step in metabolism, to proceed. Optimal temperatures for most seeds are between 25ºC and 30ºC, and most seeds will not germinate if temperature fall below 0ºC or rise above 45ºC, because extreme conditions will not allow the plant to flourish. Once the seed coat breaks, the radicle appears. This anchors the seed in the soil and allows the embryo to continue to take up water. The hypocotyl then pushes its way through the soil exposing the cotyledons to light. True leaves appear shortly thereafter, as secondary roots develop from the primary root. Follow-up Ask students to graph their data to show growth over time. Students from different groups can compare their data to examine how changing conditions affects seed germination and plant growth. Guide students in answering the above questions using the data from this experiment.

4 WATCHING GERMINATION: Student Sheet Questions to Consider 1. What is germination? 2. Where do the parts of the plant come from? 3. How is a seed able to develop into a complete, living plant? petri dish (or a small zipper bag) filter paper (coffee filter or paper towel) 5 to 10 seeds (radish seed work well) forceps and hand lens one sheet of centimeter graph paper. 1. Cut the graph paper and the filter paper to fit inside the petri dish. Name Date Period 2. Place the graph paper behind the filter paper and place inside the top half of the petri dish. 3. Moisten the filter paper with water. 4. Place 5-10 seeds across one of the top lines of the graph paper using forceps. Petri Dish Graph Paper Filter Paper Seeds Reservoir Water Level 5. Replace the bottom half of the petri dish and place the dish, seeds at the top, in a reservoir of water. Water should rise several centimeters up the filter paper, but not up to the seeds. 6. Using the back of this paper, design a chart (or charts) to record your data over the next few days. One chart may record the changes in root and stem length, while another may record the observed characteristics. 7. Graph the information from the data tables when the observations are completed. One possible graph may show the change in root length over the time of observations.

5 WHY HAVE ROOTS? Objective Students will be able to observe the structure and function of different types of root systems. different types of roots systems from several different plants (grass, carrot, radish, sweet potato, onion, corn, etc.) hand lens Questions for Students to Consider 1. What is the purpose of a root system? 2. Why are there so many different types of root systems? 3. How might root systems from desert plants differ from root systems of mountain plants? 1. Ask students to list the differences they expect to observe in the different types of root systems on the student sheet. 2. Ask students to examine the roots using a magnifying lens. 3. Ask students to pick 3 different root systems to draw in column 1 on the student sheet. Challenge students to draw with as much detail as possible, and to identify the plant they think the root came from. 4. Ask students to use available reference materials to find the name, function, and parts of each types of roots. Ask students to record the information they find in column 2, next to their root drawings. Background Information The roots of a plant aid in anchoring the plant to the ground. They also absorb water and minerals and transport those materials to the stem. Some roots store food in their fleshy tissues to be used later during reproduction. Root systems vary according to the plant s needs, but two main types of roots exist: taproots and fibrous roots. As their names suggest, a taproot is a single major root descending from the plant, while fibrous roots are smaller and fibery - extending in many directions. Encourage students to brainstorm as many ideas as they can and write using as much detail as possible when describing the roots. If time is short or references few, small groups can complete step 4 or the teacher can use this time to give the students the information. Follow-up Challenge students to think of other types of plants not observed in the activity. Ask students to speculate what type of root system those plants have and to justify their answers.

6 WHY HAVE ROOTS? Student Sheet Name Date Period Questions to Consider 1. What is the purpose of a root system? 2. Why are there so many different types of root systems? 3. How might root systems from desert plants differ from root systems of mountain plants? different types of roots systems from several different plants hand lens 1. On the back of this sheet, list the differences you expect to find in different types of root systems. 2. Using a magnifying lens, observe several different types of root systems. Pick three different systems and draw a detailed picture of each in column 1 of the table below. 3. Use available reference materials to find the name, function, and parts of each type of root that you drew in step 2 above. List the information found in column 2 of the table below, and draw arrows to the location of the part on your drawings. DRAWINGS RESEARCH

7 WATER THROUGH THE STEM Objective Students will be able to measure the amount of water that moves through a plant stem in a 24 hour period. graduated cylinder single edged razor (sharp scissors or knife) one plant stem that includes leaves and possibly a flower (celery, sunflower, bean) transparent tape modeling clay water Warn students about the risks of using a single edged razor. Questions for Students to Consider 1. What is the purpose of a plant s stem? 2. How do water and minerals get from the roots of a plant to the leaves and flower(s)? 3. What is happening when a plant wilts? 1. Brainstorm with students ideas about the purpose of a stem. Ask students why they think some plants have stems and some plants do not. This lab activity will help determine the purpose of a stem. 2. First, students should measure 50 ml of water into a 100 ml graduated cylinder. 3. Students should carefully cut the bottom portion of the stem off their plant, remove any leaves from the stem, and insert the stem into the cylinder. 4. Students should use transparent tape and then clay over the mouth of the graduated cylinder to prevent the water from evaporating. 5. Students should record the amount of water in the graduated cylinder when set-up is completed, and then place it in a sunny location or under grow lights. 6. Twenty-four hours later, students should record the amount of water in their cylinders. Ask students to record their data on the board so that the whole class can compare. Students can practice finding mean, median and mode using the class data. 7. Ask students to graph the class data for use in the following discussion. 8. Discuss the results with your students. Discuss other possible experiments that students could conduct to better understand transportation of water through stems. OR Students can research information on the structure and function of stems. Student groups can report their findings back to the class. A bar graph can display each group s data and the differences in water levels. If time is short or references are few, groups can be assigned to complete set-up 8 or the teacher can use this time to give students the information.

8 Background Information Stems provide two main functions for plants: transporting water and minerals from the roots to the flowers and leaves, and supporting and orienting the leaves to receive more sunlight. Plants without enough water may have wilting and weak stems. Follow-up Challenge students to design an experiment that will allow them to test different types of stems to investigate whether different stems transport water differently. Or, students can be challenged to design an experiment to determine what role flowers and leaves play in the transportation of water through a stem.

9 WATER THROUGH THE STEM: Student Sheet Name Date Period Questions to Consider 1. What is the purpose of a plant s stem? 2. How do water and minerals get from the roots of a plant to the leaves and flower(s)? 3. Why do some plants wilt and begin to sag? graduated cylinder single edged razor (sharp scissors or knife) one plant stem that includes leaves and possibly a flower (celery, sunflower, bean) transparent tape (or plastic wrap) modeling clay water 1. Measure 50 ml of water into a 100 ml graduated cylinder. 2. Carefully cut the bottom portion of the stem of your plant off, remove any leaves that may go into the cylinder, and insert the stem into the cylinder. 3. Use transparent tape (or plastic wrap) and then clay over the mouth of the graduated cylinder to prevent evaporation of water. (Put the tape down first.) 4. Record the amount of water in the graduated cylinder when setup is completed and then place the set up in a sunny location or under grow lights. 5. After 24 hours, record the amount of water in the cylinder in the data table and on the board for your classmates to see. 6. Graph the class data for use in a class discussion. (One way to graph the information is to make a bar graph with changes in water levels for each group in the class.) Data: Water level before Water level after Difference in water levels

10 TRANSPIRING PLANTS Objective Students will be able to compare a plant s transpiration rate to its leaf size. centimeter graph paper sandwich bags bread ties pipet several outdoor plants with leaves Questions for the Students to Consider 1. Why would it be necessary for plants to transpire? 2. What is the relationship between leave size and the amount of water transpired? 3. How have cacti or other environmentally unique plants adapted to living in their environments? 1. Brainstorm with students what happens to water once it s absorbed by a plant s roots. Ask students if they think plants sweat. (It may be appropriate to discuss the purpose of sweating.) Discuss how you could test to see if plants sweat, releasing water to the atmosphere. Direct their discussion to the procedure that follows. 2. Students should select native and non-native plants at home or at school to test. Leaving the plants still planted, ask students to place a sandwich bag over a leaf or group of leaves and secure the bag with a twist tie. You may want to test some plants that are in direct sunlight and others that are not. Note: The bag should be positioned so that any water collected will not run out of the bag. 3. Allow the bags to sit for 24 to 48 hours. If possible, students should do one native, one non-native plant, or one broad leaf and one narrow leaf plant. Students can also put a bag on a cactus spine if one is available. 4. Students should carefully remove the bags, making sure not to spill any of the water that may have been collected. 5. Students should also remove the leaf or leaves that were in the bag and take them back to the classroom for measuring. 6. Students should remove water from the bag using a pipet. All drops of water in the bag should be counted. If water cannot be collected, students can estimate how much water is in the bag by weighing the bag and water, and then weighing the dry bag. The difference will be the mass of the water (1 gram of water equals 1 cubic centimeter, or milliliter, of water). 7. Ask students to use centimeter graph paper to estimate the surface area of the leaf or leaves by tracing the leaf or leaves onto the graph paper and counting the number of squares covered. Partial squares can be combined to make complete squares until all squares and fractions of squares are counted. Students can estimate the amount of water in each drop by measuring the amount of water in 10 to 20 drops and dividing by the number of drops. 8. Encourage students to compare the amount of water collected to the surface

11 area of the leaf or leaves. Classroom data should be displayed on the board for the whole class to see. Ask students to graph leaf surface area verses amount of water transpired. Background Information Transpiration is the process by which water vapor escapes from a living plant, primarily through its leaves, to keep the plant cool. All plants store water that they release when the temperature surrounding the plant increases enough. Certain plants transpire more water than do others. Plants with larger leaves tend to transpire more than do plants with smaller leaves or cactus. Follow-up Student discussion should center on the class results of the activity. Students can be asked to write a brief conclusion for the results, before or after the discussion takes place. Amount of Water (ml) Surface Area (cm2)

12 MAKING LEAF SURFACE OBSERVATIONS Objective Students will be able to describe the texture and structure of the surface of a leaf. microscope slides clear glossy enamel nail polish transparent (clear) packing tape compound microscope Questions for Students to Consider 1. What does the surface of a leaf look like? 2. What specialized structures might be found on the surface of a leaf that are integral to the leaf s function? 3. What would be different about the surfaces of leaves from different types of plants? Note: This procedure for making a leaf impression can be done after the leaf has been removed from the plant or you may choose to keep the leaf on the plant. 1. Brainstorm with students what they think they will find on the surface of the leaf. (This should be done prior to students looking at or discussing leaf structure, so as not to give away any answers.) 2. Ask students to paint a one square centimeter section on the top of a leaf with clear enamel nail polish. Wait 4-5 minutes or until the nail polish has dried thoroughly. 3. Students should then cut a piece of packing tape to fit on a microscope slide. 4. Ask students to place the tape over the polished area of the leaf. Press lightly to make good contact with the nail polish. 5. Students should then peel the tape off the leaf, removing the nail polish impression with it. Small leaves are found on many herbaceous plants such as Arabidopsis. If small leaves are used, it may be necessary to remove the leaf from the tape in order to get a good impression. 6. Ask students to tape the impression onto the microscope slide, pressing firmly to avoid trapping air bubbles. 7. Students can now view the impression under a compound microscope. 8. Challenge students to draw a detailed picture of what they view under the microscope. 9. Ask students to share what they see and whether they have ideas about what the structures they observe do. Discuss their ideas, encouraging students to present their drawings to the class. 10. Using available reference materials, challenge students to find the names and functions of each of the leaf parts they observed. If time is short or references are few, groups can complete step 10 or the teacher can use this time to give students the information.

13 Background Information The surface of a leaf can reveal much about the functions and adaptations of a plant. For example, using this imprinting technique, students can observe structures on the leaf, called stomata, that serve to release water during photosynthesis and respiration. Follow-up Challenge students to think about the leaves of other types of plants not used in this activity. How might the structures on those leaves differ? Encourage students to make impressions of the top vs. the bottom of a leaf, or a leaf from a desert plant vs. a crop plant (e.g. lettuce, spinach, etc.). Ask students to make predictions about what they will find and then compare their new observations with the observations recorded in this activity.

14 Name Date Period SURFACE OF THE LEAF: Student Sheet Questions for Students to Consider 1. What does the surface of a leaf look like? 2. What is the function of a leaf? 3. What specialized structures might be found on the leaf s surface that might help it do its job? 4. What would be different about the surfaces of leaves from different types of plants? microscope slides clear glossy enamel nail polish transparent (clear) packing tape compound microscope 1. Select a position on a leaf for making the impression. 2. Paint a one square centimeter section of the leaf with clear enamel nail polish. Wait 4-5 minutes or until the polish has dried thoroughly. 3. Cut a piece of packing tape to fit on a microscope slide 4. Place the tape over the polished area of the leaf. Press lightly to make good contact with the polish. 5. Peel the tape off the leaf, removing the nail polish impression with it.** 6. Tape the impression onto the microscope slide, pressing firmly to avoid trapping air bubbles. 7. View the impression under a compound microscope. 8. Make a detailed drawing of what you observe. 9. Using available reference materials, find the names and functions of each of the parts of the leaf you observed. Label your drawing as best as you can. ** NOTE: On a small leaf such as Arabidopsis, it may be necessary to peel the leaf off the tape in order to get a good impression.

15 WHAT S IN A FLOWER Objective Students will be able to examine the structures and functions of a flower following a flower dissection. blank sheet of paper folded into thirds to make three columns or a copy of the student sheet glue or tape forceps magnifying lens flower (a complete flower if possible with both pistils and stamen). Questions for Students to Consider 1. What is the purpose of a flower? 2. Why do we only see flowers at specific times of the year? 3. Why do flowers have different colors and shapes? 1. Ask students to use column one to make a list of the parts of the flower that they expect to find and any ideas about their functions. Ask students to include a description of what they think the purpose of a flower is. 2. Using a magnifying lens, students should carefully observe their flower. Ask students to draw a detailed picture of the whole flower at the bottom of column one. Each part should be numbered for later reference. 3. Using forceps and a magnifying lens, students should carefully pull off parts of their flower following the numerical order used in Step 2. In column two, students should number the parts and describe what the part looks like in as much detail as possible. If they know the name and/or function of the part, they should include that information as well. 4. After describing the part, a corresponding number should be written in column three and the part should be glued or taped down next to the number until one of each of the parts of the flower is represented. 5. Using available reference materials, encourage students to find the name and function of each of the flower parts. Ask students to record this information in column three next to the corresponding number and flower part. Background Information Flowers are the reproductive structures of flowering plants. Complete flowers contain both pistils and a stigma (the pistil is the female reproductive organ containing the ovary, the stigma is the structure by which the pollen accesses the ovary) and stamen (male reproductive organ that produces pollen), meaning this flower is both male and female. In contrast, incomplete flowers only contain one or the other. Arabidopsis has complete flowers and can even selfpollinate, which not all complete flowers can. Both types of flowers contain petals and sepals that support and protect the fertile reproductive structures and help attract pollinators. Numbers from column two should correspond to numbers on the flower diagram and to numbers in column three. If time is short or references are few, groups can complete step 5 or the teacher can use this time to give students the information.

16 Follow-up Student discussion can focus on the questions above, or students can be asked to examine different types of flowers. What are the risks or benefits of a flower being complete or incomplete? What special adaptations or characteristics of a flower make it attractive to pollinators? What can act as a pollinator? Would certain pollinators be attracted to certain types of flowers?