Adaptations of Desert Plants Topic The shape and surface area of a leaf are related to its ability to gain and release water. Introduction Deserts are biomes that present great difficulties to their inhabitants. With less than 7.8 inches (in.) (20 centimeters [cm]) of rain per year, desert environments are so dry that even drought-resistance species of grasses are unable to survive. Despite these harsh conditions, populations of highly adapted plants and animals make deserts their homes. Plants adaptations to dry conditions include modifications in size and shape that conserve water. In addition, some desert plants, like cacti, have evolved thorns to deter animals from grazing on them and depleting their reserves of water and nutrients. To carry out photosynthesis, plants must have access to water, nutrients, light, and carbon dioxide. Plants take in carbon dioxide through small openings in the leaves called stomata. In this experiment, you will find out how the size and shape of a leaf affects it ability to conserve water. Time Required 40 minutes on day 1 20 minutes on day 2 Materials 2 pieces of cardboard, each about 11.8 in. 2.4 in. (30 cm 6 cm each) scissors ruler Parafilm or plastic wrap
ADAPTATIONS OF DESERT PLANTS 2 Two 50-milliliter (ml) graduated cylinders masking tape or labels pen access to water light source (lamp with 60-watt bulb or access to a window) science notebook Safety Note Please review and follow the safety guidelines. Procedure: Day 1 1. Using the masking tape or label and pen, label one graduated cylinder as B. Label the other graduated cylinder as L. 2. On one piece of cardboard, draw a broad leaf and its stem with the following dimensions: a. blade length = 3.9 in. (10 cm) b. blade width = 1.6 in. (4 cm) c. stem = 1.9 in. 0.8 in. (5 cm 2 cm) 3. Use scissors to cut out the cardboard shape of the broad leaf. 4. On the second piece of cardboard, draw a narrow leaf and its stem with the following dimensions: a. blade length = 7.8 in. (20 cm) b. blade width = 0.8 in. (2 cm) c. stem = 1.9 in. 0.8 in. (5 cm 2 cm) 5. Use scissors to cut out the cardboard shape of the long, narrow leaf. 6. Fill each of the graduated cylinders with 45 ml of water. Cover and seal each graduated cylinder with Parafilm or plastic wrap. 7. Using the tip of your scissors, slice a small slit through the center of the Parafilm or plastic wrap covering each cylinder. 8. Stick the stem of the long cardboard leaf through the slit in the cylinder marked L, as shown in Figure 1.
ADAPTATIONS OF DESERT PLANTS 3 cardboard leaves Parafilm or plastic wrap water Figure 1 9. Stick the stem of the broad cardboard leaf through the slit in the cylinder marked B. 10. Place both graduated cylinder set-ups beneath the light source or in a window. 11. Record the volume of water in each graduated cylinder on the data table in the column labeled initial volume. 12. Predict which of the two cardboard leaves will lose the most water over the next 24 hours. Record your prediction in your science notebook. Procedure: Day 2 1. Observe the volume of water in each of the two graduated cylinders. Record these volumes in the data table in the column titled final volume. 2. Determine the amount of water that evaporated from each cardboard leaf using the following formula: Initial volume Final volume Amount evaporated 3. Record the amount evaporated in the last column of the data table.
ADAPTATIONS OF DESERT PLANTS 4 Data Table Initial volume Final volume Amount evaporated Long leaf Broad leaf Analysis 1. From which leaf did the most water evaporate? Why do you think this was so? 2. In this experiment, why must the graduated cylinders be covered? 3. Both of these cardboard leaves have the same surface area and the same stem size. Why do you think this is an important factor in this experiment? 4. Desert plants do not grow as tall as plants in other biomes. Offer an explanation for this fact. What s Going On? The leaves of desert plants are distinctly different from those of plants that live in moist environments. Structurally, leaves of desert plants are long and narrow and contain the majority of their stomata on the underside of the leaf blade. Although stomata act as openings through which carbon dioxide can enter leaves, they also present a problem. Water traveling up the plant from its roots eventually reaches the stems and evaporates through the stomata. If this rate of evaporation is fast, essential water supplies can be depleted before the plant has met its photosynthetic needs. Plants with elongated, thin leaves lose water at a slower rate than those with broad leaves. Want to Know More? See Our Findings.
OUR FINDINGS ADAPTATIONS OF DESERT PLANTS Suggestion for class discussion: Ask students to describe some adaptations that animals have for their environments. Point out a few plant adaptations, such as deep roots in dry climates or short statures on windy islands, then ask student to explain why a cactus is ideally suited for life in the desert. Analysis 1. The longer leaf; less area is exposed to the air. 2. To prevent evaporation of water from the graduated cylinders. 3. To maintain constant the variable of size. 4. Answers will vary. Growing taller leads to greater surface area for the plant and thus more water evaporation through stomata.
SAFETY PRECAUTIONS Review Before Starting Any Experiment Each experiment includes special safety precautions that are relevant to that particular project. These do not include all the basic safety precautions that are necessary whenever you are working on a scientific experiment. For this reason, it is absolutely necessary that you read and remain mindful of the General Safety Precautions that follow. Experimental science can be dangerous, and good laboratory procedure always includes following basic safety rules. Things can happen very quickly while you are performing an experiment. Materials can spill, break, or even catch fire. There will be no time after the fact to protect yourself. Always prepare for unexpected dangers by following the basic safety guidelines during the entire experiment, whether or not something seems dangerous to you at a given moment. We have been quite sparing in prescribing safety precautions for the individual experiments. For one reason, we want you to take very seriously every safety precaution that is printed in this book. If you see it written here, you can be sure that it is here because it is absolutely critical. Read the safety precautions here and at the beginning of each experiment before performing each lab activity. It is difficult to remember a long set of general rules. By rereading these general precautions every time you set up an experiment, you will be reminding yourself that lab safety is critically important. In addition, use your good judgment and pay close attention when performing potentially dangerous procedures. Just because the book does not say Be careful with hot liquids or Don t cut yourself with a knife does not mean that you can be careless when boiling water or using a knife to punch holes in plastic bottles. Notes in the text are special precautions to which you must pay special attention. GENERAL SAFETY PRECAUTIONS Accidents caused by carelessness, haste, insufficient knowledge, or taking an unnecessary risk can be avoided by practicing safety procedures and being alert while conducting experiments. Be sure to
SAFETY PRECAUTIONS 2 check the individual experiments in this book for additional safety regulations and adult supervision requirements. If you will be working in a lab, do not work alone. When you are working off-site, keep in groups with a minimum of three students per groups, and follow school rules and state legal requirements for the number of supervisors required. Ask an adult supervisor with basic training in first aid to carry a small first-aid kit. Make sure everyone knows where this person will be during the experiment. PREPARING Clear all surfaces before beginning experiments. Read the instructions before you start. Know the hazards of the experiments and anticipate dangers. PROTECTING YOURSELF Follow the directions step by step. Do only one experiment at a time. Locate exits, fire blanket and extinguisher, master gas and electricity shut-offs, eyewash, and first-aid kit. Make sure there is adequate ventilation. Do not horseplay. Keep floor and workspace neat, clean, and dry. Clean up spills immediately. If glassware breaks, do not clean it up; ask for teacher assistance. Tie back long hair. Never eat, drink, or smoke in the laboratory or workspace. Do not eat or drink any substances tested unless expressly permitted to do so by a knowledgeable adult. USING EQUIPMENT WITH CARE Set up apparatus far from the edge of the desk. Use knives or other sharp-pointed instruments with care.
SAFETY PRECAUTIONS 3 Pull plugs, not cords, when removing electrical plugs. Clean glassware before and after use. Clean up broken glassware immediately. Do not touch metal conductors. Check glassware for scratches, cracks, and sharp edges. Do not use reflected sunlight to illuminate your microscope. Use alcohol-filled thermometers, not mercury-filled thermometers. USING CHEMICALS Never taste or inhale chemicals. Label all bottles and apparatus containing chemicals. Read labels carefully. Avoid chemical contact with skin and eyes (wear safety glasses, lab apron, and gloves). Do not touch chemical solutions. Wash hands before and after using solutions. Wipe up spills thoroughly. HEATING SUBSTANCES Wear safety glasses, apron, and gloves when boiling water. Keep your face away from test tubes and beakers. Use test tubes, beakers, and other glassware made of Pyrex glass. Never leave apparatus unattended. Use safety tongs and heat-resistant gloves. If your laboratory does not have heat-proof workbenches, put your Bunsen burner on a heat-proof mat before lighting it. Take care when lighting your Bunsen burner; light it with the airhole closed, and use a Bunsen burner lighter in preference to wooden matches.
SAFETY PRECAUTIONS 4 Turn off hot plates, Bunsen burners, and gas when you are done. Have a fire extinguisher on hand. Keep flammable substances away from flames and other sources of heat. FINISHING UP Thoroughly clean your work area and any glassware used. Wash your hands. Be careful not to return chemicals or contaminated reagents to the wrong containers. Do not dispose of materials in the sink unless instructed to do so. Clean up all residues and put them in proper containers for disposal. Dispose of all chemicals according to all local, state, and federal laws. BE SAFETY CONSCIOUS AT ALL TIMES!