In the Footsteps of Dr. Livingstone

Sample Discovery Activity: Blades of Life

Lesson Introduction
Different regions of the world have different soils and different plant life. The development of soil is influenced by temperature, rainfall, the plant life which decays and adds richness to the soil, and the organisms which live in the soil. Under a forest of deciduous trees, for example, the soil is rich in humus from the decaying leaves in autumn and is well mixed by the great number of creatures living on the forest floor. Coniferous trees drop their spiny leaves or needles all year around and tend to make the soil more acidic. Few animals live in this type of soil so it never gets well mixed in a coniferous forest.

Africa has many differing conditions. Parts of the continent are fairly warm and dry, and tall grasses grow naturally in these areas. It is important that these areas be protected because they are important to the land. In this lesson, the students will grow their own grassland models, and will use these terrestrial ecosystems to see the effects of vegetation on rate of evaporation, wind erosion, and water erosion.

The expedition in the video describes how the environment has fared in the 20th century. Since Africa has been colonialized, and land is usually government-owned, native people may feel cheated out of their own land. As a result, they have less respect for the land. It is often burned to save time.

Objectives
The students will:
1. make a model of a grassland ecosystem.
2. conduct an experiment with a control condition.

Time Allotment
This lesson can be completed in two 40-minute sessions, with a period of two weeks for growing grass in between: use one session to build the grassland model and introduce the experiment; take time to water the grass and make some observations during the two week growing period; use a second session for investigating erosion.

Materials
two-liter bottles
rulers
sharp knife
rocks and gravel
mixed plaster of Paris and eggshells
garden soil
rich humus or peat moss
grass seed
spray bottles
water
fan
sunny spot in the classroom

Procedure
Tap Prior Knowledge
1. Ask the students what is a habitat? Can you name some habitats? What makes them different from each other?

Share with Neighbor
2. In small groups, have the students come up with a description of a grassland.

Engage Students in a Hands-on Activity
3. Make a model of a grassland. Distribute materials to each group, including two 2-liter bottles. Tell them to cut the bottle exactly 6 inches high, then build the following layers right up to the top of the bottle edge:

first layer = 1" of rocks and gravel to simulate bedrock
second layer = 1" of plaster of Paris/eggshells to simulate mixed clay and calcium carbonate and weathered rock
third layer = 2" of garden soils (not store-bought) with organic materials to
simulate subsoil
fourth layer = 2" of rich humus soil filled with organic material or peat moss to
simulate topsoil

4. Find a place in the room which would simulate an African grassland environment. Ask students what the place would need to have? Plenty of direct sunlight, at least.

5. After making two bottles as model grasslands, have students sprinkle grass seed on one, but leave the other without grass. This second model is the control. Introduce the idea of control to the students. When scientists are doing experiments they change one variable to see its effects.

6. Spray the models with six sprays of water three times per day until the grass sprouts and the height of the grass reaches 1 inch. This will take about two weeks.

7. Spray both with water three times a day measuring the moisture with a toothpick at the beginning and end of class. Does the grass slow down evaporation of water?

8. Simulate wind erosion by continuing to spray as usual, but add the fan to represent the wind over the plants. Check at the beginning and end of the class period. Does the wind erode the soil in one container more than in another?

9. Simulate torrential rain by pouring one cup of water or spraying water directly and forcefully on the models and measuring the amount of soil runoff. Does heavy rain affect one model more than another?

Proposing Explanations and Solutions: Introduce the Scientific Concept
10. How might these factors represent what happens in Africa in the grasslands? Plants allow the soil to stay in place when heavy winds or rains would otherwise erode it. The destruction of forests in Africa is a major concern because it allows soil to erode more quickly.

Connect to Other Everyday Examples
11. Different plants are adapted to different soils. Plants that make their homes in dry soils have small narrow leaves to prevent too much water loss from evaporation. Those in damp soils usually have large leaves to help them lose excess water. The part of a plant which is under the ground is often as big as the part of the plant we can see. Prairie plants have deep root systems which allow them to survive in dry conditions and survive prairie fires.

Home Activity/Parent Involvement
Just as the African people who do not respect the land because they do not own it (the government usually does), people living in apartments here in Chicago may not respect the property as much as they would their own houses. Encourage students to discuss this with their family members and get a variety of opinions. Allow them some time to share what they have learned in class, and engage in thoughtful discussion with their peers.

Lesson Assessment
Take photographs of the grassland models for the students' portfolios. Also, have each student write a paragraph summarizing the groups' findings. Each entry should include a description of rain amounts, and erosion by wind and water.

Books to Read
Squandering Eden: Africa at the Edge, by Mort Roseblum and Doug Williamson, New York: Harcourt Brace Jovanovich Publishers, 1987

Taking Action/Additional Activities
Encourage the students to investigate their models further by using a little vinegar with the water in their spray bottles and seeing the effect of acid rain on the grassland. Make a solution of water and vinegar and test with a pH indicator. How acidic is it? The pH scale is used to measure how acidic or alkaline (basic) a substance is. Distilled water will have a pH of 7. An acid will have a pH of less than 7, with the lower the number, the more acidic the substance. An alkali will have a pH of higher than 7.

Choose two models with grass. Assign one of them to be the control model. Spray the experimental condition of the grassland model with the acid solution and the control with the regular water and note what happens. Does the acid rain have an effect on the grasses? Allow students an opportunity to find out more about acid rain and its effects at the library or on Internet.

The Harris Loan Program has a Prairie Discovery Unit. Contact the Field Museum of Natural History, Harris Educational Loan Center, Department Of Education, Roosevelt Road at Lake Shore Drive, Chicago, IL 60605-2497, FAX 312.427.7269, Phone 312.322.8853.

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