HOW DO PLANTS ADAPT TO THE ABIOTIC FACTORS OF A BIOME?A LABORATORY INVESTIGATION

Purpose:

By studying vegetation from each biome, you will discover how plants adapt to the nonliving conditions around them.

You will also discuss the tropisms plants undergo, and the hormones involved, as a means of adaptation.

Introduction:

Would you expect to see a cactus growing in a northern forest? Or an oak tree growing in a desert? Absolutely not! Butwhy does a plant grow in one area and not in another? Nonliving, or abioticfactors of the environment ultimately

determine what living things will inhabit a given area. The most common abiotic factors include soil quality, sunlight,temperature, precipitation, and wind. A large geographical area with a uniform climate and a dominant form of vegetation

is called a biome. The plants that inhabit each biome are especially adapted to the abiotic factors that influence that area.You sill see how by studying plant specimens today.

Materials:

reindeer moss rubber plant big bluestem grass water plant (Elodea)conifer leaf bromeliad buffalo grass ferndeciduous leaf philodendron cactus

Pre-Lab:1. North America has 6 major land biomes. The

tundra is a very cold, dry biome that stretches across

the northernmost part of the continent. South of the

tundra is the coniferous forest, or taiga, a cold, dry

region that extends across Canada and

northern/western regions of the U.S. The Eastern

United States is identified as the temperate deciduousforest. Here, temperatures and precipitation are both

moderate. West of the temperate forests in the central

part of the U.S. is the grassland biome, where

temperatures are moderate to warm and precipitation

is light. West of the grasslands is the very dry desert.Central America, as well as the islands in theCaribbean Sea are characterized by the tropical rain

forest biome. Here, warm temperatures are constant

and precipitation is abundant. Locate each biome

described above on the map by shading in each biomeaccording to the pattern shown in the key or by usingthe numbering system provided.

1 - Tundra

2 - Taiga (Coniferous Forest)3 - Temperate Forest (Deciduous)

4 - Grassland

5 - Desert

6 - Tropical Rain Forest

,,,d

Lab Investigation:

1. Only small, hardy plants such as mosses, lichens, grasses, and dwarf shrubs are able to survive in the tamdra. Thefrigid air temperatures prevent vegetation from growing very tall and the often frozen soil prevents the extension of rootsystems. Examine a specimen of reindeer moss.

a. Examine the moss. How is its height adapted for the tundra?

b. How is the fme root-like system well adapted for the tundra?

c. Approximately how long would a dwarf shrub in the tundra be able to produce leaves and flowering parts? (refer tothe table).

2. Conifers, or cone-bearing trees, are the dominant vegetation of the coniferous forest.

a. Examine the leaves of a conifer. They are covered by a waxy outer layercalled a cuticle in addition to having thin needlelike leaves. How are theseadaptations beneficial to the climate in the coniferous forest?

b. Refer to the illustration of a typical conifer and notice itsoverall shape. How does the overall shape of a conifer tree (like a triangle)adapt the tree to the snowy, windy winters of the coniferous forest.

c. Other than coniferous trees, would you expect a variety of plant life in this region?Use the table information about

soil type in your answer.

3. The dominant plant fife of temperate, or deciduous forest, is the deciduous tree. These trees lose their leaves each fall.The long growing season of this forest gives deciduous trees enough time to grow new leaves and to produce new seeds

each year.a. Compare the size and shape of the deciduous leaf to that of a conifer leaf. Which would be able to absorb a greater

amount of sunlight? Explain your answer.

b. Comparing the deciduous and coniferous forest soil type, which would be able to support a greater amount/varietyof plant life? Explain your answer.

c. Which word would describe the climate here best (circle one)? POLAR / TEMPERATE / TROPICAL

d. Observe a fern plant. Ferns live below the branches of trees on the forest floor. How do you think they receivesunlight, or in other words, what adaptations do they have to live in a dark, damp environment?

4. A tropism is a plant movement that is determined by the direction of an environmental stimulus. Movement toward anenvironmental stimulus is called a positive tropism, and movement away from a stimulus is called a negative tropism.Each kind of tropism is named for its stimulus. Plant tropisms include gravitropism, phototropism, and thigmotropism.Each of these responses demonstrates the ability of plants to respond effectively to external stimuli, such as gravity, light,and touch.

Gravitropism is a plant growth response to gravity. A root usually grows downward and a stem usually grows upward.Gravitropism appears to be regulated by auxins. Thigmotropism is a plant growth response to touching a solid object. Aplant that is touched regularly, for example, may be stunted in its growth--sometimes quite dramatically. It is thoughtthat two hormones, an auxin and ethylene, are involved in this response. A plantmovement in response to light coming from one particular direction is called a -,ÿ'-ÿ ÿ, --ÿUÿ:.-ÿ:---=Iÿ

%phototropism. Light causes the hormone auxin to move to the shaded side of the ; ÿ-- °,,shoot. The auxin causes the cells on the shaded side to elongate more than the cells on ÿ ÿ' ,ÿ; . ,,the illuminated side. As a result, the shoot bends toward the light and exhibits positive /, ,- / "'phototropism.

a. What would happen if you accidentally planted a seed wrong side up?

b. What hormones ensure that the roots always grow downward and the stemupward?

Figure 1

c. Why might climbing plants have a survival advantage over some nonclimbing plants in a densely grown tbrest?

d. How do plants know to grow thicker in windy areas and which hormone would regulate this?

e. Which hormone would be responsible for the response of the plant shown in Figure 1?What type of tropism is this and what is causing the response?

5. The vegetation in the tropical rain forest is lush and dense and for this reason, rain forest plants compete for sunlight.a. Examine a rubber plant, a tropical tree. Study the leaves of the rubber plant. How are the broad leaves of a rubberplant adapted for the tropical rain forest?

b. Examine a bromeliad. Although bromeliads can grow in soil, ha their native habitat, bromeliads grow on thebranches of rain forest trees. Study the leaf arrangement of the bromeliad. How does it "collect" its water in atropical rain forest if it is NOT anchored in soil?

c. Vines are also commonly found in a tropical rain forest. This is another example of thigmotropism, the growth ofvines and climbing plants. The stems of these plants do not grow straight up. Rather, the growing tip of each stempoints sideways and twists in circles as the shoot grows. When the tip encounters an object, it quickly wraps around it.Thigmotropism allows some vines to climb other plants or objects. Study a philodendron's leaf pattern and aerialroots. Determine what adaptations make the philodendron a successful tropical rain forest plant. Your answer shouldinclude sunlight, hormones, and water absorption.

d. why do you find the greatest variety of plant and animal life in this biome even though the soil is mineral andnutrient poor (due to it being washed away by rain)?_

6. Desert plants are called xerophytes because they areespecially adapted to dry conditions.

a. Study the thick, fleshy stem of a cactus. With theeraser end of your pencil, touch the cactus stem andnotice how tough it is. What is this outer layercalled and what is its function?

b. Examine a cactus that has been cut in half. What is the purpose of a thick stem?

c. Study the spines and try to determine their function. What do they do?

d. Deserts are not named for their hot temperatures, but rather, which other abiotic factor?

7. Grasslands were named for their dominant form of vegetation, thegrasses. Grasses are hardy plants that can tolerate almost any conditions,including a wide temperature range, small and irregular amounts ofprecipitation, and droughts. Examine two types of grasses, big bluestem andbuffalo grass (or refer to the diagram). The eastern U.S. receives moreprecipitation than the western U.S. Which type of grass would you expectto fred in which region of the U.S.?

Eastern U.S. (circle one):Western U.S.(circle one) :

big bluestem OR buffalobig bluestem OR buffalo

Buffalo

8. Examine the water plant, found in freshwater biomes. Big Bluestem

a. Explain why the flexibility of water plants, especially the stems, serves as an adaptation to life in an aquaticenvironment.

b. Are the leaves of this plant large and broad or are they dissected and divided?What advantage would this have in a water environment?

Co The leaves of water plants often lack the waxy cuticle thatland plants have which serve to conserve water. This allowswater to move easily into and out of the leaves. Due to thisadaptation, which plant structure is NOT found in waterplants? (Hint: which structure absorbs water in landplants?)