HOW DO PLANTS ADAPT TO THE ABIOTIC FACTORS OF A BIOME

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! But
why 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
conifer leaf
bromeliad
buffalo grass
deciduous 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 deciduous
forest. 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 the
Caribbean 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 biome
according to the pattern shown in the key or by using
the numbering system provided.
1 - Tundra
2 - Taiga (Coniferous Forest)
3 - Temperate Forest (Deciduous)
4 - Grassland
5 - Desert
6 - Tropical Rain Forest
water plant (Elodea)
fern
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Lab Investigation:
1. Only small, hardy plants such as mosses, lichens, grasses, and dwarf shrubs are able to survive in the tamdra. The
frigid air temperatures prevent vegetation from growing very tall and the often frozen soil prevents the extension of root
systems. 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 to
the 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 layer
called a cuticle in addition to having thin needlelike leaves. How are these
adaptations beneficial to the climate in the coniferous forest?
b. Refer to the illustration of a typical conifer and notice its
overall 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/variety
of 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 receive
sunlight, 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 an
environmental 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. A
plant that is touched regularly, for example, may be stunted in its growth--sometimes quite dramatically. It is thought
that two hormones, an auxin and ethylene, are involved in this response. A plant
movement in response to light coming from one particular direction is called a
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phototropism. Light causes the hormone auxin to move to the shaded side of the
shoot. The auxin causes the cells on the shaded side to elongate more than the cells on
the illuminated side. As a result, the shoot bends toward the light and exhibits positive
phototropism.
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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 stem
upward?
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 rubber
plant adapted for the tropical rain forest?
b. Examine a bromeliad. Although bromeliads can grow in soil, ha their native habitat, bromeliads grow on the
branches of rain forest trees. Study the leaf arrangement of the bromeliad. How does it "collect" its water in a
tropical 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 of
vines and climbing plants. The stems of these plants do not grow straight up. Rather, the growing tip of each stem
points 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 aerial
roots. Determine what adaptations make the philodendron a successful tropical rain forest plant. Your answer should
include 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 and
nutrient poor (due to it being washed away by rain)?_
6. Desert plants are called xerophytes because they are
especially adapted to dry conditions.
a. Study the thick, fleshy stem of a cactus. With the
eraser end of your pencil, touch the cactus stem and
notice how tough it is. What is this outer layer
called 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, the
grasses. Grasses are hardy plants that can tolerate almost any conditions,
including a wide temperature range, small and irregular amounts of
precipitation, and droughts. Examine two types of grasses, big bluestem and
buffalo grass (or refer to the diagram). The eastern U.S. receives more
precipitation than the western U.S. Which type of grass would you expect
to fred in which region of the U.S.?
Eastern U.S. (circle one):
Western U.S.(circle one) :
big bluestem OR buffalo
big 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 aquatic
environment.
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 that
land plants have which serve to conserve water. This allows
water to move easily into and out of the leaves. Due to this
adaptation, which plant structure is NOT found in water
plants? (Hint: which structure absorbs water in land
plants?)