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Week 9 - Introduction, Moving Water, Life Cycles, Structural Adaptations, and Plant Needs

Exercise 1.4

Lesson 1.4: Plant Structures Vary to Adapt to their Environment

ACTIVITY A: Structural Adaptations


Required Readings

Science in Action 7
pages 116 to 120


Science Focus 7
pages 104 to 106

All living organisms have special body features that allow them to survive in their ecosystems. These special body parts are called structural adaptations. These might include the spines on a cactus or stinger on a bee.

In this lesson we are going to look at the structural adaptations of plants. Plants want to grow to their full size, save some food, and produce as many seeds as it can. To do this it must compete with other plants in its environment and keep other organisms from eating it. Some use spines for protection; others might use poison. There is even a rain forest plant that feeds and houses ants and the ants in turn protect the plant from predators and kill other plants that might try to grow near it. As you look at the pictures of different ecosystems on this page, try to think of the adaptations that might be necessary to survive in that environment. So let's move on to the lesson and see other wonderful and interesting adaptations that plants use to survive and reproduce.



There are two basic shapes of roots, tap roots and fibrous roots. In geographical areas that receive a moderate amount of rain fall, the root systems of plants tend to be quite shallow. But in very dry (arid) areas, like deserts, roots systems can reach far below ground level. You recall that the primary purpose of roots is to draw water and nutrients from the soil. But they also have other uses.


Many plants have a single root with many, much smaller roots, coming out of it. A carrot is an excellent example of a taproot. The smaller roots and root hairs increase the surface area of the root so that it can absorb more nutrients and water from the surrounding soil.

Fibrous Roots

Fibrous roots are all similar in size and spread out in all directions in the soil. Although they tend to be rather shallow in the soil, they are able to pick up moisture very quickly. Prairie grasses have fibrous roots systems. Although the part of the plant we can see above the ground is only a few centimeters high, it may have a root system hundreds of kilometers long!


Did You Know?

A desert shrub, called mesquite has been known to produce roots up to 50 meters (164 feet) deep.

Notice that there is so little light getting through the tree canopy that smaller plants cannot grow here.

The stems of plants have two functions. First, to function as a pipeline that supplies water and food to all the cells of the plant. Second, to raise the photosynthetic parts of the plant above obstructions such, as other plants, so that it can get the maximum amount of sunlight. Plants actually compete with one another for sunlight. Those plants that can grow the fastest and tallest will win the competition, while the losers become more sickly and grow more poorly. This competition becomes very obvious in rain forest areas. When old trees die and fall over, the sunny space in the forest in leaves creates a competition among the younger plants.

A Single Trunk Design

Many trees use this strategy. They put all their energy into one trunk so that it can grow as fast as possible. Many side branches grow from this single trunk and from them even smaller branches. Large trees have been known to have so much leaf area that the leaves could cover a football field!

Multi-stemmed Plants

Smaller plants use a different strategy. They send up numerous stems. Some of these stems run along the ground. From this horizontal stem roots grow into the ground and new plants begin to grow. We call these horizontal stems runners. Some stems actually grow under ground and produce large swollen areas called corms. New plants can grow from these corms.

Stems can be Modified for Other Uses

Many desert plants have modified stems to hold water. Many species of cactus have stems that are swollen up to hold as much moisture as possible. Their stems are modified in another way - they are green. What plant process goes on in green tissue?

Photosynthesis takes place in the stem of a cactus not its leaves.


You will recall from a previous lesson that the main purpose of leaves is to produce food by photosynthesis. But if you go out and examine the leaves from different plants you will find that they look quite different from each other. Plant species have modified their leaves over thousands of years to suite their environment.


Leaf Size

If you are able, go out into a nice sunny meadow or play ground and look the shape of the leaves on the plants you find there. In general, you will find that plants that live in sunny habitats have fairly small leaves. Their small leaf size provides them with all the food they need. The sun in these habitats can be very intense and water loss through transpiration can be great as well. Small leaves minimize the amount of water lost. This can be a life saving strategy for grasses and other prairie plants who do not receive a lot of rainfall.

If you would now step into a shady forest area you would immediately feel and see that it is cooler and more shady than our meadow area. It also feels more humid as well. Low lying plants in this habitat need to use a different leaf strategy for survival. Here, water loss is not a major concern. The main concern is the lack of sunlight. These plants have larger leaves to collect more sunlight.


Conifer needles are modifies leaves.
Modified Leaves

Some species of plant have gone to great lengths to prevent water loss. Coniferous trees, like spruce and pine, have leaves that are in the shape of needles. This reduces the water loss and allows the trees to live in harsh environments where deciduous trees (those with normal leaves) cannot survive. A clear example of this can be found in the mountains. In the river valleys you will a mixture of deciduous and coniferous trees But as you look higher upon the mountain you will see only conifers.

There is another group of plants that have greatly modified leaves. Cactus plants have modified leaves into spines. This serves two purposes. No photosynthesis takes place in the spines so there is no water loss - a great advantage in a desert. So where does photosynthesis take place? Have you ever tried to touch a cactus? If you have, you will know the second reason for the spines. Food and water are hard to find in a desert, and a cactus contains both of these desirable items. If a cactus can't protect itself, it will be eaten by consumers.

Leaf Drop

One strategy we are all familiar with in Canada is leaf drop. As winter approaches, deciduous trees drop their leaves and thicken their sap. This protects the tree against the harsh winter temperatures and water loss. The thickening sap acts like antifreeze in cars. Different trees have different levels of antifreeze. Some plants can get well below -40 degrees Celcius without freezing - other can't. Freezing can be deadly to trees but freezing water expands as it freezes. This process can cause trees to literally explode.



Flowers have one main purpose- to produce seeds. If its self-fertile, or uses the wind to cross pollinate with other flowers, it doesn't need to use up energy to make flashy colorful flowers, or produce nectar that others can use for food. Conifers, like pines and spruces, have flowers of this kind. They aren't showy because they don't need to be. The wind does their work for them.


Did You Know?

Insects see different colors and patterns on flowers than we do. What may appear to us as a dull, ordinary flower actually may have runways and bright colors to attract insects
But if flowers do depend on other creatures to pollinate them, they must first attract them. They do this with color, odor and food in the form of nectar or extra pollen. Some flowers are even so specialized that only one insect, bird or mammal is attracted to them. Some flowers are designed to be traps that won't allow insects to leave until they have pollinated the flower.



Seeds are new plants waiting in storage until the right conditions or sunlight, moisture and warmth allow them to germinate. But if they try to grow beside a large parent plant they may not have enough sunlight, nutrients or water. So they need to disperse (to spread out from) their parent's location. There are a number of strategies they might use.
Many seeds use the wind to move on to new territory. Have you ever blown the seeds from a dandelion. If you did, you were helping the species move on to new territory. What kind of structural adaptation do dandelion seeds have? Maple seeds look like they have two wings on them, while the seeds of popular trees are very small and have fluff attached to them, so that the wind can carry them away.
Some plants depend on animals to disperse their seeds. In an earlier lesson we learned that plants use fruit to attract and disperse their seeds. Oak Trees supply very nutritious nuts. Animals like squirrels eat as much as they can and then they hide or bury the rest. Although a squirrel's memory is good, its not 100%, so they forget where some are buried. Not only do the seeds get moved away from their parent plant, but many are also nestled deep in the soil where they can begin to grow in the spring.
Some plants use water to help them disperse their seeds. Coconuts have been known to float to different islands before they germinate and grow into new tree.

Some seeds are designed to catch onto anything that goes by. They look like they have little Velcro hooks that fasten on to your pants or jacket and my dog looks like a seed factory after we come back from a walk. By the time we yank them off and throw them away, they are many kilometers away from where they started.