PLANT ADAPTATIONS - TRANSPIRATION

Transcription

1 WHAT AM I EXECTED TO LEARN? PLANT ADAPTATIONS - TRANSPIRATION Explain what stomata are, why leaves have them, and what is the cost to the plant of having them. Identify the stoma and guard cells on the underside of a leaf. Describe the relationship between habitat type and leaf size and transpirational water loss. VOCABULARY cuticle stoma/stomata guard cells transpiration BACKGROUND READING The earliest multicellular photosynthetic organisms lived in aquatic environments and acquired water and nutrients directly from their surroundings. 1. Think about a piece of seaweed washed up on shore. What happens to it after a while? In order to successfully make the transition to life on land, plants required features to help obtain and retain water. Terrestrial (land dwelling) plants are covered by a waxy coating called a cuticle that helps keep water in the leaves and stems. Plants need carbon dioxide for photosynthesis and it cannot pass through the waxy cuticle, so plants have pores called stoma to allow CO 2 to enter the leaves. However, water escapes through the stomata when they are open. It might seem that not much water escapes through these tiny openings, but, in fact, over 90% of the water that enters through the roots is lost from the plant body through the stomata. Hence, plants close the stomata under conditions of low moisture to reduce evaporative water loss. The stomata are surrounded by two guard cells that open when water is plentiful and close when water is scarce. PLANT ADAPTATIONS 1

2 ACTIVITIES Work in groups of 2. You have been provided with a purple Tradescantia zebrina plant. Cut a small piece of leaf and place it on a microscope slide striped side facing down. Observe it under a microscope. Look for the stomata and guard cells. The surrounding cells are epidermal cells and there may be long hair-like epidermal cells as well. Many plants have their stomata only on the lower surface of their leaves. 2. Why would it be a disadvantage to have stomata on the surface? 3. Diagram what the lower surface of the leaf looks like. Label the epidermis, guard cells and stomata. Color the guard cells green. Diagram of the lower surface of a leaf PLANT ADAPTATIONS 2

3 BACKGROUND READING Transpiration is the term used to describe the evaporation of water from plants through the stomata on the leaves. Transpiration pulls up water from the roots for photosynthesis and also minerals needed for various cellular components. The evaporation of water from the leaf s surface also helps cool the leaf. However, plants can lose too much water that they cannot readily replace. Over a single growing season an acre of corn may transpire nearly half a million gallons of water! As a result, plants in dry climates such as ours have adaptations to reduce transpirational water loss. 4. During this lab exercise you will measure transpiration rates in different size leaves. In general, the larger the leaf, the more carbon dioxide it needs and, thus, the more stomata it has. Write a hypothesis that predicts the relationship between leaf size and rate of transpirational water loss: ACTIVITIES Work in groups of 4. At the left is an illustration of a simple potometer a piece of equipment that is used to measure transpiration rate in plants. Your potometer will be set up for you. Fill it to the top line ( 0 ) with distilled water using a dropper, then stand it up in the beaker for 20 minutes. After 20minutes, record how much water has been taken up. Each number represents 1ml. 5. Record your observations in the table below and on the board for other members of the class to copy. TABLE 1 LEAF SIZE small water transpired (ml/20 min) AVERAGE water transpired (ml/20 min) small leaves 2 small 3 4 small large large leaves 5 large 6 large PLANT ADAPTATIONS 3

4 6. What did your results indicate about the relationship between leaf size and transpiration rate? 7. Do you think a plant with large leaves could survive in a habitat with little moisture? Explain your answer. 8. Write a hypothesis that predicts the relationship between availability of water in the plant s habitat and leaf size: 9. Examine the leaves from various local environments and complete the table below. HABITAT NAME OF PLANT LEAF SIZE (very small -> very large) desert AVAILABILITY OF WATER (very low -> very high) dry shrublands stream bank 10. Assuming these plants are typical of their habitats, do you think there is evidence to support your hypothesis? PLANT ADAPTATIONS 4

5 SHRUBLANDS FIELD TRIP WHAT AM I EXECTED TO LEARN? Be able to answer all the questions below, explain all the vocabulary terms, and identify any and all organisms observed on the field trip. VOCABULARY Mediterranean climate shrublands chaparral coastal sage scrub scrub oak red bush monkey flower black sage California sagebrush riparian community galls dusky-footed woodrat lichen symbiosis mutualism BACKGROUND READING Tecolote Canyon Natural Park & Nature covers a fairly large area. Long ago, Kumeyaay Indians found food and shelter there and until the 1950s it was used for farming and ranching. In 1978, the City of San Diego acquired the land and made it into a park. It now has a nature center and has roughly 6.5 miles of trails for jogging, walking and mountain biking. San Diego has a Mediterranean climate characterized by moderate temperatures and very little rain. The rain we do get comes in the winter months and our summers are very dry. The amount of rainfall also varies a lot from year to year, making this a challenging place for many plants. Contrary to the popular image of beaches and palm trees, Southern California is really about shrublands, such the ones in this canyon. The plants that do prosper in shrublands have many fascinating adaptations to the dry climate and the special challenges it brings. On this walk, you will see a variety of shrubland types. Many animals also live in shrublands, but some of them are at risk of going extinct because so many shrublands have been lost to development. You will also see a quite different biological community, a very wet system found along the banks of rivers and streams and known as a riparian community. Riparian communities are rare in the arid southwest and provide crucial wildlife habitat. As you enter the canyon, you will see lots of scrub oak with its tiny flowers. Most plants have large flowers to attract insects that carry their pollen, but the pollen of the scrub oak is carried by wind and so the flowers do not need to be big at all. Look for the caps of the acorns. Be sure to learn to recognize poison oak: Leaves of three, let it be. It can give you terrible itchy rashes that last for two weeks. Wash well with lots of soap and launder your clothing if you come in contact with poison oak. Use cool, not warm, water so as not to spread the oils. Head down the slope and stop to admire the many wildflowers: PLANT ADAPTATIONS 5

6 ! Red bush monkey flower hummingbirds love to visit this flower for its nectar; the flower has no scent because most birds cannot smell, but they like bright colors! Black sage with its little balls of flowers all stacked up and California sagebrush crush a leaf between your fingers and notice the fragrance. The scents come from oils that help keep insects from eating the leaves, but they also make these plants highly flammable! The Kumeyaay used the leaves of black sage to season food and it is related to the sage we often use in our thanksgiving stuffing. As you near the stream, notice the different plants willows and other water-loving plants grow here. This is a riparian community. There s lots of algae in the water because of the pollution. Some of the willows have small bumps on their leaves. These are caused by insect galls. Willows were very important to the Kumeyaay who used them to construct their homes, make bows and arrows, and as a medicine to relive pain. Willows have the same pain-relieving substances found in aspirin. Because there are few riparian areas left, many of the plants and animals that live in them are at risk of extinction. Woodrats of several species are found throughout California and Baja California. The dusky-footed woodrat is found statewide in most of California and in the northwestern region of the Baja California peninsula. Wood rats are generally nocturnal. They frequently carry small items in their mouths, including typical campsite trash, and much of this is added to their houses. A nest, often the result of work by several generations of wood rats, is usually occupied by a female and her young. The diet of the dusky-footed Wood rat is mostly green vegetation, but also includes fruit, nuts, seeds, and subterranean fungi. This animal often stores materials in chambers inside its nest and, hence, is also known as a packrat. These cache chambers often provide homes for various frogs, small mammals, and invertebrates. Predators of wood rats include owls, coyotes, weasels, skunks, house cats, and bobcats. Your instructor will point out lichens. These are symbiotic unions between algae (or photosynthetic bacteria) and fungi. The fungus provides protection against drying to the aquatic photosynthesizer and the latter provides the food for itself and the fungus, allowing them to live in otherwise unoccupied habitats such as on branches and bare rocks. A symbiosis in which both organisms benefit is called a mutualism. BIRDS YOU MIGHT SEE western scrub jay California towhee PLANT ADAPTATIONS 6