Lesson Plan

Plant Adaptations

Rough mules ear (Wyethia scabra)
Desert plants put up with tough growing conditions.

NPS photo by Neal Herbert

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Grade Level:
Fifth Grade
Subject:
Biology: Plants
Duration:
All lessons are 30 minutes.
Setting:
outdoors
National/State Standards:
Utah Science Core Curriculum Topic, Standard Five: Students will understand that traits are passed from parent organisms to their offspring, and that offspring may possess variations of these traits that may help or hinder survival in a given environment.
Keywords:
genetics, inherited traits, variation, mutation, plant keys, desert adaptations

Overview

Students explore genetics by comparing desert plant adaptations, riparian plant adaptations, and a few desert plants and animals adapted to nighttime activities. Their field activities include: rough observation and data collection, a clue trail, plant keys, a story, and a smelling game. In classroom activities, students take on the identity of a desert plant or animal, and later create an imaginary plant with adaptations for survival in its imaginary environment.

Objective(s)

PRET-TRIP ACTIVITY
What’s My Adaptation?

a. Describe or give an example of an adaptation.
b. Name two environmental characteristics to which an organism may adapt.


STATION #1
Desert Plant Mystery Tra
il
a. Name three desert plant adaptations.
b. List two factors that make life in the desert challenging for plants.


STATION #2
Are Leaves Adapted?

a. Find a desert plant, and explain its leaf adaptation.
b. Describe the steps of the scientific process.


STATION #3
The Riparian Ramble

a. Describe two environmental conditions of riparian zones that are different than those in the surrounding desert.
b. Name one riparian zone plant, and describe one of its adaptations.
c. Understand that parent and off spring have similar characteristics.

STATION #4
In the Cool of the Night

a. Name two plants that have nighttime adaptations.
b. Describe the relationship between an evening-blooming yucca and a yucca moth.

POST-TRIP ACTIVITY
Adaptation Art

(Project WILD, 1992, 114-115)
a. Name three adaptations of a plant living in either a desert or a riparian environment.

Background

Desert plants are adapted to their arid environment in many different ways. Stomata are the holes in plant leaves through which they transpire water. Many desert plants have very small stomata and fewer stomata than those of other plants. The stomata of many cacti lie deep in the plants’ tissues. This adaptation helps cacti reduce water loss by keeping the hot, dry wind from blowing directly across the stomata.

The leaves and stems of many desert plants have a thick, waxy covering. This waxy substance does not cover the stomata, but it covers most of the leaves, keeping the plants cooler and reducing evaporative loss. Small leaves on desert plants also help reduce moisture loss during transpiration. Small leaves mean less evaporative surface per leaf. In addition, a small leaf in the sun doesn’t reach as high a temperature as a large leaf in the sun.

Some plants, such as Mormon tea and cacti, carry out most or all of their photosynthesis in their green stems. (Cactus pads are stems, botanically speaking.) Some desert plants grow leaves during the rainy season and then shed them when it becomes dry again. These plants, including blackbrush, photosynthesize in their leaves during wet periods. When drought sets in and the plants lose their leaves, some of these plants can photosynthesize in their stems. Others cut down on water loss even further by temporarily shutting down photosynthesis.

Other desert adaptations shared by a number of plants include shallow widespread roots to absorb a maximum of rainfall moisture and spines or hairs to shade plants and break up
drying winds across the leaf surface.

Other specific desert plant adaptations follow:

Cacti - Cactus pads are modifi ed stems with a waxy coating. Their root system is very shallow, drinking up ephemeral rainwater. Small rain roots can grow as soon as soil is moistened by rain. They later dry up. Prickly spines are modified leaves that break up the evaporative winds blowing across pad surfaces and can help shade the stem. Cacti utilize CAM photosynthesis, in which stomata open only at night when the plant is relatively cool, so less moisture is lost through transpiration. Gases, including carbon dioxide going in and oxygen going out, pass through the stomata as well. This gas exchange is part of the process of photosynthesis. But, photosynthesis also requires sunlight. The CAM process includes a way of chemically storing the carbon dioxide until the sun comes out, when it can be used to complete the photosynthetic process. (A stoma is like a window; it has to be open to let air and water in or out, but sunlight can come in even if it’s closed.)

Desert Annuals - These avoid drought and heat by surviving as long-lived seeds stored in the soil, sometimes for decades. The seeds have adaptations assuring that they germinate and grow during wet periods.

Evening Primrose - Thickened taproots store water and food.

Globemallow - These are covered with dense, star-shaped grayish hairs that refl ect sunlight
and break up the wind.

Juniper - Leaves are reduced to tiny, waxy scales that cover the twigs and small branches. Fruits are also covered with a waxy coating. Junipers have the ability to cut off water to a major branch during a drought, resulting in a dead branch but a live tree.

Sego Lily - It can lie dormant as a bulb during the driest years.

Paintbrushes - They are partial parasites. Their roots tap into nearby plant roots, usually sagebrush or grasses, to suck food and moisture from their host.

Piñon Pines - They depend on enormous root systems. Piñon taproots stretch down 40 feet or more in deep soils; in shallow soils, lateral roots stretch outward the same distance.

Sagebrush - Hairy leaves insulate this plant against heat, cold, and dry winds. Retaining its leaves year-round allows the plant to produce food most of the year. Sagebrush has adaptations to cold winters; it can photosynthesize when temperatures are near freezing, and its leaves point in all directions, allowing them to catch sunlight from many different angles.

Some desert plants take advantage of the nights’ cooler temperatures to become “active.” Some evening-blooming plants in the desert include evening primrose, sacred datura, sand verbena and yucca. Cacti also take advantage of cooler nights. Cacti stomata are open mostly during the nighttime. Therefore, the plant can transpire, or lose water, during a time when it is likely to lose the least amount of it. The rest of the cacti photosynthesis process takes place during the daylight hours.

Desert animals also take advantage of nighttime’s cool refuge. Without light for visual cues, desert animals rely on their other senses to help them navigate. Nectar-eating bats use echolocation to identify evening blooming plants. Echolocation works similar to radar; the bat sends out a call, and then receives the waves that are reflected back. The reflection indicates the direction and distance of the reflecting object.

The yucca and the yucca moth have a fascinating nighttime association. After mating, the female moth gathers pollen from one yucca flower, packs it into a ball, and then flies into the night locating other yucca flowers primarily by “smelling” with her antenna. She visits several flowers, each time laying some eggs in the base of the pistil and packing some of the pollen from her pollen ball down the pistil for her young to feed on. Thus, she fertilizes the yucca flowers. Yucca flowers are only pollinated by yucca moths, and yucca moth young only feed on yucca pollen.

Procedure

Extensions

STATION #4
In the Cool of the Night

Have students create a rap about the relationship between yucca moths and yucca plants.

Additional Resources

Brady, I. (1998). The redrock canyon explorer. Talent, OR: Nature Works.

Braus, J. (Ed.). (1989). Discovering deserts. Ranger Rick’s NatureScope. Washington, DC: National Wildlife Federation.

Caduto, M. & Bruchac, J. (1994). Keepers of life: Discovering plants through native american stories and earth activities for children. Golden, CO: Fulcrum Publishing.

Cornell, J. B. (1979). Sharing nature with children. Nevada City, CA: Ananda Publications.

Fagan, D. (1998). Canyon country wildflowers: A field guide to common wildflowers, shrubs, and trees. Helena and Billings, MT: Falcon Publishing.

Hauth, K. B. (1996). Night life of the yucca: The story of a flower and a moth. Illus. by K. Sather. Boulder, CO: Harbinger House.

Nelson, R. A. (1976). The plants of Zion National Park. Springdale, UT: Zion Natural History Association. Project WILD: K-12 activity guide. (2nd ed). (1992). Bethesda, MD: Council for Environmental Education.

Project WILD Colorado, n.d. Riparian Habitat. Poster. Denver, CO: Colorado Division of Wildlife.

Tweit, S. J. (1992). The great southwest nature factbook. Bothell, WA: Alaska Northwest Books.

Williams, D. (2000). A naturalist’s guide to canyon country. Helena, MT: Falcon Publishing.

Last updated: November 15, 2017