Ag Education III

ColoradoAgricultural Curriculum

Grade and Class: / Agriculture III
Pathway: / Horticulture
Area: / Plant structures and their functions
Job: / Understanding the function of leaves
Situation/Rationale / Students need to understand the structure of the plants so that they can understand how a plant works. Students will learn how each plant structure functions and the key parts of identifying each part.
Colorado Ag Education Standards and Competencies / HT11/12.02
Student Learning Objectives: / Upon completion of this lesson the student will be able to:
  1. List the functions of leaves.
  2. Determine the structural components by reading a description of each component.
  3. Describe the different leaf types and modified leaves.

Time: / 90 Minutes
Resource(s): / Colorado State University HCC100 text
Instructions, Tools, Equipment, and Supplies: / Italicized words are instructions to the teacher, normal style text is suggested
script.
Energy Drink
Energy Jelly Beans
Protein Bar
Plant Leaves
Introduction / The main function of leaves is to make food and other chemicals (proteins, fats and oils) that are used by the plant for growth and reproduction. However, leaves are not the only place these materials are made. Any portion of the plant that is green (fruits and stems) may also produce these materials.
What do you think the functions of leaves are?
Interest Approach: / Congratulations!
You have all been selected as the new, up and coming marketing firm responsible for the new campaign slogans for a new protein bar and a new energy drink! I will group you into two by numbering you off and that will be your marketing partner. You have 5 minutes to develop a slogan for each of these products! Ready? Go and slogan!
After students have developed their slogans, have each of the marketing teams present their slogans to the classroom!
Have you ever wondered why these products have been on such a great consumption incline? These products are all about providing energy in quick form! When have you seen these products used the most? That’s correct! When quick energy is needed like when people are working out, exerting a lot of power in their hikes, games etc. Today, our lesson is about leaves and we are going to do Socratic Seminar to discuss how energy drinks relate to leaves. Remember the rules of Socratic seminar:
1. Do not stay confused; ask for clarification.
2. Stick to the point currently under discussion; make notes about ideas you want to come back to.
3. Don't raise hands; take turns speaking.
4. Listen carefully.
5. Speak up so that all can hear you.
6. Talk to each other, not just to the leader or teacher.
7. Discuss ideas rather than each other's opinions.
8. You are responsible for the seminar, even if you don't know it or admit it.
9. Be respectful of everyone
The entire food chain is made up of energy consumers. Every time we eat something, we take up energy. Remember that energy is never recycled – always consumed! The goal for today’s lesson is to better explore how food, and thus energy are utilized in the food chain. As we begin, you will need something to take notes on and something to take notes with – please get prepared now!
Objective 1: / Functions of leaves
To compete for light for photosynthesis, i.e., the manufacture of sugars
• Evapotranspiration from the leaves is what moves water and nutrients
up from the roots.
• Small openings on the leaf, known as stomata, regulate moisture and
gas exchange (water and carbon dioxide) and temperature (cooling
effect as water vapor escapes through stomata).
Horticultural uses
o Aesthetic qualities
o Feed and food
o Mulch and compost
o Plant identification
o Propagation from cuttings
o Summer cooling (Evaporative cooling accounts for 70-80% of
the shading impact of a tree.)
o Wildlife habitat
o Wind, dust and noise reduction
Objective 2: / Structure of leaves
Internal Features
The leaf blade is composed of several layers as follows:
Epidermis – outer layer of tissues
Cuticle – waxy protective outer layer of epidermis that prevents
water loss on leaves, green stems, and fruits. The amount of
cutin or wax increases with light intensity.
Leaf hairs – part of the epidermis.
Palisade layer – a tightly packed layer of parenchyma tissues filled with
chloroplasts for photosynthesis.
Chloroplasts – sub-cellular, photosynthetic structures in leaves and
other green tissues. Chloroplasts contain chlorophyll, a
green plant pigment that captures the energy in light and
begins the transformation of that energy into sugars.
Vascular bundle – xylem and phloem tissues, commonly known as leaf
veins.
Spongy mesophyll – layer of parenchyma tissues loosely arranged to
facilitate movement of oxygen, carbon dioxide, and water vapor. It
also may contain some chloroplasts.
Stomata – natural openings in leaves and herbaceous stems that allow for
gas exchange (water vapor, carbon dioxide, and oxygen).
Guard cells – specialized kidney-shaped cells that open and close
the stomata.
External Features
Leaf blade – flattened part of the leaf
Petiole – leaf stalk
Stipules – leaf-like appendages at the base of the leaf.
Objective 3: / Leaf Arrangement on stems
Alternate – arranged in staggered fashion along stem (willow)
Opposite – pair of leaves arranged across from each other on stem (maple)
Whorled – arranged in a ring (catalpa)
Rosette – spiral cluster of leaves arranged at the base (or crown)
(dandelion)
Leaflet Arrangement on Petiole
Simple – leaf blade is one continuous unit (cherry, maple, and elm)
Compound – several leaflets arise from the same petiole
Pinnately compound –leaflets arranged on both sides of a common
rachis (leaf stalk), like a feather (mountain ash)
Palmately compound – leaflets radiate from one central point
(Ohio buckeye and horse chestnut)
Double pinnately compound – double set of compound leaflets
Note: Sometimes identifying a "leaf" or "leaflet" can be confusing. Look at
the petiole attachment. A leaf petiole attaches to the stem at a bud node.
There is no bud node where leaflets attach to the petiole.
Overall Leaf Shape
Leaf shape is a primary tool in plant identification. Descriptions often go
into minute detail about general leaf shape, and the shape of the leaf apex
and base. The following are common shapes as used.
Shape of Leaf Apex and Base
Shape of the leaf apex (tip) and base is another tool in plant identification.
Leaf Margin
The leaf margin is another tool in plant identification.
Leaf Types / Leaf Venation
Conifer types
Scale-like – mature leaves common on most junipers and arborvitae
Awl-shaped – juvenile leaves common on some junipers
Linear-shaped – narrow flat needles of spruce, fir, and yews
Needle-like – in pine, the single, bundle, or cluster of needles makes
a rounded shape
Ginkgo type
Dichotomous venation – somewhat
parallel vein sections, forming a 'Y', found
in Ginkgo trees.
Monocot types
Parallel venation – veins run in parallel lines. (monocot plants, e.g.
grasses, lilies, tulips).
Dicot types
Net-veined or reticulate-veined – leaves with veins that branch
from the main rib and then subdivide into finer veinlets.
(dicot plants)
Pinnate venation – veins extend from a midrib to the edge
(elm, peach, apple, cherry).
Palmate venation – veins radiate fan-shaped from the
petiole (maple, grapes).
Modified Leaves
Adhesive disc – modified leaf used for attachment mechanism. Sometimes
referred to as a holdfast. (Boston ivy)
Bract – specialized, often highly colored leaf below
flower that often serves to lure pollinators.
(Poinsettia, dogwood)
Spine or thorn – modified leaf. (barberry,
pyracantha)
Tendril – modified sinuous leaf used for climbing or
as an attachment mechanism. (Virginia
creeper, peas, grapes)
Review/Summary: / There is a lot of content in this lesson, so to ensure that students have time to review all of itif they are going to use the Motion Moment. This allows them to come up with hand motions that reflect parts of the lesson. Choose 5-10 terms from the lesson, and write them on the board, and students will come up with movements that illustrate them.
Now that we know all about the leaves of a plant, I have a question for you. Can you come up with a simple hand motion that illustrates the key terms that I have put on the board? You may work with the same partner to “figure it out.” I will have you group together into three by drawing cards from my deck and all hearts group together, all diamonds group together, all spades group together and lastly all clubs. You only have 5 minutes to come up with movements.
Give students five minutes. Then using spinners or randomly picking students they are going to give their hand motion for one of the terms as the class guesses which term it is. You will have to whisper to the volunteer what term you want them to do.
Time. Now if I call your group up, you will demonstrate the term that I give you using the hand motions that you created. The rest of you will guess what term they are demonstrating for you.
Application--Extended Classroom Activity: /
  • Have students label a grass plant, from roots to the parts of the leaves. Include this diagram in their notebooks.
  • If resources allow, bring in a number of plant leaves to categorize and identify.
  • Teach a lesson in taxonomy classification and scientific keys to encourage students to classify plants by type.

Application--FFA Activity: / Encourage students to participate in the Range Judging CDE, whereby then will identify plants by their leaf shape, size, and formation.
Application--SAE Activity: / Encourage students with nursery SAE’s to learn as many potted plants and trees as possible.
Evaluation: / So I can see what you learned today I want you to make a diagram of a leaf using construction paper, toothpicks, glue, markers and scissors. Make sure to label the external parts of the leaf on you diagram. The parts that should be labeled are:
  1. Petiole
  2. Leaf Blade
  3. Stipules
  4. Margin
  5. Tip
  6. Base
  7. Bud
  8. Midrib
  9. Lateral Vein

Evaluation Answer Key: /