Leaves                                                  4th Grade

 

GOAL

  1. To review this plant part (anatomy) and its function for the plant.
  2. To teach the students to appreciate this plant part, and how this plant part affects their daily lives.
  3. To teach the nutritional value of leaves.

 

BEFORE CLASS

Read all the information and decide how you are going to approach this lesson and what you need to bring.

 

IN THE STATION KIT

A notebook of information, a book on leaves, and nutrition cards from the California Nutrition Education and Training Program, from the Department of Education.

 

MATERIALS TO BRING AND/OR BUY (save receipts)

Bring in different samples of leaves.  You will need some edible samples. The samples can be all edible or you can bring samples of ones that are not edible and not edible to show the difference.  See samples of both edible and non-edible below and use the enclosed California Nutrition Education cards.  They are extremely helpful in choosing edible samples.

 

EXPLANATION OF PROJECT

*FIRST ASK THE TEACHER IF ANY STUDENT IS ALLERGIC TO ANY OF YOUR SAMPLES. THEN IN EVERY GROUP KEEP ASKING THE CHILDREN IF THEY ARE ALLERGIC TO ANY OF THESE ITEMS.  NEVER FORCE ANYONE TO TASTE ANYTHING. ENCOURAGE THEM TO TRY BUT NEVER FORCE THEM.

 

NEVER USE PEANUTS. PEANUT BUTTER, OR DRESSING WITH PEANUT OIL.  COME CHILDREN CAN DIE FROM EATING EVEN SMALL AMOUNTS OF PEANUTS OR PEANUT PRODUCTS.

 

Use common sense and your ability to ask for information:

  1. Do not bring in poisonous plants. If you have a question about a plant, call a nursery or call your lead, or leave the plant at home.
  2. No tasting of non-edible plants.

 

This is a very fun station even though there are a lot of precautions above.  Now that you have taken all of the precautions, have a great time with the kids.  They really do love this station.

 

Begin by having the students wash their hands.

 

Then show the children a leaf. Ask them; what part of the plant is it? After they tell you ask them why a plant has a leaf.  Let them tell you or you tell them (see info below under “Basic Function of Leaves” and in the book provided.)  Start a conversation about how (or do) leaves affect their everyday life.  Could they live without leaves? What products come from leaves? What it s the nutritive value of leaves?

 

(A GENERAL ANSWER: Without this plant part, the plant would not be able to grow or produce another plant. This would affect humans (and other animals and insects) because we need the oxygen and depend on products plants produce. Your clothes and what you eat and drink (except maybe some rocks and water) or use has a plant involved at some point.  (There are many answers to these questions. Think about it yourself and the kids will come up with a lot of answers.) )

 

Describe the anatomy of the leaf. 

 

Proceed by bringing out your leaves samples. HINT: Once you start bringing more things out, the children will have a hard time listening to information.  This is fine! Make sure you have given instructions, had conversations, or shared information before your bring out hands-on items.

 

Have the children look at several types of leaves with a magnifying glass and identify the individual parts.  Dissect a leaf and show the individual parts. You can also have the kids look at vein pattern by choosing a leaf, placing tissue paper over the bottom of it and rub a pencil (or crayon) over it.

 

Explore the shape, smell and taste of the edible leaves.

 

WHAT TO BRING

Below are some samples for what to bring. For edible samples try to bring roots and stems that they might not have tried yet.  You can bring in pre-cut samples, plus one sample of the whole plant part, OR you can bring in a cutting board and one knife that you will handle to show them a whole plant and how it is cut.

 

DO NOT USE PEANUTS OR PEANUT BUTTER.  THERE ARE CHILDREN THAT ARE DEATHLY ALLERGIC TO PEANUTS.

 

EDIBLE LEAVES: All types of lettuce (bitter to sweet), cilantro, shard, spinach, beet tops.

NON-EDIBLE LEAVES: Tree leaves, pine needles, grass, ferns or any household plants that might exhibit the different types of leaves.

NUTRITIONAL VALUE: Most leaves are high in vitamins and minerals.  They also help your digestion.  For specific nutritional values see the enclosed nutrition cards developed by the California Nutrition Education and Training Program, from the Department of Education.

 

In addition to being a source of food, leaves provide many useful products. For example, the leaves of tea plants are made into a beverage, and the leaves of thyme, sage, and parsley are used for seasoning foods. Tobacco leaves may be smoked or chewed. Drugs are obtained from the leaves of foxglove, witch hazel, senna, and many other plants. Oils extracted from the leaves of geranium and citronella plants are used in manufacturing perfumes and soaps, and oils from mint and wintergreen leaves are made into flavoring extracts. Tannins, chemical substances used in preparing leather, are derived from sumac leaves, and dyes are made from indigo and henna leaves. The leaves of many plants may be used as fertilizer.

 

BASIC FUNCTION OF LEAVES

 

The leaf is part of a plant that serves primarily as the plant's food-making organ in a process called photosynthesis. During photosynthesis the leaves use light energy and change carbon dioxide and water into sugars or food.  Oxygen is a by-product of photosynthesis.

Leaves take part in other plant functions as well, including transpiration and guttation, both of which remove excess water from the plant, and respiration, the process by which a plant obtains oxygen and energy. Leaves also may store food and water and provide structural support.

Transpiration, evaporation of water particles from plant surfaces, especially from the surface openings, or stomata, on leaves. Stomatal transpiration accounts for most of the water loss by a plant, but some direct evaporation also takes place through the surfaces of the epidermal cells of the leaves.

Guttation is the process by which a plant loses liquid water.  Guttation takes place only when the roots rapidly absorb water, such as after a heavy rainfall, and when transpiration slows down, as on cool, humid nights. When these conditions occur together, droplets of water can be seen on the leaf early in the morning before they evaporate in the heat of the day. Unlike dew, which condenses on leaves from water vapor in the air and covers the entire leaf surface, guttation droplets form only on the edges and tips of leaves. Generally, the droplets are noticeable only on the leaves of strawberries and a few other kinds of plants.

 

BASIC LEAF ANATOMY

Some online resources for leaves:

http://ag.arizona.edu/pubs/garden/mg/botany/leaves.html#leaves

http://www.orst.edu/extension/mg/botany/leaves.html

Leaves are vital to life, as we know it.  Every leaf is a small factory. It uses air, water and sunlight to make food for the plant.  Without this food, no plant could live. Animals that eat plants would starve, and without plants and animals human beings would not live for long.

Three main leaf parts are the blade, the petiole and the stipule.

Blade:

The broad part of the leaf that holds the green food making cells is called the blade. A leaf that has only one blade is called a simple leaf. Even though the blade may have deep V’s along its edge, or some fancy outline.  Another style has a number of small blades usually lined up in two rows on each side of the petiole (stem). This called a compound leaf. The stem of a compound leaf is called the midrib.  Leaves of garden peas, locust, and ailanthus are examples. Some types have leaflets that spread out like a fan. Virginia creeper vine and horse chestnut are two.

Simple   Palmate Compound

A leaf must have lots of water to make food and keep sap moving through the growing plant. All this water comes from the earth and is collected by the roots. A leaf needs pipe lines to carry sap and water. The under surface of a leaf blade shows the veins. These are the branches of the plants pipeline. The main vein in a simple leaf may from a large easily seen midrib the length of the leaf. The veins continue to branch out till they are so small you cannot see them.  Leaves make food only in daylight, but water flows all the time. Veins also support the leaf and keep it from collapsing.  Veins running throughout the leaf have one of three patterns: Plamate-several large veins that spread from the base of the leaf, Pinnate-one main vein with smaller veins branching and parallel-all veins running from top to bottom.

Palmate Pinnate Parallel

Petiole

The petiole is a stalk like structure that supports the leaf blade on the stem. It also serves as a passageway between the stem and the blade for water and nutrients. It is made of tiny pipelines held together like a handful of straws. Another function of the petiole is to move the leaf into the best position for receiving sunlight. Petioles grow to different lengths.  It becomes extra long where it has to hold its leaf blade out farther to reach the sunlight. It might twist too, to find the sun. Because of the odd behavior, the leaves on a tree form a pattern in which few leaves are shaded by other leaves.  You can see it by standing under a tree and looking up.  The pattern is called a “leaf mosaic.” The base of the petiole is wide, has a firm grip on the twig.  The tough stem helps it withstand winds and storms.

Many plants, such as grasses and corn, do not have petioles. In these plants the base of the blade is attached directly to the stem—the base encircles the stem as a sheath. Such leaves are called sessile leaves.

Stipules

Stipules are shaped like tiny extra leaves.  They open before the blade does, and help it grow.  They add the food making power of the blade. Rose leaves have fancy stipules that look like pairs of little leaves attached to the base of each petiole.  Some have special uses. Some act as bud scales to protect winter buds and then fall early in the spring. Some vines tunes it stipules into the long wiry forms that wind around the twigs and hold them up.

The Life of Leaf

Trees are constantly making new leaves.  Even the evergreen community continuously loose old and make new leaves.  The typical leaf is born inside a bud. The bud contains a tiny leaf, or leaves, a fraction of an inch long and folded up tightly. Here, a woody plant that drops its leaves in winter has its next years buds all made by the end of summer.  They go dormant and wait for spring.  Within a few weeks after the leaf is released from its bud, the blade is fully-grown, and it actively making food.  As summer goes on, the bright green of the young leaf turns into a darker, deeper, bluer green. Then the petioles start to change. Where it joins the twig, a ring of cells grows across the petiole and blocks the veins.  Without food and water the leaf stops producing food and dies.  The fall colors happen when the chlorophyll disappears and the left over chemicals in the leaf show through. They are xanthophylls (yellow), carotene (red orange0, or anthocyanin (purple red).