Life Cycle - Plants (1B)
Lab 

   
OBJECTIVES:
  • Exploring stems and flowers.
  • Discovering why plants have stems and flowers.

VOCABULARY:

  • flower
  • leaf
  • root
  • stem
MATERIALS:  

 

Students experiment with stems.

 


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click to enlarge

BACKGROUND:

The basic parts of flowering plants include the roots, stems, leaves, and flowers. Stems are important in water and food transportation, and provide support for the leaves, flowers and fruit. Some plants store food (potatoes) or water (cactus) in stems. Flowers are necessary for seed production, without which many species would die out.

The main parts of a flower are drawn on the right. A plant with colored petals and/or a pleasant scent is usually pollinated by insects or birds. Wind or self-pollinated plants usually have rudimentary, inconspicuous flowers. Seeds develop in the ovary, and the ovary may develop into a fruit. Flowers that we eat include broccoli, cauliflower and artichokes, although the last one is actually the flower bud.

Tree trunks are a special kind of stem, and the age of a tree can be determined by counting the rings of a tree trunk. A ring is actually the new water-conducting tissue that is made each year. Thick rings mean that the tree grew a lot in the spring and summer. Thin rings reflect bad growing conditions, like drought, or just the fact that the tree grows slowly. Concentric rings mean that the tree grew straight up, and rings that are off-center, with one side wider than the other, mean that the tree grew on a slope (look at diagram to the left). The downhill side has wider rings. Seasonal variations in conditions may cause color variations inside a ring.

There are many different kinds of stems. They may be underground or above-ground, woody or soft, stiff or flexible. Stems that we eat include asparagus and potatoes. (Potatoes are very specialized stems that help to reproduce the plant. Small semi-circular leaf scars near the eyes show that they are stems.) Brussels sprouts are stem buds.

PROCEDURE:

  1. BEFORE CLASS: Stand a celery stalk in water for an hour or so. Then put it in water with food coloring for several hours. Cut cross sections off the end to show the veins (strings), which should be colored. In class you may also partially strip a string from the stalk, and it should show color. Use this as a demonstration that water moves upward through plant tissue. Discuss that the stem of a plant is very important to move water and nutrients up to the leaves where it will work with Sun to create food for the plant.

    Discuss the purpose of stems. Show a vein that you have stripped out of the celery stalk, and mention that this is how celery plants move water. Let them examine the cross sections.
        
  2. Discuss tree rings. Tell the children that they should examine the branch cross sections with their hand lens and answer the following questions
  1. How old is the branch?
  2. Did it grow on a slope?
  3. Can you find rings that were produced during a drought?
  4. Have them count the number of rings on the worksheet branch and have them color in the ring that was growing in the year they were born. 
  1. Ask the students why flowers are important to plants (i.e., they are essential to seed production.) Mention that pollen has to land in a special place so that seeds will develop. Point out the pollen and seed area on the large flower picture. Instruct students to draw the flower before they dissect it. Let them examine the flowers with a hand lens and pull them apart. Count the petals, notice the color and shape. Have them draw a picture of their flower on the worksheet. If possible, they should indicate where the pollen comes from and where the seed grows. Ask them how they think the pollen is carried on the flower they are examining.

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