Chapter 35 Plant Structure and Function

Chapter Outline
The Angiosperm Body
Plant Growth


Objectives

  1. What are angiosperms?
  2. What is the purpose of xylem? What is the purpose of phloem?
  3. What is the name given to the collective grouping of xylem and phloem in a plant?
  4. List three functions of a root.
  5. What is apical dominance?
  6. A leaf consists of two parts? What are they?
  7. What kind of tissue makes up a vein of a leaf?
  8. What is the difference between primary growth and secondary growth?
  9. What is the role of the vascular cambium of a plant?
  10. What type of tissue makes up the most of a tree trunk?
  11. Describe what accounts for the annual rings of a tree trunk.


Key Words - You should be able to define and identify the definitions of the terms listed below. They are listed in the order in which they appear in the textbook.

angiosperm phloem apical dominance vein annual rings
vascular tissue vascular bundle blade primary growth secondary xylem
xylem root hairs petiole secondary growth secondary phloem


Notes

The Angiosperm Body

Introduction

  • Angiosperms are the flowering plants.
  • Two classes: monocots and dicots. Monocots have one cotyledon, or seed leaf and dicots have two dicotyledons (seed leaves). Click on the following two links to compare the differences between monocots and dicots. There are four differences. What are they?
  • In all vascular plants , there is two types of vascular tissue for conducting substances through the plant:
    • Phloem conducts food materials, primarily dissolved sugars, throughout the plant. The food materials are the food molecules that are made by the plant through the process of photosynthesis in the leaves.
    • Xylem - Xylem conducts water from the roots up to the leaves where it is used for photosynthesis.
    • The xylem and phloem tissues are found together in all parts of a plant to form vascular bundles. These vascular bundles are visible in leaves as veins.
    • A diagram of these tissues can be seen at: Tissues
    • In this diagram, which is a cross section through a stem, you can see the vascular bundles.
  • There are two main systems in the plants – the root system and the shoot system.

 

The Root System

  • The root anchors the plant and absorbs water and minerals from the soil. Roots can also store food products (e.g., carrots).
  • Root hairs allow for the absorption of water and nutrients from the soil.
  • See root hair movie.

 

The Shoot System

Introduction

  • Shoot = stem, branches, leaves, flowers and fruit
  • Two kinds of shoots: vegetative shoots, which bear the leaves, and the floral shoots, which bear the flowers. (Flower structure will be discussed later.)
  • Vegetative shoots = stems and leaves

 

Stems

  • Consists of nodes, where the leaves are attached, and the internodes, the stem segments between the nodes. Click here to see this.
  • Stems can be herbaceous (non-woody) or woody.
  • Stem is for support and conduction.
  • Apical dominance
    • Two kinds of buds - (1) Axillary buds are found in the angle between the leaf and the stem. (2) Terminal buds are found at the end of the stem. Most growth occurs at the terminal bud.
    • The presence of a terminal bud is partially responsible for the inhibition of growth of the axillary buds. This is known as apical dominance. But the removal of the terminal bud can sometimes enhance the growth of axillary buds and thus make a plant more bushy.

 

Leaves

  • Are the primary photosynthetic organs of a plant.
  • Leaves consist of two parts - the blade and the petiole. Picture of a leaf with the petiole, node and internode are labeled.
  • The veins of a leaf are the vascular bundles, collections of xylem and phloem

 

 

Plant Growth

  • Primary Growth versus Secondary Growth - Primary growth is growth in the length of a plant whereas secondary growth refer to an growth resulting in an increase in diameter.
  • Primary Growth
    • For a picture of primary tissues in a young dicot stem with labels, click here.
  • Secondary Growth
    • There is two kinds of tissue involved in secondary growth: (1) vascular cambium, and (2) cork cambium. The vascular cambium is involved in producing secondary xylem (wood) and secondary phloem. Secondary phloem is the secondary growth tissue that conducts food that the plant makes from the leaves to the rest of the plant. The cork cambium is involved in producing the tough, thick covering of a stem and root.
    • Secondary xylem is the wood of a tree trunk. The annual rings are created by alternating bands of summer wood cells and spring wood cells. The summer wood cells are smaller in diameter, due to less available water, while the spring cells are larger in diameter due to rapid growth from more abundant water.
    • To see secondary xylem and the corresponding annual rings, click here.
    • In this diagram, you can see how the wood of a tree trunk is divided into heartwood, which is full of resin and therefore does not conduct water, and the sapwood, which is functional.