494 Chapter 13

13.1 Vascular Plant Structureand Function

Recall that plants can be placed into two major divisions: vascular plants andnonvascular plants. Table 1 summarizes the key features of four plant taxa.

In Chapter 10, you learned about some of the features that allowed someearly nonvascular plants to survive on land. You also learned about the specificfeatures of vascular plants that permitted them to be extremely successful andform the basis of terrestrial ecosystems. This chapter will concentrate on thebiology of vascular plants.

Photosynthesis, the process by which plants synthesize their own carbohy-drates, is the most important distinguishing feature of the plant kingdom. It isthese carbohydrates which supply both stored chemical energy and buildingblocks for cell growth and reproduction. They also provide the food for all otherorganisms through food webs. Photosynthesis is a cellular process. How do plants,like angiosperms, ensure that their green cells receive the sunlight, carbon dioxide,and water needed for photosynthesis? How do they distribute the manufacturedcarbohydrates to all their cells? How do plants store these products?

Cells of all multicellular organisms are organized into tissues, tissue systems,organs, and organ systems. These structures enable plants to successfully photo-synthesize, grow, and reproduce (Figures 1 and 2).

Table 1: Major Features of Plant Taxa

Taxon Waxy Vascular Pollen Seeds Flowerscuticle tissue grains and fruits

mosses X - - - -

ferns X X - - -

gymnosperms X X X X -

angiosperms X X X X X

Figure 1

Cells of all complex plants are organized intotissues, tissue systems, organs, and organsystems that enable the plants to carry outthe basic processes of life, such as photosyn-thesis, distribution and storage of carbohy-drates, growth, and reproduction.

meristems: regions of the plant wheresome cells retain the ability to divide repeat-edly by mitosis

apical meristems: regions at the tips ofall roots and shoots. They are responsible forthe primary growth, which lengthens shootsand roots throughout the life of the plant.

Meristems

Unlike animal cells, which have many kinds of cells that undergo division, plantcells divide by mitosis only in specific regions called meristems. The meristems atthe root tips and shoot tips are called apical meristems. In spermatophytes, rootand shoot systems begin to form in the tiny embryo within the seed. As the seed

Plants: Form and Function 495

13.1

shoot tip(terminal bud)

flower

axillary bud

young leaf

node

internode

node

vasculartissues

groundtissues

secondary roots

withered cotyledon

tertiary roots

primary root

Shoot system

Root system

seeds inside fruit

petiole

leaf

blade

epidermis

root tips with root caps

young secondary root

germinates, cells at the root and shoot tips divide by mitosis and elongate.Meristems at locations other than the root and shoot tips form complete orincomplete cylinders of tissue within roots and stems. Cell division in these cylin-ders, called the lateral meristems, causes an increase in the diameters of roots and lateral meristems: cylindrical regions in

roots and stems. They are responsible for allincreases in diameters of roots and stems.

Figure 2

The two main organ systems of plants arethe root system and the shoot system. Alsoshown are the major tissues, organs, andorgan systems of a typical angiosperm. Notethat not all plants will have all the partsshown, nor will parts with similar functionslook the same from species to species.

496 Chapter 13

stems. Cambium (plural: cambia) is another name for a lateral meristem. Celldivision within the vascular cambium produces cells which will become newxylem and phloem tissue.

Primary and Secondary Growth

Primary growth includes all growth in the length of roots and stems throughouta plant’s entire life and all growth in the diameters of roots and stems whichoccurs in the first year of a plant’s life. Secondary growth is the result of lateralmeristem activity throughout the rest of a plant’s life (Figure 3). Cells producedby meristematic tissue eventually differentiate into all other plant tissues. Thesetissues are arranged into the familiar specialized organs of the plant: roots, stems,leaves, and cones or flowers.

vascular cambium: a lateral meristemwhich is responsible for creating new xylemand phloem tissue

primary growth: all plant growth origi-nating at apical meristems resulting inincreases in length, as well as growth origi-nating at the lateral meristems in the firstyear of a plant’s life

secondary growth: plant growth origi-nating at lateral meristems which results inincreased diameters of roots and stems inthe second and all subsequent years of aplant’s life

shoot apicalmeristems(in buds)

lateralmeristems

shootsystem

root apicalmeristems

rootsystem

Vascular Plant Structure and Function

1. The cells of complex plants are organized into tissues, tissue systems,organs, and organ systems.

2. Primary growth is growth in length and occurs at apical meristems, plus atthe lateral meristems during a plant’s first year.

3. Secondary growth is growth in diameter and occurs at lateral meristems ofplants which live more than one year.

4. Cells produced by meristematic tissue differentiate into all other planttissues.

Figure 3

All seed plants have regions of primary(apical and lateral) growth in their first year.If a plant lives more than one year, it con-tinues to have primary apical growth, butafter the first year, it also has secondarygrowth, which is always lateral.