Plant Cells

All organisms are composed of cells. Recall that plant cells have unique structures, including a central vacuole, plastids, and a cell wall that surrounds the cell membrane. These common features are found in three basic types of plant cells—parenchyma, col-lenchyma, and sclerenchyma—which are shown in Figure 29-1. Small changes in the structure of these plant cells help make different functions possible. The three types of plant cells are arranged differently in roots, stems, and leaves.

Parenchyma (puh-REN-kuh-muh) cells are usually loosely packed cube-shaped or elongated cells with a large central vacuole and thin, flexible cell walls. Parenchyma cells are involved in metabolic functions, including photosynthesis, storage of water and nutrients, and healing. These cells usually form the bulk of nonwoody plants (plants with flexible, green stems). The fleshy parts of most fruit are made up mostly of parenchyma cells.

The cell walls of collenchyma (koh-LEN-kuh-muh) cells are thicker than those of parenchyma cells. Collenchyma cell walls are also irregular in shape. The thicker walls provide support for the plant.

(a) PARENCHYMA (b) COLLENCHYMA

objectives

• Describe the three basic types of plant cells.

• Compare the three plant tissue systems.

• Describe the type of growth that occurs in each of the three main types of meristems.

• Differentiate between primary and secondary growth.

vocabulary parenchyma collenchyma sclerenchyma epidermis cuticle tracheid pit vessel element vessel sieve tube member sieve tube sieve plate companion cell meristem apical meristem lateral meristem vascular cambium cork cambium figure 29-1

Plants are composed of three basic types of cells: (a) parenchyma,

(b) collenchyma, and (c) sclerenchyma.

figure 29-1

Plants are composed of three basic types of cells: (a) parenchyma,

(b) collenchyma, and (c) sclerenchyma.

(c) SCLERENCHYMA

Collenchyma cells are usually grouped in strands. They are specialized for supporting regions of the plant that are still lengthening. Celery stalks contain a great amount of collenchyma cells.

Sclerenchyma (skluh-REN-kuh-muh) cells have thick, even, rigid cell walls. They support and strengthen the plant in areas where growth is no longer occurring. This type of cell is usually dead at maturity, providing a frame to support the plant. The hardness of the shells around nuts is due to the presence of sclerenchyma cells.

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