Biology (Holt)

Structures of Plant Cells

The organelles described in this section are found in both animal

cells and plant cells. However, plant cells have three additional

structures that are not found in animal cells, shown in Figure 17.

Unique Features of Plant Cells

Cell wallThe cell membrane of a plant cell is surrounded by a thick

cell wall, composed of proteins and carbohydrates, including the

polysaccharide cellulose. The cell wall helps support and maintain the

shape of the cell, protects the cell from damage, and connects it with

adjacent cells.

ChloroplastsPlant cells contain one or

more. Chloroplasts are

organelles that use light energy to make

carbohydrates from carbon dioxide and

water. Chloroplasts are found not only in

plants but also in a wide variety of eukary-

otic algae, such as seaweed. Chloroplasts,

along with mitochondria, supply much of

the energy needed to power the activities

of plant cells. Like mitochondria, chloro-

plasts are surrounded by two membranes,

contain their own DNA, and are thought

to be the descendents of ancient prokary-

otic cells.

Central vacuoleAs shown in Figure 17,

much of a plant cell’s volume is taken up

by a large, membrane-bound space called

the (VAK yoo ohl). The

central vacuole stores water and may

contain many substances, including ions,

nutrients, and wastes. When the central

vacuole is full, it makes the cell rigid. This

rigidity enables a plant to stand upright.

central vacuole

chloroplasts

66 CHAPTER 3Cell Structure

Describethe role of the nucleus in cell

activities. 4B

Sequencethe course of newly made proteins

from the rough ER to the outside of the cell. 4B

Describethe role of mitochondria in the metab-

olism of eukaryotic cells. 4B

Explainhow a plant cell’s central vacuole and

cell wall help make the cell rigid. 4A

Critical ThinkingInferring Relationships

What is the importance of a cell enclosing its

digestive enzymes inside lysosomes? 4A

Which organelle serves

as the packaging and distribution center of a

eukaryotic cell? 4A 4B

Anucleus Cmitochondrion

Blysosome DGolgi apparatus

TAKS Test PrepTAKS Test Prep

Section 3 Review

Chloroplast

Central vacuole

Cell wall

Figure 17 Plant cell.Plant cells have a cell

wall, chloroplasts, and a large central vacuole

(shown in blue).