McDougal Littell Science Cells and Heredity 

Table of Contents
Page 21 (continued)

Plants and animals have eukaryotic cells.

Plant and animal cells, like all eukaryotic cells, are divided into two main compartments. The nucleus, usually the largest organelle, is the compartment that stores the instructions a cell needs to function. You will learn more about how cells use this information in Chapter 5.

Surrounding the nucleus is the cytoplasm. The cell membrane is the boundary between the cytoplasm and the outside of the cell. Plant cells also have cell walls. A cell wall is a tough outer covering that lies just outside the cell membrane. The cell wall supports and protects the cell. Having a cell wall is one important way in which plant cells differ from animal cells.

Cell
Cell

Both a plant cell (shown at left magnified 1750×) and an animal cell (shown at right magnified 12,000×) have a nucleus and a cell membrane. Plant cells also have a cell wall.

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Parts of a Eukaryotic Cell

Plant Cell

Found in plant cells, not animal cells:

PlantCell
Plant

Animal Cell

Found in animal cells, not plant cells:

AnimalCell
Animal
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Structures That Process Information

The nucleus is often the largest organelle in a cell. It contains information a cell needs to function. Some of the information is translated by ribosomes, tiny structures located in the cytoplasm and the endoplasmic reticulum. Ribosomes use the information to build important molecules called proteins.

Organelles That Provide Energy

No cell can stay alive without energy. Cells need energy to perform all the activities of life. Plants get their energy directly from the Sun. Within plant cells are chloroplasts (KLAWR-uh-PLASTS), organelles in which the energy from sunlight is used to make sugar. Plants use some of the sugar immediately, to keep their cells functioning. The rest of the sugar is stored in the cells.

Animal cells do not contain chloroplasts. As a result, animals are not able to use the energy of the Sun directly. Instead, animals get their energy from food. Much of the food an animal uses for energy comes from the sugar that plant cells have stored. Animals can get this energy by eating plants or by eating animals that have eaten plants.

Mitochondria

This plant cell is magnified 6000×.

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How can a chloroplast, a structure found in plant cells but not in animal cells, provide energy for both plants and animals?

Both plant cells and animal cells must be able to use energy to do work. The energy is made available by organelles found in all eukaryotic cells. Mitochondria (MY-tuh-KAHN-dree-uh) are the organelles that use oxygen to get energy from processing food.

Organelles That Process and Transport

You know that plant and animal cells get their energy from the sugars that the organisms make or consume. Sugars are also an important part of the starting materials that cells use to maintain themselves and grow. The job of making cell parts from the starting materials that enter a cell is divided among a number of structures in the cytoplasm.

In the illustrations on page 22, you can see that the endoplasmic reticulum is a system of twisting and winding membranes. Some of the endoplasmic reticulum contains ribosomes, which manufacture proteins. The endoplasmic reticulum manufactures parts of the cell membrane.

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The endoplasmic reticulum is also part of the cellular transport system. Portions of endoplasmic reticulum break off to form small packages called vesicles. The vesicles transport processed materials to an organelle called the Golgi apparatus. The folded membranes of the Golgi apparatus make it look something like a stack of pancakes. The Golgi apparatus takes the materials manufactured by the endoplasmic reticulum and finishes processing them.

Organelles for Storage, Recycling, and Waste

Cells store water, sugar, and other materials, which they use to function. Cells must also store waste materials until they can be removed. Inside plant and fungus cells are sacs called vacuoles. Vacuoles are enclosed by a membrane and can hold water, waste, and other materials. Vacuoles function with the cell membrane to move materials either into or out of the cell. A plant cell has a large central vacuole in which water and other materials can be stored. Water in the vacuole provides support for smaller plants.

Animal cells do not have central vacuoles. What animal cells do have are similar structures called lysosomes. Lysosomes are vesicles that contain chemicals that break down materials taken into the cell, as well as old cell parts. Remember that animals, unlike plants, take in food. Nutrients brought into the cell need to be broken down, as well as wastes contained.

central vacuole

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Compare and contrast lysosomes and central vacuoles.