Chapter 2-Sec. 3: (Discovering the Cell)

  • Learning Goal:
    The student will be able to…
    1. …define the major parts of a cell.
    2. …describe the difference between a plant cell and an animal cell.

    First, write down the vocab words. Then, click below to practice learning the parts of a cell. 

    Cell Part Animation


    cell wall
    the solid outside of a plant cell

    cell membrane
    the boundary that separates a cell from its envrionment

    the "control center" of a cell

    the place where ribosomes are made

    the organelle that makes proteins in cells

    the area between the cell membrane and the nucleus

    converts food to energy

    endoplasmic reticulum
    carries proteins from one part of the cell to another

    golgi bodies
    take proteins from the endoplasmic reticulum, package them and distribute them to othe parts of the cell 

    capture energy from sunlight and use it to produce food for the cell

    the storage areas of cells

    Enter the Cell

    Your ship doesn’t have an easy time getting inside the cell. It has to pass through the cell wall and the cell membrane.

    Cell Wall
    As you travel through the plant cell, refer to Figure 24 in this section. First, you must slip through the cell wall. The cell wall is a rigid layer of nonliving material that surrounds the cells of plants and some other organisms. The cells of animals, in contrast, do not have cell walls. A plant’s cell wall helps to protect and support the cell. The cell wall is made mostly of a strong material called cellulose. Although the cell wall is tough, many materials, including water and oxygen, can pass through easily.

    Cell Membrane
    After you sail through the cell wall, the next barrier you must cross is the cell membrane. All cells have cell membranes. In cells with cell walls, the cell membrane is located just inside the cell wall. In other cells, the cell membrane forms the outside boundary that separates the cell from its environment.

    The cell membrane controls what substances come into and out of a cell. Everything the cell needs, from food to oxygen, enters the cell through the cell membrane. Fortunately, your ship can slip through, too. Harmful waste products leave the cell through the cell membrane. For a cell to survive, the cell membrane must allow these materials to pass in and out. In addition, the cell membrane prevents harmful materials from entering the cell. In a sense, the cell membrane is like a window screen. The screen allows air to enter and leave a room, but it keeps insects out.

    parts of a cell


    Sail On to the Nucleus

    As you sail inside the cell, a large, oval structure comes into view. This structure, the nucleus, acts as the “brain” of the cell. You can think of the nucleus as the cell’s control center, directing all of the cell’s activities.

    Nuclear Envelope
    Notice in Figure 21 that the nucleus is surrounded by a membrane called the nuclear envelope. Just as a mailing envelope protects the letter inside it, the nuclear envelope protects the nucleus. Materials pass in and out of the nucleus through pores in the nuclear envelope. So aim for that pore just ahead and carefully glide into the nucleus.


    You might wonder how the nucleus “knows” how to direct the cell. The answer lies in those thin strands floating directly ahead in the nucleus. These strands, called chromatin, contain genetic material, the instructions for directing the cell’s functions. For example, the instructions in the chromatin ensure that leaf cells grow and divide to form more leaf cells.

    As you prepare to leave the nucleus, you spot a small object floating by. This structure, a nucleolus, is where ribosomes are made. Ribosomes are the organelles where proteins are produced. Proteins are important chemicals in cells.

    Organelles in the Cytoplasm

    As you leave the nucleus, you find yourself in the cytoplasm, the region between the cell membrane and the nucleus. Your ship floats in a clear, thick, gel-like fluid. The fluid in the cytoplasm is constantly moving, so your ship does not need to propel itself. Many cell organelles are found in the cytoplasm.

    Suddenly, rod-shaped structures loom ahead. These organelles are mitochondria (my tuh kahn dree uh) (singular mitochondrion). Mitochondria are known as the “powerhouses” of the cell because they convert energy in food molecules to energy the cell can use to carry out its functions. Figure 22 shows a mitochondrion up close.

    Endoplasmic Reticulum
    As you sail farther into the cytoplasm, you find yourself in a maze of passageways called the endoplasmic reticulum . The endoplasmic reticulum’s passageways carry proteins and other materials from one part of the cell to another.

    Attached to some surfaces of the endoplasmic reticulum are small, grainlike bodies called ribosomes. Other ribosomes float in the cytoplasm. Ribosomes function as factories to produce proteins. Some newly made proteins are released through the wall of the endoplasmic reticulum. From the interior of the endoplasmic reticulum, the proteins will be transported to the Golgi bodies.

    Golgi Bodies
    As you leave the endoplasmic reticulum, you see the structure shown in Figure 25. It looks like flattened sacs and tubes. This structure, called a Golgi body, can be thought of as the cell’s mail room. The Golgi bodies receive proteins and other newly formed materials from the endoplasmic reticulum, package them, and distribute them to other parts of the cell. The Golgi bodies also release materials outside the cell.

    Have you noticed the many large green structures floating in the cytoplasm? Only the0 cells of plants and some other organisms have these green organelles called chloroplasts. Chloroplasts capture energy from sunlight and use it to produce food for the cell. Chloroplasts make leaves green.

    Steer past the chloroplasts and head for that large, water-filled sac, called a vacuole (vak yoo ohl), floating in the cytoplasm. Vacuoles are the storage areas of cells. Most plant cells have one large vacuole. Some animal cells do not have vacuoles; others do. Vacuoles store food and other materials needed by the cell. Vacuoles can also store waste products.

    Your journey through the cell is almost over. Before you leave, take another look around you. If you carefully swing your ship around the vacuole, you may be lucky enough to see a lysosome (ly suh sohm). Lysosomes are small, round structures containing chemicals that break down certain materials in the cell. Some chemicals break down large food particles into smaller ones. Lysosomes also break down old cell parts and release the substances so they can be used again. In this sense, you can think of lysosomes as the cell’s cleanup crew.s.

    Click below to watch a video about the parts of a cell

    Parts of a Cell