The Cell and Its Structure

Students explore the basic structure of animal and plant cells.

Introduction

All living things are composed of cells. Strange as it may seems, cells in your body share many common characteristics as cells in plants or other organisms. Human-beings are multicellular (many-celled) organisms, while unicellular (single-celled) organisms are composed of one cell.

Cell Parts

Using an optical microscope, you will be able to see the basic cell construction in unicellular organisms and multicellular organisms.

Every cell must carry out certain activities that keep it alive. These activities include obtaining materials and supplies of energy, making products, and getting rid of wastes. To carry out these functions, cells have some basic structures in common. Structures inside the cell are known as organelles. Each organelle has a role to play in the activities necessary for life. Many of the details of cell organelles have only been discovered since the invention of the electron microscope.

Using the two figures and video below to help identify the parts of an animal and plant cell.

  • A) Cell membrane: Like the skin covering your body, the cell membrane surrounds and protects the contents of the cell. The cell membrane is not simply a container, however. Its structure helps control the movement of substances in and out of the cell.
  • B) Cytoplasm: A large part of the inside of the cell is taken up by the jellylike cytoplasm. Like the blood flowing throughout your body, cytoplasm constantly moves inside the cell. The cytoplasm distributes materials such as oxygen and food to different parts of the cell. The cytoplasm also helps support all the other parts inside the cell.
  • C) Nucleus: A large, dark, round nucleus is often the most easily seen structure in a cell. The nucleus controls the cell’s activities. It contains the chromosomes — structures made of genetic material that direct a cell’s growth and reproduction. The cell nucleus is enclosed by a nuclear membrane, which controls what enters and leaves the nucleus.
  • D) Vacuoles: Balloonlike spaces within the cytoplasm are storage places for surplus food, wastes, and other substances that the cell cannot use right away. These structures, called vacuoles, are surrounded by a membrane.
  • E) Cell wall: The cell wall occurs only in the cells of plants and fungi, and in some unicellular organisms. Cell walls are much thicker and more rigid than cell membranes, and are made mostly of a tough material called cellulose. They provide support for the cell.
  • F) Chloroplasts: Chloroplasts are the structures in which the process of photosynthesis takes place. Photosynthesis uses energy from the Sun to make carbohydrates. Folded membranes inside each chloroplast contain the green pigment chlorophyll, which absorbs sunlight. Chloroplasts are found only inside cells in green plants and in some unicellular organisms. They are not found in animal cells.

Cell Size

Cells come in a variety of sizes and shapes. Most cells, however, fall into a narrow range of size — the size in which they function most efficiently. To grow bigger, organisms add more cells to their bodies rather than growing bigger cells. This occurs when cells divide.

Cells are measured in micrometers (µm). Most cells in plants and animals have a diameter between 10-50 µm, however, bacterial cells are much smaller ranging from 1-5 µm.

The information on this page and it associated figures are from the Science Focus 8.
Science Focus 8, pp. 115-127
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