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6th Grade Science / Lesson 2 - How Cells and Tissues are Organized

Cells and Tissues
What will we be learning today?

  • In this lesson, we are going to learn all about cells and tissues.

What Types of Cells Were Discovered First?

  • Who was the first person to see cells? The first cells were seen in 1665 by Robert Hooke, an English scientist. He looked at cork under a microscope and saw little "boxes" that looked like the "cells" of a honeycomb. The invention of the microscope in the early 17th century enabled scientists such as Hooke to begin their exploration of the microscopic world. Although the cork cells that Hooke observed were not living, techniques were developed later on to view live cells.

  • Hooke's newly invented microscope enabled him to view and sketch the cells in a thinly sliced piece of cork.

  • Since Hooke's first observation of cells, improved microscopes have allowed us to make cells appear to be hundreds or thousands of times their actual size. This allows us to examine and study the cells. It was not until the work of Anton van Leeuwenhoek, beginning in 1673, that a new world of one-celled living things was opened up. Leeuwenhoek was the first to observe one-celled living things such as bacteria and paramecia.

  • What Types of Cells Are You Made Up Of?

    • If you looked at cells under a microscope, would the size and shape tell you anything about the size of the living things from which they came? Although a human is much larger than a tomato or Elodea plant, the cells are about the same size.

  • Shapes of cells may give us a clue about the function of a particular cell. A human red blood cell is about one-tenth the size of the dot on this i. Its small size and flexibility allow it to pass through tiny blood vessels. A nerve cell in your leg may be up to a meter in length. Its long shape enables it to send messages through your body.

  • How Are Cells Organized?

    • What discoveries were made because of improvements in microscopes in the 18th and 19th centuries? Scientists were further able to observe the structure and organization of cells. One-celled living things were found to carry out all of life's functions. In the 1820s a French biologist named Rene Dutrochet examined parts of animals and plants and concluded that the various parts of living things are made up of groups of cells.

    • In many-celled living things, cells do not work alone. They work in groups called tissues. A tissue is a group of similar cells working together performing the same function. Human tissues are composed of four main groups:

    • Epithelial tissue, such as the cells that line your cheek, protects, lines, and absorbs.

    • Muscle tissue is made up of cells that contract, moving bones and moving substances through the body.

    • Bone, cartilage, tendons, fat, and even blood are all connective tissue, which supports the body.

    • Cells in nerve tissue transport messages through the body.

  • Plants, too, have many different kinds of cells in their stems, roots, and leaves. The tissues in any part work together to transport food and water throughout the plant.

  • How Are Tissues Organized?

    • Groups of different tissues called organs work together to carry out certain activities. Your heart, which is made up of muscle and nerve tissue, is an example of an organ. Different organs of your body are organized into organ systems. These systems have specific functions and interact with each other in a variety of ways.

  • For example, your circulatory system delivers blood cells to and from the different parts of your body. As blood cells pass through the tissues of the lungs, a part of your respiratory system, exchange of oxygen and other gases takes place. Once the oxygen is transported to the cells of the body, it is used for growth and repair.

    • All the organ systems together make up an organism. An organism is any living thing that can carry out its life activities on its own. Many-celled organisms are organized as cells, tissues, organs, and organ systems. But one-celled living things, such as paramecia and bacteria, are organisms, too. They carry out all their life activities in just one cell.

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