1 (b.c.) Organelles
The levels of organization in the human body consist of cells, tissues, organs, organ systems and finally organism. The smallest unit of organization is the cell. The next largest unit is tissue; then, organs, then the organ system. Finally the organism, is the largest unit of organization. The smallest unit of organization is the cell. You are made of cells. Cells are the basic units of structure and function in living things. This means that cells form the parts of an organism and carry out all of an organism’s processes, or functions. The invention of the microscope made it possible for people to discover and learn about cells.
There are even smaller structures inside a cell. These tiny cell structures, called organelles, carry out specific functions within the cell. The nucleus (noo klee us), 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. Only the cells of plants have these green organelles called chloroplasts. Chloroplasts capture energy from sunlight and use it to produce food for the cell. Chloroplasts make leaves green. In a many-celled organism, the cells are often quite different from each other and are specialized to perform specific functions. Nerve cells are specialized to transmit information from one part of your body to another, and red blood cells carry oxygen throughout your body.
In many-celled organisms, cells are often organized into tissues, organs, and organ systems. A tissue is a group of similar cells that work together to perform a specific function. For example, your brain is made mostly of nervous tissue, which consists of nerve cells. An organ, such as your brain, is made of different kinds of tissues that function together. Your brain is part of your nervous system, which is an organ system that directs body activities and processes. An organ system is a group of organs that work together to perform a major function.
There are even smaller structures inside a cell. These tiny cell structures, called organelles, carry out specific functions within the cell. The nucleus (noo klee us), 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. Only the cells of plants have these green organelles called chloroplasts. Chloroplasts capture energy from sunlight and use it to produce food for the cell. Chloroplasts make leaves green. In a many-celled organism, the cells are often quite different from each other and are specialized to perform specific functions. Nerve cells are specialized to transmit information from one part of your body to another, and red blood cells carry oxygen throughout your body.
In many-celled organisms, cells are often organized into tissues, organs, and organ systems. A tissue is a group of similar cells that work together to perform a specific function. For example, your brain is made mostly of nervous tissue, which consists of nerve cells. An organ, such as your brain, is made of different kinds of tissues that function together. Your brain is part of your nervous system, which is an organ system that directs body activities and processes. An organ system is a group of organs that work together to perform a major function.
