Title: Lesson: Classification of Living Things
Course: 2024 Science 6° > Section: 2 September - 8 September

In this lesson you will learn about the cells, the levels of organization, and the structures of the animal and plant cells.

Introduction to Cells

Discovery of Cells

The first time the word cell was used to refer to these tiny units of life was in 1665 by a British scientist named Robert Hooke. Hooke was one of the earliest scientists to study living things under a microscope. The microscopes of his day were not very strong, but Hooke was still able to make an important discovery. When he looked at a thin slice of cork under his microscope, he was surprised to see what looked like a honeycomb. Hooke made the drawing in the Figure below to show what he saw. As you can see, the cork was made up of many tiny units, which Hooke called cells.

Fig. 1 Cork under the microscope.

Introduction to Cells

A cell is the smallest structural and functional unit of an organism. Some organisms, like bacteria, consist of only one cell. Big organisms, like humans, consist of trillions of cells. Compare a human to a banana. On the outside, they look very different, but if you look close enough you’ll see that their cells are actually very similar.

Cell theory:

The Cell Theory is one of the fundamental theories of biology.

 1. All life forms are made from one or more cells.

 2. Cells only arise from pre-existing cells. (mitosis or meiosis)

 3. The cell is the smallest form of life that can exist and still carry out the life processes.

Cell questions

What is a cell?

- Cells are the smallest living unit of the living things.
- Cells are not living things
- Cells are the largest living units on the living things

Structure of the Animal and plant cell

Levels of Organization in Living Things

Levels of Organization

While cells are the basic units of an organism, groups of cells can perform a job together. These cells are called specialized because they have a special job. Specialized cells can be organized into tissues. For example, your liver cells are organized into liver tissue. Your liver tissue is further organized into an organ, your liver. Organs are formed from two or more specialized tissues working together to perform a job. All organs, from your heart to your liver, are made up of an organized group of tissues.

These organs are part of a larger system, the organ systems. For example, your brain works together with your spinal cord and other nerves to form the nervous system. This organ system must be organized with other organ systems, such as the circulatory system and the digestive system, for your body to work. Organ systems work together to form the entire organism. There are many levels of organization in living things (Figure below).

Match exercise - levels of organization

Look at the pictures and match the levels of the organization with the definition.

Feedback: Are the smallest units of an organism.
Feedback: Are group of cells with similar functions.
Feedback: Are formed from two or more specialized tissues working together to perform a job.
Feedback: Group of organs that carries out more generalized set of functions.
Feedback: Several organ systems that function together.