UNIT 1 NATURAL SCIENCE: LIVING THINGS

What are living things?

All living things carry out three processes to stay alive: nutrition, sensitivity and reproduction.

• Nutrition: living things obtain nutrients and energy from food.
• Sensitivity: living things react to what the perceive around them.
• Reproduction: living things produce new individuals that are similar to themselves.

 The cell

Cells are the basic units of life. All living things are made up of cells. Also, cells are living units and they carry out the three basic life processes: nutrition, reproduction and sensitivity.

Depending on the number of cells, living things can be classified into:

• Unicellular: living things made up of a single cell.
• Multicellular: living things made up of many cells.

The parts of a cell

Cells have three parts:

• Membrane: this is the covering around the cell.
• Nucleus: this is the part that controls the function of the cell.
• Cytoplasm: this is similar to jelly. It contains the organelles.

Types of cells

There are two types of cells: animal cells and plant cells. All of them have a membrane, a nucleus and a cytoplasm. However, animal and plant cells are different in the following ways:

• Plant cells have a rigid cell wall around the membrane.
• Plant cells have specialized organelles called chloroplasts. They are esencial to make the photosynthesis.
• Plant cells are usually bigger than animal cells and have a regular shape. Animal cells can be many different shapes.

The organization of living things

Multicellular living things are made up of many different types of cells. Groups of the same type of cells join together to form tissues. Tissues join together to form organs. Organs are organized to form systems. Finally, all the different systems work together to form an organism, a living thing.