Understanding Living Organisms: Cells, Tissues, and Organs

Living Organisms: An Introduction

What Defines a Living Being?

A living being, formed by one or more cells, carries out vital operations, including:

• Nutrition: The set of processes by which living things obtain or exchange matter and energy with the environment.
• Relationships: The ability of living beings to perceive changes in the environment and respond to them in the most suitable way for their survival.
• Reproduction: The ability to produce offspring that develop and maintain the characteristics of their parents over time.

Types of Organisms

Unicellular Beings

These organisms consist of a single cell that performs all vital functions. Their shape is highly variable and adapted to their lifestyle.

Colonies

Colonies are groupings of single-celled organisms where each individual performs all vital functions.

Multicellular Organisms

These organisms are comprised of many interconnected cells that coordinate their activity for the body to act as a whole. Multicellular organisms have different types of cells, each specialized in performing certain activities. Cells of the same type are grouped into tissues, which form organs, and these organs are organized into systems. This complex organization allows for efficient performance of vital functions.

Levels of Organization in Multicellular Organisms

Organisms with Tissues:

Porifera, fungi, and algae have different types of cells, each performing a specific activity. Cnidarians and bryophytes have tissues serving specific functions.

Organisms with Organs:

Some invertebrates (including certain worms) and cormophytes have specialized organs for specific activities, although these organs are not as complex as in higher organisms.

Organisms with Systems:

The majority of invertebrates and vertebrates perform their vital functions by means of organ systems, some of which coordinate the activities of other systems in the body.

Types of Cells

Prokaryotic Cells:

These cells are like small sacs with DNA in the cytoplasm and organelles called ribosomes. Outside the plasma membrane, they have a cell wall. Some have flagella for movement. These cells are characteristic of bacteria (Monera).

Eukaryotic Cells:

Larger than prokaryotic cells, they have a greater variety of organelles. Their DNA is contained within a nucleus, which has a double membrane called the nuclear membrane. These cells are characteristic of protists, fungi, plants, and animals. There are some differences between the eukaryotic cells of different kingdoms. For example, plant cells have chloroplasts and a large central vacuole, while animal cells do not.