Section 3: From Cell to Organism Preview Bellringer Key Ideas Diversity in Cells Levels of Organization Body Types Summary

Bellringer What type of society would you prefer to live in: one in which you must do everything for yourself, including growing and gathering food, building shelter, etc., or one in which each person does the job that they do best? What are some advantages to having each person do a specialized job? What are some advantages to doing everything yourself?

Key Ideas What makes cells and organisms different? How are cells organized in a complex multicellular organism? What makes an organism truly multicellular?

Diversity in Cells Both prokaryotic and eukaryotic cells can have a variety of shapes and structures. The function of a cell is determined by its shape and the organelles found in the cell. The different organelles and features of cells enable organisms to function in unique ways in different environments.

Diversity in Cells, continued Diversity in Prokaryotes Prokaryotes can vary in shape, the way they obtain and use energy, and their ability to move. Many prokaryotes have a flagellum, a long, hair-like structure that grows out of the cell and enables the cell to move through its environment. Prokaryotes may also have pili, short outgrowths that allow the cell to attach to surfaces or other cells.

Flagella On Prokaryotic Cells Click to animate the image. B C D A E F

Diversity in Cells, continued Eukaryotic Cell Specialization Eukaryotic cells can vary in shape and external features. Depending on their function, eukaryotic cells can also vary in their internal organelles. For example, muscle cells, which use large amounts of energy, contain many mitochondria. Animal and plant cells are two types of eukaryotic cells. Both have many of the same organelles, but plant cells also have chloroplasts, a large central vacuole, and a cell wall.

Eukaryotic Cells Click to animate the image. I K H C A G D J M B D L C F I H E G F

Levels of Organization Plants and animals have many highly specialized cells that are arranged into tissues, organs, and organ systems. A tissue is a distinct group of similar cells that perform a common function. An organ is a collection of tissues that work together to form a structure which performs a specific function. An organ system is composed of a group of organs that work together to perform major body functions.

Organization in Multicellular Organisms Click to animate the image.

Body Types Unicellular organisms can thrive independently or live together in groups. Cells that are permanently associated but do not work together or integrate cell activities are called colonial organisms. A multicellular organism is composed of many individual, permanently associated cells that coordinate their activities with each other. True multicellularity occurs only in eukaryotes.

Visual Concept: Comparing Organisms that are Unicellular and Multicellular

Body Types, continued In a multicellular body, cells are interdependent. Distinct types of cells have specialized functions to help the organism survive. The individual cells in a multicellular organism cannot survive alone and are dependent on the other cells of the organism. Must multicellular organisms begin as a single cell, which divides to form more cells. These cells then grow and become specialized in a process called differentiation.

Visual Concept: Differentiation

Summary The different organelles and features of cells enable organisms to function in unique ways in different environments. Plants and animals have many highly specialized cells that are arranged into tissues, organs, and organ systems. A multicellular organism is composed of many individual, permanently associated cells that coordinate their activities with each other.