Unit 1 Lesson 1 The Characteristics of Cells Copyright © Houghton Mifflin Harcourt Publishing Company

Cell-ebrate! What is a cell? Unit 1 Lesson 1 The Characteristics of Cells Cell-ebrate! What is a cell? A cell is the smallest functional and structural unit of all living organisms. An organism is any living thing that carries out its own life processes. Robert Hooke was the first to describe cells. He looked at the bark of a cork tree under a microscope. Copyright © Houghton Mifflin Harcourt Publishing Company 2

Why are most cells small? Unit 1 Lesson 1 The Characteristics of Cells Why are most cells small? Cells are small because their size is limited by their outer surface area. If cells get too large, they cannot take in enough nutrients or get rid of enough wastes. The surface area-to-volume ratio of a cell is the ratio of the outer surface to the cell’s volume. The smaller the cell, the greater this ratio. Copyright © Houghton Mifflin Harcourt Publishing Company 3

Cell Hall of Fame What is the cell theory? Unit 1 Lesson 1 The Characteristics of Cells Cell Hall of Fame What is the cell theory? The cell theory lists three basic characteristics of all cells and organisms. All organisms are made up of one or more cells. The cell is the basic unit of all organisms. All cells come from existing cells. Copyright © Houghton Mifflin Harcourt Publishing Company 4

Unit 1 Lesson 1 The Characteristics of Cells What is the cell theory? Anton van Leeuwenhoek was the first to describe living cells. Matthias Schleiden concluded that all plants are made of cells. Copyright © Houghton Mifflin Harcourt Publishing Company 5

Unit 1 Lesson 1 The Characteristics of Cells What is the cell theory? Theodor Schwann determined that all animal tissues are made of cells. Rudolf Virchow proposed that cells could form only from the division of other cells. Copyright © Houghton Mifflin Harcourt Publishing Company 6

Unit 1 Lesson 1 The Characteristics of Cells What is the cell theory? Organisms made up of just one cell are called unicellular organisms. The single cell must carry out all of the organism’s life functions. Organisms made up of more than one cell are called multicellular organisms. The cells of multicellular organisms have specialized functions. Copyright © Houghton Mifflin Harcourt Publishing Company 7

On the Cellular What parts do all cells have in common? Unit 1 Lesson 1 The Characteristics of Cells On the Cellular What parts do all cells have in common? All cells have some structures in common. A cell membrane is a protective layer that covers a cell’s surface and controls materials moving into and out of the cell. The cytoplasm is the region inside the cell that includes the fluid and all the organelles except for the nucleus. Copyright © Houghton Mifflin Harcourt Publishing Company 8

What parts do all cells have in common? Unit 1 Lesson 1 The Characteristics of Cells What parts do all cells have in common? An organelle is a small body in the cytoplasm that is specialized to perform a specific function. The nucleus is a membrane-bound organelle that contains DNA. DNA, or deoxyribonucleic acid, is genetic material that provides instructions for all cell processes. Copyright © Houghton Mifflin Harcourt Publishing Company 9

What parts do all cells have in common? Unit 1 Lesson 1 The Characteristics of Cells What parts do all cells have in common? How many parts of a cell can you name? Copyright © Houghton Mifflin Harcourt Publishing Company 10

What are the two types of cells? Unit 1 Lesson 1 The Characteristics of Cells What are the two types of cells? Prokaryotes are single-celled organisms that do not have a nucleus or membrane-bound organelles. Prokaryotes’ DNA is in the cytoplasm. They have organelles without cell membranes called ribosomes. Some have hairlike structures called flagella that help them move. Copyright © Houghton Mifflin Harcourt Publishing Company 11

What are the two types of cells? Unit 1 Lesson 1 The Characteristics of Cells What are the two types of cells? Eukaryotes are organisms made up of cells that contain DNA in a nucleus, membrane-bound organelles, and ribosomes. Animals, plants, protists, and fungi are eukaryotes. Most eukaryotes are multicellular but some are unicellular. Copyright © Houghton Mifflin Harcourt Publishing Company 12