Download The Characteristics of Cells

Module A: Unit 1, Lesson 1 - The Characteristics of Cells
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.
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.
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.
• Anton van Leeuwenhoek was the first to describe living cells.
• Matthias Schleiden concluded that all plants are made of cells.
• 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.
• 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.
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.
• 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.
What are the two types of cells?
• Prokaryotes are single-celled organisms that do not have a nucleus or membranebound 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.
• 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.