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Unit 1 Lesson 1 The Characteristics of Cells
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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?
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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
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.
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