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Bellringer

Explore the functions and components common to all cells, the differences between prokaryotic and eukaryotic cells, and the development of the cell theory.

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Bellringer

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  1. Section 1 The Characteristics of Cells Chapter 4 Bellringer Identify some of the functions that all cells have in common. Write your ideas in your science journal.

  2. Section 1 The Characteristics of Cells Chapter 4 What You Will Learn • The cell theory explains why cells are important for living things. • All cells have a cell membrane, cytoplasm, and DNA. • Prokaryotic cells and eukaryotic cells differ in how their genetic information is contained.

  3. Section 1 The Characteristics of Cells Chapter 4 Cells and Cell Theory • Cells function similarly in all living things. • A cell is the smallest structural and functional unit of living things. • In 1665, Robert Hooke built a microscope and and observed box-like structures in a sample of cork. He called the structures cells.

  4. Section 1 The Characteristics of Cells Chapter 4 Cells and Cell Theory, continued • Because animal cells lack cell walls, Hooke could not see them. He believed that only plants and fungi were made of cells. • In 1673, Dutch merchant Anton van Leeuwenhoek made a microscope and observed swimming “animacules” in a sample of pond scum. • Today we call these single-celled organisms protists.

  5. Section 1 The Characteristics of Cells Chapter 4 Cells and Cell Theory, continued • Leeuwenhooek also observed blood cells from different animals and was the first person to observe bacteria. • Nearly 100 years later, Matthias Schleiden, a plant scientists, concluded that all plant parts were made of cells. • A year later, in 1839, Theodor Schwann concluded that all animal tissues were made of cells.

  6. Section 1 The Characteristics of Cells Chapter 4 Cells and Cell Theory, continued • Schwann went on to write the first two parts of modern cell theory: • All organisms are made up of one or more cells. • The cell is the basic unit of all living things.

  7. Section 1 The Characteristics of Cells Chapter 4 Cells and Cell Theory, continued • In 1858, Rudolf Virchow added the third part of the cell theory: • All cells come from existing cells.

  8. Section 1 The Characteristics of Cells Chapter 4 Cell Size • The vast majority of cells are too small to be seen without a microscope. • If the volume of a cell becomes too large, the surface area of its membrane will not be able to let in enough materials and let out wastes. • Cells must remain small to maintain a proper surface-area-to-volume ratio.

  9. Section 1 The Characteristics of Cells Chapter 4

  10. Section 1 The Characteristics of Cells Chapter 4 Parts of a Cell • Cells come in many shapes and sizes, and may be specialized for different functions. But all cells have some parts in common. • All cells have a cell membrane. The cell membrane is a protective layer that covers the cell’s surface and acts a barrier. • The cell membrane separates the cell’s contents from its surroundings.

  11. Section 1 The Characteristics of Cells Chapter 4 Parts of a Cell, continued • The cell membrane also controls the materials going into and out of the cell. • Most of the contents of a cell, including the fluid, is called the cytoplasm. • Organelles are part of the cytoplasm. Organelles are structures that have specific jobs inside the cell.

  12. Section 1 The Characteristics of Cells Chapter 4 Parts of a Cell, continued • All cells have DNA (deoxyribonucleic acid) at some point in their lives. DNA is the genetic material that carries instructions for making new cells. • In eukaryotic cells, including plants and animals, the DNA is found within the nucleus of the cell. • The nucleus is an organelle specialized to hold the DNA. The nucleus plays a role in growth, metabolism, and reproduction.

  13. Section 1 The Characteristics of Cells Chapter 4 Parts of a Cell, continued • Bacteria have DNA, but do not have a nucleus. Their DNA floats free in the cytoplasm. • Human blood cells have a nucleus and DNA as they are growing. Once mature, they lose their DNA and nucleus. • Most cells, however, need DNA throughout their lives. The DNA provides instructions for making proteins.

  14. Section 1 The Characteristics of Cells Chapter 4 Two Kinds of Cells • Cells that do not have a nucleus are called prokaryotes. Bacteria and archaea are prokaryotes. • Prokaryotic DNA is a round molecule, twisted like a rubber band. • Prokaryotes have cell walls. They lack the membrane-bound organelles found in other organisms.

  15. Section 1 The Characteristics of Cells Chapter 4 Two Kinds of Cells, continued • Eukaryotes are organisms made up of cells that have a nucleus enclosed by a membrane. • Eukaryotic cells are 10 times as large as prokaryotic cells, although most eukaryotic cells are still microscopic. • Eukaryotes have membrane-bound organelles to carry out the functions of the cell.

  16. Section 1 The Characteristics of Cells Chapter 4

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