Bellringer

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.

Chapter 4What 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.

Section 1 The Characteristics of Cells

Chapter 4Cells 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.


Chapter 4

• 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.


Cells and Cell Theory, continued

Chapter 4

• 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.



Chapter 4

• 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.



Chapter 4Cells and Cell Theory, continued

• In 1858, Rudolf Virchow added the third part of the cell theory:

• All cells come from existing cells.


Chapter 4Cell 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.


Chapter 4Parts 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.


Chapter 4

• 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.


Parts of a Cell, continued

Chapter 4

• 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.


Parts of a Cell, continued

Chapter 4Parts 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.


Chapter 4Two 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.


Chapter 4Two 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.


Bellringer

Documents

Transcript of Bellringer