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The Cell
Video ScriptThe Cell
1. All living things have one very important thing in common. They all possess tiny
structures that can’t be seen with the naked eye.
2. What are these tiny structures?
3. Flowers possess them.
4. Plants and trees rely on these structures to grow tall and…
5. …to convert radiant energy from the sun to simple sugars that contain chemical
energy.
6. Fish use them to carry out their lives in water,…
7. ...and even large animals such as this pelican…
8. …and this sea lion depend on these structures to move, grow, and reproduce.
9. What are the structures on which all life depends? Here is one more clue: they
often are called the building blocks of life!
10. These structures are called cells.
11. During the next few minutes we are going to take a look at the general characteristics
of cells, their designs,…
12. …and the activities they perform.
13. We are also going to take a look at how cells help human beings carry out their lives.
14. Graphic Transition - Seeing the Invisible
15. Exactly what are cells and how important are they?
16. As we have stated, all life depends on cells. The human body contains not only
millions of cells, but hundreds of different kinds of cells as well.
17. Most cells are too small to be seen with the naked eye.
18. For example, this small drop of water contains dozens of single-celled organisms not
visible to the naked eye.
19. Using a tool called a microscope, however, these invisible cells become visible.
20. The first microscopes, which contained just a single lens, were similar to a
magnifying glass.
21. But in 1590 a man who made reading glasses decided to put two lenses together in a
tube and made the first compound microscope.
22. Today, compound light microscopes are widely used. These microscopes let light
pass through an object on a glass slide and then through two or more lenses.
23. Convex lenses enlarge the image and bend the light toward the eye.
24. The most common compound light microscopes magnify objects up to 430 or 1000
times their original size, while those with more powerful lenses have even greater
magnification power.
25. Objects that are too small to be seen with a compound light microscope can only be
viewed with an electron microscope, which has the ability to magnify images up to
one million times their original size.
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The Cell
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26. Rather than using lenses to bend light, electron microscopes use magnetic fields to
bend beams of electrons.
27. This electron microscope is called a scanning electron microscope.
28. Scanning electron microscopes are used to study the outside of objects.
29. Graphic Transition- Discovering the Cell
30. Early scientists did not have the high-powered microscopes we use today.
31. Instead, they utilized simple microscopes, such as this one, to explore the
microscopic world.
32. One such scientist was the English biologist Robert Hooke
33. You Decide! What’s the object Hooke saw under his microscope?
34. In 1663, Hooke took a piece of cork, cut a very thin slice, and viewed it under the
microscope.
35. Looking at the cork he discovered tiny square-shaped forms. He called these
structures cells.
36. What Hooke was seeing was not living cells but the remaining cell walls of dead
plant cells.
37. Around the same time, a Dutch scientist named Anton van Leeuwenhoek was also…
38. …using a simple microscope to look at living microscopic organisms.
39. He was the first to discover single-celled organisms we know today as bacteria.
40. Graphic Transition- The Cell Theory
41. In 1838 a German botanist, Matthias Schleiden, used the microscope to study…
42. … parts of plants.
43. Schleiden concluded that plants were made of cells.
44. One year later, scientist Theodor Schwann, who had been looking…
45. …at different animal cells, concluded that…
46. …all animals, too, are made of cells.
47. Together, Schleiden and Schwann concluded that all living things are made of cells.
48. In the mid-1850’s, a doctor by the name of Rudolph Virchow stated that new cells
do not form on their own.
49. He stated that cells divide to form new cells.
50. In other words, new cells come from previously existing cells.
51. The combined discoveries of Schleiden, Schwann, and Virchow led to what we
know today as the cell theory.
52. The cell theory is a fundamental principle of biology and has three major parts.
53. First, it states that all living organisms are made of one or more cells.
54. This ranges from single-celled organisms, such as this bacteria,…
55. …to large organisms such as this horse.
56. Second, the cell theory states that cells are the basic units of structure and function
in all organisms.
57. This means that there is no life without cells.
58. Third, the cell theory states that all cells come from previously existing cells.
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The Cell
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59. As previously stated, new cells do not just magically appear, but come from other
cells when they divide.
60. These three main concepts make up the cell theory.
61. Graphic Transition – Organization of the Cell
62. Most cells are smaller than the head of this pin.
63. But, believe it or not, cells are made up of even smaller parts called organelles.
64. Organelles are the structures within cells that break down food, move water, and
store nutrients.
65. All parts of a cell are extremely important in carrying out functions in both plants and
animals.
66. While both plant and animal cells contain many similar cell structures, there are
some distinct differences between plant and animal cells.
67. One difference between plant and animal cells is the structure that surrounds the cell.
68. Plant cells are surrounded by a relatively rigid cell wall. The cell wall is made of
cellulose, a strong and tough material.
69. Cell walls enable trees to stand straight and tall.
70. You Decide! Do animals possess a cell wall?
71. Animal cells do not possess a cell wall, possessing only a cell membrane.
72. Plants also possess a cell membrane, but it lies inside the cell wall.
73. In both plants and animals, the cell membrane allows only certain materials to flow
into and out of the cell.
74. For example, food and oxygen move through the cell membrane into the animal
cell,...
75. …while waste products go through the membrane to exit the cell.
76. Another difference between plant and animal cells is that plants possess structures
called chloroplasts.
77. Chloroplasts are organelles that convert light energy into chemical energy that the
cell uses to carry out its activities.
78. Chloroplasts enable plants to produce their own food from the energy of the sun
79. Animal cells don’t have chloroplasts. Therefore animals need to obtain their energy
by eating food made by other living things, such as fruits, vegetables and meats.
80. Let’s now take a look at some of the other structures found in cells
81. Graphic Transition – The Nucleus
82. Our brains are the control centers of our bodies.
83. The brain guides us through all the activities we take part in during the course of a
day.
84. Cells, too, have a control center, called the nucleus.
85. The nucleus acts as the cell’s brain control center, regulating all cellular activities.
86. The nuclear membrane surrounds and protects the nucleus.
87. Like the cell membrane, the nuclear membrane allows only certain materials to pass
in and out of the nucleus.
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The Cell
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88.
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90.
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93.
Also located in the nucleus is a small, dark, round structure called the nucleolus.
The nucleolus is where RNA is built and ribosome pieces are created.
Graphic Transition- Cytoplasm
You Decide! What is the material seen flowing through this cell?
If you said water, then you are close. The liquid is called cytoplasm.
Cytoplasm contains a large amount of water as well as many chemicals and
structures that help carry out the life processes of the cell.
94. Within the cytoplasm are many organelles that we’ll now explore.
95. Graphic Transition- Endoplasmic Reticulum and Ribosomes
96. This network of roads used to transport cars and trucks is like a cell organelle...
97. ...called the endoplasmic reticulum.
98. Its function is to transport materials such as proteins throughout the cell, or in and
out of the cell.
99. The endoplasmic reticulum forms a series of tubular passageways, seen here.
100. Attached to the inner surface of the endoplasmic reticulum and scattered in the
cytoplasm are small, round structures called ribosomes.
101. Ribosomes play a very important role in the cell because they contain a
chemical,called RNA,that directs the production of proteins.
102. Proteins speed up chemical reactions in the cell, as well as control cell growth
and repair.
103. Graphic Transition- Golgi Bodies and Mitochondria
104. This loading dock contains material that has been packaged …
105. …and will soon be transported to other locations.
106. Golgi bodies, or the Golgi Apparatus, are stacks of membrane-covered sacs that
package and move particles to the outside of the cell.
107. The Golgi Apparatus can be thought of as the cell’s conveyor belt, transporting
material.
108
This electrical generating plant provides energy for thousands of people.
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109. Similarly, structures called mitochondria are the powerhouses of the cell.
110. These rod-shaped structures seen here supply most of the energy for the cell.
111. They break down food to produce large amounts of energy.
112. Muscle cells, which expend large amounts of energy, also contain many
mitochondria.
113. Graphic Transition- Vacuoles and Lysosomes
114. This silo, located on this farm, stores food that will…
115. …eventually be fed to cows.
116. Similarly, vacuoles located in the cell store food and other materials for later use by
the cell. They can also store waste.
117. In plant cells, vacuoles are the main area where water is stored.
118. The last cell organelles we’ll explore are lysosomes.
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The Cell
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119. Lysosomes, seen here, contain enzymes. Enzymes break down large food particles
into smaller particles, which are then burned in the mitochondria to provide energy
for the cell.
120. Lysosomes also digest old parts of the cell when they lose their effectiveness.
121. For example, as this tadpole grows, its tail cells are slowly digested by the
lysosomes until the tail disappears.
122. You Decide! What do lysosomes do with the old tail cells?
123. This material is reused to make new body parts to become an adult frog.
124. Graphic Transition- Summing Up
125. During the past few minutes we have explored many different characteristics of
cells.
126. We studied how different scientists have made many different discoveries about
cells using microscopes...
127. ...and how they developed the cell theory, which states that...
128. ...all living things are made of cells, and . . .
129. ...that cells are the basic unit of structure and function in living things . . .
130. ...and that new cells come from previously existing cells.
131. We also explored some of the important differences between plant and animal cells.
132. Finally, we took a look at some of the important organelles in cells, including the
nucleus, . . .
133. ...the endoplasmic reticulum, and ribosomes, . . .
134. ...golgi bodies and mitochondria, . . .
135. ...as well as vacuoles and lysosomes.
136. So the next time you see a plant . . .
137. ...or animal, or see other...
138. ...people, think about how all these living things contain cells. You just might look
at your world a little differently.
Video Quiz
Fill in the correct word when you hear this tone. Good luck and let’s get started.
1. All living things possess _____.
2. Robert Hooke discovered cells while looking at a piece of ____.
3. ________ microscopes use magnetic fields to magnify objects.
4. All cells come from ________ _____.
5. _______ are structures within cells that have specific roles.
6. Animal cells do not have a cell ____.
7. _______ are found in plants, and change light energy into chemical energy.
8. The _______ acts as the cell’s control center.
9. _______ is the fluid that fills the cells.
10. __________ break down food to produce energy in the cell.
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