A Framework for Function Lexile 930L

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Ethel Palmer
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Plant and nimal ell Organelles Framework for Function Lexile 930L 1 What makes up a cell? id you know that there are billions of cells moving around in your body at this very moment?

1 Plant and nimal ell Organelles Framework for Function Lexile 930L 1 What makes up a cell? id you know that there are billions of cells moving around in your body at this very moment? Without cells, our bodies would not be able to function. When was the cell discovered? In 1665, a scientist named Robert Hooke looked through his microscope to study a piece of cork. When he gazed upon the cork, he saw rows and rows of small rectangular holes. Robert Hooke had just discovered cells. This exciting discovery led to the invention of a better microscope by nton Van Leeuwenhoek in His microscope was specifically designed to view the interesting animalcules described by Hooke. With this improved microscope, Van Leeuwenhoek saw single-celled protozoa in pond scum and discovered blood cells! It is because of scientists like Van Leeuwenhoek and Hooke that we know so much about cells today. 2 cell is the smallest unit that is truly alive. Our basic knowledge of cells is summarized in the cell theory that was proposed by scientists nearly 150 years ago. ell theory is composed of three major points: all living things are composed of cells, all cells come from pre-existing cells, and cells are the smallest units of life. 3 There are two different types of cells known prokaryotes and eukaryotes. Prokaryotes are simpler and smaller. They only have a membrane and a cell wall that enclose the rest of their insides. Eukaryotic cells are much more complex and have a nucleus. Your body is composed of eukaryotic cells. Eukaryotes are up to ten times larger than the average prokaryote cell. nother important characteristic of the eukaryotic cell are the membrane-enclosed sub-cellular organelles that will be further explained later in this passage. 4 ll cells are surrounded by a cell membrane. cell membrane is a boundary that separates the cell from the outside environment. asically, it is like a fence. Like the skin on your body, this membrane acts as a protective layer that covers the cell's surface. It allows some things to be excreted out of the cell, such as wastes, and allows some things in, like nutrients and oxygen. 1

2 Plant and nimal ell Organelles 5 Plant cells also have a cell wall, which is not found in animal cells. ell walls are also found in the cells of fungi and bacteria. The cell walls give support to the plant cell and provide a basic framework. It is a second layer around the cell membrane for double protection. The cell wall is different from the cell membrane in that it is rigid and strong. The cell wall is very important because it provides support for plant cells to grow tall. 6 ytoplasm is a gel-like material that fills all cells. This clear, thick, jelly-like material holds all of the cell's material together on the inside. In eukaryotic cells, it is found between the cell membrane and the nucleus. Organelles move about freely in the cytoplasm, and other cell activity occurs here. In prokaryotic cells, all cellular activities occur in the cytoplasm. This gellike material is held in by the cell membrane and is constantly moving. 7 Eukaryotic cells contain organelles, but prokaryotes do not. Organelles are structures inside a eukaryotic cell that perform the functions necessary for the cell to survive. There are several different types of organelles within a cell that allow it to survive. Let's get an even closer look at some of these vital cellular components. 8 If the cell was a ship, then the nucleus would be the captain. The nucleus is an organelle inside the cell that guides all activity. It is the most important part of the eukaryotic cell because the nucleus contains N, which provides specific instructions for the cell's actions. N tells the cell how to produce new cells and perform all the cell's jobs. It also contains hereditary material, which will pass on specific information to future cells. Without N, the cell would not know how to operate. The nucleus is in all eukaryotes, while in prokaryotic cells, the N floats freely in the cell's cytoplasm. The nucleolus is a special structure within the nucleus, and its function is to make ribosomes. Ribosomes produce proteins. The nucleus is protected by the nuclear membrane. It is like an additional guard that controls the movement of materials in and out of this special area. 9 The motors that fuel the entire cell's production are known as the mitochondria. These are a cell's power plants. Located in plant and animal cells, mitochondria produce TP, the energy source for everything a cell needs to do. TP is like gas for a car, and the mitochondria are responsible for producing it. They do this by breaking down sugars using oxygen. The breakdown process is known as cellular respiration. 10 lthough plants use mitochondria to make TP as an energy source, these cells also produce their own sugar through unique organelles called chloroplasts. hloroplasts are organelles that produce chlorophyll, which traps the Sun's energy. The chlorophyll transforms this energy into sugar to be used in its mitochondria. This process is called photosynthesis, and the end waste product is oxygen. Without plant cells and the process of photosynthesis, humans and other organisms would not have oxygen to breathe. 11 These are just some of the remarkable organelles found in the cells of eukaryotes. Remember that the cell wall and chloroplasts are found in plant cells, but not animal cells. Who would have guessed there would be so much to see when we take a closer look inside of cells? 2

They are membrane-bound organelles with a second, folded membrane inside to provide extra area for cellular respiration.

3 Plant and nimal ell Organelles For questions 1 and 2, use this diagram of the cell where one of the mitochondria has been enlarged. 1 From the information in the passage and the diagram, what can you conclude about the structure of mitochondria? They are membrane-bound organelles with a second, folded membrane inside to provide extra area for cellular respiration. They take instructions from N and make proteins. They break down sugars to provide energy for the cell. They are organelles, which are a group of flattened membrane sacs stacked on top of each other. 3

4 Plant and nimal ell Organelles 2 From the information in the passage and the diagram, what can you conclude about the function of mitochondria? They are membrane-bound organelles with a second, folded membrane inside to provide extra area for cellular respiration. They take instructions from N and make proteins. They break down sugars to provide energy for the cell. They are organelles, which are a group of flattened membrane sacs stacked on top of each other. 3 Which of the following statements best captures the main point of paragraph 3? cell is the smallest unit that is truly alive. ll cells are surrounded by a cell membrane. ytoplasm is gel-like material that fills all cells. Plant cells have cell walls. 4

5 Plant and nimal ell Organelles 4 In the passage, an analogy was given describing the function of a cell in simple terms by comparing it to a ship. omplete this analogy about the function of cell parts. cell is to a board game as N is to the rule book. a nucleus is to the rule book. endoplasmic reticulum is to the rule book. a ribosome is to the rule book. 5 What does the word sub-cellular in paragraph 3 mean? more complex than a cell taken away from a cell hidden underneath a cell located within a cell 5

Discovery of the Cell

Cell Structure Discovery of the Cell Who discovered cells? 1665 Robert Hooke used a compound microscope to examine a piece of cork (20X magnification) He saw little boxes in the cork and called them cells