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Transcript
7.12D: Plant and Animal Cell Organelles Organisms and Environments A Framework for Func>on Lexile 990L 1 What makes up a cell? Did 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 func>on. When was the cell discovered? In 1665, a scien>st named Robert Hooke sat down and curiously peeked through his microscope to study a piece of cork. When he gazed upon the cork, he discovered small moving objects. Robert Hooke had just discovered a living cell. This exci>ng discovery led to the inven>on of a beJer microscope by Anton Van Leeuwenhoek in 1673. His microscope was specifically designed to view the interes>ng “animalcules” described by Hooke. With this improved style of microscope, Van Leeuwenhoek encountered a single‐celled protozoa in pond scum and even in blood cells! It is because of scien>sts like Van Leeuwenhoek and Hooke that we are able to know so much about cells today. 2 A cell is the smallest unit of life that can perform all life processes. It is included in the cell theory that was proposed by scien>sts nearly 150 years ago. Cell theory is composed of three major points: all livings things are composed of cells, all cells come from pre‐exis>ng cells, and cells are the smallest units of life. 1 7.12D: Plant and Animal Cell Organelles Organisms and Environments 3 Two specific types of cells are known as the prokaryotes and eukaryotes. A cell membrane is a boundary that separates the cell from the outside environment. Basically, it is like a fence. Prokaryotes only have a membrane and a cell wall that enclose the rest of their insides, including cytoplasm. Cytoplasm is a semi‐ fluid substance inside the membrane. An example of a prokaryote is bacteria. Eukaryo>c cells have a much more complex membrane system than prokaryotes, including one around their nucleus. Eukaryotes are the cells that aid in most of your body’s func>ons. Eukaryotes are up to ten >mes larger than the average prokaryote cell. Other important characteris>cs of the eukaryo>c cell are it has a cytoskeleton and a membrane enclosed by sub‐ cellular organelles that will be further explained in this passage. Now that we have established the two major cells, let’s get an even closer look at what really comprises these vital cells. 4 Organelles are structures inside a cell that perform the func>ons necessary for the cell to survive. There are several organelles within a cell that allow it to survive. Let’s begin with the cell membrane. Remember earlier that a cell membrane is like a fence. Like the skin on your body, this membrane acts as a protec>ve layer that covers the cell’s surface. It allows some things to be excreted out of your body, such as sweat, and allows some things in, like an>bio>c ointment to be used to heal an injury. The cell membrane is located in both eukaryo>c and prokaryo>c cells. 5 The cell wall is also an organelle, but it is only found in plant cells. The cell walls give support to the plant cell and provide a basic framework. It is a second layer around the cell membrane and can be described as an extra fence for double protec>on. It is found in cells that belong to plants, fungi, and bacteria. The cell wall is different from the cell membrane in that it is rigid and strong. The cell wall is very important because it allows support for plant cells to grow tall and to protect it from harm. It is like a guard gate that allows water, oxygen, and carbon dioxide to pass in and outside of the cell. 2 7.12D: Plant and Animal Cell Organelles Organisms and Environments 6 If the cell was a ship, then the nucleus would be the captain. The nucleus is an organelle inside the cell that guides all ac>vity. It is the most important part of the eukaryo>c cell’s existence because the nucleus contains deoxyribonucleic acid (DNA), which provides specific instruc>ons for the cell’s purpose and ac>ons. DNA tells the cell how to reproduce new cells and perform all the cells jobs. It also contains hereditary material, which will pass on specific informa>on to future cells. Without DNA, the cell would not know how to operate. The nucleus is in all cells except prokaryotes. In prokaryo>c cells, the DNA floats freely in the cell’s cytoplasm. The nucleolus is a special organelle within the nucleus, and its func>on is to make ribosomes. Ribosomes produce proteins. The nuclear membrane is the last part of the nuclear complex. Its purpose is to protect the nucleus from harm by serving as a double membrane. It is like an addi>onal guard that controls the movement of materials in and out of this special nucleus. 7 The delivery system of the cell is known as the endoplasmic re>culum (ER). Found in all eukaryo>c cells only, it is a network of tubes and membranes that carries materials and aids in making proteins. There are two forms of endoplasmic re>culum, smooth and rough. The ER connects to the nuclear envelope and the cell membrane. Another responsibility of the ER is to move important proteins and carbohydrates to Golgi bodies. What are Golgi bodies? They serve as extensions of the endoplasmic re>culum system, packaging, and moving proteins around in the cell. Unlike the folded membranes of the ER, Golgi bodies look like stacks of flaJened paper sacks. Both organelles work together to modify and export proteins throughout the cell. 8 The motors that fuel the en>re cell’s produc>on is known as the mitochondria. These are a cell’s “power plants.” Located in plant and animal cells, mitochondria produce ATP, an energy source found in food molecules. ATP is like gas for a car, and the mitochondria is responsible for producing it. It does this by breaking down sugar, or glucose, molecules to release energy. The breakdown process is known as cellular respira>on. 3 7.12D: Plant and Animal Cell Organelles Organisms and Environments 9 Although plants use mitochondria as an energy source, these cells also produce energy through unique organelles called chloroplasts. Chloroplasts are organelles that produce chlorophyll that works as chemical photosynthesis to provide power. Chlorophyll traps the Sun’s energy and then transforms this energy into sugar to be u>lized as its own power source. 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. 10 Cells have a lot of organelles, but eventually organelles wear out from the constant input and output that daily life demands. When cell parts become worn out, a special organelle eats up and digest these worn parts. It is called a lysosome, and its sole purpose is this par>cular job. Equipped with special diges>ve enzymes, lysosomes are scaJered throughout the cytoplasm and seek out debris. They are found in both plant and animal cells as small, rounded shapes with a single membrane. Lysosomes are also useful in breaking down larger food molecules into smaller molecules. These unique organelles can be thought of as a garbage truck clearing the cell’s environment. 11 The outer framework of a cell is known as the cytoskeleton. All cells have a cytoskeleton to strengthen the cell and maintain its shape. It also moves organelles around the cell as needed. Within the cytoskeleton is the cytoplasm. This clear, thick, jelly‐like material also supports and protects the cells’ organelles. The cytoplasm’s purpose is to keep organelles in their arrangements, rather than drieing around the cell. Cytoplasm is a lot like glue. Essen>ally, the cytoskeleton is the frame that keeps the cells in its respected, circular shape, while the cytoplasm holds all the material together on the inside. Both protect the cell and preserve its structural integrity. 4 7.12D: Plant and Animal Cell Organelles Organisms and Environments 1 3 The passage describes a cell as — A the smallest unit of life that can perform all life processes. A Golgi bodies. B a prokaryote. B mitochondria. C a cell wall. C ribosome. D nucleus. D molecules surrounded by membranes and cell walls. 2 The “motor” that fuels the en>re cell’s produc>on is known as — 4 Organelles are — A prokaryotes. B eukaryotes. C structures inside a cell that perform the func>ons necessary for the cell to survive. In the passage, an example of a cell was given in simple terms to describe its func>on: If a cell is to a ship then — A a nucleus is to a captain. D the smallest unit of life that perform all life processes. B DNA is to a captain. C endoplasmic re>culum is to a captain. D a ribosome is to a captain. 5 7.12D: Plant and Animal Cell Organelles Organisms and Environments 5 6 Which special organelle’s sole purpose is to consume and digest worn out cells? The cell wall is also an organelle, but it is found only in — A cell membranes. A Cytoskeleton B Chlorophyll C Lysosome B plant cells. C prokaryo>c cells. D DNA. D Cytoplasm 6