Cell Theory - Barren.k12.ky.us

Chapter 7: Cell StructureSection 1: Introduction to CellsThe Discovery of CellsMicroscope observations of organisms led to the discovery of the basic characteristics common to allliving things. Scientists first discovered cells in the 1600s using crude microscopes.Observations made by scientists using more powerful microscopes in the 1800s led to theformation of the celltheory.Visual Concept: Cell TheoryDescribe what is being illustrated:Looking at CellsCells vary greatly in their size and shape. A cell’s shape reflects its function. Cell size is limited by a cell’s surfacearea-to-volume ratio.Cells can be branched, flat, round, or rectangular.All substances that enter or leave a cell must cross the surface of the cell.A cell’s ability to move substances across its surface can be estimated by finding its surfacearea-to-volume ratio. Cells with greater surface area-to-volume ratios can exchange substances moreefficiently. When comparing cells of the same shape, small cells have greater surface area-to-volumeratios than large cells. So, small cells function more efficiently than large cells.Cell FeaturesAll cells share common structural features, including a cell membrane, cytoplasm, ribosomes, andDNA. The cell membrane is the outer layer that covers a cell’s surface and acts as a barrierbetween the outside environment and the inside of the cell.The cytoplasm is the region of the cell within the cell membrane. The cytoplasm includes thefluid inside the cell called the cytosol. A ribosome is a cellular structure that makes proteins.The DNA of a cell provides instructions for making proteins, regulates cellular activities, andenables cells to reproduce.Features of Prokaryotic andEukaryotic CellsA prokaryote is anorganism made of a single

prokaryotic cell. Prokaryotic cells do not have a nucleus or other internal compartments. The genetic material of a prokaryotic cell is a single loop of DNA.For millions of years, prokaryotes were the only organisms on Earth.A eukaryote is an organism made up of one or more eukaryotic cells. All multicellular organismsare made of eukaryotic cells. The DNA of a eukaryotic cell is found in an internal compartment of the cell called thenucleus. All eukaryotic cells have membrane-bound organelles. An organelle is a small structurefound in the cytoplasm that carries out specific activities inside the cell.Each organelle in a eukaryotic cell performs distinct functions.The complex organization of eukaryotic cells enables them to carry out more specializedfunctions than prokaryotic cells.Visual Concept: Comparing Prokaryotes and EukaryotesDescribe what is being illustrated:Summary1. Microscope observations of organisms led to the discovery of the basic characteristics commonto all living things.2. A cell’s shape reflects its function. Cell size is limited by a cell’s surface area-to-volume ratio.3. The complex organization of eukaryotic cells enable them to carry out more specializedfunctions than prokaryotic cells.Concept Check1. How were cells discovered?2. Why does cell shape vary?3. What enables eukaryotes to perform more specialized functions than prokaryotes?Test Prep1. The discovery of cells is linked most directly withA. the development of the microscope.B. early investigations of causes of disease.C. observations of large, unicellular organisms.D. efforts to reproduce organisms in the lab.2. Eukaryotic cells differ from prokaryotic cells in that eukaryotic cellsA. have a nucleus.B. lack organelles.C. lack ribosomes.D. have a cell wall.3. The Dutch scientist Anton van Leewenhoek used a microscope that made objects appear 300 timeslarger than they were. If a cell appeared to be 6 mm long under this microscope, how long was thecell in real life?A. 0.02 mmB. 0.20 mmC. 0.05 mmD. 0.50 mm

Section 2: Inside the Eukaryotic CellThe Framework of the CellEukaryotic cells have an intricate network of protein fibers called the cytoskeleton whichprovides the interior framework of the cell. The cytoskeleton helps the cell move, keep its shape, and organize its parts. There are three different kinds of cytoskeleton fibers: microfilaments,microtubules, and intermediate fibers.Directing Cellular ActivityDNA contains instructions for making proteins which control most of the activity of the cell. The DNA of eukaryotic cells is stored in the nucleus. DNA instructions are copied as RNA messages, which leave the nucleus. In the cytoplasm,ribosomes use the RNA messages to assemble proteins.Nucleus A double membrane called the nuclear envelope surrounds the nucleus.Nuclear pores located on the nuclear envelope act as channels to allow certain molecules tomove in and out of the nucleus.The nucleolus is a structure within the nucleus where ribosome parts are made. These ribosome parts are transported out of the nucleus into the cytoplasm where they areassembled to form a complete ribosome.RibosomesEach ribosome in a cell is made of RNA and many different proteins. Ribosomes that are suspended in the cytosol are called “free” ribosomes. Free ribosomes make proteins that remain inside the cell.Ribosomes that are attached to the membrane of another organelle are called “bound”ribosomes. Bound ribosomes make proteins that are exported from the cell.Ribosomes can switch between being bound or free, depending on what proteins the cellneeds to make.Protein ProcessingSome proteins that a cell manufactures are needed outside the cell that makes them. Proteins that are sent outside the cell are packaged in vesicles. Vesicles are small,membrane-bound sacs that enclose the proteins and keep them separate from the rest of thecytoplasm.The endoplasmic reticulum and Golgiproteins for extracellular export.apparatus are organelles involved in preparingEndoplasmic Reticulum The endoplasmic reticulum, or ER, is an extensive system of internal membranesthat moves proteins and other substances through the cell.

The membranes of the ER are connected to the outer membrane of the nuclear envelope.The endoplasmic reticulum is divided into two portions: rough ER and smooth ER. The portion of the ER with attached ribosomes is called rough ER because it has arough appearance when viewed with an electron microscope.The portion of the ER with no attached ribosomes is called smooth ER because ithas a smooth appearance when viewed with an electron microscope.The ribosomes on the rough ER make proteins that are packaged into vesicles.Enzymes of the smooth ER make lipids and break down toxic substances.Visual Concept: Endoplasmic Reticulum (ER) and RibosomesDescribe what is being illustrated:Golgi Apparatus The Golgi apparatus is a set of flattened, membrane-bound sacs.The Golgi apparatus helps modify, sort, and package cell products for distribution.Making and Exporting Proteins The ribosomes located on the rough ER make proteins which then cross into the membranes of the ER. The ER membrane then pinches off and forms a vesicle around the proteins.Vesicles transport the proteins from the rough ER to the Golgi apparatus, where they aremodified by enzymes and repackaged in new vesicles.These new vesicles transport the modified proteins to the cell membrane to be released outsidethe cell.Storage and MaintenanceLysosomes Vesicles help maintain homeostasis by storing and releasing a variety of substances asthe cell needs them.A lysosome is a vesicle produced by the Golgi apparatus that contains enzymes that break downlarge molecules.Lysosomes recycle old or damaged organelles and digest food particles to providenutrients for the cell.Vacuoles A vacuole is a fluid-filled vesicle found in the cytoplasm of many plant cells.Plant cells contain a large compartment called the central vacuole, which stores water, ions,nutrients, and wastes.When water fills the central vacuole, the cell becomes rigid, allowing the plant to stand up.When the vacuole loses water, the cell shrinks, and the plant wilts.Visual Concept: VacuolesDescribe what is being illustrated:

Other Vacuoles Some protists have contractile vacuoles which pump excess water out of the cell inorder to control the concentration of salts and other substances.A food vacuole is another type of vacuole. It is formed when the cell membrane surrounds foodparticles outside the cell and pinches off to form a vesicle inside the cell.Energy ProductionCells need a constant source of energy. The energy for cellular functions is produced by chemical reactions that occur in themitochondria and chloroplasts. In both organelles, chemical reactions produce adenosineform of energy that fuels almost all cell processes.triphosphate (ATP), theChloroplastsA chloroplast is an organelle found in plant and algae cells that uses light energy to makecarbohydrates from carbon dioxide and water. Chloroplasts are surrounded by two membranes and have several stacks of flattened sacs whereenergy production takes place. Plant cells may have several chloroplasts.MitochondriaMitochondria are cell organelles that use energy from organic compounds to make ATP. Most of the ATP needed by a cell is produced inside mitochondria. Both animal and plant cellscontain mitochondria. A smooth outer membrane and a folded inner membrane surround a mitochondrion. ATP isproduced by enzymes on the folds of the inner membrane.Summary1. The cytoskeleton helps the cell move, keep its shape, and organize its parts2. DNA instructions are copied as RNA messages, which leave the nucleus. In the cytoplasm,ribosomes use the RNA messages to assemble proteins.3. The endoplasmic reticulum and Golgi apparatus are organelles involved in preparing proteinsfor extracellular export.4. Vesicles help maintain homeostasis by storing and releasing a variety of substances as the cellneeds them.5. The energy for cellular functions is produced by chemical reactions that occur in themitochondria and chloroplasts.Concept Check1. What does the cytoskeleton do?2. How does DNA direct activity in the cytoplasm?3. What organelles are involved in protein production?

4. What are vesicles and vacuoles?5. How does the cell get energy?Test Prep4. Which organelle produces proteins that are exported from the cell?A. nucleolusB. rough ERC. free ribosomeD. bound ribosome5. Which structure helps a plant stand upright?A. lysosomeB. chloroplastC. central vacuoleD. contractile vacuole6. Ribosome : protein synthesis :: mitochondria :A. cell supportB. energy releaseC. nutrient storage D. protein transportThe graph shows the amount of ATP in the muscles of a squid after it had been exposed to low oxygenconcentrations.7. At what time during the experiment were the mitochondria inthe squid’s muscles producing the most energy?A. 0 minutesB. 15 minutesC. 30 minutesD. 45 minutesSection 3: From Cell to OrganismDiversity in CellsBoth prokaryotic and eukaryotic cells can have a variety of shapes and structures. The function of a cell is determined by its shape and the organelles found in the cell.The different organelles and features of cells enable organisms to function in unique ways indifferent environments.Diversity in ProkaryotesProkaryotes can vary in shape, the way they obtain and use energy, and their ability to move. Many prokaryotes have a flagellum, a long, hair-like structure that grows out of the cell andenables the cell to move through its environment. Prokaryotes may also have pili, short outgrowths that allow the cell to attach to surfaces orother cells.Eukaryotic Cell SpecializationEukaryotic cells can vary in shape and external features. Depending on their function, eukaryotic cells can also vary in their internal organelles. Forexample, muscle cells, which use large amounts of energy, contain many mitochondria. Animal and plant cells are two types of eukaryotic cells. Both have many of the sameorganelles, but plant cells also have chloroplasts, a large central vacuole, and a cell wall.Levels of OrganizationPlants and animals have many highly specialized cells that are arranged into tissues, organs, and organsystems.