7.2 Cell Structure Lesson Summary Cell Organization Eukaryotic cells contain a nucleus and many specialized structures. Cytoplasm is the fluid portion of a cell. Organelles are structures that have specialized functions in eukaryotic cells. The nucleus contains DNA and controls the activity of a cell. Organelles That Store, Clean Up, and Support These structures include: vacuoles: membrane-enclosed saclike structures that store water, salts, and organic molecules lysosomes: small organelles filled with enzymes that break down large molecules and organelles that are no longer useful the cytoskeleton: a network of protein filaments; it helps the cell maintain its shape and is involved in movement centrioles: organelles made from tubulins; they help organize cell division in animal cells Organelles That Build Proteins Three kinds of organelles work with the nucleus to make and distribute proteins: ribosomes: small particles of RNA and protein found throughout the cytoplasm in all cells; they produce proteins by following coded instructions from DNA the endoplasmic reticulum (ER): an internal membrane system where lipid components of the cell membrane are assembled, along with proteins and other materials the Golgi apparatus: an organelle that appears as a stack of flattened membranes; it modifies, sorts, and packages proteins and other materials from the ER for storage in the cell or release outside the cell Organelles That Capture and Release Energy Two types of organelles act as power plants of the cells. Both types are surrounded by two membranes. Chloroplasts capture the energy from sunlight and convert it into food that contains chemical energy in a process called photosynthesis. Cells of plants and some other organisms contain chloroplasts, which contain chlorophyll. Mitochondria are found in nearly all eukaryotic cells; they convert the chemical energy stored in food to a usable form. 101
Cellular Boundaries All cells are surrounded by a cell membrane. Many cells also have a cell wall. Both cell membranes and cell walls separate cells from the environment and provide support. Cell walls support, shape, and protect the cell. Most prokaryotes and many eukaryotes have them. Animals do not have cell walls. Cell walls lie outside the cell membrane. Most cell walls allow materials to pass through them. A cell membrane consists of a lipid bilayer, a strong but flexible barrier between the cell and its surroundings. The cell membrane regulates what enters and leaves the cell and also protects and supports the cell. Most biological membranes are selectively permeable, allowing some substances, but not others, to pass across them. Lesson Objectives Describe the structure and function of the cell nucleus. Describe the role of vacuoles, lysosomes, and the cytoskeleton. Identify the role of ribosomes, endoplasmic reticulum, and Golgi apparatus in making proteins. Describe the function of the chloroplasts and mitochondria in the cell. Describe the function of the cell membrane.
BUILD Vocabulary A. The chart below and on the next page shows key words from the lesson with their definitions. B. Term Definition Structure around plant cells, fungus cells, and some bacterial cells that supports and protects Structure in animal cells that helps organize cell division Structure in plant cells that captures the sun s energy and changes it into chemical energy Fluid portion of the cell outside the nucleus Network of protein filaments that gives a cell its shape and organizes its organelles Internal membrane system of a cell where proteins are assembled Series of flattened sacs that prepares proteins and other materials for export from the cell Enzyme-filled structure that breaks down complex molecules or worn-out organelles Organelle that changes the chemical energy in food into a form that is easier for the cell to use Structure within a cell that acts like a specialized organ Structure that assembles proteins Saclike structure that stores materials like water and nutrients
BUILD Understanding Venn Diagram A Venn diagram is made up of overlapping circles. It is a useful tool for comparing two or even three topics. Use terms from the box to complete the Venn diagram. cell membrane cytoskeleton mitochondria cell wall DNA found in cytoplasm nucleus containing DNA centriole endoplasmic reticulum ribosome chloroplast Golgi apparatus vacuole cytoplasm lysosome Prokaryotes Eukaryotes Both
Cell Organization An organelle is a specialized cell structure. Each organelle functions in a different way. All of the organelles help the cell carry out life processes. Use the terms in the box to write the name of the organelle underneath its picture. endoplasmic reticulum Golgi apparatus mitochondrion nucleus Organelle Function Controls most cell processes and stores genetic material Where lipid parts of the cell membrane and proteins for export are assembled and stored Modifies, sorts, and packages materials from the endoplasmic reticulum Converts the energy stored in food into a more usable form BUILD Connections The Cell As a Living Factory An analogy takes two things that seem to be different and shows how they can be similar. 1. If the cell were a factory, what part would serve as the main office? 2. Which cell part would provide electricity? 3. With a partner, discuss how the actions of the forklifts are related to actions in cells. 99
Cell Organization Follow the directions. 1. Use the words below to label the plant cell. Some structures have been labeled for you. cell wall mitochondrion ribosome chloroplast nucleus vacuole Plant Cell smooth endoplasmic reticulum Golgi apparatus rough endoplasmic reticulum cell membrane 2. Use the words below to label the animal cell. Some structures have been labeled for you. cell membrane mitochondrion rough endoplasmic reticulum Golgi apparatus nucleus ribosome Animal Cell smooth endoplasmic reticulum centrioles Use the diagrams to answer the questions. 3. Which structure is found in a plant cell but not in an animal cell? Circle the correct answer. chloroplast cell membrane ribosome 4. What is the main function of vacuoles? 100