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Transcript
Cell Structure and Function The Cell Cell Shape and Movement Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Cells come in many shapes and sizes. The size and shape of a cell is part of the function of the cell. Some cells, such as human red-blood cells, can be seen only by using a microscope. The cells can pass easily through small blood vessels because of their small size. Their disk shapes are important for carrying oxygen. Nerve cells have parts that jut out. These projections on nerve cells can send signals over long distances. Some plant cells are hollow. These hollow cells make up tubelike structures that can carry water and dissolved substances to parts of the plant. The size and shape of a cell make it possible for the cell to carry out its functions. The parts that make up a cell have their own functions as well. A cell’s parts are like the players on a football team who perform different tasks on the playing field. A cell is made up of different parts that perform different functions to keep the cell alive. Plant Cell Mitochondrion Rough endoplasmic reticulum Ribosome Smooth endoplasmic reticulum Central vacuole Cytoskeleton Vesicle Cell wall Genetic material Nucleus Nucleolus Nuclear membrane Chloroplast Cell membrane Golgi apparatus Cell Membrane All cells have some parts, or structures, in common. One of these structures is a cell membrane. A cell membrane is a flexible covering that protects the inside of a cell from the environment outside the cell. You can see the cell membrane in both drawings on this page. Cell membranes are made of proteins and phospholipids. Centriole Smooth endoplasmic reticulum Lysosome Cell membrane Rough endoplasmic reticulum Vesicle Nucleus Genetic material Nucleolus Nuclear envelope Golgi apparatus Ribosome Cytoskeleton Mitochondrion Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Animal Cell Cell Wall Every cell has a cell membrane. But some cells also have a cell wall. Plant cells, fungal cells, bacterial cells, and some protists have cell walls. A cell wall is a stiff structure outside the cell membrane. A cell wall protects a cell from viruses and cell wall helps the cell keep its shape and gives it support. Cell Appendages If you look at a cell using a microscope, you might see structures on the outside of the cell. These appendages might look like hairs or long tails. They often help a cell move. Flagella (fluh JEH luh) (singular, flagellum) are long and taillike. They whip back and forth to move the cell. Cilia (SIH lee uh) (singular, cilium) are short, hairlike structures. They can move a cell or move molecules away from a cell. The cilia in your windpipe move harmful particles away from your lungs. Cytoplasm and the Cytoskeleton The fluid inside a cell is made of water, salts, and other molecules and is called the cytoplasm. The cytoplasm contains a cell’s cytoskeleton. The cytoskeleton is made of threadlike proteins that are joined together. The cytoskeleton is a framework that gives a cell its shape and helps it move. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Cell Types Microscopes helped scientists discover that cells can be grouped into two types. There are prokaryotic (proh ka ree AH tihk) cells and eukaryotic (yew ker ee AH tihk) cells. Prokaryotic Cells The genetic material in a prokaryotic cell is not surrounded by a membrane. Look at the drawing below. Prokaryotic cells also do not have many of the cell parts other cells have. Most prokaryotic cells are unicellular organisms and are called prokaryotes. DNA Ribosome Cytoplasm Flagellum Cell membrane Cell wall Capsule Eukaryotic Cells The cells of plants, animals, fungi, and protists are eukaryotic cells. The genetic material of eukaryotic cells is surrounded by a membrane. Every eukaryotic cell also has organelles—other parts that are surrounded by a membrane and have specialized functions. Eukaryotic cells are usually larger than prokaryotic cells. Cell Organelles The organelles of eukaryotic cells have different functions in the cell. Organelles help a cell carry out different functions at the same time. These functions include getting energy from food, storing information, and getting rid of waste material. The Nucleus The largest organelle inside most eukaryotic cells is the nucleus. The nucleus is the part of a eukaryotic cell that directs cell activities and contains genetic information stored in DNA. DNA is in structures called chromosomes. The number of chromosomes in a nucleus is different for different species of organisms. Manufacturing Molecules You learned that proteins are important molecules in cells. Proteins are made of small organelles called ribosomes. A ribosome is not surrounded by a membrane. Ribosomes are in the cytoplasm of a cell. Ribosomes can be attached to an organelle called the endoplasmic reticulum (en duh PLAZ mihk • rih TIHK yuh lum), or ER. ER with ribosomes on its surface is called rough ER. Rough ER is where proteins are produced. ER without ribosomes on its surface is called smooth ER. It makes lipids such as cholesterol. Smooth ER also helps remove harmful substances from a cell. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. The nucleus also contains proteins and an organelle called the nucleolus (new KLEE uh lus). The nucleolus makes ribosomes, organelles that help produce proteins. Two membranes form the nuclear envelope that surrounds the nucleus. The nuclear envelope has many pores. Certain molecules, such as ribosomes and RNA, move into and out of the nucleus through these pores. Processing Energy All living things must have energy to survive. Cells process some energy in specialized organelles called mitochondria (mi tuh KAHN dree uh) (singular, mitochondrion). Most eukaryotic cells contain hundreds of mitochondria. Some cells in a human heart can contain 1,000 mitochondria. ATP A mitochondrion is surrounded by two membranes. Chemical reactions within mitochondria release energy. This energy is stored in high-energy molecules called ATP— adenosine triphosphate (uh DEH nuh seen • tri FAHS fayt). The energy in ATP molecules is used by the cell for growth, cell division, and transporting materials. Chloroplasts The cells of some organisms, such as plants and algae, contain organelles called chloroplasts (KLOR uh plasts). Chloroplasts are membrane-bound organelles that use light energy and make food, a sugar called glucose, from water and carbon dioxide in a process called photosynthesis (foh toh SIHN thuh sus). The sugar has stored energy that can be used when the cells need it. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. Processing, Transporting, and Storing Molecules The Golgi (GAWL jee) apparatus is an organelle that looks like a stack of pancakes. It gets proteins ready for their specific jobs. It then packages the proteins into tiny membrane-bound, ball-like structures called vesicles. Vesicles are organelles that transport substances to other parts of the cell. Some vesicles in an animal cell are called lysosomes. Lysosomes help break down and recycle different parts of the cell. Some cells also have structures called vacuoles (VA kyuh wohlz). Vacuoles are organelles that store food, water, and waste materials for a cell. A plant cell usually has one large vacuole. Some animal cells have many small vacuoles.
