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Chapter 7: Structure and Function - Summary "Seeing is believing" - microscopes weren't used until the 1600s Robert Hooke: Used a microscope to look at cork and coined the term "cells" One of the First Microscopes: Anton von Leewenhoek. FIRST person to OBSERVE and DESCRIBE MICROSCOPIC ORGANISMS and LIVING CELLS. 1665, the English Scientist Robert Hooke used a microscope to examine a thin slice of cork and described it as consisting of "a great many little boxes". It was after his observation that Hook called what he saw "Cells". They looked like "little boxes" and reminded him of the small rooms in which monks lived, so he called the "Cells". 1838, German Botanist Matthias Schleiden studied a variety of PLANTS and concluded that all PLANTS "ARE COMPOSED OF CELLS". The next year, German Zoologist Theodor Schwann reported that ANIMALS are also made of CELLS and proposed a cellular basis for all life. 1855, German Physician Rudolf Virchow induced the cell theory: 1. All living things are composed of cells 2. Cells are the basic unit of structure and function 3. new cells come from preexisting cells CELL DIVERSITY Not all cells are alike. Even cells within the same organism show Enormous Diversity in Size, Shape, and Internal Organization. Your Body contains at least 200 Different Cell Types. CELL SIZE A few types of cells are large enough to be seen by the unaided eye. The Female Egg is the largest cell in the body, and can be seen without the aid of a microscope. MOST CELLS ARE SMALL FOR TWO REASONS: A. Cells are limited in size by the RATIO between their Outer Surface Area and Their Volume. A SMALL CELL HAS MORE SURFACE AREA THAN A LARGE CELL FOR A GIVEN VOLUME OF CYTOPLASM. This is important because the nutrients, oxygen, and other materials a cell requires must enter through it surface. As a cell grows larger at some point its surface area becomes too Small to allow these materials to enter the cell quickly enough to meet the cell's need. B. THE CELL'S NUCLEUS (THE BRAIN) CAN ONLY CONTROL A CERTAIN AMOUNT OF LIVING, ACTIVE CYTOPLASM. CELL SHAPE Cells come in a variety of Shapes. the shape is determined by its function INTERNAL ORGANIZATION Cells contain a variety of Internal Structures called ORGANELLES. (PERFORMS SPECIFIC FUNCTIONS FOR THE CELL.) The entire cell is Surrounded by A THIN MEMBRANE, called the CELL MEMBRANE. NUCLEUS. IT CONTAINS THE CELL'S AND CONTROLS THE ACTIVITIES OF THE A Large Organelle near the Center of the Cell is the GENETIC INFORMATION CELL. The PRESENCE OR ABSENCE of a NUCLEUS is important for Classifying Cells. ORGANISMS WHOSE CELL CONTAIN A NUCLEUS AND OTHER MEMBRANE-BOUND ORGANELLES ARE CALLED EUKARYOTES. ORGANISMS WHOSE CELLS NEVER CONTAIN (OR LACK) A NUCLEUS AND OTHER MEMBRANE-BOUND ORGANELLES ARE CALLED PROKARYOTES. UNICELLULAR ORGANISMS such as bacteria and their relatives are Prokaryotes. All other organisms are Eukaryotes; plants, fish, mammals, insects and humans. PARTS OF THE EUKARYOTIC CELL Eukaryotic Cells generally have THREE Main Components: A Cell Membrane, A Nucleus, and other Organelles. THE NUCLEUS (plural, Nuclei) The Nucleus is the CONTROL CENTER (BRAIN) of the Cell. Most Cells have a Single Nucleus some cells have more than one. The nucleus is surrounded by a Double Layer Membrane called the NUCLEAR ENVELOPE. The Nucleus contains DNA, the HEREDITARY MATERIAL OF CELLS. The DNA is in the form of a long Strand called CHROMATIN. During Cell Division, Chromatin strands COIL and CONDENSES into thick structures called CHROMOSOMES. RIBOSOMES (RIE-buh-SOHMZ) Ribosomes Are Not Surrounded by a membrane. They are the site of PROTEIN SYNTHESIS (Production or Construction) in a cell. ENDOPLASMIC RETICULUM (ER) (EN-doh-PLAZ-mik ri-TIK-yuh-luhm) The ER is a system of membranous tubules and sacs which act as an Intracellular Highway, which transports materials through the cell. It Can be ROUGH OR SMOOTH. A. ROUGH ER is studded with RIBOSOMES and processes PROTEINS to be exported from the cell. B. SMOOTH ER IS NOT Covered with RIBOSOMES and processes LIPIDS and CARBOHYDRATES. The Smooth ER is involved in the synthesis of steroids in gland cells, the regulation of calcium levels in muscle cells, and the breakdown of toxic substances by liver cells. CYTOPLASM (SIET-oh-PLAZ-uhm) EVERYTHING BETWEEN THE CELL MEMBRANE AND THE NUCLEUS IS THE CELL'S CYTOPLASM. GOLGI APPARATUS (GOHL-jee) The Golgi Apparatus is the Processing, Packaging and Secreting Organelle of the Cell that is made of flattened SAC . LYSOSOMES (LIE-suh-sohmez) Lysosomes are small spherical organellesthat are filled with enzymes. It's function is digestion, or breakdown of lipids, carbs, and proteins. VACUOLES The SECOND prominent structure in Plant Cells is the large VACUOLE. The VACUOLE is a large membrane-bound sac that takes up a large amount of space in most Plant Cells. MITOCHONDRIA (MET-oh-KAHN-dree-uh) Mitochondria are the sites of Chemical Reactions that transfer Energy from Organic Compounds to ATP (Cellular Respiration). Energy contain in food is released. Converted to ATP. ATP is the molecule that most Cells use as their main Energy Currency. THE "POWERHOUSE" OF THE CELL. PLASTIDS A common kind of PLASTID is the CHLOROPLAST, (figure 4-17) an organelle that converts SUNLIGHT, CARBON DIOXIDE, AND WATER INTO SUGARS. This process is called PHOTOSYNTHESIS. CYTOSKELETON In Animal Cells, an internal framework called CYTOSKELETON maintains the Shape of the Cell and helps it to move.The CYTOSKELETON consists of TWO Types of structures: MICROFILAMENTS AND MICROTUBULES. CILIA AND FLAGELLA Cilia and Flagella are Hairlike Organelles that extend from the surface of the cell, where they assist in movement. CILIA ARE SHORT HAIRLIKE PROJECTIONS. FLAGELLA ARE LONG WHIPLIKE PROJECTIONS. PLANT CELLS 1. Most of the Organelles and other parts of the cell are common in ALL Eukaryotic Cells. Cell from different organisms have even greater difference in structure. 2. Plant Cells have Three Additional Structures Not found in animals cells - CELL WALLS, VACUOLES, AND PLASTIDS that are extremely important to Plant Function. 3. In addition to their unique structures, Plant Cells have: MITOCHONDRIA, RIBOSOMES, AND the other organelles. THE CELL MEMBRANE The Cell Membrane is a complex barrier separating the cell from it's external environment. The "Selectively Permeable" Membrane regulates what passes into and out of the cell. All cells, from all organisms, are surrounded by a CELL MEMBRANE. Cell Membranes are made mostly of PHOSPHOLIPID MOLECULES. (Figure 4-5) Phosphate + Lipid. Phospholipids are a kind of Lipid that consists of TWO FATTY ACIDS (TAILS), and PHOSPHATE GROUP (HEADS). The Phosphate Head is HYDROPHILIC meaning "WATER LOVING". Because of its hydrophilic nature, the head of a Phospholipid will orient itself so is as close as possible to water molecules. The Lipid Tails are HYDROPHOBIC meaning "WATER-FEARING", the Hydrophobic tails will tend orient themselves away from water. that it to Cell Membranes CONSIST of TWO Phospholipid LAYERS Called a LIPID BILAYER. (Figure 4-5) MEMBRANE PROTEINS (Refer to Figure 4-5) Some Proteins are Attached to the surface of the cell membrane, these are called PERIPHERAL PROTEINS, and are located on both the Internal and External Surface. The Proteins that are Embedded in the Lipid Bilayer are called INTEGRAL PROTEINS. Carbhydrates act as "ID" tags for the cells CELL WALL One of the most important differences between Plant and Animal CELLS is the Presence of a CELL WALL IN PLANT CELLS. A Cell Wall DOES NOT REPLACE the Cell Membrane; Cells with WALLS also have a CELL MEMBRANE. Plant Cells are covered by a Rigid Cell Wall that lies Outside the Cell Membrane. PASSIVE TRANSPORT Cell membranes help organisms maintain Homeostasis by controlling what substances may enter or leave cells. Some substances can cross the cell membrane without any input of Energy by the cell. The movement of such substances across the membrane is known as PASSIVE TRANSPORT. To stay alive, a CELL MUST EXCHANGE Materials such as Food and Waste With Its ENVIRONMENT. These materials must cross the Cell Membrane. DIFFUSION The Simplest type of PASSIVE TRANSPORT, Does Not require the cell to use Energy, is DIFFUSION. THE MOVEMENT OF MOLECULES FROM AN AREA OF HIGHER CONCENTRATION TO AN AREA OF LOWER CONCENTRATIONS. This difference in the Concentration of Molecules across a space is called a CONCENTRATION GRADIENT. DIFFUSION ALWAYS OCCURS DOWN A CONCENTRATION GRADIENT, FROM THE AREA OF GREATER or HIGHER CONCENTRATION TO THE AREA OF LESS OR LOWER CONCENTRATION. When the Concentration of the molecules of a Substance is the Same Throughout a Space, a State of EQUILIBRIUM EXISTS. OSMOSIS THE PROCESS BY WHICH WATER MOLECULES DIFFUSE ACROSS A CELL MEMBRANE FROM AN AREA OF HIGHER CONCENTRATION TO AN AREA OF LOWER CONCENTRATION IS CALLED OSMOSIS. OSMOSIS OCCURS IN RESPONSE TO THE CONCENTRATION OF SOLUTES DISSOLVED IN WATER. Water Moves from AREAS of LOW Solute Concentration to AREAS of HIGH Solute Concentration. Water will cross the Membrane toward the Higher Solute Concentration until the Concentration Gradients of BOTH WATER and SOLUTES EVEN OUT. 11. The Net Direction of Osmosis DEPENDS on the Relative IN A HYPERTONIC SOLUTION, THE CONCENTRATION OF SOLUTE MOLECULES OUTSIDE THE CELL IS HIGHER THAN THE CONCENTRATION OF SOLUTES INSIDE THE CELL CYTOSOL. WATER DIFFUSES OUT OF THE CELL until Equilibrium is established. If the cell loses too much water, the cell will shrivel and shrink. PLASMOLYSIS 16. IN A HYPOTONIC SOLUTION, THE CONCENTRATION OF SOLUTE MOLECULES OUTSIDE THE CELL IS LOWER THAN THE CONCENTRATION OF SOLUTES INSIDE THE CELL CYTOSOL. WATER DIFFUSES INTO THE CELL until Equilibrium is established. The Flow of water into a cell causes it to swell.CYTOLYSIS Plant Cells do not burst because of their Rigid Cell Wall. The pressure that Water molecules exert against the cell wall is called TURGOR PRESSURE. IN AN ISOTONIC SOLUTION, THE CONCENTRATION OF SOLUTES OUTSIDE AND INSIDE THE CELL ARE EQUAL. FACILITATED DIFFUSION is PASSIVE TRANSPORT across a Membrane requires NO ENERGY and ALWAYS occurs DOWN A CONCENTRATION GRADIENT. Some Molecules are CARRIED across by CARRIER PROTEINS EMBEDDED IN the Cell Membrane that CHANGE SHAPE when Molecules ATTACH to them. Ex: Glucose into the Cell. ACTIVE TRANSPORT (USE OF ENERGY) In many cases, cells must move materials up their concentrated gradient, from and area of lower concentration to an area of higher concentration. Such movement of materials is known as ACTIVE TRANSPORT. Unlike Passive Transport, Active Transport REQUIRES A CELL TO EXPEND ENERGY (ATP). CELL MEMBRANE PUMPS Cells often move molecules across the membrane AGAINST a Concentration Gradient. From an area of LOW Concentration to areas of HIGH Concentration. Active Transport often involves CARRIER PROTEINS like those in Facilitated Diffusion. The CARRIER PROTEINS act as PUMPS that USE ENERGY to move IONS and Molecules across the membrane. SODIUM-POTASSIUM PUMPS ARE IMPORTANT FOR MUSCLE CONTRACTIONS, THE TRANSMISSION OF NERVE IMPULSES, AND THE ABSORPTION OF NUTRIENTS. SODIUM-POTASSIUM PUMPS IN ANIMAL CELLS PUMP SODIUM IONS OUT, AND POTASSIUM IN, UP THEIR CONCENTRATION GRADIENT. TYPES OF BULK TRANSPORT, INCLUDING ENDOCYTOSIS,EXOCYTOSIS, PINOCYTOSIS, AND PHAGOCYTOSIS. During ENDOCYTOSIS the Cell Membrane (figure 5-7) Folds into a POUCH that Encloses the Particles that pinches off INSIDE the Cell to form a VESICLE (membrane-wrapped bubbles). PINOCYTOSIS IS SOMETIMES CALLED "CELL DRINKING". PHAGOCYTOSIS IS LIKE PINOCYTOSIS, EXCEPT THE CELL ENGULFS A FOOD PARTICLE OR OTHER CELLS INSTEAD OF A DROP OF LIQUID. "CELL EATING" DURING EXOCYTOSIS, WASTE AND CELL PRODUCTS LEAVE THE CELL. Unicellular organisms vs. multicellular organisms Cell take on specific tasks - cell specialization Levels of organization In most Multicellular Organisms, we find the following organization: Cellular Level: The smallest unit of life capable of carrying out all the functions of living things. Tissue Level: A group of cells that performs a specific function in an organism form the TISSUE. Organ Level: Several different types of tissue that function together for a specific purpose form an ORGAN. Organ System Level: Several organs working together to perform a function make up an ORGAN SYSTEM. The different organ systems in a multicellular organism interact to carry out the processes of life Organismal Level: all organ systems working together to form an organism