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7-4 Cellular Transport Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Cell Size • Surface area-to-volume ratios affect a biological system’s ability to obtain necessary resources or eliminate wastes • As cells increase in volume, the relative surface area decrease and demand for material resources increases – More cellular structures are necessary to adequately exchange materials and energy with the environment Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Cell Size Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Cell Size • The surface area of the plasma membrane must be large enough to adequately exchange materials – In other words, smaller cells have a more favorable surface area-to-volume ratio for exchange of materials with the environment. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Cell Size • Examples of how increasing surface area increases the function of the cell include – Root hairs - increases water absorption in roots of plants – Cells of the alveoli - increase gas exchange in the lungs – Cells of the villi or microvilli - increases absorption of food in the intestinal lining Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Root Hairs Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Alveoli Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Diffusion • Recall that when organisms adjust internally to changing external conditions they are maintaining homeostasis • One way cells maintain homeostasis is by controlling the movement of substances across their cell membrane. • Cells must use energy to transport some substances across the cell membrane by active transport • Other substances move across the cell membrane without any use of energy by the cell by passive transport. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Diffusion, continued Random Motion and Concentration • Movement across the cell membrane that does not require energy from the cell is called passive transport. • A difference in the concentration of a substance across a space is called a concentration gradient. • Equilibrium is a condition in which the concentration of a substance is equal throughout a space. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Equilibrium Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Diffusion, continued Movement of Substances • The movement of a substance from an area of high concentration to an area of lower concentration caused by the random motion of particles of the substance is called diffusion. • Many substances, such as molecules and ions dissolved in the cytoplasm and in the fluid outside cells, enter or leave cells by diffusing across the cell membrane. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Diffusion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Diffusion, continued • Because of diffusion, food coloring (blue) will gradually move through uncolored gelatin (yellow), as shown in the beakers below. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. • https://www.youtube.co m/watch?v=VY0mZUDv bH4&index=3&list=PLql JYrIFRy9W9GhPxERL7TYWgO3xYtSR Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Osmosis • The diffusion of water through a selectively permeable membrane is called osmosis. • Like other forms of diffusion, osmosis involves the movement of a substance—water—down its concentration gradient. • Osmosis is a type of passive transport. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Osmosis Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Osmosis https://www.youtube.com/watch?v=La3m hoghCBQ&index=2&list=PLqlJYrIFRy9W 9Gh-PxERL7TYWgO3xYtSR Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Osmosis, continued There are three possibilities for the direction of water movement: • Water moves out. When water diffuses out of the cell, the cell shrinks. A solution that causes a cell to shrink due to osmosis is a hypertonic solution. • Water moves in. When water diffuses into the cell, the cell swells. This is a hypotonic solution. – If too much water enters the cell it will rupture. • No net water movement. A solution that produces no change in cell volume because of osmosis is called an isotonic solution. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Osmosis, continued • In a hypertonic solution a plant cell will lose water, mainly from the central vacuole. The membrane shrinks away from the cell wall. This causes wilting. [plasmolysis] • In a hypotonic solution the central vacuole fills with water, pushing the membrane against the cell wall. The cell becomes firmer because turgor pressure has increased. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Hypertonic, Hypotonic, and Isotonic Solutions Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Crossing the Cell Membrane Diffusion Through Ion Channels • An ion channel is a transport protein with a polar pore through which ions can pass. • The pore of an ion channel spans the thickness of the cell membrane. • An ion that enters the pore can cross the cell membrane without contacting the nonpolar interior of the lipid bilayer. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Ion Channels Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Diffusion Through Ion Channels Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Crossing the Cell Membrane Facilitated Diffusion • Most cells also have a different kind of transport protein, called carrier proteins, that can bind to a specific substance on one side of the cell membrane, carry the substance across the cell membrane, and release it on the other side. • When carrier proteins are used to transport specific substances—such as amino acids and sugars—down their concentration gradient, that transport is called facilitated diffusion. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Facilitated Diffusion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. • https://www.youtube.com/watch?v=vKGN_Zhz8AY&i ndex=4&list=PLqlJYrIFRy9W9GhPxERL7TYWgO3xYtSR Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 1 Passive Transport Passive Transport: Facilitated Diffusion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Active vs. Passive • Passive Transport = High Concentration Low Concentration – No energy expenditure from the cell. • Active Transport = Low Concentration high Concentration – Energy need; ATP Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 2 Active Transport Comparing Active and Passive Transport Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 2 Active Transport Movement Against a Concentration Gradient • The transport of a substance across the cell membrane against its concentration gradient is called active transport. (Requires Energy) • Most often, the energy needed for active transport is supplied directly or indirectly by ATP. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 2 Active Transport Active Transport Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 4 Section 2 Active Transport Movement Against a Concentration Gradient, continued Sodium-Potassium Pump • One of the most important membrane pumps in animal cells is a carrier protein called the sodium-potassium pump. • In a complete cycle, the sodium-potassium pump transports three sodium ions, Na+, out of a cell and two potassium ions, K+, into the cell. • Without the pump, the sodium ions in the cell would cause water to diffuse into the cell in turn causing it to burst. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 2 Active Transport Sodium-Potassium Pump Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 2 Active Transport Sodium-Potassium Pump https://www.youtube.com/wa tch?v=P-imDC1txWw Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. https://www.youtube.com/watch ?v=yz7EHJFDEJs Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 2 Active Transport Movement in Vesicles • Many substances, such as proteins and polysaccharides, are too large to be transported by carrier proteins. These substances are moved across the cell membrane by vesicles. • The movement of a substance into a cell by a vesicle is called endocytosis. • The movement of a substance by a vesicle to the outside of a cell is called exocytosis. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. • https://www.youtube.com/watch?v=qpw2p1x9Cic&list =PLqlJYrIFRy9W9GhPxERL7TYWgO3xYtSR&index=5 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 2 Active Transport Endocytosis and Exocytosis Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 7 Section 2 Active Transport Endocytosis and Exocytosis Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. • https://www.youtube.com/watch?v=prfMUwjobo8 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.
