8.1 Section Objectives – page 195 Explain how the processes of diffusion, passive transport, and active transport occur and why they are important to cells. Section Objectives: Predict the effect of a hypotonic, hypertonic, or isotonic solution on a cell.

Section 8.1 Summary – pages Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. Osmosis: Diffusion of Water In a cell, water always moves to reach an equal concentration on both sides of the membrane.

Section 8.1 Summary – pages The diffusion of water across a selectively permeable membrane is called osmosis. Osmosis: Diffusion of Water Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell.

Section 8.1 Summary – pages Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis. What controls osmosis? Before Osmosis After Osmosis Water molecule Sugar molecule Selectively permeable membrane

Section 8.1 Summary – pages Most cells whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions. Cells in an isotonic solution H2OH2O H2OH2O Water Molecule Dissolved Molecule

Section 8.1 Summary – pages Cells in an isotonic solution In an isotonic solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell. H2OH2O H2OH2O Water Molecule Dissolved Molecule

Section 8.1 Summary – pages Cells in an isotonic solution In an isotonic solution, water molecules move into and out of the cell at the same rate, and cells retain their normal shape. H2OH2O H2OH2O Water Molecule Dissolved Molecule

Section 8.1 Summary – pages Cells in an isotonic solution A plant cell has its normal shape and pressure in an isotonic solution.

Section 8.1 Summary – pages Cells in a hypotonic solution In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell. H2OH2O H2OH2O Water Molecule Dissolved Molecule

Section 8.1 Summary – pages Cells in a hypotonic solution Plant cells swell beyond their normal size as pressure increases.

Section 8.1 Summary – pages Cells in a hypertonic solution In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink. H2OH2O H2OH2O Water Molecule Dissolved Molecule

Section 8.1 Summary – pages Cells in a hypertonic solution Plant cells lose pressure as the plasma membrane shrinks away from the cell wall.

Section 8.1 Summary – pages Osmosis in action

Section 8.1 Summary – pages Passive Transport

Section 8.1 Summary – pages Active Transport Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell. Plasma membrane Concentration gradient Carrier proteins Cellular energy Step 1Step 2

Section 8.1 Summary – pages How active transport occurs

Section 8.1 Summary – pages Transport of Large Particles Endocytosis is a process by which a cell surrounds and takes in material from its environment. Endocytosis Exocytosis Digestion Nucleus Wastes

Section 8.1 Summary – pages Transport of Large Particles The material is engulfed and enclosed by a portion of the cell’s plasma membrane. Exocytosis Digestion Nucleus Wastes Endocytosis

Section 8.1 Summary – pages Transport of Large Particles The resulting vacuole with its contents moves to the inside of the cell. Exocytosis Digestion Nucleus Wastes Endocytosis

Section 8.1 Summary – pages Transport of Large Particles Exocytosis is the expulsion or secretion of materials from a cell. Endocytosis Exocytosis Digestion Nucleus Wastes

Section 8.1 Summary – pages Transport of Large Particles Endocytosis and exocytosis both move masses of material and both require energy. EndocytosisExocytosis Digestion Nucleus Wastes

Let’s Recap! Watch this short video on passive and active transport ! Active transport video

Section 1 Check Question 1 B. endocytosis A. active transport The diffusion of water across a selectively permeable membrane is called __________. Water molecule Sugar molecule Selectively permeable membrane

Section 1 Check Question 1 D. osmosis C. exocytosis The diffusion of water across a selectively permeable membrane is called __________. Water molecule Sugar molecule Selectively permeable membrane

Section 1 Check The answer is D, osmosis. Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within the cell. Water molecule Sugar molecule Selectively permeable membrane Before osmosisAfter osmosis

Section 1 Check What is the expected result of having an animal cell in a hypertonic solution? Question 2 D. The cell retains its normal shape. C. The cell swells up. A. The cell shrivels up. B. The plasma membrane shrinks away from the cell wall.

Section 1 Check The answer is A. In a hypertonic solution, cells experience osmosis of water out of the cell. Animal cells shrivel because of decreased pressure in the cells. H2OH2O H2OH2O Water molecule Sugar molecule

Section 1 Check A grocer mists the celery display with water to keep it looking fresh. What type of solution is the celery now in? Question 3 D. exotonic C. hypertonic B. hypotonic A. isotonic

Section 1 Check The answer is B. Plant cells contain a rigid cell wall and do not burst even in a hypotonic solution.

Plasma membrane Section 1 Check Transport of materials across the plasma membrane that does not require energy from the cell but does use transport proteins is called __________. Question 4 B. simple diffusion A. osmosis Concentration gradient Channel proteins

Section 1 Check Transport of materials across the plasma membrane that does not require energy from the cell but does use transport proteins is called __________. Question 4 D. active transport C. facilitated diffusion Plasma membrane Concentration gradient Channel proteins

Section 1 Check The answer is C. Facilitated diffusion is a type of passive transport and requires no energy from the cell. Plasma membrane Concentration gradient Channel proteins