Name:

Biology 12: Cell MembraneText:

Vocabulary:

active transport, carbohydrates, carrier protein, cell membrane, channel protein, cholesterol, concentration gradient, diffusion, endocytosis, exocytosis, facilitated transport, fluid-mosaic membrane model, glycolipid, glycoprotein, hydrophilic, hydrophobic, hypertonic, hypotonic, isotonic, osmosis, passive transport processes, phagocytosis, phospholipid, phospholipid bilayer, pinocytosis, pressure gradient, protein, selectively permeable, surface area-to-volume ratio, tonicity

Goals:

B9 Analyse the structure and function of the cell membrane

B9.1 apply knowledge of organic molecules – including phospholipids, proteins, glycoproteins, glycolipids, carbohydrates, and cholesterol – to explain the structure and function of the fluid-mosaic membrane model

B9.2 identify the hydrophobic and hydrophilic regions of the phospholipid bilayer

B9.3 explain why the cell membrane is described as “selectively permeable”

B9.4 describe passive transport processes including diffusion, osmosis, and facilitated transport

B9.5 explain factors that affect the rate of diffusion across a cell membrane (e.g., temperature, size of molecule, charge of molecule, concentration gradient, pressure gradient)

B9.6 predict the effects of hypertonic, isotonic, and hypotonic environments on osmosis in animal cells

B9.7 describe active transport processes including active transport, endocytosis (phagocytosis and pinocytosis), and exocytosis

B9.8 compare specific transport processes – including diffusion, osmosis, facilitated transport, active transport, endocytosis, and exocytosis – in terms of

– concentration gradient, use of channel or carrier protein, use of energy, types/sizes of molecules transported

B9.9 devise an experiment using the scientific method (e.g., to investigate the tonicity of cells)

B10 Explain why cells divide when they reach a particular surface area-to-volume ratio

B10.1 differentiate between cells that have a high or low surface area-to-volume ratio

B10.2 demonstrate an understanding of the significance of surface area-to-volume ratio in cell size

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Part A: Cell Membrane Structure

-Why does our cell membrane exist as a phospholipid bilayer? Why not a monolayer?

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-Examine the diagram above. The phospholipid bilayer is called a fluid-mosaic model. What part is fluid and what does the term mosaic refer to?

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-What role does cholesterol have in animal cell membranes?

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-Cell membrane proteins have a variety of functions:

a) Transport can be facilitated (passive) or active (energy required)

c) Signal molecules do not enter the cell, but the effect they have on the membrane protein is relayed into the cell.

d) Glycoproteins have sugars added to them and allow cells to recognize each other. This is how white blood cells recognize dangerous pathogens.

e) Proteins can help to keep the cells of a tissue together (e.g. blood vessels would leak if cells separated).

Part B: How do Substances Cross the Cell Membrane?

1. Diffusion

-Examine the diagram below. How does diffusion work?

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-Can all molecules diffuse freely through the cell membrane?

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-What are some molecules that can pass through the membrane by simple diffusion?

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2. Passive Transport and Active Transport

-Examine the diagram right. What is the difference between diffusion and facilitated diffusion?

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-What type of molecules require facilitated transportation to cross the cell membrane?

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-What do you think the difference is between Passive and Active Transport?

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-There are three active methods of transport:

a) Active Transport

-Sodium Potassium Pump uses energy to transport sodium against its concentration gradient.

-Potassium follows its [gradient].

-What is the cell membrane’s net change in charge created by this process?

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b) Exocytosis

-What is exocytosis and what molecules would leave the cell in this way?

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-Why is exocytosis considered a form of active transport?

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c) Endocytosis

-What is endocytosis and in what cells would it occur frequently?

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-What happens to the vesicle?

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-Why is endocytosis considered a form of active transport?

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-There are two types of endocytosis. What is the difference between them?

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3. Rate of Diffusion

-Brainstorm with a peer, what factors do you think would influence the rate at which diffusion occurs?

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4. Osmosis

-Osmosis is the movement of H2O from [High] to [Low] across a selectively permeable membrane to reach equilibrium.

-Water is actually moving from areas with high amounts of free water molecules-less solute (hypotonic)- to areas with lower amounts of free water molecules-more solute (hypertonic).

-Why is there a difference in plant and animal cells’ responses to being placed in isotonic (equal [solute]), hypotonic (lower [solute]) and hypertonic (higher [solute]) solutions?

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*Complete the concept map to help you understand how substances cross the cell membrane.

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Part B: Cell Membrane Surface vs Cell Volume

-The diagram right shows the size of animal and plant cells in relation to a standardized measurement system and other biological materials.

-Examine the diagram below. What does it suggest about cell size?

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-Why are cells’ size limited by their surface area to volume ration?

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-What is a way that we might be able to improve the surface area of the cell membrane to volume of the cytoplasm ration? Draw your solutions below.

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