ECA Cell Membranes: Directions: Work in your lab groups to answer the following questions, make sure each member of the group understands all the concepts. Any figures that are mentioned are found in the 8th Edition.

 

  1. What are the major components of cell membranes? Explain how the major components of cell membranes are amphipathic.  Why is this characteristic a major advantage?
  2. Are there any differences between prokaryotic and eukaryotic membranes?
  3. Relate the 2nd law of thermodynamics to the movement of materials through membranes.
  4. What factors affect plasma membrane permeability? (consider the composition of the membrane).
  5. Contrast tonicity with water potential (solute and water concentration). Compare and contrast diffusion with osmosis.
  6. Why is “equilibrium” dynamic? Compare animal and plant cells in terms of equilibrium. Why do plants prefer to exceed equilibrium and animal cells must maintain equilibrium?
  7. Explain “selectively permeable” using an example.
  8. Many systems rely on membranes to move materials, briefly explain what the nervous system, endocrine system, digestive system, and the excretory system moves by passive diffusion.
  9. How do cells move materials against the concentration gradient? (There are several ways, use examples).

ECA: Membranes and Organelles

1. What are the major similarities and differences between prokaryotes and eukaryotes? (Example: flagella in both types of organisms).

2. How does the existence of mitochondria and chloroplasts provide evidence to supports the "endosymbiotic theory"

3. How do the extracellular components and connections between cells coordinate cellular structure?

4. What are the major components of the fluid mosaic of the lipid membrane? What are the major functions of the components? How do the components contribute to the "fluidity" of the membrane?

5. What are the various functions of the membrane proteins (integral, transmembrane, peripheral)? (Figure 7.9) Include a discussion of the tertiary and quaternary structure of proteins and how polar, non-polar, acidic, and basic R groups contribute to structure and function.

6. What is the role of carbohydrates in cell-to-cell recognition?

7. What is the relationship between diffusion and osmosis? (2nd law of thermodynamics, concentration gradients, passive transport)

8. Discuss how biological membranes are selectively permeable. What role do transport proteins (channel, carrier, aquaporins) play in the movement of materials of through the membrane?

9. Why does water molecules require a transport protein (aquaporins) to move rapidly and in large quantities across a membrane? What structure must the aquaporin have to allow the movement of water? What is the difference between facilitated diffusion (ion channels and gated channels), cotransport and active transport (electrogenic pump and proton pump)? (Cite an example of each)

10.  Compare the relationships between tonicity (solute concentration) with water potential (water concentration) in plant and animal cells? Using the following word: hypertonic, isotonic, hypotonic, turgid, flaccid, plasmolyzed, diagram cells to demonstrate these conditions. Illustrate the movement of water.

11. Discuss bulk transport (exocytosis and endocytosis; phagocytosis, pinocytosis, and receptor-mediated endocytosis).

College Board Objectives:

1.B.1 Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today. Structural evidence supports the relatedness of all eukaryotes. Students should be able to demonstrate understanding of the above concept by using an illustrative example such as:

Cytoskeleton (is a network of structural proteins that facilitate cell movement, morphological integrity and organelle transport)

Nucleus

Membrane-bound organelles (mitochondria and/or chloroplasts)

Linear chromosomes

Endomembrane systems

Learning Objective: The student is able to pose scientific questions that correctly identify essential properties of shared, core life processes in order to provide insights into the history of life on earth.

 Learning Objective: The student is able to describe specific examples of conserved core biological processes shared by all domains or within one domain of life and how these shared, conserved core processes support the concept of common ancestry for all organisms.

Learning Objective: The student is able to justify the claim that organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.

BIG IDEA 2: Biological systems utilize energy and molecular building blocks to grow, to reproduce, and to maintain homeostasis.

2.A.3. Organisms must exchange matter with the environment to grow, reproduce, and maintain organization. a. Water and macronutrients are essential for energy transfer and building new molecules. Evidence of student learning is a demonstrated understanding of the following concepts:

3. Living systems depend on unique properties of water.

b. Differences in surface-to-volume ratios affect a biological system’s ability to obtain necessary resources or eliminate waste products. Evidence of student learning is a demonstrated understanding of the following concepts:

1. As surface area increases, volume increases, but the surface-to-volume ratio decreases.

2. The surface area of the plasma membrane must be large enough to adequately exchange materials; smaller cells have a more favorable surface area- to-volume ratio where diffusion is sufficient for exchange of materials with the environment.

3. As cells increase in volume, the relative surface area decreases, and demand for material resources increases; more cellular structures are necessary to adequately exchange materials and energy with the environment.

Learning Objective: The student is able to justify the selection of data relevant to the question of what types of molecules will an animal, plant, or bacterium take up as necessary building blocks and excrete as waste products.

Learning Objective: The student is able to graphically represent or quantitatively model relationships that exist when organisms exchange molecules with the environment and build new molecules to maintain organization.

Enduring Understanding 2.B. Growth, reproduction, and homeostasis require that cells create and maintain internal environments that are different from their external environments.

2.B.1. Cell membranes are selectively permeable due to their structure. a. Cell membranes are important because they separate the internal environment of the cell from the external environment. b. Selective permeability is a direct consequence of membrane structure, as noted in the fluid mosaic model. Evidence of student learning is a demonstrated understanding of the following concepts:

1. Cell membranes consist of a structural framework of phospholipid molecules, embedded proteins, cholesterol, glycoproteins, and glycolipids.

2. The phospholipids give the membrane both hydrophilic and hydrophobic properties. The hydrophilic phosphate portions of the phospholipids are oriented towards the aqueous external or internal environments, while the hydrophobic fatty acid portions face each other within the interior of the membrane itself.

3. Embedded proteins can be hydrophilic, with charged and polar side groups, or hydrophobic, with non-polar side groups.

4. Only small, uncharged polar molecules, including H2O and CO2, and hydrophobic substances (O2 and lipid-solubles) freely pass across the membrane; hydrophilic substances such as large polar molecules (including glucose) and ions move across the membrane through embedded channel and transport proteins. Water moves through channels proteins called aquaporins.

c. Cell walls provide structural boundaries, as well as a permeability barrier for some substances to the internal environments of plant cells. Cell walls are made of cellulose and are external to the cell membrane of plant cells.

Learning Objective: The student is able to pose scientific questions about the properties of cell membranes and selective permeability based on molecular structure.  Growth and homeostasis is maintained by the constant movement of molecules across membranes.

a. Passive transport does not require the input of energy; net flow of populations of molecules move from high concentration to low concentration.

1. Passive transport plays a primary role in the import of resources and the export of wastes.

2. Membrane proteins play a role in facilitated diffusion of charged and polar molecules through a membrane. There is no particular protein that is required for teaching this concept. Teachers are free to choose a protein that best fosters students’ understanding.

3. Internal environments of cells can be hypotonic, hypertonic, or isotonic to their external environments

 b. Active transport requires energy and moves molecules from low concentration to high concentration.

1. Active transport is a process where free energy provided by converting ATP to ADP is used by proteins embedded in the membrane to ―pump‖ molecules and/or ions across the membrane from low concentration to high concentration and to establish and maintain concentration gradients important for homeostasis.

2. Membrane proteins are necessary for active transport.

c. Exocytosis and endocytosis are processes by which large molecules are moved across cell membranes.

1. In exocytosis vesicles fuse with the plasma membrane to secrete large  macromolecules out of the cell.

2. In endocytosis the cell takes in macromolecules and particulate matter by forming new vesicles derived from the plasma membrane.

 Learning Objective: The student is able to construct models that connect the movement of molecules across membranes to cellular structure and function.

Learning Objective: The student is able to use representations and models to analyze situations or solve problems qualitatively and quantitatively to demonstrate that homeostasis is maintained by the active movement of molecules across membranes.  Eukaryotic cells maintain internal membranes that partition the cell into specialized regions.

a. Internal membranes facilitate cellular processes by minimizing conflicting interactions and increasing surface area where reactions can occur.

b. Compartmentalization or membrane-bound organelles localize different processes or enzymatic reactions.

c. Evidence of student learning and knowledge level is further clarified in 4.A.2.

Learning Objective: The student is able to explain how internal membranes and cell organelles contribute to cell functions.

Learning Objective: The student is able to use representations and models to describe how eukaryotic cells use internal membranes that partition the cell into specialized regions.

2.D.2. Homeostatic mechanisms reflect both continuity due to common ancestry and divergence due to adaptation in different environments. a. Continuity is attributed to common ancestry, while changes may occur in different environmental conditions. b. Organisms have various mechanisms for obtaining nutrients and ridding wastes. Students should be able to demonstrate understanding of the above concept by using an illustrative example such as:

Gas exchange in plants

Respiratory systems of animals

Nitrogenous waste production in animals

c. A sampling of homeostatic control systems and species of microbes, plants, and animals supports common ancestry. Students should be able to demonstrate understanding of the above concept by using an illustrative example such as:

Excretory systems in flatworms, earthworms, or vertebrates

Osmoregulation in freshwater and saltwater fish or protists

Osmoregulation in aquatic or terrestrial plants

Learning Objective: The student is able to describe changes in homeostatic mechanisms from an evolutionary perspective.

Learning Objective: The student is able to analyze data to identify patterns or relationships showing that homeostatic mechanisms reflect both continuity due to common ancestry and change due to evolution in different environments. Learning Objective: The student can refine representations and models to show that homeostatic mechanisms reflect both continuity due to common ancestry and change due to evolution in different environments.