Every objective will NOT necessarily be covered during class time; you will be independently responsible for some of them.

  1. Explain how the phospholipid bilayer structure of the cell membrane contributes to the cell membrane’s strength, flexibility, and selective permeability
  2. Identify which molecules can and cannot diffuse directly across the phospholipid bilayer
  3. Explain how the various components of the cell membrane (including integral and peripheral proteins, cholesterol, and glycoproteins) render the membrane a fluid mosaic model and how they enable its functions, including transport and communication
  4. Compare and contrast the four methods of transport across the cell membrane (simple diffusion, facilitated diffusion, osmosis, and active transport)
  5. Explain how endocytosis and exocytosis permit the transport of large quantities into and out of the cell
  6. Given information on relative concentrations, classify solutions on either side of a membrane as hypertonic, hypotonic, or isotonic, and identify the likely direction of net water movement and effect upon the size of the cell
  7. Name strategies cells have for managing water balance
  8. Calculate water potential, and interpret the results to determine likely direction of net water movement and effect upon the size of the cell
  9. Explain the implications of surface area to volume ratio for the optimum size of cells
  10. State the functions of key cell organelles, which cellular processes they participate in, and which types of cells contain each organelle*
  11. Connect the functions of cell organelles to their structures*
  12. Connect the functions of cell organelles to the functions of other cell organelles*

  • = self-study

Enduring Understandings

Enduring Understandings are the College Board's AP Biology course concepts that you need to know for the AP exam. Below, you'll find those Enduring Understandings relevant to this unit. Numbering and lettering matches the document linked from the main page of this website.
Every Enduring Understanding will NOT necessarily be covered during class time; you will be independently responsible for some of them.

A. Growth, reproduction and maintenance of the organization of living systems require free energy and matter.
3. Organisms must exchange matter with the environment to grow, reproduce and maintain organization.
  • e. Surface area-to-volume ratios affect a biological system’s ability to obtain necessary resources or eliminate waste products.
  • f. 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. These limitations restrict cell size.
  • g. 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 for exchange of materials with the environment.

B. Growth, reproduction and dynamic homeostasis require that cells create and maintain internal environments that are different from their external environments.
1. Cell membranes are selectively permeable due to their structure.
  • a. Cell membranes separate the internal environment of the cell from the external environment.
  • b. Selective permeability is a direct consequence of membrane structure, as described by the fluid mosaic model.
  • c. Cell membranes consist of a structural framework of phospholipid molecules, embedded proteins, cholesterol, glycoproteins and glycolipids.
  • d. Phospholipids give the membrane both hydrophilic and hydrophobic properties. The hydrophilic phosphate portions of the phospholipids are oriented toward the aqueous external or internal environments, while the hydrophobic fatty acid portions face each other within the interior of the membrane itself.
  • e. Embedded proteins can be hydrophilic, with charged and polar side groups, or hydrophobic, with nonpolar side groups.
  • f. Small, uncharged polar molecules and small nonpolar molecules, such as N2, freely pass across the membrane. Hydrophilic substances such as large polar molecules and ions move across the membrane through embedded channel and transport proteins. Water moves across membranes and through channel proteins called aquaporins.
  • g. Cell walls provide a structural boundary, as well as a permeability barrier for some substances to the internal environments.
  • h. Plant cell walls are made of cellulose and are external to the cell membrane.
  • i. Other examples are cell walls of prokaryotes and fungi.
2. Growth and dynamic homeostasis are maintained by the constant movement of molecules across membranes.
  • a. Passive transport does not require the input of metabolic energy; the net movement of molecules is from high concentration to low concentration.
  • b. Passive transport plays a primary role in the import of resources and the export of wastes.
  • c. Membrane proteins play a role in facilitated diffusion of charged and polar molecules through a membrane.
  • d. External environments can be hypotonic, hypertonic or isotonic to internal environments of cells.
  • e. Active transport requires free energy to move molecules from regions of low concentration to regions of high concentration.
  • f. Active transport is a process where free energy (often provided by ATP) is used by proteins embedded in the membrane to "move" molecules and/or ions across the membrane and to establish and maintain concentration gradients.
  • g. Membrane proteins are necessary for active transport.
  • h. The processes of endocytosis and exocytosis move large molecules from the external environment to the internal environment and vice versa, respectively.
  • i. In exocytosis, internal vesicles fuse with the plasma membrane to secrete large macromolecules out of the cell.
  • j. In endocytosis, the cell takes in macromolecules and particulate matter by forming new vesicles derived from the plasma membrane.
3. Eukaryotic cells maintain internal membranes that partition the cell into specialized regions.
  • a. Internal membranes facilitate cellular processes by minimizing competing interactions and by increasing surface area where reactions can occur.
  • b. Membranes and membrane-bound organelles in eukaryotic cells localize (compartmentalize) intracellular metabolic processes and specific enzymatic reactions.
  • c. Archaea and Bacteria generally lack internal membranes and organelles and have a cell wall.

A. Interactions within biological systems lead to complex properties.
2. The structure and function of subcellular components, and their interactions, provide essential cellular processes.
  • a. Ribosomes are small, universal structures comprised of two interacting parts: ribosomal RNA and protein. In a sequential manner, these cellular components interact to become the site of protein synthesis where the translation of the genetic instructions yields specific polypeptides.
  • b. Endoplasmic reticulum (ER) occurs in two forms: smooth and rough.
  • c. Rough endoplasmic reticulum functions to compartmentalize the cell, serves as mechanical support, provides site-specific protein synthesis with membrane-bound ribosomes and plays a role in intracellular transport.
  • d. In most cases, smooth ER synthesizes lipids.
  • e. The Golgi complex is a membrane-bound structure that consists of a series of flattened membrane sacs (cisternae).
  • f. Functions of the Golgi include synthesis and packaging of materials (small molecules) for transport (in vesicles), and production of lysosomes.
  • g. Mitochondria specialize in energy capture and transformation.
  • h. Mitochondria have a double membrane that allows compartmentalization within the mitochondria and is important to its function.
  • i. The outer membrane is smooth, but the inner membrane is highly convoluted, forming folds called cristae.
  • j. Cristae contain enzymes important to ATP production; cristae also increase the surface area for ATP production.
  • k. Lysosomes are membrane-enclosed sacs that contain hydrolytic enzymes, which are important in intracellular digestion, the recycling of a cell's organic materials and programmed cell death (apoptosis). Lysosomes carry out intracellular digestion in a variety of ways.
  • l. A vacuole is a membrane-bound sac that plays roles in intracellular digestion and the release of cellular waste products. In plants, a large vacuole serves many functions, from storage of pigments or poisonous substances to a role in cell growth. In addition, a large central vacuole allows for a large surface area to volume ratio.
  • m. Chloroplasts are specialized organelles found in algae and higher plants that capture energy through photosynthesis.
  • n. The structure and function relationship in the chloroplast allows cells to capture the energy available in sunlight and convert it to chemical bond energy via photosynthesis.
  • o. Chloroplasts contain chlorophylls, which are responsible for the green color of a plant and are the key light-trapping molecules in photosynthesis. There are several types of chlorophyll, but the predominant form in plants is chlorophyll a.
  • p. Chloroplasts have a double outer membrane that creates a compartmentalized structure, which supports its function. Within the chloroplasts are membrane-bound structures called thylakoids. Energy-capturing reactions housed in the thylakoids are organized in stacks, called "grana," to produce ATP and NADPH2, which fuel carbon-fixing reactions in the Calvin-Benson cycle. Carbon fixation occurs in the stroma, where molecules of CO2 are converted to carbohydrates.

Textbook Reference

This is the part of your textbook that covers the material for this unit.
Ch. 4-5 (except concept 5.6)

Relevant Files

Here, you'll find files for this course. Copies of lecture notes will go here, as will others.


These connect to materials on other teachers' websites that you may find helpful. Generally speaking, I put links to helpful review materials - like video lectures summarizing the material - towards the top, and links to interesting extensions towards the bottom.
Basic Cell Biology Self-Quizzes
Basic Cell Biology Self-Quiz 1
Basic Cell Biology Self-Quiz 2
Basic Cell Biology Self-Quiz 3
Action potential fill in the blank
Cell Organelles Diagram
Cell Size Interactive
Evolution of the Cell
Inside a Cell
How Vessels Transport Cargo
Amazing Membranes
Osmosis and Diffusion
Nobel Prize Cell Organelle Game
Cell Biology Animations
Virtual Cell