Cell Structure and Function Major Concepts and Learning Activities

Cell Structure and Function – Major Concepts and Learning Activities

These Teacher Notes supplement a typical textbook description of the cell and its components. The key concepts and suggested activities provided below are designed to engage students in active learning and to overcome some common student misconceptions and confusions.

Students often think of a cell as a static structure consisting of multiple independent parts. Students often do not understand how the parts of the cell work together to accomplish the multiple functions of a dynamic living cell. Students also often confuse different levels of organization such as molecules, organelles and cells.

To overcome these limitations in student understanding, key concepts and learning activities are presented in three sections:

· Molecules, Organelles and the Dynamic Functioning of Eukaryotic Cells

· How Substances Move Into and Out of Cells and Within Cells

· Diversity of Cell Structure and Function

Many of the activities are designed for students who already have a basic understanding of the functions of cell organelles and biological molecules. Some of the recommended activities are explicitly aligned with the Next Generation Science Standards (as indicated by (NGSS) in the description and explained in the Teacher Notes for these activities on the Serendip website).

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I. Molecules, Organelles and the Dynamic Functioning of Eukaryotic Cells

Key Concepts

· Inside a living cell there is constant activity.

· Each cell is made up of many molecules. In eukaryotic cells, many of these molecules are organized in tiny organelles that perform specialized functions inside the cell.

· Different organelles work together to accomplish the functions of life.

Learning Activities

A. Video and animations provide an excellent way to give students an intuitive feel for the dynamic nature of living cells. Two of the best for this purpose are:

Neutrophil (a phagocytic cell) Chasing a Bacterium – a video of two cells in motion,

available at:

https://www.youtube.com/watch?v=5yimbhkTqJo and

https://www.youtube.com/watch?v=I_xh-bkiv_c

A eukaryotic phagocytic cell uses chemical information to pursue and then eat a bacterium. Students see the dynamic changes in shape as the neutrophil moves as well as the extreme difference in size between eukaryotic and prokaryotic cells.

For an excellent dynamic animation showing how different parts of the cell cooperate, see

http://multimedia.mcb.harvard.edu/anim_innerlife_hi.html

I suggest showing only part of this animation, beginning about halfway through with microtubules and transport vesicles or a little bit later with pores in the nuclear membrane that allow mRNA to leave the nucleus, and continuing through exocytosis of secreted proteins and membrane proteins (excellent approximately three-minute segment). You probably will want to turn off the narration (which is very detailed) and give a student-friendly narration. You may want to use the relevant section from http://sparkleberrysprings.com/innerlifeofcell.html to develop your script. You may also find it helpful to view the version with labels available at http://biogeonerd.blogspot.com/search?q=leukocyte ; in this version the animation of motor proteins carrying vesicles is shown beginning at about 3 minutes and 40 seconds.

B. Analysis and Discussion Activities

Structure and Function of Molecules and Cells, available at

http://serendip.brynmawr.edu/exchange/bioactivities/SFMolecCell

In this analysis and discussion activity, students learn how the function of molecules and cells is related to their structure (including shape, constituent components, and relationships between components). Students analyze multiple examples of the relationship between structure and function in diverse proteins and eukaryotic cells. In addition, students learn that cells are dynamic structures with constant activity, students learn about emergent properties, and students engage in argument from evidence to evaluate three alternative claims concerning the relationship between structure and function. (NGSS)

Cells as Molecular Factories, available at

http://serendip.brynmawr.edu/exchange/bioactivities/cellmolecular

The questions in this analysis and discussion activity prompt students to think about how the different parts of a eukaryotic cell cooperate to function as a protein-producing factory and as a recycling plant. Additional questions require students to identify the locations and functions of different types of molecules in eukaryotic cell organelles.

C. Card Sort Activity – From Coffee to Carbon available at

http://teach.genetics.utah.edu/content/cells/CoffeetoCarbon.pdf

This activity has students sort cards (each with a molecule, organelle or cell) according to size. To use this activity to reinforce student understanding of different levels of organization, I recommend that you begin by having your students sort the cards into four categories: molecules, organelles, cells, and other. After you have discussed this initial card sort, then have your students organize the cards from smallest to largest. (Depending on your students, you may want to omit some cards such as adenine, influenza virus, baker's yeast.) After students have completed the card sort by size, discuss the results and show the animation which illustrates the relative sizes (available at http://learn.genetics.utah.edu/content/begin/cells/scale/). The order of magnitude differences in size can be used to help students realize that eukaryotic cells are made up of many many organelles and each organelle is made up of many many molecules.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

II. How Substances Move Into and Out of Cells and Within Cells

Key Concepts:

· Diffusion plays a very important role in moving substances into and out of cells and moving substances around inside of cells. However, diffusion has important limitations.

· Diffusion is relatively rapid over very short distances, but extremely slow over longer distances.

· The rate of diffusion into and out of a cell is proportional to the surface area of the plasma membrane. In contrast, the rate that a cell uses substances such as O2 is proportional to cell volume. Therefore, diffusion can only supply adequate amounts of O2, nutrients, etc. if the surface-area-to-volume ratio is large enough.

· As cell size increases, the rate of diffusion from the plasma membrane to the center decreases and the surface-area-to-volume ratio decreases. This is a very important reason why most cells are tiny.

· Another limitation of diffusion is that diffusion is very slow for large molecules. Also, diffusion only moves substances from regions of higher concentration to regions of lower concentration. To overcome these limitations of diffusion, cells use a variety of energy-requiring processes to pump substances into or out of the cell and to move substances within the cell.

Learning Activities

A. Hands-On Activities

Introduction to Osmosis, available at http://serendip.brynmawr.edu/sci_edu/waldron/#osmosis

This activity provides a sequence of learning activities designed to optimize student learning and understanding of osmosis by beginning with a student investigation of osmosis at the macroscopic level and then moving to analyzing osmosis at the molecular and cellular levels. In Part I, "What is happening to these eggs?" students observe and analyze the effects of osmosis on eggs. In Part II, "Osmosis – Effects on Animal and Plant Cells", analysis and discussion questions introduce students to a molecular and cellular understanding of osmosis and challenge students to apply their understanding of osmosis to several real-world phenomena. (NGSS)

Diffusion Across a Selectively Permeable Membrane, available at

http://serendip.brynmawr.edu/sci_edu/waldron/#diffusion

Students investigate the effects of molecule size on diffusion across a synthetic selectively permeable membrane. This investigation includes a brief introduction to osmosis. Additional questions introduce students to the roles of proteins in transporting polar substances across the cell membrane and guide students in analyzing the relative advantages of two different types of model of the cell membrane. (NGSS)

B. Analysis and Discussion Activity

Diffusion and Cell Size and Shape, available at

http://serendip.brynmawr.edu/exchange/bioactivities/celldiffusion

This analysis and discussion activity helps students understand that cell size is limited by the very slow rate of diffusion over any substantial distance and the insufficient surface-area-to-volume ratio for larger cells. In addition, students calculate why these problems do not apply to long slender cells or parts of cells such as the axons of neurons.

C. Web-based Animations and Videos of Energy-Requiring Processes that Cells Use to Move

Substances

Cell membranes contain protein molecular pumps which move substances from areas of low concentration to areas of high concentration (opposite from the direction of net flow due to diffusion). An animation is available at:

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

Within eukaryotic cells, large molecules such as proteins are often moved in transport vesicles carried by motor proteins along microtubules. This can be observed in the excellent animation available at http://multimedia.mcb.harvard.edu/anim_innerlife_hi.html

Large eukaryotic cells also use cytoplasmic streaming e.g. in the pseudopods of amoebae and to move the food vacuole of paramecia, as shown in the animation at http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter4/animation_-_cytoplasmic_streaming.html

Time-lapse video of cytoplasmic streaming is available at

http://web.bf.uni-lj.si/bi/botanika/aleskl/timelapse/elodea-kloroplasti-1.mov http://www.youtube.com/watch?v=6hJ_i_-K--k

http://www.youtube.com/watch?v=PFtzs_cUddI&feature=related

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

III. Diversity of Cell Structure and Function

Key Concepts

· Different types of eukaryotic cells have different shapes and different amounts of specific types of organelles, corresponding to their different functions in different parts of an organism or in different eukaryotic organisms (e.g. animals vs. plants).

· Eukaryotic and prokaryotic cells differ substantially in size and internal structure, but eukaryotic and prokaryotic cells share some important similarities (plasma membrane, ribosomes, and many identical or similar molecules) and both types of cells carry out the activities of life.

Learning Activities

Analysis and Discussion activities

Structure and Function of Molecules and Cells, available at

http://serendip.brynmawr.edu/exchange/bioactivities/SFMolecCell

Structure and Function of Cells, Organs and Organ Systems, available at http://serendip.brynmawr.edu/exchange/bioactivities/SFCellOrgan

In this analysis and discussion activity, students learn how the structure of cells, organs and organ systems is related to their functions. (Structure includes shape, constituent components, and relationships between components.) Students analyze multiple examples of the relationship between structure and function in diverse eukaryotic cells and in the digestive system. In addition, students learn that cells are dynamic structures with constant activity and they learn how body systems interact to accomplish important functions. (NGSS)

Prokaryotic vs. Eukaryotic Cells, available at

http://mrobiology2012.pbworks.com/w/file/fetch/47637831/prokar

This worksheet provides students with information about the similarities and differences between prokaryotic and eukaryotic cells and asks them to create a detailed Venn diagram comparing and contrasting these two types of cells. You may want to supplement this with the concept map on the next page of these Teacher Notes.

Hands-on Activity

Using a Microscope to See Different Types of Cells, available on the cell biology page at

https://sites.google.com/site/biologypd/home

In this activity students learn about diversity of cell structure and function by examining human red blood cells and white blood cells, frog red blood cells, cheek cells, bacteria, and different Protista.

IV. Additional Resources for Teaching about Cells

A. Source Materials and Animation

Inside the Cell – chapters 1 and 2 provide a very informative overview of the cell, available at http://publications.nigms.nih.gov/insidethecell/

Inside a Cell – animation available at

http://learn.genetics.utah.edu/content/begin/cells/insideacell/

B. Review Activities

Cell Vocabulary Review Game, available at http://serendip.brynmawr.edu/exchange/bioactivities/cellvocab

Crossword puzzles on cell structure available at http://www.cellsalive.com/puzzles/index.htm

Place the following words or phrases into the concept map:

activities of life, all organisms, animals, bacteria, cells, eukaryote, fungi,

membrane-bound organelles, nucleus, plants, prokaryote, protists, unicellular, viruses

[1] These Teacher Notes and multiple activities for teaching biology are available at http://serendip.brynmawr.edu/exchange/bioactivities.