Teacher Notes for Structure and Function of Cells, Organs and Organ Systems1

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. Students also learn that cells are dynamic structures with constant activity, and they learn how body systems interact to accomplish important functions.

This activity is aligned with Next Generation Science Standards for middle school students (see below). Some of the questions in this activity are also included in "Structure and Function of Molecules and Cells" (http://serendip.brynmawr.edu/exchange/bioactivities/SFMolecCell) which is aligned with Next Generation Science Standards for high school students.

Before students begin this activity, they should have a basic understanding of the functions of organelles in animal and plant cells. You may want to have students explore the animation, "Inside a Cell" available at http://learn.genetics.utah.edu/content/begin/cells/insideacell/

Learning GoalsIn accord with the Next Generation Science Standards2: This activity helps students to prepare for the Performance Expectations:

o MS-LS1-2. "Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function."

o MS-LS1-3. "Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells."

o HS-LS1-2. "Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms."

Students learn the following Disciplinary Core Ideas (LS1.A): o "All living things are made up of cells, which is the smallest unit that can be said to be

alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular)."

o "Within cells, special structures are responsible for particular functions…"o "Multicellular organisms have a hierarchical structural organization, in which any one

system is made up of numerous parts and is itself a component of the next level." Students engage in recommended Scientific Practices, including "constructing explanations",

engaging in "argument from evidence", and "obtaining, evaluating and communicating information".

This activity focuses on the Crosscutting Concept: Structure and function. "The functions and properties of natural and designed objects and systems can be inferred from their overall structure, the way their components are shaped and used, and the molecular substructures of its various materials."

Specific Learning Goals include: Analysis of the different components and relationships between components helps us to

understand the function of cells and the function of the digestive system

1 By Ingrid Waldron, Department of Biology, University of Pennsylvania, 2016. These Teacher Notes and the Student Handout are available at http://serendip.brynmawr.edu/exchange/bioactivities/SFCellOrgan.

2 Quotations are from http://www.nextgenscience.org/sites/default/files/HS%20LS%20topics%20combined%206.13.13.pdf

Different types of eukaryotic cells have differences in structure that correspond to their different functions in different eukaryotic organisms (e.g. animals vs. plants vs. Paramecia) or in different types of cells in a human body.

This activity reinforces student learning about the functions of different types of organelles and how these different types of organelles help to accomplish the activities of life.

Cells are dynamic and active. The structure of the digestive system and the structure of the wall of the small intestine

illustrate how structure is related to function at the body system and organ level. The digestive system and circulatory system cooperate to bring nutrients to every cell in

the body. Differences in the structure of the digestive system between ruminants and humans

correspond to differences in the food eaten.

Instructional Suggestions and Background Information To maximize student participation and learning, I suggest that you have your students work individually or in pairs to complete groups of related questions and then have a class discussion after each group of related questions. In each discussion, you can probe student thinking and help them develop a sound understanding of the concepts and information covered before moving on to the next group of related questions.

A key is available upon request to Ingrid Waldron (iwaldron@sas.upenn.edu). The following paragraphs provide additional instructional suggestions, links for recommended videos, and biological information – some for inclusion in your class discussions and some to provide you with relevant background that may be useful for your understanding and/or for responding to student questions.

When you introduce the concept that structure is related to function, you may want to: explain that this relationship applies at multiple levels from cells to organ systems explain that structure includes not only overall shape, but the makeup of and relationships

between constituent parts introduce familiar examples such as the different shapes of different types of teeth and

the hard enamel surface of teeth explain that the relationship between structure and function is a result of natural selection.

In the discussion about how the parts of the cell help to carry out the various activities of life (question 1 in the Student Handout), you may want to include other activities of life (e.g. growth and reproduction) if your students have the relevant background knowledge.

The differences between plant and animal cells are best understood in the context of differences in how plants and animals obtain food. For example, plants’ ability to photosynthesize means that plants do not require the mobility that many animals need to obtain food, so the rigidity of cell walls and the weight of the water in the central vacuole are not significant disadvantages for plant cells. This illustrates that the adaptive value of a given characteristic varies, depending on the other characteristics of an organism.

This activity focuses on eukaryotic cells in plants and animals. If your students are learning about prokaryotic cells, you may want to discuss with them how eukaryotic and prokaryotic cells have different internal structure, but both types of cells carry out the activities of life. In part, this is because eukaryotic and prokaryotic cells share multiple important structural similarities (e.g. plasma membrane, ribosomes, and many identical or similar molecules).

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You may want to show your students a video of sperm swimming (available at http://en.wikipedia.org/wiki/Sperm ). Notice that some of these sperm move quite rapidly, reflecting selection for characteristics that contribute to being the first sperm to reach an egg and fertilize it. This figure shows how small human sperm are relative to a human egg. The egg is a large cell with a lot of cytoplasm; once the egg has been fertilized, this large amount of cytoplasm is useful to supply the cytoplasm for the multiple cells that are produced by the cell divisions in early development before the developing embryo implants in the wall of the uterus.

(Figure from Krogh, Biology -- A Guide to the Natural World, Fifth Edition)

An epithelium that consists of a single layer of flattened epithelial cells (also known as a simple squamous epithelium) is observed in the walls of capillaries and also the walls of the alveoli in the lungs. In both cases, transport across the epithelium depends on diffusion, which is reasonably rapid over very short distances but very slow over any substantial distance. Thus, it is advantageous to have a minimal barrier to diffusion.3 The flattened or squamous epithelial cells also reflect the fact that the cells of capillaries and alveoli have minimal metabolic activity, so there is minimal need for cytoplasm.

To help your students appreciate the dynamism of cells, I recommend that you show your students a time lapse video of a phagocytic cell (neutrophil) chasing a bacterium (available at https://www.youtube.com/watch?v=5yimbhkTqJo or https://www.youtube.com/watch?v=I_xh-bkiv_c). In this video, the phagocytic cell uses chemical information to pursue a bacterium and then eat it. This video shows the dynamic changes in shape as the phagocytic cell moves.

3 Polar substances diffuse through the interstitial fluid between the cells of the capillary wall, whereas lipid soluble substances like oxygen and carbon dioxide diffuse across the cells; the latter drastically increases the area available for diffusion of oxygen and carbon dioxide since the cells of the capillary wall have more than 100 times as much area as the spaces between the cells. The epithelium that lines the blood vessels is often called an endothelium.

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The figure on the left below gives some more information about how phagocytic white blood cells move from the blood to kill bacteria or other microorganisms by phagocytosis. After a phagocytic white blood cell has engulfed a microorganism, the phagosome merges with a lysosome which produces nitric oxide and hydrogen peroxide to kill the microorganism and digestive enzymes to break down the microorganism to components the cell can use or the body can dispose of.

(http://getting-in.com/wp-content/uploads/2012/09/Picture-2212.png)

You may want to point out to your students that when they complete the table in question 6 they have produced a scientific argument with evidence (their examples) and justification (their explanations) to support the claim that "The structure of a cell is related to its function." If your students are not familiar with scientific argumentation, you may want to introduce them to the idea that, in a scientific argument, a claim is supported by observable evidence with justification to explain how the evidence is relevant to the claim. The Student Handout version of question 6 is designed to ensure that students include both the evidence and justifications explaining how each piece of evidence supports the claim. If you prefer not to include the table, you can use the following alternative version:

6. Write an argument to support the claim that "The structure of a cell is related to its function." Give examples and explain how your examples support this claim.

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Criteria for evaluating a scientific argument include: how well the claim fits with all the available evidence the sufficiency of the claim (i.e. it includes everything it needs to) the relevance and sufficiency of the evidence (as explained in the justification) the quality of the evidence (which in this case your students will not be able to evaluate).4

Additional information for teaching about scientific argumentation is available at http://www.indiana.edu/~ensiweb/Sci.Argumentation.html http://undsci.berkeley.edu/article/0_0_0/howscienceworks_07 . (This website takes a

somewhat different approach, referring to a scientific idea, expectations and observations as the components of a scientific argument.)

For your discussion of question 7, you may want to include additional examples of the dynamism of cells, including: A eukaryotic cell can produce hundreds of protein molecules per second; the ribosomes in

these cells typically add two amino acids per second to a growing polypeptide. A typical cell in a human body uses an average of 10 million ATP molecules in an average

second and produces an equal amount of replacement ATP molecules. Many cells in the body are constantly being replaced, e.g. skin cells and the epithelial cells

that line that gut. Mitochondria are replaced approximately every 10 days.(Source: Freeman et al., Biological Science, Fifth Edition)

The Challenge Question on page 3 of the Student Handout provides an additional example of diversity of cell structure and also challenges students to develop their skills in obtaining and evaluating information. A useful resource for students to learn about Paramecia is available at http://labs.7bscience.com/lab-2---paramecium.html . This webpage includes an excellent video video that shows the motion of cilia, contraction of the contractile vacuoles, and food being swept into the oral groove; seeing this video will help students understand how dynamic cells are, with constant activity of their organelles.

To introduce page 4 in the Student Handout, you may want to show the helpful animation available at https://www.youtube.com/watch?v=b20VRR9C37Q. Additional information about the digestive system is available at:

http://www.webmd.com/heartburn-gerd/your-digestive-system http://www.biog1445.org/demo/05/humandigestion.html http://www.innerbody.com/image/digeov.html .

In discussing structure and function of the digestive system, you may want to mention the familiar example of different types of teeth for different functions (http://www.ncsu.edu/project/lancet/third_grade/teeth.pdf). You may also want to explain the importance of chewing food into smaller particles to increase the surface-area-to-volume ratio of food particles so digestive enzymes have greater access to food molecules.

The two diagrams of the digestive system on page 4 of the Student Handout illustrate how different diagrams of the same structure convey somewhat different information and are useful for different purposes. The first diagram clearly shows the sequence of the organs in the digestive system, whereas the second diagram more accurately shows the relative sizes and arrangement of the organs of the digestive system.

4 These criteria are paraphrased from Argument-Driven Inquiry in Biology (by Sampson et al., NSTA Press). This book presents a very useful, more extensive format for developing students’ ability to engage in scientific argument as well as multiple argument-driven inquiry laboratory investigations designed for high school students.

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You may need to discuss the figure on page 5 of the Student Handout to ensure that your students understand the cutaway view on the left and the magnification of a villus on the right. The following figure shows some additional details of the structure of the lining of the small intestine, as well as the blood vessels that carry blood from the small intestine to the liver which processes some of the food molecules that have been absorbed into the blood in the small intestine. For example, after a meal glucose levels are high in the blood coming to the liver from the small intestine; the liver removes some of the glucose from the blood and converts it to a storage form (glycogen) which will subsequently be available for use between meals. From the liver, the blood flows to the heart which pumps blood containing nutrients to capillaries near every cell in the body.

http://www.daviddarling.info/images/small_intestine_cross-section.jpg

The length of the small intestine, the folds, the villi and the microvilli all increase the surface area for absorption.

The cells in the epithelium that lines the inner surface of the small intestine synthesize protein enzymes that help to complete the digestion of food molecules and these cells also pump in sugars and amino acids to increase absorption of these useful molecules into the blood. To accomplish these functions, these cells need lots of cytoplasm with lots of mitochondria, ribosomes, rough endoplasmic reticulum and Golgi complex (the latter two are needed since the digestive enzymes and pump proteins are inserted in the cell membrane on the apical surface of these epithelial cells). These metabolically active epithelial cells in the lining of the small intestine are tall and have much more cytoplasm per epithelial area than the relatively inactive flattened cells in the capillary wall. (The capillary wall cells do not synthesize enzymes or pump useful molecules; instead the flattened shape provides a minimum barrier to diffusion, as discussed above.) This is another example of how structure is related to function.

In discussing the role of the circulatory system (questions 11 and 12), you may want to explain that nutrients diffuse into the blood in the capillaries in the villi of the small intestine and then later diffuse out of the blood in capillaries in other parts of the body (as shown in question 4).

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You may want to use this figure to help your students understand how the digestive and circulatory systems cooperate to provide cells all over the body with digested food molecules that can be used for cellular respiration and as building blocks to synthesize needed molecules.

Question 12 illustrates the important general principle that our bodies consist of multiple body systems that cooperate to accomplish important functions. You may want to include additional examples such as the cooperation between the respiratory system and the circulatory system to provide the oxygen to every cell in the body and also to remove the waste product, carbon dioxide. This diagram illustrates how the circulatory system is crucial for allowing the specialized digestive, respiratory and excretory systems to serve needed functions for all the cells in the body.

You also may want to point out the role of the nervous system in controlling the activity of the tongue and jaw muscles, regulating other aspects of digestion, controlling breathing, and regulating the circulatory system (e.g. heart rate). A rap video that reviews body systems is available at http://mr.powner.org/b/lessons/humans/So%20Many%20Systems%20-%20Human%20Body%20Systems%20Rap.mp4. A useful introduction to the cow’s digestive system is available at http://commtechlab.msu.edu/sites/dlc-me/zoo/zacmain.html. The article available at http://sci.waikato.ac.nz/farm/content/animalstructure.html provides a more detailed description of the digestive system of ruminants (including the cow), as well as "hindgut fermenters" like horses and rabbits which have digestive systems that extract a lot of the energy in high-fiber diets by bacterial breakdown of cellulose after food has passed through the small intestine. Discussion of the Challenge Question on page 6 of the Student Handout introduces the concept that the digestive systems of different types of animals show different structures, corresponding to differences in their diet (as well as their evolutionary history and ecological niche). You might even want to mention that tapeworms that live in the small intestine where they are surrounded by a solution of digested nutrient molecules do not have any digestive system, but rather absorb the nutrients through their body surface (http://animals.pawnation.com/tapeworms-obtain-food-digestive-system-11144.html).

You may also want to mention that the human gut is home to many bacteria which help to provide nutrients, protect against invasion by disease germs, and stimulate the development of the intestine and immune system (http://www.karger.com/Article/FullText/89775 ).

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If you would like to review levels of organization in biological organisms and relative sizes at these different levels of organization, the following resources and figure may be helpful. Brief introductions to levels of organization are available at: http://wps.pearsoncustom.com/wps/media/objects/3014/3087289/Web_Tutorials/01_A02.swf http://wps.aw.com/wps/media/objects/451/462581/CH01/html/ch1_3.html https://www.boundless.com/biology/textbooks/boundless-biology-textbook/the-study-of-life-

1/themes-and-concepts-of-biology-49/levels-of-organization-of-living-things-269-11402/

(http://www.protein-structure.net/images/Body-Systems.jpg)

Related Activities Cell Structure and Function – Major Concepts and Learning Activities http://serendip.brynmawr.edu/exchange/bioactivities/cellsThis overview presents key concepts that students often do not learn from standard textbook presentations and suggests a sequence of learning activities to help students understand how the parts of a cell work together to accomplish the multiple functions of a dynamic living cell. Suggested activities also reinforce student understanding of the relationships between molecules, organelles and cells and the importance and limitations of diffusion. This overview provides links to web resources, hands-on activities, and discussion activities.

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