9.4.1.1 Homeostasis
Explain how cell processes are influenced by internal and external factors, such as pH and temperature, and how cells and organisms respond to changes in their environment to maintain homeostasis.
Describe how the functions of individual organ systems are integrated to maintain homeostasis in an organism.
Overview
MN Standard in Lay Terms
The organ systems of the body must work together to keep the body environment the same at all times so all cells have what they need to function continuously and properly. This begins in the cellular system as cells respond through feedback mechanisms to internal and external factors and maintain the appropriate internal environment needed to continue function and metabolic processes.
Big Idea
Homeostasis is controlled first at the cellular level as cells react to changes in their environment and feedback signals that inform the system that is is not meeting the set-point goal. This, in turn, affects various organ systems as they work together to maintain an environment in which the organism operates and metabolic processes proceed.
MN Standard Benchmarks
9.4.1.1.1 Explain how cell processes are influenced by internal and external factors, such as pH and temperature, and how cells and organisms respond to changes in their environment to maintain homeostasis.
9.4.1.1.2 Describe how the functions of individual organ systems are integrated to maintain homeostasis in an organism.
The Essentials
See this page.
The complexity and organization of organisms accommodates the need for obtaining, transforming, transporting, releasing, and eliminating the matter and energy used to sustain the organism.
pg 133 of Vol 1. How cells relate to systems
A system usually has some properties that are different from those of its parts, but appear because of the interaction of those parts.
Most systems above the molecular level involve so many parts and forces and are so sensitive to tiny differences in conditions that their precise behavior is unpredictable, even if all the rules for change are known.
See AAAS Atlas above
Framework for K-12 Science Education
Systems of specialized cells within organisms help them perform the essential functions of life, which involve chemical reactions that take place between different types of molecules, such as water, proteins, carbohydrates, lipids, and nucleic acids. All cells contain genetic information in the form of DNA molecules. Genes are regions in the DNA that contain the instructions that code for the formation of proteins, which carry out most of the work of cells. 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. Feedback mechanisms maintain a living system’s internal conditions within certain limits and mediate behaviors, allowing it to remain alive and functional even as external conditions change within some range. Outside that range (e.g., at a too high or too low external temperature, with too little food or water available), the organism cannot survive. Feedback mechanisms can encourage (through positive feedback) or discourage (negative feedback) what is going on inside the living system. 12LS1.A
In multicellular organisms individual cells grow and then divide via a process called mitosis, thereby allowing the organism to grow. The organism begins as a single cell (fertilized egg) that divides successively to produce many cells, with each parent cell passing identical genetic material (two variants of each chromosome pair) to both daughter cells. As successive subdivisions of an embryo’s cells occur, programmed genetic instructions and small differences in their immediate environments activate or inactivate different genes, which cause the cells to develop differently—a process called differentiation. Cellular division and differentiation produce and maintain a complex organism, composed of systems of tissues and organs that work together to meet the needs of the whole organism. In sexual reproduction, a specialized type of cell division called meiosis occurs that results in the production of sex cells, such as gametes in animals (sperm and eggs), which contain only one member from each chromosome pair in the parent cell. 12LS1.B
Common Core Standards
Math standards can be easily incorporated into this topic.
Math 9.3.1.5 Make reasonable estimates and judgments about the accuracy of values resulting from calculations involving measurements.
Students can calculate the % change to the mass or volume of the eggs and determine the relationship to the concentration of the solutions.
Math 9.4.2.3. Design simple experiments and explain the impact of sampling methods, bias and the phrasing of questions asked during data collection.
This standard can be addressed with all data collection methods from the vignette to the egg circumference and more.
Statistical analysis and Graphing can be done - especially using line graphs to depict increasing concentration of solvent as related to increases in weight in eggs or dialysis tubing.
Common Core Language Arts: Students can write a laboratory report in the proper form and using their knowledge of technical writing skills. Common core standards addressed:
RST.9-10.1. Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.
RST.9-10.2. Determine the central ideas or conclusions of a text; trace the text's explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text.
RST.9-10.3. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
Misconceptions
1. Temperature is regulated by external physical factors.
- Atmospheric temperature
- Heat leaving pores of the body
2. Respiration occurs in the lung rather than the mitochondria. In reality cellular respiration happens in the cytoplasm (glycolysis) and mitochondria (aerobic respiration) of the cell. Respiration as in breathing is the process that takes place in the lungs.
3. Lungs and other organs need more blood due to exercise. In reality the blood is merely the transport system for the oxygen and glucose needed to do cellular respiration and is proportional to oxygen and glucose needs.
4. High school students have difficulty thinking of the human body as a chemical system and have little knowledge about the elements composing the living body. (Atlas, p.76)
5. Homeostasis is only the measurement of a body function that is maintained. In reality homeostasis adjusts a system to a set point indicated by external or internal conditions and which will achieve the needed results.
Vignette
This is a good opportunity to apply inquiry-based learning. After a discussion on how exercise affects the body, lab groups select a variable to explore and collect data on how exercise impacts the body. Groups could also select the same variable (heart rate for example) and apply different rates of exercise. There are many ways to approach this and gives students more say in what is measured in lab. See Strand 1 (The Nature of Science and Engineering, Substrand 1 The Practice of Science 9.1.1.2.1)
Ms. M.'s biology class was studying homeostasis today. When students entered the classroom they were surprised to see exercise equipment and blood pressure cuffs at the lab stations.
Students come up with a testable question: How does exercise affect the body? The groups would then choose a variable(an effect ) to test such as heart rate or breathing rate then propose a hypothesis predicting what they expect to happen. As they design their investigation they plan how to conduct their tests without bias and how they will collect their data. This implies inquiry based learning using a constructivist methodology as students claim ownership of their own learning.
Ms. M. tells the class that they are going to see how exercise affects blood pressure by measuring and observing certain conditions of the human body. She asks for volunteers to jump rope for eight minutes. Before they start group members record the following:
1. Perspiration level (none, mild, medium, high)
2. External body temperature (place the thermometer under the subjects arm pit for one minute; the thermometer should be directly against the skin)
3. Breathing rate (count the number of breaths in 1 minute)
4. Heart rate (find the pulse at the wrist and count the number of beats in 1 minute)
5. Blood pressure (use the blood pressure monitor to get a reading)
After 2 minutes each of the measurements are taken again. The data is analyze and graphed. Now students delve into the process of asking how the body knew that these changes were needed and how the changes affected the functioning of the various body systems. Students consider feedback and response. They then derive testable questions that could be persued experimentally based on the control of homeostatsis in these systems.
Resources
Suggested Labs and Activities
9.4.1.1.2 Carbon dioxide lab Before and after mild exercise, students blow through a straw into a solution of weak NaOH solution to which several drops of phenolphthalein have been added. Students are instructed to blow at a steady rate for 5 seconds, take a breath and repeat until the solution turns clear. The number of breathes this takes represents the amount of carbon dioxide released in each breathe. Students will then consider the reason for this adjustment and the feedback processes that took place during the adjustments. This activity is especially effective as it ties directly into the vignette and connects homeostasis to other standards such as energy transfer in photosynthesis and respiration (could also be used for 9.4.2.2.1)
9.4.1.1.1 and 9.4.1.1.2 Demonstrations
Hypertonic/Hypotonic solutions and carrots (or other firm, porous vegetables) demonstrate the homeostasis of plant cells and turger pressure. Place in solutions of various concentrations and distilled water. After 24 hours check for crispness. (9.4.1.1.1). Due to the balance of the water vacuole and the cell wall, the plant responds with the proper water pressure and is able to maintain proper cellular pressure to function and maintain rigidity.
9.4.1.1.1. Osmosis Laboratory Dialysis Tubing
After the vocabulary of osmosis, diffusion and homeostatic forces has been introduced in 9.4.1.1.2), the following can be explored. Dialysis tubing soaked in distilled water is made into tubes to hold solution and are tied in balloon style at each end.. Each tube is filled with a different concentration of solution (sugar, starch etc) The tubes are massed and immersed in distilled water or another liquid for a period of time and then removed, dried and massed again. Students graph the difference in mass of each tube before and after the immersion in distilled water or in relation to the concentration of the solution in the tube. A discussion ensues about the homeostatic forces of the liquids involved and the osmotic pressure of the solutions. Although there are no inherent feeback mechanisms in dialysis tubing other than osmotic pressure, this does demonstrate some of the processes in the kidney as water balance and ionic concentration is maintained. A discussion of Kidney and medical dialysis may be done at this point to illustrate the homeostatic properties of water balance in the human kidney. Other organ systems may enter the discussion as they contribute to this homeostasis. A discussion of disease as an interruption/disruption to homeostasis can be discussed. (Note: This may also be related to water balance in other organisms from protozoa up throught mammals)
9.4.1.1.1. Osmosis Laboratory - Eggs
The shell is removed from chicken eggs (by soaking overnight in vinegar), the egg membranes can then serve as excellent examples of osmotic homeostasis. After the eggs are weighed and measured (circumference), they are placed in a variety of solutions of varying concentration (distilled water, sucrose solutions, starch solutions, molasses or corn syrup). When left overnight they start to achieve equilibrium as a means to homeostasis through osmosis. Students can determine the osmolarity of the solution in relation to the concentration of the interior of the egg and have the conversations necessary to understand the potential. This lab is similar to the dialysis tubing lab but it takes into account a real life homeostatic problem involving chicken eggs osmotic concentration which needs to be maintained during the hatching process. The balance between the air sac and the water concentration of the egg is critical not just to the albumin concentration but also to the chick's ability to exit the egg successfully at hatching.
9.4.1.1.1. Heart Rate in Daphnia or Goldfish
This inquiry may be done with either Goldfish or Daphnia. The heart rate or breathing rate is monitored by observing the heart directly in Daphnia magna or counting the operculum movement in goldfish. The water with the organism in it is gently heated by putting the beaker with the goldfish or slide with daphnia in a larger vessel with either warm water or ice water. When the temperature cools or heats up approximately 10 degrees, the heart rate or operculum movements are counted again. The change indicates regulation of metabolism as it maintains a "set-point". As the metabolic needs decrease or increase so does the need for oxygen and/or energy sources to the tissues. Caution should be taken not to overheat or over-cool the organism, especially in the case of goldfish which is a vertebrate organism.
Plant Phototropism (9.4.1.1.2)
Plants can be grown as a light source is systematically moved around them. Especially with plants such as sunflowers the plant will adjust it's leaves so that it maintains homeostasis with the amount of light it received and therefore attempts a constant level of photosynthesis.
Transpiration (9.4.1.1.2)
Leaves can be examined from plants that have been watered sufficiently and those that have not. Using clear nail-polish on the bottom side of leaves and peeling it off, the stomata can be observed. Plants that have received adequate moisture will have open stomata. Plants that have not will have closed stomata indicating homeostatic control of water concentration in the plant in an attempt to maintain the proper water content and concentration in order to efficiently produce energy. This can be directly related to the turger pressure in the guard cells as they effectively collapse when the water vacuoles are empty or low thus closing the stomata as the rigidity of the guard cells is lost.
Instructional suggestions/options
For any of the demonstrations/labs above students should make predictions of what will happen. The are most effectively taught as inquiry based projects in which students devise testable questions and then pursue the results. After analyzing the results students discuss the need for the function and the signals needed by the organism to correct any deviations from the "set-point" in the system.
Using plants and animals in the classroom requires some logistical planning. Ordering ahead of time to get live specimens and maintaining cultures requires time, patience and space. Having plants available and the best varieties requires planning and care. Student involvement in this process can not only be of help to the teacher but provide interesting and authentic learning and experience for the student.
The Carbon Dioxide lab is very physical. Most students are very involved : be aware of student health concerns and safety in the classroom.
Homeostasis can be a very complicated topic with a wide variety of feedback mechanisms and controls and signals. This is especially true when talking about mammalian homeostasis. For this reason it can be less abstract for many sttudents to begin the discussion with simpler systems in simpler organisms. Organisms that work well may include plants, reproductive eggs, and even ecosystems. All experience some forms of homeostasis in order to function efficiently and the feedback mechanisms may be easier to understand than the more complicated mammalian systems. The results when these systems fail can be easily documented in a very concrete way for the beginning student.
Additional resources
Biggs, Alton et. al., Biology, Columbus, OH: Glencoe, 2009. Print
Campbell, Neil et. al., Biology AP Edition. 8th edition, San Francisco, CA: Pearson, 2008, Print.
Vocabulary/Glossary
- Cellular Respiration - The process of capturing energy found in carbon compounds such as glucose and using that energy to make ATP.
- Circulation - The movement of blood through the vessels of the body induced by the pumping action of the heart.
- Homeostasis - A relatively steady state or a tendency toward such a state between the different but interdependent elements of an organism, population or group.
- Diffusion - The process by which particles of liquids, gases, or solids intermingle as the result of their spontaneous movement from a region of higher concentration to one of lower concentration in dissolved substances.
- Osmosis - Movement of water particles through a membrane from areas of high water concentration (low solute concentration) to areas of low water concentration (high solute concentration).
- Metabolism - The chemical changes in living cells by which energy is provided for vital processes and activities and new material is assimilated.
2. How Stuff Works "Homeostasis" 25 February 2005.
citing the above "Homeostasis" 25 February 2005. HowStuffWorks.com. 02 February 2011
The egg laboratory can be paired with "Foods" classes. There are many recipes that use eggs where the shell is removed and the eggs put into various solutions. Cooking and biology and chemistry overlap nicely and bring a hands-on, applied purpose to the concepts.
Connection to physiology, anatomy and health involving the anatomy and physiology of the excretory system. Body temperature maintainance may be discussed and all of the inherent feedback mechanisms involved can be assessed. Although technically difficult for beginning biology students, this can be an interesting discussion when done with students taking anatomy and/or AP Biology and have the advanced knowledge to recognize the implications of the system.
Health with dehydration effect of alcohol and/or dehydration sickness from heat and/or failure to drink enough water.
Botany and horticulture can be included on a variety of levels. Homeostasis as applies to gravitropism, phototropism and transpiration can make interesting inquiry based experiments and learning opportunities.
Assessment
Assessment of Students
Formative: 9.4.1.1.2. As a formative assessment, student's write a paragraph about the body's ability to maintain homeostasis and how the activity in the vignette demonstrates this concept.
Summative - 9.4.1.1.1.Explain the relationship among cell specialization, multicellular organisms, and homeostasis. Answers may include different types of cells such as blood cells, nerve cells that work together to contribute to the functioning and equilibrium of the whole system.
Summative 9.4.1.1.2- Name the levels of organization in a living organisms and explain how they build upon each other and interact to maintain homeostasis in the organism. Answers may include: Levels from atom to molecule to organelle to cell to tissue to organ to organ system to organism and a description of how they relate feed back mechanisms involved in homeostasis as they support each other and work together for the organism as a whole.
Summative 9.4.1.1.1.- Explain what happens when a cell is placed in a salt water solution. Answer: The cell is placed in a hypertonic solution if the concentration of salt is greater than the concentration inside the cell. Water will diffuse from the cell to the salt and the cell will shrink (plasmolysis). If however, the salt solution is less concentrated than the solution inside the cell, the water will diffuse out of the cell and the cell will swell and may burst (cytolysis). If, however, the salt solution is at the same concentration as the cell, then the cell will reach equilibrium and will not change in size.
Formative 9.4.1.1.2- Explain how a home heating system is a good model for feedback inhibition in the body? Answers may include: The system heats until the thermostat indicates that the optimal upper temperature has been reached. It then turns off and the house naturally cools. It turns on again when the lower temperature limit is reached. Students may mention that a fan system operates to maintain equilibrium and therefore temperature stability in all areas of the home.
9.4.1.1.1.Formative - Name another condition, other than temperature that needs to be stable in the human body. Answers may include: pH, solute concentration of glucose, water concentration etc.
Assessment of Teachers
When breathing and/or circulation increase or decrease, how are metabolic processes affected? How is this related to temperature? Does a change in temperature affect breathing and/or circulation?
All are inter-related. When breathing and circulation increase or decrease such as in exercise, metabolic processes also increase. In fact, the increase in metabolic processes such as energy consumption during exercise may be the causal effect of the breathing and circulation increases or decreases. Temperature therefore also increases and may affect the breathing and/or circulation as the body strives to maintain homeostasis. (this may be expanded to include complicated interactions between metabolic chemistry, the nervouse system and carrier systems)
How do we define cold blooded verses warm blooded animals? How do cold blooded animals maintain homeostasis and how is this different than how warm blooded animals do this?
Cold blooded animals are those that rely on the environment in order to maintain their body temperature. Temperature is controlled only by the ability of the animal to move from one environment to another. Homeostasis is maintained in this way. Metabolic chemical changes then equilibrate to the level of external stimuli. Example: As the temperature decreases so does the activity level of the animal and the metabolic processes in it. Warm blooded animals have systems built into their metabobolic processes and nervous systems which compensate for the environmental changes. Example: Shivering to keep warm or sweating to keep cool.
How does homeostasis work in the nervous system? Give several examples.
One example would be: The nervous system responds to signals from the sense organs. As the sensation is detected in the sensory nerves the system sends signals to the motor neurons to correct the equilibrium.
Differentiation
Struggling and At-Risk:
Struggling and At-risk students often have difficult problems with concentration and interest due to outside influences that may be beyond teacher control. These may manifest themselves as learning disabilities but in effect they are not truly learning disabled. Experience has shown that building personal relationships with the students and teaching with concrete hands-on examples that are interesting and challenging, has the best result. Allowing students to pick up on an interest or common experience and experiment within it, is often effective. One example of this would involve allowing them to experiment with different soft drinks and/or energy drinks to induce osmosis in either eggs or dialysis tubing. Further research on the "drinks" allow students to determine the solute concentration and explain the result of the experiment in a way that may have more relevance to them.
Homeostasis at cellular level: Use a volleyball net and ball to demonstrate molecules moving through the holes in the net. Practice using the terms relating to diffusion as this is demonstrated. This also ties in well with standard 9.4.1.2.
Homeostasis at the system level: Have students maintain the temperature of a beaker of water for 15 minutes. Graph the results as temperature is taken at intervals. Label the graph appropriately. How is this related to temperature in organisms?
Both biological language and vocabulary as well as academic language and vocabulary need to be taken into consideration when working with ELL students. Vocabulary lists and practice are a must. Any time words can be associated with physical examples students will have an easier time understanding.
Test questions may be augmented with pictorial representations such as power point to add clarity.
For cellular level homeostasis - Intended for students who understand chemistry (some schools teach Chemistry before Biology). They could explore chemical homeostasis using pH and buffers. Systems involving the production of carbonic acid and bicarbonate may be explored in ecological systems and their ability to maintain homeostasis with in a limited range in an environment that is constantly changing..
For systems homeostasis - Students research and find examples of positive feedback in the human body. For truly advanced students, the endocrine system would also introduce some outstanding examples (eg. hormone regulation). Choosing a system such as the circulatory, respiratory, digestive, excretory and nervous system, students research an aspect in which homeostasis is maintained and then report their findings to the class. If working in groups this may be a nice time to introduce a collaborative writing system such as "google docs".
As per ELL, it is critical that all students have the same mental picture at the same time in order to follow the conversation and understand any analogies.
Sharing examples from different cultures or families can be very effective. Using vegetables and/or plants that are common to one group can add both interest and familiarity. Example: Using Asian radishes instead of carrots to demonstrate osmotic balance in plants.
For cellular level homeostasis - Rather than working with dialysis tubing, use eggs. Remove the shell by soaking the eggs in vinegar overnight. Then put them in various concentrations of solutions ranging from distilled water to corn syrup. This works well to demonstrate that the concentration of liquids on both sides of the membrane are attempting to reach equilibrium. It also ties in well with a study of reproductive processes in organism which reproduce through eggs (amphibians, fish, reptiles and birds) and the mechanisms they use to maintain water concentration.
For cellular level homeostasis - Another demonstration that is very concrete and visible is to cut a carrot lengthwise down the middle. One piece is placed in distilled water and the other piece in relatively concentrated salt water and leave them overnight. The students discuss and predict the results. The next day, let the students handle them and discuss what has happened at the cellular level. This can then be applied to food preparation and the need for fresh vegetables to be stored in water and also to the ability of plant cells to maintain turger pressure.
For systems level homeostasis - Draw a cycle showing how feelings of hunger and fullness are a feedback loop to help maintain homeostasis. This can be done as a research project determining the signals inherent in different nutrients which control hunger.
Parents/Admin
Administrators
The teacher would be asking students to predict what they think will happen when the eggs are placed in different liquids. Students will write and/or draw (in notebooks) what they think will happen. Students also share their ideas on how to measure any differences. Then students would conduct the measurements (massing) the eggs and then place the eggs in the liquids. After the eggs have been in the liquids for the required amount of time, the students would gently remove the eggs, re-mass the egg and measure the circumference. This data would then be recorded and graphed individually and as a class. At this end of the experimental procedures students will hypothesize as to the importance of concentration in maintaining the integrity of the egg in the embryology and hatching process of the chick. This can be especially effective if students are simultaneously hatching eggs as a project.
The egg lab above can be done at home using different liquids. Students would have to explain why the differences in the size of the eggs to their parents and how this might relate to the conditions needed for proper hatching in precocial birds (chickens and ducks). In a high school setting parental involvement is often at the level of discussion and clarification of ideas given in the classroom. Keeping parents informed as to the topic under discussion has value and this can be done easily over a website or newsletter.
Food preparation is also an excellent opportunity to explore homeostasis as applied to osmosis and diffusion. The preparation of relish trays is an especially authentic opportunity to apply these principles.