Module 5 – Cell Structure and Function
Incomplete Files
Exam needs to be completed and polished.
Detailed instructions and rubric needed for culminating product.
Skills to review before beginning this unit:
Proper use of light microscopic techniques including determining total power of magnification.
Instructional Goals
· Use microscopes to observe a variety of cells with particular emphasis on the differences between plant and animal cells and the organelles within.
· Summarize the structure and function of organelles in eukaryotic cells and ways that these
organelles interact with each other to perform the function of the cell.
· Compare and contrast plant and animal cells.
· Explain how the structure and function of the cell relate to the structure and function of the
organism and the organism in the context of its environment.
· Investigate and analyze the cell as a living system including movement of materials into and out
of cells.
· Compare the mechanisms of active vs. passive transport (diffusion and osmosis).
· Explain how the plasma membrane functions.
· Explain changes in osmotic pressure that occur when cells are placed in solutions of differing
concentrations.
· Explain how homeostasis is maintained in the cell and within an organism in various environment including temperature and pH.
Standards
B.1.3 Explain and give examples of how the function and differentiation of cells is influenced by
their external environment (e.g., temperature, acidity and the concentration of certain
molecules) and changes in these conditions may affect how a cell functions.
Core Standard: Describe features that are common to all cells and contrast those with distinctive
features that allow cells to carry out specific functions.
B.2.1 Describe features common to all cells that are essential for growth and survival. Explain their functions.
B.2.2 Describe the structure of a cell membrane and explain how it regulates the transport of material into and out of the cell and prevents harmful materials from entering the cell.
B.2.3 Explain that most cells contain mitochondria (the key sites of cellular respiration), where stored chemical energy is converted into useable energy for the cell. Explain that some cells, including many plant cells, contain chloroplasts (the key sites of photosynthesis) where the energy of light is captured for use in chemical work.
B.2.4 Explain that all cells contain ribosomes (the key sites for protein synthesis), where genetic
material is decoded in order to form unique proteins.
B.2.5 Explain that cells use proteins to form structures (e.g., cilia, flagella), which allow them to
carry out specific functions (e.g., movement, adhesion and absorption).
B.2.6 Investigate a variety of different cell types and relate the proportion of different organelles
within these cells to their functions.
B.3.3 Recognize and describe that metabolism consists of all of the biochemical reactions that occur inside cells, which include the production, modification, transport, and exchange of materials that are required for the maintenance of life.
Misconceptions
· Cells are the components of many things including carbohydrates and proteins.
· There are two kinds of cells: plant and animal.
· Cells are within the human body, but do not make up the body.
· Osmosis will continue until equilibrium is reached, with equal concentrations of solute on
both sides of the semi-permeable membrane.
· The overall direction of osmosis is based on the concentration of the solute.
· Common solute molecules such as salt and sugar will diffuse through a semi-permeable
membrane.
· Everything a cell needs is able to enter by diffusion.
· Cells are flat, not three dimensional.
· All cells are the same.
· Plant cells only have chloroplasts, not mitochondria.
· All cell and organelle membranes are constructed similarly.
· The cell membrane is not dynamic.
Vocabulary
phospholipid / eukaryote / cell membrane / cell wall / nucleusnucleolus / golgi apparatus / mitochondria / chloroplast / ribosome
vacuole / endocytosis / exocytosis / lysosome / peroxisome
osmosis / diffusion / active transport / passive transport / solute
solvent / equilibrium / homeostasis / concentration / isotonic
hypertonic / hypotonic / rough endoplasmic reticulum / smooth endoplasmic reticulum
Sequence
*Class Session = 45-50 minutes
Activity 5.1: Model Paradigm: Basic Unit of Life 1-2 class sessions
Activity 5.2:Design an Artificial Living Unit of Life (Prototype)1 class session
Activity 5.3: Movement of Materials1 class session
Activity 5.4: Movement of Materials across a Boundary1-2 class sessions
Activity 5.5: How Aquatic Plant Cells Respond to Different Environments 1 class session
Activity 5.6: How Cells Respond to Different Concentrations of Sucrose2-3 class sessions
5.6 Post Activity Assignment – Exercise 1 – Potato Lab Storyboard
5.6 Post Activity Assignment – Exercise 2 – Structure and Function of a Membrane
Activity 5.7: An Animal Cell as a Basic Unit of Life1 class session
Activity 5.8: Culminating Product1-4 class sessions
Review and Exam2 class sessions
Online textbook for additional resource:
Activity 5.1 Model Paradigm: Basic Unit of Life
Apparatus
MicroscopeProtist Cultures – Amoeba, Paramecium, Euglena
Pond Mix Depression Slides
CoverslipsProto-slo
Pre-Skills Activity (OPTIONAL):
If the teacher feels a need for a microscope skills lab, this activity is included for the teacher to use.
Pre-Activity Discussion:
We have looked at different aspects of life and how life is interconnected. We are now going to observe the smallest unit of life. Before this activity we want to come to a class consensus on the necessary functions for a living unit of life.
(Whiteboard Activity-each group comes up with a list and then board meeting to reach a class consensus.)
Lab Investigation:
OBJECTIVE: The objective of this lab is for the students to make observations about the characteristics and functions essential to life. Students should be drawn toward the central question of the unit: How do the different parts of a cell work together to sustain life? This activity gets students to observe and examine different cells to construct a model of the cell as the complex interaction of different parts working to sustain the smallest unit of life. This lab allows flexibility with the type of cells and living specimens which are observed. As long as several different types of cells are used, the central ideas of this activity are preserved.
The following procedure can be edited for the specimens that are available:
PROCEDURE:
Using a pipette place a drop of culture on a clean glass depression slide. Several organisms are located on the bottom of the culture jar, so you will want to put the pipette on the bottom to get them. Also, do not blow air bubbles into the jars as that will mix up the organisms and make it harder to get a sample. Add a drop of Proto-slo to the slide culture and cover with a coverslip. Using the low power objective of your microscope, locate the organism. Switch to medium, and then use high power.
Make a data table and include the following for each organism:
• Draw each in color.
• Describe how each moves.
• List any essential characteristics for the organism to sustain life.
It might be helpful to have students practice using a virtual light microscope before using their actual scopes. The following link not only gives students an idea of what they should be seeing, but it shows them how to correctly position a slide, which objective to use and when, and how to use the coarse and fine focus. There are three sample slides for practice as well.
Post-Activity Discussion
Compare and contrast life functions for unicellular and multicellular organisms. WB and discuss.
Activity 5.2: Design an Artificial Living Unit of Life (Prototype)
Lab Instructions:
OBJECTIVE: The purpose of this lab is to get students to think about the necessary components of a living unit in order to accomplish the complex and essential life functions and processes generated above.
Pre-Activity WB:
In small groups, students use a whiteboard to create lists for the following questions. Think of your school. How does the school carry out its essential functions? What parts of the school are necessary? How do these parts work together to carry out the functions?
PROCEDURE:
Students need to apply the analogy from the pre-activity to design a model of the basic unit of life. Students will draw the life unit and label the different parts necessary for life. Students need to explain why each part is necessary for life and explain how the parts work together to carry out the functions of life.
Students may present their ideas informally using whiteboard or the teacher may choose to have students present more formal posters or other presentation formats with an assessment rubric.
Wrap up Activity:
Video showing the parts of the cell as a complex and dynamic system working together to sustain life functions.
Activity 5.3: Movement of Materials
Introduction
Introduce the concept of diffusion by showing the following video:
Model Development Activity – How do materials move in air? In water?
Demo: Diffusion in air and diffusion in water
Apparatus
Spray fragrance, air freshener, Lysol etc.
Beaker of cool H2O
Beaker of hot H2O
Food coloring
Pre-Activity Discussion
How do particles move in the air?
How do particles move in water (is it different in cool vs hot?)
INSTRUCTIONS - IN AIR
Ask students to observe the movement of fragrance in the classroom. How we can “observe” (detect) fragrance we cannot see? When the use of the sense of smell is identified, it may be necessary to discuss (briefly!) how this sense operates.
Students often do not understand that the sense of smell behaves in a similar manner as the sense of taste. Food cannot be tasted at a distance; contact must be made first. Likewise the sensors in our nose require contact with the thing being smelled. With this one idea in mind, spray the fragrance in a central location in the classroom and ask them to indicate by raised hand when their “fragrance sensors” detect the arrival of the fragrance at their seat.
Once a pattern of spread has been observed, the students are asked to hypothesize what matter must be like at its simplest level to explain their observations. Most students come to the course with some idea of atoms or molecules, and are likely to use these terms. It is important at this point to have them describe what they are envisioning is happening at this microscopic level in everyday language with sufficient detail to elicit a mental picture. It is helpful to ban the terms atom and molecule until these ideas are actually developed so students cannot hide behind language they may not understand adequately. Instead, encourage them to use words that are common to everyday speech (though, hopefully used more carefully than everyday speech!). We are, at this stage, essentially using the idea of simple particles first proposed by Democritus in the 4th century B.C.
It is also important to encourage the students to view the entire system of particles involved. If they do not readily include the air particles in their discussion, ask them to explain how the fragrance particles could have left the bottle (upward) and then moved in so many directions (outward). The mental images they are ‘seeing’ can be communicated through drawings on whiteboards. It should become evident that a static picture cannot represent what is happening adequately. The model of matter that fits the observations should include microscopic particles (commonly seen as spheres) that are in constant motion and collide with one another randomly.
Post-Activity Discussion
Following a discussion in class, students are asked to prepare a storyboard of the diffusion process by drawing a sequence of 5-7 particle diagrams that show how the arrangement of particles change over the time from when the fragrance was sprayed until the fragrance had well-permeated the room. They must include all matter particles involved in their system (the closed room) that were involved in producing the pattern of diffusion they observed.
Since students frequently forget about the role of the particles of air in the room in diffusion, it might be useful to have the students visit the Davidson web site to view an applet on diffusion. The second simulation is more appropriate for the level of Biology I.
INSTRUCTIONS - IN WATER
For the second demonstration, obtain two large beakers or flasks. Fill one with cool to cold water and the other with very warm water (not boiling). Allow the water to become still on a demo table before beginning the demonstration. Add 1-2 drops of a dark food dye to the water in each flask and observe the diffusion of the dye in the water. Using two different colors, such as red and blue, makes it easier to keep track of which beaker is hot and cold during discussion.
Students are asked to describe what they saw macroscopically, and then explain their observations in terms of the particle model we have developed so far (small, separate particles in motion that move randomly by collision). The discussion should draw students to explain the observed behavior in terms of the effect that adding energy to the system of particles has on temperature and the speed of the particles. An important aspect of our model of matter that is being developed is that particles interact via collision to change motion and transfer energy from particle to particle.
Post-Activity Discussion
This demonstration is followed up with the assignment to prepare two storyboard sequences, one each for the hot water and cold water diffusion observations. To contrast the difference in rate, each storyboard sequence should contain the same number of frames at the same time intervals. These can be prepared individually as a homework assignment or, if preferred and class time allows, prepared in groups on whiteboards.
Activity 5.4: Movement of Materials across a Boundary
Model Development Activity – How do materials move into/out of the cells through a membrane?
Apparatus
- Dialysis tubing cut into 15-cm strips (1 per group) (generic sandwich baggies can be used in place of
dialysis tubing)
- String or tubing clips
- 15 mL of 15% glucose/starch solution for each group
- Beaker
- Distilled water
- Iodine Potassium Iodide (IKI) (Lugol’s Indicator Solution)
- Glucose Test Strips (could use Benedict’s solution for glucose indication)
Pre-Activity Discussion
Are cells open to their environment? Can all things enter the cell? What type of things can pass into a cell?
INSTRUCTIONS
Create a data table for observations made at the start of the lab and after 30 minutes. Include the color of the solution in the tube and that of the distilled water in the beaker; the mass of the tube and the presence of glucose.
Obtain a 15-cm piece of 2.5-cm dialysis tubing that has been soaking in water. Tie off one end of the tubing to form a bag. To open the other end of the bag, rub the end between your fingers until the edges separate.
Test the glucose/ starch solution for the presence of glucose using the Test Strip. Record the results in the table.
Remove a small amount of the solution and test for the presence of starch using the Iodine Potassium Iodide (IKI; Lugol’s) indicator solution. Record the results.
Caution: Iodine is an irritant; it affects skin and eyes, and can stain clothing. Handle the solution with caution. Wash off spills and splashes with water. Place 15 mL of the glucose/starch solution in the bag. Tie off the other end of the bag, leaving space in the bag (fill bag only 2/3 full). Record the color of the solution. Dry the bag and mass it. Record the data.
Fill a 250-mL beaker or cup two-thirds full with distilled water. Add approximately 4 mL of Lugol's solution to the distilled water and record the color of the solution. Test this solution for glucose and record the results. Immerse the bag in the beaker of solution.
Allow your set-up to stand for approximately 30 minutes. Record the final color of the solution in the bag, and of the solution in the beaker. Test the liquid in the beaker and in the bag for the presence of glucose. Record the results. Dry and mass the bag. Record the data.
Post-Activity Discussion
While waiting for the reaction to occur, have students view the elodea leaf.
Whiteboard Activity - Provide a verbal representation for what occurred during the lab. Include a diagram to show what traveled into or out of the cell. Cite the evidence for your conclusions.
Which substance(s) are entering the bag and which are leaving the bag?
What evidence supports your answer?
Why did the weight of the bag change?
How did you know that starch did not diffuse out of the bag?
How did you know if glucose diffused out of the bag?
Activity 5.5: How Aquatic Plant Cells Respond to Different Environments
Apparatus
Microscope Slide
Coverslip Elodea