Download Course 2000020 Advanced Life Science 7th Grade

Course 2000020 Advanced Life Science 7th Grade
Curriculum Extension
Laboratory investigations which include the use of scientific inquiry, research, measurement, problem
solving, laboratory apparatus and technologies, experimental procedures, and safety procedures are
an integral part of this course.
The content should include, but not be limited to, the following:
Next Generation Sunshine State Standards Big Ideas
Big Idea 1: Practice of Science
Big Idea 2: The Characteristics of Scientific Knowledge
Big Idea 3: The Role of Theories, Laws, Hypotheses, and Models
Big Idea 14: Organization and Development of Living Organisms
Big Idea 15: Diversity and Evolution of Living Organisms
Big Idea 16: Heredity and Reproduction
Big Idea 17: Interdependence
Big Idea 18: Matter and Energy Transformations
Florida’s Frameworks for K-12 Gifted Learners Goals:
By graduation, the student identified as gifted will be able to:
Goal 1: critically examine the complexity of knowledge: the location, definition, and
organization of a variety of fields of knowledge.
Goal 2: create, adapt, and assess multifaceted questions in a variety of
fields/disciplines.
Goal 3: conduct thoughtful research/exploration in multiple fields.
Goal 4: think creatively and critically to identify and solve real-world problems.
Goal 5: assume leadership and participatory roles in both gifted and heterogeneous
group learning situations.
Goal 6: set and achieve personal, academic, and career goals.
Goal 7: develop and deliver a variety of authentic products/performances that
demonstrate understanding in multiple fields/disciplines.
CELLULAR PROCESSES 2
Curriculum Extension
Project Standards/Benchmarks and Goals/Objectives
Next Generation Sunshine State Standards1
SC.6.L.14.3
Recognize and explore how cells of all organisms undergo
similar processes to maintain homeostasis, including
extracting energy from food, getting rid of waste, and
reproducing.
1
FL Frameworks for K-12 Gifted Learners
Goal 1, Obj. 3: Investigative Methodologies
Trait: Investigative Methodologies (Understand):
Understands, identifies, and analyzes relationships
among variables, constants, and controls in
research
Goal 3, Obj. 1: Research Tools & Methodologies
Trait: Scientific Method (Understand):
Analyzes the impact or effect of chosen alternatives
(variables) within the scientific method
Goal 4, Obj. 2: Analyze Data
Trait: Forecasting Solutions (Understand):
Organizes facts and information using various
methods to predict potential outcomes
The Sunshine State Next Generation Standards and FL Frameworks referenced in this Project Outline are meant as an overview and do
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not constitute an exhaustive list of the standards covered in this Advanced Life Science 7 Grade class. For a complete list of the
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standards covered in the course, see the course description for course 2000020 Advanced Life Science 7 Grade at the FL Department of
Education. The web site address is: <http://www.floridastandards.org/Courses/CourseDescriptionSearch.aspx>
The student will:
I.
Students will microscopically observe various sub-cellular components and determine the
effects of different salt solutions on Elodea plant cells.
I.
Plasmolysis in Elodea Plant Cells
Context
Students should understand that the eukaryotic cell is a highly structured unit composed of
several subcellular components. These subcellular components are specialized parts, each of
which performs a unique function necessary for the survival of the cell. Most of these
structures are difficult to see in living cells not only because they are small, but also because
they are colorless.
In this lesson, students will microscopically detect the presence of chloroplasts, cell walls, and
cell membranes of the common aquarium plant, Elodea. Students will then determine the
effects of different salt solutions on the Elodea plant cell structures.
By adding salt water to the Elodea cell environment, students will observe the process of
plasmolysis, shrinkage of the cell contents due to water loss. However, you should not focus on
terminology, but rather what happens during plasmolysis. By conducting this lab, students will
be able to develop an operational understanding of plasmolysis, as well as reinforce their
understanding of osmosis and diffusion.
Research indicates that it may be easier for students to understand that the cell is the basic unit
of structure (which they can observe) than that the cell is the basic unit of function (which has
to be inferred from experiments). It is important to emphasize that cellular processes have an
impact on the entire organism.
Students should know that within cells, many of the basic functions of organisms are carried
out and that the way in which cells function is similar in all living organisms. Students should
also be familiar with the use of a microscope.
This lesson should follow some discussion about the various subcellular structures in animal
and plant cells. It does not introduce the cell membrane, cell wall, and chloroplasts to students;
rather, it demonstrates the presence of these cell components and the process of plasmolysis.
Planning Ahead
Materials:
 Plasmolysis in Elodea Plant Cells student sheet
 Lab Notebooks—it is recommended that students use lab notebooks for entering
observations; it should have the following format:
o Title
o Purpose or objective
o Materials
o Brief summary of procedures
o Observations
o Conclusions
 Per student or pair of students: 3 droppers, test tube of tap water, test tube of 5% salt
solution, test tube of 10% salt solution, 1 microscope slide, 1 cover slip, microscope, 1 paper
towel, lens paper
 Per class: Fresh Elodea in water, NaCl (sodium chloride or table salt), distilled water, 100-mL
graduated cylinder, balance
The student sheet can be distributed to students prior to the lab. As homework, students
can enter the relevant information into their lab notebooks and use these notebooks in lab
rather than the worksheet.
Preparation:
 Elodea is available locally at:
Driftwood Garden Center
5051 Tamiami Trail North
Naples FL 34103
(239) 261-0328
Elodea can also be purchased from Carolina Biological Supply
(www.carolina.com/onlinecatalog) or by calling customer support at 1-800-334-5551. A
pack of 25 Elodea is approximately $9.00.
 To make a 5% salt solution, weigh 5 grams of NaCl and place in a graduated cylinder.
Bring volume up to 100 mL with distilled water.
 To make a 10% salt solution, weigh 10 grams of NaCl and place in graduated cylinder.
Bring volume up to 100 ml with distilled water.
Motivation
Have students go to the following two sites: Cell Membrane, on the Life Science Connections
website, and The Cell Membrane, on the University of South Dakota website.
Ask students:
 What is the major function of a cell membrane?
 Why did the first site depict the cell membrane as a gate?
 Describe the structure of a cell membrane.
 How is the structure of the cell membrane related to its function?
Use these questions to discuss the necessity for the cell membrane to act as a physical barrier
marking the boundary of the cytoplasm and protecting the contents of the cell. In this
discussion, lead students to an exploration of the nature of the interaction of the cell with its
surroundings.
The analogy of a gate is an effective one because it allows students to understand that anything
going into or out of the cell must first cross the cell membrane. Thus, the cell membrane plays a
critical role in the acquisition of gases (such as oxygen necessary for cellular respiration),
nutrients, and water. Similarly, the cell membrane also allows things to leave the cell such as
carbon dioxide gas, water, and wastes.
Have students go to the Plant Cell Wall website.
Ask students:
 What is the major function of the cell wall?
 Describe the structure of the cell wall and its composition.
 How is the structure of the cell wall related to its function?
Discuss with students the differences and similarities between the cell membrane and the cell
wall. Surrounding every cell is some sort of covering that keeps what's inside the cell inside and
prevents harmful particles in the external environment from diffusing into the cell. Both the cell
membrane and the cell wall serve this function. All cells have a cell membrane, and certain cells
(plant and bacterial) also have a cell wall.
The cell membrane's main function is to regulate the movement of materials into and out of
the cell. However, not everything can just pass through the cell membrane—only certain
materials. Thus, scientists say that the cell membrane is selectively permeable, which means
that only selective (certain) substances can permeate (go through) the membrane. The cell wall
is a structure that surrounds the cell membrane and provides strength and rigidity to cells.
Unlike the cell membrane, the cell wall is not selectively permeable; things can easily pass
through the wall.
Development
Introduce the activity to students by saying: "As we have discussed, one of the functions of the
cell membrane is to control the flow of materials into and out of the cell. In this investigation,
you will observe the effects of placing plant cells in solutions of various salt concentrations."
Ask students to predict what will happen when an Elodea plant cell is placed in water vs.
varying concentrations of salt solutions. Do not confirm right or wrong answers at this point.
Guiding questions that may be used are:
 What do you think will happen to the plant cell when it is placed in water?
 What will be the effect on the cell membrane? The cell wall? Why?
 What do you think will happen to the plant cell when it is placed in salt water?
 What will be the effect on the cell membrane? The cell wall? Why?
 Will increasing the concentration of salt solution have a different effect on the cell? Why or
why not?
Pre-lab
Distribute copies of the Plasmolysis in Elodea Plant Cells student sheet to all students. While
the drawings and observations can be made directly on the sheet, it is recommended that
students enter this information in lab notebooks. Review the directions for the lab, focusing on
the techniques of slide preparation. Demonstrate how to make a wet mount slide and review
the use of the microscope.
Ask students:
 Why do you think we will observe the Elodea plant cell in tap water first? (The tap water is
the experimental control. It will allow students to observe Elodea plant cells in their normal
freshwater environment. Thus, when the salt water solutions are added, any changes that
occur to the plant cells can be attributed to the salt water solutions only.)
Lab
Encourage students to make careful sketches of their observations using colored pencils and to
attempt to label as many structures as they can identify. The students will likely need help in
identifying suitable regions of the Elodea to observe. You can prepare a typical slide and project
it to help students do this.
Post-lab
The post-laboratory discussion should center on the students' explanations of the changes
observed in the Elodea cells. Discuss what happens to the cell wall as the salt concentration
increases. Students should have been able to distinguish between the cell walls and the cell
membrane more clearly as more water leaves the cell and the cytoplasm shrinks.
Ask students the following questions to guide the post-lab discussion. As students answer the
questions, sketch an Elodea plant cell on the board, filling in the cell with the subcellular
structures being discussed.
 What color were the Elodea cells? (They were colorless except for green bodies.)
 What were the green bodies inside the Elodea cells? (Chloroplasts.)
 Where were these green bodies mostly located? (They were mostly located at the edges of
the cell.)
 Describe the shape of these chloroplasts. (Ovals.)
 Why are these chloroplasts green? (They are green because of the presence of chlorophyll,
the light-absorbing pigment necessary for photosynthesis.)
 Were the chloroplasts stationary or moving around the cell? (They should have been
moving.)
 Why were the chloroplasts moving around? (The cytoplasm within the cell is constantly
moving, thereby moving the various subcellular structures within the cell as well. This is
known as cytoplasmic streaming.)
 Did anyone notice a large space inside the cell?
 What is this large space? (The central vacuole.)
 What is the function of the central vacuole? (The central vacuole is an organelle in plant
cells that stores nutrients and water for the cell. It can take in and release water depending
on the cell's needs. Animal cells do not have a central vacuole; they have many small
vacuoles, which contain proteins, carbohydrates, water, and nutrients.)
 Describe what happened to the Elodea cells in the presence of 5% salt solution. (You should
draw Elodea in 5% salt solution on the board.)
 Describe what happened to the Elodea cells in the presence of 10% salt solution. (You
should draw Elodea in 10 % salt solution on the board.)
 Why did the cells shrink? (Higher salt concentration caused the diffusion of more water from
within the cell to outside the cell.)
 Why didn't the salt from the outside just move inside the cell instead of the water moving
out of the cell? What does this tell you about the cell membrane? (The cell membrane is
selectively permeable. It allows the movement of water but not salt.)
 What structure did the shrinking of the cell allow you to observe? (The cell wall.)
 Why didn't the cell wall shrink? (It is rigid and provides support to the Elodea plant cell. Also,
it allows salt to go through so it does not shrink, unlike the cell membrane.)
 Predict what would happen if we used a 20% salt solution.
 Describe what happened when you flushed out the salt solution with salt water.
 From your observations, is Elodea a freshwater or saltwater plant?
See the Plasmolysis! website for pictures of Elodea cells in various salt solutions. You can review
these with the class and ask students to compare these with what they saw in their
observations.
The following key concepts should be discussed with students:
 When plant cells are surrounded with salt water, the water inside the plant moves from
where there is more water (less salt) through the cell wall and membrane to the outside
where there is less water (more salt). This process of water movement from a high
concentration of water to a lesser concentration of water is called osmosis.
 When the water movement is out from a cell, we call this plasmolysis.
 Plasmolysis is the shrinking of the cytoplasm of a plant cell in response to diffusion of water
out of the cell and into a high salt concentration solution.
 During plasmolysis, the cell membrane pulls away from the cell wall. This does not happen
in low salt concentration because of the rigid cell wall. Plant cells maintain their normal size
and shape in a low salt concentration solution.
 Plasmolysis is a reversible process
Assessment
Ask students to use what they have observed to answer the following questions:
 Elodea normally lives in fresh water. What changes would you observe in the cells of an
Elodea plant that was suddenly moved from fresh water to salt water? Why? How would
plasmolysis affect the entire plant? (Plasmolysis would occur because the high concentration
of salt outside the cells would cause the diffusion of water from within the cell to outside the
cells. This would result in the entire plant becoming very flaccid.)

If you wish to restore flabby, wilted green vegetables or carrot sticks to crispy "freshness,"
would you soak them in salt water or in plain water? Explain your answer. (Vegetables
should be soaked in plain water. Because of the high concentration of water outside the
cells, water will flow into the cells. As the cells and central vacuole fill up with water, cells
will become rigid.)
Have students answer the Conclusions questions of the worksheet in their lab notebook. These
questions can be used as an assessment tool to check student understanding.
Suggested Additional Resources
 As a creative way of exploring cell structures, the Access Excellence lesson Analogy of Cell
Parts has students devise an analogy between some part of the cell and an everyday item.
 A website with an active description about osmosis and the movement of water in and out
of cells is How Substances Get Into and Out of Cells. Students can read the information on
this site and view the animations until the section entitled "Demonstration of Osmosis Using
Visking Tubing".
 From this activity, students should proceed to activities that enhance their understanding of
dynamic equilibrium within cells, diffusion, and osmosis. The Diffusion, Osmosis, and Cell
Membranes site has exploratory activities that can be used as extensions.
 From Access Excellence, Using Bubbles to Explore Membranes is a hands-on activity that
simulates cell membrane structure and function
 From Access Excellence, Diffusion and Osmosis with Data Analysis is a lab derived from an
AP Biology course in which data is collected and analyzed using Texas Instruments graphing
calculators.