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Title: PLANT CELL INVESTIGATIONS - A LOOK AT THE STRUCTURE AND FUNCTION OF PLANT ORGANELLES and MAKING A PLANT CELL MODEL
Principle(s) Investigated: The structure of a plant cell and the function of the plant cell organelles
California Standards :
BIOLOGY
Cell Biology
1. a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.
LIFE SCIENCE - 7TH GRADE
Cell Biology
1. a. Students know cells function similarly in all living organisms.
1. b. Students know the characteristics that distinguish plant cells from animal cells, including chloroplasts and cell walls
Next Generation Science Standards NGSS- MS-LS 1-2
LS1.A Structure and Function - Within cells, special structures are responsible for particular functions, and the cell membrane forms the boundary that controls what enters and leaves the cell.
Materials: Microscope - cover slips- glass slide
Elodea -waterweed Obtain at local Pet/fish shop
distilled water, cup and pipette
Colored Pencils - Plant cell drawing and labeling Handout
Organelle laminates - organelle name and corresponding definition
Cup of cell - model kit Each kit is comprised of yarn, button, thimble, screw, wire, plastic cap...
- Elodea
Procedure:
Lesson Part I
Guided Practice and Review: Distribute 10 laminated Plant Organelles to 10 students
Distribute 10 laminated Organelle functions to 10 students
Students walk the room to find their matching partner
For Example: Cell Wall
Finds student with definition: The rigid layer of nonliving material that surrounds the cell
The student pairs keep their matching organelle and function together for the Plant Cell Model Activity
Distribute- Cup of Cells
In Lab groups comprised of 4 or 5 students, the students will make a model of a plant cell using the miscellaneous items in the cup. Students discuss and decide what items would be used to represent the cells organelle. Once the cell model is complete the students will take the matching laminate organelle name and function and place the label along side the corresponding representing object.
Students will elect one member of their group to take a photo of their model and email the photo to the teacher. Name of students in the lab group should be included in the email.
Lesson Part II
Obtain a glass slide from teacher. Place 1 leaf up to 1 cm in length on the slide. Using pipette, place 1 drop of water on leaf piece, place cover -slip on specimen. Slide specimen is placed on microscope stage and clipped. Low power is used (10x=100 times magnification)
View Video for demonstration:
Elodea Plant Cells - wet mount slide set up
View, draw, and identify and label function of 3 organelles viewed.
Adjust to objective lens 40x = 400 times actual size
Organelles viewed: Cell Wall- a rigid layer of nonliving material that surrounds the cells of plants and other organisms
Chloroplasts-capture energy from sunlight and use it to produce food for the cell
Cytoplasm - gel-like substance located inside the cell membrane in which organelles move and chemical processes take place
Student prior knowledge:
Proper use and practice with the microscope.
Plant Organelles structure and function
Explanation: Elodea is a is common plant used to decorate aquariums. Elodea is easy to obtain in a pet store. Because the Elodea is only two cells thick it can be used to observe the structure of a plant cell including the cytoplasm, cell wall, vacuole and chloroplasts. The leaves of the Elodea are only two cells thick and therefore ideal for microscopic observation.
The Elodea plant lives in freshwater. Freshwater is (less) hypotonic when compared to the cytoplasm of the cell. This hypotonic environment promotes osmosis but the cell prevents rupture of the membrane.
A Closer Look at Plant and Animal Cells in Hypotonic Environments
Click on the "animate" buttons to see the effects of hypotonic environments on plant and animal cells.
Turgor in Plants
Plant cells are surrounded by rigid cell walls. When plant cells are exposed to hypotonic environments, water rushes into the cell, and the cell swells, but is kept from breaking by the rigid wall layer. The pressure of the cell pushing against the wall is called turgor pressure, and is the desired state for most plant tissues. For instance, placing a wilted celery stalk or lettuce leaf in a hypotonic environment of pure water, will often revive the leaf by inducing turgor in the plant cells.
Lysis in Animals
Animal cells lack rigid cell walls. When they are exposed to hypotonic environments, water rushes into the cell, and the cell swells. Eventually, if water is not removed from the cell, the pressure will exceed the tensile strength of the cell, and it will burst open, or lyse. Many single-celled protists living in freshwater environments have contractile vacuoles that pump water back out of the cell in order to maintain osmotic equilibrium and avoid lysis.
Extension activities can be made using the Elodea Plant hypertonic solutions
http://www.csun.edu/~laa50120/sed695b/elodea_plasmolysis/index.htm
A hypertonic solution (a solution highly concentrated with salt) will demonstrate how the chloroplasts will move towards the center of the cytoplasm. Plasmolysis is when a cell loses water in a hypertonic solution.
Questions & Answers:
Water moves in and out of a plant cell through a process called osmosis. How can evidence be collected that to prove that water leaves plants to the atmosphere?
Measure transpiration by placing a plastic bag around its leaves.
What is the function of chloroplasts?
Chloroplasts capture energy from sunlight and use it to produce food for the cell.
This balanced equation is called photosynthesis.
6CO2 + 6H2O ------> C6H12O6 + 6O2
Sunlight energy
What evidence can be provided to show the movement of water from the soil, root, stem to the vacuole?
Several simple class room demonstrations illustrate the movement of water through a plant structure.
A wilted houseplant such as an impatiens or coleus can regain its structure within one class period. Looking at the structure of plant organelles, a vacuole is a sac that stores water, flood, waste products and other materials.
Applications to Everyday Life:
The plant cell wall resembles brick work on a building or retaining wall. The "bricks" are not stacked in a linear fashion, but staggered for flexibility and strength. What would happen if a building was built with bricks stacked one on top of another?
Images in the microscope provide evidence that the plant observed has water. You can see the chloroplast that appear to be swimming within the cell wall. Over time, without water, what happens to a plant? The flow of water out of a plant is called transpiration. Maintaining proper watering is essential for plant survival.
Since it is possible to over water a plant causing the plant to die, is it possible to over water a human being?
Imagine the cell membrane in an animal cell flooded with water. Excess water would dilute pertinent concentrations of nutrients such as salt. The human body is made of 66% water. Hyponatremia is a condition when sodium is diluted in the blood stream. Sodium is a electrolyte that regulates water in the cell. If the amount of sodium concentrate drops in the blood stream, additional water through osmosis will flow into the cell. Brain cells swollen with water can cause mild to severe to extreme repercussions.
Photographs:
Videos: Elodea Plant Cell
references: vccs.edu- lecture 3 transpiration
nim.nih.gov Hyponatremia
Plant Cell Illustration
https://docs.google.com/document/d/1Oihk224tMiDKZW2ixrQ-JOocRF-Ax50T2gz4s9brAsI/edit
Plant Cell Organelle and Function
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