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Title: Properties of phospholipids in cell membrane
Principle(s) Investigated:
- Hydrophobic
- Hydrophilic
Standards : Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells.
[Assessment Boundary: Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis.]
Materials:
- Magic Sand/Space Sand
- Beach Sand
- Beakers
- Water
- Pipette
- Plastic spoon
- Coffee filter
Procedure:
- Fill two 150ml beakers with water
- Scoop a spoonful of beach sand into a coffee filter
- Pour it into one of the 150ml beaker
- Record observations
- Scoop a spoonful of magic sand/space sand into a coffee filter
- Pour it into the second 150ml beaker
- Record observations
- Using the pipette, slowly drop one water droplet at a one. Keep track of the number of droplets it takes to sink the magic sand. Record the number of droplets.
- Clean up. Use the coffee filter to filter the sand.
Click here to see results in spreadsheet form.
Student prior knowledge:
- Sand will sink to the bottom when poured into water
- Cells have many organelles
- Cells have a membrane that protects the organelles
Explanation:
Unlike regular sand, magic sand has been coated with hydrophobic substances. The coating of the sand repels water similar to that of oil. When magic sand is mixed with water, the coating repels the water, preventing the sand from getting wet like that of the regular sand. When water droplets are added to the top of the magic sand until the droplets of the water becomes too heavy for the thin layer of magic sand to hold, the magic sand folds itself, keeping the sand particles as closely as possible preventing water to enter the inside of the sand.
This repulsion of water from the magic sand can be used to demonstrate the concept of hydrophobic of phospholipids in cell membrane. A cell membrane is consist of 2 layers of phospholipids. Each phospholipid is made up of a hydrophilic phosphate head and two hydrophobic hydrocarbon tails. Due to the composition of the phospholipids, it is important that the cell membrane must exist as a lipid bilayer in order to interact with water. The tails of both layers face each other on the
inside of the membrane (intracellular) while the phosphate heads are facing outwards of the membrane (extracellular) for water interactions. This composition of the cell membrane only allows very particular substances to enter and exit the cell, hence the name selectively permeable membrane.
Questions & Answers: Give three thought-provoking questions and provide detailed answers.
- Explain what might happen if the cell membrane is sliced in half leaving only one layer of lipids available?
- Answer: If the cell membrane is sliced in half, the phospholipid molecules will rearrange themselves. The hydrophobic tails will face each other on the inside and the hydrophilic heads will be on the outside.The molecules will create a circular like structure.
- What might happen if the phospholipids are placed in oil?
- If phospholipid molecules are placed into oil, the hydrophilic heads will rearrange itself into a circular shape with the heads on the inside and the tails on the outside.
Applications to Everyday Life: Explain (don't just list) three instances where this principle can be used to explain other phenomenon.
- Soap has the ability to strip away grease due to its nature of having both hydrophilic and hydrophobic proper
- ties (amphipathic). The hydrophobic side sticks to the grease while the hydrophilic side is attracted to water. Therefore, soap is a great invention to wash greasy pots and pans.Hydrophobic substances such as sorbents can be used to remove oil in water. Hydrophobic will attract hydrophobic substances, therefore, this method will attract the oil without withdrawing the water out of the ocean.
Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.
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