IBDP CORE>TOPIC 2.4>CELL MEMBRANES
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ASSESSMENT STATEMENT2.4.1 Draw and label a diagram to show the structure of membranes.
2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes. 2.4.3 List the functions of membrane proteins. 2.4.4 Define diffusion and osmosis. 2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion. 2.4.6 Explain the role of protein pumps and ATP in active transport across membranes. 2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane. 2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis. |
DAY 1- LAB ACTIVITY
After completing the lab activity, answer the following questions-
- What changes were observed in P1, P2 and P3?
- What changes were observed in A1, A2 and A3?
- What co-relation can be derived from the above observations?
- What can you infer about the solutions based on your observations?
- Predict reason for your observation.
2.4.1 Draw and label a diagram to show the structure of membranes.
2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.
The main component of the biological membrane is a molecule- phospholipid. It consists of
1. The polar head (hydrophilic) made from glycerol and phosphate 2. The non-polar part which has two fatty acid tails (hydrophobic).
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2.4.3 List the functions of membrane proteins.
The proteins in the plasma membrane help the interaction of the cell with its environment.
For example, transporting nutrients across the plasma membrane, receiving chemical signals from outside the cell, translating chemical signals into intracellular action, hormone binding sites and sometimes anchoring the cell or cell adhesion. |
Membrane proteins vary in their positions within the membrane and in their functions. Outline the positions and functions of proteins in membranes. 8M
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Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain the structure of cell membranes. 6M
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Integral proteins are embedded in the membrane/phospholipid bilayer;
peripheral proteins are on the surface of the membrane; some integral proteins (are transmembrane proteins that) extend from one side ofthe membrane to the other; hormone binding sites; e.g. insulin; enzymes; e.g. sucrase / succinate dehydrogenase; cell adhesion; cell-to-cell communication recognition / antigenic markers / glycoproteins / contact inhibition; Channels/pores for passive transport/facilitated diffusion; pumps/carriers for active transport; Receptors for neurotransmitters; such as acetylcholine;electron carriers; e.g. electron transport chain of cellular respiration;pigments (in rods/cones); (Award any of the above points if clearly drawn in an annotated diagram.) |
Membranes are surrounded by water;
hydrophilic molecules are attracted to water; hydrophobic molecules are attracted to one another/repel water; phospholipids are amphipathic/have a hydrophobic tail and a hydrophilic head; tails are positioned away from water / heads are positioned towards water; phospholipids have a hydrocarbon tail and a phosphate head; phospholipid bilayer/ membranes self-assemble in water; protein association with membrane is determined by hydrophobic interactions; phospholipid bilayer is hydrophilic on the outside and hydrophobic on the inside; |
2.4.4 Define diffusion and osmosis.
2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion.
The cell membrane is hydrophobic inside thus hydrophobic (lipid soluble) molecules will pass through easily. This is by simple diffusion. However hydrophilic molecules and charged particles will not be able to cross the cell membrane. They will need the help of protein channels, this is facilitated diffusion.
Simple diffusion involves the diffusion of molecules through the phospholipid bilayer while facilitated diffusion involves the use of channel proteins embedded in the membrane. Water moves through by osmosis which is also by passive transport. Osmosis involves the movement of water molecules from a region of low solute concentration, to a region of high solute concentration. So if the solute concentration is higher inside the cell than outside the cell, water will move in and vice versa. |
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2.4.6 Explain the role of protein pumps and ATP in active transport across membranes.
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2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.
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2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.
The plasma membrane is held together by the relatively weak hydrophobic associations between phospholipids. This allows membrane fluidity and flexibility.
Thus the breaking and remaking of membranes is possible, allowing larger substances access into and out of the cell. There are two processes based on the entry and exit of substances. Endocytosis
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Stephantaylorwrksht2.4cells.pdf | |
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References-
Damon, Alan et al, Higher level Biology for the IB diploma. Pearson Baccalaureate
Clegg, CJ, Biology for the IB diploma. London: Hodder Murrray, 2007, 978-0340926529
Taylor, Stephan, Science Video resources Wordpress,
Burell, John. Click 4Biology(online)
All picture have been downloaded from Google images for educational purpose only
Damon, Alan et al, Higher level Biology for the IB diploma. Pearson Baccalaureate
Clegg, CJ, Biology for the IB diploma. London: Hodder Murrray, 2007, 978-0340926529
Taylor, Stephan, Science Video resources Wordpress,
Burell, John. Click 4Biology(online)
All picture have been downloaded from Google images for educational purpose only