Revision:Membranes 1

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Draw a diagram to show the fluid mosaic model of a biological plasma membrane

File:Mosaic membrane.jpg

Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membrane

The head of the phospholipids is polar and hydrophilic (water-loving) and the heads make it up the outside of the phospholipid bilayer. The tail of the phospholipid is located inside the membrane and is not non-polar and hydrophobic. Because of this difference the phospholipids naturally form bilayers where the head is facing towards the water and the tail is facing outwards the water. This enables the phospholipid to maintain a stable structure.

List the functions of membrane proteins

List the functions of membrane proteins including hormone binding sites, enzymes, electron carries, channels for passive transport and pumps for active transports== The membrane proteins functions are;

• hormone binding sites
• enzymes
• electron carrier
• channels for passive transport
• pumps for active transport

Define diffusion and osmosis

Diffusion: The passive movement of small uncharged particles going from a high concentration region to a low concentration region.

Osmosis: The passive movement of water molecules going through channels in the plasma membrane from a high concentration to a low concentration.

Explain passive transport across membranes in terms of diffusion

If there is a concentration gradient (difference between the concentrations) then passive transports happen naturally as it requires no energy.

Explain the role of protein pumps and ATP in active transport across membranes

Energy is required in the form of ATP because of the transportation of a substance going from low concentration to higher concentration. The particles are transported by protein pumps.

Explain how vesicles are used to transport materials within a cell

Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.

Vesicles are membranous sacs in which materials are transported and stored throughout the cell. The materials within a vesicle can go through the membrane when the membranous vesicle becomes a part of the organelles plasma membrane and then released.

Describe how fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis

Endocytosis is the movement of particles in to a cell when the plasma membrane engulfs the particles. Exocytosis is the movement of particles out of a cell when the particle is enclosed within a vesicle and then fuses. The fluid in the cell membrane is in constant motion and when the phospholipids move, the cell membranes changes shape which then forms holes in the membrane for particles to move in and out. If the membrane wasn’t of fluid, the vesicle would not be able to fuse.

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