Cell Membrane

Question 1

Homeostasis

Answer 1

• Body systems work together to ensure that the cellular environment remains stable/kept constant.
• This is called homeostasis.
• The cells are maintained at a constant temperature, surrounded by fluids with a constant concentration.
• To carry out their function cell need to take in and remove certain substances.

Question 2

Structure of the Cell Membrane (Part 1)

Answer 2

• The details of the cell membrane are too small to be seen, even with an electron microscope.
• Models have been proposed to account for the behaviour and composition of the cell membrane.
• The currently accepted model for cell membrane structure is called the fluid mosaic model.

Question 3

Structure of the Cell Membrane (Part 2)

Answer 3

• The main structure of the membrane is composed of phospholipid molecules, which are lipid molecules containing a phosphate group.
• The phospholipids are arranged in two layers (bilayer)
• Each phospholipid molecule has a head that is hydrophilic (water-loving) and a tail that is hydrophobic (water-hating).

Question 4

Structure of the Cell Membrane (Part 3)

Answer 4

• The phospholipids are arranged in two layers with their heads on the outside and tails on the inside.
• Embedded in the phospholipid bilayer are cholesterol and protein molecules. These molecules are important for the function integrity and stability of the membrane.
• Cell membranes have a variety of protein molecules, including receptor proteins, channel proteins, carrier proteins and cell identity markers.

Question 5

Function of the Cell Membrane

Answer 5

1. It acts as a physical barrier between the inside and outside of the cell
2. It regulates the passage of materials
3. It is sensitive to changes e.g. receptors detect environmental changes
4. It helps support the cell e.g. the internal part of the cell membrane is attached to the cytoskeleton.

Question 6

Passive and Active Transport

Answer 6

• Passive processes DO NOT use energy

- Active processes USE the cell’s energy in the form of adenosine triphosphate (ATP).

Question 7

Simple Diffusion

Answer 7

• Diffusion results in the movement of particles until they are evenly distributed over the space available.
• It occurs in fluids.
• Particles move from a higher concentration to a lower concentration until they are evenly distributed.
• E.g. oxygen, carbon dioxide, alcohol, steroids and other fat soluble substances move via diffusion

Question 8

Osmosis

Answer 8

• It is the diffusion of a solvent through a differentially permeable membrane in order to balance the concentration of another substance. E.g. water
• The higher level on one side of the membrane results from a pressure, known as osmotic pressure. The higher the concentration of the solute, the higher the osmotic pressure.