2.1.2 - Cell membranes

Question 1

What are organelles?

Answer 1

defined as the sub-cellular bodies found in the cytoplasm of cells

Question 2

What are eukaryotes?

Answer 2

a group of organisms with cells that have the genetic material contained in a membrane-bound nucleus

(they also contain a number of membrane-bound organelles such as mitochondria and chloroplasts)

Question 3

What are prokaryotes?

Answer 3

a group of organisms including bacteria and blue-green algae that have few organelles and do not have their genetic material contained in a membrane-bound nucleus

Question 4

What is a cell surface membrane?

Answer 4

the membrane that forms the outer boundary of the cytoplasm of a cell and controls the movement of substances into and out of the cell

Question 5

What is the main function of a membrane?

Answer 5

to control what passes in and out of the cell, allowing fluids either side of it to have different compositions

Question 6

What is an important characteristic of a membrane?

Answer 6

• its ability to be flexible
  this is to allow the cell to change shape slightly as its water content changes
• some membranes must be able to break and fuse together quickly due to vesicles

Question 7

What is a vesicle?

Answer 7

membrane ‘bags’ that hold secretions made in cells

Question 8

What are membranes made up of?

Answer 8

lipids and proteins (arranged in a very specific way)

Question 9

What is a polar lipid?

Answer 9

lipids with one end attached to a polar group e.g a phosphate group

Question 10

Describe the structure of the phospholipid bilayer.

Answer 10

• in the membrane
• polar lipids
• structure of phospholipid bilayer = unit membrane
• phosphate group forms the polar part of the molecule
• bilayer is formed with the hydrophilic heads on the outside pointing to the water
• hydrophobic tails stay protected in the middle

Question 11

Other than lipids, what is found in the phospholipid bilayer? What does this allow to dissolve through?

Answer 11

• proteins (can move within the bilayer)
• allows vital ionic chemicals to pass through
• a simple lipid bilayer can’t do this

Question 12

What makes the protein in the phospholipid bilayer able to move?

Answer 12

• the more unsaturated fatty acids, the more fluid the membrane is
• proteins can move within the bilayer but dependent on proportion of phospholipids containing unsaturated fatty acids

Question 13

What is the positioning of proteins in the bilayer?

Answer 13

• some penetrate all the way through the lipid

- others only go part of the way

Question 14

define a gated channel

Answer 14

protein channels through the lipid bilayer of a membrane that are opened or closed (depending on the conditions of the cell)

Question 15

What is the main function of the membrane proteins?

Answer 15

• to help substances move across the membrane
• proteins will form pores or channels known as gated channels
• allow specific molecules to go through
• some protein pores are active carrier systems that use energy to move the molecules

Question 16

What is attached to some membrane proteins?

Answer 16

• carbohydrates chains
• means it is a glycoprotein/ glycolipid
• important on surface of cells as it allows cells to recognise each other

Question 17

What is the fluid mosaic model?

Answer 17

• model of the structure of the cell membrane

- includes floating proteins forming pores, channels and carrier systems in the lipid bilayer