4. Cell Membranes And Transport

Question 1

why is the fluid mosaic model membrane described as “fluid”

Answer 1

because phospholipids and proteins can move around via diffusion

Question 2

why is the fluid mosaic membrane described as “mosaic”

Answer 2

because the scattered pattern produced by the proteins within the phospholipid bilaterally looks like a mosaic when viewed from above.

Question 3

what are the three types of lipids in the cell membrane

Answer 3

phospholipid
cholesterol
glycolipids

Question 4

what are the two types of protein in the cell membrane

Answer 4

glycoprotein
transport proteins (carrier and channel)

Question 5

what are the four main receptor types?

Answer 5

signaling receptors for hormones and neurotransmitters
receptors involved in endocytosis
receptors involved in cell adhesion
cell marker/antigen for cell to cell recognition

Question 6

what are the stages of a pathway in cell signaling

Answer 6

-a stimulus is received by a receptor
-signal is converted to a ‘message’ that can be passed on
-‘message’ is transmitted to a target

Question 7

What is diffusion

Answer 7

The net movement of molecules from a region of its higher concentration to a region of its lower concentration as a result of their random movement

Question 8

What is facilitated diffusion

Answer 8

Certain substances cannot move through the phospholipid bilayer without the help of certain proteins like channel and carrier proteins.

Question 9

What is osmosis

Answer 9

The net movement of water molecules from, a region of higher water potential to a region of lower potential through a partially permeable membrane

Question 10

What is active transport

Answer 10

The movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration
Requires carrier proteins

Question 11

What is meant by endocytosis

Answer 11

The bulk movement of Particles or molecules into the cell.
The cell membrane engulfs material to form a small vesicle.

Question 12

Describe the steps in endocytosis

Answer 12

Phagocytosis- the bulk uptake of solid material
The vacuoles are called phagocytic vacuoles.
Eg engulfing of bacteria by white blood cells.

Pinocytosis- the bulk uptake of a liquid
The vesicles are often very small in which case the process is called micropinocytosis.

Question 13

What is exocytosis

Answer 13

The reverse of endocytosis.
Process by which materials are removed from cells by the fusion of vesicles containing the substance with the cell membrane

Question 14

Explain what happens during exocytosis

Answer 14

Secretory vesicles from the Golgi apparatus carry the enzymes to the cell surface and release their contents.

Question 15

Function of cholesterol

Answer 15

-Regulates the fluidity of the membrane
-Contributes to the impermeability of the membrane to ions

Question 16

Function of glycolipids and glycoproteins

Answer 16

They act as receptor molecules
Some act act cell markers or antigens for cell to cell recognition

Question 17

Explain how ligands are involved in the stages of a cell signaling pathway.

Answer 17

-ligands are secreted from a cell into the extra cellular space
-ligands are then transported through the extra cellular space to the target cell
-ligands bind to surface receptors on the target cell
-the message carried by the ligand is relayed through the chain of chemical messengers inside the cell triggering a response

Question 18

When is active transport important?

Answer 18

-reabsorption of useful molecules and ions into the blood after filtration into the kidney tubules.
-absorption of some products of digestion from the digestive tract
-loading sugar from the photosynthesizing cells of leaves into the phloem tissue for transport around the plant
-loading inorganic ions from the soil into root hairs