4) Cell Transport Mechanisms

Question 1

What does the size of the organism, specifically the SA:V determine?

Answer 1

The efficiency of transport of substances by diffusion in an organism.

Question 2

How do SA:V and efficiency correlate?

Answer 2

The higher the SA: V ratio, the more efficient diffusion is.

Question 3

SA: V in large/small objects

Answer 3

Smaller objects have a larger SA/V
Larger objects have a smaller SA/V

Question 4

How to calculate surface area? (A cube which has 6 faces and each side is 4cm)

Answer 4

6 x 4 x 4 = 96cm²

Question 5

How to calculate volume? (A cube which has 6 faces and each side is 4cm)

Answer 5

4 x 4 x 4= 64cm³

Question 6

Which is more efficient for diffusion, smaller or large objects?

Answer 6

Smaller objects

Question 7

Give examples of organisms that are efficient for diffusion

Answer 7

Small single celled organisms (bacteria)
Very small multicellular organisms (worms)

Question 8

What 3 factors determine why small organisms can expel waste and CO2 through diffusion?

Answer 8

The diffusion distance is short
The SA/V ratio is high
Metabolic demands are low

Question 9

Why is diffusion for large organisms not adequate?

Answer 9

They have a low SA/V ratio

Can not meet demand and removal of waste due to the large distances involved

Question 10

What 3 factors affect the rate of diffusion?

Answer 10

Area of diffusion
Difference in concentration
Thickness of diffusion surface

Question 11

What is the optimum features of an organisms for diffusion?

Answer 11

Organisms that surfaces with a large area and are thin. Also, a high difference in concentration.

Question 12

What is the function of the cell surface membrane?

Answer 12

Contains the cell
Controls movement of substances in and out of the cell
Maintains the osmotic balance of the internal environment
Allows the cell to be recognised e.g. by hormones

Question 13

What is the chemical structure of the cell membrane?

Answer 13

Lipids (In the form of phospholipids and cholesterol)
Proteins
Carbohydrates (In the form of glycoproteins and glycolipids)

Question 14

What are the properties of the cell membrane?

Answer 14

Flexible
Fluid
Selectively Permeable

Question 15

Label fluid mosaic model

Answer 15

Refer to textbook or workbook

Question 16

What does fluid lipid bilayer consist of?

Answer 16

It has a mosaic of proteins and carbohydrates (glycoproteins and glycolipids) floating in it

Question 17

Why do phospholipids form bilayers in aqueous environments?

Answer 17

Phospholipids are both hydrophobic and hydrophilic.

Question 18

What does microscope images of a cell membrane show?

Answer 18

Proteins sticking out of the cell membrane.

Question 19

What substance passes in and out of the cell membrane sometimes?

Answer 19

Some water-soluble substances pass in and out of cells.

Question 20

What substances pass through the membranes easily, and which substances don’t?

Answer 20

Lipid-soluble substances pass easily through membranes. Ionic and polar molecules do not pass easily through membranes.

Question 21

What other models were there besides the fluid mosaic model?

Answer 21

The Davson-Danielli model was proposed in 1935, showing a phospholipid bilayer in between 2 protein layers.

Question 22

What is the downside to the Davson-Danielli model?

Answer 22

The model does not explain the many known facts about membranes

Question 23

What is the similarity between the fluid mosaic model and the Davson-Danielli model?

Answer 23

They both have a phospholipid bilayer with proteins

Question 24

What are the 2 differences between the fluid mosaic and Davson-Danielli models?

Answer 24

The fluid mosaic model has proteins within the phospholipid bilayer, while the Davson-Danielli model has a protein layer outside the membrane.

The fluid mosaic model has glycoproteins, glycolipids and cholesterol, whereas the Davson-Danielli model doesn’t.

Question 25

What is the difference between active transport and passive transport?

Answer 25

Passive transport doesn't require energy whereas active transport requires energy.

Question 26

What is passive transport?

Answer 26

When there is a high concentration of particles and a low concentration of particles, more particles move away from the high concentration area than the low concentration area, so the net movement is AWAY from the high concentration to the low.

Question 27

What are the 3 kinds of passive transport/movement?

Answer 27

Diffusion Facilitated Diffusion Osmosis

Question 28

What is equilibrium?

Answer 28

When the concentration is the same on both sides of the membrane, particles are still moving across in both directions but the net movement is ZERO.

Question 29

What factors do there need to be in order for diffusion to occur?

Answer 29

Even if there is a higher concentration on one side than the other, diffusion can only occur when: -The membrane is permeable -The particle and/or pore is charged -The particle is soluble

Question 30

What is osmosis?

Answer 30

Osmosis is the diffusion of free water molecules.

Question 31

What does osmosis involve?

Answer 31

-The net movement of water molecules from a solution with a high water potential (low solute concentration) to a solution with a low water potential (higher solute concentration) -Movement through a partially permeable membrane (permeable to water but not the solute)

Question 32

What is facilitated diffusion?

Answer 32

The process of passive transport of molecules across a membrane, with the help of membrane proteins

Question 33

What type of molecules can pass through the lipid bilayer?

Answer 33

Small, non charged molecules like O2 and CO2

Question 34

What do bigger, charged molecules like glucose or sodium ions need to pass through?

Answer 34

A channel in form of a channel protein

Question 35

What are channel proteins?

Answer 35

A membrane protein that allows molecules through a pore

Question 36

What are carrier proteins?

Answer 36

A membrane protein that the molecule causes it to change shape, so it carries the molecule across the membrane

Question 37

What are the properties of carrier proteins?

Answer 37

They are passive or active when transporting molecules down a concentration gradient (high to low)

Question 38

What is active transport?

Answer 38

A movement of molecules across a cell membrane from an area of low concentration to an area of high concentration, against the concentration gradient

Question 39

How are channel proteins given energy?

Answer 39

From ATP

Question 40

What is an ATP molecule made up of?

Answer 40

Ribose 3 Phosphate Groups Adenine Base

Question 41

How is energy released from an ATP molecule?

Answer 41

When the bond between the 3rd and the 2nd phosphate is broken by hydrolysis, energy is released

Question 42

How do we create ATP again?

Answer 42

Energy is required to add a 3rd phosphate bond to ADP to create ATP again

Question 43

What is endocytosis

Answer 43

Movement of large molecules into the cell by vesicles, requires energy in the form of ATP

Question 44

What is exocytosis

Answer 44

Movement of large molecules out of the cell by vesicles, requires energy in the form of ATP

Question 45

How is exocytosis and endocytosis possible?

Answer 45

Through the fluid nature of the cell membrane

Question 46

Give an example of endocytosis

Answer 46

Phagocytosis (cell-eating)

Question 47

What is phagocytosis?

Answer 47

A large structure e.g. molecule is surrounded by the cell membrane and engulfed in a vesicle which moves into the cell

Question 48

What is pinocytosis?

Answer 48

Cell-drinking, if the material taken in is a liquid

Question 49

How does exocytosis occur?

Answer 49

Large molecules in the cell is engulfed in the vesicle, which moves to the cell membrane where it fuses with the membrane. The contents that were engulfed are then released out of the cell