Topic 2.3 - Transport of substances

Question 1

What is the function of the phospholipid bilayer ?

Answer 1

selectively permeable: only allows small, non-polar, lipid soluble substances through
allows to form vesicles
-> provides fluidity

Question 2

What is the function of the glycoprotein ?

Answer 2

-> used fro cell recognition and cell signaling
-> different organisms have different glycoproteins and can be used to initiate immune responce

Question 3

What is the function of glycolipids ?
(Chain of carbohydrates attached to a protein)

Answer 3

-> used for cell recognition and also a source of energy by hydrolysed to release glucose for respiration

Question 4

What is the function of extrinsic proteins ?

Answer 4

-> receptor site for proteins: detects chemicals released from other cells

Question 5

What is the function of transport proteins ?

Answer 5

-> two transport proteins: carrier and channels
-> carrier proteins can be used for faciliated diffusion and active transport
-> channel proteins can be used for facilated diffusion

Question 6

What is the function of cholestrol ?

Answer 6

-> decreases fluidity and increases rigidity

Question 7

Why is the plasma membrane referred as fluid-mosaic ?

Answer 7

-> molecules within the membrane are able to move
-> mixture of phospholipds, glycoproteins, glycolipids,cholestrol, transportproteins

Question 8

Define diffusion

Answer 8

It is passive NET movement of substances from an area of high concentration, to an area of low concentration, down a concentration gradient.

Question 9

Which substances can simply diffuse across the phospholipid bilayer?

Answer 9

Small, non-charged (or non-polar), lipid soluble

Question 10

Explain why molecules of oxygen and carbon dioxide are able to diffuse across membranes.

Answer 10

-> The hydrophobic fatty acid part of membrane is non-polar
-> Oxygen and carbon dioxide are small non-polar molecules;
-> Oxygen/carbon dioxide can diffuse through the fatty acid layer
-> Down a concentration gradient

Question 11

Write the equation for Fick’s law

Question 12

What could limit the rate of facilitated diffusion?

Answer 12

-> The number of transport proteins available in the membrane
-> the concentration gradient
-> the surface area

Question 13

Define active transport

Answer 13

Active transport is the movement of a substance against its concentration gradient.

This requires the use of a carrier protein that uses energy released from ATP hydrolysis.

Question 14

How does active transport move substances against their concentration gradient?

Answer 14

Substance binds to a carrier protein

ATP binds to carrier protein

ATP is hydrolysed into ADP and Pi and this releases energy

This causes the carrier protein’s tertiary structure to change (undergoes a conformational change)

The substance is released on the other side of the membrane

Question 15

What could limit the rate of active transport?

Answer 15

The number of carrier proteins

The amount of oxygen available for respiration. (this affects the amount of ATP available)

Very High temperature – if the temperature is high it could denature enzymes involved in respiration so ATP cannot be produced.

Question 16

Give two ways in which active transport differs from diffusion?

Answer 16

In active transport ATP is used;

and movement is against a concentration gradient

Question 17

Contrast the processes of facilitated diffusion and active transport.

Answer 17

Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins;

Facilitated diffusion does not use ATP whereas active transport uses ATP;

Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient.

Question 18

Define osmosis

Answer 18

The net movement of water from an area of high water potential to an area of lower water potential through a partially permeable membrane

Question 19

What does it mean if 2 solutions are isotonic?

Answer 19

They have the same water potential

Question 20

Vegetables are made of different types of tissue, in an experiment where do you take a cutting from and why?

Answer 20

When taking a cutting you must ensure it’s through one tissue only in order for it to be a fair test. As different tissues may affect water potential differently.

Question 21

Why are bungs are placed on test tubes when conducting an experiment overnight?

Answer 21

To stop water from evaporating and therefore changing the water potential

Question 22

Ratio’s or % change in mass are calculated to

Answer 22

allow a valid comparison when the initial length/mass is not the same.

Question 23

Summarise how the products of carbohydrate digestion or the products of protein digestion are absorbed

Answer 23

Na+/K+ pump moves 3 Na+ ions out of the cell (into the blood) and 2K+ ions into the cell by active transport. This uses ATP.

This creates a lower concentration of Na+ in the epithelial cell than in the lumen of the intestine

Na+ ions move into the epithelial cell by facilitated diffusion. They travel through a symport protein and bring glucose with them. This is called co-transport.

The glucose is moving into the cell cell against its concentration gradient

The glucose concentration in the epithelial cell increases

Glucose moves into the blood from the epithelial cell through a carrier protein by facilitated diffusion.

Question 24

Adaptations of the epithelial cell

Answer 24

Lots of mitochondria 🡪 Release energy in the form of ATP 🡪 ATP is needed for active transport

Lots of enzymes attached to their membrane 🡪 Breaks down maltose into glucose

Microvilli 🡪 provide a large surface area for maximum absorption

Carrier proteins for active transport

Channel/Carrier proteins for facilitated diffusion