2.1.5e Active Transport & Bulk Transport

Question 1

Define Active transport

Answer 1

The movement of molecules or ions
…into or out of a cell
…from an area of lower concentration to an area of higher concentration
…against a concentration gradient
…across a partially permeable membrane

Question 2

Is Active transport a PASSIVE or ACTIVE process

Answer 2

ACTIVE - Process requires:
- ATP energy from respiration
- A carrier protein

Question 3

Purpose of the carrier protein in Active transport

Answer 3

A molecule attaches to the carrier protein, the protein changes shape & this ‘pumps’ the molecule, in one direction, across the membrane, releasing it on the other side

Question 4

Purpose of ATP energy in Active transport

Answer 4

Needed to move the solute against its concentration gradient

Question 5

Active transport is important in:

Answer 5

1. Reabsorption of useful molecules & ions into the blood after filtration into the kidney tubules
2. Absorption of some products of digestion from the digestive tract
3. The loading of sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant
4. The loading of inorganic ions from the soil into root hairs

Question 6

Eg of substances moved by Active transport

Answer 6

• Uptake of glucose by epithelial cells in the villi of small intestine
• Uptake of mineral ions from soil by root hair cells in plants

Question 7

Why is the movement by carrier proteins ONE DIRECTIONAL

Answer 7

• The carrier proteins are complementary to the molecule they transport
• Once the molecule collides with the protein, it is transported across the membrane & released on the other side
• It cannot then be transported back since the carrier protein is no longer complementary to it

Question 8

How do cells take in substances

Answer 8

by Endocytosis

Question 9

How do cells secrete substances

Answer 9

By Exocytosis

Question 10

What is Bulk transport

Answer 10

Another from of Active transport
- This type of transport moves substances (eg. enzymes, hormones) that are too large to move through channel or carrier proteins

Question 11

What are the 2 types of Bulk transport

Answer 11

• Exocytosis
• Endocytosis

Question 12

What is Endocytosis

Answer 12

• Some molecule are too large to be taken into a cell by carrier proteins (eg. proteins, lipids)
  1. Instead a cell can surround a substance with a section of its plasma membrane
  2. The membrane then pinches off to form a vesicle inside the cell, containing the ingested substance*
• This process uses ATP for energy
• There are 2 types: Phagocytosis (movement of solids) & Pinocytosis (movement of liquids)

Question 13

Eg of movement by Endocytosis

Answer 13

Some WBCs (mainly phagocytes) use endocytosis to take in microorganisms & dead cells so that they can destroy them

Question 14

What is Exocytosis

Answer 14

• Some substances produced by the cell (eg. digestive enzymes, hormones) need to be released from the cell
  1. Vesicles containing these substances Pinch off from the sacs of the Golgi apparatus & move towards the plasma membrane
  2. The vesicles fuse with the plasma membrane & release their contents outside the cell
• Some substances (like membrane proteins) arent released outside the cell - instead they are inserted straight into the plasma membrane
• Uses ATP for energy

Question 15

see pg57 for dia of exocytosis & endocytosis

Question 16

How do molecules move by Active transport

Answer 16

1. The molecule or ion binds to receptors (w complementary shape) on the carrier protein on outside of cell
2. ATP binds to the carrier protein on the inside of the cell. It is hydrolysed to ADP + P w the release of energy. Phosphate molecules remains bound to the protein (phosphorylating it)
3. This provides the energy required for carrier protein to change shape (conformational change)
4. The molecule or ion is released to inside of cell
5. The phosphate is released from carrier protein & recombines w ADP to form ATP
6. The carrier protein returns to its og shape

Question 17

Factors that affect the rate of Active transport

Answer 17

1. Speed of individual carrier proteins - the faster they work, faster the rate of Active transport
2. Number of carrier proteins - the more carrier proteins present, faster the rate of Active transport
3. Rate of respiration - release of ATP molecules. The more ATP molecules, faster the rate of Active transport

Question 18

Why is ATP energy required for Bulk transport

Answer 18

• To transport vesicles to & from the cell surface membrane along the cytoskeleton
• For fusing the vesicle to the membrane