2. Transport across the cell membrane

Question 1

Define Cell membrane.

Answer 1

An organelle which controls what enters and leaves the cell. It is selectively permeable.

Question 2

What is the name given to describe the structure of the cell membrane?

Answer 2

Phospholipid Bilayer or Fluid Mosaic Model.

Question 3

Describe the structure of the phospholipid bilayer.

Answer 3

Consists of 2 layers of phospholipids and is mosaiced with proteins

Question 4

What is a phospholipid?

Answer 4

A component of the cell Membrane.
EXTENSION - Each phospholipid has a water loving phosphorous head & water hating a lipid tail.

Question 5

Name molecule X in the diagram

Answer 5

Protein

Question 6

What is the functions of proteins embedded in the plasma membrane?

Answer 6

Remember CASPER!!!
Carriers – for active transport
Antigenic markers – for cell recognition
Structural support – strength
Pores – for movement of larger molecules
Enzymes – to speed up reactions
Receptors – for hormones (cell signalling

Question 7

Define Selectively permeable

Answer 7

A property of the plasma membrane which only allows certain substances to pass the cell membrane. E.g., Oxygen glucose and carbon dioxide are allowed but Starch is too big so is not allowed!

Question 8

What is passive transport?

Answer 8

The transport of molecules across the cell membrane. The main types of passive transport is diffusion & osmosis. Passive transport occurs DOWN a concentration gradient and does not require ENERGY.

Question 9

Define concentration gradient

Answer 9

The DIFFERENCE in the concentration of a substance between two areas (on either side of a cell membrane). The bigger the difference, the steeper the gradient.

Question 10

What is diffusion?

Answer 10

An example of passive transport. The movement of molecules from an area of high concentration to a low concentration gradient across a selectively permeable membrane. It does not need energy.

Question 11

Describe 3 molecules which move by diffusion in body cells.

Answer 11

Diffusion occurs in the lungs where oxygen moves from the lungs (high concentration) into the blood (low concentration).
Carbon dioxide moves in the opposite direction.

Glucose will also diffuse from the blood (high concentration) into cells (low concentration) where it is needed for respiration.

Question 12

Define osmosis

Answer 12

The movement of WATER molecules from an area of high-WATER molecule concentration to a low WATER molecule concentration gradient across a selectively permeable membrane.

Question 13

I say osmosis you say…

Answer 13

WATER

Question 14

Explain why osmosis is described as a passive process

Answer 14

Osmosis moves water molecules from an area of high to low water concentration freely/ passively (It requires no energy).

Question 15

Why are animal and plant cells affected differently by osmosis

Answer 15

Due to the presence or absence of the cell wall. (STRONG CELL WALL MADE OF CELLULOSE)

Question 16

In reference to osmosis what does the acronym PPT stand for?

Answer 16

PLANT cells become PLASMOLYSED and TURGID

Question 17

Define Plasmolysed

Answer 17

When too much water moves out of a plant cell, the cell contents shrink. This pulls the cell membrane away from the cell wall.

Question 18

Define Turgid

Answer 18

When a plant cell takes in excess water by osmosis. The cell looks swollen but does not burst due to the presence of a cell wall.

Question 19

Past Paper Question

The diagram shows a model cell. Describe and explain what will happen to it during this experiment

3 marks

Answer 19

The model cell will gain mass. This is due to osmosis. Water will move from higher water concentration outside the cell, to a lower water concentration inside the cell. The water molecules are small enough to pass across the selectively permeable membrane.

Question 20

In reference to osmosis what does the acronym ABS stand for?

Answer 20

ANIMAL cells BURST and SHRINK

Question 21

What happens to an animal cell placed in pure water?

Answer 21

It bursts

Question 22

What happens to an animal cell placed in high sugar or salt solution?

Answer 22

It shrinks (SOLUTE SUCKS!)

Question 23

What happens to a plant cell placed in high sugar solution?

Answer 23

Becomes plasmolysed

Question 24

What happens to a plant cell placed in pure water?

Answer 24

Becomes Turgid

Question 25

Define Active transport

Answer 25

The movement of molecules from a low concentration to a high concentration against the concentration gradient. This requires energy.

Question 26

What component of cell membrane helps to pump molecules to where they are needed during active transport

Answer 26

PROTEINS

Question 28

Describe one difference between active and passive transport

Answer 28

Passive transport does not require energy. Active transport does require energy (in the form of ATP)
OR
Passive transport moves molecules DOWN a concentration gradient. Active transport moves molecules AGAINST the concentration gradient