Transport across cell membranes

Question 1

What is the cell surface membrane made up of?

Answer 1

The cell surface membrane is made up of lipids and proteins.

Question 2

What is the most common lipid found in living organisms?

Answer 2

The most common lipid found in living organisms is triglycerides.

Question 3

What are phospholipids made up of?

Answer 3

The glycerol and phosphate “head” and a tail containing long hydrocarbon chains of the fatty acid.

Question 4

What do the phospholipids do when mixed with water?

Answer 4

When mixed with water phospholipids create a structure with their hydrophobic tails on the inside and hydrophilic heads on the outside. This is called a phospholipid bilayer and forms the basis of membranes.

Question 5

How thick is the cell surface membrane generally?

Answer 5

The cell surface membrane is generally 7 nm thick. This is important as it means we cant see its structure even under an electron microscope.

Question 6

The cell surface membrane can move, what is this called?

Answer 6

The movement is called it being fluid

Question 7

Membrane proteins have very different functions. Name some:

Answer 7

• They act as enzymes and digest disaccharides. These are found in the epithelium of the small intestine
• they act as channels through the membrane and allow certain ions to pass through.
• they act as carrier proteins and play a role transporting substances in and out of the cell
• they act as receptors for hormones
• they are linked to cell recognition

Question 8

What are glycoproteins and glycolipids?

Answer 8

They are combinations of carbohydrates, lipids and proteins

Question 9

someone add images

Answer 9

https://alevelbiology.co.uk/wp-content/uploads/dlm_uploads/2017/06/AQA-AS-Biology-3.2.3-Transport-across-cell-membranes.pdf

Question 10

Active transport definition:

Answer 10

Active transport is the movement of particles from an area of low concentration to an area of high concentration (against their concentration gradient) across a cell membrane, using ATP and carrier proteins.

Question 11

What processes are used to transport things across the membrane?

Answer 11

○ simple diffusion (involving limitations imposed by the nature of the
phospholipid bilayer)
○ facilitated diffusion (involving the roles of carrier proteins and channel
proteins)
○ osmosis (explained in terms of water potential)
○ active transport (involving the role of carrier proteins and the importance of
the hydrolysis of ATP)
○ co-transport (illustrated by the absorption of sodium ions and glucose by
cells lining the mammalian ileum).

Question 12

Difference between eukaryotic and prokaryotic cell membranes?

Answer 12

The basic structure of all cell membranes, including cell-surface membranes and
the membranes around the cell organelles of eukaryotes are the same.

Question 13

How can you increase the rate of transport across a membrane?

Answer 13

‒ Cells may be adapted for rapid transport across their internal or external membranes by an increase in surface area of, or by an increase in the number of
protein channels and carrier molecules in, their membranes.

Question 14

What is a cell membrane? (Long)

Answer 14

Also known as the plasma membrane, the cell membrane is a semi-permeable area in a
cell that separates the interior components of the cell from the extracellular matrix.
Ions and organic molecules can selectively pass through the membrane. Transport of
material across the cell membrane is important in the operation of the cell.
The cell membrane is composed of a lipid bilayer with some proteins embedded in it.
The hydrophobic tails of the lipid components of the membrane is placed in the middle
of the bilayer, protected from the polar extracellular and interstitial fluids. Aside from
the proteins, cholesterol molecules are also embedded in the cell membranes. It
maintains the fluidity of the membrane and increases its stability

Question 15

What are the functions of the cell membrane?

Answer 15

1. Separation between the extracellular fluid and the internal components of the cell
2. Communication with other cells
3. Recognition of external substances
4. Structural support
5. Transport of materials

Question 16

What is simple diffusion used for related to membranes?

Answer 16

This is the primary mode of transport for small molecules and gases like oxygen and carbon dioxide. It is important that these two gases readily diffuse through
the membrane because oxygen is needed by the cells for metabolism, and carbon dioxide need to be expelled by the cell for eventual release to the environment.

Question 17

Give an example of active transport in cell membrane transport:

Answer 17

An example of active transport is the transport of potassium and sodium ions through the sodium-potassium pump. An electrochemical gradient is present because of the imbalance in the concentration of positive charges across the membrane. ATP provides the energy needed to produce a conformational change for the eventual release of the ions to the other side of the membrane.