Membrane Transport

Question 1

Explain the plasma membrane

Answer 1

• Phospholipid bilayer
• Semi permeable
• Contains proteins

Question 2

Explain membrane transport releasing energy or cost energy

Answer 2

• Process that ensures the smooth movement of various molecules, ions and substances across cell membranes
• Empowers the cell to maintain an internal equilibrium, known as homeostasis
• Assumes a central role in nutrient absorption, waste elimination, intercellular exchange…
  Separates the cell’s inner realm from the external surroundings

Question 3

Explain gradients

Answer 3

• Gradient = Describes any such difference between two neighbouring regions
• Concentration gradient = a solute is more concentrated in one region than in a neighbouring region
• If a substance moves from an area where it is more concentrated to an area where it is less concentrated, it is said to be ‘moving down’ or ‘following its concentration gradient
• As the solutes move, the gradient dissipates/ disappears, unless energy is expended to maintain it

Question 4

What is cell transport

Answer 4

Encompasses the movement of substances across the cell membrane to uphold cellular balance and necessary functions

Question 5

Explain passive transport

Answer 5

• Does not require energy input
• A substance moves across a membrane without the direct expenditure of energy
• There are three types of passive transport:
  1. Simple diffusion
  2. Facilitated diffusion
  3. Osmosis

Question 6

Explain facilitated diffusion fully

Answer 6

• Polar molecules, along with ions, navigate the cell membrane through the utilization of integral membrane proteins functioning as channels or carriers. Also does not require energy.
• Two types: Channel mediated diffusion and Carrier mediated diffusion
  Differ in the type of protein used to move the substances across the membrane
• Channel mediated: Leak channel ( Always open) and Gated channel (Open due to stimulus)
• Carrier mediated: By carrier protein

Question 7

Explain simple diffusion fully

Answer 7

• A form of passive transport in which a substance moves down its concentration gradient without the use of a carrier molecule or protein.
• Substances may enter or leave cells by simple diffusion only if they can pass freely through the membrane, e.g. lipids, oxygen, carbon dioxide.

Question 8

Explain the factors affecting rate of diffusion

Answer 8

• Extent of the concentration gradient: The greater the difference in concentration, the more rapid the diffusion. The closer the distribution of the material gets to equilibrium, the slower the rate of diffusion becomes.
• Mass of the molecules diffusing: More massive molecules move more slowly because it is more difficult for them to move between the molecules of the substance they are moving through; therefore, they diffuse more slowly.
• Temperature: Higher temperatures increase the energy and therefore the movement of the molecules increasing the rate of diffusion.
• Solvent density: As the density of the solvent increases, the rate of diffusion decreases. The molecules slow down because they have a more difficult time getting through the denser medium.

Question 9

Explain osmosis fully

Answer 9

• This intriguing process entails the diffusion of water molecules across a selectively permeable membrane, responding to discrepancies in solute concentrations.
• This depends on tonicity of the environment: The ability of the solution to cause water movement

Question 10

Explain the 3 solutions for osmosis

Answer 10

1. Isotonic solution same solute concentration as the cell. When cell is placed in an isotonic solution no nett movement of water is found, i.e. the amount of water moving into the cell is equal to the amount flowing out. The cell size will remain constant.
2. Hypotonic solution has less solutes and is less concentrated resulting in a higher water potential. When cell is placed in hypotonic solution water will move into cell resulting in cell swelling.

3.Hypertonic solution has more solutes and is more concentrated resulting in a lower water potential. When cell is placed in hypertonic solution water will move out of cell resulting in cell shrinking.

Question 11

Explain active transport fully

Answer 11

• The cell uses a Transport Protein to move a substance against its concentration gradient
• Energy needed comes from ATP

Question 12

Explain endocytosis

Answer 12

• Allows a cell to engulf fluids and large molecules and bring them into the cell.

Question 13

Explain exocytosis

Answer 13

• The opposite of endocytosis, uses vesicles to transport fluids and large particles out of cells. Vesicles within the cells move to the cell membrane and join with it, releasing the substance outside the membrane

Question 14

How do particles enter and leave the cell

Answer 14

• help from vesicles