BIO 102: Transport across the Membrane

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24 Questions

What is the primary difference between facilitated diffusion and active transport?

The requirement of energy input

What is the energy source used by the Sodium-Potassium pump?

ATP

What is the purpose of the Sodium-Potassium pump in animal cells?

To maintain ion gradients for nerve and muscle function

What is the direction of solute movement in active transport?

Against the concentration gradient

What is the ratio of sodium ions expelled to potassium ions admitted by the Sodium-Potassium pump?

3:2

What is the result of active transport in cells?

Creation of a concentration gradient

Why is it essential to maintain high concentrations of potassium and low concentrations of sodium in animal cells?

For nerve and muscle function

What is the primary function of transport proteins in active transport?

To move solutes against their concentration gradient

What is the net transfer of charge with each 'crank' of the sodium-potassium pump?

One positive charge from the cytoplasm to the extracellular fluid

What is the main function of electrogenic pumps?

To generate voltage across a membrane

What is the primary use of proton gradients in the cell?

For ATP synthesis during cellular respiration

What is the mechanism by which a co-transporter couples the transport of two solutes?

The downhill diffusion of one solute drives the uphill transport of another solute

What is the role of the proton pump in co-transport?

To maintain the electrochemical gradient of H+

What is the direction of H+ transport during co-transport?

Down its concentration gradient from the extracellular fluid to the cell

What is the purpose of H+ /sucrose co-transport in plants?

To load sucrose into cells in the veins of leaves

What is the characteristic of an electrogenic pump?

It generates voltage across a membrane

What is the primary function of exocytosis in cells?

To export products out of the cell

Which type of molecules generally cross the cell membrane by bulk transport?

Large molecules like proteins and polysaccharides

What is the process by which the cell membrane engulfs fluids and large molecules to bring them into the cell?

Endocytosis

Which of the following requires energy?

Exocytosis and endocytosis

What is the role of microtubules in exocytosis?

To provide a pathway for vesicles to move to the plasma membrane

What is the result of the fusion of vesicle and plasma membranes during exocytosis?

The vesicle membrane becomes part of the plasma membrane

Which type of cells use exocytosis to export products?

All of the above

What is the result of the indentation of the cell membrane during endocytosis?

A 'bubble' of membrane closes in on itself

Study Notes

Transport across the Membrane

  • Despite the help of transport proteins, facilitated diffusion is considered passive transport because the solute is moving down its concentration gradient, requiring no energy.
  • Active transport, on the other hand, uses a transport protein to move a substance against its concentration gradient, requiring energy input, often from ATP.

Active Transport

  • One active transport system is the Sodium-Potassium pump, which uses ATP to expel 3 Na+ for every 2 K+ it admits, contributing to the membrane potential.
  • This process is essential for nerve and muscle function in animals, where high concentrations of potassium (K+) and low concentrations of sodium (Na+) are necessary.

Electrogenic Pumps

  • The sodium-potassium pump is an electrogenic pump, generating voltage across a membrane.
  • In plants, fungi, and bacteria, the main electrogenic pump is a proton pump, actively transporting protons (H+) out of the cell.

Co-transport (2ry Active Transport)

  • Co-transport couples the "downhill" diffusion of a solute to the "uphill" transport of a second substance against its own concentration gradient.
  • For example, in plants, the gradient of H+ generated by ATP-powered proton pumps drives the active transport of amino acids, sugars, and other nutrients into the cell.

Bulk Transport

  • Bulk transport occurs by Exocytosis and Endocytosis, allowing large molecules and particles to cross the plasma membrane.
  • Like active transport, these processes require energy.

Exocytosis

  • Exocytosis is the process by which the cell secretes certain molecules by the fusion of vesicles with the plasma membrane.
  • Vesicles that have budded from the Golgi apparatus move along microtubules to the plasma membrane, fuse with the membrane, and release their contents outside the cell.

Endocytosis

  • Endocytosis is the process by which the cell engulfs fluids and large molecules to bring them into the cell.
  • The cell membrane indents, and a "bubble" of membrane closes in on itself, forming a vesicle.

This quiz covers transport across the membrane, including passive and active transport, and the role of transport proteins in facilitating the movement of solutes.

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