Active Transport

What is Active Transport

Active transport is an energy or ATP-dependent, cellular transport process that selectively moves substances from an area of low concentration to an area of high concentration or ‘against the concentration gradient’, with the help of a membrane protein.

Characteristics of Active Transport

Substances are transported against their concentration gradient
It is a fast process
Requires cellular energy
Needs a helper transmembrane protein structure called ‘pumps’ for transport

Types of Active Transport with Examples

1) Primary Active Transport

A primary active transport process is one in which metabolic energy obtained from the breakdown of high-energy phosphate molecules – adenosine triphosphate (ATP), is used to transport solutes across the cell membrane. It is also called direct active transport or uniport.

What it Transports: Charged ions such as Na⁺, K⁺, Mg²⁺, and Ca²⁺.

Example: Sodium-potassium pump, which helps to move potassium into the cell and carry sodium out.

2) Secondary Active Transport

Also called coupled transport or cotransport, it involves the movement of substances across the cell membrane utilizing energy in other forms than ATP. This energy comes from the electrochemical gradient created by pumping ions out of the cell, which powers the movement of another ion or molecule in the same direction (symport) or opposite direction (antiport) of the membrane.

What it Transports: Na⁺, K⁺, adenosine triphosphate (ATP), adenosine diphosphate (ADP), and inorganic phosphate (Pi).

Example: Cotransporting glucose and sodium in the small intestine using sodium-glucose transporter.

Functions of Active Transport in Cells

In Plants

Essential for the absorption of water and minerals from the soil by the root hair cells

In Animals

Necessary for the secretion of metabolic products such as ions, digestive enzymes, and hormones, and the elimination of toxic wastes from cells, by a form of active transport, called exocytosis
Helps in the absorption of nutrients by cells, engulfing pathogens by white blood cells, and swallowing food by bacteria occurs by a process called endocytosis, another form of active transport
Helps in signal transduction that prepares the cell to adapt to its changing environment

FAQs

Q1. Why does active transport require energy?

Ans. Active transport needs energy either directly as ATP or that generated from the electrochemical gradient to transport substances from their low to a high concentration across the cell membrane.

Q2. What is the main difference between primary and secondary active transport?

Ans.The main difference is that in primary active transport, the energy to carry out the process is derived directly from the breakdown of ATP, while in secondary active transport, the energy is derived from the difference in concentration of ions between the two sides of a membrane.

Q3. How is active transport similar to facilitated diffusion?

Ans.The similarity is that both use helper transmembrane proteins to transport ions, sugars, and salts in and out of the cell.

Q4. How is facilitated diffusion different from active transport?

Ans.The main difference is that facilitated diffusion does not require energy to carry out the process, whereas active transport uses either metabolic or electrochemical energy to perform the process.

Q5. What are the membrane structures that function in active transport?

Ans.The membrane structures that function in active transport are proteins and lipids.

Q6. How does diffusion different from active transport?

Ans. Diffusion is a physical or biological process involving the spontaneous movement of substances from their high concentration to low concentration without the need for energy. In contrast, active transport is an energy-dependent biological process that involves the movement of substances from an area of low concentration to an area of high concentration across the cell membrane.

Q7. How is osmosis different from active transport?

Ans. Osmosis is the movement of solvent molecules from an area of high solute concentration to an area of low solute concentration across a selectively permeable membrane. In contrast, active transport is the movement of solute from an area of their low concentration to an area of high concentration across a selectively permeable membrane.

Q8. What organelle produces the energy required in active transport?

Ans. Mitochondria is the cell organelle that produces the energy required for active transport.

Q9. Why must active transport function continuously?

Ans. Active transport moves essential ions and molecules from their low to the high concentration and thus helps to maintain their right balance inside the cell.

References
- 1. Active Transport – Khanacademy.org
  2. Active Transport- Types and Significance – Microbenotes.com
  3. What is Active Transport? – News-medical.net
  4. Active Transport – Openstax.org