How do things move across a cell membrane? | Cells | MCAT | Khan Academy

Summary

This video explains how cells use various transport mechanisms to move essential nutrients and expel waste. It introduces passive transport, including diffusion, osmosis, and facilitated diffusion, which do not require energy. Active transport mechanisms, such as the sodium-potassium pump, use energy to move ions against their gradients. The video also discusses secondary active transport, endocytosis, and exocytosis, which are used for larger molecules and vesicles. These processes are crucial for maintaining cellular function and can be disrupted in diseases, highlighting the importance of understanding cell transport for combating infections.

Takeaways

• 😀 The cell is the smallest unit of life, requiring nutrients and producing waste that need to be transported across its membrane.
• 😀 Transport across the cell membrane is crucial for survival, and larger molecules require more complex transport mechanisms.
• 😀 Potassium leak channels allow potassium ions to flow out of the cell, following their concentration gradient in passive transport.
• 😀 Passive transport requires no energy and includes diffusion, osmosis, filtration, and facilitated diffusion using protein channels.
• 😀 The sodium-potassium pump is an example of active transport, using energy (ATP) to move sodium and potassium ions against their concentration gradients.
• 😀 Active transport can be primary (direct use of ATP) or secondary (using gradients created by primary active transport).
• 😀 In secondary active transport, sodium ions create a gradient that helps glucose enter cells in symport, utilizing the sodium gradient indirectly.
• 😀 Antiport is a type of secondary active transport where two molecules move in opposite directions across the membrane.
• 😀 Larger molecules like proteins are transported into cells via endocytosis, where the cell membrane engulfs and forms a vesicle.
• 😀 Exocytosis is the reverse of endocytosis, where a vesicle inside the cell fuses with the membrane to expel substances, such as neurotransmitters.
• 😀 Understanding these transport mechanisms is vital for comprehending diseases, as viruses can hijack these processes to cause harm.

Q & A

What is the smallest unit of life in the human body?

The smallest unit of life in the human body is the cell.

Why do cells need to transport substances across their membrane?

Cells need to transport substances across their membrane to bring in nutrients and remove waste products necessary for survival.

What determines the size of the transport mechanisms needed for substances?

The size of the transport mechanism needed depends on the size of the substance being transported, with larger molecules requiring more complex mechanisms.

What is a potassium leak channel, and how does it function?

A potassium leak channel allows potassium ions to passively flow out of the cell, down their concentration gradient, since there is a higher concentration of potassium inside the cell than outside.

What is passive transport, and can you give an example?

Passive transport is the movement of substances across a membrane without using energy. An example is the potassium leak channel, where potassium flows out of the cell naturally.

What is the difference between primary and secondary active transport?

Primary active transport directly uses ATP to move substances across a membrane, like the sodium-potassium pump. Secondary active transport uses the ion gradients created by primary active transport to move other substances, like sodium helping glucose enter the cell.

What does the sodium-potassium pump do?

The sodium-potassium pump actively transports sodium out of the cell and potassium into the cell, both against their concentration gradients, using ATP as energy.

What is symport in secondary active transport?

Symport is a form of secondary active transport where two substances are moved in the same direction across a membrane, such as sodium and glucose in the gut.

What is the process of endocytosis?

Endocytosis is the process by which a cell engulfs large molecules or particles, such as proteins, by enclosing them in a vesicle that fuses with the cell membrane, allowing the contents to enter the cell.

How does exocytosis differ from endocytosis?

Exocytosis is the process by which a cell expels substances, such as acetylcholine, using vesicles that fuse with the cell membrane to release their contents, while endocytosis involves substances entering the cell.