Cell Transport Osmosis

This section provides an overview of Osmosis and Active Transport within the topic of cell transport.

Osmosis

Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration. This process occurs due to a concentration gradient and does not require energy.

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Key Points:

• Osmosis is a type of passive transport, meaning it does not require ATP (energy).
• Water moves through the partially permeable membrane, allowing only small molecules (such as water) to pass through, but not larger molecules (such as solutes).
• Osmosis is essential in maintaining cell turgidity in plant cells and homeostasis in animal cells.

Osmosis in Plant Cells

• When placed in a hypotonic solution (higher water concentration outside the cell), water moves into the cell, causing it to become turgid (swollen but firm).
• In an isotonic solution (equal concentration inside and outside), there is no net movement of water, and the cell remains normal.
• In a hypertonic solution (higher solute concentration outside), water moves out of the cell, causing it to become plasmolysed (shrunken and weak).

Osmosis in Animal Cells

• In a hypotonic solution, water moves into the cell, which may cause it to burst (lysis) due to lack of a cell wall.
• In a hypertonic solution, water moves out, causing the cell to shrink (crenation).

Active Transport

Active transport is the movement of molecules against a concentration gradient, from a low concentration to a high concentration, using energy from ATP. This process requires carrier proteins found in the cell membrane.

Key Points:

• Active transport requires energy from respiration.
• It moves substances against the concentration gradient.
• It uses specific carrier proteins to transport molecules across the membrane.

Example: Root Hair Cells

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Root hair cells in plants use active transport to absorb mineral ions (e.g., magnesium and nitrate ions) from the soil, where they are in lower concentration compared to inside the root hair cell.

• Root hair cells have large surface areas to maximise absorption.
• Energy from mitochondria powers the active transport process.
• Minerals are transported into the plant against the concentration gradient, ensuring the plant gets essential nutrients for growth.

Comparison of Osmosis and Active Transport

Both osmosis and active transport are crucial for maintaining cell function. Osmosis ensures cells maintain the correct water balance, while active transport enables cells to absorb essential nutrients even when they are in lower concentrations in the surrounding environment. Understanding these processes is essential for explaining how substances move in and out of cells efficiently.