Osmosis in Plants & Animals: A Vital Balancing Act

Osmosis is essential for life, ensuring that plants stay upright and hydrated while animals maintain the balance of fluids in their cells. Let’s explore how osmosis works in plants and animals and why it’s so important for both.

 

What is Osmosis?

Key Definition:

Osmosis is the net movement of water molecules from an area of higher water potential (dilute solution) to an area of lower water potential (concentrated solution) through a partially permeable membrane.

 

Osmosis in Plant Cells

• Plant cells rely on osmosis to absorb water, maintain structure, and transport nutrients.
• When water diffuses into plant cells by osmosis the vacuole in the plant cell gets bigger which causes the cell membrane to push against the cell wall
• This is good for two reasons, one being the increased pressure by the cell wall means it prevents too much water getting inside and the cell bursting, also it helps the cell to remain firm and provides support and strength for the plant
• When plants don't have enough water, the opposite happens, the plant isn't rigid and strong and the plant will wilt

Here’s what happens when plant cells are exposed to different solutions:

 

Plant Cells In Different Solutions:

Hypotonic Solution (Dilute):

• When placed into solutions that have a higher water potential than the cell, water moves into (diffuses into) the cell by osmosis.

• The cell becomes turgid (swollen and firm) from the water molecules pushing the cell membrane against the cell wall.

• Turgor pressure: The pressure of water inside the cell pushes against the cell wall, supporting the plant.

 

Isotonic Solution (Balanced):

• Water moves in and out at the same rate.

• The cell stays in its normal state, neither turgid nor flaccid.

 

Hypertonic Solution (Concentrated):

• When placed into solutions that have a lower water potential than the cell, water moves out (diffuses out) of the cell by osmosis.

• The cell becomes flaccid (soft and limp) as there is lack of water there is no build of pressure to keep the cell rigid.

• Severe water loss leads to plasmolysis, where the cell membrane pulls away from the cell wall.

 

Importance in Plants:

• Support: Turgid cells keep stems upright.

• Water Transport: Osmosis helps water move from the soil into root hair cells and up to other parts of the plant.

 

 

Osmosis in Animal Cells

• Animal cells also depend on osmosis to regulate water levels and maintain balance. However, animal cells lack a rigid cell wall, so they react more extremely to osmosis.
• If an animal cell is placed in a dilute solution, i.e distilled water, where the water potential is higher than the cell, the cell will have water diffuse into the cell by osmosis. As there is no cell wall to create the turgor pressure, this will continue and the cell membrane will continue to stretch until it bursts
• When an animal cell is placed into a concentrated sugar solution, i.e has a lower water potential, water will diffuse out by osmosis and can become crenated (shrivelled)

 

 

Importance in Animals:

• Hydration: Keeps cells hydrated for proper function.

• Fluid Balance: Maintains the balance of fluids in tissues and organs.

 

Comparing Plant and Animal Cells in Osmosis

Feature	Plant Cells	Animal Cells
Rigid Cell Wall	Present; prevents bursting.	Absent; cells may burst.
Response to Hypotonic	Becomes turgid (healthy state).	Swells and may burst (lysis).
Response to Hypertonic	Becomes flaccid or plasmolysed.	Shrinks (crenation).
Role of Osmosis	Supports structure and water transport.	Balances hydration and fluids.