Biology Chapter: Osmosis and Tonicity

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Questions and Answers

Which type of solution causes animal cells to lose water by osmosis?

Isotonic solution

Isometric solution

Hypotonic solution

Hypertonic solution (correct)

What is the main function of active transport in cells?

To increase the internal temperature of the cell

To equalize solute concentration inside and outside the cell

To move substances against their concentration gradient (correct)

To facilitate osmosis through a semipermeable membrane

Which process involves taking in solid particles across the plasma membrane?

Endocytosis (correct)

Exocytosis

Crenation

Osmosis

What occurs when a cell is placed in a hypotonic solution?

The cell swells and may burst due to water gain Signup and view all the answers

What role does ATP play in active transport?

It provides energy for the movement of substances Signup and view all the answers

What is the result of crenation in animal cells?

The cell loses water and shrinks Signup and view all the answers

During phagocytosis, what is formed when a solid particle is engulfed?

Phagosome Signup and view all the answers

What happens to cells in an isotonic solution?

There is no net movement of water Signup and view all the answers

What is a characteristic of passive transport mechanisms?

They occur down a concentration gradient. Signup and view all the answers

What is the role of ATP in active transport processes?

ATP provides energy to move substances against their concentration gradient. Signup and view all the answers

Which type of transport involves the movement of molecules through transport proteins?

Facilitated diffusion. Signup and view all the answers

Which statement accurately describes osmosis?

Osmosis is the diffusion of water across a selectively permeable membrane. Signup and view all the answers

What is a primary function of the selective permeability of plasma membranes?

To maintain different concentrations of ions in the cytoplasm. Signup and view all the answers

Which mechanism involves the cellular engulfing of large particles?

Bulk transport. Signup and view all the answers

What is a consequence of the presence of one or more cis double bonds in fatty acids?

Decreased stability of membrane aggregates. Signup and view all the answers

What occurs during exocytosis?

Membrane vesicles fuse with the membrane to release contents outside the cell. Signup and view all the answers

What is the primary function of channel proteins?

To provide a passageway for specific ions or molecules to move down their concentration gradient Signup and view all the answers

How do carrier proteins differ from channel proteins?

Carrier proteins selectively bind to their substrate and change shape to transport it Signup and view all the answers

What is the process of osmosis?

The diffusion of water across a selectively permeable membrane Signup and view all the answers

What does tonicity refer to in cellular biology?

The total concentration of all solutes in a solution affecting cell water movement Signup and view all the answers

What happens when a cell is placed in a hypertonic solution?

Water leaves the cell, potentially causing it to shrink Signup and view all the answers

Why is ATP important for active transport processes?

It provides energy to move substances against their concentration gradient Signup and view all the answers

What role do aquaporins play in cellular transport mechanisms?

They facilitate the rapid movement of water across membranes Signup and view all the answers

Which of the following statements about carrier-mediated transport is true?

The transporter protein binds the solute and undergoes a shape change to release it Signup and view all the answers

Study Notes

Osmosis and Tonicity

Water moves from a region of low solute concentration to a region of high solute concentration until solute concentration is equal on both sides of the membrane.
This movement of water across a selectively permeable membrane is called osmosis.
Isotonic solution: Solute concentration outside the cell equals the solute concentration inside the cell. There is no net movement of water by osmosis.
Hypertonic solution: Solute concentration outside the cell is greater than the solute concentration inside the cell. Water will move out of the cell by osmosis.
- Animal cells will undergo crenation (shrinkage)
- Plant cells will undergo plasmolysis (shrinkage of cytoplasm and pulling away from the cell wall)
Hypotonic solution: Solute concentration outside the cell is less than the solute concentration inside the cell. Water will move into the cell by osmosis.

Active Transport

Moves substances across membranes against their concentration gradient.
This type of transport requires energy in the form of ATP.
Specific proteins embedded in the membrane carry out active transport.
Active transport allows cells to maintain high concentrations of certain ions inside the cell compared to the concentration outside the cell.
- For example, cells maintain high K+ concentration inside the cell and low Na+ concentration inside the cell through active transport.

Bulk Transport (Uses Energy)

Endocytosis: The general process of taking bulky material into a cell.
- Phagocytosis: Solid particles are taken in across the plasma membrane.
  - White Blood Cells (WBCs) carry out phagocytosis of bacteria and viruses.
  - This creates a phagosome, which fuses with a lysosome to form a phagolysosome.
  - The material is then hydrolysed by hydrolytic enzymes.
  - Nutrients are released into the cell's cytoplasm and waste is released by exocytosis.
Exocytosis: The general process of releasing bulky material from the cell.

Fluidity of Cell Membranes

The fluidity and selective permeability of plasma membranes are important for the following:
- Cells can change shape in response to the environment.
- Allows exocytosis and endocytosis.
- Allows free diffusion of molecules such as oxygen, carbon dioxide, and small hydrocarbons.
- Allows the cell to maintain the composition of the cytoplasm independent of the external environment.

Transport of Ions and Molecules across Cell Membranes

Cells must exchange material with the extracellular environment.
There are three mechanisms by which substances can cross cell membranes:
- Passive transport: No energy required.
- Active transport: Energy required
- Bulk transport: Energy required.

Passive Transport

Movement that does not require the cell to use energy.
- Simple Diffusion: Movement of molecules or ions down a concentration gradient from a high concentration to a low concentration.
  - Molecules that cross the plasma membrane in this way are: CO2, O2, urea, and other small nonpolar molecules that dissolve and move through the hydrophobic membrane interior.
- Facilitated diffusion: Polar molecules and ions cross the membrane aided by transport proteins.
  - Channel proteins:
    - Provide a protein-lined passageway through which specific molecules or ions move down their concentration gradient.
    - Examples: Aquaporins (carry water molecules), ion channels (carry ions like Na, K+, Cl- and open/close in response to stimuli).
  - Carrier proteins:
    - Have a binding site that binds specifically to the substance they are supposed to carry.
    - Change shape in order to carry the molecule across the membrane.

Osmosis is A Type of Passive Transport

Osmosis is the diffusion of water across a selectively permeable membrane.
Effect of Osmolarity on Cell Balance:
- The tonicity of a solution describes the ability of a surrounding solution to cause a cell to gain or lose water by osmosis.
- A solution's tonicity is related to its osmolarity, which is the total concentration of all solutes in the solution.

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Test your understanding of osmosis and tonicity in biological systems. Explore concepts such as isotonic, hypertonic, and hypotonic solutions, and how they affect cell behavior. This quiz will help reinforce your knowledge of how water movement influences cells.