Osmosis and Concentration Gradients

This page delves deeper into the concepts of diffusion and osmosis, focusing on concentration gradients and their effects.

The page begins by explaining how the concentration gradient affects diffusion rates. It emphasizes that diffusion occurs down the concentration gradient, from areas of high concentration to low concentration.

Highlight: The bigger the difference in concentration, the steeper the concentration gradient and the faster the rate of diffusion.

An example of diffusion in respiration is provided:

Example: Oxygen needed for respiration passes from the air in lungs into red blood cells through cell membranes by diffusion, moving down the concentration gradient from high to low oxygen concentration.

The page then transitions to discussing osmosis, introducing key terminology:

Vocabulary: A dilute solution contains a high concentration of solvent $e.g., water$ and a low concentration of solute $e.g., sugar$. A concentrated solution has the opposite composition.

The fundamental principle of osmosis is explained:

Definition: In osmosis, water moves from a dilute solution $high concentration of water molecules$ to a concentrated solution $fewer water molecules in a given volume$ across the membrane of a cell.

This information provides a solid foundation for understanding the mechanisms of diffusion and osmosis in cells.

Visual Representation of Osmosis

This page presents a detailed diagram illustrating the process of osmosis in cells under different conditions. The visual aid helps to reinforce the concepts discussed in previous sections.

The diagram shows two scenarios:

1. A model cell in a hypotonic solution
2. A model cell in a hypertonic solution

In both cases, the cell is represented by a partially permeable membrane bag containing a concentrated sugar solution. The surrounding solution differs in each scenario.

Example: In the hypotonic solution, water moves into the bag by osmosis, causing the water level in the glass tube to rise. In the hypertonic solution, water moves out of the bag by osmosis, lowering the water level.

This visual representation effectively demonstrates how the concentration gradient drives the movement of water molecules during osmosis. It also illustrates the concept of semi-permeable membranes, which allow water to pass through but not larger molecules like sugar.

The diagram is particularly useful for understanding the differences between diffusion and osmosis, as it clearly shows the selective movement of water molecules across the membrane.

Effects of Osmosis on Cells

This page explores the effects of osmosis on animal cells in different types of solutions. It introduces key terminology related to solution tonicity and illustrates the cellular responses.

Three types of solutions are defined:

Definition:

• Isotonic solution: The concentration of solutes outside the cell is the same as inside.
• Hypertonic solution: The concentration of solutes outside the cell is higher than inside.
• Hypotonic solution: The concentration of solutes outside the cell is lower than inside.

The page then describes how cells react in each type of solution:

1. In an isotonic solution, the cell remains normal.
2. In a hypertonic solution, water moves out of the cell by osmosis, causing it to shrivel.
3. In a hypotonic solution, water moves into the cell by osmosis, causing it to swell and potentially burst.

Highlight: If the solution outside the cell becomes much more concentrated $hypertonic$ than the cell contents, water will move out of the cell by osmosis. The cytoplasm will become too concentrated, and the cell will shrink/shrivel up and can no longer survive.

This information is crucial for understanding how osmosis affects cells in different environments and is particularly relevant for topics like diffusion and osmosis in cells GCSE.

Osmosis in Plant Cells

This page focuses on the effects of osmosis in plant cells, highlighting the unique features of plant cells that influence their response to osmotic pressure.

The page begins by emphasizing the importance of osmosis for plants:

Highlight: Plants rely on osmosis to support their stems and leaves.

It then describes the process of water movement into plant cells:

When water moves into a plant cell by osmosis, it causes the vacuole to swell. This swelling presses the cytoplasm against the plant cell wall, building up pressure until no more water can enter the cell. This pressure is known as turgor pressure.

The page illustrates three states of plant cells based on their water content:

1. Turgid $normal$: The cell is fully hydrated and maintains its shape.
2. Flaccid: The cell has lost some water but the cell membrane is still in contact with the cell wall.
3. Plasmolysed: The cell has lost so much water that the cell membrane has pulled away from the cell wall.

Vocabulary:

• Turgid: A plant cell that is fully hydrated and maintains its shape.
• Flaccid: A plant cell that has lost some water but the cell membrane is still in contact with the cell wall.
• Plasmolysed: A plant cell that has lost so much water that the cell membrane has pulled away from the cell wall.

This information is crucial for understanding the differences between diffusion and osmosis in plant cells, and how plant cells maintain their structure through osmotic regulation.

Page 5: Plant Cell Osmosis

This page focuses on osmosis in plant cells and their unique responses.

Definition: Turgor pressure is the force exerted by water against the cell wall in plant cells.

Highlight: Plant cells have distinct responses to osmosis due to their cell walls.

Example: Examples of osmosis in cells in plants include the maintenance of stem and leaf rigidity through turgor pressure.

Diffusion and Osmosis Fundamentals

This page introduces the key concepts of diffusion and osmosis in biology.

Diffusion is defined as the movement of particles from an area of high concentration to low concentration. Osmosis specifically refers to the movement of water molecules across a semi-permeable membrane from high to low concentration areas. The page also mentions active transport, which uses energy to move particles against the concentration gradient.

Definition: Diffusion is the movement of particles from an area of high concentration to low concentration.

Definition: Osmosis is the movement of water particles from an area of high concentration to low concentration via a semi-permeable membrane.

The page provides examples of diffusion in biological systems:

Example: Diffusion examples in the human body include gas exchange in lungs and nutrient absorption in small intestines. In plants, diffusion of carbon dioxide into leaves occurs during photosynthesis.

Factors affecting the rate of diffusion are listed, including concentration gradient, temperature, distance, molecule size, and surface area. The concentration gradient is highlighted as a key factor.

Highlight: The difference between two areas of concentration is called the concentration gradient. The steeper the gradient, the faster the rate of diffusion.