Diffusion, Osmosis, and Active Transport

This page provides a comprehensive overview of the three main types of cell transport: diffusion, osmosis, and active transport. Each process is defined and explained in terms of particle movement and energy requirements.

Definition: Diffusion is the spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration.

Example: Oxygen diffuses from the air into the alveoli in the lungs.

Highlight: Diffusion and osmosis are passive processes that do not require energy, while active transport needs energy from respiration.

The page also discusses factors affecting the rate of diffusion:

1. Difference in concentration: A steeper concentration gradient leads to faster diffusion.
2. Temperature: Higher temperatures increase the rate of diffusion.
3. Surface area: Larger surface areas result in faster diffusion rates.

Vocabulary: Concentration gradient refers to the difference in concentration between two areas.

The text explains adaptations for exchanging substances, comparing single-celled and multi-cellular organisms:

Example: Single-celled organisms have a large surface area to volume ratio, allowing efficient molecule transport across cell membranes.

Multi-cellular organisms, with their smaller surface area to volume ratio, require specialized organ systems for effective substance exchange.

Specific Examples of Adaptations for Substance Exchange

This page delves into specific examples of adaptations for efficient substance exchange in different biological structures.

Villi in the Small Intestine (Absorbing Nutrients)

Villi are adapted for efficient nutrient absorption with:

• A network of capillaries
• Large surface area due to folding
• Thin wall (only one cell thick)
• Good blood supply

Highlight: These adaptations of villi for absorption significantly increase the efficiency of nutrient uptake in the small intestine.

Alveoli in the Lungs (Gas Exchange)

Alveoli are specialized for gas exchange with:

• A network of capillaries providing good blood supply
• Large surface area
• Moist surface
• Thin wall (one cell thick) for a short diffusion pathway

Example: The thin, moist walls of alveoli allow for efficient oxygen and carbon dioxide exchange between the air and bloodstream.

Fish Gills (Gas Exchange)

Fish gills are adapted for aquatic gas exchange:

• Made up of stacks of thin filaments
• Provide a large surface area to increase diffusion
• Contain a network of capillaries for good blood supply

Vocabulary: Filaments are thin, thread-like structures that increase the surface area of gills.

The page concludes with information about a required practical skill:

Highlight: Students must be able to accurately measure length, mass, and volume to study osmosis in cells, using various tissue examples.

These examples illustrate how different organisms and structures are adapted for efficient substance exchange, a key concept in GCSE Biology and AQA Combined Science.