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Gas exchange

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**Gas Exchange Principles:**
Gas exchange occurs via diffusion down a concentration gradient.
– Diffusion follows Fick’s Law and requires gases to dissolve in a liquid.
– Higher concentration gradients lead to faster diffusion rates.
– Thinner gas-exchanging surfaces enhance gas diffusion efficiency.

**Importance of Surface Area in Gas Exchange:**
– Gas molecules move from high to low concentration areas.
– Diffusion coefficient varies based on gas and membrane properties.
– Increased surface area boosts the amount of diffused gas.
– Moist environments are essential for biological gas exchange systems.

**Interaction with Circulatory Systems:**
– Specialized respiratory organs aid gas exchange.
– Co-current and countercurrent flow systems impact efficiency.
– Channels must be contiguous for effective gas exchange.
– Diffusion alone may not meet gaseous requirements of deep tissues.

**Gas Exchange in Mammals:**
– Alveoli in mammalian lungs facilitate gas exchange.
– Oxygen moves from alveoli to capillaries due to concentration gradient.
– Carbon dioxide moves from capillaries to alveoli following concentration gradient.
– Alveoli provide a large surface area for efficient gas exchange.

**Gas Exchange in Different Organisms:**
– Land plants, methanogenic archaea, and bacteria perform various gas exchange processes.
– Giant tube worms rely on bacteria for gas exchange.
Gas exchange systems in different organisms vary based on their environments.
– Various systems like countercurrent flow and cocurrent flow are used for gas exchange.

Gas exchange (Wikipedia)

Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a biological membrane that forms the boundary between an organism and its extracellular environment.

Gas exchange

Gases are constantly consumed and produced by cellular and metabolic reactions in most living things, so an efficient system for gas exchange between, ultimately, the interior of the cell(s) and the external environment is required. Small, particularly unicellular organisms, such as bacteria and protozoa, have a high surface-area to volume ratio. In these creatures the gas exchange membrane is typically the cell membrane. Some small multicellular organisms, such as flatworms, are also able to perform sufficient gas exchange across the skin or cuticle that surrounds their bodies. However, in most larger organisms, which have small surface-area to volume ratios, specialised structures with convoluted surfaces such as gills, pulmonary alveoli and spongy mesophylls provide the large area needed for effective gas exchange. These convoluted surfaces may sometimes be internalised into the body of the organism. This is the case with the alveoli, which form the inner surface of the mammalian lung, the spongy mesophyll, which is found inside the leaves of some kinds of plant, or the gills of those molluscs that have them, which are found in the mantle cavity.

In aerobic organisms, gas exchange is particularly important for respiration, which involves the uptake of oxygen (O
) and release of carbon dioxide (CO
). Conversely, in oxygenic photosynthetic organisms such as most land plants, uptake of carbon dioxide and release of both oxygen and water vapour are the main gas-exchange processes occurring during the day. Other gas-exchange processes are important in less familiar organisms: e.g. carbon dioxide, methane and hydrogen are exchanged across the cell membrane of methanogenic archaea. In nitrogen fixation by diazotrophic bacteria, and denitrification by heterotrophic bacteria (such as Paracoccus denitrificans and various pseudomonads), nitrogen gas is exchanged with the environment, being taken up by the former and released into it by the latter, while giant tube worms rely on bacteria to oxidize hydrogen sulfide extracted from their deep sea environment, using dissolved oxygen in the water as an electron acceptor.

Diffusion only takes place with a concentration gradient. Gases will flow from a high concentration to a low concentration. A high oxygen concentration in the alveoli and low oxygen concentration in the capillaries causes oxygen to move into the capillaries. A high carbon dioxide concentration in the capillaries and low carbon dioxide concentration in the alveoli causes carbon dioxide to move into the alveoli.

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