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Exchange (Exchange basics (Passively (Osmosis), Actively (Active…
Exchange
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Exchange of gases
Alveoli have a large surface area, and are only 1 cell thick so there is a short diffusion pathway. There are pulmonary capillaries close
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The distance between the alveolar air and red blood cells is reduced as they are flattened against the capillary walls
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Gas Exchange in Fish
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Countercurrent flow
Oxygenated blood flows parallel to water high in Oxygen in the capillaries, and Oxygen diffuses across. This maintains a concentration gradient
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Mechanism of Breathing
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Inspiration
Internal IC muscles relax, whilst External IC muscles contract
The ribs are pulled upwards and outwards, increasing the volume of the thorax
The diaphragm muscles contract, causing it to flatten and increase the volume of the thorax
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Atmospheric pressure is now greater than pulmonary pressure, so air is sucked into the lungs
Expiration
Internal Intercostal Muscles Contract, External IC muscles relax
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The diaphragm muscles relax and is pushed up again by the contents of the abdomen that were compressed during inspiration. As a result the volume of the thorax decreases
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Pulmonary Pressure is now greater, so air is forced out
Limiting Water Loss
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Xerophytes
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Rolling up of leaves, Water gets trapped
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Enzymes and Digestion
The Digestive System
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The Stomach has an inner layer that produces enzymes. Its role is to store and digest food, especially proteins. It has glands that produce enzymes which digest proteins
The Ileum digests food further through more enzymes that are produced by its walls. The inner walls are folded into villi, giving it a large Surface Area. The surface area is further increased by millions of microvilli, on the epithelial cells of each villus. This adapts it for absorbing products of digestion into the blood
Large Intestine absorbs water. Most of the water that is absorbed is from the secretions of the many digestive glands
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The pancreas produces Amylase, Proteaes, and Lipase
Protein Digestion
Endopeptidases hydrolyse the peptide bonds between AA in the central region of a protein molecule forming a series of peptide molecules
Exopeptidases hydolyses the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. In this way they progressively release dipeptides and single amino acids
Dipeptidases hydrolyse the bond between two AA at a dipeptide. Dipeptidases are membrane-bound, being part of the cell-surface epithelial cells lining the ileum
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