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Extracellular Digestion Questions

Question 1

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Answer 1

Fungi are heterotrophic, and can use a wide variety of organic molecules for their energy requirements. Most commonly, saprophytic fungi use simples sugars such as glucose and small polypeptides for their energy needs when the compounds are available. However, some fungi are unable to use simple sugars, and they may require more complex molecules, or a specific combination of molecules. Thus specificity of food source is widespread, meaning that each fungus utilises a limited range of molecules.

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Question 2

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Answer 2

If the fungus is bathed in a solution containing simple organic molecules, these may be absorbed directly through the wall of the fungus. However, where the only energy resources are complex molecules, which are too large to pass through the wall, then the molecule is first digested outside the cell and the breakdown products absorbed.

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Question 3

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Fungi utilise extracellular digestion to acquire their energy. Most heterotrophic bacteria also use this process of digestion. In contrast, some protists use phagocytosis, where the digestion takes place inside the cell, and the waste products are expelled following digestion within a food vacuole.

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Question 4

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Answer 4

The release of enzymes is generally controlled genetically. In the presence of glucose, formation and excretion of enzymes to degrade more complex molecules in repressed. As glucose is released following enzymic digestion of cellulose and several other complex carbohydrates, the process of enzyme formation and release is finely balanced between repression and induction.

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Question 5

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Question 6

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Question 7

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