Edexcel IGCSE Biology: Double Science 复习笔记 1.1.3 Living Organisms: Excretion
Edexcel IGCSE Biology: Double Science 复习笔记 1.1.3 Living Organisms: Excretion
Excretion
- Chemical reactions that take place inside living cells are described as metabolic reactions
- Metabolic reactions produce waste products, some of which may be toxic
- These toxic products must be eliminated from the body
- Excretion is the removal of toxic materials and substances from organisms
Excretion in animals
- Waste products excreted by animals include:
- Carbon dioxide from respiration
- Water from respiration and other chemical reactions
- Urea which contains nitrogen resulting from the breakdown of proteins
Excretion in humans, the waste products and organs involved
Excretion in plants
- Waste products excreted by plants include:
- Oxygen from photosynthesis
- Carbon dioxide from respiration
- Water from respiration and other chemical reactions
Excretion in plants, the waste products and the difference between day and night
Exam Tip
Excretion is often confused with egestion. Remember that the waste products removed through excretion have originated from chemical reactions in the cells. However, the waste products produced in egestion are in the form of faeces and originate from the remains of the substances not absorbed during digestion.
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