Study Notes
Excretion is the process of removing waste substances from metabolic reactions, toxic materials, and substances in excess of requirements. In plants, excretion involves the release of gases like oxygen and carbon dioxide, and the removal of chemical waste products.
- Excretion — removal of waste substances from metabolic reactions, toxic materials, and substances in excess. Example: Carbon dioxide and oxygen are excreted by plants through the stomata.
- Photosynthesis — process by which plants use sunlight to synthesize foods from carbon dioxide and water. Example: During the day, photosynthesis produces excess oxygen as a waste product.
- Respiration — process of breaking down glucose to release energy, producing carbon dioxide and water as waste. Example: At night, plants respire, producing excess carbon dioxide.
- Transpiration — process of water movement through a plant and its evaporation from aerial parts. Example: Water vapour is lost from the plant in the transpiration stream.
- Deamination — process by which excess amino acids are broken down in the liver. Example: Amino acids are converted into urea for excretion.
- Ultrafiltration — process in the kidneys where blood is filtered under high pressure. Example: Small molecules like glucose and urea are filtered into the Bowman's capsule.
- Selective Reabsorption — process where useful substances are reabsorbed back into the blood from the nephron. Example: Glucose is reabsorbed in the proximal convoluted tubule.
- ADH (Antidiuretic Hormone) — hormone that regulates water absorption in the kidneys. Example: ADH increases water reabsorption in the collecting ducts.
Exam Tips
Key Definitions to Remember
- Excretion
- Photosynthesis
- Respiration
- Transpiration
- Deamination
- Ultrafiltration
- Selective Reabsorption
- ADH (Antidiuretic Hormone)
Common Confusions
- Mixing up 'ureter' and 'urethra'
- Confusing excretion with egestion
Typical Exam Questions
- What is excretion? Removal of waste substances from metabolic reactions.
- How do plants excrete oxygen? Through the stomata during photosynthesis.
- What role does the liver play in excretion? It breaks down excess amino acids into urea.
What Examiners Usually Test
- Understanding of the processes of excretion in plants and animals
- Differences between excretion and egestion
- The role of the liver and kidneys in excretion
- How ADH regulates water content in the blood