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Introduction

Water and nitrogen are essential for all life on Earth. In GCSE Biology, you will learn about how organisms maintain water and nitrogen balance, which is crucial for their survival. Let's explore the importance and applications of this topic.

Water Balance

• Key Concepts
• Water potential: The tendency of water to move from an area of high water potential to an area of low water potential.
• Transpiration: The evaporation of water from plant leaves, creating a water potential gradient that draws water up from the roots.
• Osmosis: The movement of water across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration.
• Processes and Systems
• Water uptake in plants: Water is absorbed through the roots and transported up the stem by xylem vessels.
• Water loss in animals: Water is lost through sweating, urination, and exhalation.
• Regulation of water balance: The kidneys and hormones (ADH) regulate water reabsorption in the nephrons.

Nitrogen Balance

• Key Concepts
• Nitrogen cycle: The series of processes that convert nitrogen gas into usable forms for organisms and return it to the atmosphere.
• Nitrogen fixation: The conversion of atmospheric nitrogen into ammonia by bacteria.
• Nitrification: The conversion of ammonia into nitrate and nitrite by bacteria.
• Processes and Systems
• Nitrogen fixation: Occurs in specialized bacteria in the soil or in root nodules of legumes.
• Assimilation: Plants absorb nitrate from the soil and convert it into amino acids and proteins.
• Excretion: Nitrogen is excreted as ammonia or urea in animals and as nitrogenous waste in plants.

Exam Preparation

• Common Mistakes to Avoid
• Confusing water potential with solute potential.
• Forgetting the role of transpiration in water uptake.
• Overlooking the significance of nitrogen fixation in the nitrogen cycle.
• Exam Tips
• Understand the key concepts and processes involved in water and nitrogen balance.
• Use diagrams and flowcharts to illustrate the systems.
• Practice solving problems related to water potential and nitrogen balance.
• Review past exam papers and mark schemes.

Practice Problems

• Water Balance
• A plant has a water potential of 100 kPa. Calculate the water potential of the soil if the plant is absorbing water.
• Nitrogen Balance
• Explain the role of nitrifying bacteria in the nitrogen cycle.
• Describe how nitrogen is excreted in animals.

Conclusion

Maintaining water and nitrogen balance is essential for the survival of living organisms. Understanding the key concepts and processes covered in this guide will equip you with the knowledge and skills to excel in your GCSE Biology exam. Remember, the ability to maintain water and nitrogen balance is a testament to the remarkable adaptations and resilience of life on Earth.