After heavy rain, fertiliser from a field enters a pond. Algae grow rapidly, then many algae die. The number of fish decreases.
Which explanation links the dead algae to the decrease in fish?
Dead algae absorb nitrate from the water, leaving too little nitrate for fish respiration.
Dead algae continue to respire faster than live algae, removing oxygen from the water.
Decomposers respire as they break down algae, reducing dissolved oxygen.
Decomposers release oxygen as they break down algae, increasing oxygen above a safe level.
44 exam-style questions on Edexcel GCSE Biology 4.3 Selective breeding and genetic modification, covering 4.3.1 Selective breeding and its impact, 4.3.2 Tissue culture, 4.3.3 Genetic engineering overview, 4.3.4 Main stages of genetic engineering, 4.3.5 Advantages and disadvantages of GM organisms, 4.3.6 Agricultural solutions for a growing population, and 4.3.7 Evaluating genetic engineering and breeding. Each one has a worked solution and a mark scheme showing where the marks go.