Inorganic ionsEdexcel A-Level Biology B: Mind map

Exam questions on Inorganic ions

1. A grower raises young tomato plants in hydroponic culture, where the roots sit in a nutrient solution. Plants given a complete solution grow normally. Plants given a solution lacking nitrate ions grow slowly and their older leaves turn pale yellow. Plants given a solution lacking magnesium ions have leaves that turn yellow between the veins.
   Explain why plants lacking nitrate ions grow slowly.2 marks
2. A strawberry grower compares three nutrient solutions. In solution 1 all essential ions are present and the plants grow well. In solution 2 phosphate ions are missing: the roots grow poorly, the plants take up fewer ions by active transport and the leaves are dull and dark. In solution 3 calcium ions are missing: new tissue at the shoot and root tips is weak and soft, and its cells separate easily when handled.
   Explain why plants in solution 2 take up fewer ions by active transport.2 marks
3. Young wheat plants in a sandy field are stunted and have pale yellow leaves. A farmer adds ammonium nitrate to one half of the field and magnesium sulfate to the other half. Three weeks later, plants in the nitrate-treated half have green leaves and have grown well. Plants in the magnesium-treated half show no improvement. Chlorophyll content was low in the plants before treatment and is still low in the magnesium-treated plants, but is high in the nitrate-treated plants.
   Deduce which ion was lacking in the soil, and explain why the stunted growth is consistent with this.3 marks