Plant mineral requirementsEdexcel International A Level Biology: Subtopic test

1. 1
   A farmer notices that the older, lower leaves of her wheat crop have turned pale yellow and the plants are shorter than normal, while the youngest leaves are still green. A soil test shows that the soil is very low in nitrate ions.

   (a)

   Which of these molecules contains nitrogen that the plant obtains from nitrate ions?

   [1 mark]

   • AGlucose
   • BCellulose
   • CA triglyceride
   • DAn amino acid

   (b)

   Which statement best explains why nitrate deficiency makes the leaves pale yellow?

   [1 mark]

   • ANitrate ions are needed to make cellulose for the leaf wall
   • BNitrate ions are the source of the carbon in chlorophyll
   • CLess nitrogen is available for making chlorophyll, so less is made
   • DNitrate ions are needed to produce calcium pectate

   (c)

   Suggest why the older leaves show the symptoms before the youngest leaves.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener grows tomato plants in compost. Some of the plants show yellowing between the veins of their leaves, and others have young leaves that are distorted. The gardener thinks that the plants are short of mineral ions.

   (a)

   Which is the role of magnesium ions in a plant?

   [1 mark]

   • AThey are needed to make calcium pectate
   • BThey are a component of the chlorophyll molecule
   • CThey are a component of amino acids
   • DThey are a component of nucleotides

   (b)

   Which effect results from a lack of calcium ions?

   [1 mark]

   • AWeak cell walls, because less calcium pectate is made for the middle lamella
   • BLess chlorophyll is made, because calcium is part of the molecule
   • CFewer amino acids are made, because calcium supplies nitrogen
   • DLess water is taken up, because calcium is needed for osmosis

   (c)

   Explain why a tomato plant short of magnesium ions grows poorly.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigated the effect of mineral deficiency on the growth of barley seedlings. Seedlings were grown for 21 days in four aerated culture solutions: a complete solution, a solution lacking nitrate, a solution lacking magnesium and a solution lacking calcium. At the end, the mean dry mass per seedling was 148 mg in the complete solution, 61 mg without nitrate, 97 mg without magnesium and 112 mg without calcium.

   (a)

   Explain why the student also grew seedlings in a complete solution, and describe two variables that the student should control.

   [3 marks]

   (b)

   Calculate the percentage decrease in mean dry mass of the seedlings grown without nitrate compared with those in the complete solution, and explain, using the roles of nitrate ions, why the lack of nitrate reduced growth more than the lack of magnesium or calcium.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A commercial greenhouse grows tomato plants hydroponically, with their roots in a nutrient solution of water containing dissolved nitrate, calcium and magnesium ions. In one section the pump failed and the plants received too little solution. They wilted, their older leaves turned yellow and their young leaves became distorted.

   (a)

   Explain the importance of nitrate, calcium and magnesium ions to the growth of the tomato plants.

   [6 marks]

   (b)

   Explain the importance of water to the tomato plants and why the lack of solution caused them to wilt.

   [6 marks]

   Total for question 4: 12 marks

End of questions