C2g - Fertilisers and crop yields

Question 1

Why must fertilisers be dissolved in water before they can be absorbed to the plant

Answer 1

plants can only absorb minerals dissolved in water through their roots, as only dissolved substances are small enough to be absorbed

Question 2

What are some essential elements for plant growth (3)

Answer 2

nitrogen

phosphorous

potassium

Question 3

What are some benefit of fertilisers

Answer 3

world population is rising quickly so we need to provide more food and fertilisers can help increase food supply

Question 4

What are some problems with fertilisers

Answer 4

excessive use of fertilisers can pollute water supplies, contaminating drinking water and leading to problems such as the death of aquatic organisms (eutrophication)

Question 5

How does the use of fertilisers increase crop yield? (2)

Answer 5

fertiliser replaces essential elements used by a previous crop or prov ides extra essential elements

more nitrogen gets incorporated into plant, so plant can make more protein, so faster and increased growth, increased crop yield

Question 6

Explain the process of eutrophication (6)

Answer 6

excess fertiliser washed off land to rivers/lakes

increase of nitrate/phosphate in the water

algae use these minerals to grow at much higher rate and produce thick green layer on the water (algal bloom)

algal bloom blocks off sunlight to other plants in the water, cannot photosynthesise, so they have no food and die

aerobic uses up oxygen bacteria to break down dead plants

most living organisms in the water die due to lack of oxygen

Question 7

Describe the preparation of fertiliser by the reaction of an acid and alkali (4)

Answer 7

use a measuring cylinder to add known volume of alkali to conical flask; add a few drops of phenolphthalein indicator; add acid from burette until indicator just changes colour (neutralised; salt formed). note volume of acid added.

repeat step 1 without indicator: just use burette to add correct volume of acid

heat salt solution from (2); evaporate water, reduce volume and increase concentration; leave remaining to cool down so crystals form

filter mixture using filter tunnel and filter paper to separate crystals, leave to dry