2. After completing this topic you should be able to : State that the increasing world population has led to a need for more efficient food production. State that growing plants require nutrients, including compounds of phosphorus, potassium and nitrogen. State that fertilisers are substances, which restore the essential elements for plant growth to the soil. Explain the importance of the decomposition of plant and animal protein in the recycling of nitrogen. Give examples of the effect of artificial fertilisers on lochs and rivers. Explain why fertilisers are a mixture of different chemicals to provide a balance of nutrients.

3. The population of the world showed a gradual increase for thousands of years until the end of the 19 th century. The world population has increased dramatically over the last 100 years, and continues to increase at an increasing rate. This increase in the population is due to improvements in housing, sanitation, healthcare and food production. Production of food has become very efficient resulting in better nutrition for a lot of people. However, in many parts of the world people experience famine when their crops fail to grow, due to drought.

4. Plants are important to life on the planet as they make food. Plants are eaten for food or animals are eaten which have eaten plants. As plants grow they make c cc carbohydrates, proteins, v vv vitamins and o oo oils.

5. Effects of Shortages of Nutrients on Plants NutrientRole in Plant growthEffect of Shortage Nitrogen Needed to make protein and chlorophyll Stunted growth, pale leaves, weak roots Phosphorus Needed for strong roots, stem and seeds and for energy transfer Slow growth of plants, poor fruit Potassium Needed to make protein and sugars Plants stunted with poor resistance to frost, drought and disease

6. The Nitrogen Cycle

7. Using w ww waste plant and animal protein is much cheaper than fertilisers but it is not available in large enough quantities.

9. Some plants called l ll leguminous plants contain little nodules on their roots, which contain n nn nitrifying bacteria. These bacteria can convert n nn nitrogen i ii in the air into nitrates. Examples of l ll leguminous plants are p pp peas, b bb beans and c cc clover. Farmers used to rotate which crop was grown in a field each year. In the rotation they would plant p pp peas, b bb bean or c cc clover. This would return the n nn nitrogen to the soil and ensure that the crops grown in the field the following year would have a high yield.

11. essential nutrient elements

12. nitrogen oxygen nitrogen dioxide During lightning storms the energy of the electrical discharge provides the energy for nitrogen in the air to react with oxygen to produce nitrogen dioxide. Nitrogen dioxide nitric acid Nitrogen dioxide dissolves in rainwater to form a very dilute solution of nitric acid. nitrogen oxygen nitrogen dioxide During lightning storms the energy of the electrical discharge provides the energy for nitrogen in the air to react with oxygen to produce nitrogen dioxide. Nitrogen dioxide nitric acid Nitrogen dioxide dissolves in rainwater to form a very dilute solution of nitric acid. growing plants death & decay eaten animalwaste Nitrifying bacteria in leguminous plants

13. The chemicals in fertilisers have to be soluble in water to be of use to plants. The fertilisers then cause the water p pp plants to grow rapidly. This results in these stretches of water becoming choked with p pp plants and rapid growing microscopic plants called a aa algae. Fertilisers are easily washed out of the soil by rain into streams, rivers and lochs. Fertilisers in water run-off from fields. When these p pp plants and a aa algae die, their decay removes dissolved o oo oxygen in the water, which deprives the fish of o oo oxygen, so many of the fish get killed off.