Global challenges Study Guide

Plants require various nutrients to grow and thrive. Among these, nitrogen (N), phosphorus (P), and potassium (K) are considered macronutrients because they are needed in larger quantities than other elements. These elements are vital components of many essential molecules within plants and are often depleted from soil through crop harvesting. Farmers replenish these nutrients by adding fertilisers, which typically contain compounds of nitrogen, phosphorus, and potassium. Nitrogen is crucial for producing proteins, enzymes, and chlorophyll, which are fundamental for plant growth, photosynthesis, and overall greenness. A lack of nitrogen leads to stunted growth and yellowing leaves. Phosphorus is essential for energy transfer (ATP), root development, flowering, and seed formation. It plays a key role in photosynthesis and respiration. Deficiencies can result in poor root systems, delayed maturity, and reduced fruit/seed production. Potassium is important for water regulation, nutrient transport, enzyme activation, and disease resistance. It helps maintain turgor in cells and improves fruit quality and winter hardiness. Without enough potassium, plants may exhibit weak stems, poor fruit development, and increased susceptibility to disease. Understanding the specific roles of N, P, and K allows farmers to apply fertilisers strategically, ensuring healthy crop yields and efficient agricultural production.

Naturally occurring polymers are large molecules formed by linking many smaller repeating units, called monomers. These polymers are essential for life and play diverse roles in biological systems. One crucial example is Deoxyribonucleic Acid (DNA). DNA is a polymer that carries genetic instructions for the development, functioning, growth, and reproduction of all known organisms and many viruses. It is made up of four different types of monomers called nucleotides. Each nucleotide consists of a phosphate group, a deoxyribose sugar, and one of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), or thymine (T).

Besides DNA, other important natural polymers are constructed from different types of monomers. Carbohydrates, for instance, are a broad class of naturally occurring molecules that include sugars. Polysaccharides, which are complex carbohydrates, are polymers formed from repeating monomer units of simple sugars (monosaccharides). Examples include starch, glycogen, and cellulose, all vital for energy storage or structural support in living organisms.

Proteins are another critical group of natural polymers. They are formed from monomer units called amino acids. There are 20 common amino acids, and they can be linked together in various sequences to form a vast array of proteins. Proteins perform countless functions within living organisms, including catalyzing metabolic reactions, DNA replication, responding to stimuli, and transporting molecules from one location to another. The specific sequence and folding of amino acids determine the unique function of each protein.