Our body needs about 25 different chemicals for normal growth. The complex organization of these chemicals produces organic compounds which contain Carbon, as well as mostly Oxygen and Hydrogen. Substances that do not contain Carbon are called inorganic compounds. The organic nutrients, which come primarily from green plants, are classified into four major groups.
| Organic Compounds | Function / Role in nutrition | Dietary Sources |
|---|---|---|
| Carbohydrates | They are organic molecules consisting of carbon, hydrogen, and oxygen. They are a source of energy for metabolism | sugar, starch, cellulose, glucose. food sources such as rice, grains, potatoes, fruits |
| Lipids | They are compounds composed of many carbon, hydrogen, and oxygen atoms. They function as storage of unused chemical energy. They act as a source of energy especially when carbohydrates are depleted. | Vegetable oils, nut oils, some dairy products |
| Proteins | They are organic compounds made up of amino acids. Each protein has its own unique number, combination and arrangement of amino acids. They have several functions in the body including growth and repair, as well as a source of energy. | Fit closely together to form a continuous protective layer |
| Nucleic Acids | These are large complicated molecules that play a major role in heredity and in controlling the cell's activities. Examples include DNA and RNA. | They make up the genetic material that plays a role in heredity. They are also building units for genes that then get translated into proteins. All proteins in the body are derived from DNA through a process called translation. |
Plants require carbon, oxygen and hydrogen from the air, and nitrogen, phosphorus, potassium, magnesium, calcium and sulfur from the soil. Plants require these nine elements in large quantities for them to gorw so they are called macronutrients. There are other elements that are also needed, but not in large quantities. These elements are called trace elements or micronutrients.
Green plants require 18 elements for proper growth and functioning, while humans need 25 elements, which are used by for growth and function. The process of taking in the nutrients (elements and compounds) we need is called ingestion.
Some of the macronutrient elements are required to synthesize enzymes and vitamins. Enzymes are special protein molecules that regulate chemical reactions in living organisms. Vitamins are large organic molecules with several functions including helping enzymes function properly. The body cannot synthesize the elements so they must be provided in food.
Most elements are found in food as large complex compounds that require to be broken down first into smaller units. The digestive system is mostly esponsible for this break-down of large food molecules into smaller units through a process called hydrolysis. For example 1 molecule of maltose is broken down, in the presence of water and a specific enzyme, into 2 molecules of glucose. The products of digestion, such as glucose and amino acids, are then absorbed through cell membranes and into the bloodstream, which carries them to where they will be used or stored.
Below is a list of macronutrients and their importance in plants and humans:
| Nutrient | Function /Importance in Plants | Importance in Humans |
|---|---|---|
| Nitrogen | Proteins & chlorophyll. Leaf and stem growth | Composition of proteins & nucleic acids, growth and repair of tissue |
| Phosphorus | Root and flower growth, cellular respiration & photosynthesis | Composition of bones, teeth & DNA. Important in several metabolic reactions |
| Potassium | Stimulates early growth, starch and protein production, disease resistance, - chlorophyll production & tuber formation | Muscle contraction & nerve impulses |
| Magnesium | Chlorophyll structure, photosynthesis | Composition of bones & teeth, enhance the absorption of calcium & potassium |
| Calcium | Cell wall structure, cell division | Composition of bones & teeth, blood clotting, muscle & nerve function |
| Sulfur | Production of fruits and grains | Protein synthesis, enzyme activation and detoxification |
| Sodium | Controls osmotic pressure in plant cells and results in a more efficient use of water | Helps regulate nerve impulses in nerves and muscles |
Below is a list of micronutrients and their functions:
| Nutrient | Function /Importance |
|---|---|
| Chlorine | Helps regulate water balance, plays a role in cell membrane function, part of the hydrochloric acid in stomach that helps digest foods |
| Iron | Crucial part of red blood cells, regulating oxygen transport |
| Zinc | Essential component in enzymes which regulate formation of proteins and carbohydrate metabolism |
| Iodine | Major component in thyroid hormones which regulate metabolism |
| Selenium | Component of antioxidant enzyme that helps decay of cell function |
| Copper | Promotes iron absorption and utilization, component of many enzymes and helps regulate nerve activity |
| Manganese | Component of some enzymes involved in bole formation and protein metabolism |
| Fluorine | Helps regulate calcium deposition |
| Chromium | Activates vitamin B3 to control use of blood sugar in energy production |
| Molybdenum | Key component of 3 enzymes that regulate metabolism |
| Cobalt | Component of vitamin B12, which helps regulate red blood cells |
The optimum amount of a substance is the amount of that substance that provides an organism with the best health. A micronutrient may be present in larger amounts than normal. If this occurs it can have harmful effects. Not enough of an element can also have harmful effects.
Plants take in inorganic compounds to make organic compounds. Consumers use the organic compounds made by plants for their energy, growth and repair. When organisms take in these compounds, other substances are also taken. These substances may or may not be harmful.
Some nutrients enter the roots by diffusion. This action continues until the areas are equal concentrations.
Water moves through plants by osmosis. In this process, water moves through the walls of the plant's roots from an area where there are more water molecules to an area where there are fewer water molecules.
Plants need some nutrients at high concentrations in their roots. These nutrients may have higher concentrations in the roots than in the surrounding soil. To maintain these high concentrations, (against diffusion gradient), plants move more nutrients into their roots from areas of lower concentration (in the soil) by a process called active transfer. This process requires energy.
Some organisms get the nutrients they need by restricting other organisms from accessing the same nutrients.
Plants obtain nutrients from the soil and over time can deplete the nutrients available in the soil. Fertilizers are substances that can be applied to the soil to replenish the lost nutrients. The three numbers on a bag of fertilizer refer to the percentage of nitrogen, phosphate and potassium that is available to plants from that bag of fertilizer. For example, a bag labeled 5-10-5 indicates it has 5 % nitrogen, 10 % phosphate and 5 % potassium. The remaining 80% contains some micronutrients and some fillers necessary for the effectiveness of the fertilizer.
Until the early 1900s, plants received their nitrates exclusively from nature. The artificial production of fertilizers increased the nitrogen levels available to plants in the soil. Crop production has doubled worldwide due to the use of artificial fertilizers and high-yield varieties. Nitrogen is used by plants for increased plant growth. Crop and livestock production requires a lot of water and fertilizers, which also increases the costs of production. The planting of only one crop (monoculture) means the same nutrients are continually depleted from the soil. Monoculture also increases the chance of disease spreading through the entire crop. Chemical agents used to protect the crop (pesticides and herbicides) reduce the amount of damage, but they are costly and have harmful effects on the environment.
Chemical Agents from Agriculture
Pesticide, herbicide and fungicide use is now common agricultural practice worldwide. Herbicides control weeds, insecticides control insects and fungicides control fungal diseases in crops. The increased prevalence of these challenges might be related the current commercial agriculture practices such as monocropping.
The invention of DDT by Swiss chemist Paul Müller was originally seen as a breakthrough in medicine. Typhus a disease transmitted by lice was rampant during the World War II and was the disease that wiped out Napoleon’s army in the 1800s. DDT wiped it out. It proved to be so effective that Müller was awarded the Nobel Prize in Medicine for his discovery. During the 1950s it was used to try to control an outbreak of malaria. DDT undergoes bioaccumulation within the food chain and can cause devastating effects. The use of DDT was recognized as having potentially harmful effects. Banning its use would also negate the positive effects it was having in controlling malaria (In Zanzibar alone – the incidence of malaria dropped from 70% to 5% over a 6 year span). When a restriction on the use of DDT was implemented in 1984, the incidence of malaria returned to the 50-60 % level. Nothing else proved to be as effective in controlling the insects that carried malaria.
Research into newer and safer pesticides has resulted in the development of pesticides that can break down faster in the environment after they have been applied. It is now widely recognized that natural processes and cycles can minimize the effects of these pesticides, but it still remains a hotly debated topic.
Chemical Agents from Industries
Sulfur, nitrogen and carbon oxides emitted from industries (such as smelters) combine with water vapor in the air to produce sulfuric, nitric and carbonic acid. These pollutants then fall to the ground as acid precipitation. Acid rains can have several effects including:
To neutralize acid rain precipitation and reduced soil pH from fertilizers, lime (calcium hydroxide) can be added to agricultural soils and lakes.
In 1996 an agreement between Canada and the US targeted a 10% reduction in industrial exhaust emissions by the year 2000. Vehicle emissions for cars built before 1998 was also targeted to be reduced by 60%. As a result total emissions are on the decline. Catalytic converters contain a ceramic or wire honeycomb-like structure that is coated with a thin layer of metallic catalysts, which speed up chemical reactions, without being used up. A converter helps the formation of CO2 and H2O, reducing CO and NO2. The purpose of the converter is to encourage complete oxidation.
An Acceptable Risk
Every chemical has the potential to be harmful, even the ones we take to help us. It is the dose, our susceptibility and how it reacts with other chemicals that determine it toxicity. Tough decisions need to be made to determine if it is more beneficial than harmful. Evaluation of the risks and benefits of any chemical, form the basis of how chemical use is regulated.
As the world population grows, waste production also increases and the proper handling of this waste should always be addressed.
Environmental Monitoring
Persistent pollutants accumulate and take a long time to degrade. It is the concentration of these wastes that can affect living organisms. To determine the concentration scientists test wastes, persistent and non-persistent to determine how to handle them and deal with their effects in the environment. Monitoring keeps track of something for a specific purpose. Clarity may be one indicator, but clear water does not indicate what chemicals are present. Water Quality is determined using chemical and biological indicators according to what the water is going to be used for.
Most types of pollution adversely affect water quality and directly affect living organisms. Microscopic organisms (bacteria) can cause serious health problems if they are present in sufficient numbers. Samples are taken to identify their presence to avoid contamination of the water supply. Chemical indicators of water quality include: dissolved oxygen, acidity, heavy metals, nitrogen, phosphorus, pesticides, salts – such as sodium chloride and magnesium sulfate.
Pollutants entering the environment from specific locations are point source pollutants. These are easy to monitor and control. Non-point source pollutants are those that enter the environment from locations that cannot be easily monitored or controlled. They occur as a result of run-off or leaching and they get dispersed quickly. The 4Rs – Reduce, Reuse, Recycle and Recover can be used to develop a basic framework to reduce the amount of waste pollutants that are produced. Some of this waste can be reduced, recycled, recovered or reused, but most of it is placed in landfill sites. The most preferred option is to reduce – in other words don’t make as much waste and the problem of disposal will take care of itself.
Biodegradation occurs in the environment because living things (earthworms, bacteria and fungi) are actively breaking down organic substances, including many pollutants. Microorganisms are especially important in the biodegradation of pollutants. The existing organic molecules provide carbon atoms, which are used to build biological compounds, such as carbohydrates and proteins. During the winter, biodegradation is slow, because temperature is one factor that affects the rate of biodegradation. Other factors include soil moisture, pH, oxygen supply and nutrient availability.
Bioremediation:
Bioreactors are a new technology that speeds up the rate of biodegradation by adding water to organic waste in a sanitary landfill site. Planting vegetation also encourages faster biodegradation because the populations of bacteria and fungi are larger around plant roots and this higher level means more microbial activity. Phytoremediation is a technique that can be used to reduce the concentration of harmful chemicals in the soil or groundwater. Plants have been used to clean up metals, hydrocarbons, solvents, pesticides, radioactive materials, explosives, and landfill leachates. The plants are able to absorb and accumulate large amounts of these chemicals. When the plants have matured, they are harvested, burned or composted. Photolysis is the breakdown of compounds by sunlight. The formation of ozone is an example of this process. Another example of photolysis is photodegradable plastic. Photodegradable plastic is made of chemicals that react when exposed to sunlight. In three months, the plastic becomes a fine powder that is easier to dispose of.
Solid waste includes the garbage collected from households, industries, commercial retailers, institutions and construction or demolition sites.