Plants require a large number of elements to function properly, mainly carbon, oxygen and hydrogen, essentially used in many biochemical pathways.
In addition to these essential elements, plants also require a dose of nitrogen, phosphorous, potassium and magnesium. A well known fertiliser used to increase crop yield is nicknamed NPK, the chemical symbols for the first three of these macro elements.
A lack of any of these elements can result in the following phenotypes
- Lack of nitrogen causes an excessive growth of roots and a red leaf base
- Lack of phosphorous also presents a red leaf base and stunted growth of roots
- Lack of potassium can lead to similar effects to lack of phosphorous
- Lack of magnesium can result in pale leaves due to a lack of pigmentation
Herbicides are artificially created chemicals that are used by humans on plants considered as 'pests'. These may be weeds in someone's garden, a farmers crop, or an undesired influx of a species into a foreign environment.
They are effective by accelerating the plants metabolism rate to such an extent that food supplies are totally exhausted, leaving the plant to die. Herbicides are applied by humans to destroy these pests and minimise competition for the other desirable plants in the area.
Animals have to actively find sources of food to be used in their bodies, and therefore a variety of substances are required by animals, i.e. proteins, carbohydrates, vitamins, minerals and fats. Their are also many macro-elements which are of use to the body. However, some elements are also dangerous to the health of animals, as indicated below
The presence of lead in the bloodstream can cause a variety of complications to the animal at hand. Lead can lead to brain damage, and prevent the action of the enzyme catalase, which is responsible for the breakdown of poisonous hydrogen peroxide which accumulates in the body
Calcium is required for the proper formation of bones and teeth in animals. They are also an important constituent in exoskeletons, such as the outer shell of tortoises.
Vitamins are required for a variety of reasons in the animal body.
- Citrus fruits are rich in vitamin C, which is required in the formation of red blood cells and antibodies. Deficiency of vitamin C can lead to scurvy.
- Vitamin A is commonly found in dairy products, and is required for growth and night sight. Lack of vitamin A can result in stunted growth and night blindness
- Vitamin D is obtained by humans from sunlight, but can also be found in some dairy products and fish. It is required for the absorption of some materials into cells and the lack of it can result in rickets, a softening of the bones.
More information relating to vitamins and a balanced diet is available in the developmental biology tutorial.
Iron is a constituent of some enzymes, and also forms cytochrome, required in respiration, and haemoglobin, which is a respiratory pigment responsible for absorption of oxygen. Anaemia is a condition resulting in iron lacking in an animals diet, which results in a lack of red blood cells, or a depletion of haemoglobin content.
Nicotine is a mild stimulant found in tobacco plants, and can be smoked or chewed. It contains thousands of carcinogenic substances, most notably carbon monoxide and tar. Carbon monoxide is poisonous and found to be around 200 times more absorbable into the blood stream than oxygen, therefore reducing the amount of oxygen available to the body through the bloodstream.
Tobacco has been found to cause cancer, narrow the arteries and generally leads to a declining health due to its numerous substances taking their toll on the body. Nicotine is smoke to produce a mild relaxing effect and is believed to induce a feeling of psychological dependence.
Alcohol is also a poison to the body, yet produces a stimulating effect on the nervous system, and produces a relaxing effect as a depressant.
Alcohol has a toxic effect on the liver, and also effects the uptake of certain ions in the body, and in this instance can prove lethal to an unborn child.
For men, it is believed that alcohol can damage sperm production, and lower sperm count over the longer term. Alcohol can be physiologically and psychologically addictive, with withdrawal effects including delirium, high blood pressure and a high risk of liver disease.
To conclude the control of growth and development tutorial, the next two pages look at growth patterns and the effect of light on growth.