- CARBOHYDRATES AND PROTEINS
All the chemicals derived from living organisms contain the element carbon (C), whether they are proteins or carbohydrates. Carbohydrates contain only carbon, oxygen and hydrogen, whereas proteins also contain nitrogen. Proteins are made up of CNOH. Examples of carbohydrates are sugars, such as sucrose, maltose, glucose, fats and oils. Examples of proteins are numerous; muscle protein and enzymes.
THE FUNCTIONS OF CARBOHYDRATES AND PROTEINS
Carbohydrates are manufactured by plants and one of two things can happen to them. Firstly, they can be “burned up” by the plant for energy by respiration. Secondly, they can be modified and converted into more sophisticated carbohydrates or amino acids and proteins. Insoluble carbohydrates, such as cellulose are used as structural support in plant cell walls. Proteins form enzymes make up most of the structure of protoplasm.
TRANSPORT AND STORAGE OF CARBOHYDRATES AND PROTEINS
Carbohydrates are moved around the plant as sucrose in the phloem. Phloem sap is composed of 90% sucrose. Carbohydrates are stored in the form of starch, which is a large insoluble compound. Starch granules are to be found in the cortex of stems (potato tubers) and roots (carrots). However, in seeds, carbohydrates are often stored as fats and oils.
Proteins are not moved around the plant although amino acids often are. This is usually on a seasonal basis, i.e. during Winter amino acids leave the upper half of a plant and pass down the phloem and are stored in the roots or lower stem in the cortex tissues as amino acids. In seeds, protein is stored as large insoluble granules called aleurone grains.
- MINERALS AND TRACE ELEMENTS
|Minerals: A mineral is an element that is not organic and is normally found in the soil.|
Many minerals are needed by the plant and these are said to be essential nutrients. Some minerals are needed in quite large concentrations and are called macro-nutrients. However others are required in very small amounts and too much can be very toxic and
these are called micro-nutrients or trace elements.
A NUTRIENT IS SAID TO BE ESSENTIAL IF:
- The plant cannot complete its life cycle without it;
- Its action must be specific and cannot be replaced by another element; and
- Its effect on the plant must be direct.
Macro-nutrients are: N, C, K, Ca, Mg, P and S.
Micro-nutrients are: Mn, B, Zn. Cl, Cu. Fe,
UTILISATION OF MINERALS AND TRACE ELEMENTS:
Nitrogen is needed by plants for incorporation into amino acids to make proteins.
Is needed to make sugars and amino acids.
Is needed in the early stages of plant development and nobody is quite sure why. It may be involved in disease resistance and photosynthesis.
This is an essential ingredient of the cell wall. Lack of calcium often leads to failure of the meristematic regions.
This is a necessary component of chlorophyll, the green photosynthetic pigment of leaves. A deficiency results in the yellowing of the leaves.
This forms part of a very essential biochemical called Adenosine Triphosphate (ATP).
A number of proteins contain sulphur and sulphur must be available to make them.
Many trace elements help in the plant’s chemical reactions and have to be present in the cell before many essential processes can occur. Trace elements may be involved in fertility. Examples of trace elements are:
- Manganese (Mn)
- Boron (B)
- Zinc (Zn)
- Chlorine (Cl)
- Copper (Co)
- Iron (Fe)
- Molybdenum (Mo)
TRANSPORT AND STORAGE OF MINERALS AND TRACE ELEMENTS
Minerals are transported mainly in the xylem; however, they also move in the phloem. Minerals are generally stored in plants, but are known to build up, from time to time, in the plant tissue.
Temperature is just one aspect of climate. Some crops cannot grow in cold climates. Frost is a main factor in governing what species can be grown in an area. In wheat, frost actually increases the yields by stimulating tillering and results in more ears. Generally, the cooler the temperature the slower the development of a crop and vice versa.
The intensity of light will affect the rate of photosynthesis which has obvious consequences. The length of the day is important in some crops and some will not thrive if the days are too short or too long. Some varieties of Soya beans can be grown only between certain latitudes because of the shortness of the days in these latitudes.
Most crops need an adequate supply of water, either naturally by rainfall or artificially by irrigation. Some crops show an ability to withstand dry conditions whereas others do not. The timing of the rainfall is also vital in many crops because certain stages of crop development are more affected by water stress than others. In maize, lack of water just prior to the development of the reproductive organs causes them to develop out of phase so that pollen is ready before the cob silks and pollination does not occur which results in a reduced yield.
The genetic potential of certain plant species is an important factor in crop development and yield. For example, SR 52 is a much higher yielding maize plant in good rainfall areas than R 201 which does not yield as highly.
Some crop varieties are more resistant to pest attack and disease than others, which has obvious consequences. Some varieties are more frost and drought resistant than others.
The soil in which the crop is being grown must have plenty of phosphates, nitrogen and other minerals. If these are deficient, the crop will not develop properly. Any lacking nutrients can be applied artificially as fertilizers. The acidity of the soil is also an important factor as some crops do not thrive in very acid soils. The nutrients in the soil must be available. Just because they are present does not necessarily mean that they can be used. Some nutrients actually become locked up in the soil and are not available to the plant. The soil structure can also affect the crop’s development. Excessive rainfall or irrigation can leach nutrients out of the soil, especially nitrogen.
|Deficient: not having enough of a specified quality or ingredient. Artificially: made or produced by human beings rather than occurring naturally, especially as a copy of something natural.|