GROWTH IN LIVING ORGANISMS
WHAT IS GROWTH?
GROWTH IS SIMPLY THE INCREASE IN SIZE, OR MASS OF A BODY
We have already talked about a lot of things concerning growth in both plants and animals but in this very post I am going to deal mainly on the structural aspect of growth. It is sometimes very difficult to determine growth in organisms. So growth varies from one organism to another, so I am going to deal extensively on the parameters used to measure growth in organisms which includes but not limited to the following
• LENGTH, HEIGHT OR WIDTH
• AREA OR VOLUME
1. In most of our studies, mass is measured as wet mass and dry mass. So let us take closer look at them critically
i. Wet mass: wet mass is the mass of the organism under normal condition. Wet mass is not a reliable indication of growth
ii. Dry mass: dry mass is the mass of the organism after all the water in the body has been removed. Most often measuring growth in terms of dry mass is an accurate and reliable method, the organisms most times are killed in the process. It then simply means it is not easy to measure the weight of an organism.
So to study the growth of an organism by measuring the dry mass, we must carry out the measurement or study on a large number of organisms. Therefore growth can then be estimated by removing a given number of organisms at a time and estimating their dry weight
2. SIZE AND LENGTH: size and length can be measured at successive intervals on the same organism. Say the height of a man and length of a snake
3. INCREASE IN NUMBER OF CELLS: increase in numbers of cell is also a proof growth. A popular example of growth in organism is the yeast. The yeast cell is capable of budding or dividing into two, two into four, four into eight etc.
The yeast culture continues to double its numbers as long as none of the cells dies or loses its power of division
REGIONS OF GROWTH IN PLANTS
The regions of fastest growth in plants are the roots and stem apices. In the root, the root tips are where the cells are dividing rapidly. The roots and stem apices of cell division can be divided into the regions of cell division, followed by the region of elongation and the region of the cell maturation.
The region of cell division is also known as the epical meristem. It consist of meristematic cells that is cells capable of active division. The root tips is covered by the root cap.
In the region cell elongation, the cells become enlarged to the maximum size by the stretching of their ways. The cells in the region of maturation attain their permanent size and become specialized to carry out certain functions.
NOTE: THE STEM APICES INCLUDES THE TERMINAL BUDS AND THE LATERAL OR AXILLIARY BUDS.
EPICAL MERISTEMS BRINGS ABOUT THE GROWTH IN LENGTH OR OF THE PLANT. IN THE SHOOT, THEY ALSO GIVES RISE TO BRANCHES, FLOWERS AND LEAVES.
EPICAL MERISTEM BRING ABOUT PRIMARY GROWTH KNOWN AS FIRST GROWTH OF A PLANT.
HOW TO DETERMINE THE AREAS OF GROWTH
Here a young germinating seedling is taken and its radicle is marked with an Indian ink at interval of 2mm. the seedling is then pinned onto a cork and is placed in a bottle containing some water. The apparatus and experiment is then left in dark room for up to 8hrs.
Then, the seedling is taken out and the distances between the successive ink marks are measured. The difference between new and the old intervals i.e. 2mm would give the increase in the length of that interval in 8hrs. From this, the growth of root can be calculated.
FACTORS AFFECTING GROWTH
WHAT ARE THE FACTORS THAT AFFECTS GROWTH?
Factors which affects the growth of organisms are grouped into two parts which are
1. EXTERNAL FACTORS AND
2. INTERNAL FACTORS
i. External factors includes the following temperature, light, humidity, PH, accumulation of metabolic product and availability of nutrients
ii. Internal factors includes the hormones.
The external factors that affects the growth of living things are
1. AVAILABILITY OF NUTRIENTS: all living things require nutrients or food and water in order to which are necessary for normal growth and development of the body.
2. HUMIDITY: all living things requires a certain level of humidity to enable them grow effectively any imbalances on humidity, either too low or too hot will definitely affect growth
3. LIGHT: most plants require the presence of sunlight to enable them carry out photosynthesis. In is mainly from this source that they drive energy necessary for growth. Most animals, bacteria and fungi can live in darkness and grow in their habitat
4. TEMPERATURE: All metabolic processes are accelerated at a certain level of temperature. Any imbalance temperature can adversely affect the rate of growth and retard major processes in the body
5. PH: the PH of the fluid in contact with a cell has a gross effect on all its activities. So growth can be hampered at certain level acidity or alkalinity
6. ACCUMULATION OF METABOLLIC PRODUCTS: most metabolic products which accumulates within the body can affect growth. Excessive accumulation is toxic and harmful to the entire body system and can affect growth immensely.
7. HORMONES: hormones are internal factors which are known to affect the rate of growth in plants and animals. Plants hormones which affect the growth of plants are Auxin and gibberellins.
The Auxin promotes or inhibits cell elongation in stems and roots. They also stimulate cell division
Gibberellins promote cell elongation and bring about growth in the stem. They also affect cell division and cell differentiation to a certain extent.
In animals, the hormones are secreted by endocrine glands.
The hormones mainly concerned with growth are secreted by anterior pituitary gland, the thyroid gland and the gonads. Abnormal growth in humans, like Dwarfism or gigantisms is due to errors in the secretion of one these hormones.
You can read more about hormones by going here
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52. SOIL MICRO-ORGANISMS
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85. RETENTION OF WATER BY VARIOUS SOIL TYPES
86. DETERMINATION OF SOIL PH REACTION
87. COLORIMETRIC DETERMINATION OF SOIL PH LEVEL
88. PH SOIL TEST
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