13 Growth Study Guide to Growth and Measurement of Growth in Living Organisms
Definition and Fundamental Processes of Growth
- General Definition of Growth: Growth is characterized as a permanent increase in the size of an organism. Growth and development are features common to all living organisms.
- Cellular Mechanisms of Growth: * Cell Division: In multicellular organisms, growth occurs as cells undergo cell division specifically through the process of mitosis (refer to page 145 for detailed mechanics of mitosis). * Protoplasm Synthesis: Following division, new cells grow to reach their full size by manufacturing additional protoplasm.
- Specialized Growth Processes: * Plant Growth: Plant cells achieve further increases in size by absorbing water into their vacuoles. * Differentiation: Most cells undergo differentiation, also known as specialization, to carry out specific functions within the organism. * Animal Growth: In addition to cell division, animals grow by producing more extracellular materials. Named examples of these materials include: * The mineral of bones. * The fibres of connective tissue.
Parameters and Methods for Measuring Growth
Methodology Overview: Measuring growth involves tracking and measuring changes in various growth parameters over specific intervals of time.
Table 13.1: Specific Methods Used to Measure Growth:
Height: * Organisms Measured: Humans and small plants. * Advantages: * It is a quick method to measure. * It is easy to perform. * The process does not harm the organism. * Disadvantages: * It only measures growth in a single dimension. * In plants, it can be difficult to determine exactly where the top of the plant is.
Length: * Organisms Measured: The bodies of animals; specific parts of animals such as legs, wings, and tails; and plant stems. * Advantages: * Measurements are quick to obtain. * It is easy to measure. * The process does not harm the organism. * Disadvantages: * It only measures growth in one dimension. * It may only capture the growth of a specific part of an organism rather than the whole.
Wet Mass: * Organisms Measured: Most animals and small plants. * Advantages: * Quick and easy to measure. * It does not cause harm to animals. * It provides a more accurate measure of overall growth compared to height or length. * Disadvantages: * Measurements may be inconsistent because the water content within the bodies of organisms can change. * In plants, growth is disturbed because they must be uprooted and their roots must be cleaned for measurement.
Dry Mass: * Organisms Measured: Germinating seeds and seedlings, small plants, and small animals (specifically invertebrates). * Advantages: * This is considered the most accurate measure of growth because it isolates and measures cellular and extracellular material by removing all water. * Disadvantages: * The process is time-consuming. * Organisms must be dried at until they reach a constant mass. * The organisms are killed during the process. * Large numbers of organisms are required for the study.
Number of Leaves: * Organisms Measured: Small plants. * Advantages: * It is relatively quick to perform. * The leaves are easy to count. * Disadvantages: * It only measures a single aspect of the plant's overall growth.