ECOLOGY QUESTION: The two questions are on PAGE 2 on the bottom right corner. he
ID: 57792 • Letter: E
Question
ECOLOGY QUESTION: The two questions are on PAGE 2 on the bottom right corner.
hen we think of growth rate, what typically comes to mind is a measure of change in size during some period of time, such as change in weight during the period of a week (grams weight gain/week). However, this conventional measure of growth is often misleading when comparing individuals of different sizes or tracking the growth of an individual through time. Although larger individuals may have a greater absolute weight gain when compared with smaller individuals, this may not be the case when weight gain is expressed as a proportion of body weight (proportional growth). A more appropriate measure of growth is the mass-specific or relative growth rate. Relative growth rate (RGR) expresses growth during an observed period of time as a function of the size of the individual. This calcula- tion is found by dividing the increment of growth during some observed time period (grams weight gain) by the size of the in- Leaf area ratio total area of leaves (leaf area) per total plant weight (cm2/g) Leaf weight ratio= total weight of leaves per total plant weight (g/g) LAR (cm2/g)-LWR × SLA Specific leaf area total area of leaves (leaf area) per total weight of leaves (cm2/g) Using RGR to evaluate the growth of plants has an addi- dividual at the beginning of that time period (grams weight gain/ iovalue; i can be partitioned into components reflecting total grams weight at the beginning of observation period) andthe influences of assimilation (photosynthesis) and allocation then dividing the period of time to express the change in weight on growth-the assimilation of new tissues per unit leaf area (g/cm2/time) called the net assimilation rate (NAR), and the leaf area per unit of plant weight (cmIg), called the leaf area ratio (LAR) as a rate (g/g/time) Relative growth rate-weight gain during the period of observation per plant weight at the beginning of the observation period per time interval of observation period (g/gtime) The NAR is a function of the total gross photosynthesis of the plant minus the total plant respiration. It is the net assimila- tion gain expressed on a per unit leaf area basis. The LAR is a function of the amount of that assimilation that is allocated to the production of leaves-more specifically, leaf area-expressed on a per unit plant weight basis RGR (g/g/time)-NAR (g/cm2/time) × LAR (cm2/g) Net assimilation rate weight gain during the period of observation per total area of leaves (leaf area) per time interval of observation period (g/cm2/time) The LAR can be further partitioned into two components that describe the allocation of net assimilation to leaves, the leaf weight ratio (LWR), and a measure of leaf density or thickness, the specific leaf area (SLA). The LWR is the total weight of leaves expressed as a proportion of total plant weight (g leaves/g total plant weight), whereas the SLA is the area of leaf per gram of leaf weight. For the same tissue density, a thinner leaf would have a greater value of SLA Leaf area ratio= total area of leaves (leaf area) per total plant weight (cm2/g)Explanation / Answer
The leaf size and shape is affected by multiple factors such as light, temperature, stomata etc.
The leaves located in shady area large in size when compared to leaves that are located in light. The plants growing in hot and arid environment have small leaves, while humid conditions favor large leaves. The leaves with large surface area have maximum water using efficiency. Thus, these leaves exist in warm to hot areas with low light conditions, while small leaves are favored in sunny environment and in cold climatic conditions.
The leaf dimension on leaf boundary layer resistance and efficiency with which heat and moisture are transported away from a leaf are the characteristics that decide the size of leaf. The boundary layer resistance decreases with smaller leaf size or deeper lobes at a particular wind speed. The small surface area of area of leaf allows greater heat and moisture transfer. This is because small leaves have thin boundary layer compared to large leaves that have thick boundary layer.
The leaf size increases transpiration. The high concentration of carbon dioxide favors small size and fewer stomata leaves. In contrast, low concentration of carbon dioxide favors increased number of stomata and large leaves. This is because large leaves with fewer stomata are prone to overheating.
The carbon dioxide absorbed by the leaves is used during photosynthesis and to maintain cellular structure and grow tissues. The large leaves promote capture of more carbon dioxide but the low water and nutrient absorption cannot allow the sustenance of leaves. Thus, in low concentration of carbon dioxide, the available carbon dioxide is allocated for root development, which results in small leaf size.
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