Question

explain why the narrow leaves still do
their job well​

Answer 1

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Needle-shaped leaves have a very low light absorptive surface area. Each needle, then, is not able to capture very much sunlight energy for photosynthesis. Needles also have a very thick, outer cuticle coating and special "pit-like" stomatae designed to prevent excessive water loss. Trees with needle-shaped leaves are especially well suited to site's that have drier soils and to climates in which the careful conservation of water is an important survival strategy.

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Answer 2

Answer:

Leaves high in the tree canopy receive a great deal of sunlight. These leaves tend to be smaller in size (and, therefore, have reduced light absorptive surface area) and tend also to have complex edges and lobes (which enables them to disperse absorbed heat very rapidly). Leaves in the lower tree canopy are more shaded. These lower canopy leaves tend to be larger (more light absorptive surface area) and tend to have reduced expressions of lobes and edges. These trends may be observed in comparing the leaves of high canopy trees (like oaks) to the leaves of low canopy trees (like dogwoods), or they can also be observed in an individual tree that has leaves in both the upper and lower canopies (the white oak, for example). In the white oak the smaller upper canopy leaves are also noted to allow significant amounts of light to pass through the upper canopy in order to keep the lower leaves supplied with sufficient light to allow their continued photosynthesis.

Needle-shaped leaves have a very low light absorptive surface area. Each needle, then, is not able to capture very much sunlight energy for photosynthesis. Needles also have a very thick, outer cuticle coating and special "pit-like" stomatae designed to prevent excessive water loss. Trees with needle-shaped leaves are especially well suited to site's that have drier soils and to climates in which the careful conservation of water is an important survival strategy. Needle-shaped leaves also differ from broad leaves (in our climate zone anyway) in that needles last for three or four years while broad leaves only "live" for a single growing season. These 'evergreen" needled trees, then, have a great advantage over the "deciduous" broad leafed trees in that the metabolic cost of the leaf's synthesis can be recovered via photosynthesis over several growing seasons. Also, the continuous presence of the needles means that whenever environmental conditions are sufficiently moderate (even in the middle of winter!) the needles can photosynthesize and thus gather energy for the tree! A study in Germany compared energy production in beech trees (which have broad, flat leaves) and Norway spruce trees (which have needles). It was found that the beech trees photosynthesize for 176 days in a year while the Norway spruce photosynthesize 260 days in a year! The bottom energy line was that with this increased time base for photosynthesis, the smaller leafed surface area of the Norway spruce was actually 58% more productive than the beech!