Report on photosynthesis lab Example | Topics and Well Written Essays - 2000 words

On photosynthesis - Lab Report Example Classically the effects of temperature on photosynthetic rates follow a parabolic relationship, with rates being low at extremely low and high temperatures and high at moderate temperatures (Rabinowitch and Govindjee, 1969). Consequent to this relationship, plant growth and productivity is often limited by extremes of temperature, with either too low or high temperatures affecting the growth and productivity of plants (Rabinowitch and Govindjee, 1969; Govindjee, 1975). Obviously it appears that extremes of temperature could adversely affect the apparent photosynthetic rate of leaves. Further, while tissue respiration rates may remain unaltered under extreme temperatures, decrease in the photosynthetic rates can lead to a negative carbon balance in the plant (Hipkins, 1987). Under such conditions, the growth and productivity and consequently the adaptability of plants would be jeopardized. These arguments pre-suppose that plant species in nature have an optimum temperature at which th eir photosynthetic rates are maximized. Extreme temperatures either too low or too high depress the photosynthetic rates. In recent years, there has been renewed interest in evaluating plant responses to elevated temperature owing to the green house effect. In this paper we explicitly examine the hypothesis that within a limited range of temperatures, the photosynthetic rates of leaves would scale positively with temperature. We discuss the results in the light of existing knowledge on the role of temperature in influencing apparent photosynthetic rates in species and how such relation could have implications for plant growth and productivity. Materials and Methods Rationale of the experiment The experiments were performed on spinach leaf disks. Leaf disks contain spongy mesophyll layer of cells, which largely comprise of large air spaces. By depleting the air spaces under vacuum, the leaf disks sink in water. However, under sufficiently lighted conditions when the leaf disks photosynthesize, the air spaces are refilled with oxygen (a product of photosynthetic oxygen evolution) and tend to float again. The rate at which the leaf disks begin to float can be used as a surrogate measure of the photosynthetic rate of the leaf disks. Thus leaf disks that fail to float are those in which photosynthetic oxygen evolution has not occurred (and hence in which photosynthesis is absent). On the other hand and keeping everything else constant, it can be inferred that leaf disks that float slowly are those were the photosynthetic rates are relatively slow compared to disks that float rapidly. Preparation of leaf disks for incubation Leaf disks were made using a hole puncher. About 60 leaf disks were prepared from 2 or 3 fresh leaves of spinach at each effort. With the help of a surgical syringe, air was removed from the spongy tissue of the leaf disks by creating vacum and replaced with sodium bicarbonate solution (0.2 percent w/v). After this process, most of the disks sink to the bottom of the syringe, indicating that in these disks the air spaces were successfully evacuated and replaced with bicarbonate solution. Disks that remained afloat were discarded. The sunken disks were transferred to fresh sodium bicarbona