Some students wanted to investigate the effect of light intensity on the rate of photosynthesis in the Brazilian waterweed, Egeria densa. This plant is found in freshwater ponds. The students used the apparatus shown in Fig. 1.1 in their investigation. A stand and clamp were used to hold the apparatus in a vertical position. [Figure 1.1] The students carried out these steps to set up the apparatus shown in Fig. 1.1. • Some sodium hydrogencarbonate was added to a sample of pond water as a source of carbon dioxide. • The syringe barrel was filled with the pond water containing sodium hydrogencarbonate. • A fresh piece of E. densa was cut under water. • The cut stem was quickly placed in the pond water in the syringe barrel. • The plunger was replaced, as shown in Fig. 1.1, and adjusted until the meniscus in the capillary tubing was near the top of the scale. • A bench lamp was used as a light source. The students noticed that bubbles of gas were given off from the E. densa. As the gas collected in the syringe barrel, the meniscus moved down the capillary tube. The plunger of the syringe did not move. The students used the apparatus to investigate the effect of different light intensities on the rate of photosynthesis in E. densa.