RI N21 H2 P2 Answers

2021 H2 Biology Paper 2 9744/02 1 (a) Name the structures labelled A, B and C in Fig. 1.1. [3] A middle lamella of cell wall B cytoplasm C chloroplasts (b) The magnification of the photomicrograph is x560. Calculate the length of cell X in m, along the line Y–Z. Show your working. magnification = Picture length Y-Z in mm x1000/ actual length = x 560 actual length = picture length in um/560 length of cell X =………… m [2] (c) The leaves of mosses typically consist only of a single sheet of photosynthetic tissue that is one cell thick across its entire surface. There are no air spaces. (i) Describe how carbon dioxide in the air travels to the site of photosynthesis in the leaves of the mosses. [3] 1. Carbon dioxide dissolves at the film of water surrounding/ at the cell wall and diffuses into the cytoplasm; 2. down a carbon dioxide concentration gradient; 3. Dissolved carbon dioxide further diffuses into stroma across the double membrane of chloroplast; 4. where carbon fixation takes place via Calvin cycle of photosynthesis; R: across the stomata as the leaf is single cell thick (ii) Suggest why moss plants require damp conditions in which to grow. [2] 1. Absence of vascular bundle/xylem and thus moss plants depend on water moving into cells from the surrounding via osmosis; 2. Damp conditions prevent water from being lost to surrounding via evaporation thus preventing the plant from drying up; 3. Water is needed for photolysis* during non-cyclic photophosphorylation* 4. It is also needed as a medium for diffusion of molecules and other biochemical reactions within the cell; [Total: 10] 2 (a) escribe the relationship between the speed of the ants and the temperature, as shown in Fig. 2.1. [3] 1. As temperatures increase from 9oC to 26oC, speed of ant movement increase gradually from 0.4 cms-1 to 2.8 cms-1; 2. As temperatures increase further from 26oC to 32 oC, speed of ant movement increase more sharply from 2.8 cms-1 to 4 cms-1; 3. As temperatures increase from 32oC to 38oC, speed of ant movement experience the steepest increase from 3.8 cms-1 to 6.6 cms-1;

(b) Explain the effect of temperature on the speed of the ants, as shown in Fig. 2.1. [4] 1. As temperature increase from 90C to 380C, there is increase in kinetic energy; 2. which increases frequency of effective collisions* between substrate and enzyme active sites thus rate of formation of enzyme-substrate complex* increases; 3. increasing temperature also increases number of molecules having sufficient energy to overcome activation energy barrier to form products of metabolic reaction; 4. Rate of reaction could possibly be at maximum 380C with most of active sites* of enzymes being saturated with substrate; (c) Suggest and explain what will happen to the speed of the ants as the temperature continues to increase above 40oC. [4] 1. As the temperature increases above 40°C,