Identify structures C, D, and A in the provided diagram of the human digestive system and explain their functions.

You're on a roll — SECTION A (40 marks) 1. The diagram below represents the digestive system of man and the associated organs a) Identify structure labeled C. C: Liver* b) What is the significance of the structure labelled C above? The liver* (C) plays a crucial role in metabolism, detoxification of harmful substances, production of bile for fat emulsification, storage of glycogen, and synthesis of plasma proteins and clotting factors. c) Explain digestive and hormonal function of structure labelled D. D represents the pancreas*. Digestive function: The pancreas produces pancreatic juice*, which contains digestive enzymes such as amylase (for carbohydrates), lipase (for fats), and proteases (e.g., trypsin, for proteins). These enzymes are released into the small intestine to aid digestion. Hormonal function: The pancreas contains the islets of Langerhans, which secrete hormones like insulin (lowers blood glucose) and glucagon* (raises blood glucose) directly into the bloodstream to regulate blood sugar levels. d) State significance of structures labelled A. A represents the salivary glands. Their significance is to produce saliva*, which contains salivary amylase (ptyalin) to begin carbohydrate digestion, lubricates food for swallowing, and helps in taste perception. 2. a) What characteristics do gills of fish and mouth cavity of frog have in common that enable them to be efficient in gaseous exchange. Both have a large surface area* for gas exchange. Both have thin walls* (one cell thick) to facilitate rapid diffusion of gases. Both have a rich blood supply* (dense capillary network) to transport gases efficiently. Both maintain a moist surface* for gases to dissolve before diffusion. b) Describe the change that occur to the rib cage and the diaphragm during inspiration. During inspiration (inhalation), the external intercostal muscles contract, pulling the rib cage upwards and outwards. Simultaneously, the diaphragm muscle contracts and flattens*, moving downwards. These actions increase the volume of the thoracic cavity, leading to a decrease in internal pressure and drawing air into the lungs. 3. In an experiment, some discs cut from living potato tuber tissue were placed in distilled water for 30 minutes. The discs were then placed in concentrated sucrose solution for another 30 minutes. At regular intervals of time the discs were out of the liquid, dried, weighed and replaced in the liquid The Results obtained from the experiment are as shown in the graph below Explain the state of the cells of tissue discs at: I) A At point A (30 minutes), the potato discs were in distilled water and had gained maximum weight (approximately 21g). The cells are turgid*, meaning they have absorbed water by osmosis and their cell membranes are pressed firmly against their cell walls. II) B At point B (50 minutes), the potato discs were in concentrated sucrose solution and had lost significant weight (approximately 15g). The cells are plasmolysed* (or flaccid), meaning they have lost water by osmosis, causing the cell membrane to pull away from the cell wall. III) Work out the change in weight between A and B. Weight at A (30 minutes) ≈ 21 g Weight at B (50 minutes) ≈ 15 g Change in weight = 21 g - 15 g = 6 g decrease IV) Name the process which brings about change C -D. The process is osmosis*. (C is initial weight ~18g, D is final weight ~15g, overall decrease due to water movement). V) Name the process which brings about the change in weight. The process is osmosis*. VI) Why is it possible for this process to occur? This process is possible because plant cells have a partially permeable cell membrane and there is a water potential gradient* between the potato cells and the surrounding solutions. 4. The chart below is a summary of the blood clotting mechanism in man X: Damaged tissues and platelets* (which release thromboplastin) Y: Calcium ions* (Ca^2+) (and Vitamin K, which is a cofactor for prothrombin synthesis) Z: Fibrin* Keep up the great work! What's next?