2.2. Carbohydrates and lipids
A subsection of Biology, 9700, through 2. Biological molecules
Listing 10 of 368 questions
Adipose tissue, which is composed of cells known as adipocytes, stores large quantities of triglycerides and functions as an energy storage tissue. is a photomicrograph of adipose tissue. Adipocytes can be very large in size compared to other body cells. This is due to a large lipid droplet within the cell. The largest adipocyte in has a mean diameter of 35 µm. A person with good eyesight can see cells of 0.05 mm or greater diameter without a magnifying glass or any other optical aid. State whether the person can see this adipocyte without any optical aid. Show your working to justify your answer. Only some of the organelles within the adipocyte can be seen using a high quality light microscope set at the highest magnification. Organelles such as rough endoplasmic reticulum, smooth endoplasmic reticulum and ribosomes are only visible using an electron microscope. Explain why these organelles are not visible using a light microscope. Adipocytes synthesise triglyceride lipase (ATGL), an enzyme that catalyses the formation or breakdown of triglycerides, as shown in . triglyceride lipase fatty acids glycerol + The balance between triglyceride formation and breakdown is controlled by hormones. is a summary of events occurring in an adipocyte when glycogen energy stores have been used up. hormone tissue fluid cell surface membrane ATP second messenger molecule cytoplasm inactive enzyme active enzyme active ATGL inactive ATGL triglyceride fatty acids + glycerol Name the type of bond broken by active ATGL to produce fatty acids and glycerol. Name and outline the process by which the fatty acids shown in exit the cell. is an example of cell signalling within the body. With reference to , outline the process of cell signalling. The fatty acids released from adipocytes are transported in blood plasma and are taken up by cells. Although most cell types can metabolise fatty acids to synthesise ATP in the presence of oxygen, red blood cells cannot do this. Suggest why red blood cells cannot metabolise fatty acids to synthesise ATP.
9700_s18_qp_23
THEORY
2018
Paper 2, Variant 3
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Phospholipids are components of cell surface membranes. Describe how phospholipid molecules are arranged in a cell surface membrane. You may use the space below for a simple annotated diagram if you wish. shows the structure of the lipids: • tristearin, which is a triglyceride; • phosphatidylcholine, which is a phospholipid. H H H C O C = O C = O C = O H O H O C C H H H C O C = O C = O H O O H C C P O C H C O – O = H H N + CH3 CH3 CH3 H tristearin phosphatidylcholine Use [T State two ways, visible in , in which phosphatidylcholine differs from tristearin. 1. 2. Explain how the structure of triglycerides, such as tristearin, makes them more suitable for energy storage than carbohydrates, such as glycogen. The enzyme lipase catalyses the hydrolysis of ester bonds in triglycerides. As the reaction proceeds there is a decrease in pH. The progress of the reaction may be followed by using a pH meter. A solution containing tristearin was placed in a water bath at 25 °C. When the solution had reached this temperature, lipase was added and the mixture stirred. The pH of the reaction mixture was recorded every minute for 20 minutes. The results are shown in . Using the data in , state the time when lipase was added; the reaction ended. Explain why the pH decreases during this reaction. A similar solution was placed in a water bath at 35 °C and left for the same length of time to reach this temperature. Lipase was added as before. Sketch on the results that you would expect. pH time / min
9700_w05_qp_2
THEORY
2005
Paper 2, Variant 0
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