Exampro A-level Biology

Transcription

1 Exampro A-level Biology YEAR 12 BIOLOGY CHRISTMAS WORK Name: Class: Author: Date: Time: 54 Marks: 49 Comments: Page 1 of 12

2 Q1. (a) Describe how phospholipids are arranged in a plasma membrane (b) Cells that secrete enzymes contain a lot of rough endoplasmic reticulum (RER) and a large Golgi apparatus. (i) Describe how the RER is involved in the production of enzymes Describe how the Golgi apparatus is involved in the secretion of enzymes (Total 5 marks) Q2. (a) An enzyme catalyses only one reaction. Explain why Page 2 of 12

3 (b) Gout is a disease caused by the build-up of uric acid crystals in joints. Uric acid is produced from xanthine in a reaction catalysed by the enzyme xanthine oxidase. Allopurinol is a drug used to treat gout. The diagram shows the structures of xanthine and allopurinol. Use this information to suggest how allopurinol can be used to treat gout (Extra space) (3) (Total 5 marks) Page 3 of 12

4 Q3. Gangliosides are lipids found in the cell surface membranes of nerve cells. Hexosaminidase is an enzyme present in blood that breaks down gangliosides. If gangliosides are not broken down, they damage nerve cells. (a) Hexosaminidase only breaks down gangliosides. It does not break down other lipids. Explain why this enzyme only breaks down gangliosides. (3) (b) Hexosaminidase is found in the blood of healthy people. People with Tay Sachs disease do not have this enzyme in their blood. Doctors confirm Tay Sachs disease by using a blood test. The technician carrying out the test adds a solution containing a high concentration of gangliosides to a sample of blood from the person being tested. The technician then measures the concentration of gangliosides in the person s blood at regular intervals. (i) Complete the graph below by sketching a curve to show the results you would expect for a person with Tay Sachs disease. Label this curve T. Sketch a curve on the same graph to show the results you would expect for a healthy person who does not have Tay Sachs disease. Label this curve H. Page 4 of 12

5 (c) Scientists are trying to find a way to give the missing enzyme to people with Tay Sachs disease. Suggest why they cannot give the enzyme as a tablet that is swallowed. (Total 7 marks) Q4. (a) Name the monosaccharides of which the following disaccharides are composed. (i) Sucrose monosaccharides...and... Lactose monosaccharides...and... (b) Amylase and maltase are involved in the digestion of starch in the small intestine. Complete the table by identifying where these enzymes are produced and the product of the reaction they catalyse. Name of enzyme Where the enzyme is produced Product of the reaction catalysed by the enzyme Amylase Maltase (Total 4 marks) Page 5 of 12

6 Q5. The diagram shows a cell cycle. (a) In prophase of mitosis, the chromosomes become visible. Describe what happens in (i) metaphase anaphase. Page 6 of 12

7 (b) (i) Cells lining the human intestine complete the cell cycle in a short time. Explain the advantage of these cells completing the cell cycle in a short time. The time required for a cell to complete the cell cycle was 4 hours 18 minutes. Calculate the time required in minutes for this cell to multiply to produce eight cells. Show your working. Answer... (c) Mikanolide is a drug that inhibits the enzyme DNA polymerase. Explain why this drug may be effective against some types of cancer. (Total 9 marks) Q6. (a) Mitosis is important in the life of an organism. Give two reasons why Page 7 of 12

8 A biologist used a microscope to investigate plant tissue where some of the cells were dividing by mitosis. She examined 200 cells and counted the number of cells in interphase and in each stage of mitosis. The table shows some of the cells she saw, and the percentage of cells in interphase and in two stages of mitosis, A and B. Stage of cell cycle Percentage of cells Interphase 90 Stage A 3 Stage B 1 Images by Edmund Beecher Wilson [Public domain], via Wikimedia Commons (b) (i) Explain why the biologist chose to examine 200 cells Name Stage A and Stage B. Give the evidence from the photograph that you used to identify the stage. Name of Stage A... Evidence..... Name of Stage B... Evidence..... (4) Page 8 of 12

9 (c) In this tissue one complete cell cycle took 20 hours. Using information from the table, calculate the mean time for these cells to complete mitosis. Show your working. Answer... (Total 9 marks) Q7. (a) A plant cell was observed with an optical microscope. Describe how the length of the cell could be estimated. (b) The water potential of a plant cell is 400 kpa. The cell is put in a solution with a water potential of 650 kpa. Describe and explain what will happen to the cell. (3) Page 9 of 12

10 (c) A group of students investigated the effect of sucrose concentration on the change in length of cylinders of tissue cut from a young carrot. They measured the initial lengths of the carrot cylinders, then placed one in each of a number of sucrose solutions. After 18 hours, they removed the carrot cylinders and measured their final lengths. Some of the results are shown in the table. Concentration of sucrose / mol dm 3 Percentage decrease in length of carrot cylinder (i) The carrot cylinders were left for 18 hours in the sucrose solutions. Explain why they were left for a long time. Explain how you would use a graph to predict the concentration of sucrose that would result in no change in length of the carrot cylinders. Page 10 of 12

11 (iii) Young carrots store sugars in their tissues but, in older carrots, some of this is converted to starch. How would using cylinders of tissue from older carrots affect the results obtained for a sucrose solution of 0.6 mol dm 3? Give a reason for your answer. (Total 10 marks) Page 11 of 12

12 Page 12 of 12