7 Answers to end-of-chapter questions

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1 7 Answers to end-of-chapter questions Multiple choice questions 1 B 2 B 3 A 4 B 5 A 6 D 7 C 8 C 9 B 10 B Structured questions 11 a i Maintenance of a constant internal environment within set limits i Concentration of glucose in the blood Concentration of individual inorganic ions in the blood (e.g. calcium ions) Water potential of blood and body fluids ph of the blood and body fluids Core body temperature Hydrostatic pressure of the blood (blood pressure) Any valid point The chemical reactions which make up the metabolism of all living organisms are controlled by enzymes. Enzymes operate most efficiently at a particular optimum temperature and ph Also necessary to maintain the correct water potential of body fluids in animals at all times. If the water potential of tissue fluid is higher or lower than cells, cells would be affected (can burst or shrink) The ability to maintain a favourable constant internal environment when external conditions are unfavourable or fluctuating gives organisms independence from the external conditions. Allows them to lead an active life Any valid point Each point Max [2] Any point well explained Max [2] Biology Unit 2 for CAPE Examinations Original material Cambridge University Press

2 b Negative feedback means that whenever a change occurs in a system, the change automatically Causes a corrective mechanism to start, which reverses the original change and brings the system back to normal c i Is the specific level/concentration of factor or substance which the body requires to function effectively e.g. the set point of glucose is 90 mg/100 cm 3 / 0.1% per 100cm 3 / 4 mmol per 100cm 3 Regulator: compares the actual output/value of a particular physiological factor with the set point value Effector: restores the output of the physiological factor to set point Detector: sensory receptors which monitor the output of the physiological factor i Hormones Nerve impulses d Gives greater control if there are two systems controlling changes in each direction 12 a Respiration b i Days 1 4: fairly constant around 20 cm 3 CO 2 kg -1 h -1 Day 5 7: steep increase up to 80 cm 3 CO 2 kg -1 h -1 Days 7 10: steady decrease to 58 cm 3 CO 2 kg -1 h -1 Days 1 3: no ethylene Day 4 6: steep increase from 2 dm 3 kg -1 h -1 to 41 dm 3 kg -1 h -1 Days 7 10: steady decrease to 13 dm 3 kg -1 h -1 c Day 6 d Rise in respiration rates Increase in levels of certain enzymes e.g. amylase, pectinase, hydrolases Chlorophyll broken down and colour changes from green to yellow Degradation of starch into sugars Breakdown of cell walls making the fruit softer Any valid point e Do a starch test on the banana for each day of ripeness Description of starch test: add 2 drops of iodine on a fixed size of banana Do a colour chart of known concentration of starch Compare fruit with chart Any valid point: use of reducing sugar test Any point Max [3] Each point Max [4] Biology Unit 2 for CAPE Examinations Original material Cambridge University Press

3 13 a Insulin = beta cells of islets of Langerhans in pancreas Glucagon = alpha cells of islets of Langerhans in pancreas b 4.4 mmol dm -3 Glucose level was constant until sports drink was given then it returns to this level at 5 hours c To maintain a constant internal environment for optimum conditions for enzyme to work d Increases rapidly To 7.6 mmol dm -3 Falls rapidly below set point value (4.4 mmol dm -3 ) Returns to set point at 5 hours Any point Max [3] e i Increase in glucose detected by β cells of islets of Langerhans in the pancreas/ change from set point detected by β cells of islets of Langerhans in the pancreas The β cells acts as a regulator which produces hormone insulin Glucose levels decrease Detector senses glucose level is at set point β cells no longer stimulated Insulin secretion stops Insulin broken down in body 1 2 points f At 4 hours glucose falls below set point Detected by α cells of islets of Langerhans α cells stimulated to produce glucagon Causes conversion of glycogen to glucose by liver cells Blood glucose levels increase to set point Essay questions 5 points [3] 1 2 points 1 a i Is the specific level/concentration of factor or substance which the body requires to function effectively Well explained Example: the set point of glucose is 90mg/100cm 3 Example Cells or tissues which respond to the change in order to return system to set point by communicating to the effectors through hormones or the nervous system via the coordination centre Well explained Example: the β cells of pancreas are also regulators since they produce insulin which then travels the effectors Example Biology Unit 2 for CAPE Examinations Original material Cambridge University Press

4 i Cells with surface proteins that sense the concentrations of factors or molecules. These cells/ tissues respond to the variations by causing a reaction Well explained Example: detectors for blood glucose concentration occur in the pancreas. β cells are sensitive to a rise in glucose levels. α cells are sensitive to a drop in glucose and secrete glucagon Example iv Tissues and organs/target organs which bring about the corrective mechanism which restores the factor towards its set point Well explained Example: insulin targets the liver, muscles, other body cells while glucagon targets the liver Example b Can be shown on an annotated flow diagram Homeostasis maintenance of a constant internal environment Example: blood glucose levels at 90 mg per 100 cm 3 of blood is set point Sensory receptors known as detectors monitor the actual output value And the regulator determines if there is a difference between the set point and the actual output The regulator communicates with the effector via nerve impulses or hormones to bring about a change so as to reverse the output value negative feedback Example: if glucose levels > set point, β cells of islets of Lagerhans in pancreas acts as both detector and regulator They secrete insulin which acts on the effector/liver and muscle cells These cells increase uptake of glucose thereby lowering glucose levels If glucose levels < set point, α cells of islets of Langerhans in pancreas acts as both detector and regulator They secrete glucagon which acts on the effector/liver cells These cells increase conversion of glycogen into glucose which diffuses into the blood thereby increasing glucose levels Any valid point: other effects of insulin respiration etc points [7] points [6] 9 10 points [5] 7 8 points [4] 5 6 points [3] 1 2 points 2 a Made up ductless glands Rich supply of blood vessels Chemical communication by means of hormones Which are secreted directly into the bloodstream Which act on specific cells known as target cells 1 2 points Biology Unit 2 for CAPE Examinations Original material Cambridge University Press

5 b Chemical messengers/steroid/peptide Which is small and soluble Travels in the blood Acts on a specific target organ Which has a complementary receptor site for the hormone Small amounts bring about changes in metabolism, growth etc 5 6 points [3] 1 2 points c On cell membranes attaches to cell membranes Signals for vesicles to merge with cell membrane Example: insulin causes glucose channels to merge with cell membrane Through second messenger: binds to cell membrane which then causes another molecule to trigger a series of reactions Example: glucagon binds to receptor site on cell membrane which then triggers cyclic AMP to trigger series of enzyme controlled reactions of glycogenolysis On genes: lipid soluble hormones act directly on nucleus of cell Example: steroid hormones d Any point well explained with example [2] Max [6] Insulin: Increase in cell permeability to glucose/increase in glucose channels Increase rate of conversion of glucose to fat in adipose tissue Increase rate of conversion of glucose to glycogen in liver and muscle cells More intracellular enzymes become active/increase respiration Any valid point Any 2 points [2] Glucagon: Activates enzymes in liver cells which speed up conversion of glycogen to glucose/glycogenolysis Increase production of glucose from other nutrients such as amino acids and fatty acids in liver cells/ gluconeogenesis Any 2 points [2] 3 a A plant growth regulator is an organic compound, either natural or synthetic, that modifies or controls one or more specific physiological processes within a plant Well explained [2] Partial b Gaseous Biology Unit 2 for CAPE Examinations Original material Cambridge University Press

6 c A characteristic rise in respiratory rate before the ripening phase The ethylene acts at the genetic level, activating regulatory genes Ethylene causes an increase in enzymes Amylase, which breaks down starch to produce simple sugars Fruit becomes sweet Pectinase, which breaks down pectin, a substance that keeps fruit hard Fruit becomes soft Hydrolases to help break down chemicals inside the fruits Chlorophyll is broken down and sometimes new pigments are made so that the fruit skin changes colour from green to red, yellow, or blue Enzymes break down large organic molecules into smaller ones that can be volatile (evaporate into the air) producing an aroma d Ripened fruits do not ship well They become bruised and rot before arrival Green unripened fruits ship better However they may be sour and still unripened when they arrive at destination Depending on length of trip, fruits are stored in low oxygen, cold rooms To lower respiration rates Fruits are then placed in a room with ethylene gas which stimulates ripening process The fruits can then be taken out of the room depending on state of ripeness needed, and stored in a cold room Any point Max [6] Any point Max [6] Biology Unit 2 for CAPE Examinations Original material Cambridge University Press