MODEL OF SPECIFICITY

Transcription

1 MODEL OF SPECIFICITY A simple model can be a drawing. The models on the following page show the two main types of reactions that enzymes are involved in: Example 1 (Figure 3): An endergonic reaction (requires energy to proceed): Example 2 (Figure 4): An exergonic reaction (releases energy): Some common enzymes include: 1. Maltase: Found in saliva and pancreatic juice, acts on maltose. 2. Sucrase: Acts on the carbohydrate sucrose. 3. Catalase: Found in all living cells acts on the poison hydrogen peroxide. QUESTION 1 Which of the following sequences most correctly represents the result of a reaction involving an enzyme? KEY: E=Enzyme, P1=Product 1, P2=Product 2, S=Substrate A P1+ S P2 + E B S + E P1 + P2 C P1 + P2 + E E + S D S + E P1 + P2 + E QUESTION 2 The diagram below shows an enzyme and substrate. Which number correctly identifies the active site? A 1 B 2 C 3 D The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 1

2 QUESTION 3 (4 marks) Identify the role of enzymes in the process of metabolism and use a simple model to describe their action. (Try answering on your own and then use the notes above to check your response.) Solution Identify the ph as a way of describing the acidity of a substance. The ph of a solution is the measure of concentration of ions per litre of solution. The ph of a neutral solution (for example, pure water) is. A ph value below 7 indicates an acidic solution. The lower the number is, the more acidic the solution. A ph value above 7 and up to 14 indicates a basic solution. The higher the number is, the more basic the solution. The ph scale is a log scale, which means that a single number shift on the scale changes the acidity 10x. Most biological solutions have a ph of between 6 and 8, for example human is maintained at a ph of about 7.4. There are a few exceptions to this, for example gastric juice in the stomach has a ph of about 2. QUESTION 4 What does the term ph describe? A B C D The amount of hydrogen gas in a solution. The acidity of a solution. The solute concentration of a solution. The acidity of water. The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 2

3 Identify data sources, plan, choose equipment or resources and perform a first-hand investigation to test the effect of: Increased temperature. Change in ph. Change in substrate concentrations on the activity of named enzyme(s). FIRST HAND INVESTIGATION EXPECTED RESULTS There are various factors that affect enzyme activity. Some of these include: Temperature: Each enzyme has an optimum temperature. In humans this is typically 37ºC. At high temperatures enzymes are denatured, that is their active sites are permanently altered in shape. If the shape is altered, then the enzyme and substrate cannot lock together and the enzyme won't work on the substrate. At low temperatures enzymes become less active due to reduced molecular movement. However, they can regain their former activity again when the temperature rises back to optimum level. ph: Each enzyme has an optimum ph, for example pepsin has an optimum ph of 1.5 working in the human stomach, whereas trypsin, active in the small intestine, works best at a ph of 8. A change in ph can change the shape of the enzyme active site. The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 3

4 Substrate concentration: As substrate concentration increases, rate of reaction will also increase (assuming the presence of free enzymes) until a certain concentration where the enzymes cannot be recycled any faster and hence the rate of reaction plateaus. You should have conducted three controlled experiments, one to test the effect of each of the above factors on enzyme activity. Make sure you can describe or outline these experiments and discuss certain aspects such as accuracy, validity and reliability. QUESTION 5 A space probe recently returned to Earth from a distant planet with samples containing bacteria X. Biologists are interested in comparing the activity of an enzyme found in bacteria X with that found in bacteria E from Earth. Both bacteria contain an enzyme that produces a gas as a product of its activity on the same substrate. Environmental condition where bacteria were collected Bacteria Temperature ( o C) ph X E State a hypothesis to be tested and plan an investigation you could carry out to compare the activity of the enzyme found in the TWO bacteria under ONE of these conditions. (7 marks) The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 4

5 QUESTION 6 The sweet taste of freshly picked corn is due to the high sugar content in the kernels. Enzyme action converts about 50% of the sugar to starch within one day of picking. To preserve its sweetness, the freshly picked corn is immersed in boiling water for a few minutes, and then cooked. Which of the following explains why the boiled corn kernels remain sweet? A B C D Boiling destroys sugar molecules so that they cannot be converted into starch. Boiling inactivates the enzyme responsible for converting sugar to starch. Boiling kills a fungus on the corn that is needed to convert sugar to starch. Boiling activates the enzyme that converts starch into sugar. The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 5

6 Explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency. Chemical reactions within a cell involve enzymes that combine and break apart many complex molecules. The total of these reactions is called. Some of them occur in one step, but often a complex set of reactions is involved in a metabolic change. If the internal environment does not remain stable, the rate of reactions that are catalysed by enzymes decreases. This can then affect entire pathways that are required to make essential compounds (for example, haemoglobin). Some of the variables that need to be maintained at optimal levels for maximum metabolic activity include, ion concentrations, core body, ph, oxygen levels, water levels and blood. QUESTION 7 Explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency. (3 marks) The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 6

7 Describe homeostasis as the process by which organisms maintain a relatively stable internal environment. Homeostasis is one of the key characteristics of living things. It is the condition of maintaining a relatively stable environment regardless of the conditions in the external environment. The internal environment consists of the body and cells while the external environment is that outside the body. Homeostasis = staying the same. We need to keep key variables in our bodies within a narrow range so they can function optimally for example so that enzymes can perform a variety of chemical reactions. These variables include body temperature, ph (percent H+ ions), water, gas concentrations (CO2) salt concentrations (Na+, Cl-, Ca+) and glucose levels. In animals, homeostasis is achieved through the action of and. In plants, homeostasis is achieved through the action of hormones only as plants do not have a nervous system. If homeostasis is not maintained the organism will be unable to function properly and is likely to die. QUESTION 8 Which process is an example of homeostasis? A B C D Heart rate increasing with exercise. Blood pressure increasing with exercise. Body temperature falling in cold weather. Removal of glucose from the blood. Explain that homeostasis consists of two stages: Detecting changes from the stable state. Counteracting changes from the stable state. DETECTING CHANGES FROM THE STABLE STATE For homeostasis to take place there must be an external (Eg. the temperature going up) telling our bodies the stable state has changed. A (Eg. Thermo-receptors in our skin) must recognise this. The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 7

8 COUNTERACTING CHANGES FROM THE STABLE STATE There must also be a (sweating) by our bodies in order to correct the change in temperature detected by the. An (pores in the skin) must initiate the response. Homeostasis allows a change to take place. If it is a counter change, it is known as a feedback system. Outline the role of the nervous system in detecting and responding to environmental changes. The nervous system is only found in multi-cellular animals and involves rapid responses which only last for a short time, i.e. it forms the quick source of communication between cells. It is composed of the brain, spinal cord ( nervous system) and all the surrounding nerves of the body ( nervous system). The nervous system coordinates the responses between the receptors and the effectors via the in the brain and the network of nerves around the entire body. Receptors detect a change from external stimuli. Humans have light receptors in their eyes, gravity and sound receptors in their ears, chemical sensors in their noses and tongues, pressure and pain sensors on their skin. These sensors send an electro-chemical signal along many interconnected nerve cells (peripheral nervous system) to the hypothalamus (central nervous system) in the brain. Here, the effect is coordinated and transmitted via the peripheral nervous system. Stimulus Transmission of Message Effector QUESTION 9 Homeostasis involves two stages. (1) Detecting changes from a stable state and (2) Counteracting changes from the stable state. Using an example, describe the role of the nervous system in the above stages. (3 marks) The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 8

9 Gather, process and analyse information from secondary sources and use available evidence to develop a model of a feedback mechanism. Feedback is the mechanism by which homeostasis is maintained. It is called this because information about the change has been fed to the control centre, which then feeds back a response to the system in which the set value is being maintained. Homeostasis involves the operation of feedback mechanisms, whereby the response affects the original stimulus. If a set value or point deviates from this value, negative feedback causes the system to correct the deviation and return the value to the set Value negative feedback the change. For example, if the blood glucose levels get too high from eating a high GI meal, the response counteracts this change by stimulating processes that reduce the blood sugar concentration. Negative feedback is the commonest type of feedback in biological systems. SECONDARY SOURCE INVESTIGATION You would have drawn a model of a negative feedback mechanism for a plant, human, animal other than a human or a machine such as a heater. QUESTION 10 Draw a labelled diagram to show how a specific feedback mechanism plays a role in homeostasis. (4 marks) The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 9

10 Identify the broad range of temperatures over which life is found compared with the narrow limits for individual species. Most organisms prefer to live in an environment with temperatures between 0 C and 45 C. Water freezes at 0 C, and as it expands when it freezes, cell membranes can break and rupture if the water in them freezes. Similarly, temperatures above 45 C can cause the enzymes in an organism to denature. Most individual species have a very specific temperature range in which they can exist. They are most comfortable in a temperature range where their adaptations allow them to survive, be active and reproduce. For example, you would not find giraffes in the Arctic as their adaptations would not allow them to survive at such low temperatures. QUESTION 11 The table below shows information about four species of bacteria and their reproductive rates at different temperatures. Bacterial Species Temperature range found in ( C) Generations per hour (average) Species W -2 to Species X 15 to Species Y 42 to Species Z 69 to What conclusion can be drawn from this table? All bacterial species can adapt to a broad range of temperatures: A B C D Individual species can reproduce in a broad range of temperatures. All bacterial species are limited to a range between 0 C and 100 C. Species Y is able to reproduce the best across all temperature ranges. Individual species reproduce in a relatively narrow range of temperature The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 10

11 Compare responses of named Australian ectothermic and endothermic organisms to changes in the ambient temperature and explain how these responses assist temperature regulation. ECTOTHERM Ectotherms use (mostly) the energy in their to control their internal temperatures. Reptiles, amphibians and are ectotherms. ENDOTHERM Endotherms use (mostly) their energy to maintain their internal temperatures. Birds and are endotherms. AMBIENT TEMPERATURE The ambient temperature is the immediate environmental temperature. Australia has a great range of environmental conditions, from Alpine regions (for example, The Snowy Mountains) to desert in Central Australia. Australian animals possess various responses to cope with the environments within which they live. RESPONSE A response is a type of adaptation. Not all adaptations are responses. A response is something that takes place after a stimulus rather than a feature that exists constantly. For example, a kangaroo licking its paws when it is hot is an adaptation and a response. The large ears of a bilby used to dissipate heat are an adaptation. QUESTION 12 Compare responses of Australian Ectotherm and Endotherm to changes in ambient temperature. (3 marks) The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 11

12 Identify some responses of plants to temperature change. Eucalypts can hang their downward during the hottest part of the day so they are pointing away from the sun. This reduces the surface facing the direct heat. Frangipanis slow their growth rate in response to low temperatures i.e. below 15 C. Banksia release seeds in response to the heat of a bushfire. Many plants keep their closed during the hottest part of the day. QUESTION 13 Which adaptation assists temperature regulation in plants? A B C D Large leaves for cooling. Increased production of seeds. Movements of glucose to roots. Evaporation of water from stomates. QUESTION 14 Identify a response of a named plant to temperature change. (2 mark) The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 12

13 Analyse information from secondary sources to describe adaptations and responses that have occurred in Australian organisms to assist temperature regulation. SECONDARY SOURCE INVESTIGATION You will have used various resources to prepare case studies of a few Australian plants and a few Australian animals showing the adaptations and responses that have assisted them in regulating their temperature. ANALYSE Look at the relationship between the adaptations/responses and the benefit they provide for the organism. How common are some of the adaptations/responses? QUESTION 15 A small Australian mammal that lives in the alpine regions of New South Wales has specific features that enable it to retain body heat. Identify the features that are most likely to be present in the mammal described. A B C D Long ears, rounded body, long legs. Short ears, rounded body, short legs. Short ears, slender body, long legs. Short ears, slender body, short legs. QUESTION 16 Outline how you made sure the information you analysed to describe adaptations and responses that have occurred in Australian organisms to assist temperature regulation was reliable. (2 marks) The School For Excellence 2011 Trial Exam Preparation Lectures Biology Book 1 Page 13