Читать книгу Manual for laboratory classes in biological physics - Коллектив авторов - Страница 3

The temperature range on the Earth from -80 °C to +85 °C significantly exceeds the borders within which the active life is possible. Temperature determines the activity level and distribution of animals. In an open ocean, the temperature of the surface water layers is -2 – +30 °C. Vital processes are only possible at 0-40 °C. In an inactive state, animals tolerate not only negative temperatures, but freezing. For example, small nematodes tissue cultures (epithelial, muscles, etc.), protozoa get frozen when placed in liquid air (-197 °C) and comes to life if to warm them slowly. Some animals inhabit hot springs, like a few bacteria and algae that can reproduce at +70 °C .

Temperature, as a measure of the velocity of molecular movement, determines the rate of chemical reactions, and is considered to be one of the factors limiting growth and metabolism. Animals that change their body temperature in accordance with the change in environmental temperature are called poikilothermic (changeable, labile). In this case, temperatures of bode and surroundings are not necessarily equal. Body temperature can be higher, especially, at the active state. Thus, fish of 40g have the muscle temperature higher by 0,44 °C.

Animals able to regulate their temperature are homoeothermic (birds and mammals). This is due to the thermoinduction, protectional behavior, thermoisolation changes, circulation and other factors changing heat transfer. Periods of hibernation or lethargy, is accompanied by the decrease in body temperature. And the physiological thermostat switches to a lower temperature. Sensor mechanisms demonstrate the change in temperature, causing corresponding feedback reactions. Relatively few animals – heterothermic animals – can partially regulate body temperature that is limited by body regions or by environmental conditions. There are a lot of such animals among insects, for example, bees or ants, but most of arthropods are typical poykilothermic organisms. Temperature of any active cell must be higher than the temperature of the environment, as during oxidation processes and glycolysis heat is released. body temperature depends on several factors affecting the thermal balance in a contrary manner. The heat source can be metabotic thermogenesis (endothermy) or environment, mostly, solar energy (ectothermy). Heat transfer occurs by radiation, convection, heat conduction and water evaporation. Blood circulation from insite to outside of the body promotes heat losing, while thermo isolation obstacles it.

Thermal conductivity of water is 0,0014 kcal/(cm · c · degrees), it is lower than in metals but higher than in other liquids (for example, ethanol – 0,00042 kcal/(cm · c · degrees)). Specific heat ··capacity of water – 1 kcal/g·degrees, ethanol – 0,09 kcal/g·degrees, most of animal tissues – 0,07-0,09 kcal/g·degrees. The coefficient of temperature conductivity is equal to the coefficient of thermal conductivity divided by the product of specific weigh and specific heat capacity. Low temperature conductivity leads to slow cooling or heating of tissues and limitation in heat distribution within the organism. Fat is a good isolator for animals. Animals with a big tissue mass warm and cool themselves slowly, heat transfer is conducted by circulating liquids. Water evaporation cools any surface, the evaporation of 1 kg of water at 20 °C cost 585 kcal. Most of terrestrial animals use this to avoid body overheating.

Biokinetics studies the rate of biological processes and their dependence from concentrations of substances which participate in biochemical conversions, and also the dependence from external conditions, especially, from temperature. Such dependence is comprehensible if to take into account that any chemical conversion occurs if chaotically moving molecules collide. As temperature rises, the mean free path of the molecules increases, and thus, the likelihood of their collision also increases. So, the relative number of molecules able to participate in the reaction, or active molecules, increases with the rise of temperature, and the rate of the reaction also increases.

The parameter indicating how many times the number of active molecules and the rate increased at the temperature rise by 10 °C is called temperature coefficient Q₁₀.

Q₁₀= Vт₂ / Vт₁ (1.1),

where Vт₁ – reaction rate at the initial temperature, Vт₂ – the rate increased at the temperature rise by 10 °C

There is a ratio between t coefficient and excessive energy that molecules should possess so that their collision could cause a chemical reaction. (so-called Activation Energy)

Е = 0,46 Т₁ · Т₂ · lgQ₁₀ (1.2)

where Е – activation energy, kcal/mol, Т₁ и Т₂ – temperatures with the difference of 10 °C , i.е. Т₂ = Т₁ + 10°, lgQ₁₀– decimal log of Q₁₀.

It is clear that with the rise of temperature by 10 °C, the number of molecules with the energy exceeding the critical value will double, although the increase in kinetic energy proportional the absolute temperature will be much lower. In biological range, the temperature of Q₁₀ values for most metabolic reactions lays in the interval between 2 and 2,5. Some complex changes in rates of physiological processes for example, circadian rhythms, are relatively independent from temperature, and Q₁₀ for oxygen consumption of some poykilothermic animals is between 1 and 2. If to compare oxygen consumption at rest and at the active state, we can determine the characteristic exchange levels at different temperature conditions.

In CАrdium mollusks Q₁₀ values for active state and rest are equal to 1,84 and 1,20 respectively. For most of invertebrates Q₁₀ values are small. Temperature parameters of enzymatic reactions can lower with the decrease in substrate concentration to the limiting level, thus the measurements of temperatures coefficient have no sense. So, in the case of complex reactions with parallel and consecutive stages, with the contrary influence on Q₁₀ it is impossible to perform an elementary analysis of temperatures coefficient. Even though, in biological research, studies of adaptation and acclimatization of animals to different environmental conditions the study and determination of Q₁₀ coefficient are widely used.

Laboratory work № 1
Determination of temperature coefficient and calculation of the activation energy of the frog’s heart

Objective: Determination of temperature coefficient and calculation of the activation energy of the frog’s heart

Tasks:

1. Measure heartbeat at the room temperature;

2. Measure heartbeat at the increase in temperature by 10 °C;

3. Measure heartbeat at the decrease in temperature by 10 °C;

4. Calculate the temperature coefficient and activation energy using the formulas;

5. Make conclusions of the observed phenomena and prepare a report.

Equipment and Materials:

Thermometer (0 – 30 °C), vessel for the heart (50 mL), thermostat, ice, hot water, Ringer-Lock solution for the cold-blooded, stopwatch, dissecting tools (scissors, scalpel, dissecting needle, tweezers, gauze.

Procedure:

In this lab work students should register the heartbeat of frog’s heart at 2 or 3 different temperatures, with differences between each other by 10 °C).

After the immobilization of the frog, the heart should be taken from the chest and placed it in a vessel full by 2/3 with Ringer-Lock solution for the cold-blooded.

1^st measurement is after 5-7 min. Heartbeat during 1 min is measured 3-4 times and the average is calculated.

Picture 1.1. 1 – thermometer; 2 – vessel; 3 – Ringer-Lock solution; 4 – frog’s heart

Measure room temperature. Place the vessel with the heart in the thermostat with the temperature 10 °C higher than room T. After 3-4 min perform the 2^nd measurement with the calculation of the average.

Return the vessel to the room conditions and observe restoring of the initial heartbeat. After 3-5 min the heartbeat during 1 min is measured 3-4 times and the average is calculated.

Put the heart into the camera being cooled by the mixture of ice and water. When the temperature would be 10 °C lower than room’s temperature, heart rate should be measured again, the measurements should be done 3-4 times and calculated mean of heart rate.

Return the vessel to the room conditions and observe restoring of the initial heartbeat again. After 3-5 min the heartbeat during 1 min is measured 3-4 times and the average is calculated.

All data should be written in table 1.1.1

Table 1.1.1

Example:

During the experiment we have been seeing that the frog’s heart at 18 °C (Т1 = 273 + 18 = 291) has HR (heart rate) = 31 beat/minute, and at 28 °C (Т2 = 273 + 28 = 301) – 60 beat/minute. So, Q10=60/31=1,9.

In the table Bradis value of lgQ10 is 0,27875. By inserting obtained data into the formula (1.2) calculate the energy of activation:

Т=0,46 · 291·301·0,27875= 11,239 kcal/mol

Report design. The results are inserted into the table and the calculations are made. Define measurement deviations and make conclusions.

Laboratory work № 2
Determination of the temperature coefficient and calculation of the action energy of respiration of elodea plant branch

Objective: to get sure with the experiment that physical chemical laws are maintained in the living systems.

Tasks:

1. Count the amount of gas bubbles at room temperature;

2. Count the amount of gas bubbles during the rise of the temperature by 10 °C;

3. Count the amount of gas bubbles during the declination of the temperature by 10 °C;

4. To calculate the temperature coefficient and the energy of activation using formulas.

5. To make a conclusion and process the results.

Equipment and materials: Elodea plant in the small vessel, two big vessels with water more and less than room temperature by 10 °C; thermometers, timer, Bradice table.

Procedure:

To complete this work you need observe the gas bubbles emission by the elodea plant in the 3 different vessels with waters with temperatures which differ from each other by 10 °C.

Elodea is a typical alga of most of the aquariums, which with sufficient amount of light emits the oxygen bubbles from the tips of its leaves. You can count the quantity of emitted bubbles by watching the plant.

The first count of gas bubbles is done after 5-7 minutes after termostation of the vessel with plant. To make it, you should place the vessel with elodea into the bigger vessel with fixed temperature of the water. Then, you should count the emitted quantity of gas bubbles during 1 minute. You should repeat it for 3-4 times and the find an average quantity. Also you should define the temperature under the normal (room) conditions.

Then you should transport the vessel with plant into a thermostat with water hotter by 10 °C than in the first one. After 3-5 minutes count again the quantity of bubbles, repeat it 3-4 times and the find the average.

After that, you should transport the vessel with elodea into the first one with room temperature to retain the initial gas emission state. Then after 3-5 minutes repeat the counting like previous times.

Repeat all the same but with the vessel with colder water.

Fill the table 1.2.1.

EXAMPLE.

During the experiment following was obtained: at the temperature 18 °C (Т1 =273 + 18=291) 31 gas bubble was emitted but at the 28 °C (Т2 =273 + 28=301) 60 bubbles per minute. Thus, Q₁₀ = 60/31 = 1,9. Using the table Bradis find lgQ₁₀= 0,27875. By inserting obtained data into the formula (1.2) calculate the energy of activation:

Е=0,46 · 291·301·0,27875 = 11,239 kkal/mol.

Тable 1.2.1.

Report design: Fill the table the obtained results and calculate the energy of activation using formulas. Find the error of calculations and make conclusion.

Chapter 1. «Thermodynamics» questions:

How the dependence, which is expressed via this formula, is called?

Е = 0,46 Т₁ · Т₂ · lgQ₁₀

1. To which type of thermodynamic systems living organisms belong?

2. Why our planet is considered an open thermodynamic system?

3. Which animals regulate their body temperature by homeostatic regulation (change of the metabolic processes) and change in the behavior.

4. What is an energy of activation – Е?

5. Give an examples of warm-blooded and cold-blooded animals.