Bio 20700 -- Lecture 9: Influence of Size and Temperature on Metabolic Rate

Flashcards covering the concepts of energy flow, metabolic rates, thermodynamics, and the effects of body size and temperature on metabolism as discussed in Bio 20700 Lecture 9.

Steady state (Homeostasis)

The maintenance of an internal variable, such as temperature or gas concentrations, at a constant level that is generally different from that of the environment; this process requires energy.

Heat energy

Molecular kinetic energy.

Chemical energy

Energy that is stored, liberated, or required when atoms are rearranged into new assemblages.

Electrical energy

The energy that a system possesses due to the separation of electrical charge.

Mechanical energy

The energy of organized motion, such as moving a limb or the circulation of blood.

Kinetic energy

The energy used during the state of motion.

Potential energy

Energy that is stored for later use, such as the chemical energy contained within food.

1st law of thermodynamics

States that energy cannot be created or destroyed, but can be transformed from one form to another.

2nd law of thermodynamics

States that when energy is converted from one form to another, some usable energy always degrades into a less usable form and is lost as heat, leading to an increase in entropy.

Efficiency of energy conversion

The proportion of energy that remains for useful work after a conversion has taken place.

Assimilation efficiency (AE)

The fraction of energy in ingested food that is absorbed and used in metabolism, calculated as AE = rac{E_{in} - E_f - E_u}{E_{in}} imes 100.

Metabolism

The set of chemical reactions used by living organisms to carry out their various functions and activities, including muscle use.

Biosynthesis

The synthesis of biological molecules and materials where chemical energy is stored in body tissues or exported in organic matter like milk, hair, or skin.

Maintenance

Metabolic processes including heart beat, respiration, gut motility, and the maintenance of electrochemical potentials (e.g., $Na^+/K^+$ pumps) that do not act upon the external world.

External work

Energy used for potential energy (lifting things) or kinetic energy (making something move relative to the external world).

Metabolic rate (MR)

The rate at which metabolism occurs, often measured while an animal is at rest.

Resting metabolic rate (RMR)

Metabolic rate measured while an animal is at rest, alert (but not highly aroused), and not physically active, defined as $RMR = BMR + SDA + ext{thermoregulation}$.

Direct calorimetry

A method of measuring metabolic rate based on the rate at which an organism produces heat.

Aerobic metabolism equation

$C_6H_{12}O_6 + 6 O_2 + ext{~29 ADP} ightarrow 6 CO_2 + 6 H_2O + ext{~29 ATP}$.

Anaerobic metabolism equation (lactic acid)

$C_6H_{12}O_6 + 2 ADP ightarrow 2 C_3H_6O_3 + 2 ATP$.

Basal metabolic rate (BMR)

The metabolic rate of an animal at rest that is not digesting, not thermoregulating, not reproducing, and not growing.

Specific dynamic action (SDA)

The metabolic cost of digestion, including the production of digestive enzymes, nutrient transport, and liver function.

Allometric relationship (Metabolic Rate)

The relationship between metabolic rate and body size, expressed as $MR = a imes M^b$, where b < 1 (typically $0.7 - 0.75$).

Mass-specific metabolic rate (MSMR)

The resting metabolic rate expressed per gram of tissue (e.g., a mouse has a rate of $2,ml,O_2/g/h$ while an elephant has only $0.07,ml,O_2/g/h$).

Poikilotherm / Ectotherm

An organism whose body temperature tracks the environment and which relies primarily on external heat.

Standard metabolic rate (SMR)

The metabolic rate of an ectotherm, which is dependent on the ambient temperature.

Q10

A metric that quantifies the change in metabolic rate for a $10^{\circ}C$ change in temperature; Q_{10} = inom{R_{T1}}{R_{T2}}^{rac{10}{T1 - T2}}.

Endothermy

An animal’s ability to generate internal heat to regulate its body temperature.

Homeothermy

An animal’s ability to maintain a constant body temperature.

Hypothalamus

A brain region that regulates physiological homeostasis, including water balance, stress, hunger, thermoregulation, and sleep-wake cycles.

Negative-feedback control

A process that changes the direction of a stimulus; for thermoregulation, the hypothalamus acts to lower temperature if it is too high or raise it if it is too low.

Regional heterothermy

Large variations in body temperature between different regions of an animal's body, such as in the swimming muscles of a tuna.