Energetics & Phase Changes

Energetics in Chemical Reactions and Phase Changes

• Exothermic reactions release energy and heat their surroundings.
• Endothermic reactions absorb energy, cooling their surroundings.

Phase Changes

• Phase changes can be either endothermic or exothermic.
• Endothermic phase changes add energy to water.
• Exothermic phase changes remove energy from water.
• A diagram can be used to illustrate the phase changes of a substance, with temperature on the y-axis and heat energy on the x-axis.
• A mnemonic is used to remember that exo is up and endo is down
• Phase types from bottom to top = solid, liquid, gas

Examples of Endothermic and Exothermic Changes

• Examples include determining if melting ice cubes, freezing ice cubes, evaporation, or cooking an egg is endothermic or exothermic.
• Another set of examples involve determining if snow formation, photosynthesis, burning, or condensation is endothermic or exothermic.
• Physical change or chemical change?

Homeostasis

• Homeostasis refers to maintaining a stable internal environment.
• The marathon runner Martina experiences changes in body mass, heart rate, breathing rate, core body temperature, skin surface temperature, blood flow, and blood glucose level (fuel).

Cell Respiration and Energy

• Burning is an exothermic reaction releasing heat and light.
• Cellular respiration is controlled by enzymes and releases energy in tiny amounts so we can harness and use it
• Muscle contractions require ATP

Physiological Changes during Exercise

• During a marathon, several physiological changes occur.
• It is important to understand how the level of carbon dioxide changes in cells and lungs.
• Understanding the physiological response to changes in carbon dioxide levels is key.
• The body generates heat during exercise.
• Sweating helps to deal with body heat.

Homeostasis Lab Activity

• The lab activity will consist of four stations.
• Station 1 focuses on what happens to the carbon dioxide produced during exercise.
• Station 2 explores how to get more carbon dioxide out of the body.
• Station 3 examines what happens to our body heat produced during exercise.
• Station 4 discusses how sweating helps.

Body Temperature and Respiration

• Extra body heat comes from cell respiration, an exothermic process.
• Only about 40% of the energy in glucose is used to make ATP; the rest becomes heat.

Body Temperature Adaptations

• Chemical reactions in cells function most efficiently between 36.5 and 37.5°C
• Hyperthermia or hypothermia can be life-threatening.
• Adaptations to maintain body temperature (37°C) can be anatomical/physiological or behavioral.

Body Temperature Regulation

• Sweating (perspiration) cools the body when it is too hot.
• Sweat is secreted from sweat glands in the skin.
• Evaporation of sweat is endothermic and takes heat from the skin.
• Shivering (rapid muscle contractions) occurs when the body is too cold.
• Cell respiration increases, releasing more heat.
• Vasodilation occurs when the body is too hot, causing blood vessels at the skin surface to widen (redness).
• More blood flows to the skin, carrying heat from the core to the surface.
• Heat is lost to air by radiation (absorbed by sweat).
• Vasoconstriction occurs when the body is too cold, causing blood vessels at the skin surface to become narrower.
• Less blood flows to the skin, and heat is conserved.

CO₂ Production and Homeostasis

• CO₂ comes from cell respiration.
• Every cell in the body needs ATP.
• ATP is produced in specialized organelles in all cells (mitochondria).
• Carbon dioxide reacts with water in blood plasma to form carbonic acid: CO₂ + H₂O → H₂CO₃
• Thisalters the blood pH, which causes the brain to send a signal to the body increase breathing rate.

Homeostasis and Feedback

• Homeostasis occurs through negative feedback, in which the body maintains the right range of temperature and chemistry.
• Negative feedback corrects conditions to bring them back to normal.

Endocrine System

• The endocrine system produces hormones.
• Hormones are chemicals secreted by endocrine glands into the blood that act as signals to regulate physiological functions and maintain homeostasis.
• Insulin and glucagon are examples of hormones.

Achieving Homeostasis

• Sensory receptors collect information about conditions in the body.
• Control centers respond by correcting conditions.
• The hypothalamus is a major control center, but other centers, such as the pancreas, can also respond.
• Negative feedback involves a response that brings conditions back to within a normal range.

Negative Feedback Loop

• Achieving balance of physiological conditions (homeostasis) requires negative feedback loop.
• Physiological conditions include temperature, water, blood sugar, blood pH/breathing rate, blood calcium, heart rate, blood pressure, etc.

Body Temperature Control

• Homeostasis and Temperature Regulation

Temperature Control in Animals

• Endotherms (mammals and birds) generate heat internally and maintain a constant internal body temperature.
• Ectotherms (reptiles, amphibians, and fish) rely on the environment to control temperature.

Questions for further review

• Why do we get a fever?
• How might a fever be helpful as an immune response?
• How might it harm us?

Control of Blood Sugar

• Mammals need to maintain a concentration of glucose in the blood within a narrow range (about 90mg/100ml).
• Too much or too little glucose can cause damage to tissues.

Hormones controlling blood sugar

• The pancreas produces two hormones.
• Insulin signals for glucose from all body cells.
• Glucagon signals the liver cells and release glucose.

Diabetes

• Diabetes is a body's failure to regulate blood glucose levels.
• Type 1 is a result of not enough insulin.
• Type 2 is caused by receptors in the cells.