Respiration is the chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
Unlike breathing, which is the mechanical movement of air into and out of the lungs, respiration is a microscopic process that occurs continuously inside every living cell.
Living organisms do NOTproduce energy. They RELEASE it from food and use it to drive metabolic processes. There are seven specific uses of energy.
Muscle contraction: To allow movement of the whole body, as well as internal movements (e.g. churning of stomach, heart beating).
Protein synthesis: To link amino acids together into long chains to create proteins (e.g. enzymes, hormones, antibodies).
Cell division: To power processes like mitosis and meiosis for growth and tissue repair.
Active transport: To move substances across cell membranes against their concentration gradient (e.g. root hair cells absorbing mineral ions, or small intestine absorbing glucose).
Reminder that active transport is the movement of ions or molecules across the cell membrane, against a concentration gradient, using energy from respiration.
Growth: To make new cells and build complex biological molecules.
Passage of nerve impulses: To pump ions across axon membranes, allowing electrical signals to travel through the nervous system.
Maintenance of a constant body temperature: Used by mammals and birds to release heat energy to keep their internal core temperature steady, even when the environment is cold.
Yeast is a single-celled fungus that respires to break down sugar. Because respiration is an enzyme-controlled reaction, it is highly sensitive to changes in temperature.
Mix a fixed volume of yeast suspension with a fixed volume of glucose solution in a test tube.
Place the test tube into a water bath set at a specific temperature.
Leave the tube for 5 mins. to allow the mixture to acclimatize(to adapt or adjust to a new environment) to the temperature.
Attach a delivery tube leading from the test tube into a gas syringe, or invert a measuring cylinder over water to collect gas. Alternatively, count the number of bubbles produced per minute.
Record the volume of carbon dioxide gas produced in a set time frame.
Repeat the entire process using water baths set at different temps.
At low temperatures (e.g. 10°C – 20°C), the rate of respiration is low. Kinetic energy is low, meaning enzymes and glucose molecules move slowly and rarely collide.
At optimum temperatures (~35°C – 40°C), the rate of respiration increases. Molecules gain more kinetic energy, leading to more frequent successful collisions between active sites and substrates.
Past optimum temperatures (e.g. above 45°C – 50°C), the rate of respiration drops to zero. The high temperature disrupts the bonds holding the respiratory enzymes together which alters the shape of their active sites. The enzymes are denatured, and the reaction stops.