Energy and Respiration in Biology

• Biology is the scientific study of life, encompassing molecular mechanisms within cells and interactions between organisms in ecosystems.

Energy and Respiration

• Energy is the capacity to do work and is essential for growth, movement, and maintaining homeostasis.
• Respiration converts nutrients into energy, producing ATP (adenosine triphosphate) and releasing waste.
• Aerobic respiration needs oxygen and includes glycolysis, the Krebs cycle, and the electron transport chain.
• Glycolysis in the cytoplasm breaks down glucose into pyruvate, yielding a small amount of ATP and NADH.
• The Krebs cycle (citric acid cycle) in the mitochondrial matrix oxidizes pyruvate, generating ATP, NADH, FADH2, and carbon dioxide.
• The electron transport chain in the inner mitochondrial membrane uses NADH and FADH2 to create a proton gradient, synthesizing ATP via oxidative phosphorylation.
• Anaerobic respiration occurs without oxygen, producing less ATP than aerobic respiration.
• Fermentation, a type of anaerobic respiration, regenerates NAD+ from NADH, enabling glycolysis to continue.
• Lactic acid fermentation in muscle cells during low-oxygen conditions converts pyruvate to lactic acid.
• Alcoholic fermentation in yeast and some bacteria converts pyruvate to ethanol and carbon dioxide.

Photosynthesis

• Photosynthesis converts light energy into glucose in plants, algae, and some bacteria.
• Chloroplasts, containing chlorophyll, are where photosynthesis takes place.
• 6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2 is the basic equation for photosynthesis.
• Light-dependent and light-independent reactions (Calvin cycle) are the two main stages of photosynthesis.
• Light-dependent reactions in the thylakoid membranes use light energy to split water into oxygen, protons, and electrons.
• ATP and NADPH, which store energy for use in the Calvin cycle, are produced during the light-dependent reactions; oxygen is released as a byproduct.
• Light-independent reactions (Calvin cycle) in the stroma use ATP and NADPH to fix carbon dioxide into glucose.
• RuBisCO catalyzes the reaction between carbon dioxide and ribulose-1,5-bisphosphate (RuBP) during carbon fixation.
• The Calvin cycle regenerates RuBP and produces glucose.
• The rate of photosynthesis is affected by light intensity, carbon dioxide concentration, and temperature.

Homeostasis

• Homeostasis maintains a stable internal environment despite external changes.
• Regulating body temperature, pH, water balance, and blood glucose levels are all components of homeostasis.
• Sensors, control centers, and effectors maintain homeostasis through feedback mechanisms.
• Negative feedback loops counteract changes in the internal environment, returning conditions to a set point.
• Body temperature regulation: sweat glands activate to cool the body when temperature rises, is an example of a negative feedback loop.
• Blood glucose regulation: the pancreas releases insulin to promote glucose uptake by cells, lowering blood glucose levels when they rise, is another example of a negative feedback loop.
• Positive feedback loops amplify changes in the internal environment, moving conditions away from a set point.
• Blood clotting: platelets aggregate and release chemicals to attract more platelets, forming a clot, when a blood vessel is damaged and is an example of a positive feedback loop.
• Thermoregulation maintains a stable body temperature.
• Endotherms (warm-blooded animals) produce their own body heat through metabolic processes.
• Ectotherms (cold-blooded animals) depend on external heat sources.
• Osmoregulation maintains a stable water balance.
• Kidneys regulate osmoregulation by filtering blood and adjusting water and solute reabsorption.
• Disruptions in homeostasis can cause disease or death.