Energy and Its Forms in Biology

Energy

• Energy is the capacity to do work.
• The ultimate source of energy for all living organisms is the sun.
• Energy is the primary function of food.
• The body requires a constant supply of energy for survival.
• Energy is vital for maintaining basal body functions, body weight, physical activity, growth, and development, pregnancy, and lactation.

Forms of Energy

• Chemical Energy is stored in food and is released during metabolism.
• Solar Energy is used for vitamin D synthesis in the skin and for photosynthesis in plants.
• Mechanical Energy is responsible for muscle movement.
• Electrical Energy powers brain and nerve cell functioning.
• Heat Energy is produced when energy is transformed from one form to another.
• Energy from food is converted into heat energy.
• Different forms of energy are interconvertible.

Obtaining Energy from Food

• Glucose, fatty acids, and amino acids are the primary sources of energy derived from food.
• These components are combined with oxygen to produce carbon dioxide, water, and energy.
• Energy from food is stored as ATP (Adenosine Triphosphate), which is the primary energy currency used by living cells

Energy Requirement

• An adequate diet must provide enough energy and essential nutrients.
• Energy requirement is the amount of energy needed to maintain body size, composition, and physical activity levels for optimal long-term health.
• Energy requirements vary based on age, gender, activity level, pregnancy, and lactation.

Energy Requirement of Children and Adolescents

• Energy needs are higher in children and adolescents due to growth and development.
• Energy needs for growth are used to synthesize and deposit new tissues.

Energy Requirement of Adults

• Energy requirements vary based on gender, activity level, and body weight.
• The ICMR (Indian Council of Medical Research) uses "Reference Man" (65 kg) and "Reference Woman" (55 kg) to determine energy requirements.

Energy Requirements During Pregnancy and Lactation

• Energy needs increase during pregnancy to support fetal growth, placenta development, and increased maternal metabolism.
• Energy is also required for weight maintenance, physical activity, and milk production during lactation.

Body Mass Index (BMI)

• BMI is a predictor of the impact of body weight on morbidity (disease) and mortality (death) risks.
• BMI is calculated as weight in kilograms divided by the square of height in meters.
• BMI is also known as Quetelet's index.

Energy Imbalance

• Energy imbalance refers to the difference between energy intake and expenditure.
• Undernutrition occurs when energy intake falls short of requirements.
• Overnutrition or obesity occurs when energy intake exceeds expenditure.

Chronic Energy Deficiency (CED)

• CED is a condition characterized by a less than adequate intake of energy over an extended period.
• CED can be further categorized into acute and chronic forms.
• Acute CED involves rapid weight loss and is associated with declining body weight.
• Chronic CED involves a gradual, stable decrease in body weight and is characterized by a low BMI.

Obesity

• Obesity is a global health problem characterized by an imbalance between energy intake and expenditure.
• Increased incidence of obesity is attributed to lifestyle changes and dietary habits.
• Genetics, food intake, physical inactivity, and metabolic conditions contribute to obesity.
• Regular physical activity (30 minutes of moderate to vigorous activity at least three times a week) is beneficial for overall health.

Measurement of Energy Expenditure

• Energy expenditure is measured in calories (kcal or Cal).
• Direct Calorimetry measures heat production by placing individuals in a controlled environment (whole-room calorimeter). This method is limited by its confined nature, high cost, and complex engineering.
• Indirect Calorimetry measures oxygen consumption and carbon dioxide production during respiration, indirectly estimating energy expenditure.
• The Respiratory Quotient (RQ), the ratio of CO₂ produced to O₂ consumed, provides insights into the fuel mixture being metabolized.