Question

Bears expend about \(25 \times 10^{6} \mathrm{~J} /\) day during periods of hibernation, which may last as long as seven months. The energy required to sustain life is obtained from fatty acid oxidation. How much weight (in kilograms) do bears lose after 7 months of hibernation? How could a bear's body minimize ketosis during hibernation? (Assume the oxidation of fat yields \(38 \mathrm{~kJ} / \mathrm{g}\).)

Short answer

Bears lose approximately 138.2 kg. To minimize ketosis, they should ensure a slow, steady fat metabolism with adequate protein supply.

Step-by-step solution

Calculate Total Energy Expenditure

First, determine the total energy expenditure for the entire hibernation period. Since there are 30 days in a month, the total number of days in 7 months is 210 days. Multiply the daily energy expenditure by the number of days:\[ 25 \times 10^6 \text{ J/day} \times 210 \text{ days} = 5.25 \times 10^9 \text{ J} \]

Convert Joules to Kilojoules

Next, convert the total energy expenditure from joules to kilojoules since 1 kJ = 1000 J:\[ \frac{5.25 \times 10^9 \text{ J}}{1000} = 5.25 \times 10^6 \text{ kJ} \]

Calculate Weight Loss

Given that the oxidation of fat yields 38 kJ/g, we need to find out how many grams of fat correspond to the total energy expenditure:\[ \frac{5.25 \times 10^6 \text{ kJ}}{38 \text{ kJ/g}} \approx 138,158 \text{ g} \]Convert grams to kilograms to find the weight loss:\[ \frac{138,158 \text{ g}}{1000} \approx 138.158 \text{ kg} \]

Minimizing Ketosis Discussion

Ketosis can be minimized by a constant and gradual release of fatty acids and ensuring small portions of protein breakdown. This process helps maintain gluconeogenesis, thus providing glucose to the brain and minimizing the effects of ketosis during hibernation.

Key concepts

Hibernation Energy Expenditure

Bears enter a state of hibernation to survive harsh winter conditions when food is scarce. During this time, they drastically lower their metabolism to conserve energy. However, even in this reduced metabolic state, bears still require significant energy to sustain their basic physiological functions. This energy is acquired primarily through the breakdown of stored fat.

To better understand their energy needs, we can look at their daily energy expenditure. For example, a bear uses approximately 25 million joules per day during hibernation. When extended over a typical hibernation period of seven months, or around 210 days, the total energy expenditure is a staggering 5.25 billion joules.

Through fatty acid oxidation, the bear can tap into its massive fat reserves. By breaking down fats, the bear efficiently generates the necessary energy while remaining in a low-energy-consumption state. This ability to sustain life for months without taking in food is vital for their survival during times of limited resources.

Ketosis Prevention in Bears

During hibernation, bears face the challenge of preventing ketosis, a condition where excess ketone bodies accumulate due to fat breakdown. This state is akin to extreme low-carbohydrate diets in humans. Since the brain and other vital organs primarily rely on glucose, preventing ketosis is essential for normal functioning.

Bears have evolved special adaptations to avoid ketosis. They achieve this by managing their fat and protein metabolism strategically:

• Their bodies release fatty acids gradually instead of all at once. This steady release controls and moderates the acid levels in the blood.
• A balanced breakdown of proteins occurs in small, manageable quantities, supporting sugar formation through gluconeogenesis. This process helps provide the necessary glucose to the brain continually.

By efficiently regulating these processes, bears limit ketone buildup, thus preventing ketosis and maintaining homeostasis throughout the hibernation period.

Biochemistry of Fat Metabolism

Fat metabolism is central to how bears sustain their long periods of hibernation. At the core of this process is the biochemical oxidation of fatty acids, which provides the energy vital for survival without food intake for extended times.

Fatty acids are stored in adipose tissues in the form of triglycerides. When energy is needed, these triglycerides are broken down into glycerol and free fatty acids. The fatty acids undergo oxidation within mitochondria, the energy powerhouses of cells, generating ATP—a direct energy currency the body can use.

This oxidation of fat yields approximately 38 kJ per gram of fat, illustrating its high energy content. In bear hibernation, this efficient biochemical conversion allows bears to lose substantial weight, such as 138 kg over seven months, while simultaneously providing enough energy to cover their daily requirements.

Understanding these biochemical processes highlights how brilliantly adapted bears are to their environment, securing their survival allowing them to emerge from hibernation healthy and ready for the new season.