Question

Arctic ground squirrels are small (~ 1 kg) animals that live in a very cold climate. As such, they have evolved to spend a significant portion of the year in hibernation where their body temperature can drop as low as -3 C.

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(A) If, at the time hibernation starts, the squirrel is 30% fat (stored as tripalmitoylglycerol; 40 kJ/g) and consumes 15 kcal/day while hibernating, how long can the squirrel stay in hibernation? Provide your answer in days.

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(B) During hibernation the squirrel requires very little water, what is the source of this water?​

(C) Arctic squirrels survive on a diet of bilberries (largely water and simple carbohydrates); leaves (largely water and complex carbohydrates) and seeds (largely fat and protein). Which of these food sources would contribute most most to building the adipose tissue of the squirrel in advance of winter? Which would contribute the least?

Answer 1

1)

Artic ground squirrels weigh (~1kg).

If 30 % of body weight is fat ,then total amount of fat is 300g.

1 g of fat (stored as tripalmitoylglycerol) yields 40 KJ/g

Therefore 300 g yields- 300*40= 12000KJ

Converting KJ to Kcal

4.184 KJ = 1 Kcal

therefore 12000 KJ = 12000 / 4.184 = 2868 Kcal

Energy consumption per day in hibernation is 15 kcal

No of days that a squirrel can survive with 2868 Kcal = 2868/15 = 191 Days

The squirrel can stay in hibernation for approximately 191 days

2)

The source of water for squirrel is the stored fat in the adipose tissue.This fat is decomposed to co2 and water. co2 is expelled out through their lungs while the water mixes in the blood.

3)

Adipose tissue is made of fats. So to build the tissue the squirrel must consume a diet rich in fats.

Complex carbohydrates are broken into glycogen.This glycogen is converted into glucose when energy requirement is more.when energy requirement is less,the glucose formation is therefore less.So all the excess glycogen that is not converted into glucose is converted into fats.The release of glucose in blood is very slow and  the formation of fats from complex carbohydrate takes more time as it is stored in an intermediate form glycogen.

Simple carbohydrates immediately cause a spike in glucose level in the blood.So to regulate it they are immediately converted into fats instead of glycogen.

So the foods that contribute  to fat accumulation and adipose tissue formation   are arranged in descending order

Seeds contribute more because of large fat content ,followed by simple carbs  as the rate of conversion of glucose to fat is more than in complex carbs.

Complex carbs contribute the least to fat formation,accumulation and adipose tissue formation.