A Little Bit More
If you’ve ever passed a farmer’s field and saw cows quietly standing or lying down, they were probably chewing their cud. Cows spend a fair amount of time in this activity. If you’re able to get close enough, you can even see the bolus of food move down their throat when they finish cud-chewing and swallow or just the reverse when the bolus comes up from the stomach to be chewed. This digestive strategy allows ruminants to quickly graze where food is abundant or lush and then retire to a secluded, safe area to complete the chewing process. During the initial grazing, food is quickly swallowed but later the food is regurgitated into the mouth, rechewed thoroughly, and then swallowed for a second time. Of course most of the ruminants in North America don’t have many, if any, large predators stalking them today, but this behavior developed in the past and remains the same despite North America’s few major predators.
Keep in mind that all plant eaters, not just the ruminants, are stuck with the same problem of digesting tough plant cell walls. Many plant eaters have unusually long small intestines that provide more time and space for adequate digestion to take place. Frog tadpoles are an easy example to see. If you look at a tadpole’s belly, you can see a long coil of intestines beneath their thin skin – they need that length to digest their plant food. Adult frogs are carnivores (feed on small animals) and their intestines, on the other hand, are short by comparison – remember that meat is easier to digest. Legs and mouth aren’t the only structures that change as a tadpole grows and changes into an adult frog!
If herbivores have long intestinal tracts for efficient digestion and carnivores have short digestive tracts because they don’t need all that length, what about omnivores (eat both plant and animal material)? As you might guess, omnivores (and this includes humans) have digestive tracts that are typically intermediate in length between plant eaters and carnivores.
Activities
Science & Math – Chew It Up
Objectives: Graphic demonstration of surface area
Materials: Orange or grapefruit
Basically, the ungulates have two digestive “strategies” going for them. On the one hand, by cud chewing, they greatly reduce the size of the food particles and this greatly increases the surface area of their food upon which microbes and digestive enzymes can act. And secondly, their stomach arrangement and longer digestive tract allows for a slower passage through their digestive system which also allows time for maximum nutrient extraction.
We aren’t going to demonstrate the stomach portion of this process but we can easily demonstrate the benefit of the cud chewing part.
1. Look at an orange and notice the entire surface area that is available. If you want to get fancy, you can use this formula for the surface area of the sphere (surface area = 4Πr2).
2. Now carefully remove the skin and separate the individual orange wedges.
3. Note that the “back” or outer portion of each orange wedge mirrors the peel of the intact orange rind
4. Also note that each orange wedge now has two additional surface areas (one surface area is the back of the wedge that touched the skin, and the second and third surface areas are the two inner surface areas of the wedge). Thus the surface area of the orange that has been dismembered, has increased greatly
5. If we extrapolate from this simple example, we can see that by reducing a food material into many more individual portions when we chew, we increase the surface area. And, as we increase its surface area, digestion can take place more quickly and more completely.
I hope it’s obvious now that well-chewed food has more surface area and can be better digested and assimilated by the body.
Key Concepts
Adaptations and Diversity, Behavior and Regulation
Questions
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