Animals eating

The levels of lead may build up in plants and animals from areas where air, water, or soil are contaminated with lead. If animals eat contaminated plants or animals, most of the lead that they eat will pass through their bodies. Chapters 4 and 5 contain more information about what happens to lead in the environment. 

The nature section of the BBC Website describes several examples of animals eating kaolin clay to immobilize toxins by adsorption on the clay s surface. For example, see the first entry on the page http //www.bbc.co.uk/nature/weird/az/mo.shtml. Alternatively, read The Life of Mammals by Sir David Attenborough, BBC Books, 2002, p. 170. 

Another example is the faulty old syllogism Animals eat Food Cows are Animals Beefburgers are Food hence Cows eat Beefburgers. The mistake is that the first statement should not be taken to mean that every object conforming to the type Animal can eat... 

Monofluoroacetic acid (fluoroacetate) (Fig. 7.61) is a compound found naturally in certain South African plants, which causes severe toxicity in animals eating such plants. The compound has also been used as a rodenticide. The toxicity of fluoroacetate was one of the first to be studied at a basic biochemical level, and Peters coined the term "lethal synthesis" to describe this biochemical lesion. 

These changes in demand for urea cycle activity are met over the long term by regulation of the rates of synthesis of the four urea cycle enzymes and carbamoyl phosphate synthetase I in the liver. All five enzymes are synthesized at higher rates in starving animals and in animals on veiy-high-protein diets than in well-fed animals eating primarily carbohydrates and fats. Animals on protein-free diets produce lower levels of urea cycle enzymes. 

This carbon-14 isotope, which makes up less than one-millionth of 1 percent of the carbon in the atmosphere, is radioactive and has eight neutrons. (The most common isotope, carbon-12, has six neutrons and is not radioactive.) Because both carbon-12 and carbon-14 are forms of carbon, they have the same chemical properties. Both of these isotopes, for example, form carbon dioxide, which is taken in by plants. This means that all plants contain a tiny bit of radioactive carbon-14. All animals eat either plants or plant-eating animals, and therefore all animals have a little carbon-14 in them. In short, all living things on Earth contain some carbon-14. 

Carbon dioxide molecules get absorbed by plants and are used during a process called photosynthesis. Some of the carbon dioxide absorbed by the plants will contain carbon-12 atoms, while other carbon dioxide molecules will contain carbon-14 atoms. Since humans and animals eat plants, their bodies also contain some carbon-12 and some carbon-14. 

Whether fallout is by washout or dry deposition, a certain fraction of the deposited activity is intercepted by foliage. Foliar deposition, followed by uptake by grazing animals, is an important pathway into food chains. The leaf area of herbage eaten by cattle and sheep is large. Also, animals eat herbage as it is, whereas humans usually wash leaf vegetables and discard outer leaves, pods and husks. 

Macaws, tapirs, howler monkeys and other animals eat clay, presumably for adsorbing toxins in their food. Macaws eat more clay during the dry season when they have to rely more on seeds with their potentially harmful secondary plant metabolites. They even feed their nestlings clay before they venture outside the nest cavity (Brightsmith 2002). 

Cows are large animals in the family Bovidae that are kept as sources of meat, hides, and milk. Cows are grazing animals, eating grasses and other types of herbaceous plants. 

When an animal eats more carbohydrate than it uses up, it stores the excess some as the polysaccharide glycogen (Sec. 35.9), but most of it as fats. Fats, we know (Sec. 33.2), are triacylglycerols, esters derived (in most cases) from long straight-chain carboxylic acids containing an even number of carbon atoms. These even numbers, we said, are a natural consequence of the way fats are synthesized in biological systems. 

As a result, all animals that eat plants contain the same ratio of carbon-14 to carbon-12 as the plants do. Other animals eat those animals, and so on up the food chain. So all animals and plants have the same ratio of carbon-14 to carbon-12 throughout their lives. Any carbon-14 that decays while the organism is alive is replaced through photosynthesis or eating. But when a plant or animal dies, it stops taking in carbon-containing substances, so the carbon-14 that decays is not replaced. 

Because humans and most other mammals lack the enzymes needed for digestion of cellulose, they require starch as their dietary source of carbohydrates. Grazing animals such as cows, however, have in their first stomach microorganisms that are able to digest cellulose. The energy stored in cellulose is thus moved up the biological food chain when these ruminant animals eat grass and are then used for food. 

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