Exercise 2. Read the following facts about caffeine and coffee trees to check your answers in Exercise 1

What is caffeine? An alkaloid found in coffee, cocoa beans, tea, kola nuts and guarana. Also added to many fizzy drinks, energy drinks, pep pills and cold and flu remedies. For a single portion of espresso, 50 to 55 roasted coffee beans are required; a single imperfect bean will taint the whole sufficiently to be noticeable. This is because human olfaction and taste senses originated as defense mechanisms that protected our ancestors from rotten—hence, unhealthy—foods.

What does caffeine do? A stimulant of the central nervous system. Pure caffeine is a moderately powerful drug and is sometimes passed off as amphetamine. In small doses, such as the 150 milligrams in a typical cup of filter coffee, it increases alertness and promotes wakefulness. Caffeine also raises heart and respiration rate and promotes urine production. Higher doses induce jitteriness and anxiety. The fatal dose is about 10 grams.

How does caffeine work? Caffeine blocks receptors for the neurotransmitter adenosine, which is generally inhibitory and associated with the onset of sleep. Also raises dopamine levels, and stimulates the release of the fight-or-flight hormone adrenalin (From Newscientist.com).

What is coffee? Raw coffee beans are the seeds of plants belonging to the Rubiaceae family, which comprises at least 66 species of the genus Coffea. The two species that are commercially exploited are Coffea arabica, which accounts for two thirds of world production, and C. canephora, often called robusta coffee, with one third of global output. Robusta coffee plants and all wild coffee species have 22 chromosomes, whereas arabica has 44. Therefore, arabica and other coffee species cannot be crossed to produce a hybrid plant.

Robusta is a high-yielding and disease-resistant tree standing up to 12 meters tall that grows best in warm, humid climates. It produces a cup featuring substantial body, a relatively harsh, earthy aroma, and an elevated caffeine content that ranges from 2.4 to 2.8 percent by weight. Although robusta is sold by many purveyors, it does not give rise to the highest-quality coffee.

Arabica, which originated in the Ethiopian highlands, is a medium- to low-yielding, rather delicate tree from five to six meters tall that requires a temperate climate and considerable growing care. Commercially grown coffee bushes are pruned to a height of 1.5 to 2.0 meters. Coffee made from Arabica beans has an intense, intricate aroma that can be reminiscent of flowers, fruit, honey, chocolate, caramel or toasted bread. Its caffeine content never exceeds 1.5 percent by weight. Because of its superior quality and taste, arabica sells for a higher price than its hardy, rougher cousin.

A good rainfall induces coffee plants to blossom, and some 210 days afterward red or yellow fruit called cherries appear. Each cherry contains two oblong seeds—the coffee beans. The ultimate quality of the resulting coffee beans depends on the genetics of the plant, the soil in which it grows and the microclimate, which encompasses factors such as altitude, the amount of rainfall and sunlight, and daily temperature fluctuations. Along with the roasting processes that are applied, these agricultural and geographical considerations are responsible for the taste differences among the many varieties of coffee beans that suppliers combine to produce the various distinctive blends one can purchase (From Scientific American, June 2002).

Exercise 3. Now read detailed explanation of the effects of caffeine provided by biologist Neal J. Smatresk, Dean of the College of Science at the University of Texas at Arlington, and find answers to these questions:

1. What is a neurotransmitter? What is a second messenger?

2. How does caffeine affect heart?

3. Does caffeine affect all animals?

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