Researchers have made significant technological progress toward increasing the amount of p

Researchers have made significant technological progress toward increasing the

amount of plastic that plants can grow and altering the composition of the plastic to

endow it with useful properties, but achieving both a useful

Line composition and high plastic content in the plant proves to be a formidable task.

(5) The chloroplasts of the leaves have so far shown themselves to be the best

location for producing plastic, but the chloroplast is the green organelle that

captures light, and high concentrations of plastic could thus inhibit

photosynthesis and reduce grain yields, and the challenges of separating the

plastic from the plant are awesome. Given sufficient time and funding,

(10) researchers could overcome these technical obstacles, but a greater concern has

made us question whether those solutions are worth pursuing. When calculating

all the energy and raw materials required for each step of growing a

biodegradable plastic made from plant sugar polyhydroxyalkanoate in plants, we

discovered that this approach would consume even more fossil resources than

(15) most petrochemical manufacturing routes.

In a recent study, scientists found that making one kilogram of

polyhydroxyalkanoate from genetically modified corn plants would require about

300 percent more energy than the 29 megajoules needed to manufacture an

equal amount of fossil fuel-based polyethylene (PE). Given this comparison, it

(20) is impossible to argue that plastic grown in corn and extracted with energy from

fossil fuels would conserve fossil resources. What is gained by substituting the

renewable resource for the finite one is lost, through a tremendous irony, in

the additional requirement for energy. Fueling this process requires 20 to 50

percent fewer fossil resources than does making plastics from petroleum, but it

(25) is still significantly more energy intensive than most petrochemical processes

are, even though developing alternative plant-sugar sources that require less

energy to process, such as wheat and beets, would eventually attenuate the use

of fossil fuels.

The energy necessary for producing plant-derived plastics gives rise to a

(30) second, perhaps even greater, environmental concern: fossil petroleum is the

primary resource for conventional plastic production, but making plastic from

plants depends mainly on coal and natural gas used to power the corn-farming

and corn-processing industries. Any of the plant-based methods, therefore,

involves switching from a less abundant fuel (petroleum) to a more abundant

(35) one (coal). Some experts argue that this switch is a step toward sustainability.

Missing in this logic, however, is the fact that all fossil fuels used to make

plastics from renewable raw materials (corn) must be burned to generate

energy, whereas the petrochemical processes incorporate a significant portion

of the fossil resource into the final product. Burning more fossil fuels

(40) exacerbates an established global climate problem by increasing emissions of

greenhouse gases, such as CO2, and SO2, which contribute to acid rain; thus

the environmental benefit of growing plastic in plan

A．expose the fragile nature of the foundations on which bioengineering research rests

B．argue that bioengineering is ultimately infeasible as a means of manufacturing plastic

C．argue that the advances in organically-based plastic manufacture cannot solve environmental issues

D．explain the reasons for and objectives of current research on the development of organically-based plastic manufacture

E．describe the nature of the organic plastic manufacturing process