Flowering plants (angiosperms) make up about 90 percent of the Kingdom Plantae. The total number of described species is over 250,000, and many tropical species are as yet unnamed. During the past 130 million years, flowering plants have colonized every possible habitat on earth, from sun-baked deserts and windswept alpine (阿尔卑斯) summits to fertile grasslands and dense forests.
However, hundreds of millions of years ago, the Earth was dominated by ferns and conifers (针叶植物和蕨类植物). Then, how have flowers evolved and spread to all parts of the world, thus changing the landscape from green and brown to a variety of colours?
Actually, why angiosperms are successful and diverse on Earth has been debated for centuries. Even Charles Darwin himself called it a “mystery”, fearing this apparent sudden leap might challenge his theory of evolution.
Now, to this puzzle, some scientists claim they have the answer.
Kevin Simonin, from San Francisco State University in California, US and other researchers wondered if the size of the plant’s genetic material -- or genome (基因组) -- might be important. They analyzed data held by the Royal Botanic Gardens, on the genome size of thousands of plants, including flowering plants, gymnosperms (a group of plants including conifers) and ferns. They then compared genome size with anatomical (结构上的) features.
This provides “strong evidence”, that the success and rapid spread of flowering plants around the world is due to “genome downsizing.”
By shrinking the size of the genome, which is contained within the nucleus of the cell, plants can build smaller cells. In turn, this allows greater carbon dioxide uptake (摄入) and carbon gain from photosynthesis, the process by which plants use light energy to turn carbon dioxide and water into sugar and oxygen.
The researchers say genome downsizing happens only in the angiosperms, and this was “a necessary condition for rapid growth rates among land plants”.
32. According to this passage, what do we know about angiosperms?
A.They belong to gymnosperms. |
B.They add colors to the landscape of the earth. |
C.They ruled the earth hundreds of millions of years ago. |
D.They make up approximately 90% of the living species on earth. |
33. It can be inferred that____________.
A.Charles Darwin was quite confident of his theory of evolution |
B.Kevin Simonin is probably an American biologist |
C.Kevin Simonin works in the Royal Botanic Gardens |
D.Charles Darwin succeeded in figuring out the flower evolution |
34. Which of the following contributes to the success and diversity of angiosperms?
A.Phtotsynthesis. | B.The larger nucleus. |
C.The smaller genome. | D.The stronger cell. |
35. What kind of passage is it?
A.a brochure | B.a biography |
C.a science fiction | D.a popular science article |