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Researchers are finding that in many ways an individual bacterium is more analogous to a component cell of a multicellular organism than it is to a free-living, autonomous organism. Anabaena, a freshwater bacteria, is a case in point. Among photosynthetic bacteria, Anabaena is unusual: it is capable of both photosynthesis and nitrogen fixation. Within a single cell, these two biochemical processes are incompatible: oxygen produced during photosynthesis, inactivates the nitrogenase required for nitrogen fixation. In Anabaena communities, however, these processes can coexist. When fixed nitrogen compounds are abundant, Anabaena is strictly photosynthetic and its cells are all alike. When nitrogen levels are low, however, specialized cells called heterocysts are produced which lack chlorophyll (necessary for photosynthesis) but which can fix nitrogen by converting nitrogen gas into a usable form. Submicroscopic channels develop which connect the heterocyst cells with the photosynthetic ones and which are used for transferring cellular products between the two kinds of Anabaena cells.
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[数学 ]【新版】冲分救命题 -11998
The integers a, b, and c are positive, and a>b>c. When a, b, and c are divided by 3, the remainders are 0, 1, and 1, respectively.
[数学 ]【新版】冲分救命题 -11997
For all positive even integers n. n* represents the product of all even integers from 2 to n, inclusive. For example, 12*=12×10×8×6×4×2. What is the greatest prime factor of 20*+22*?
[数学 ]【新版】冲分救命题 -11996
[数学 ]【新版】冲分救命题 -11995
[数学 ]【新版】冲分救命题 -11994
In a game, the cards in a certain deck are distributed to players one at a time until each player has the same number of cards and there are not enough cards left in the deck to distribute one more card to each player. The number of cards in the deck is between 60 and 100. If the cards in the deck are distributed o 5 players, 2 cards will be left in the deck. If the cards in the deck are distributed to 6 players, 4 cards will be left in the deck. If the cards in the deck are distributed to 7 players, how many cards will be left in the deck?
[数学 ]【新版】冲分救命题 -11993
Let a be the greatest integer such that is a factor of 1,500, and let b be the greatest integer such that is a factor of 33,333,333. Which of the following statements are true? Indicate all such statements.
[数学 ]【新版】冲分救命题 -11992
A set consists of all three-digit positive integers with the following properties.Each integer is of the form JKL,where J,K,and I are digits;all the digits are nonzero;and the two-digit integers JK and KL are each divisible by 9.How many integers are in the set?
[数学 ]【新版】冲分救命题 -11991
[数学 ]【新版】冲分救命题 -11990
The number of children in a certain family is a prime number less than 10. The number of boys in the family is greater than the number of girls, and the number of boys is a prime number. If at least 1 of the children in the family is a girl, which of the following could be the number of boys in the family?Indicate all such numbers.
[数学 ]【新版】冲分救命题 -11989
[数学 ]【新版】冲分救命题 -11988
x and y are integers.
[数学 ]【新版】冲分救命题 -11987
x and y are integers.
[数学 ]【新版】冲分救命题 -11986
a and b are distinct odd prime numbers.
[数学 ]【新版】冲分救命题 -11985
When the integer n is divided by 33, the remainder is 24. Which of the following must be a divisor of n?
[数学 ]【新版】冲分救命题 -11984
4.What is the length of an edge of the smallest solid cube that can be made by placing together solid rectangular blocks of size 7 by 6 by 3?
[数学 ]【新版】冲分救命题 -11983
Light travels at approximately 186,000 miles per second.Which of the following is closest to the number of miles that light travels in 3 hours.
[数学 ]【新版】冲分救命题 -11982
The number n is the least positive integer for which 108n is the square of an intege
[数学 ]【新版】冲分救命题 -11981
The number n is the least positive integer for which 108n is the square of an intege
[数学 ]【新版】冲分救命题 -11980
If x=2y+1, and y=2w, where w, x, and y are integers, which of the following must be an odd integer?
[数学 ]OG -11979
If x=2y+1, and y=2w, where w, x, and y are integers, which of the following must be an odd integer?
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