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Orlov [11]
3 years ago
12

20. The Calvin cycle takes place in the

Biology
1 answer:
tatyana61 [14]3 years ago
8 0
C thylakoid membranes
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During light reactions, ATP is produced when hydrogen ions move:
Natalija [7]

Answer:

The correct answer will be option-C.

Explanation:

Light-dependent reactions are the reaction of photosynthesis which takes place in the presence of light.

During light reaction, ATP and NADPH intermediates are produced which are utilized during the light-independent reaction. The main reactions that take place during light reactions are photolysis of water and ATP synthesis due to the electron transport chain.

Electron transport chain generates electrochemical gradient across the thylakoid membrane sue to the accumulation of protons in the thylakoid lumen and fewer protons in the stroma of the chloroplast.

This causes the osmotic movement of protons down their concentration gradient through ATP synthase. The movement if hydrogen ions take place from thylakoid lumen to stroma forming ATP molecules.

Thus, Option-C is the correct answer.

5 0
3 years ago
A molecule that can be used as a molecular clock has a neutral mutation rate of one mutation per 5 million years. How many years
gregori [183]

Answer:To put dates on events in evolutionary history, biologists count how many mutations have accumulated over time in a species’ genes. But these “molecular clocks” can be fickle. A paper in the 28 September Physical Review Letters mathematically relates erratic “ticking” of the clock to properties of the DNA sequence. Researchers may eventually use the results to select which genes make the best clocks.

Although mutations in DNA are rare, they are crucial for evolution. Each mutation in a gene changes one small piece of a protein molecule’s structure–sometimes rendering it non-functional and occasionally improving it. The vast majority of mutations, however, neither hurt nor help, often because they affect an unimportant part of their protein. Such a “neutral” mutation usually dies out over the generations, but occasionally one proliferates until virtually every individual has it, permanently “fixing” the mutation in the evolving species.

Over thousands of generations, these fixed mutations accumulate. To gauge the time since two species diverged from a common ancestor, biologists count the number of differences between stretches of their DNA. But different DNA segments (genes) often give different answers, and those answers differ by much more than would be expected if the average rate of mutations remained constant over evolutionary time. Sometimes they also disagree with dates inferred from fossils. Now Alpan Raval, of the Keck Graduate Institute and Claremont Graduate University, both in Claremont, California, has put precise mathematical limits on this variation.

Raval’s work is based on representing possible DNA sequences for a gene as a network of interconnected points or “nodes.” Each point represents a version of the gene sequence that differs by exactly one neutral mutation–a single DNA “letter”–from its immediate neighbors. The network contains only neutral mutations; non-functional versions of the sequence aren’t part of the network.

Models and simulations had suggested that if the number of neighbors varies from point to point–that is, if some sequences allow more neutral mutations than others–mutations accumulate erratically over time, making the molecular clock unreliable. Raval calculates precise limits on how unsteady the clock could get, based on properties of the network, such as the average number of neighbors for each node or the number of “jumps” connecting any two randomly chosen nodes. “The great strength of this paper is that it’s now mathematically worked out in much more detail than before,” says Erik van Nimwegen of the University of Basel and the Swiss Institute of Bioinformatics in Switzerland, who developed the framework that Raval uses.

Still, the relevant network properties are “not very intuitive,” van Nimwegen observes. Raval agrees. “The real question from this point on would be to identify what kinds of proteins would be good molecular clocks.” He says that according to his results, for a protein to be a good clock, “virtually all single mutations [should] be neutral”–many neighbors per node–but “as you start accumulating double and triple mutants, it should quickly become dysfunctional.” Raval is working to relate these network features to protein properties that researchers could measure in the lab.

Researchers have suggested other explanations for the erratic behavior of molecular clocks, such as variations in the mutation rate because of changes in the environment. But such environmental changes are relatively fast, so their effect should average out over evolutionary time, says David Cutler of Emory University in Atlanta. He says that in network models, by contrast, changes in the mutation rate are naturally slow because the point representing the current sequence moves slowly around the network as mutations accumulate.

Explanation:

4 0
3 years ago
Read 2 more answers
What is the name of the connective tissue membrane found lining the joint cavities?
blsea [12.9K]
<span>The connective tissue membranes that are found lining the joint cavities are called the synovial membranes. Joint cavities, like the shoulders, elbows, or knees, are known as freely movable joints. The synovial membranes line joint cavities that are not open to the outside.</span>
4 0
3 years ago
True or false carbohydrates also make up part of the cell membrane
timofeeve [1]
True because carbohydrates are in the cell membrane.
6 0
3 years ago
Which of the following objects will exert the greatest gravitational force on a box, if the distance between them stays the same
Mumz [18]

Answer:

D). 8 kg mass

Explanation:

Acceleration of Falling Objects

Heavier things have a greater gravitational force AND heavier things have a lower acceleration. It turns out that these two effects exactly cancel to make falling objects have the same acceleration regardless of mass.

The greater an object's mass, the greater its gravitational force. The earth has a strong attracting force for objects with smaller mass (including the moon), and the sun has an attracting force on the earth and other planets in our solar system. ... The stronger the pull of gravity on an object, the greater its weight.

6 0
2 years ago
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