Answer:
Watson and Crick proposed the double helical model of DNA.
Explanation:
- This model says that DNA exist as double helix. It has two polynucelotide strands running in opposite direction i.e the strands are anti-parallel.
- Each polynucleotide strand is made up of several nucleotide liknked together by phophodiester bonds.
- The two strands are not coiled upon each other but the double strand is coiled upon itself around a common axis like the spiral stair case. Here base pairs forms the stairs and backbone of two strands form railing. Back bone contains sugar and phosphate.
- The base pairing is specific, adenine always pairs with thymine and guanine always pairs with cytosine. Thus if we see any base pair, it consists of one purine and one pyrimidine.
- The two strands of DNA thus show complementary base pairing.
- The strands are held together because of hydrogen bonding between the bases in opposite strand.
- One full helical turn involves ten base pairs and the base pairs are stacked 3.4 A apart.
- This form is called as B-form of DNA.
An organism that obtains energy and nutrients by feeding on other organisms or their remains. A food web is a model of the feeding relationships between many different consumers and producers in an ecosystem. Without plants (the primary producers) consumers and decomposers would not be able to live. Producers always start every food chain. A consumer, also called a heterotroph, is an organism that cannot make its own food. It must eat producers or other organisms for energy.
Answer:
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It is D The medication helped patients recover faster. I’m glad to help others if you have any questions I will be likely to help. Thank you
The upper (landward) end of the intertidal zone, dominated by barnacles, limpets, chitons, and other encrusting species; The mid-intertidal zone, where fucoid algae and mussels provide structure and habitat; and. The low-intertidal zone is made up of kelps, fleshy seaweeds, and seagrasses.
