Which of the following statements regarding restriction enzymes is NOT true? A) Most restriction enzymes recognize sequences of 20-25 bp in length.
B) Bacteria can add methyl groups to their DNA to prevent digestion by endogenous restriction enzymes.
C) Most restriction enzymes recognize palindromic sequences in host DNA.
D) Restriction enzymes may produce either sticky or blunt ends when digesting host DNA.

The correct option is option A

Explanation:

Restriction enzymes are endocleases that cleave DNA fragment (of usually four, five or six nucleotide long) at specific sites to produce blunt or sticky ends. They recognize palindromic sequences of host DNA when cleaving the specific sites. The sequences below (on complementary strands) give an example of a palindromic sequences.

5'-CCC║GGG-3'

3'-GGG║CCC-5'

As can be seen above, when read from 5' to 3', the two sequences are the same despite being on opposing strands. And when cut between the guanine (G) and cytosine (C) (as shown above), it produces a blunt end. But when cut as shown below produces a sticky end.

5'- G║AATTC -3'

3'- CTTAA║G -5'

The explanation above shows options C and D are right while option A is wrong (hence the correct option).

Also, bacteria prevent their own DNA from been digested by restriction enzymes by adding methyl group to their restriction sites which prevents restriction enzymes from recognizing restriction sites of their DNA; this generally makes bacterial DNA to be highly methylated. This explanation makes option B right also.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!