Cell Biology Questions

[FlameWave515]

I'm having trouble with a few of these questions which appeared in a state-wide test administered recently. I would appreciate any help on them, especially an explanation if possible.

1. If cells in the process of dividing are subjected to colchicine, a drug that interferes with the functioning of the spindle apparatus, at which stage will mitosis be arrested?
a. anaphase
b. prophase
c. telophase
d. metaphase
e. interphase

2. What do both mitochondria & chloroplasts have in common?
a. ATP is produced
b. DNA is present
c. Ribosomes are present
d. Only b & c are correct
e. a, b, and c are correct

3. Gram-Negative Bacteria
a. lack a second plasma membrane outside the cell wall
b. stain violet when Gram-stained
c. tend to resist many of the body's natural defenses and antibiotics making many of them pathogens
d. completely lack a cell wall

4. All of the following are true about crossing over EXCEPT:
a. it involves the exchange of pieces of chromatids of tetrads
b. the farther away from the centromere, the more likely it is to occur
c. it produces two sets of identical chromatids from a tetrad
d. it results in genetic recombination

5. The carbon that makes up organic molecules in plants is derived directly from
a. combustion of fuels
b. carbon fixed in photosynthesis
c. carbon dioxide produced in respiration
d. carbon in the lithosphere
e. coal mines

-Any help would be greatly appreciated.

[mith]

1.It's either anaphase or metaphase when spindles appear. But it's probably metaphase 'cause that's when they first appear.

2. I believe a,b,c are correct. See description for the organelles.

4.C
It does what it does, see your book for details. sparknotes.com would work in a pinch.

5. B

Look over the formula for photosynthesis.

[moe222]

plzzzzz i wanna ask from where did u get these questions ??????????????????????

[Poison]

From their books and homeworks, I guess.

[victor]

By the way, where's the answer of number 3? If I may answer, I'll give C for number 3.

[cookie]

I guess, Q3 is C too ~
Actually, do you have the model answer ???

[Enzyme]

1.It's either anaphase or metaphase when spindles appear. But it's probably metaphase 'cause that's when they first appear.

The effect of colchicine in Metaphase is very little in spite of the beginning of the formation of acromatic spindle (c-metaphasic chromosomes show their chromatids shorter and swelled, adopting a diverging layout with "X" shape), but the effect is more notable in Anaphase.

In Metaphase, the acromatic spindle start to appear. But it is in Anaphase when chromatids migrate to the poles of the cell. So the effect is more seen in Anaphase (as acromatic spindle doesn't exist due to colchicine, chromatids don't migrate to the poles of the cell and cytokynesis doesn't occur. Due to this, the 4n chromatids will shown as 4n chromosomes in the next cell division. I mean, we will have cells with four chromosomic sets <<tetraploid cells>> instead of two).

I'd choose the first option: A. Anaphase.

[Enzyme]

Cookie and Victor, I'm in agree with you. Also I think that the answer of the question number three is the third option (C. Tend to resist many of the body's natural defenses and antibiotics making many of them pathogens).

My explaination is:

Because Gram Negative bacteria have specific O-Polysaccharides chains. This characteristic makes a difference between two vines: Smooth bacteria (they contain a lot of water molecules due to the presence of O-specific chains) and Rough bacteria (S bacteria suffer a mutation). O-specific chains give to S bacteria a selective advantage: they are more resistant to phagocytosis by leukocytes and for that, more virulent.

The large variety of O-specific polysaccharides in pathogenic bateria, can be due to a selection of new types O-antigenic (mutants) every time. For that, they have an advantage in development because the host can't dispose antibodies against a lot of different antigenes at the same time (because until the host don't form antibodies and these recognise the polysaccharides, the bacteria can't be attacked). I don't know if you understand what I mean (my English is very bad and I can't explain it very well).

Many of Gram Negative bacteria are pathogens due to their external layer. This external layer is composed of lipopolysaccharides which are the most active endotoxines of bacteria.

Are you in agree with me? C'mon! More possible explainations to this option (C)!