Biology MCQ thread..!!

[Xthegreat]

2. Surgery on the septum in the lower region of the human heart may cause damage to the nerve fibers within the septum (bundle of His).

Wch phase of the cardiac cycle wuld b directly affected by such damage.?

A. atrial systole
B. atrio ventricular node stimulation
C. diastole
D. ventricular systole.

the fibres in the septum is to transmit impulses to the ventricles so the answer is D

 

[hassam]

6 One complete turn of the double helix of DNA contains 10 pairs of bases and is 3.4 nm long. What is the approximate number of amino acids in an enzyme coded by a 132 nm length of DNA?
A 388
B 150
C 129
D 38

 

[hassam]

12 At prophase of mitosis, a eukaryote chromosome consists of two chromatids. What is the structure of a single chromatid?
A one molecule of single-stranded DNA coiled around protein molecules
B two molecules of single-stranded DNA each coiled around protein molecules
C one double helix of DNA coiled around protein molecules
D two double helices of DNA each coiled around protein molecules

 

[hassam]

 

[imissknow2]

Can anybdy please solve w10/q24

I do not know which variation are you refering to thus I provide the explanations for all of them. Hope this helps.

9700/11 Winter
QN24 answer is C

Explanation:

mature phloem sieve tube cells are living cells thus have cytoplasm, the presence of end wall is to prevent the sap to flow out in case of a breakage (ie graze by animals) It does not hav nucleus though and the nutrients are supplied by the companian cells attached to the phloem sieve tube cells.

Mature xylem cells are dead cell, they cannot have cytoplasm or end wall as they need capillary action and mass flow ( which is when the body of water move together via cohesion and adhesion to the lignin wall ), If there is air bubble present this mass flow will be affected.

The question test the candidate concept on knowing that phloem cell are living cell while mature xylem cells are dead cells.

9700/12 Winter
QN24 What is the main function of a companion cell in mature phloem tissue?

QN24 answer is A
(A) providing cytoplasmic contact with the sieve tube element for loading

Explanation:

Companian help load sucrose into the phloem sieve tube for translocation of sucrose to other parts of the plant.

Using ATP, the companion cells pump H+ ions out of the companion cell thus creating a electrochemical gradient.
There are protein on the surface of the companion cells know as co-transporter protein which then transport in H+ ions TOGETHER with the sucrose from the surrounding mesophyll cells (this is why it is called co-transporter protein).

9700/13 Winter
QN24 The diagram shows a stage micrometer, with divisions 0.1 mm apart, viewed through an eyepiece containing a graticule.

Answer is B

Explanation:

From the given diagram 1 stage micrometer coincides with 40EPG divisions. so each division of EPG is (0.1/40)=0.0025mm aka 2.5 micrometer. So a white cell of 10micrometer will cover (10/2.5)=4EPG division.

 

[hassam]

5 Which statement is FALSE about the effects of various conditions on the activity of an enzyme?
A Higher temperatures generally increase the activity of an enzyme up to a point.
B Above a certain range of temperatures, the protein of an enzyme is denatured.
C A change in pH can cause an enzyme to be inactivated.
D An enzyme's activity is generally reduced by an increase in substrate
concentration.

 

[histephenson007]

6 One complete turn of the double helix of DNA contains 10 pairs of bases and is 3.4 nm long. What is the approximate number of amino acids in an enzyme coded by a 132 nm length of DNA?
A 388
B 150
C 129
D 38

Answer is C ?

388/3

 

[hassam]

6 A particular cell has half as much DNA as some of the other cells in a mitotically
active tissue. The cell in question is most likely in _________.
A prophase
B anaphase
C G1
D G2

 

[histephenson007]

12 At prophase of mitosis, a eukaryote chromosome consists of two chromatids. What is the structure of a single chromatid?
A one molecule of single-stranded DNA coiled around protein molecules
B two molecules of single-stranded DNA each coiled around protein molecules
C one double helix of DNA coiled around protein molecules
D two double helices of DNA each coiled around protein molecules

again C?

 

[histephenson007]

B

 

[histephenson007]

5 Which statement is FALSE about the effects of various conditions on the activity of an enzyme?
A Higher temperatures generally increase the activity of an enzyme up to a point.
B Above a certain range of temperatures, the protein of an enzyme is denatured.
C A change in pH can cause an enzyme to be inactivated.
D An enzyme's activity is generally reduced by an increase in substrate
concentration.

not sure about this one,... D?

 

[aquariangurl]

5 Which statement is FALSE about the effects of various conditions on the activity of an enzyme?
A Higher temperatures generally increase the activity of an enzyme up to a point.
B Above a certain range of temperatures, the protein of an enzyme is denatured.
C A change in pH can cause an enzyme to be inactivated.
D An enzyme's activity is generally reduced by an increase in substrate
concentration.

C rite?

 

[histephenson007]

6 A particular cell has half as much DNA as some of the other cells in a mitotically
active tissue. The cell in question is most likely in _________.
A prophase
B anaphase
C G1
D G2

C!

 

[aquariangurl]

5 Which statement is FALSE about the effects of various conditions on the activity of an enzyme?
A Higher temperatures generally increase the activity of an enzyme up to a point.
B Above a certain range of temperatures, the protein of an enzyme is denatured.
C A change in pH can cause an enzyme to be inactivated.
D An enzyme's activity is generally reduced by an increase in substrate
concentration.

not sure about this one,... D?

Why would you say it's D? the statement IS true!

 

[histephenson007]

why is it true??
An enzyme's activity is supposed to increase when the substrate concentration is increased

 

[aquariangurl]

why is it true??
An enzyme's activity is supposed to increase when the substrate concentration is increased

IF the enzyme is increased along with the substrate THEN activity might increase, it's true cauze see, more substrate molecules, less no. active sites, rate of reaction decreases.

 

[imissknow2]

6 One complete turn of the double helix of DNA contains 10 pairs of bases and is 3.4 nm long. What is the approximate number of amino acids in an enzyme coded by a 132 nm length of DNA?
A 388
B 150
C 129
D 38

Answer is C ?

388/3

Answer to Hassam's qn
Answer is C

Explanation:

Using simple ratio calculation we know that on a 132nm DNA there is 388 pairs of bases
calculation : (132/3.4) x 10 = 388 base pairs

You know that each amino acid is coded by 3 base pair (codon) so divide 388 by 3 = 129.333= 129 amino acids
Hope this helps.

Sorry, i couldn't quote cause xtreme paper says that someone has posted a new post?? which is rediculous..

 

[histephenson007]

why is it true??
An enzyme's activity is supposed to increase when the substrate concentration is increased

IF the enzyme is increased along with the substrate THEN activity might increase, it's true cauze see, more substrate molecules, less no. active sites, rate of reaction decreases.

but the statement doesn't mention that there are a limited number of enzymes. So lets think that there is a constant amount of enzymes. starting from zero substrate concentration, if we increase the substrate concentration, the rate of reaction is going to increase. cuz more substrate molecules can form an enzyme-substrate complex with the enzymes. (instead of some enzymes having to wait for a substrate molecule to collide with its active site)

Also, if we change the pH of the solution, the enzyme will be denatured too. So, it WILL be inactivated!

 

[imissknow2]

I would quite confidently say that the answer is B
The saturated fats do not have double bonds unlike unsaturated fats. This double bonds allow formation of kinks, which disrupt the orderly pattern of cell membrane arrangement. Thus these kinks in unsaturated fats help increase fluidity.

The cholesterol helps disrupt this orderly pattern of cell membrane phospholipid bilayer too as it prevent the phospholipids from coming too close to each other.

 

[histephenson007]

I would quite confidently say that the answer is B
The saturated fats do not have double bonds unlike unsaturated fats. This double bonds allow formation of kinks, which disrupt the orderly pattern of cell membrane arrangement. Thus these kinks in unsaturated fats help increase fluidity.

The cholesterol helps disrupt this orderly pattern of cell membrane phospholipid bilayer too as it prevent the phospholipids from coming too close to each other.

yea, rite!!!