Common Mistakes and Misconceptions

Common Mistakes & Misconceptions in Biology Cell Structure and Cell Membrane 

Cisterna ≠ crista Cisterna = lumen of RER or Golgi Apparatus Crista (cristae= plural  (cristae=  plural ) = infolding of the inner mitochondrial membrane Wrong

Correct

Ions are polar…..

Ions  Ions  are charged hence charged hence they cannot pass through the hydrophobic core of the Cell urface !embrane.

"ucleolus co contains rR rR"A

"ucleolus synthesizes rR"A rR"A (#hi (#hich ch form forms s part part of  ribosome)$ but it itself is made of %"A (coiled around histones)

&atty acid' hydrocarbon tails

&atty acid' hydrocarbon tails interact #ith hydrophobic

inte intera ract ct

interactions

#ith #ith

hydr hydrop opho hobi bic c

bonds Ribosomes

hae

one

Ribosomes do not hae membranes

membrane &acilitated diffusion uses only

&aci &acili litat tated ed diff diffus usio ion n uses uses both channel channel protein protein and

chan channe nell

carr carrie ierr

prot protei eins ns..

Acti ctie e

prot protei eins ns..

he he

carr carrie ierr

prot protei ein n

can can

chan change ge

tran transp spor ortt uses uses only only carr carrie ier  r  conformation #ithout A* A* hydrolysis. proteins.

 Actie transport uses only carrier proteins #hich can chan change ge

conf confor orma mati tion on th

only only

(Campbell +  edition pg ,-).

upon upon

A*

hydr hydrol olys ysis is..

Once, Cambridge question goes

agains againstt this this rule rule (see (see 2006/P 2006/P2/Q 2/Q1) 1) but ou still still ha!e ha!e to ans"er ans"er the question based on diagram#

*assage

of

hyd hydrophob hobic thro throug ugh h

the the

small$ mole olecules les

*assage *assage of small$ small$ hydrophobic hydrophobic molecules molecules through through the phospholipid bilayer is called /simple diffusion0

phos phosph phol olip ipid id

bilayer is called /diffusion0 E1oc E1ocyt ytos osis is is the same same as

E1ocytosis E1ocytosis is a type of bul2 transport transport re3uiring re3uiring esicles$

actie transport

#hile actie transport uses carrier proteins.

Biological Molecules Wrong

Correct

Cell Cellul ulos ose e is a prot protei ein n 4R

Cellulose is a polysaccharide A"% collagen is a (fibrous)

collagen is a polysaccharide

protein

Collagen is made up of triple

Tropocollagen is Tropocollagen is made up of triple heli1.

heli1 Globular protein is globular in shape

Globular protein is spherical is spherical in shape. $se snonms% 

Enzymes 

Actie site can only be used #hen describing enzymes! &or other proteins eg. Receptors$ pumps$ transcription factors$ use allosteric sites " binding sites!



&ailure to name the tpes of bonds affected #hen sub5ected to denaturation agents' factors. E.g. Candidates must mention hydrogen"ionic bonds  #hen high temperature is applied$ ionic bonds  #hen p6 is changed or heay metals added$ hydrophobic interactions #hen organic solents added and disulphide bonds #hen a reducing agent is added.



%enaturation has t#o meanings7 8

&or proteins7 disruption of tertiary structure$ causing the protein to lose its -% conformation

8

&or %"A 7 brea2ing of hydrogen bonds bet#een complementary base pairs causing the t#o %"A strands to separate

Cell and #uclear $iision 

Chromatids separate to become chromosomes Chromatids are no longer called chromatids a&ter the separate &rom the centromere Wrong

Correct

Chromosomes are pulled to opposite

Chromosomes are pulled to opposite poles of 

ends of the cells by spindle fibres

the cells by spindle fibres

Centromere split

Centromere diide

Chromosome replicate

%"A replicate (so each chromosome is no# seen comprising of t#o sister chromatids)

!itosis

has

no

homologous

chromosomes

6omologous chromosomes are already in cells irregardless of #hether they are undergoing cell and nuclear diision. All humans hae 9pairs of homologous chromosomes.

%iploid number = amount of %"A

%iploid

number

is

the

total

number

of  

chromosomes. %"A amount is t#ice in a chromosome

#ith

9

sister

chromatids

compared to a chromosome that does not hae sister chromatids. %"A

replication

occurs

in

the

%"A replication occurs once only in the

interphase bet#een meiosis I and II

interphase before meiosis I

4rganism is sterile because gametes

4rganism is sterile because the organism itself 

hae odd number of chromosomes

hae odd number of chromosomes and'or hae een number of chromosomes that do not occur in homologous pairs