3 Answers to end-of-chapter questions
1
D
[1]
2
C
[1]
3
B
[1]
4
B
[1]
5
C
[1]
6
B
[1]
7
C
[1]
8
D
[1]
Structured questions
9
a
b
c
One point for each column correct:
Volume of
Volume of water
10% betalain
added/cm3
3
added/cm
10.0
0.0
8.0
2.0
5.0
5.0
4.0
6.0
2.0
8.0
1.0
9.0
0.0
10.0
Final concentration
of standard
solution/%
10.0
8.0
5.0
4.0
2.0
1.0
0.0
One point required:
• To wash away the pigment that seeps out of the vacuole when the beetroot disc is
cut
• If the discs were not rinsed, the final colour at end of the experiment would be
more intense than it should be; results would not be reliable or valid
i
ii
iii
One point required:
• Stir contents of both sets of test tubes
• Place test tubes in front of plain white paper
As temperature increased, the colour intensity increased
At 30 °C, the colour corresponded to 2% betalain
At 50 °C, the colour corresponded to 5% betalain
At 80 °C, the colour corresponded to 10% betalain
[3]
[1]
[1]
[1]
[1]
Each cause and effect 1 mark:
• Betalain diffused out of the vacuoles in to the water
• Betalain passed from the vacuole across the tonoplast through the cytoplasm
and across the plasma membrane
• As temperature increased, there was more kinetic energy, and so more rapid
diffusion of betalain
• There were also more vibrations in the protein molecules in the membrane
which broke the hydrogen bonds of their tertiary structure
• The proteins were denatured in both the tonoplast and plasma membrane
• This allowed the membrane to become more permeable to the pigment
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• The phospholipids also became more fluid
• This allowed for the passage of more of the soluble pigment
iv
d
10 a
b
[max 4]
One point required:
• Increasing temperature increases the permeability of the cell membrane
• Increasing temperature denatures the proteins of the membrane making it more
permeable
• Increasing temperature disrupts the components of the cell membrane making it
more permeable
[1]
Limitations (one point required):
• Based on colour matching the colour standard and experiment tubes. This is
subjective
• Intermediate results would have to be estimated
• Any valid point
[1]
Sources of error (two points required):
• Not all the discs would be the same thickness
• Discs not rinsed until water was clear
• Discs not dried after rinsing so could have pigment on surface before experiment
started
• Depending on the apparatus used to measure the water for each tube, the volume of
water added to each tube may not be the same
• Any valid point
[2]
The amount by which the dissolved solute lowers the water potential of a solution
[1]
So that the contents of the cell would be easily visible under the microscope
[1]
c
Well drawn [1]
3 labels [1]
Drawing showing a fully plasmolysed plant cell
d
e
Concentration of sucrose solution/M
Total number of cells observed
Number of cells plasmolysed
Percentage plasmolysis
0.2
50
8
16
0.4
50
18
36
0.6
50
38
76
0.8
50
48
96
2 correct [1]
4 correct [max 2]
Three points required:
• Not all the cells in each sample had the same water potential
• Hence not all the cells behaved exactly the same way in each sample
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2
•
In 0.2 M sucrose solution, only 16% of the cells were plasmolysed.
This shows that the solution may have had the same water potential
(isotonic) as most of the cells or higher water potential (hypotonic)
than the cells
From 0.4 M to 0.8 M sucrose solution, there was increasing
plasmolysis. The solutions had a lower water potential than the cells
Water moved from a higher water potential inside of the vacuoles of
cells through the cell membrane to each of the solutions
0.8 M had the most negative solute potential and therefore the lowest
water potential
•
•
•
Axes labelled with appropriate units: concentration of sucrose on x-axis – ½ mark; %
plasmolysis on y-axis – ½ mark; points plotted accurately and clearly marked – 1 mark;
Points joined to show cause and effect relationship / best fit – 1 mark.
Percentageplasmolysis/%
plasmolysis/%
Percentage
f
[max 3]
Concentration of sucrose/M
Graph showing the effect of sucrose concentration on
plasmolysis of onion cells
[max 3]
g
0.45 M
[1]
h
From table: 1280 kPA
[1]
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i
11 a
Discrepancy in counting cells – same cells can be counted more than
once or some cells not counted at all.
•
•
b
c
d
e
f
‘Fluid’ refers to the fact that the molecules in the membrane are in
constant motion, moving around within their own phospholipid
monolayer
‘Mosaic’ refers to the way the membrane would look if viewed from
above – ‘protein icebergs in a lipid sea’
I – intrinsic glycoprotein / transmembrane protein
II – cholesterol
III – phospholipid bilayer
IV – extrinsic protein
V – extrinsic protein
VI – glycoprotein
VII – channel / intrinsic / integral protein
[1]
[1]
6–7 points [3]
4–5 points [2]
2–3 points [1]
i
Y
[1]
ii
Because exterior surface (X) has the glycocalyx / carbohydrate
chains which act(s) as receptor site / mechanical support
[1]
Extrinsic – do not interact with the hydrophobic fatty acid tails of the
phospholipid bilayer / they are usually bound to the membrane
indirectly by interactions with integral membrane proteins or directly by
interactions with lipid polar head groups
Intrinsic – each arranged in an amphipathic structure; that is, with the
ionic and highly polar groups protruding from the membrane into the
aqueous environment, and the nonpolar groups largely buried in the
hydrophobic interior (fatty acid tails) of the membrane
•
•
•
•
•
transport proteins – carrier and channel
enzymes
receptor sites for hormones, neurotransmitters
attachment for cells (e.g. form tight junctions etc.)
markers on cells for cell recognition
•
The hydroxyl groups of the amino acids and other R groups that have
small electrical charges are attracted to the charged poll
heads
of the phospholipids
The hydrophobic regions of the protein are attracted to the
hydrophobic lipid tails, by hydrophobic interactions
•
g
[1]
1 point [1]
1 point [1]
Any 2 points [2]
Phospholipid bilayer
• Constituent of each phospholipid: phosphate, glycerol, two fatty acids
• Condensation reaction to form an ester linkage
• Made up of hydrophilic phosphate head oriented towards the aqueous
medium
• With two nonpolar / hydrophobic fatty acid tails oriented away from
the aqueous medium
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[1]
[1]
[2]
4
Essay questions
12 a i
phospholipid
bilayer – made
up of
monecules
with
hydrophilic
phosphate
oriented
towards
the aqueous
medium and
two
hydrophobic
fatty acid tails
oriented away
from the
aqueous
medium
glycolipid – made up of
carbohydrate chains attached to
phosphate head of
phospholipids, found on exterior
channel
proteins –
transmembrane
protein with a
pore
glycoprotein – made up
of carbohydrate chain
attached to a protein,
found on exterior of
membrane
Transmembrane / integral
protein – spans entire
membrane, the polar
groups protruding from the
membrane into the
aqueous environment, and
the nonpolar groups
largely buried in the
hydrophobic interior (fatty
acid tails) of the
membrane
ii
b
extrinsic protein – located
on surfaces of membrane;
do not interact with
hydrophobic part of
membrane
cholesterol –
made up of polar
head, which is
aligned to polar
head of
phospholipid, and
a nonpolar tail
aligned with fatty
acid tails of
phospholipid
Functions
• Phospholipid – a barrier which separates cell contents from
exterior / allows for diffusion of lipid-soluble compounds /
prevents entry of hydrophilic substances
• Cholesterol – helps to maintain the fluidity of the membrane,
preventing it from becoming too stiff when temperatures are
low, or too fluid when temperatures are high / prevents entry
of polar substances / mechanical stability of membrane
• Proteins – as transport proteins / carrier proteins for active
transport / channel proteins for facilitated diffusion / as
enzymes / for cell adhesion / as markers for cell recognition
• Glycolipids and glycoproteins – as receptor sites / cell
signalling for hormones, neurotransmitters / as an antigen
Drawing neat
and clear [1]
Any 5
annotations [3]
3–4 annotations
[2]
1–2 annotations
[1]
Drawing with
no annotations
but 5 or more
labels [1]
[max 4]
Any 3 points [3]
i
Oxygen and carbon dioxide – by diffusion: down a concentration
gradient without the use of ATP (passive)
Process well described [1]
ii
• Sodium and potassium ions – by active transport / use of Na+–
K+ pump: direct active transport where the ions are moved
against a concentration gradient with the use of ATP and
carrier proteins
• Sodium and potassium ions – by facilitated diffusion:
uses channel proteins / down a concentration gradient / without use
of ATP
Processes well described [2]
iii
Water – by osmosis: from an area of high water potential to an area of
lower water potential / down a water potential gradient / across a
partially permeable membrane
Process well described [1]
iv
Glucose – by facilitated diffusion: uses channel protein / down
concentration gradient / no ATP
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Glucose – by indirect active transport: cotransported with Na+
ions / uses symport protein / ATP required / against a
concentration gradient
Processes well described [2]
v
13 a
b
Diffusion is the net movement of molecules or ions down their
concentration gradient (from a place where they are in high
concentration to a place where they are in lower concentration)
i
[1]
smaller molecules diffuse faster / can pass between the phospholipid molecules /
have more kinetic energy
[2]
ii
as temperature increases, more kinetic energy / more movement / faster diffusion
[2]
iii
more soluble in lipids, the rate of diffusion increases / can pass faster across
hydrophobic fatty acid tails
[2]
steeper the concentration gradient, faster the diffusion rate
[2]
iv
c
Enzymes – by exocytosis: vesicle containing enzyme merges
with plasma membrane / membrane is fluid and easily breaks
and rejoins / enzyme released outside of cell / uses ATP. Processes well described [2]
Similarities
• Both involve the use of transport proteins
• Both are selective
• Both become saturated
• Both are inhibited by substances which denature proteins
2 similarities [2]
Differences
Active transport
• uses ATP
• substances move against a
concentration gradient
• transport protein changes
shape / carrier proteins
3 differences [4]
2 differences [3]
1 difference [2]
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Facilitated diffusion
• does not require ATP
• substances move down a
concentration gradient
• transport protein does not
change shape / channel protein
Original material © Cambridge University Press 2011
6
14 a
i
Isotonic solution – same water potential as cell: no net movement of water; no
change in size of cells
Red blood cell in isotonic solution
ii
Plant cell in isotonic solution
[3]
Hypotonic solution – water potential outside cell is greater than inside cell
Red blood cell in hypotonic solution
[3]
Plant cell in hypotonic solution
iii Hypertonic solution – water potential outside cell is less than inside cell
[insert diagram 1-4 on bottom of page 65 figure 3.11] [3]
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7
b
•
•
•
Acetylcholine – by exocytosis
Vitamin A – diffusion through hydrophobic fatty acid tails
since it is fat-soluble
Vitamin C – by facilitated diffusion through water-filled
channel proteins / cannot pass through hydrophobic
membrane since it is water soluble
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2 points each[6]
Original material © Cambridge University Press 2011
8