Cambridge International A Level Biology Revision Guide

Cambridge International AS Level Biology
Answers to end-of-chapter questions
7
d both intrinsic proteins;
both have specific shape;[2]
e channel proteins have a fixed shape / carrier
proteins have a variable shape;[1]
f width of C measured in mm;
mm converted to µm and µm converted to
nm;
correct formula used magnification: M = I/A =
width of C/7 accept mm, µm or nm;
correct answer in nm;[4]
[Total: 15]
Process
Uses
energy
Uses
proteins
Specific
Controllable
by cell
diffusion ✘ ✘ ✘ ✘
osmosis ✘ ✘ ✔ ✘
facilitated
diffusion
active
transport
✘ ✔ ✔ ✘
✔ ✔ ✔ ✔
endocytosis
and
✔ ✘ ✔ ✔
exocytosis
[20]
NB: It could be argued that facilitated
diffusion is controllable, because the number
of channel proteins in the membrane can
affect the rate.
8 Award 1 mark for each correct row
Feature Cell wall Cell
membrane
is the thickness
normally
measured in nm
or µm?
location
chemical
composition
accept any
statements
that serve to
distinguish
between cell
wall and cell
membranes.
Examples are
given.
µm nm
surround some
cells / not animal
cells / only outside
/ surrounding cells
contains cellulose
in plants,
peptidoglycans
/ murein in
prokaryotes, (chitin
in fungi) / contains
a strengthening
material / contains
a polysaccharide
(or polysaccharidelike
substance) AW
surround all
cells / may be
found inside
cells
phospholipids,
protein,
(sometimes)
cholesterol
permeability freely permeable partially
permeable
function
mechanical
strength
fluid or rigid rigid fluid
selective
barrier AW
[6]
9 description:
rate of entry of water is rapid at first but
slows down gradually;
until rate is zero / no further entry of water
or water enters until water potential of
cell = water potential of pure water = 0
(= equilibrium);
exponential / not linear;
rate depends on / proportional to, difference
in water potential between cell and external
solution; [max. 3]
explanation:
water (always) moves from a region of higher
water potential to a region of lower water
potential;
Cambridge International AS and A Level Biology © Cambridge University Press 2014