Answers To Saqs: Cambridge International As Level Biology

Cambridge International AS Level Biology Answers to self-assessment questions
Answers to SAQs
Chapter 1 ■■ mitochondria have a surrounding double
membrane (envelope), the inner layer
1 Structures found in both animal and plant cells: forming finger-like folds pointing inwards
■■ nucleus with nucleolus and chromatin ■■ endoplasmic reticulum is extensive
■■ cytoplasm containing mitochondria, Golgi throughout the cell, some with ribosomes
body and other small structures (rough) and some without (smooth)
■■ cell surface membrane. ■■ small structures seen under the light
Structure found only in animal cells: microscope can be distinguished by the
■■ centriole. electron microscope as lysosomes and
Structures found only in plant cells: vesicles
■■ chloroplasts ■■ free ribosomes are seen throughout the cell
■■ large, permanent central vacuole ■■ the centriole is seen to be two separate
■■ cell wall with middle lamella and centrioles
plasmodesmata. ■■ finger-like extensions of the cell surface
membrane, known as microvilli, are seen
2 a
Actual diameter = 20 µm (see caption) ■■ microtubules are visible in the cytoplasm.
Diameter on diagram = 60 mm = 60 000 µm
Magnification, M = size of image, 5 Detail seen with the electron microscope, but
I not apparent using a light microscope:
= actual size of specimen, A ■■ in the nucleus, chromatin can be
= 60 000
20 distinguished
Therefore, magnification = × 3000 ■■ the nuclear membrane can be seen as a
double structure (envelope), continuous
b Magnification = × 16 000 (see caption)
with the rough endoplasmic reticulum,
Length on micrograph = 51 mm = 51 000 µm
and with pores in it
Size of specimen, A = size of image,
■■ there is extensive rough and smooth
I

= magnification, M endoplasmic reticulum throughout the cell
= 51 000 ■■ free ribosomes in the cytoplasm
16 000
■■ microtubules are visible in the cytoplasm
Therefore actual size of chloroplast = 3.19 µm
■■ the mitochondria have a double
3 The resolution of a microscope is limited by membrane (envelope), the inner layer

the radiation used to view the specimen. having folds into the matrix
Resolution equals half the wavelength of the ■■ chloroplasts have a double outer
radiation used. The shortest wavelength of membrane (envelope)

light is 400 nm, therefore the resolution of a ■■ grana can be seen in the chloroplast, as
light microscope is 200 nm. The diameter of a stacks of sacs connected to other grana by
ribosome is much smaller than this, namely longer sacs (thylakoids).
25 nm.
6 Cell surface membrane: essential because it
4 Detail seen with the electron microscope, but forms a partially permeable barrier between
not apparent using a light microscope: the cell and its environment, regulating
■■ in the nucleus, chromatin can be movement of materials into and out of
distinguished the cell. This is necessary to maintain an
■■ the nucleus is seen to be surrounded by a environment inside the cell which is different
double membrane (envelope) with pores from that outside the cell.
in it Cytoplasm: site of metabolic activity;
contains biochemicals in solution.
Cambridge International AS and A Level Biology © Cambridge University Press 2014

Cambridge International AS Level Biology Answers to self-assessment questions
Ribosomes: sites of protein synthesis, an

essential activity of all cells. (DNA controls
cells by controlling which proteins are made.)
Protein synthesis is a complex process
involving the interaction of many molecules;
the ribosome provides a site where this can
happen in an organised way.
DNA: the genetic material. Contains the
information which controls the activities
of the cell. Has the ability to replicate itself,
enabling new cells to be formed.
Cell wall (absent in animal cells):
prevents the cell from bursting as a result
of osmosis if it is exposed to a solution of
higher water potential.
Cambridge International AS and A Level Biology © Cambridge University Press 2014

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Cambridge International AS Level Biology Answers to self-assessment questions

3 The resolution of a microscope is limited by membrane (envelope), the inner layer

radiation used. The shortest wavelength of membrane (envelope)

Cambridge International AS and A Level Biology © Cambridge University Press 2014

Ribosomes: sites of protein synthesis, an

Cambridge International AS and A Level Biology © Cambridge University Press 2014

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