e.f.academy
I.B. Biology Core
Topic 1: Cell Biology
JWh
8/8/2014
Introduction to cells
Ultrastructure of cells
Membrane structure
Membrane transport
The origin of cells
Cell Division
1.1 Cell Theory
Discuss the theory that living organisms are composed of
cells
Cells are the building blocks of life.
Cells have metabolism
Cells are capable of independent existence.
Cells can only form from already existing cells.
Cells contain hereditary materials (DNA)
Skeletal muscle and some fungal hyphae are not divided into
cells but have multinucleate cytoplasm.
Some biologists consider unicellular organisms to be
acellular.
State that a virus is a non-cellular structure consisting of DNA
or RNA surround by protein coat
A virus is a non-cellular structure consisting of DNA or RNA
surrounded by protein coat.
Qa. Fig 1.
imagesCAPH40CR
Label the structures (7)
State that all cells are formed by other cells
All cells are formed from other cells.
Explain three advantages of using light microscopes
Some advantages are:
Colour images instead of monochrome
A larger field of view
Easily prepared sample material
The possibility of examining living material and observing
movement
Cheaper equipment
Outline the advantages of using electron microscope
The advantages of using an electron microscope are that they
have greater magnification, which means that they can magnify more
than light microscope. This means that they can see things that are
smaller than with using a light microscope. They also have a higher
resolution, which means that they can also show the images as
separated particles and clear instead of blurry.
Qb. Cholera bacteria can be viewed using a transmission electron
microscope (TEM) or a scanning electron microscope (SEM).
(i) Give one advantage of using a TEM rather than a SEM.
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(1)
(ii) Give one advantage of using a SEM rather than a TEM.
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(1)
Defineorganelle
An organelle is a discrete structure within a cell, and has a
specific function.
Compare the relative sizes of molecules, cell membrane
thickness, viruses, bacteria, organelles and cells, using
appropriate SI units=
Molecules can be up to 1 nm
Cell membrane thickness can be up to 10 m
Viruses can be up to 100 nm
Bacteria can be up to 1 m
Organelles can be up to 10 m
Most cells can be up to 100 m
Calculate linear magnification of drawings
Magnification = size of the picturemultiplied withsize of the
real object
Size of the real object = size of the picturedivided
withmagnification
Explain the importance of the surface area to volume ratio as a
factor limiting cell size
The volume increases faster than the surface area when a cell
grows. The surface to volume ratio thus decreases. In order to
carry out metabolic functions (different chemical reactions) the
cell needs the surface area and when it grows, it needs to carry
out more functions. The size is thus limited since the cell needs
to maintain a certain surface area to volume ratio.
Qc.
Explain one advantage of a biconcave disc over a spherical cell
of the same volume in transporting oxygen.
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(2)
State that unicellular organisms carry out all the functions of
life
Unicellular organisms carry out all the functions of life.
Explain that cells in multicellular organisms differentiate to
carry out specialised functions by expressing some of their genes
but not others
The multicellular organisms contain all the genes but they do
not use all of them. The cells differentiate to carry out
specialised functions because they only express some of their
genes.
Definetissue,organandorgan system
Tissue:An integrated group of cells with common function and
structure.
Organ:A body function centre that is specialised into one
function and composed of different tissues.
Organ system:A group of organs that are specialised into a
certain function, working together.
1.2 Draw a picture of prokaryotic cell structure
Draw a picture of prokaryotic cell structure showing Ribosomes,
Mesosome, Slime Capsule, Cell Wall, Flagellum, Cell Surface
Membrane, Plasmid, and Naked Nucleic Acid. (8 Things).
https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcSOjdIDbBfr0lNhOcX6bf1kOV_JJDpd6IcTBMYjGoV0bXmHm61H
State the function of...
Ribosomes - Carries out protein synthesis; small 70S,
Mesosome - Site of respiration (formed by the folding of the
plasma membrane),
Slime Capsule Protective physical barrier to predatory
protoctists, white blood cells or bacteriophages only found in
pathogenic bacteria,
Cell Wall - Provides structure,
Flagellum - Organelle of propulsion,
Cell Surface Membrane (plasmalemma) - Barrier between cell and
environment. Regulates transport of substances,
Plasmid Small self-replicating loops of DNA carrying 10-30
genes; enable resistance to antibiotics,
Naked Nucleic Acid (nucleoid) - Carries genetic material.
Pili allow bacteria to attach to other surfaces or other
bacteria
http://veja0.abrilm.com.br/assets/images/2011/5/38595/Escherichia-coli-surto-alemanha-20110530-size-598.bmp
Qd.
. The diagram shows a cholera bacterium. It has been magnified
50 000 times.
(a) Name
A.........................................................................................................
(1)
(b) Name two structures present in an epithelial cell from the
small intestine that are not present in a cholera bacterium.
1
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2
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(2)
Mostprokaryotes reproduce asexuallythrough a process called
binary fission. During binary fission, the single DNA molecule
replicates and the original cell is divided into two identical
cells.
Binary fission begins with the single DNA molecule replicating
and both copies attaching to the cell membrane.
Next, the cell membrane begins to grow between the two DNA
molecules. Once the bacterium just about doubles its original size,
the cell membrane begins to pinch inward.
A cell wall then forms between the two DNA molecules dividing
the original cell into two identicaldaughter cells.
2.3 Eukaryotic cells
2.3.1Draw and label a diagram of the ultrastructure of a liver
cell as an example of an animal cell.
http://ibguides.com/images/2.3.1.png
Annotate the diagram with the functions of each named
structure.
Ribosomes: Found either floating free in the cytoplasm or
attached to the surface of the rough endoplasmic reticulum and in
mitochondria and chloroplast. Ribosomes are the site of protein
synthesis as they translate messenger RNA to produce proteins.
Large 80s ribosomes are found in the cytoplasm and attached to
the RER, small 70S Ribosomes are found in the mitochondria and
chloroplasts.
Rough endoplasmic reticulum: Can modify proteins to alter their
function and/or destination. Synthesizes proteins to be excreted
from the cell and packages them into membrane bound vesicles.
Lysosome: Contains many digestive enzymes to hydrolyse
macromolecules such as proteins and lipids into their monomers.
Golgi apparatus: Receives proteins from the rough endoplasmic
reticulum and may further modify them. It also packages proteins
before the protein is sent to its final destination which may be
intracellular or extracellular.
Mitochondrion: Is responsible for aerobic respiration during
which chemical energy is converted into ATP using oxygen.
Nucleus: Contains the chromosomes and therefore the hereditary
material. It is responsible for controlling the activity of the
cell.
Qe.
Cholera bacteria are prokaryotic cells. Give three structures
found in prokaryotic cells but not in eukaryotic cells.
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3
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(3)
Identify structures in electron micrographs of liver cells.
http://ibguides.com/images/2.3.2.png
Figure 2.3.2 - Electron micrograph of an animal cell
Qf. (a) The diagram shows two organelles found in a eukaryotic
cell.
A B
(i) Name the organelles.
A
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B
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(1)
(ii) Explain how the inner membrane is adapted to its function
in organelle A.
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(2)
Compare prokaryotic and eukaryotic cells.
Prokaryotic cells have naked DNA which is found in the cytoplasm
in a region named the nucleoid. On the other hand, eukaryotes have
chromosomes that are made up of DNA and protein. These chromosomes
are found in the nucleus enclosed in a nuclear envelope.
Prokaryotes do not have any mitochondria whereas eukaryotes
do.
Prokaryotes have small ribosomes (70S) compared to eukaryotes
which have large ribosomes (80S).
In prokaryotes there are either no or very few organelles
bounded by a single membrane in comparison to eukaryotes which have
many of them including the Golgi apparatus and the endoplasmic
reticulum.
Qg.
Cell A is a eukaryotic cell. Give two features that may be found
in a prokaryotic cell which are not found in cell A.
1
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2
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(2)
State three differences between plant and animal cells.
Animal cells only have a plasma membrane and no cell wall.
Whereas plant cells have a plasma membrane and a cell wall.
Animal cells do not have chloroplasts whereas plant cells do for
the process of photosynthesis.
Animal cells store glycogen as their carbohydrate resource
whereas plants store starch.
Animal cells do not usually contain any vacuoles and if present
they are small or temporary. On the other hand plants have a large
vacuole that is always present.
Animal cells can change shape due to the lack of a cell wall and
are usually rounded whereas plant cells have a fixed shape kept by
the presence of the cell wall.
Outline two roles of extracellular components.
The plant cell wall gives the cell a structural strength and
prevents it from bursting under high pressure. It is made up of
cellulose arranged in groups called microfibrils, held together by
large numbers of Hydrogen bonds. It gives the cell its shape,
prevents excessive water up take by osmosis and is the reason why
the whole plant can hold itself up against gravity.
The animal cell contains glycoproteins in their extracellular
matrix which are involved in the support, movement and adhesion of
the cell.
1.3 Membranes
Draw and label a diagram to show the structure of membranes.
http://ibguides.com/images/2.4.1.png
Annotated drawing of a cell membrane
Explain how the hydrophobicand hydrophilic properties of
phospholipids help to maintain the structure of cell membranes.
Phospholipid molecules make up the cell membrane and are
hydrophilic (attracted to water) as well as hydrophobic (not
attracted to water but are attracted to other hydrophobic
tails).
They have a hydrophilic (polar) phosphate head and two
hydrophobic (non-polar) hydrocarbon tails.
Cell membranes are made up of a double layer of these
phospholipid molecules. This is because in water the hydrophilic
heads will face the water while the hydrophobic tails will be in
the centre because they face away from the water.
The phospholipid bilayer makes the membrane very stable but also
allows flexibility. The phospholipid in the membrane are in a fluid
state which allows the cell to change its shape easily.
List the functions of membrane proteins.
Membrane proteins can act as:
hormone binding sites
electron carriers
pumps for active transport
channels for passive transport
enzymes.
In addition they can be used for cell to cell communication as
well as cell adhesion.
Definediffusionandosmosis.
Diffusion is the passive movement of particles from a region of
high concentration to a region of low concentration, down a
diffusion gradient.
Osmosis is the passive movement of water molecules, across a
partially permeable membrane, from a region of lower solute
concentration to a region of higher solute concentration.
Qh. Oxygen and water move through plasma membranes into cells.
Describe two ways in which these movements are similar.
1
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2
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(2)
Explain passive transport across membranes by simple diffusion
and facilitated diffusion.
Membranes are partially-permeable which means that they allow
certain molecules through but not others.
The molecules can move in and out through passive transport
which is a method that does not require any input of outside energy
in the form of ATP.
It can either be done by simple diffusion or facilitated
diffusion.
Molecules will go from a region of high concentration to a
region of low concentration as they move randomly and eventually
become evenly distributed within the system if they are permeable
to the membrane. Simple diffusion involves the diffusion of
molecules through the phospholipid bilayer while facilitated
diffusion involves the use of specific channel proteins embedded in
the membrane.
The cell membrane is hydrophobic inside so hydrophobic (lipid
soluble) molecules will pass through by simple diffusion whereas
hydrophilic molecules and charged particles will use facilitated
diffusion.
Water moves through by osmosis which is also by passive
transport. Osmosis involves the movement of water molecules from a
region of low solute concentration, to a region of high solute
concentration. So if the solute concentration is higher inside the
cell than outside the cell, water will move in and vice versa.
Qi. Give two ways in which active transport is different from
facilitated diffusion.
1
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2
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(2)
Explain the role of protein pumps and ATP in active transport
across membranes.
Active transport involves the movement of substances through the
membrane using energy from ATP.
The advantage of active transport is that substances can be
moved against the concentration gradient, meaning from a region of
low concentration to a region of high concentration. This is
possible because the cell membrane has protein pumps embedded it
which are used in active transport to move substances across by
using ATP.
Each protein pump only transports specific substances so the
cell can control what comes in and what goes out.
Qj. The graph shows the effect of concentration on the rate of
uptake of magnesium ions by root hair cells.
(b) For curve Y name the process the cells are using to absorb
magnesium ions between concentrations A and B. Use information in
the graph to explain your answer.
Name of process
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Explanation
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(2)
Explain how vesicles are used to transport materials within a
cell between the rough endoplasmic reticulum, Golgi apparatus and
plasma membrane.
After proteins have been synthesized by ribosomes they are
transported to the rough endoplasmic reticulum where they can be
modified.
Vesicles carrying the protein then bud off the rough endoplasmic
reticulum and are transported to the Golgi apparatus to be further
modified .g. by adding carbohydrate or lipid fractions..
After this the vesicles carrying the protein bud off the Golgi
apparatus and carry the protein to the plasma membrane.
Here the vesicles fuse with the membrane expelling their content
(the modified proteins) outside the cell. The membrane then goes
back to its original state.
This is a process called exocytosis.
Endocytosis is a similar process which involves the pulling of
the plasma membrane inwards so that the pinching off of a vesicle
from the plasma membrane occurs and then this vesicle can carry its
content anywhere in the cell.
Qk.
The diagram shows part of an epithelial cell from an animals
gut.
This cell is adapted for the three functions listed below. Use
the diagram to explain how this cell is adapted for each of these
functions.
Use a different feature in the diagram for each of your
answers.
(i) the active transport of substances from the cell into the
blood
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(ii)the synthesis of enzymes
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(iii)rapid diffusion of substances from the lumen of the gut
into the cytoplasm
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(1)
Describe how the fluidity of the membrane allows it to change
shape, break and re-form during endocytosis and exocytosis.
The phospholipids in the cell membrane are not solid but are in
a fluid state allowing the membrane to change its shape and also
vesicles to fuse with it.
This means substances can enter the cell via endocytosis and
exit the cell via exocytosis. The membrane then returns to its
original state. In exocytosis the vesicles fuse with the membrane
expelling their content outside the cell. The membrane then goes
back to its original state. Endocytosis is a similar process which
involves the pulling of the plasma membrane inwards so that a
vesicle is pinched off it and then this vesicle can carry its
content anywhere in the cell.
1.5 The origin of cells
Cells can only be formed by division of pre-existing cells.
The first cells must have arisen from non-living material.
The origin of eukaryotic cells can be explained by the
endosymbiotic theory
The theory ofEndosymbiosisexplains the origin ofchloroplasts and
mitochondria and their double membranes.
This concept suggests that chloroplasts and mitochondriaare the
result of years of evolution initiated by theendocytosis of
bacteria and blue-green algae.
According to this theory, blue green algae and bacteriawere not
digested; they became symbiotic instead.
Endocytosisis when a substance gains entryinto a cell without
passing through its cell membrane.
A cell's plasma membrane folds in and fuses to lock foreign
material inside.
An intracellular vesicle is formed as a result.
The ribosomes of the inner structure (in chloroplasts and
mitochondria)resemble prokaryotic ribosomes.
C:\Users\JON\Downloads\download.jpg
1.6 Cell division
Outline the stages in the cell cycle, including interphase (G1,
S, G2), mitosis and cytokinesis.
The first stage of cell division is interphase which is divided
into 3 phases;
G1 - The cell cycle starts with G1 (Gap phase 1) during which
the cell grows larger.
S - S (synthesis) during which the genome is replicated.
G2. Finally, G2 (gap phase 2) is the second growth phase which
marks the end of interphase.
The fourth stage is mitosis which is divided into:
Prophase
Metaphase
Anaphase
Telophase.
During mitosis spindle fibres attach to the chromosomes by the
centromere and pull sister chromatids apart. This stage separates
the two daughter genomes.
Finally, cytokinesis is the last stage during which the
cytoplasm divides to create two daughter cells. In animal cells the
cell is pinched in two while plant cells form a plate between the
dividing cells.
Ql.
The diagram shows a cell cycle.
(a) The table shows the number of chromosomes and the mass of
DNA in different nuclei.
All the nuclei come from the same animal. Complete this
table.
Nucleus
Number of chromosomes
Mass of DNA / arbitrary units
At prophase of mitosis
26
60
At telophase of mitosis
From a sperm cell
(4)
Qm. A doctor investigated the number of cells in different
stages of the cell cycle in two tissue samples, C and D. One tissue
sample was taken from a cancerous tumour. The other was taken from
non-cancerous tissue. The table shows his results.
Percentage of cells in each stage of the cell cycle
Stage of the cell cycle
Tissue sample C
Tissue sample D
Interphase
82
45
Prophase
4
16
Metaphase
5
18
Anaphase
5
12
Telophase
4
9
(i)In tissue sample C, one cell cycle took 24 hours. Use the
data in the table to calculate the time in which these cells were
in interphase during one cell cycle. Show your working.
Time cells in interphase ......................................
hours
(2)
State that tumours (cancers) are the result of uncontrolled cell
division and that these can occur in any organ or tissue.
Tumours are formed when cell division goes wrong and is no
longer controlled, the cells replicate constantly. This process can
happen in any organ or tissue.
Qn. . (a) Boxes A to E show some of the events of the cell
cycle.
A Chromatids separate.
B Nuclear envelope disappears
C Cytoplasm divides
D Chromosomes condense and become visible
E Chromosomes on the equator of the spindle
(i) List these events in the correct order starting with D.
.......D....... ................. .................
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(1)
(ii) Name the stage described in box E.
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(1)
(b) Name the stage of the cell cycle during which DNA
replication occurs.
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(1)
(c) Scientists produced a model to show how chemotherapy works
in the treatment of cancer. The model is shown in the diagram.
(i) Explain the difference in curves A and B before chemotherapy
starts.
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(2)
(ii) Chemotherapy drugs must be given a number of times if the
treatment is to be successful. Use the diagram to explain why.
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(2)
(Total 7 marks)
State that interphase is an active period in the life of a cell
when many metabolic reactions occur, including protein synthesis,
DNA replication and an increase in the number of mitochondria
and/or chloroplasts.
Interphase is an active period in the life of a cell during
which many metabolic reactions occur such as protein synthesis, DNA
replication and an increase in the number of mitochondria and/or
chloroplast.
Describe the events that occur in the four phases of mitosis
(prophase, metaphase, anaphase and telophase).
Prophase: the spindle microtubules grow and extend from the
centriole, at each pole, to the equator. Also chromosomes condense
and become short and bulky and the nuclear envelope disappears.
Metaphase the chromosomes, pairs of chromatids, move to the
equator and the spindle microtubules from each pole attach to each
centromere on opposite sides.
Anaphase the spindle microtubules pull the sister chromatids
apart splitting the centromeres. This splits the sister chromatids
into chromosomes. Each identical chromosome is pulled to opposite
poles.
Telophase the spindle microtubules break down and the
chromosomes uncoil and so are no longer individually visible. The
nuclear membrane reforms. The cell then divides by cytokinesis to
form two daughter cells with identical genetic nuclei.
Explain how mitosis produces two genetically identical
nuclei.
Mitosis is divided into four stages; prophase, metaphase,
anaphase and telophase. During prophase, the chromosomes become
visible under a light microscope as they condense and therefore
they get shorter and more bulky. The nuclear envelope disintegrates
and the spindle microtubules grow and extend from each pole to the
equator. At metaphase the chromatids move to the equator. The
sister chromatids are two DNA molecules formed by DNA replication
and are therefore identical. These sister chromatids are then
separated in anaphase as the spindle microtubules attaches to
centromere and pulls the sister chromatids to opposite poles. As
the sister chromatids separate they are called chromosomes. This
means that each pole has the same chromosomes (same genetic
material). Finally the microtubules break down, the chromosomes
uncoil and the nuclear membrane reforms. The cell then divides into
two daughter cells with genetically identical nuclei.
Qo. The graph shows information about the movement of chromatids
in a cell that has just started metaphase of mitosis.
(i)What was the duration of metaphase in this cell?
minutes
(1)
(ii)Use line X to calculate the duration of anaphase in this
cell.
minutes
(1)
(iii)Complete line Y on the graph.
(2)
(c) A doctor investigated the number of cells in different
stages of the cell cycle in two tissue samples, C and D. One tissue
sample was taken from a cancerous tumour. The other was taken from
non-cancerous tissue. The table shows his results.
Percentage of cells in each stage of the cell cycle
Stage of the cell cycle
Tissue sample C
Tissue sample D
Interphase
82
45
Prophase
4
16
Metaphase
5
18
Anaphase
5
12
Telophase
4
9
(i)In tissue sample C, one cell cycle took 24 hours. Use the
data in the table to calculate the time in which these cells were
in interphase during one cell cycle. Show your working.
Time cells in interphase ......................................
hours
(2)
(ii)Explain how the doctor could have recognised which cells
were in interphase when looking at the tissue samples.
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(1)
(iii)Which tissue sample, C or D, was taken from a cancerous
tumour?
Use information in the table to explain your answer.
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(2)
State that growth, embryonic development, tissue repair and
asexual reproduction involve mitosis.
Growth, embryonic development, tissue repair and asexual
reproduction all involve mitosis.
Control of the Cell Cycle
Cyclinsare agroup of proteinsthat control the stages thecell
cycleby activatingcyclin-dependent kinase(Cdk)enzymes
Cyclins were originally named because their concentration varies
in a cyclical fashion during the cell cycle.
The changes in concentration of the cyclins, caused by
differences in cyclin gene expression and destruction, causes
fluctuations in Cdk activity to drive the cell cycle.
A cyclin forms a complex with Cdk, which activates the Cdk.
Complete activation also requires phosphorylation.
Complex formation results in activation of the Cdkactive
site.
Cyclins themselves have no enzymatic activity but have binding
sites for some substrates and target the Cdks when at specific
locations within the cell
Cyclins, are responsible for specific events during cycle
division such asmicrotubuleformation.
Cyclins can be divided into four classes based on their
behaviour in the cell cycle:
G1/S cyclins, begins the initial DNA replication
S cyclins, The levels of S cyclins remain high throughout S
phase, G2 and early mitosis. Starting early events in mitosis.
M cyclins, the destruction of M cyclins during metaphase and
anaphase, causes the end of mitosis and cytokinesis
G1 cyclins. The presence of G cyclins coordinate cell growth and
the start of a new cell cycle
C:\Users\JON\Documents\Cyclins_White_Updated.png
Regulation at Internal Checkpoints
It is essential that the daughter cells are exact duplicates of
the parent cell.
Mistakes in the duplication or distribution of the chromosomes
lead tomutationsthat may be passed forward to every new cell
produced from an abnormal cell.
To prevent a compromised cell from continuing to divide,
internal control mechanisms operate at three main cell cycle
checkpoints.
A checkpoint is one of several points in the eukaryotic cell
cycle at which the progression of a cell to the next stage in the
cycle can be halted until conditions are favourable (e.g. the DNA
is repaired). These checkpoints occur;
near the end of G1,
at the G2/M transition,
during metaphase .
https://figures.boundless.com/18890/full/figure-10-03-01.jpe
Internal Checkpoints During the Cell Cycle
The integrity of the DNA is assessed at the G1 checkpoint.
Proper chromosome duplication is assessed at the G2
checkpoint.
Attachment of each centromere to a spindle fibre is assessed at
the M checkpoint.
The G1Checkpoint
The G1checkpoint determines whether all conditions are
favourable for cell division to proceed.
The G1checkpoint is a point at which the cell irreversibly
commits to the cell division process.
External influences, such asgrowth factors, play a large role in
carrying the cell past the G1checkpoint. The cell will only pass
the checkpoint if it is an appropriate size and has adequateenergy
reserves.
At this point, the cell also checks for DNA damage.
A cell that does not meet all the requirements will not progress
to the S phase.
The cell can halt the cycle and attempt to remedy the problem,
or the cell can advance into G0(inactive) phase and await further
signals when conditions improve.
If a cell meets the requirements for the G1checkpoint, the cell
will enter S phase and beginDNA replication.
This transition, as with all of the major checkpoint transitions
in the cell cycle, is signalled bycyclinsand cyclin dependent
kinases (CDKs).
Cyclins are cell-signallingmoleculesthat regulate the cell
cycle.
The G2Checkpoint
The G2checkpoint prevents entry into themitotic phaseif certain
conditions are not met e.g. cell size and protein reserve
levels.
However, the most important role of the G2checkpoint is to
ensure that all of the chromosomes have been accurately replicated
without mistakes or damage.
If the checkpoint mechanisms detect problems with the DNA, the
cell cycle is halted and the cell attempts to either complete DNA
replication or repair the damaged DNA.
If the DNA has been correctly replicated, cyclin dependent
kinases (CDKs) signal the beginning of mitotic cell division.
The M Checkpoint
The M checkpoint occurs near the end of the metaphase stage of
mitosis.
The M checkpoint is also known as thespindle checkpointbecause
it determines whether all thesister chromatidsare correctly
attached to the spindle microtubules.
Because the separation of the sister chromatids during anaphase
is an irreversible step, the cycle will not proceed until the
centromeres of each pair of sister chromatids are firmly anchored
to at least two spindle fibres arising from opposite poles of the
cell.
Severe defects in chromosomes block progression through the cell
cycle, and can lead to cell suicide, orapoptosis.
In addition, cells have afinite lifespan,and at some point are
no longer able to divide.
Cancer
Cancers are diseases in which there is adefect in the regulation
of the cell cycle.
Cancer cells are cells that divide slowly but constantly and
which no longer are controlled by the mechanisms listed above.
Cancer cells can form tumours due to this unchecked growth.
Cancers are caused by geneticmutations.
Sometimes these mutations are found in thegermline,and result in
inherited cancers or a predisposition to cancer.
Most often these mutations are found in somaticcells.
Somatic mutations accumulate over our lifetime.
Cancers are caused bymultiplegenetic mutations.
Except in rare cases, cancer cells have accumulated a number of
mutations.
Three classes of genesare involved in cancer:
Oncogenes,
Tumour suppressor genes,
DNA repair genes.
Proto-oncogenes (unmutated oncogenes) stimulate cell division in
a regulated manner.
Proto-oncogenes produce growth factors, growth factor receptors,
and cyclins.
Oncogenesare mutated forms of these genes that result in
unregulated stimulation of cell division.
Tumour suppressor genesprevent cell division.
Mutations in tumour suppressor genes result in the loss of this
prevention of cell division.
DNA repair genespromote repair of mutations that occur during
the cell cycle.
Loss of DNA repair genes results in the accumulation of many
mutations within a cell.
The effect of proto-oncogenes, oncogenes, and tumour suppressor
genes on cell division.
http://biology.kenyon.edu/courses/biol114/Chap07/oncogenes-tumorsup.gif
Diagram showing the location of cancer causing genes in the
human
genomehttp://biology.kenyon.edu/courses/biol114/Chap07/humanchr.gif
Q1.The photograph shows part of the cytoplasm of a cell.
(a)(i)Organelle X is a mitochondrion.
What is the function of this organelle?
..............................................................................................................
..............................................................................................................
(1)
(ii)Name organelle Y.
..............................................................................................................
(1)
(b) This photograph was taken using a transmission electron
microscope. The structure of the organelles visible in the
photograph could not have been seen using an optical(light)
microscope. Explain why.
.......................................................................................................................
.......................................................................................................................
.......................................................................................................................
.......................................................................................................................
(2)
(Total 4 marks)
Q2. An amoeba is a single-celled, eukaryotic organism.
Scientists used a transmission electron microscope to study an
amoeba. The diagram shows its structure.
(a)(i) Name organelle Y.
..............................................................................................................
(1)
(ii)Name two other structures in the diagram which show that the
amoeba is a eukaryotic cell.
1
............................................................................................................
2
.........................................................................................................
(b) What is the function of organelle Z?
.......................................................................................................................
.......................................................................................................................
.......................................................................................................................
(1)
(c) The scientists used a transmission electron microscope to
study the structure of the amoeba.
.
(2)
(Total 6 marks)
Q3. The flowchart shows how chloroplasts may be obtained from
leaves.
Leaves homogenised by grinding in cold buffer solution
Homogenised leaves filtered. Filtrate centrifuged at low
speed
Pellet A
Supernatant centrifuged
at high speed
Pellet B containing chloroplast
Supernatant C
(a) In the first step in this procedure, the leaves were
homogenised by grinding in cold buffer solution. Explain why
(i) the leaves were homogenised,
.............................................................................................................
.............................................................................................................
(1)
(ii) a buffer solution was used.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(2)
(b) The table shows some of the organelles present in the leaf
cells.
Organelle
X
Y
Z
Fraction containing organelle
(i) Complete the table to show in which of pellet A, pellet B or
supernatant C you would expect to find each of these
organelles.
(2)
(ii) Organelle X is found in large numbers in cells which take
up substances by active transport. Explain why.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(2)
(Total 7 marks)
Q4. Liver was ground to produce a homogenate. The diagram shows
how fractions containing different cell organelles were produced
from the filtered homogenate.
(a) Explain why the homogenate was filtered before spinning at
low speed in the centrifuge.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
(b) The main organelles present in sediment B were mitochondria.
Suggest the main organelles present in
(i) sediment A;
.............................................................................................................
(1)
(ii) sediment C.
.............................................................................................................
(1)
(c) What property of cell organelles allows them to be separated
in this way?
......................................................................................................................
......................................................................................................................
(1)
(d) Explain why the organelles in sediment C could be seen with
a transmission electron microscope but not with an optical
microscope.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
(Total 7 marks)
Q5. The diagram shows part of a plasma membrane. The arrows show
the path taken by sodium ions and by substance X when they diffuse
through the membrane into a cell.
(a) An optical microscope cannot be used to see a plasma
membrane. Explain why.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
(b) Give one property of the molecules of substance X which
allows them to diffuse through the membrane at the position
shown.
......................................................................................................................
......................................................................................................................
(1)
(c) The effect of the concentration of sodium ions in the
surrounding solution on their rate of diffusion across the membrane
was investigated. The graph shows the results.
(i) What limits the diffusion of sodium ions across the membrane
between
A and B on the graph? Give the evidence for your answer.
Limiting factor
.....................................................................................
Evidence
.............................................................................................
.............................................................................................................
(2)
(ii) Explain the shape of the curve between C and D.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(2)
(Total 7 marks)
Q6. Read the following passage.
The plasma membrane plays a vital role in microorganisms. It
forms a barrier between the cell and its environment, controlling
the entry and exit of solutes. This makes bacteria vulnerable to a
range of antiseptics and antibiotics
When bacteria are treated with antiseptics, the antiseptics bind
to the proteins in the membrane and create tiny holes. Bacteria
contain potassium ions at a concentration many times that outside
the cell. Because of the small size of these ions and their
concentration in the cell, the first observable sign of antiseptic
damage to the plasma membrane is the leaking of potassium ions from
the cell.
Some antibiotics damage the plasma membrane in a similar way.
One of these is tyrocidin. This is a cyclic polypeptide consisting
of a ring of ten aminoacids. Tyrocidin and other polypeptide
antibiotics are of little use in medicine.
Other antibiotics also increase the rate of potassium movement
from cells. It is thought that potassium ions are very important in
energy release and protein synthesis, and a loss of potassium ions
would lead to cell death.
Gramicidin A coils to form a permanent pore passing through the
plasma membrane. This pore enables potassium ions to be conducted
from the inside of the cell into the surrounding medium.
Vanilomycin also facilitates the passage of potassium ions from
the cell. A molecule of vanilomycin forms a complex with a
potassium ion and transports it across the membrane. The potassium
ion is released on the outside and the vanilomycin is free to
return and pick up another potassium ion. Vanilomycin depends on
the fluid nature of the plasma membrane in order to function.
Polyene antibiotics have flattened ring-shaped molecules. The
two sides of the ring differ from each other. One side consists of
an unsaturated carbon chain. This part is strongly hydrophobic and
rigid. The opposite side is a flexible, strongly hydrophilic
region. It has been shown that polyene antibiotics bind only to
sterols. Sterols are lipids found in the membranes of eukaryotes
but not in the membranes of prokaryotic organisms. It is thought
that severalsterol-polyene complexes come together. The plasma
membranes of eukaryotic cells treated
with these polyene antibiotics lose the ability to act as
selective barriers and small ions and molecules rapidly leak
out
Use information in the passage and your own knowledge to answer
the questions.
(a) (i) By what process do potassium ions normally enter a
bacterial cell? Explain the evidence for your answer.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(2)
(ii) Use Ficks law to explain why leakage of potassium ions
occurs following antiseptic damage to the plasma membrane (lines 7
- 8).
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(2)
(b) (i) Draw a peptide bond showing how the COOH group of one
amino acid joins to the NH2 group of another.
(1)
(ii) How many peptide bonds are there in a molecule of tyrocidin
(lines 9 - 10)?
.............................................................................................................
(1)
(c) Experiments have shown that vanilomycin is unable to
transport potassium ions across a membrane when it is cooled.
Gramicidin A continues to facilitate the movement of potassium ions
at these low temperatures. Explain these results.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(3)
(d) Draw a simple diagram of one of the phospholipid layers to
show how polyene antibiotics allow small ions and molecules to leak
rapidly through a plasma membrane. Use the following symbols to
represent the different molecules.
Note that the zigzag line on the symbol for the polyene
antibiotic represents its hydrophobic region.
(2)
(Total 11 marks)
Q7. The thyroid gland is an organ in the neck. The diagram shows
the process in which epithelial cells from the thyroid gland make
and secrete a protein called thyroglobulin.
(a) Name
(i) organelle A;
.............................................................................................................
(1)
(ii) the process by which thyroglobulin is secreted from the
cell at C.
.............................................................................................................
(1)
(b) (i) Describe the part played by the organelles labelled
B.
.............................................................................................................
.............................................................................................................
(1)
(ii) Organelle B is very small. It cannot be seen when thyroid
cells are examined with an optical microscope but it can be seen
with an electron microscope. Explain why this organelle can be seen
with an electron microscope.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(2)
(Total 5 marks)
Q8. A scientist investigated the effect of cyanide on the uptake
of sodium ions by animal tissue.
He set up two beakers, J and K.
He put equal volumes of a solution containing sodium ions and equal
masses of an animal tissue in each beaker.
He added cyanide to beaker J.
He did not add cyanide to beaker K.
He measured the concentration of sodium ions remaining in the
solution in each beaker, for
80 minutes. The graph shows his results.
(a) Calculate the rate of uptake of sodium ions by the tissue in
beaker K for the first
30 minutes. Show your working.
Answer ........................... arbitrary units per
minute
(b) Adding cyanide affects the uptake of sodium ions by the
tissue. Use the graph to
describe how.
.......................................................................................................................
.......................................................................................................................
.......................................................................................................................
.......................................................................................................................
.......................................................................................................................
(2)
(c) Cyanide is a substance which affects respiration.
Use information in the question to explain the effect of cyanide on
the uptake of
sodium ions by the tissue.
.......................................................................................................................
.......................................................................................................................
.......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(3)
(Total 7 marks)
Qa. \\GBO-IA-RODC01\Users\jon.whitlow\My
Pictures\imagesCAFX67S3.jpg
Qb. (i) Higher resolution/higher (maximum)
magnification/higher
detail (of image);
OR
Allows internal details/structures within (cells) to be
seen/cross section to be taken;
1
(ii) Thin sections do not need to be prepared/shows surface
of
specimen/can have 3-D images;1
Qc. Large (surface) area;
For diffusion;
or
Short distance to centre of cell;
For diffusion;(2max)
Qd.
(a) (Plasma/cell) membrane;
Reject: nuclear membrane
1
(b) Nucleus/nuclear envelope/nuclear membrane/nucleolus;
Accept: membrane-bound organelles only if an example has not
been given
Mitochondrion;
(Smooth/rough) ER;
Lysosome;
Golgi;
Linear/non-circular DNA/chromosome;
80S/denser/heavier/larger ribosomes;
2 max
Qe.Capsule/glycocalyx/slime layer;
Circular/ring of/non-linear DNA/DNA without proteins;
Plasmid;
Flagellum;
Pilus;
70s ribosomes;(2max)
Qf. Mitochondrion
Nucleus
Large surface are over which reactions can occur
Qg. See question (e)
Qh. Passive/do not require energy/ATP;
Movement down a concentration gradient / by diffusion;
Go through phospholipid (bilayer) / not by protein/carriers;
2 max
Qi.1. Uses energy / ATP;
2. Against concentration gradient / low to high
concentration;
3. Does not use channel proteins / only uses carrier
proteins;
2 max
Qj. Active transport;
1
Occurs when oxygen present because energy/respiration
required,
or against a concentration gradient because there is no uptake
in
curve Z;
1
Qk. 1. Mitochondria respire;
2. Release energy / produce ATP;
2.Do not credit make energy
3. Transport against gradient;
OR
4. Infolding of membrane;
5. Increases area;
6. More proteins for active transport;
2 max
(ii)1. Ribosomes make proteins / enzymes;
2. Enzymes are proteins;
OR
3. Mitochrondria respire;
4. Release energy/produce ATP;
5. (Energy / ATP) for protein / enzyme synthesis;
2
(iii)Microvilli increase area / have large area;
1
Ql.
Nucleus
Number of chromosomes
Mass of DNA/arbitrary units
At telophase of mitosis
26;
30;
From a sperm cell
13;
15;
4
Qm. (i)18;
(ii)10;
1
Qn. (a) (i) (D) B E A C;
1
(ii) Metaphase;
1
(b) Interphase/S phase;
1
(c) (i) Healthy cells not dividing so number stays
constant;
Cancer cells dividing (uncontrollably) so increasing in number;
2
(ii) Drug only kills some cancer cells;
These continue to divide;
2
Qo.(i)18;
1
(ii)10;
1
(iii)1. Horizontal until 18 minutes;
2. (Then) decreases as straight line to 0 m at 28 minutes;
2
(c)(i)Two marks for correct answer of 19.68 or 19.7;;
One mark for incorrect answers in which candidate clearly
multiplies by 0.82;
2
(ii)1. No visible chromosomes / chromatids;
2. Visible nucleus;
1 max
(iii)D (no mark)
1. Lower % (of cells) in interphase / higher % (of cells) in
mitosis / named stage of mitosis;
2. (So) more cells dividing / cells are dividing quicker;
2
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