1 What are the specific roles of each of the following organelles when deployed in the synthesisof a specific protein destined for discharge from the cell?a nucleus
b RER
c Golgi apparatus
d vesicle
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2 The following is an account of an investigation of development of a multicellular organism.The experiment was conducted before the nature of stem cells was understood. Read the textand then fill in the blanks, using the most appropriate term from this list:
genome in vitro stem cells embryomedium totipotent genes zygotenutrients expressed
How do we know that all cells in an adult, multicellular organism retain the same genes
throughout life, identical with those of the single cell (__________) from which that
individual originally grew, as a product of sexual reproduction?
This was first demonstrated by F.C. Steward and co-workers, at Cornell University, USA, in
the 1950s, working with plants. This team found that a mature cell (it was a parenchyma cell
obtained from carrot root tissue) could be dislodged, isolated, and then cultured in an
appropriate liquid nutrient medium. To be successful, this __________ contained not only
essential __________, but also certain plant growth substances.
Each isolated cell not only survived, but started to divide and form an aggregate of living
cells. These cells then formed an embryonic plant with a root (radicle), stem (plumule), and
embryonic leaves (cotyledons). This occurred when cultured in glass apparatus (__________),
when supplied with nutrients and growth factors. Further, this isolated __________ then
developed into an entire, mature plant, also in vitro.
The conclusion of this experiment was that the cells of an organism, from first formed till last,
had the same __________. During the life an organism, different __________ of the total
complement are activated (we say they are __________), and responsible for development
whilst other genes are temporarily inactive. In effect, genes are selectively active as the zygote
develops into an embryo, and then the embryo grows into an adult.
4 Male and female mammalian gametes are specialised cells, but are different in formation,structure and behaviour. Complete the table of possible features of sperms and eggs by placinga tick (✓) or cross (✗) as appropriate.
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Feature Sperm Egg
adapted for swimming motion
has a haploid nucleus
carries an organelle packed with hydrolytic enzymes
cytoplasm contains cortical granules
has region packed with mitochondria
surrounded by jelly coat and follicle cells
largest dimension less than 10 μm
largest dimension more than 10 μm
5 Explain the difference between a tissue, an organ and an organ system by reference to aspecific example.
7 a Draw a labelled diagram showing the distinctive structural features of a bacterium.
b Detail how a mammalian liver cell differs from a bacterium in terms of size, geneticmaterial and organelles, by completing the table.
Liver cell Feature Bacterial cell
size
genetic material
organelles
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8 Our knowledge of ultrastructure of animal cells is based on interpretation of images obtainedfrom thin sections of tissue examined by electron microscopy.a Explain why cells from an animal tissue require the following treatments, prior to
examination by the transmission electron microscope:i killing and fixing
b The diagram below is of a mammalian liver cell. Identify the structures labelled A–E.
AB
E
D
C
A _______________________ B _______________________
C _______________________ D _______________________
E _______________________
c The magnification of the above image of a liver cell is �1800. What is the length of thiscell in μm (microns)? Show your workings.
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9 a During prophase of mitosis in an animal cell, what changes occur to the followingstructures?i chromatin
ii nuclear membrane
iii centrioles
b How do the structure, position and behaviour of the chromosomes differ during metaphaseand anaphase of mitosis?
Structure:
Position and behaviour:
c Identify the particular tissue of a named organism that you would select to observe stagesin mitosis, and state why.
d Outline the steps by which the tissue selected in part c above is prepared for microscopicexamination of stages in mitosis.
e When preparations showing stages in mitosis are examined under the microscope, thenumbers of cells observed in the four phases varies consistently. For example, most arefound to be at prophase and fewest at anaphase. How can this difference be bestexplained?
10 a What do you understand by the term ‘genetic variation’?
b Explain how independent assortment arises in meiosis.
c When does crossing over occur in the process of meiosis and how does it contribute togenetic variation?
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11 a Define ‘fertilisation’.
b The events leading to fertilisation in flowering plants commence after pollen has reachedthe stigma. Answer the questions below concerning the steps involved in fertilisation ofthe egg cell in an ovule.i How does the germinating pollen grain deliver its male nuclei to the embryo sac?
ii There are two male nuclei delivered to the embryo sac. Describe the fate of bothnuclei, separately, together with the specific products of this double fertilisation event.
c The process of fertilisation in the mammal commences with the arrival of one or moresperms at the secondary oocyte. Answer the questions below concerning the stepsinvolved in fertilisation of the oocyte.i Where does fertilisation occur within the female?
ii How is the jelly coat outside the oocyte penetrated?
iii Once the head of a sperm has penetrated the oocyte plasma membrane, how is entryof a further sperm nucleus prevented?
d Explain the importance of fertilisation in sexual reproduction.
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12 a Stem cells occur at some stage in all multicellular organisms. Explain what the term ‘stemcell’ means.
b In the life cycle of the mammal, some stem cells are described as ‘embryonic’ and some as‘adult’. Establish the differences between ‘embryonic’ and ‘adult’ stem cells, in terms of:i where they are found
c In stem cell research, these cells have often been obtained from ‘spare embryos’, madeavailable in the process of human infertility treatments involving fertilisations outside thebody (IVF). Explain how it is now possible to obtain embryonic stem cells from earlyembryos without destruction of the embryo’s potential for further development andimplantation.
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13 Read the following excerpt from a newspaper report and discussion of a development in thesearch for new sources of stem cells, achieved by two separate research teams from Japan andthe United States. Then answer the questions by reference to the source and in the light ofyour own understanding and views.
The creation of stem cells of the most versatile type without destroying human embryos hasbeen hailed by scientists and religious groups as an ethical breakthrough. A shortage ofgood-quality human embryos has so far restricted the number of ES cell lines available toscientists.
The new technique involves the following steps:
1 skin fibroblasts are taken from the adult donor
2 four of the genes in these cells are altered by infecting the cell with a retrovirus
3 one in 5000 of the infected cells becomes re-programmed to behave as if it were anembryonic stem (ES) cell.
Once perfected, the technique would allow scientists to take skin cells from patients withconditions such as diabetes, spinal paralysis or Parkinson’s, and turn them into stem cells.These could then be grown into ‘spare part’ tissue, which could be transplanted without fearof rejection by the body’s immune system.
The moral significance of the new technique for making powerful master cells withoutembryos, however, has been exaggerated. Whilst it is indeed a remarkable advance, its trueworth is not ethical but practical.
Previous studies of ES cells have been fundamental to the achievements of the Japanese andUS teams. Without examining the biological characteristics that give ES cells their hithertounique ability to form every kind of human tissue, neither team would have discovered howto turn back the clock on adult cells to give them similar properties. Therapies based on the
new induced pluripotent cells will not have involved the direct destruction of embryos, butthey will ultimately owe their origins to ES cell research.
Plenty more research with ES cells will be needed if induced pluripotent cells are to becometherapeutically useful. These are not quite identical to ES cells, and further study will have todetermine whether the differences are important to their behaviour. The technique also risksinducing tumours, and will have to be refined before transplants can be attempted safely.
adapted from ‘Breakthrough as stem cells are produced from skin not embryos’ and ‘Avaluable development, but moral case is exaggerated’ by Mark Henderson, in The Times,
Wednesday 21 November, 2007, page 4.
a Explain why a retrovirus might be used in order to genetically ‘re-programme’ cells (line 7).
b How can you account for the estimate that only one in 5000 of the ‘infected’ cells is likelyto be reprogrammed (line 8)?
c Explain why in this circumstance the new ES cells could be used without ‘fear of rejection’(line 12).
d Why is the real value of this advance seen as ‘not ethical but practical’ (line 16)?
e It is stated that the ‘technique also risks inducing tumours’. Why is this so (line 26)?
f Outline two points or issues you might develop in a discussion of the ethics of stem cellresearch, speaking in favour of using cells obtained in this way, despite its dependence onearlier research involving spare embryos.
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14 a Genes control development. What do you understand by ‘gene regulation’?
b Outline how the presence of the metabolite lactose activates a particular gene regulatormechanism in prokaryotes.
c Outline the reasons why the gene regulation mechanisms in eukaryotes are necessarilymore complex.
