topic 2 q's Flashcards
why do gram positive and gram negative bacteria react differently to some antibiotics
- gram positive bacteria have a thicker peptidoglycan cell wall
- the antibiotic does not pass through the layer hence harder to treat
- some enzymes inhibit formation of peptidoglycon so are effective
why are viruses not affected by antibiotics
- viruses cannot be killed
- viruses do not have a cell so antibiotics cannot pass through
why is there a delay before the number of lysed cells start to increase
- virus enters host cell so DNA of virus enters
- DNA is synthesised
- transcription and translation occur
- new viruses are assembled
why is an electron microscope used
- greater resolution
- smaller wavelength
describe the lytic cycle of a virus
- once virus enters host cell, its DNA is replicated immediately, independently of the host cell DNA
- eventually host cell bursts and cell lysis occurs
what is meant by latency
- virus is not disease causing
- virus is replicated each time host cell divides
what happens to cells in the body when they have taken up a virus
- viral RNA is made
- viral capside is made
- viruses are assembled
evaluate ethical implications of using untested drugs
- using untested drugs may worsen the situation rather than better it due to side effects that could occur
- it will also be difficult to decide who gets drug first whether this is health workers or local people
- using untested drugs is not ethical under any circumstances as the drugs have not completed full human trials
- new drug is unlikely to affect other people
compare and contrast the structure of a bacterial cell with the structure of HPV
- both contain DNA
- HPV is surrounded by a protein capsid and chlamydia by peptidoglycan
- HPV is hollow and chlamydia has a cell membrane
Animals infected with stealth spheres develop gastroenteritis very quickly and with severe
symptoms.
Animals infected with individual noroviruses develop gastroenteritis more slowly and with
less severe symptoms. Why?
- more viruses are delivered
- sphere can pass through cell membrane without binding to any cell
- the sphere protects viruses from enzymes
explain how targeting the stealth sphere could be used to treat
these infections
- lipids in sphere could be targeted
- hence destroying the virus
what happens to RNA viruses when inside a host cell
- used in translation to make viral protein
- more RNA is produced
describe the methods used to prevent the spread of Ebola
- isolation of patients infected
- wear face covering when leaving house to avoid coughing in open space (no droplets)
- rapid identification of disease
- identify who may have been in contact with the infected individual and isolate them
describe the lytic cycle of a virus
- virus attaches to host cell
- viral DNA is immediately replicated, independently of the host cell
- lysis of host cell
why can antibiotics not be used to treat viruses
- viruses are not living cells
- antiviral drugs used because they inhibit virus replication
what is the role of glycoproteins
- attach to virus molecules on the epithelial cells
why are radioactive nitrogen, oxygen & carbon not used in experiments
they are already present in DNA
why are viruses dependant on living cells
- they cannot replicate themselves
- as they do not have appropriate organelles
Explain why crossing over between two different genes, located on a pair of homologous
chromosomes, results in a maximum of 50% of gametes with the recombinant alleles.
- in prophase 1, chromosomes condense with 2 chromatids joined at the centromere and crossing over occurs.
- In anaphase 1, one chromosome from each pair moves to opposite ends of the cell.
- Each chromosome contains half the number of chromosomes.
- Hence why there is 50% of gametes with recombinant alleles.
- However, crossing over does not always occur so it can be less than 50%
Explain how meiosis results in genetic variation in the gametes.
- chromatids cross over
- chromosomes line up on equator and independent assortment occurs
- in anaphase 1 chromosomes move to opposite ends of the cell and contains half the number of chromosome
describe the events that take place during metaphase of mitosis
- chromosomes line up on the equator
- they are attached by the centromere to the spindle fibres
explain the role of centrioles in the sperm cells following fertilisation
- act as a source of centrioles for the zygote
- so that spindle fibres can be synthesised in the zygote
- so that the fertilised egg cell can divide by mitosis
describe how the process of fertilisation results in the formation of a zygote from the gametes in humans
- tip of acrosome touches surface of the egg cell
- acrosome reaction is triggered
- 2nd meiotic division is complete
- cortical reaction occurs
- fusion of sperm with genetic material of ovum
- low sperm count
- structural defects of sperm cells
- absence of an acrosome
- mutations in the mitochondrial DNA
- chromosome mutations
Comment on how each of these five factors could result in male infertility.
- fewer sperm reduces the likelihood of fertilisation occurring
- not enough enzymes for fertilisation
- defect in head may prevent sperm from penetrating to egg cell
- defect in flagellum could affect motility
- mid-piece defects would affect the energy in the sperm - may not be able to swim to egg cell
- sperm would not be able to digest through the outer layer of egg cell
- therefore genetic material won’t be released inside the egg
- less energy available to flagellum
- without energy sperm cannot swim through female
- could result in too much or too little genetic information being passed on
- cell division may be affected
when are oocytes produced in a female human
during pregnancy, before birth
state one structural difference between a spermatid and mature spermatozoon
- spermatids do not have a flagellum
explain why men with azoospermia are infertile
Men with this condition produce semen that contains spermatids instead of mature
spermatozoa
- because there is no flagellum, the spermatids are unable to swim to the egg
- spermatids are hence unable to penetrate the egg
(iii) Infertility caused by azoospermia can be treated by using intracytoplasmic sperm
injection (ICSI).
This procedure injects a single spermatid directly into an ooctye.
One concern about this procedure is that it uses selected spermatids. This
eliminates the normal competition between sperm that precedes fertilisation.
Explain the advantage of competition between sperm
- fittest sperm cell will fertilise the oocyte
- advantageous alleles passed on
describe two ethical implications of the use of ICSI
- interference with natural process
- embryo may be abnormal due to lack of competition
explain the importance of DNA replication during the development of a zygote into a blastocyst
- zygote divides by mitosis to form blastocyst
- identical copies of DNA are made
- all cells in the blastocyst will be diploid
- when mitochondria divide they will have a copy of the DNA
Explain why mutations in nuclear DNA can be inherited from either the mother or the father
whereas mutations in mtDNA are only inherited from the mother
mtDNA - mithochondrial DNA
- nuclear DNA is inherited from both mother and father due to their gametes containing DNA
- mitochondrial DNA is only present in the female gamete
Describe how the products of oogenesis differ from the products of spermatogenesis in mammals
- ova are larger cells
- spermatozoa contain an acrosome whereas ova do not
- spermatozoa have tails, ova do not
- the number of spermatozoa produced is much larger than the ova as there is only one
- oogenesis produces polar bodies
explain the significance of mitosis in stage 1 of spermatogenesis
- to produce several diploid primary spermatocytes
- so that lots of sperm can be produced from a single spermatogonium
explain the events that take place in meiosis 1 of spermatogenesis that result in genetic variation
- crossing over occurs in prophase 1
- new combinations of alleles on a chromatid are produced
- independent assortment occurs in metaphase 1
- this increases the combination of chromosomes in each daughter cell
compare and contrast the products of stage 2 and stage 3 in spermatogenesis with the products from these stages in oogenesis
- both produce haploid cells from diploid cells
- stage of spermatogenesis results in 2 spermatocyte but only one oocyte produced in oogenesis
- stage 3 results in 4 spermatids but one ovum
- polar bodies produced in oogenesis
explain the importance of acrosome that develop in stage 4
- contain enzymes
- to enable the sperm to digest through the membrane of the secondary oocyte
explain how meiosis produces new combinations of alleles in gametes
- crossing over occurs
- DNA is swapped between homologous chromosomes
- independent assortment
- as there is random movement of homologous chromosomes to poles
describe the process of spermatogenesis
- germ cells divide by mitosis to form primary spermatocytes
- these undergo first meiotic cell division to produce secondary spermatocytes
- 2nd meiotic cell division results in formation of spermatids
- spermatids mature into spermatozoa
describe the process of double fertilisation in flowering plants
- one male nucleus fuses with two polar nuclei
- a triploid 3n nucleus is formed
- a diploid zygote is formed
devise an investigation to determine the effect of pH on the rate of growth of pollen tubes
- test at least 5 different pH values
- add sucrose solution
- measure length of pollen tube every 10 minutes
- measure using a staged micrometer and calibrated graticule
- calculate rate of growth (length / time)
- control the temperature
- repeat at each pH and calculate a mean
why did the student plot standard deviation bars on the graph
- shows variation from the mean
- hence gives an indication of significant difference
The styles of some plants secrete RNAase enzymes when pollen from the same flower germinates on the stigma.
Explain how these RNAase enzymes affect the growth of the pollen tube.
- enzymes digest the mRNA
- this prevents translation
- hence pollen tube growth is preventede
explain the role of double fertilisation in flowering plants
- one male nucleus fuses with 2 polar nuclei
- a triploid endosperm is formed
- one male nucleus fuses with the female gamete nucleus
- this produces the diploid zygote
describe the role of enzymes in the growth of the pollen tube
- enzymes digest the tissue of the style
- this provides nutrients needed for pollen tube growth
- allows the pollen tube to enter the ovule
