Bio topic 3 - Voice of the Genome

Q1. (ii) Analyse the graph to explain the route taken by these amino acids within the pancreatic cells (4)

Polypeptide chain formed on the rER
Proteins transferred from rER to Golgi in vesicles
Proteins modified inside Golgi
Packaged into vesicles by Golgi

Q2. Describe three structural differences between prokaryotic and eukaryotic cells (3)

Prokaroytic cells have smaller ribosomes than eukaryotic
DNA in prokaryotic is circular, DNA in eukaryotic is linear
Prokaryotes have plasmid, Eukaryotes don’t

(b) Explain what is meant by the term molecular phylogeny (3)

Comparing molecular differences in DNA / RNA / Ribosome size in proteins / aa sequences to study evolutionary relationships between organisms / find closely related species

c) (i) Using information from this table, give evidence that supports Woese’s conclusion that Archaea are distinct from both the Bacteria and Eukaryota (2)

Archaea are distinct because they have Branched hydrocarbon chains instead of unbranched
They have a different no. of protein molecules in RNA polymerase

Q6. Describe the features shown in the photograph that allow this structure to be identified as a nucleus (3)

Contains nuclear envelope
Contains nuclear pores
Contains nucleolus

Q3. Describe how DNA is organised in a bacterial cell (3)

Large circular DNA
DNA not associated with histone proteins
Contains small plasmids
Located in cytoplasm not nucleus

Q5. Describe what happens to lysosomes once their contents have been digested (2)

Lysosome fuses with cell surface membrane
Contents released from cell by exocytosis

Q6. Describe how scientists could have determined that P. falciparum is a eukaryotic organism and not a prokaryotic organism (4)

Larger ribosomes (80S) than prokaryotic (80S)
Linear DNA instead of circular
No plasmids
Contains membrane-bound organelles

Q13. Explain why the nucleus can’t be observed at the end of prophase in a eukaryotic cell (2)

Nuclear membrane broken down because DNA is condensed into individual chromosomes

Q14. (i) Give 2 functions of the Golgi apparatus (2)

To package proteins into vesicles
To modify proteins

(ii) Explain the purpose of each phase of this protocol for a phospholipase inhibitor (3)

Phase 1 - to make sure it isn’t harmful / test for side effects
Phase 2 - to see if it’s effective in treating the condition / test for side effects
Phase 3 - Testing for rare side effects and gathering data

Q15. Describe how this polypeptide is then processed to make AFGP (4)

Polypeptide chain moves through ER then Golgi
Folded in rER
Proteins modified inside Golgi
Packaged into vesicles by Golgi and transported around cell

Q17. Describe what happens to these proteins following the process of translation until they’re released from the cell (3)

Proteins are folded in rER
Proteins are packaged into vesicles
Protein is modified in Golgi
Secreted by exocytosis

Q1. (ii) Explain how epigenetic events might be involved in regulating collagen synthesis in rats given alcohol (2)

Exposure to alcohol may result in changes of methylation of DNA
so collagen gene more likely to be activated / transcribed / expressed

Q2. (i) State what is meant by the term stem cell (2)

Undifferentiated cell that can give rise to specialised cells and divide to produce more stem cells / divide continuously / have no hayflick limit

(ii) Compare and contrast the results of mitosis and meiosis in the production of sperm cells from stem cells (4)

Both increase no. of cells
Mitosis produces genetically identical cells (less genetic variation)
Mitosis results in 2 daughter cells, Meiosis results in 4
Mitosis produces diploid cells, Meiosis produces haploid

Q3. Describe how pluripotent stem cells become specialised beta cells (4)

Chemical stimulus activates some genes
Active genes transcribed to produce mRNA
mRNA translated to produce protein
Protein determines cell structure / function / modifies cell

Q5. (ii) Explain how DNA of snail could be damaged (2)

Interferes with DNA replication potentially leading to mutations

Q7. Describe how you could use a plant tissue culture technique to show totipotency in cotton plant seedlings (4)

Using cuttings
Using agar containing growth substances / hormones
Using aseptic technique, covering top of container to prevent contamination
Supply light and leave to grow for 1 week
Look for roots / complete plant forming

(d) Describe the differences between a totipotent stem cell and pluripotent stem cell (2)

Totipotent cells can give rise to any cell, Pluripotent can’t
Totipotent cells can give rise to other totipotent cells
Totipotent cells can give rise to an entire human being, pluripotent can’t

Q8. (ii) Explain how these stem cells become specialised and develop into heart muscle cells (4)

Chemical stimulus activates some genes
Only activated genes are transcribed
mRNA translated on ribosomes
Protein made which determines cell structure / function
Differentiation takes place

(b) Explain the advantages of using stem cells from the patient instead of using stem cells from a donor (2)

No risk of rejection
No need to take immunosuppressant drugs
less risk of infection

(c) Suggest why this form of stem cell therapy is less controversial than embryonic stem cell therapy (2)

No destruction of embryos
Embryo has potential to become a human life

Q1. (i) Give the meaning of term polygenic (2)

A characteristic showing continuous variation caused by multiple genes at different loci

Q2. Explain how epigenetic changes affect development of tissues in embryo (3)

DNA in chromosome is wrapped around histones
Modification / Acetylation of histone affects binding of RNA polymerase / chromosome unwinding
Methylation of DNA affects transcription of genes
therefore gene expression is altered

(ii) Explain why these stem cells may prevent HIV causing AIDS (4)

Stem cells from the bone marrow can differentiate into specialised cells
Stem cells will differentiate into T helper cells that are resistant to HIV / have the mutated protein
T helper cells are destroyed by HIV so patient can’t produce an immune response
Mutated CD4 receptor prevents HIV entering the replacement T helper cells
T helper cells are not destroyed therefore HIV is not present in the blood

Q4. Give one difference between a tissue and an organ (1)

Organ is made up of different tissues, a tissue is made of one type of cell

Q5. Describe the decisions society has to make about the use of these embryonic stem cells (3)

Embryonic stem cells are totipotent and can be used in a wider range of therapies
Source of embryonic stem cells has to be considered
Moral / ethical issues as the use of embryonic cells destroys embryos
Need for research establishments to be regulated / licensed

Q6. (i) Give the meaning of the term totipotent cell (2)

A cell that can give rise to all cell types

(ii) Describe how cells become specialised (3)

Chemical signals cause some genes to be activated
Only activated genes are transcribed into mRNA
mRNA leads to synthesis of specific proteins which determine structure of cell

Q7. (i) Explain why stem cells from the heart can’t be used to grow cells to repair the cornea (3)

Cells aren’t totipotent
therefore some genes have already been activated and deactivated
therefore won’t be able to specialise into cornea cells

(ii) Explain why chemicals from the eye are needed to produce corneal cells from suitable source of stem cells (4)

Chemical stimulus activates some genes
Activated genes are transcribed to make mRNA
mRNA translated to produce a specific protein
Proteins cause the cell to develop into a corneal cell

Q8. Deduce why age affects time taken to recover from injuries (3)

Time will increase with age due to fewer mesenchymal stem cells in bone marrow
Fewer mesenchymal stem cells to replace cells in bone / muscle / cartilage tissues

Q11. (i) Explain what is meant by the term sex-linked disorder (2)

Disorder caused by a mutated gene located on sex chromosome
therefore the disorder is more likely in one gender than another

(iii) Explain why stem cells from a healthy donor may provide a treatment for this disorder (3)

Stem cells can differentiate into muscle cells
These cells won’t have the affected allele
The protein will be produced

Q12. Explain how epigenetic changes can cause differences in a characteristic (3)

DNA methylation affects activation of genes affecting enzyme production / metabolism

Q13. Explain how epigenetic changes affect activation of genes in daughter cells (3)

Genes activated in stem cells because of methylation of DNA
therefore same genes will be activated in daughter cells

Q14. Explain why an individual may have a greater adult height than their biological parents (4)

Height is affected by environment as well as genotype
Height is an example of polygenic inheritance
therefore offspring can inherit a mixture of alleles from both parents that increase height
e.g more calcium in diet

Q23. (i) Describe how a tissue differs in structure from a system (2)

Tissue contains one type of cell
System contains many different organs

(ii) Describe how mesenchymal stem cells can give rise to different types of cell (4)

DIfferent stimuli activate different genes
Activated genes are transcribed to make mRNA
mRNA is translated at ribosome to produce proteins
Proteins determine structure / function of cells
Different genes activated result in different types of cell being produced

Q24. *(iii) Explain how a mutation in the gene for succinate dehydrogenase can increase the risk of developing cancer (6)

Mutation is a change in the base sequence in DNA
Succinate dehydrogenase is less / non-functional
Succinate therefore accumulates
Accumulation of succinate inhibits TET
therefore increased methylation of DNA affects transcription of a gene
Greater methylation of DNA is associated with increased risk of cancer

Q1. Compare and contrast the acrosome reaction and the cortical reaction (3)

Both involve vesicles
Both involve release of chemicals / enzymes by exocytosis
Acrosome reaction = hydrolytic enzymes digest zona pellucida
Cortical reaction = thickening of zona pellucida

Q3. Describe the events of fertilisation that occur after the acrosome reaction (3)

Fusion of sperm cell membrane with egg cell membrane
Cortical granules release contents into zona pellucida
Zona pellucida thickens / hardens
Fusion of sperm and egg nuclei Sperm

Q4. *(a) Describe and explain how, in mammals, events following the acrosome reaction prevent more than one sperm fertilising an egg (4)

Sperm cell fuses with egg cell membrane
Cortical granules move towards egg cell surface membrane
Exocytosis of cortical granules
Cortical granules released into jelly layer
Zona pellucida hardens

(b) Explain how meiosis gives rise to genetic variation in gametes (2)

Independent assortment and crossing over
Independent assortment gives rise to new / diff combinations of paternal and maternal chromosomes
Crossing over involves swapping of sections of chromatids / new combinations of alleles on a chromosome

Q2. (ii) Devise an investigation to determine the effect of exposure time to Agil on the rate of mitosis in onion root tips (6)

Use controlled concentration of Agil
Gather root tips of same type / age / source and expose to Agil for a range of time intervals
Macerate root tips and use hydrochloric acid
Use toluidine blue to stain tips
Count no. of cells undergoing mitosis and calculate mitotic index

Q7. Explain why the following techniques are used when producing a root tip squash to observe cell division (4)
Adding hydrochloric acid
Adding a stain

Adding hydrochloric acid to root tip is used to break down middle lamella and separate cells / produce a thin layer of cells to allow light to pass through
Adding a stain to root tip is used to make chromosomes visible so stages of mitosis can be identified

Q8. Explain how preventing the shortening of spindle fibres affects mitosis (2)

Sister chromatids can’t be separated
Chromosomes remain at equator / anaphase can’t occur
Daughter cells produced w incorrect numbers of chromosomes

Q15. Explain why the production of these abnormal sperm cells may reduce fertility (3)

Presence of two flagella would affect motility / ability of sperm to swim
This may prevent sperm from reaching egg
Preventing fertilisation

Q17. Explain how vesicles are involved in the successful fertilisation of an egg cell by only one sperm (2)

Exocytosis / Cortical granules fuse with egg cell surface membrane
releases contents / enzyme that hardens zona pellucida

Q23. (ii) Explain how crossing over and independent assortment can produce gametes with new combinations of the alleles shown on the diagram of 2 pairs of chromosomes (4)
Crossing over
Independent assortment

Crossing over - Chromatids are produced with different combinations of alleles e.g Ab / aB
Independent assortment - Different combinations of chromosomes are produced therefore alleles for A and B would be in the same gamete as C or c

Q25. (ii) Explain why DNA is replicated before mitosis begins (2)

To ensure correct no. of chromosomes in each cell / one copy of each chromosome in each daughter cell
To ensure daughter cells are genetically identical

(iii) Explain how large numbers of cells with the same phenotype can be produced in a tissue (2)

Phenotype is determined by the genotype and effect of environment
Mitosis produces cells with same genotype

Q33. Describe the events that occur during prophase in an animal cell (3)

Nuclear envelope breaks down
Spindle fibres formed
Chromosomes condense
Centrioles migrate to opposite ends of the cell

Q36. Give a reason for the high density of mitochondria found in the midpiece of a sperm cell (1)

Provides energy / ATP for movement of flagellum
or - to release energy for sperm to swim

Q37. (ii) Explain why genes found on the sex chromosome pair have a pattern of inheritance that’s different from genes found on other chromosome pairs (2)

X chromosome carries genes not present on Y
Males only have 1 copy of some genes
If only one allele inherited, it will be expressed

Q39. (iii) Describe how a slide can be prepared from a root tip sample to produce this image (3)

Use root tip meristem
Use toluidine blue to stain
Use hydrochloric acid to prepare tissue sample / squash under cover slip

Q41. (i) Describe the role of the acrosome in fertilisation (3)

It fuses with the cell surface membrane of the sperm cell
Digestive enzymes are released to break down zona pellucida