30 marks on article Flashcards
State the level of organisation of the liver in an organism and explain your answer (1)
Organ-made up of various tissues grouped to work together to perform a function
State what is meant by ‘embryonic stem cells’ (2)
They are unspecialised totipotent cells that are found when an embryo consists of only 8 cells(1) and can differentiate into any specialised cell.
Describe in full the stages that lead to the fertilisation of the egg starting with the acrosome reaction and ending with the fusion of the 2 haploid nuclei. (6)
- When sperm touches zona pellucida’
- Acrosome swells and releases digestive enzymes via exocytosis
- Enzymes hydrolyse channel through follicle cells and zona pellucida
- Cell surface membrane of egg and sperm touch and fuse allowing haploid sperm nuclei to enter egg Cortical reaction occurs when cortical granules perform exocytosis with egg cell surface membrane and harden the zona pellucida;
- Preventing polyspermy
- Meiosis restarts in egg nuclei
- One egg haploid nuclei breaks down, the other combines with the haploid sperm nuclei.
- Only when this happens is fertilisation said to have occurred.
Describe how the egg is adapted for its role. (3)
- Cortical granules to harden outer layer
- Haploid nuclei to allow diploid number to be restored.
- Large supply of lipids to supply energy for initial growth
Explain how an unspecialised zygote produces body tissues. (4)
- Correct stimulus is given e.g. transcription factor Some new genes are switched on and become active, others remain off
- Active mRNA is made from the newly activated genes
- mRNA moves to the ribosome for translation and a new protein is made (e.g. globular enzyme or structural fibrous protein)
- The new protein permanently alters the structure and the function of the cell.
A zygote develops into a blastocyst by cell division. State the type of cell division responsible, state the name of each stage and briefly describe what happens in each stage.
- mitosis
- State process of mitosis
State the 2 pre-natal tests that can identify genetic birth defects and evaluate their use (4)
- Amniocentesis-less chance of miscarriage, done later so a termination is less ethical
- Chorionic villus sampling- More chance of miscarriage but can be done earlier so more ethical if termination a consideration
- Conclusions: CVS best to use if termination the outcome and Amniocentesis best if only trying to prepare for living with the disease
Explain why some scientists deem it more ethical to experiment on fruit flies rather that mice. (3)
- Mice are vertebrates
- And more likely to feel pain
- Which needs to be considered in a utilitarian framework
Evaluate the use of genetic experiments on mice to model human development (3)
- Strength- Mice are vertebrates, as are humans, and so may share similarities that lead to accurate conclusions.
- Weakness- Mice and humans split from a common ancestor many years ago and now they are so dissimilar, the results of the experiment will not accurately reflect what would happen to humans
Name the stage of a pharmaceutical drug trial where mice would be used.
Pre-clinical trials
Explain how ‘many developmental processes and patterning events are conserved throughout diverse animal species’ (3)
- developmental processes have a genetic basis
- alleles for the processes are passed down via sexual reproduction
- and so alleles stay within the species.
State what is meant by the term phenotype
the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.
Explain how a mutant genotype and then phenotype are produced (6)
- A mutation during the semi-conservative replication of d.n.a. during the production of the gamete cell;
- During the s (synthesis) phase of the cell cycle; Due to a base-deletion, substitution, addition;
- These create new d.n.a triplet that are transcribed into a new codon;
- The new codon can code for a different amino acid during translation;
- This will change the primary structure of the protein due to a different r group being present; e.g. a hydrophobic r group replaced by a hydrophilic r group;
- This could change the phenotype;
- This may not happen due to the degenerate nature of the code
Discuss the ethical consideration when using mice (3)
- Mice can’t give informed consent so it is unethical
- The result of the experiment may be for the greater good of humans (and possibly mice) if the experiments produce new medical treatments;
- This is ethical from a utilitarian stand point.
State the term best used to describe an experiment that is controlled
Valid
State 4 conditions that stem cells could be used to treat and describe what the stem cells actually repair. (8)
- Parkinson’s disease-replace dopamine secreting neurones that have died
- Multiple sclerosis replace neurones whose Schwann cells have died, losing the myelin sheath.
- Type 1 diabetes-replace insulin secreting Beta Islets of Langerhans cells that have been destroyed by t killer cells (auto immune disease)
- Burns-replace damaged skin cells
Explain why somatic cell nuclear transfer could produce organs that won’t be rejected and why this is the most controversial use of stem cells. (4)
- A diploid body cell of patient is inserted into an enucleated human egg cell
- This is then used to grow into the required organ
- The organ will have ‘self’ proteins and glycoproteins protruding from the cell membranes
- And so T killer cells will not be stimulated to cause the cell lysis
- However, in the wrong hands, this could lead to human cloning.
State 3 condition required ‘in vitro’ to culture these cells successfully
- Warm for optimum enzyme temperature
- Oxygen for aerobic respiration
- Source of carbohydrate for respiration
Careful experimentation has determined many of the genes and signals involved in patterning the early embryo Name a possible ‘signal’ (1)
Transcription factor
Explain 2 ways how signals can modify gene expression (hint epigenetics) (7)
- DNA can have methyl groups removed from cytosine (demethylation);
- This allows RNA polymerase to bind and transcribe producing active mrna and therefore switching gene on The histone with the dna wrapped around (called a nucleosome) can be caused to uncoil by the addition of an acetyl group.
- This allows rna polymerase to bind and transcribe, switching gene on.
- The same uncoiling can also be achieved by demethylating the histone
Describe an endothelial cell and give an example where you can find them. (2)
- A cell that lines the inside of tissue
- e.g. lining arteries, arterioles, veins, venules
Compare the structure of the zika virus with a bacterium. (3)
- Both can contain DNA, bacteria always circular, virus can have circular dna
- Neither has a nucleus or any membrane bound organelles.
Differences - Viruses can have linear dna bacteria do not
- Viruses can have rna bacteria only have dna
- Bacteria have a cell membrane and cell wall, viruses do not.
- 0.5-50 micrometers (bacteria) whereas viruses are between 20 and 40 nm
Compare the structure of the zika virus with a eukaryote (3)
Similarities
- Eukaryotes always have dna and some viruses have dna
- Eukaryotes have linear dna and some viruses also do. Differences
- Viruses can have rna and eukaryotes can’t
- Viruses can have circular dna but eukaryotes can only have linear.
- Eukaryotes have membrane bound organelles such as a nucleus, virus only have a protein coat
Compare the structure of the zika virus with a plant cell (3)
Similarities
- Eukaryotes always have dna and some viruses have dna
- Eukaryotes have linear dna and some viruses also do.
- Neither has cell wall
- HIV can have host cell surface membrane surrounding it.
Differences
- Viruses can have rna and eukaryotes can’t
- Viruses can have circular dna but eukaryotes can only have linear.
- Eukaryotes have membrane bound organelles such as a nucleus, virus only have a protein coat
