30 marks on article

Question 1

State the level of organisation of the liver in an organism and explain your answer (1)

Answer 1

Organ-made up of various tissues grouped to work together to perform a function

Question 2

State what is meant by ‘embryonic stem cells’ (2)

Answer 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.

Question 3

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)

Answer 3

• 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.

Question 4

Describe how the egg is adapted for its role. (3)

Answer 4

• 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

Question 5

Explain how an unspecialised zygote produces body tissues. (4)

Answer 5

• 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.

Question 6

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.

Answer 6

• mitosis

- State process of mitosis

Question 7

State the 2 pre-natal tests that can identify genetic birth defects and evaluate their use (4)

Answer 7

• 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

Question 8

Explain why some scientists deem it more ethical to experiment on fruit flies rather that mice. (3)

Answer 8

• Mice are vertebrates
• And more likely to feel pain
• Which needs to be considered in a utilitarian framework

Question 9

Evaluate the use of genetic experiments on mice to model human development (3)

Answer 9

• 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

Question 10

Name the stage of a pharmaceutical drug trial where mice would be used.

Answer 10

Pre-clinical trials

Question 11

Explain how ‘many developmental processes and patterning events are conserved throughout diverse animal species’ (3)

Answer 11

• developmental processes have a genetic basis
• alleles for the processes are passed down via sexual reproduction
• and so alleles stay within the species.

Question 12

State what is meant by the term phenotype

Answer 12

the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

Question 13

Explain how a mutant genotype and then phenotype are produced (6)

Answer 13

• 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

Question 14

Discuss the ethical consideration when using mice (3)

Answer 14

• 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.

Question 15

State the term best used to describe an experiment that is controlled

Answer 15

Valid

Question 16

State 4 conditions that stem cells could be used to treat and describe what the stem cells actually repair. (8)

Answer 16

• 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

Question 17

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)

Answer 17

• 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.

Question 18

State 3 condition required ‘in vitro’ to culture these cells successfully

Answer 18

• Warm for optimum enzyme temperature
• Oxygen for aerobic respiration
• Source of carbohydrate for respiration

Question 19

Careful experimentation has determined many of the genes and signals involved in patterning the early embryo Name a possible ‘signal’ (1)

Answer 19

Transcription factor

Question 20

Explain 2 ways how signals can modify gene expression (hint epigenetics) (7)

Answer 20

• 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

Question 21

Describe an endothelial cell and give an example where you can find them. (2)

Answer 21

• A cell that lines the inside of tissue

- e.g. lining arteries, arterioles, veins, venules

Question 22

Compare the structure of the zika virus with a bacterium. (3)

Answer 22

• 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

Question 23

Compare the structure of the zika virus with a eukaryote (3)

Answer 23

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

Question 24

Compare the structure of the zika virus with a plant cell (3)

Answer 24

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

Question 25

Explain how the pregnant mother will respond to the Zika virus. (5)

Answer 25

• The Zika virus will leave antigens on surface of infected cells in the mother;
• Creating an antigen presenting cell
• T helper cells with the specific CD4 receptor will bind to the antigen causing them to differentiate into t helper memory and active t helper cells;
• Killer t cells with specific receptor proteins will also bind to the infected antigen presenting cell (clonal selection);
• The active t helper cell will release cytokines onto the bound t killer cell causing it to replicate rapidly (clonal expansion) into t killer memory cells and active t killer cells;
• This produces many active t killer cells that find and bind to all cells with the same antigens on their surface;
• The t killer cells secrete digestive enzymes that punch holes in the infected cell;
• causing cell lysis

Question 26

Explain how the zika virus with cause ‘neurological disorders such as microcephaly’ (3)

Answer 26

• Zika virus uses its surface proteins to bind to host cell membranes which allows it to enter the cell (infect);
• The virus inserts it dna or cdna created by reverse transcriptase into the genome of the host cell The host cell transcribes and translates viral proteins
• New viruses form from these proteins and bud out of the cell, eventually killing it leading to disorders such as microcephaly

Question 27

Explain why individuals with transplanted organs need to take immunosuppressant drugs. (5)

Answer 27

• The surface of the tissues of transplanted organs will contain non-self antigens;
• Because they have been made by genes from another human
• This means T killer cells with specific receptor proteins, under the influence of cytokines, will bind to the cells in the tissue and release toxins that will cause cell lysis, destroying the organ.
• Immunosuppressant drugs prevent this from happening.

Question 28

Some immunosuppressant drugs reduce the production of cytokines. Which cells are they inhibiting? (1)

Answer 28

T helper

Question 29

State the source of human embryos used in research. (1)

Answer 29

Spare embryo’s not used in fertility treatment

Question 30

Explain why it is unethical to destroy human embryos after use in research

Answer 30

• Embryos have the potential to become a human;

- Humans need to give informed consent which they can not give

Question 31

Explain why it is ethical to destroy human embryos after use in research. (2)

Answer 31

• At an early stage of development the embryo’s are just a potential life and not a life.
• It can not feel pain but the research may have benefited many people.
• The greater good-utilitarian

Question 32

Neurulated means that a central nervous system has started to be created. What is the name of the system that surrounds the central nervous system? (1)

Answer 32

Peripheral

Question 33

Describe the process of how researchers publish their findings to other professional scientists. (4)

Answer 33

• Publish a paper in a journal; - That has been peer reviewed
• To check the conclusions are accurate, methods valid, statistics correct
• The reviewers may try to reproduce the results themselves.
• They may present the paper at a scientific conference.

Question 34

Describe how researchers communicate their findings to wider public (2)

Answer 34

• The internet
• Scientific magazines
• Social media (whatever that is)
• Television programs