Targeted Revision

Question 1

SB2i
1) How does the nervous system react to stimuli?
2) What do motor and relay neurons do, and what do they look like?
3) What is a synapse and what is its function?

Answer 1

1) When the brain coordinates a response to the stimulus, impulses are sent to effectors and these carry out an action.
2) Motor neurons carry impulses to effectors. Relay neurons are short neurons that are found in the spinal chord, where they link motor and sensory neurons. Neither of them have a dendron, only dendrites on the cell body.
3) A synapse is a small gap between two neurons. When an impulse reaches an axon terminal, a neurotransmitter substance is released into the gap. This is detected by the next neuron which creates a new impulse. This allows impulses to be passed on from the axon terminal of one neuron to the dendrites of another neuron.

Question 1

SB2i
Explain how a signal is transmitted at a synapse and how the painkillers reduce the pain felt by the person.

Answer 1

Synapse transmission
- Neurones transmit electrical impulses the synapse is a gap between 2 neurones triggering the release of neurotransmitters which diffuse across the synapse as a chemical signal
- Neurotransmitters bind to receptors on the next neurone
- Triggering an electrical impulse in the next neurone
Painkillers
- Prevent neurotransmitters binding to receptors in the next neurone
- Electrical impulse is not triggered
- Signal is not received by the central nervous system
- Person does not feel pain

Question 2

SB3e
1) How is gene transcription regulated?
2) What are the effects of mutations on protein synthesis?
3) How can mutations influence RNA polymerase binding and so alter protein production?

Answer 2

1) Gene expression (or gene regulation) is the process by which specific genes are activated to produce a required protein. The gene expression process is made up of the transcription and translation of DNA sequences.
2) The change in codons will create a different amino acid, which will create a different protein, as the amino acids will fold into a different shape.
3) If mutations occur in the non-coding section of DNA that the RNA polymerase attaches to, it can make it easier or more difficult for the RNA polymerase to bind to the coding region. If it is more difficult, then less mRNA will be transcribed, and less protein will be produced. This can affect the phenotype.

Question 3

SB3c - Core Practical
1) What is the aim for the DNA extraction core practical?
2) What are the steps for the DNA extraction core practical?

Answer 3

1) Explain how DNA can be extracted from fruit
2) A) Dissolve 3 g of salt in 100 cm3 of water in a large beaker. Add 10 cm3 of washing-up liquid and stir gently until the salt dissolves. Do not make the mixture foamy! The detergent in this solution breaks down cell surface membranes and the membranes around nuclei. The salt makes the DNA more likely to clump together, which is important in step G.
B) Thoroughly mash 50g of peas. Put the mashed peas into an empty beaker and add the solution made in step A. Stir slowly for one minute.
C) Place the beaker in a water bath at 60°C for 15 minutes.
D) Filter the mixture and collect the filtrate in a small beaker.
E) Measure 10 cm3 of the filtrate and pour it into a boiling tube.
F) Add two drops of protease enzyme solution. (Proteases break down proteins.)
G) Tilt the boiling tube slightly and pour in ice-cold ethanol, letting the ethanol run down the inside of the tube very slowly. Stop when as much ethanol has been added as there is filtrate. DNA is insoluble in ethanol and so it forms a precipitate.
H) Leave the tube for a few minutes. A white layer forms between the filtrate and the ethanol. This is DNA, and it can be wound around a glass stirring rod and lifted out of the tube.

Question 4

SB3j
1) What was the main aim of the human genome project?
2) How can the knowledge gained from the Human Genome Project be used to create new and better medicines?
3) How has the Human Genome Project affected the testing or treatment of inherited disorders?
4) List the 4 aims of the Human Genome Project

Answer 4

1) The aim of the human genome project was to identify every single gene in the human genome.
2) The knowledge of the genetic variations that affect how we respond to a medicine could help scientists to develop personalised medicine and drugs that are tailored to these variations.
3) - Scientists are now able to identify the genes or alleles suspected of causing an inherited disorder much more quickly than they could do in the past.
- Detecting faulty alleles will allow people to have early treatment.
- Scientists can target treatment and personalise medicine for a genetic disorder if the alleles are known.
4) The four aims are:
- To identify all the approximately 20,000 - 25,000 genes in human DNA
- To find where each gene is located
- To determine the sequence of the 3 billion chemical base pairs that make up human DNA.
- To store this information in databases

Question 5

SB3c - Core Practical
1) What are the risks for the DNA extraction core practical?
2) What is the role of detergent, salt, protease and ethanol in the DNA extraction core practical?

Answer 5

1) Ethanol is an irritant - use in a well ventilated area, wear goggles and gloves.
2) - The detergent in this solution breaks down cell surface membranes and the membranes around nuclei.
- The salt makes the DNA more likely to clump together.
- Proteases break down proteins.
- DNA is insoluble in ethanol and so it forms a precipitate so that the DNA can be visible.

Question 6

SB4f
1) What is tissue culture and what does it form?
2) Are tissue cultured cells similar or different to each other and why?
3) Which part of the plant is most useful for producing a tissue culture and why?

Answer 6

1) Tissue culture is the growing of cells or tissues in a liquid containing nutrients or on a solid medium. These may form a callus (a clump of undifferentiated cells), which are sometimes treated to form specialised cells.
2) Tissue culture produces many genetically identical cells which are clones. This is because small clippings are taken from one plant, so the plant that is grown will have the same DNA.
3) Shoot tips are the best for plant culture because they grow quickly.

Question 7

SB4g
1) What are the main stages of genetic engineering?
2) What are some uses of selectively bred organisms (in agriculture)?
3) What are some uses of genetically engineered organisms (in agriculture, in medicine)?

Answer 7

1) The main steps in the process of genetic engineering:
- Restriction enzymes are used to isolate (cut out) the required gene, this leaves sticky ends on the DNA.
- The same restriction enzymes are also used to cut the vector open, leaving it with corresponding sticky ends
- Any DNA molecule used to carry new DNA into another cell is called a vector.
- The vector is usually a bacterial plasmid (a piece of circular DNA found inside bacterial cells) or a virus
- The gene is joined to the plasmid using an enzyme called ligase
- The recombinant DNA plasmid is transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics
2) To produce crops or animals with a high yield.
To produce crops that are disease resistant.
3) In agriculture: Golden rice contains genes that makes it produce a chemical that is turned into vitamin A in the human body, which could be used in areas where Vitamin A deficiency is common and so can help prevent blindness.
In medicine: The gene for human insulin can be inserted into bacteria which then produce human insulin which can be collected and purified for medical use to treat people with diabetes.

Question 8

SB4f
1) Why are animal tissue cultures are useful for testing the effects of drugs?
2) How could you produce a tissue culture of an animal organ or muscle for drug testing?

Answer 8

1) Using animal tissue culture allows scientists to investigate the effects of a drug on a single animal tissue, without the complications of a whole organism.
2) Extract a sample of cells from the animal organ/ muscle. Add enzymes to the sample of tissue to separate the cells from each other. Place the separate cells in a culture vessel containing a growth medium with all of the nutrients that they need to grow and divide. After several rounds of cell division, split cells into separate vessels to encourage further growth.

Question 9

SB4c
Describe some of the evidence that Darwin and Wallace used to support their idea

Answer 9

Darwin went on a voyage around the world and he noticed that there was variation in members of the same species; he noticed that individuals with characteristics most suited to their environment were more likely to survive; and he noticed that characteristics could be passed onto offspring.
Alfred Russel Wallace was a scientist who, after conducting his own travels around the world and gathering much evidence, independently developed his own theory of evolution based on the process of natural selection. He proposed that the bright colouration on many animals are warning signals to predators. This is an example of a beneficial characteristic that had evolved by natural selection.

Question 10

SB3c
Explain the impact of the theory of evolution by natural selection on modern biology

Answer 10

• Now that we understand evolutionary relationships, we can classify organisms based on their evolutionary ancestry.
• Now that we understand how antibiotic-resistant bacteria evolve, we know that we have to keep developing new antibiotics.
• Our understanding of the importance of genetic diversity and how it helps populations adapt to changing environments has influenced conservation projects to protect species.

Question 11

What are the advantages and disadvantages of genetic modification?

Answer 11

Advantages
- Genetic modification is a faster and more efficient way of getting the same results as selective breeding.
- Improve crop yields or crop quality, which is important in developing countries. This may help reduce hunger around the world.
- Introduce herbicide resistance, which results in less herbicides being used, as weeds are quickly and selectively killed.
- Insect and pest resistance can be developed and inserted into the plants. The plant produces toxins, which would discourage insects from eating the crop.
- Can produce proteins that are used for medical research
Disadvantages
- GM crops could be harmful for people’s health, for example toxins from the crops have been detected in some people’s blood.
- Transfer of the selected gene into other species. What benefits one plant may harm another.
- GM seed crops are often more expensive

Question 12

SB4a
1) What evidence is there that might be used to show that one ancestral species (eg. Ardipithecus ramidus) inhabited the Earth earlier than Homo habilis?
2) Suggest an explanation for the extinction of a certain ancestral species

Answer 12

1) Differences in the structural features of the fossil, and one ancestral species would be deeper in the rock layer than another ancestral species.
2) The ancestral species is likely to have been outcompeted by another ancestral species for resources essential for survival due to the presence of a new selection pressure (eg. environmental change or disease.)

Question 13

Why is it an advantage for an asexually reproducing plant, such as strawberries, to grow seeds?

Answer 13

Seeds introduce variation into the population, which allows for the natural selection of fitter plants, and increased chance of the population surviving.

Question 14

SB5c
1) Explain why exercise and diet affect obesity.
2) Compare how cardiovascular diseases are treated (medication, stents, and heart transplants)

Answer 14

1) A poor diet and lack of exercise can lead to obesity. This is because eating too much saturated fat and not burning the fat through exercise can can cause fat to build up below the skin and around the organs, which causes obesity.
2) Medication: Statins are drugs that help to lower cholesterol in the blood.
Anticoagulants make blood clots less likely.
Stents: Coronary arteries that are blocked or have become narrow can be stretched open and a stent inserted to maintain blood flow to the heart.
The benefits that are surgery is quick and the stents can last a long time. The issues are that surgery has risks, such as the risk of infection to bleeding, and a blood clot can occur near the stent.
Heart transplants: A heart transplant is required in cases of heart failure. Coronary heart disease can lead to heart failure. This is where heart fails to pump sufficient blood and organs are starved of oxygen.
The issues are that trying to find a new human biological heart takes a long time, and the heart could be rejected.
Artificial hearts don’t work very well and are only temporary. However, a benefit is that they can’t get rejected.

Question 15

SB5d
Explain how signs of a disease can be used to identify the pathogen

Answer 15

The process to identify a disease may include the following steps:
1) Following a report of a possible infection, scientists will visit the location.
2) To avoid any confusion it is essential they look at other factors that might cause similar symptoms. For example, damage to leaves might be caused by a pathogen or grazing animals.
3) The scientists will try to identify any environmental causes such as pollution that might be affecting the plants.
4) Finally they will photograph the symptoms and take samples for laboratory analysis.

Question 16

SB5f
1) Describe the lysogenic pathway of a virus life cycle.
2) Compare and contrast the lytic and lysogenic pathways.
3) How do you calculate the cross-sectional area of viral cultures and clear agar jelly?

Answer 16

1) The lysogenic cycle: The virus injects its DNA into the host cell and the DNA becomes incorporated into the host DNA
As the host cell replicates, the viral DNA replicates also, but no new virus particles are made during this time (the virus is dormant).
An environmental change acts as a trigger for the viral DNA to exit the genome of the host. Then the viral DNA enters the lytic cycle so the proteins of the host cell are used to make new components of the virus.
2) In the lytic cycle, the viruses infect the host cell and uses its metabolism to multiply, causing the lysis or death of the cell. Whereas, the lysogenic cycle consists of a virus that lies dormant, and the host cell is reproducing instead.
3) Formula: cross sectional area = πr²
You measure to the centre of the cross-sectional area.

Question 17

SB5i
1) Explain how the spread of the STIs Chlamydia and HIV can be reduced or prevented.
2) Why may a person be symptomless for a long time after the initial period of infection by HIV?
3) Explain why a person with AIDS become seriously ill due to infection by another pathogen

Answer 17

1) Chlamydia is a disease caused by bacteria that may result in infertility. Chlamaydia is transmitted by bodily fluids. Therefore, using a condom prevents the mixing of bodily fluids during sexual intercourse. HIV is a virus that eventually leads to a disease called AIDS in the people it infects. They are most commonly spread by sexual contact, and a method to prevent it spreading is using a condom during sex.
2) After entering cells, HIV enters the lysogenic stage of its life cycle and becomes dormant. Therefore, the virus is not active and will not be causing any symptoms in the infected person.
3) HIV kills white blood cells, which are an important part of the immune response, so the immune system is weakened. This means that the person is more vulnerable to infection by other pathogens.

Question 18

SB5j
1) What is the role of the immune system?
2) What does it mean if a person is immune to a disease?
2) Describe how antigens trigger the release of antibodies and the production of memory lymphocytes, including how it looks on the graph
3) Describe the role of antibodies in the immune response.

Answer 18

1) The immune system protects the body by attacking pathogens.
2) The immune system can respond quickly if the pathogen which causes the disease enters their body again.
3) The first exposure to the pathogen is shown on the graph right before the antibodies are produced and the graph line goes up. Lymphocytes bind to antigens and produce specific complementary antibodies. Then, the antibodies defend against pathogens. They bind on the pathogen’s antigen and directly destroy them. Lymphocytes can also produce antitoxins. These antitoxins can also neutralise the toxins released by the pathogen. Memory lymphocyte production is also triggered. The point when it is produced is show on the graph after the first pathogen exposure by a horizontal, dashed line. At the time of second exposure (right before the second curve) the body has some memory lymphocytes that will recognise the pathogen’s antigens, and trigger more antibodies to be made. This means antibodies will be produced much more quickly (shown by a steeper curve) following the exposure, and the curve will be steeper.
4) Antibodies are produced by the lymphocytes to target and neutralize pathogens and toxins. They recognize and bind to the complementary antigens on specific pathogens so that they can be destroyed.

Question 19

SB5j
1) Describe the role of memory lymphocytes in triggering a secondary response.
2) Explain how immunisation protects against infection by a pathogen.
3) Discuss advantages and disadvantages of immunisation

Answer 19

1) Memory lymphocytes (also known as B-lymphocytes) detect antigens on a pathogen in the blood. B-lymphocytes produce specific antibodies, which lock onto the pathogen and destroy it. The antibodies are produced rapidly and flow throughout the body to find all similar pathogens.
2) - A weakened form of a pathogen which cannot cause disease is injected into someone.
- This causes lymphocytes to make and then release complementary antibodies to attack and kill the specific antigen that was injected.
- Some memory lymphocytes remain in the bloodstream which can produce the specific antibody for the antigen.
- If the body is infected by the real pathogen, the memory lymphocytes will release antibodies to fight off the pathogen and quickly destroy it.
3) Advantages of immunisation:
- Less likely to get a disease from a pathogen
- Develop herd immunity, which keeps vulnerable unvaccinated individuals safe
- Possibly eradicate the pathogen
- Vaccination is cheaper than treating a sick patient.
Disadvantages of immunisation:
- Possible side effects
- Poor vaccine distribution, not everyone can receive or afford it
- Low vaccination rates within certain groups due to religious and ethical reasons

Question 20

SB5l
1) Define the term monoclonal antibody.
2) Define the term hybridoma cell.
3) Describe how monoclonal antibodies are produced by lymphocytes.

Answer 20

1) Monoclonal antibodies are identical copies of one type of antibody. They are specific to one type of antigen, and engineered by scientists.
2) A hybridoma cell is a cell where lymphocytes are combined with a particular type of tumour cell.
3)- An antigen is injected into a mouse. (Scientists must first inject the animal with an antigen so that the animal makes B-lymphocytes which produces antibodies that are complementary to the antigen that’s injected.)
- The mouse naturally produces lymphocytes, which produce antibodies specific to the antigen.
- Spleen cells which produce the lymphocytes are removed during a small operation.
- The spleen cells are fused with human cancerous white blood cells called myeloma cells to form hybridoma cells which divide indefinitely. (Tumour cells are used because tumor cells divide rapidly, so using them means the hybridoma cell will divide rapidly to produce many clones, which can produce more of the monoclonal antibodies.)
- These hybridoma cells divide and produce millions of monoclonal antibodies specific to the original antigen.

Question 21

SB5l
1) Explain how monoclonal antibodies are used in pregnancy testing.
2) Explain how monoclonal antibodies are used in diagnosis of disease (including blood clots and cancer).
3) Explain the advantages of monoclonal antibodies compared with drug and radiotherapy treatments to target cells.

Answer 21

1) During pregnancy, a woman begins to produce hCG hormone, which becomes present in her urine. To use the test, the woman should urinate on the patch containing the blue beads. If hCG is present in her urine, then the monoclonal antibodies on the blue beads will attach to the hormone. The urine carries the beads and the hormone to the test strip, where they bind to the antibodies secured on the strip. The test strip will then turn blue, showing a positive result.
2) Cancer: When injected into a person’s body, the monoclonal antibodies will bind with these cancer cells and clump them together. This makes it easier to identify a cancerous tumour , which can then be treated or removed.
The monoclonal antibodies are also used in the diagnosis of the cancer. The antibodies are made slightly radioactive. The antibodies then attach to the cancer cells and then radiation can be detected using a PET scanner, for example.
Blood clots: Monoclonal antibodies have been developed that bind to the proteins which form blood clots. These antibodies can be labelled with a radioactive element and injected into the bloodstream. A camera which detects radiation can then be used to visualise where the antibodies have accumulated, and so the position of any blood clots.
3) Monoclonal antibodies allow the specific targeting of drugs to cancer cells. This means that fewer body cells are affected compared with normal drug and radiotherapy treatments, so there are fewer side effects.

Question 22

Core practical - SB5k
1) What are the safety isssues for the antibiotics core practical?
2) How would the forceps and control filter paper disc be sterilised and why?
3) Why are the tapered dishes kept in a warm place/ at a certain temperature?

Answer 22

1) The disinfectant is flammable, so keep it away from naked flames. The naked flames could cause burns, so be careful around the Bunsen burner.
2) Suitable suggestions include: wrapping the forceps and control filter disc in foil and placing in an autoclave/pressure cooker; dipping the forceps in an ethanol solution and the flaming them; leaving the forceps in disinfectant solution for a set length of time.
Sterilising the forceps at each stage reduces the risk of infection of the culture with other microorganisms, which could affect results.
3) Bacteria grow faster in warm conditions. Keeping the plates at a certain temperature provide optimal growth conditions.

Question 23

SB5c
Compare the advances and disadvantages of a lifestyle change vs surgery (such as stents and a heart bypass) as treatment for coronary heart disease

Answer 23

A lifestyle change is cheaper than a heart bypass or stent as surgery can be expensive.
A lifestyle change has less risks than a heart bypass of stent, as it does not require surgery.
However, the impact is not immediate, the patient may find it difficult and may not have the will power, and it is not an option in a medical emergency such as a heart attack.

Question 24

SB5k - Core Practical
1) Explain why aseptic precautions are used
2) Why are agar plates usually incubated with the surface of the agar facing downwards?

Answer 24

1) Aseptic precautions are used so only the desired bacteria are transferred to the spreader, and no unwanted microorganisms are spread to the agar plate. Using aseptic techniques kills the microorganisms on the spreader.
2) So condensation doesn’t run down on to agar and to avoid contamination.

Question 25

SB5d
State the type of disease, how the disease is spread and the symptoms for the following diseases:
1) Cholera
2) Chalara dieback
3) Ebola

Answer 25

1) Cholera: bacterial disease, is spread as a waterborne disease, causes watery diarrhoea and dehydration.
2) Chalara dieback (affects ash trees only): spread by wind, causes wilting in the branches and tree death.
3) Haemorrhagic fever (Ebola): Viral disease, spread by contact with bodily fluids, causes high fever, vomiting, and aches and pains.

Question 26

SB5d
State the type of disease, how the disease is spread and the symptoms for the following diseases:
1) Malaria
2) Tuberculosis

Answer 26

1) Malaria: Vector disease, spread by mosquitoes, causes high fever, vomiting and death
2) Tuberculosis: Bacterial disease, airborne, causes coughing up blood and weight loss

Question 27

SB5d
State the type of disease, how the disease is spread and the symptoms for the following diseases:
1) AIDS
2) Stomach Ulcers

Answer 27

1) AIDS: Viral disease, spread by unprotected sexual activities, causes a weak immune system and death
2) Stomach Ulcers: Bacterial disease, spread by saliva or vomit, causes a stomach lining attack