B18-21. Variation & Selection, Biotech, GE, Organisms & Environment

Question 1

5 reasons why bacteria are useful in biotechnology and genetic engineering

Answer 1

1. High reproduction rate
2. Have the ability to produce complex molecules
3. Lack of ethical concerns over their manipulation and growth
4. Genetic code shared with all other organisms
   - gene from human/animal/plant cell can be placed into a bacterial cell to produce complex molecules, eg. protein
5. Presence of plasmids
   - circular strands of DNA that are small and easy to extract and handle

Question 2

4 examples of genetic engineering

Answer 2

1. Insertion of human genes into bacteria to produce human insulin
2. Insertion of genes into crop plants to confer resistance to herbicides
3. Insertion of genes into crop plants to confer resistance to insect pests
4. Insertion of genes into crop plants to provide additional vitamins

Question 3

3 advantages of genetically modifying crops

Answer 3

1. Less use of herbicides and pesticides is better for the environment, saves time, effort and cost for farmers
2. Crop yield increases
3. Overcomes problems like weeds and pests

Question 4

5 disadvantages of genetically modifying crops

Answer 4

1. Reduces biodiversity (using herbicides reduces plant species, less food for insects & insect-eating birds)
2. Cost of seed increases
3. Herbicide resistance gene might spread to other crop plants nearby, producing ‘superweeds’
4. Pest insects are evolving to become resistant to the Bt toxin
5. GM food might contain substances that could cause allergies in some people

Question 5

The 8 processes of the nitrogen cycle

Answer 5

1. decomposition of plant and animal protein to ammonium ions (by decomposers)
2. nitrification (by nitrifying bacteria)
3. nitrogen fixation by lightning and bacteria (nitrogen-fixing bacteria)
4. absorption of nitrate ions by plants
5. production of amino acids and proteins
6. feeding and digestion of proteins
7. deamination
8. denitrification (by denitrifying bacteria)

Question 6

3 factors affecting the rate of population growth

Answer 6

1. food supply
2. predation
3. disease

Question 7

5 ways modern technology has resulted in increased food production

Answer 7

1. Agricultural machinery to use larger areas and improve efficiency
2. Chemical fertilisers to improve yield
3. Insecticides to improve quality and yield
4. Herbicides to reduce competition with weeds
5. Selective breeding to improve production by crop plants and livestock, eg. cattle, fish, poultry

Question 8

2 negative impacts to an ecosystem of large-scale monocultures of crop plants

Answer 8

1. Reduces biodiversity
2. Increases use of insecticides
   - could kill harmless and beneficial organisms (eg. predatory insects that would help reduce insect pests population)

Question 9

3 negative impacts to an ecosystem of intensive livestock production

Answer 9

1. Disease can kept easily among livestock due to crowded contains they are kept in
2. Giving animals regular doses of antibiotics increases risk of bacteria developing resistance to antibiotics
3. Waste from intensive farming unit can pollute land and rivers nearby

Question 10

4 problems contributing to famine

Answer 10

1. Unequal distribution of food
2. Drought and flooding
3. Increasing population
4. Poverty

Question 11

3 main reasons for habitat destruction

Answer 11

1. Increased area for food crop growth, livestock production and housing
2. Extraction of natural resources
3. Marine pollution

Question 12

4 undesirable effects of deforestation

Answer 12

1. Extinction of many species of plants and animals
2. Loss of soil
   - lack of tree roots holding soil leads to soil erosion
3. Flooding
   - soil can be washed into rivers, silting them and causing floods
4. Increase of carbon dioxide in the atmosphere

Question 13

3 sources and effects of pollution of land AND water

Answer 13

1. Insecticides
   - DDT pesticide was used to kill insects and to control malaria by killing mosquitoes
   - but it is a persistent insecticide (does not break down but remain in soil/bodies) so it bioaccumulates in organisms
   - also it is nonspecific, so it is harmful to all living things not just harmful insects
2. Herbicides
   - nonspecific, difficult to break down, pass along food chains
3. Nuclear fall-out
   - from leak from nuclear station/nuclear explosion
   - exposure to ionising radiation increases rate of DNA mutation which may lead to cancer

Question 14

4 sources and effects of pollution of water (rivers, lakes, the sea)

Answer 14

1. Chemical waste
   - may contain heavy metals, eg. lead, cadmium, mercury, which is very poisonous to living organisms; stop enzymes from working, could lead to death
2. Discarded rubbish
   - plastics are non-biodegradable, bioaccumulate in living organisms, trap small animals, choke fish and birds
3. Untreated sewage
   - food source for bacteria so bacteria population increases and oxygen levels go down, eutrophication
4. Fertilisers
   - contain nitrates and phosphates; nitrates are easily washed away from soil when it rains, leached nitrates may run into streams and cause algal bloom and eutrophication

Question 15

Sources and effects of pollution of the air

Answer 15

• caused by methane and carbon dioxide
• increases in their concentrations trap more infrared radiation and make the atmosphere warmer, causing an ENHANCED greenhouse effect which leads to CLIMATE CHANGE
• enhanced greenhouse effect causes global warming

Question 16

Causes and 5 effects on the environment of acid rain

Answer 16

• caused by sulfur dioxide and oxides of nitrogen that dissolve in rainwater
  1. Soil pH decreases
  2. pH of lakes and rivers decreases, many aquatic plants and animals cannot live in them
  3. Corrodes buildings/statues
  4. Skin irritation in humans
  5. Kills plants and trees
• acid rainwater washes out ions in soil so plants have shortage of nutrients

Question 17

3 measures taken to reduce sulfur dioxide pollution and reduce the impact of acid rain

Answer 17

1. ‘Scrub’ waste gases from power stations to remove SO2
2. Use catalytic converters in car exhausts to remove oxides of nitrogen
3. Use alternatives to gasoline, eg. alcohol, hydrogen

Question 18

2 negative impacts of female contraceptive hormones in water courses

Answer 18

1. Caused feminisation of (male) aquatic organisms, eg. frogs and fish become female and produce eggs
2. Reduced sperm count in men

Question 19

6 steps of sewage treatment

Answer 19

1. Raw sewage is passed through screens to trap grit and stones
2. Primary settlement tank - semi-solid waste materials sink as sludge and are sent to the anaerobic digester
3. Anaerobic digester - anaerobic bacteria feed on the organic matter and produce methane; no air present here so all bacteria that need oxygen are killed
4. Aeration tank - aerobic microorganisms (bacteria and protoctists) grow and feed on the organic matter, leaving fairly pure water; oxygen provided by bubbling air through tank
5. Secondary settlement tank - microorganisms sink and from sludge (activated sludge) that is returned to the aeration tank
6. Effluent can be safely released into rivers or the sea - clear liquid, without smells, no pathogenic organisms

Question 20

3 ways to conserve forests

Answer 20

1. Education can help to ensure people understand the importance of conserving forests, so that they may then be able to use renewable sources of energy
2. Governments can refuse to grant licenses to companies who want to cut down forests
3. Cut down only a small proportion of trees (selective felling) instead of cutting down all trees (clear-felling)
   - new trees should be planted to replace cut down ones

Question 21

2 ways to conserve fish stocks

Answer 21

1. Impose legal quotas to limit the quantity of fish that can be caught in a year in a fishing area
2. Re-stocking
   - breed large numbers of a particular species of fish in fish hatcheries, then release them

Question 22

5 reasons why organisms become endangered or extinct

Answer 22

1. Climate change
2. Habitat destruction (due to human activities)
3. Hunting
4. Pollution
5. Introduced species
   - native species did not evolve adaptations to avoid predation

Question 23

Connection between decreasing population size of a species and reduction in variation

Answer 23

• If the population size of a species drops, genetic variation among individuals reduces.
• Variation in a population is important because the population as a whole has higher chances of survival if there is a disease/change in environment.
• This is because there will be some individuals that can survive and reproduce although the rest are killed.
• So, when variation reduces in a species, the species is more likely to become extinct.

Question 24

4 ways to conserve endangered species

Answer 24

1. Monitoring and protecting species and habitats
2. Education
   - educate people about the importance of conserving the particular endangered species and what they can do to help
3. Captive breeding programmes
4. Seed banks

Question 25

3 main reasons for conservation programmes

Answer 25

1. Reducing extinction
2. Protecting vulnerable environments
3. Maintaining ecosystem functions
   - nutrient cycling
   - resource provision (fuel, food, drugs, genes)

Question 26

2 things that sustainable development requires

Answer 26

1. Management of conflicting demands

2. Planning and co-operation at local, national and international levels

Question 27

5 adaptive features of xerophytes (plants adapted to live in dry conditions)

Answer 27

1. Stomata in sunken pits in lower epidermis
   - sunken pits trap moist air to reduce transpiration
2. Thick waxy cuticle
3. Hairy leaves
4. Needle-shaped leaves (less surface area)
5. Deep or spreading roots

Question 28

3 adaptive features of hydrophytes (plants adapted to live in wet conditions)

Answer 28

1. Air-filled cavities in stems and leaf stalks
   - help float on water to get light for photosynthesis
2. Lots of stomata on both upper and lower surfaces
   - to allow CO2 to diffuse in for photosynthesis
3. Thin cuticle on both surfaces
   - no need to prevent water loss

Question 29

Evolution

Answer 29

The change in adaptive features of a population over time as the result of natural selection