Natural Selection And Genetic Modification

Question 1

What was the theory of evolution?

Answer 1

• Variation exists within species due to DNA mutations
• Organisms with characteristics most suited to be environment are more likely to survive and reproduce
• The beneficial characteristics are passed on to the next generation
• Over many generations the frequency of alleles for this characteristic increase within the population

Question 2

How does bacteria resistance support Darwin’s theory?

Answer 2

• Bacteria reproduce at a fast rate
• Random mutation occurs in the genes individual bacterial cells
• Exposure to antibiotics create a selection pressure and bacteria without the mutation will die
• Those with antibiotic resistance can reproduce and pass on the resistant gene
• Supports his theory as the new bacteria is selected by environment to have an advantageous feature for survival

Question 3

When did the Ardi species live?

Answer 3

4.4 billion years ago

Question 4

When did the Lucy species live?

Answer 4

3.2 million years ago

Question 5

What evidence for human evolution did the Ardi skeleton give?

Answer 5

• Contains ‘humanoid’ features but resembles an ape so is phenotypically between the two
• Ardi’s bones show she was able to walk upright but had long arms
• Bone structure in Ardi’s feet is different from chimpanzees, suggesting they evolved separately

Question 6

What evidence for human evolution did the Lucy skeleton give?

Answer 6

• Bone structure suggests she walked upright but she had a small chimp-like skull and brain
• Represents another intermediate between apes and early humans

Question 7

What evidence for human evolution did Leakeys’ discoveries give?

Answer 7

• Discovered fossils from 1.6 million years ago
• The skeleton (homo habilis) looked more like a modern human than Ardi or Lucy
• They also discovered stone tools

Question 8

How have stone tools developed over human evolution?

Answer 8

• Early Stone Age (Homo habilis 1.5 million years), used basic tools created by smashing rocks together
• Late stone Age (homo neanderthalensis 40,000 years), used pointed arrowheads, spears and hooks

Question 9

What are the two methods that stone tools can be dated?

Answer 9

Radiometric carbon dating - by looking at the natural radioactive decay of a carbon isotope

Stratifying rock layers – looking at the layer of sediment in which a rock was found

Question 10

How does the pentadactyl limb provide evidence for evolution?

Answer 10

• A pentadactyl limb has five digits
• This is seen in many organisms, implying they all come from a common ancestor
• They have each ‘branched off’ at some stage of evolution, due to different selection pressures of different environments

Question 11

What was the five kingdoms system?

Answer 11

• All organisms were split into: animals, plants, fungi, prokaryotes, protists
• Each kingdom was then divided into: phylum, class, genus, order, species
• The binomial naming system was based on the genus and species e.g. Homo (genus) Sapiens (species)

Question 12

What are the three domains?

Answer 12

Archaea: primitive bacteria, usually live in extreme environments, no nucleus

Bacteria: true bacteria, no nucleus

Eukaryota: organisms who have a nucleus enclosed in membranes, includes the kingdoms protists, fungi, plants and animals

Question 13

What is are some reasons for selective breeding?

Answer 13

• Disease resistance
• Increased yield
• Better ability to cope with difficult conditions
• Faster growth
• Better flavour

Question 14

What is the process of selective breeding?

Answer 14

• Parents or plants with desired characteristics are bred together
• The offspring with desired characteristics are bred together
• This is repeated many times until all the offspring have the desired characteristics

Question 15

What is the issue with selective breeding?

Answer 15

• Inbreeding
• Reduces gene pool, as number of different alleles reduces
• If environment changes the species could become extinct because little variation
• Small gene pool means more chance of genetic defects, as recessive characteristics are more likely 

Question 16

What is tissue culture?

Answer 16

• A method of culturing living tissue within a growth medium
• Used to grow many identical cells

Question 17

What are the stages of tissue culture for a plant?

Answer 17

• Take a plant with desirable characteristics
• Remove a piece of tissue in a fast-growing region (e.g. the root or shoot tip)
• Using aseptic technique, place the tissue on a growth medium (containing hormones and nutrients)
• Once developed enough it is transferred to compost for further growth

Question 18

What are the advantages of cell cultures for animals?

Answer 18

• To test the effect of drugs and other chemicals on cells
• To check for cancer cells in a sample from a patient
• To produce important proteins, e.g. antibodies

Question 19

What are the advantages of cell cultures for plants?

Answer 19

• Produce thousands of identical plants from just one parent 
• To make plant products (e.g. to treat cancer)
• Produce disease free plants

Question 20

What is genetic engineering?

Answer 20

Modifying a genome to introduce desirable characteristics

Question 21

What are the stages of genetic engineering?

Answer 21

• Genes from chromosomes are ‘cut out’ using restriction enzymes
• This leaves a few unpaired bases at each end (called sticky ends)
• Restriction enzymes are used to cut the vector
• Ligase enzyme attaches the sticky ends of the gene and vector together producing a recombinant gene product
• Vector is placed in another organism at early stage of development

Question 22

What are the uses of genetic engineering?

Answer 22

• In medicine to produce certain hormones in microorganisms
• Improve yields by improving growth rates, crops can grow in different conditions and make their own pesticide
• Crops with extra vitamins in areas where they are difficult to obtain
• Greater yields can help solve world hunger

Question 23

What are the risks of genetic engineering?

Answer 23

• May transfer gene to other species, what benefits one plant may harm another
• Some believe its unethical to interfere with nature
• GM crops seeds are often more expensive so developing countries may not afford them
• Could lead to genetic engineering in humans (designer babies)
• Create a selection pressure which leads to increased resistance, creating super weeds and pests

Question 24

How are Bt crops created?

Answer 24

• The bacteria naturally produces toxins that kill insect larvae
• The gene for Bt toxin is ‘cut out’ of the bacterial DNA using restriction enzymes
• It is then inserted into the DNA of a plant cell using ligase
• The crop will then produce the toxin and any insects that eat it will die

Question 25

What are the benefits of selective breeding?

Answer 25

• Increased yield, produce higher quality or larger mass of food
• Can be bred to be resistance to a particular disease
• Cheaper than genetic modification

Question 26

What are the disadvantages of selective breeding?

Answer 26

• May get rid of characteristics that would be useful in the future
• Animal welfare, ethical concerns
• Lack of genetic variation, susceptible to same diseases
• Can cause severe health problems
• Takes a while

Question 27

What are the advantages of disadvantages of fertilisers?

Answer 27

Advantages:
- Provide useful nutrients (nitrates and phosphates)
- These help them grow and be resistant to environmental conditions
- Good way to use animal waste

Disadvantages:
- Excess fertiliser can pollute waterways, causing eutrophication
- Artificial fertilisers are expensive to make
- Artificial fertilisers can reduce soil biodiversity

Question 28

What are the advantages and disadvantages of biological control?

Answer 28

Advantages:
- The pest cannot become resistant
- If well chosen, it is specific to the pest
- Avoids using chemical pesticides which can leave harmful residues
- Reduces work/effort

Disadvantages:
- May not completely get rid of the pest
- The control agent may become a pest itself