B6 Questions

Question 1

Explain how the DNA bases in a gene code for a specefic chain of amino acids( 2 marks)

Answer 1

1) Each sequence of 3 bases code for one specific protein.

2) Gene contains information to arrange the amino acids in a particular sequences to form a specific protein

Question 2

Explain how DNA can be used in the synthesis of proteins when it is unable to leave the nucleus? (2)

Answer 2

Free nucleotides complimentary base pair with the strand of DNA forming a strand of mRNA which is small enough to leave the nucleus (1) and carry the code from the DNA to site of protein synthesis (2)

Question 3

Describe the process that takes place at the site of protein synthesis to produce chains of amino acids? ( 3 marks)

Answer 3

1) Carrier molecules bring the amino acids(1) coded for by the mRNA to the side of protein synthesis(1) in the correct order (1)

Question 4

Explain what happens to the chain of amino acids once it has been assembled? (2)

Answer 4

It folds to form a unique shape (1) which allows the protein to perform the task it was meant to do (1)

Question 5

Explain how mutations can lead to a change in the protein being synthesised? (3)

Answer 5

Mutations can affect the sequence of amino acids (1) and it is this sequence that codes for specific amino acids in a protein(1) and this can change what the protein will code for.

Question 6

Suggest one possible effect of a mutation in a gene that codes for a particular enzyme?

Answer 6

The active site can change (1) and therefore the enzyme would be unable to bind to the substrate to break it down and therefore the enzyme would no long be able to catalyse the reaction (1)

Question 7

An unfavourable experimental change affects a population of organisms. Explain why sexual reproduction increases the chances of the population surviving (4)

Answer 7

1) Sexual reproduction introduces genetic variation which can lead to mutations as there are different genes/ alleles and allow a new phenotypic trait to develop (1) which can be advantageous if the environment changes (1) and individuals of the genes are more likely to survive and reproduce successfully and pass the gene on to the future generations will will (1) allow them to survive in the environment (1)

Question 8

Briefly outline the discoveries made after Mendel’s work that built on his discovery of ‘hereditary units’. Include how these led to our current understanding of genes ( 5 marks)

Answer 8

1) In the mid 19th century, Mendel did experiments on his pea plants and saw how characteristics were passed as ‘units’ unchanged into the next generation.
2) In the late 19th century, scientists were able to observe how chromosomes behaved during cell division
3) Early 20th century- they saw that chromosomes behaved in a similar way to Mendel’s units.
4) Based on this, the ‘units’ were found on chromosomes and we now know them as genes.
5) Mid 20th century- structure of DNA allows us to see how genes worked.

Question 9

Mutations can occasionally lead to a rapid change in species. Explain how a mutation can lead to a rapid change in a species? (3)

Answer 9

1) Mutations can cause a new phenotypic trait or characteristic to develop
(2) which can make an individual more suited to the environment.
(3) It could then become more common through species relatively quickly by natural selection.

Question 10

What were some of the evidence Darwin collected to base his theory of evolution by natural selection? Give 3 examples.

Answer 10

(1) - New knowledge of fossils
(2) and geology.
(3) his round the world trip.

Question 11

Why does a variation by natural selection occurs ( 1)

Answer 11

• due to a difference in genes/ alleles/

Question 12

Give 3 examples of evidence for the theory of evolution by natural selection?

Answer 12

• discovery of how characteristics were passed on by genes.
• fossils will allow us to see how change in organism develops over time.
• the discovery of how bacteria are able to become resistant to antibiotics.

Question 13

The gene is inserted into the target organism’s genome in GE. Explain how this is achieved so that the organism develops desirable characteristics? (3 marks)

Answer 13

1) Gene is first inserted in a vector.
2) The vector is introduced to target organism
3) Insert the gene into the organism’s cell so organism develops with desirable characteristics.

Question 14

Describe how embryo transplants can be used to produce genetically identical piglets? (5)

Answer 14

1) Take the desirable sperm cells from the male pig and egg from the female pig with the desirable characteristics.
2) Combine it in a Petri dish and the sperm would artificially fertilise the egg.
3) The embryo that develops could then be split to form clones.
4) before any of the cells become specialised.
5) These cloned embryos could then be implanted in lots of female pigs to produce genetically identical offspring.

Question 15

Describe how an animal cell cloning can be used to produce genetically identical piglets? (5)

Answer 15

1) An unfertilised egg cell of a pig would have to have it’s nucleus removed.
2) An adult body cell from the pigg being cloned is taken and the nucleus is removed.
3) The nucleus from the body cell would be inserted into the empty egg cell.
4) The cell would be then stimulated by an electrical shock to divide into a normal embryo.
5) When the embryo was a ball of cells, it would then be implanted in a female pig surrogate.

Question 16

What happens to to the cells in the embryo as it develops in order to form the whole organism? (1)

Answer 16

• the cells differentiate to form a specific function and become specialised.

Question 17

Scientists are unable to use the fossil record as conclusive evidence to support or disprove theories o how life on Earth first began. Explain why this is the case (3 marks)

Answer 17

Many early life forms were soft bodies and decayed completetly without forming fossil fuels(1)
Fossils that died from being destroyed by geological activity(1)
This means that fossil record is incomplete (1)

Question 18

Explain how antibiotic resistant strains of bacteria develop and spread. (5)

Answer 18

1) naturally occuring mutations occur in the DNA of the bacteria, leading it to develop the characteristic that ename some to be less affected by antibiotic.
2) these bacteria are better to survive and reproduce in hosts undergoing antibiotic treatmenet.
3) meaning that the gene becomes more common in the population, forming antibiotic resistant strains bacteria.
4) as there is no effective treatment for these strains, they can spread easily between individuals.

Question 19

When a 6 marker on how different species developed, how do you answer it; refer to mark scheme directly?

Answer 19

1) Two ancestral populations separated by (geographical barrier- name barrier if specified)
2) Genetic variation in each population led to mutations and different alleles to develop.
3) These alleles enabled the species to survive in different conditions- GIVE EXAMPLE.
4) Natural selections occurs where these alleles were advantageous
5) Favourable alleles/ mutations passed on in each population
6) Eventually, 2 types cannot breed successfully to produce fertile offspring due to DIFFERENCES LEADING TO THIS INABILITY