16. Adaption And Selection

Question 0

How does adaption increase the long term reproductive success of a species?

Answer 0

By helping its members to survive long enough to breed.

Question 1

Define adaption.

Answer 1

Through the process of natural selection, organisms adjust to suit the changing environment in which they live.

Question 2

What are two major factors in evolution?

Answer 2

Adaption

Selection

Question 3

What is one of the most diverse and adaptable group of living organisms?

Answer 3

Bacteria.

Question 4

Name two ways changes in DNA can occur.

Answer 4

Mutation: changing the quantity or he structure of the DNA of an organism.

The recombination of existing DNA of two individuals - this occurs during sexual reproduction.

Question 5

Name two ways that DNA can change in bacteria.

Answer 5

By mutations
By conjugation (not strictly sexual reproduction, even though it recombines the DNA of two individuals).

Question 6

How do mutations occur?

Answer 6

One of more bases in a DNA sequence may be added, deleted or replaced by others during replication.

Different base sequence=different amino acid sequence=different polypeptide=different protein=(if enzyme) disrupts metabolic pathway leading to the production of other substances, including proteins. Organisms characteristics could change.

Question 7

What happens in conjugation?

Answer 7

Conjugation occurs when one bacterial cell transfers DNA to another bacterial cell.

Question 8

Give the five steps in conjugation:

Answer 8

One cell produces a thin projection that meets another cell and forms a thin conjugation tube between two cells.

The donor cell replicates one of its small circular pieces of DNA (plasmid).

The circular DNA is broken to make it linear before it passes along the tube into the recipient cell.

Contact between the cells is brief, leaving only time for a portion of the donor’s DNA to be transferred.

In this way the recipient cell acquires new characteristics from the donor cell.

Question 9

In conjugation DNA in the form of genes can be passed from one species to another species. What is this known as?

Answer 9

Horizontal gene transmission.

Question 10

What is it called when genes are passed down from one generation of a species to the next generation of the same species?

Answer 10

Vertical gene transmission.

Question 11

Give an example of the experiments done to prove conjugation.

Answer 11

Strain 1: needs methionine and biotin to grow
Strain 2: needs threonine and leucine to grow

Strains 1 and strains 2 grown together on minimal medium = a few colonies!

Question 12

The word antibiotic comes from the Greek work…

Answer 12

‘Against life’

Question 13

Most antibiotics are made by:

Answer 13

Bacteria, but a few are made by fungi.

Question 14

Define antibiotic.

Answer 14

A substance produced by living organisms that can destroy or inhibit the growth of Microorganisms.

Question 15

Who by and when was penicillin discovered?

Answer 15

By Alexander Fleming in 1928.

Question 16

What usually happens with osmosis and the bacterial cell wall?

Answer 16

Water constantly enters plant and bacterial cells by osmosis. The cell does not burst because the cell wall is made of tough material which is not easily stretched and so resists expansion and halts entry of further water.

Question 17

How are antibiotics effective against bacteria?

Answer 17

Antibiotics kil bacteria by preventing them from forming cell walls. They inhibit the synthesis and assembly of important peptide cross-linkages in bacterial cell walls. This weakens the walls making them unable to withstand pressure. Osmotic lysis occurs.

Question 18

When are antibiotics effective?

Answer 18

When the bacteria are growing. Penicillin works this way.

Question 19

Why are viruses not killed by antibiotics that work by weakening cell walls?

Answer 19

They enter a host cell

They have a different covering from bacteria and so are not killed by antibiotics.

Question 20

How does antibiotic resistance occur?

Answer 20

By a chance mutation within the bacteria.

Question 21

Describe the mutation which causes bacteria to become resistant to penicillin?

Answer 21

The mutation results in the bacteria being able to make a new protein which is an enzyme which can break down antibiotic penicillin before it is able to kill bacteria.

Question 22

What is the name of the enzyme which breaks down penicillin?

Answer 22

Penicillinase

Question 23

Mutations…

Answer 23

Occur randomly and are very rare but as there are so many bacteria around the total number of mutations is large.

Question 24

If a bacterium becomes resistant to penicillin, what events proceed?

Answer 24

The penicillin will kill all the normal bacteria without penicillinase but not the mutant type with penicillinase. The mutant type will survive and divide. The bacteria produced from this survivor would be resistant to penicillin.

Question 25

Which form, the penicillin resistant form or the non-resistant form is selected when exposed to penicillin?

Answer 25

The penicillin resistant form.

Question 26

How is the gene for penicillinase passed?

Answer 26

By vertical gene transmission. E.g from one generation to the next and by horizontal gene transmission.

Question 27

When a penicillin resistant bacteria survives and divides what happens eventually?

Answer 27

The penicillin-resistant bacteria gradually predominate in the population. The prequel cry of the allele for penicillin resistance increases in the population.

Question 28

How can the resistance to penicillin find its way into other bacterial species when a bacteria from one species has the mutation?

Answer 28

By conjugation, this can result in certain bacteria accumulating DNA that gives them resistance to a range of antibiotics: ‘superbugs’.

Question 29

What increases the chance of antibiotic resistance in bacteria?

Answer 29

Using antibiotics more. There is an increased chance that the mutant bacterium will gain an advantage over the normal variety.

Question 30

What is one problem with antibiotic treatments for TB?

Answer 30

The period for which the antibiotics must be taken is 6-9 months. People stop taking them after they feel better but this is bad because the few bacteria that do remain are the most resistant to the antibiotic.

Question 31

Why is it an issue in the treatment of TB that the most resistant bacteria survive due to patients not finishing the course of antibiotics?

Answer 31

The resistant strains multiply and spread to others. There is therefore a selection pressure that leads to the development of strains of the bacteria which do not respond to the antibiotics. These strains then interchange genes for resistance by conjunction with other strains. This leads to multiple-antibiotic-resistant strains of bacteria developing.

Question 32

How have we overcome the problem of multiple-antibiotic-resistant strains of TB.

Answer 32

A ‘cocktail’ of three or four antibiotics is given to ensure at least one of them will be effective.

Question 33

Which bacterium is carried by many people in their throats?

Answer 33

Staphylococcus aureus (only causes minor symptoms in healthy individuals).

Question 34

What is MRSA?

Answer 34

MRSA is the name given to any strain of this bacterium that is resistant to one or more antibiotics.

Question 35

Where is MRSA particularly prevalent?

Answer 35

In hospitals.

Question 36

Why is MRSA dangerous in hospitals?

Answer 36

People in hospitals tend to be older, sicker and weaker than the general population making them more vulnerable to infection.

Conditions are crowded and transmission is likely through nurses etc touching patients.

Many antibiotics are present. Strains can develop multiple resistance more easily.

Question 37

Why is MRSA so difficult to treat?

Answer 37

Some strains have developed resistance to almost every known antibiotic.

Question 38

Give some reasons why antibiotic resistance is on the increase:

Answer 38

Antibiotics are used to treat minor ailments.

Antibiotics are sometimes used to treat viruses as they may help prevent secondary bacterial infections to which patients may be vulnerable.

Patients do not always complete the course of antibiotics as prescribed.

Patients keep unused antibiotics and then take them in smaller doses than they should if the bacteria return.

Doctors accept patients demands for antibiotics even when they are not absolutely necessary.

Antibiotics are used for animals.