A level Biology AQA Unit 4

The ecological role (1) of hermit crabs (2) includes scavenging in rock pools (3).

What ecological terms are represented by the numbers 1, 2 and 3?

• A

• B

• C

• D

Limiting factors affect population size. Which of these factors acts independently of the density of the population?

• air temperature

• disease

• food supply

• territory size

An experimental pond was set up by placing water containing a little plant fertilizer in a tank and leaving it outside. Various organisms, X, Y and Z, were subsequently found in the tank and their inter-relationships were observed. The graph shows how their populations changed over time. Which line identifies the trophic levels of X, Y and Z?

• A

• B

• C

• D

Which of the following bonds are broken during DNA replication?

• hydrogen bonds between bases

• phosphodiester bonds

• covalent bonds between bases

• ionic bonds between bases and phosphate groups

Which technique was used to determine the double-helical structure of DNA?

• electrophoresis

• chromatography

• centrifugation

• X-ray crystallography

Analysis of a molecule of DNA found it to contain 200 adenine bases, 20% of the total number of bases in the strand.

How many phosphate groups did it contain?

• 200

• 400

• 800

• 1000

Thymine comprised 36% of the nitrogen bases present in a sample of double stranded DNA.

What was the percentage of guanine in the sample?

• 14

• 28

• 36

• 64

Foot and mouth disease virus (FMDV) is the pathogen that causes foot and mouth disease in livestock.

An analysis of the genetic material of the ‘O’ strain of FMDV showed that it contains 1996 adenine bases, 2131 guanine bases, 1642 uracil bases and 2365 cytosine bases.

Which one of the following describes the genetic material of the virus?

• single-stranded DNA

• single-stranded RNA

• double-stranded DNA

• double-stranded RNA

In which stage of meiosis are chiasmata formed?

• prophase 1

• anaphase 1

• prophase 2

• telophase 2

Why is the formation of chiasmata an important feature of meiosis?

• It ensures that the same genetic characteristics appear in daughter cells as in the parent.

• It ensures that the number of genes in the new chromosomes changes to produce variation.

• It provides opportunities for new genotypes to arise.

• It prevents homologous chromosomes from pairing.