BlogBiologyQCAA Practice Questions for Unit 3 & 4 Biology External Assessment

QCAA Practice Questions for Unit 3 & 4 Biology External Assessment

If you’ve been struggling to source QCAA Biology practice questions for your external assessment (EA), no need to stress anymore because you’ve come across the right page!

We’ve got 25 practice questions you can use for studying for the exam. The solutions to each of the questions are also included so you can review how you’ve gone.

There is no better way to prepare for your EA than to answer some practice questions. So, let’s get started!

QCAA Biology EA Practice Questions

Question 1

Define the term clade (1 mark)

Question 2

Paramecium aurelia and Paramecium caudatum are both species of protozoa who thrive in environments with a lot of moisture. A group of scientists wanted to get a better understanding of the relationship between these two species and the degree to which their needs for survival are similar. From their studies, the following data was collected:

QCE Biology EA Practice Questions - Q2

Image sourced from

(a) Define the term niche (1 mark)

(b) Using this definition, describe what can be seen in the data collected with reference to the competitive exclusion principle (3 marks)

Question 3

Recall the three assumptions of cladistics (3 marks)

Question 4

Based on the following food web:

QCE Biology EA Practice Questions - Q4

Image sourced from

(a) Define the term keystone species (1 mark)

(b) Identify the keystone species in the food web above (1 mark)

(c) Predict what would happen if this species were to be removed from the ecosystem (4 marks)

Question 5

A zoologist with a passion for wombats sets out to monitor a population of them in the nearby bushland. With their first random sample, they collected 100 wombats. They tagged them and released them back into the wild. Two weeks later, the zoologist returned to the same location and took another sample. This time, the sample consisted of 90 wombats — 10 of whom were tagged from the previous capture. 

Using the Lincoln Index, estimate the size of this wombat population (2 marks)

Question 6

Describe the carbon cycle (3 marks)

Question 7

Explain why the biological definition for species is limited (2 marks)

Question 8

(a) Define the term carrying capacity (1 mark)

(b) Explain how population size is limited by the carrying capacity (2 marks)

Question 9

Scientists wanted to monitor the population growth of a species of bacteria. The bacteria was left in a petri dish and the following data was collected:

Time (hours)Number of Bacteria

(a) Construct a graph of the results (1 mark)

(b) Identify the carrying capacity (1 mark)

(c) Identify the mode of population growth (1 mark)

Question 10

Identify the four features of pioneer species that make them effective colonisers (4 marks)

Question 11

Compare the roles of helicase and DNA polymerase in DNA replication (2 marks)

Question 12

Explain the importance of independent assortment and random fertilisation for ensuring genetic variation in offspring (2 marks)

Question 13

Blue eyes are a recessive trait. Individuals who are heterozygous for the gene will not exhibit the trait in their phenotype but are said to be carriers of the trait. 

(a) Construct a Punnett square for the potential offspring of an individual who is heterozygous (carrying the genes for brown and blue eyes) and an individual who is homozygous for the recessive trait (2 marks)

(b) Determine the genotypes and phenotypes of the offspring (4 marks)

Question 14

Explain the process, occurring during protein synthesis, during which genes are transcribed into messenger RNA (3 marks)

Question 15

Based on the karyotype below:

QCE Biology EA Practice Questions - Q15

Image sourced from UNSW Embryology

(a) Identify the abnormality in this assortment of chromosomes (1 mark)

(b) Determine a potential cause for this mutation (2 marks)

Question 16

(a) Define the aneuploidy (1 mark)

(b) Explain how aneuploidy is a result of non-disjunction (2 marks)

Question 17

Describe the process of making recombinant DNA (5 marks)

Question 18

(a) Define the term evolution (1 mark)

(b) Contrast micro- and macroevolution (4 marks)

Question 19

Explain how genetic drift leads to microevolution (2 marks)

Question 20

Recall two of the four diversification patterns between species (4 marks)

Question 21

Explain how population bottlenecks increase the risk of extinction (2 marks)

Question 22

Using the following table:

SpeciesNumber of Individuals

Calculate the Simpson’s Diversity Index for this location (2 marks)

Question 23

Explain how chemical mutagens result in mutation (2 marks)

Question 24

Explain K- and r-selection (4 marks)

Question 25

Define the term genome (1 mark)

Solutions to QCAA Biology EA Practice Questions

Click here to download the solutions to the 25 practice questions above!

If you’ve been looking for other resources to help you study for QCAA Biology, here are some you can access:

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Katelyn Smith was a pioneer in the Queensland ATAR system. After graduating in 2020 with an ATAR of 98.40, she now studies a Bachelor of Advanced Science (Honours) at The University of Queensland — majoring in Physics. Through her studies, she hopes to develop a greater appreciation for how the wonders of the universe work. When she isn’t slaving away behind her unnecessarily large textbooks, she enjoys catching up with friends, scrolling mindlessly through TikTok, and sleeping.

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