Leaving Cert Biology: the new 2027 exam, the investigation and practice questions

The Leaving Cert Biology exam in 2027

The weightings are in the NCCA specification, introduced to schools in September 2025, and the marks and question choice are in the Assessment Arrangements 2027. As a new subject, Biology doesn't get the extra choice older subjects have. The SEC sets and marks both parts, and its sample papers are linked from the arrangements.

The SEC hasn't published 2027 exam dates yet (as of 7 November 2026). In 2026 the written exams ran from 3 to 23 June, with results on Friday 21 August (Department of Education and Youth).

The Biology in Practice Investigation

The SEC issues a brief during fifth year, and the 2027 brief is out. The specification expects the investigation to take up to 20 hours. You research an issue linked to the brief, design and carry out your own experiment to collect primary data, analyse it, and present an evidence-based response in a report you submit in sixth year. Keep a log as you go, so the report can give an honest account of what you did and what you'd change.

What Leaving Cert Biology covers

• Nature of Science (the unifying strand): how biological knowledge is built, tested and used.
• Organisation of Life: the characteristics of life and viruses, biomolecules, cells, genetic inheritance and evolution.
• Structures and Processes of Life: enzymes, photosynthesis and respiration, cell division and protein synthesis, responses including the immune system, reproduction, and transport systems such as the kidneys.
• Interactions of Life: ecology, ecosystems and biodiversity, carrying capacity, microorganisms and nutrient cycling, and genetic engineering.

Grades run from H1 to H8 and O1 to O8, in 10% bands, with CAO points from 100 for an H1 (CAO grading scale).

Leaving Cert Biology practice questions

We wrote these Higher level questions for this guide.

1. Enzymes: the induced fit model

Question: describe the induced fit model of enzyme action. Answer: the active site isn't a rigid shape. When the substrate binds, the active site changes shape slightly to fit it more closely, which strains the substrate's bonds and helps the reaction happen. The products then leave and the enzyme returns to its original shape, ready to be used again.

2. Simpson's Diversity Index

Question: a quadrat survey finds 10 daisies, 6 buttercups and 4 clover plants. Calculate the species diversity index. Answer: the specification gives the formula, where n is the number of one species and N the total:

N = 20. The sum is 10 × 9 + 6 × 5 + 4 × 3 = 132, and N(N − 1) = 380. So D_s = 1 − 132 ÷ 380 = 0.65. Values nearer 1 mean more diversity.

3. Genetic inheritance

Question: in pea plants, tall (T) is dominant to short (t). Two Tt plants are crossed. What fraction of the offspring is expected to be short? Answer: the offspring genotypes are TT, Tt, Tt and tt, so 1 in 4 is tt and short, a 3 : 1 ratio of tall to short. Work through a cross yourself in our Genetics and DNA course and press Mark.

4. Carrying capacity

Question: a rabbit population grows quickly, then levels off. Explain why. Answer: as numbers rise, limiting factors such as food, space and predation hold the population at the carrying capacity: the largest population the habitat can support. Model it in the Population Growth simulator.

Common mistakes

• Leaving the investigation late. It's 40% of the grade: start the research and experiment early.
• Describing a rigid active site when asked about induced fit.
• Mixing up n and N in the diversity index.
• Saying enzymes are killed. They're denatured, because their 3D shape changes.

Use a daily paper as a short timed mock

Our daily papers can only practise part of the written exam, which is 60% of your grade, and none of the investigation. Cells and Molecules covers cells, enzymes, DNA and the immune system; Physiology and Genetics covers photosynthesis, respiration, the kidney, genetics and ecosystems; and Biology (Ordinary Level) suits Ordinary level. A few topics, such as the Hardy Weinberg principle, go beyond the Leaving Cert specification. For when mocks happen, see our Leaving Cert mocks guide.

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