Biology HL Paper 1 Questions

Each of these questions is designed to assess a student's understanding of key topics within the IB Biology HL course, covering areas like cell biology, genetics, and ecology. They range from specific knowledge about biological processes and structures to understanding broader ecological principles.

Question 1:

• Topic: Cell Biology

• Question: Which of the following organelles is primarily responsible for the synthesis of lipids?

  • A) Rough Endoplasmic Reticulum

  • B) Smooth Endoplasmic Reticulum

  • C) Golgi Apparatus

  • D) Mitochondria

1. Question 2:

   • Topic: Genetics

   • Question: In a certain species of plant, the allele for red flowers (R) is dominant over the allele for white flowers (r). A heterozygous plant is crossed with a white-flowered plant. What is the probability of producing a red-flowered offspring?

     • A) 25%

     • B) 50%

     • C) 75%

     • D) 100%

2. Question 3:

   • Topic: Ecology

   • Question: Which of the following best describes the role of decomposers in an ecosystem?

     • A) They convert inorganic materials into organic matter.

     • B) They capture energy from sunlight and convert it into chemical energy.

     • C) They break down organic matter and release nutrients back into the ecosystem.

     • D) They are primary consumers feeding on producers.

Take the moment to try these questions before referring to the worked solutions below:

Solution to Question 1:

• The question asks about the organelle primarily responsible for the synthesis of lipids.

• The Rough Endoplasmic Reticulum (RER) is studded with ribosomes and is primarily involved in protein synthesis.

• The Smooth Endoplasmic Reticulum (SER) lacks ribosomes and is involved in lipid synthesis and metabolism.

• The Golgi Apparatus is mainly involved in modifying, sorting, and packaging of proteins and lipids.

• Mitochondria are involved in energy production (ATP synthesis).

• Therefore, the organelle primarily responsible for lipid synthesis is the Smooth Endoplasmic Reticulum.

• Answer: B) Smooth Endoplasmic Reticulum

1. Solution to Question 2:

   • The genotype of the heterozygous red-flowered plant is Rr, and the genotype of the white-flowered plant (recessive) is rr.

   • A Punnett square can be used to determine the genotypes of the offspring from this cross.

   • The possible combinations in the offspring are Rr, Rr, rr, and rr.

   • Therefore, there are two chances in four (or 50%) that an offspring will have the Rr genotype, which results in red flowers.

   • Answer: B) 50%

2. Solution to Question 3:

   • This question is about the role of decomposers in an ecosystem.

   • Decomposers, like bacteria and fungi, break down dead organisms and waste products into simpler substances.

   • They release nutrients back into the ecosystem, which can be reused by producers (like plants).

   • Decomposers do not convert inorganic materials into organic matter (like producers do through photosynthesis) nor do they capture energy from sunlight.

   • They are not consumers in the traditional sense; they break down organic matter instead.

   • Answer: C) They break down organic matter and release nutrients back into the ecosystem.

These solutions provide insight into the reasoning behind each answer, helping students understand the fundamental concepts of biology required for IB HL Biology.