IB Biology B1.1 Carbohydrates and lipids: practice questions

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B1.1-01 · Paper 1A style · multiple choice · 1 mark

How a steroid hormone enters cells

Testosterone is a steroid hormone. It acts by binding to receptor proteins inside its target cells.

How does testosterone get into its target cells? [1]

1. It binds to a pump protein, which uses ATP to carry it into the cell.
2. It is polar, so it diffuses in through the channels formed by aquaporins.
3. It is non-polar, so it can diffuse between the phospholipids of the bilayer.
4. It is a large molecule, so it can only enter the cell by endocytosis.

Show the answer and the reasoning

Answer: C. C is correct. Testosterone, like oestradiol, is a steroid: a lipid built on four fused carbon rings with very few polar groups. It dissolves in the hydrophobic core of the membrane and diffuses straight through the bilayer, down its concentration gradient, before binding to its receptor in the cytoplasm. A is wrong because no energy is needed: simple diffusion is enough for a non-polar molecule. B is wrong on both counts: the molecule is mostly non-polar, and aquaporins are selective channels for water. D is wrong because steroids are small molecules; endocytosis is used for large particles and macromolecules that cannot cross the bilayer.

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The 4 questions in B1.1

1. B1.1-01 How a steroid hormone enters cellsPaper 1A style · multiple choice · 1 mark
2. B1.1-02 Fatty acids and melting pointPaper 1A style · multiple choice · 1 mark
3. B1.1-03 Glycogen as an energy storePaper 1A style · multiple choice · 1 mark
4. B1.1-04 Fat layers in penguinsPaper 2 style · short answer · 5 marks

More of B Form and function

• B1.2 Proteins
• B2.1 Membranes and membrane transport
• B2.2 Organelles and compartmentalization
• B2.3 Cell specialization
• B3.1 Gas exchange
• B3.2 Transport
• B3.3 Muscle and motility
• B4.1 Adaptation to environment
• B4.2 Ecological niches

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Every Biology and Chemistry question here is original, written for practice in the style of the papers set since the 2025 syllabus, with invented data. Developed independently from the International Baccalaureate Organization, which has not endorsed it. Found a mistake? Email vytis@limeadmissions.com with the question id.