A Level Biology Practice Exam

What is the function of the tonoplast?

1. to protect the nucleus of plant cells

2. to form a membrane around a vacuole in plant cells

3. to facilitate photosynthesis within chloroplasts

4. to regulate the flow of nutrients into the mitochondria

The correct answer is: to form a membrane around a vacuole in plant cells

The tonoplast is a vital component of plant cell structure, specifically serving as the membrane that surrounds the vacuole. The vacuole itself plays several important roles, including the storage of nutrients, waste products, and maintaining turgor pressure within the cell. The tonoplast is selectively permeable, which means it regulates what enters and leaves the vacuole, thus playing a key role in maintaining cellular homeostasis. By regulating the flow of substances, the tonoplast helps manage the internal environment of the vacuole, which is essential for processes like ion storage, pH regulation, and the breakdown of macromolecules. This is critical for the overall health of the plant and contributes to processes such as plant growth and response to environmental changes. The other choices reference functions associated with different organelles or processes; thus, they do not correctly describe the role of the tonoplast.