A Level Biology Practice Exam

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Master the A Level Biology Exam. Use flashcards and multiple choice questions with hints and explanations to ace your test. Start your journey to excellence!

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What type of cells in the phloem provide metabolic support?

Tracheids
Parenchyma
Companion cells
Sieve tube elements

The correct answer is: Companion cells

Companion cells play a crucial role in providing metabolic support to the phloem tissue. They are specialized cells that are closely associated with sieve tube elements, the primary cells responsible for the transport of sugars and other organic nutrients in plants. Companion cells are packed with organelles, including mitochondria, which are essential for providing the energy required for the active transport of substances into and out of the sieve tubes. These cells assist in maintaining the concentration gradient necessary for the flow of nutrients by loading and unloading sugar into the sieve tube elements. The metabolic activity within companion cells supports the overall functionality of the phloem, ensuring that sieve tubes can effectively transport vital nutrients throughout the plant. They act as the control center for the sieve tube elements, facilitating communication and enabling the efficient transport system that is essential for plant health and growth.