Edexcel GCSE Combined Science: Plant Transport

Edexcel GCSE Combined Science: Plant Transport

Introduction

Plants, like all living organisms, require a constant supply of water and nutrients to survive. This tutorial will explore the specialized tissues within plants responsible for transporting these essential substances: xylem and phloem.

Xylem

• Function: Xylem transports water and dissolved minerals upwards from the roots to the rest of the plant.
• Structure: Xylem is made up of dead, hollow cells joined end-to-end, forming long, continuous tubes. These cells are thickened with lignin, providing structural support.
• Transpiration: The movement of water up the xylem is driven by the process of transpiration. Transpiration is the loss of water vapor from the leaves, creating a negative pressure that pulls water upwards.

Phloem

• Function: Phloem transports sugars (produced during photosynthesis) from the leaves to other parts of the plant, where they are used for growth, respiration, or storage.
• Structure: Phloem consists of living cells with sieve plates, which are porous structures that allow the flow of sugars.
• Translocation: The movement of sugars through the phloem is called translocation. It is driven by a pressure gradient created by the active loading of sugars into the phloem at the source (leaves) and the active unloading at the sink (e.g., roots, fruits, growing shoots).

Factors Affecting Transport

Several factors can affect the rate of water and nutrient transport in plants:

• Temperature: Higher temperatures increase the rate of transpiration, leading to faster water movement in the xylem.
• Humidity: Low humidity increases the rate of transpiration, as there is a greater difference in water vapor concentration between the plant and the surrounding air.
• Light intensity: High light intensity increases the rate of photosynthesis, leading to increased sugar production and faster translocation in the phloem.
• Wind: Wind increases the rate of transpiration by removing water vapor from the surrounding air, creating a steeper concentration gradient.

Exam Information

• This topic is covered in Edexcel GCSE Combined Science Biology Paper 1.
• You should be able to describe the structure and function of xylem and phloem.
• You should also be able to explain how transpiration and translocation work, and how factors like temperature, humidity, light intensity, and wind affect these processes.

Key Terms

• Xylem: The plant tissue that transports water and dissolved minerals.
• Phloem: The plant tissue that transports sugars.
• Transpiration: The loss of water vapor from leaves.
• Translocation: The movement of sugars through the phloem.
• Lignin: A substance that strengthens the cell walls of xylem cells.
• Sieve plates: Porous structures that allow the flow of sugars through phloem cells.

Further Study

• You can learn more about plant transport by conducting experiments to investigate the factors affecting transpiration and translocation rates.
• Research different types of xylem and phloem cells, and their adaptations for efficient transport.

Remember to practice answering exam-style questions to solidify your understanding of this topic. Good luck!