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phloem

Primary Information
Secondary Information

Definition

Phloem is a living tissue in plants that transport organic compounds, such as sugars, amino acids, and hormones, from the source (usually the leaves) to the sink (usually the roots, growing tips, and storage organs). Phloem is made up of two types of cells: sieve elements and companion cells.

Sieve elements are the long, thin cells that make up the majority of phloem. They have no nuclei and their cytoplasm is filled with sieve tubes. Sieve tubes are connected to each other by sieve plates, which are areas where the cell walls are perforated. This allows the cytoplasm and solutes to flow freely from one sieve element to the next.

Companion cells are smaller cells that are closely associated with sieve elements. They provide support and energy to the sieve elements, and they also play a role in transporting solutes.

Phloem is a vital tissue for plants. It allows plants to transport the resources they need to grow and survive. Phloem is also important for the economy, as it is used to transport sugar from sugarcane and other crops.

How can the word be used?

The phloem is made up of sieve tubes, companion cells, and phloem fibres.

phloem

Different forms of the word

Noun:

  • phloem (the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, to the rest of the plant).
  • phloem fibre (a type of fibre that is found in the phloem).

Adjective:

  • phloem (of or relating to the phloem).

Etymology

The word "phloem" comes from the Greek word "phloios", which means "bark". The word "phloem" was first used in English in the 19th century.

The phloem is a tissue that transports food made in the leaves during photosynthesis to all other parts of the plant. It is made up of sieve tubes, companion cells, and phloem fibres. Sieve tubes are the main cells of the phloem. They are long, thin cells that are connected end to end. Companion cells are smaller cells that are found next to the sieve tubes. They help to support the sieve tubes and transport nutrients. Phloem fibers are strong, supportive cells that are found in the phloem.

Question

What is phloem?

AQA Science Exam Question and Answer

Question:

Explain the role of phloem in plant transportation. Describe how phloem tissue facilitates the movement of organic nutrients throughout the plant. Provide examples of these nutrients and their significance in plant growth and development.

Answer:

Phloem is a vital plant tissue responsible for the transportation of organic nutrients, primarily sugars produced during photosynthesis, throughout the plant. This tissue forms a network of tubes that run from leaves, where sugars are synthesised, to other parts of the plant, such as roots, stems, and fruits.

The movement of nutrients through the phloem occurs through a process called translocation. Sugars, primarily sucrose, are actively transported into the phloem cells from source regions (areas with high sugar concentration, usually leaves). This creates a high osmotic pressure within the phloem cells. As a result, water moves into the phloem cells from adjacent xylem vessels, generating a pressure that pushes the nutrient-rich sap to regions of lower osmotic pressure, known as sinks (areas where sugars are actively used or stored).

Examples of sink regions include growing roots, developing fruits, and storage organs like tubers. In these areas, sugars are utilised for energy production, cell growth, and storage.

Phloem's role in transporting organic nutrients is essential for overall plant growth, development, and reproduction. It ensures that sugars produced in photosynthetic leaves are efficiently distributed to meet the metabolic needs of the entire plant.