(2) 4.2 Xylem, Phloem, and Nutrient transport (Part 2: Phloem)

what is phloem?

phloem = the vascular tissue in plants that conducts dissolved sugars and other metabolic products throughout plant via translocation

Key cellular components: Sieve tube cells / Sieve tube element

• living cells with no nuclei and few organelles

• form chain of elongated, thin-walled cells

• cytoplasm freely diffuses between cells via sieve plate

Key cellular components: Companion cells

• healthy, nucleated and organelle rich cells

• carry out essential cellular processes and share products via paired sieve tube

Key cellular components: Fiber cells

• Secrete lignin (protein) glue that, with cellulose, encases and supports phloem

• fiber cells die in immunity (only dead cells)

Key cellular components: Phloem parenchyma

• store nutrients and immune mechanism to support phloem

what substances does phloem carry

• sugars, amino acids, proteins, hormones, etc.

what are source and sink tissues

source tissues = parts of the plant where nutrients are produced

sink tissues = parts of plants where nutrients are consumed/stored

what is translocation and how does it move nutrients to sink cells

translocation = the active process of moving soluble nutrients from source to sink tissues via phloem

what is the pressure flow theory and what does it do

the pressure flow theory explains bidirectional nutrient movement

The pressure flow theory states that food moves in the phloem from a region of high pressure (source) to low pressure (sink) due to osmotic pressure differences.

Label Phloem :

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