exam questions

• Explain how nitrate ions are transported from the root to the leaves (2) 

  -       They are transported through the xylem 

  -       In water/solution
• Name a plant tissue that has lignin in its cell walls (1) 

  -       Sclerenchyma fibres or xylem 
• Give 2 reasons why a sieve tube element does not require rough endoplasmic reticulum or ribosomes (2) 

  -       There will be no transcription/MRNA therefore ribosomes not required for translation 

  -       No proteins will be synthesised to be processed in endoplasmic reticulum
• Describe the structure labelled Z that connects the cytoplasm of the companion cell to the sieve tube element (2)

  -       Plasmodesmata, which is a continuation/strand of cytoplasm between the sieve tube element and companion cell, allows for transport of substances 
• Explain the difference in the number of mitochondria between the ST and CC (3) 

  -       Companion cells need more mitochondria for atp 

  -       To load and unload sugars from the sieve tube element 

  -       Role of ST is to provide a channel, so cellular contents are kept at a minimum
• Describe the positions in the stem of those tissues that contain lignin (2) 

  -       Sclerenchyma fibres on the outside of vascular bundle 

  -       Xylem vessels on the inside of the vascular bundle
• Which plant stem is a nucleus found? (1) 

  -companion cell 
• What do the walls of sieve tube elements contain (1) 

  -        Hemicellulose, microfibrils and pectin