STPM Biology - chapter 2: Revision essay question 2

               2. Explain how the structure of

i)                   Parenchyma, and

ii)                 Xylem tissue sre suited to their function

Answer:

·        Parenchyma cells are unspecialized cells with variety of functions.

·        They are isodiametric cells and function as [packaging tissue and storage tissue.

·        They have thin cellulose cell wall which is permeable, permit passage of materials.

·        The cell walls are transparent and permit entry of light in photosynthesis cells.

·        Cells are loosely packed with many large intercellular spaces.This provide spaces for storage of substances.Entry of water causes vacuole to expand and cells to become turgid,giving support to herbaceous plant.

·        Choloroplast present in some cells permit photosynthesis to take place.

·        Leucoplasts act as storage of starch.

·        Choromoplast present in some cells e.g. petals attaract insects for pollination.

·        Parenchyma can become specialized to carry put specific functions e.g. epidermis,mesophyll,endodermis and aerenchyma.

   ii)   -  Xylem vessel consist of long,hollow xylem  elements joined end to end.

-         When mature,the end walls dissolved to form continuous tube.

-         The xylem walls are impregnated with lignin of different patterns.

-         The lignified wall strengthened the vessels and prevent them from collapsing when water flows through the vessel under high pressure.

-         Xylem vessel consist of dead cell with no protoplasm.More water can flow through the hollow vessels with less obstruction.

-         The lignified wall prevent water escaping except through certain region e.g. pit to the surrounding living cells.

-         Vessels are thin and narrow,help to pull water up by capillarity.


Assignment submitted by group chee tian 2011/2012 (IBM)