Transport in plants (1)

Xylem vessels

Xylem vessels

Elongated cells, joined end to end

Structure of xylem vessels and how its related to its function

1. No organelles present, hollow lumen to allow for more volume of water to be transported

2. Less resistance to flow of water

3. Thick walls made up of cellulose for structural support and adhesion of water

4. Cell walls contain lignin, prevents inward collapse as vessel is under tension

5. Waterproof to prevent loss of water

6. No end walls for less resistance to water

Function and structure of pits in xylem vessels

1. Pits are formed from plasmodesmata

2. Pits are little holes in the xylem that have no lignin and allow lateral movement of water

3. Connect/allow transport of water to all parts of the plant

4. If there is an air bubble, pits allow water to move from one xylem vessel to another bypassing airlock

Function of phloem

Transport of assimilates (sucrose) from source to sink via translocation

Different types of cells in phloem tissue

1. phloem sieve tube (joined end to end to form sieve tubes)

2. companion cells

Structure of sieve tube elements

1. elongated cells joined end to end to form a continuous column

2. sieve elements are living cells

Structure of sieve tube elements and how its related to its function

1. have many plasmodesmata that allow loading of sucrose from companion cells + rapid entry of water near source

2. strong cellulose walls to prevent excessive bulging under pressure

3. has peripheral cytoplasm that lines the cell wall

   less resistant to flow

   max volume of phloem sap containing assimilates transported

4. has sieve plates (perforated cell walls) that contain sieve pores so that cytoplasm of cells are connected

   also acts as a structural feature to prevent excessive cell bulging

Companion cells

next to and closely related with the sieve tube element

Companion cells structures and how its related to its function

1. many mitochondria for ATP during anaerobic respiration

   and for active transport in translocation

2. many ribosomes/RER for polypeptide production

3. numerous plasmodesmata to allow transport of assimilates into sieve tube

Transport of gases in plants

by simple diffusion, leaves are thin and flat, have a branching shape and a network of airspaces meaning that it has a high SA:V which is effective for diffusion