Practise IB Biology HL 3.2.8 by evaluating how lignified xylem walls, hollow vessels and pits support transport under negative pressure.
Ehlers-Danlos syndrome (EDS) causes joint hypermobility, where joint movement extends well beyond the normal range. Researchers used two different methods to measure angles of movement at a joint of the smallest (fifth) finger.
Joints are part of the musculoskeletal system of animals, which provides support and movement to the body. Xylem provides support in plants and also transports water and minerals. Explain the adaptations of xylem for its functions.
Structure
a. lignified/lignin in walls provides support/prevents collapsing/resists (negative) pressure/tension;
b. polar walls allow for the adhesion of water molecules (for capillary action);
Transport
c. no cell contents/empty/hollow so transport is not impeded;
d. end walls absent/incomplete/perforated for unimpeded flow OR
long continuous tubes allowing for continuous column of water;
e. pits/gaps/pores in walls allow (lateral) movement/entry and exit of water/minerals;
f. small diameter allows for capillary action/tension in water column;
Each structure must include an explanation.
a. Do not accept cellulose instead of lignin.
b. Accept hydrogen bonding as indicating polar bonding to the walls through adhesive forces.
e. Do not accept reference to osmosis but accept reference to water movement into/out of phloem.
3
Marking guidance:
max