Question

Why do hornwort sporophytes differ from those of all other plants?

• A. They have a foot and a basal meristem, so sporogenous tissue is formed continuously

• B. The leaves are short and round, but contain enough conductive tissue to maintain the entire structure

• C. They produce chemicals that are toxic to animals, so can only be spread by wind

• D. They sporophyte is much larger than the gametophyte, which is different than other closely related species

Answer 1

ANSWER:---

THE CORRECT OPTION FOR THIS QUESTION IS - OPTION A IS CORRECT

HORNWORT SPOROPHYTES DIFFER FROM THOSE OF ALL PLANTS BECAUSE ,-- THEY HAVE A FOOT AND A BASAL MERISTEM , SO SPOROGENOUS TISSUE IS FORMED CONTINUOUSLY.

EXPLANATION----

HORNWORTS---

• THEY ARE ALSO CALLED AS ANTHOCEROTOPSIDA, THIS IS A CLASS OF BRYOPHYTA.
• THE SPOROPHYTE OF HORNWORTS IS NOT FULLY DEPENDED UPON GAMETOPHYTE.
• SPOROPHYTE OF HORNWORTS ARE SEMI PARASITE BECAUSE THEY PERFORM PHOTOSYNTHESIS AND PREPARE THEIR FOOD,BUT THEY DEPEND ON GAMETOPHYTE ONLY FOR WATER AND SHELTER.

SPOROPHYTE OF HORNWORTS--

• ZYGOTE IS THE FIRST CELL OF SPOROPHYTE. BY REPEATED SEGMENTATION IT BECOMES AN ELONGATED EMBRYO. AGAIN BY CELL DIVISION , CELL DIFFERENTIATION AND CONTINUOUS GROWTH IT BECOME AN ELONGATED ,SPINDLE SHAPE STRUCTURE CALLED SPOROPHYTE.
• SPOROPHYTES OF HORNWORTS IS DIVIDED INTO TWO REGION FIRST IS FOOT AND SECOND IS CAPSULE.
• MOST IMPORTANT THING IS THE SPOROPHYTE IS APPEAR LIKE A BRISTLE OR HORN SO IT CALLED AS HORNWORTS.
• NOW DIFFERENT PART OF SPORONGIUM -
  • (a) FOOT --
  • IT IS ROUNDED AND BULBOUS STRUCTURE AND DIPPED IN THE TISSUE OF THALLUS. BY FOOT SPOROPHYTE ATTACHED TO THALLUS.
  • THE FOOT IS MADE UP OF MAINLY PARENCHYMA CELLS..
  • IT ACTS AS A HAUSTORIUM AND ABSORBS FOOD AND WATER FROM THE ADJOINING GAMETOPHYTIC CELLS FOR THE DEVELOPING SPOROPHYTE.

SETA IS ABSENT IN HORNWORTS SPOROPHYTE ,PLACE OF THIS THERE IS A ZONE OF MERISTEMATIC IS FOUND ,BY THE ACTIVITY OF THESE MERISTEMATIC CAPSULE IS FORMED.

MERISTEMATIC ZONE---

• THIS IS ALSO CALLED AS INTERMEDIATE ZONE OR INTERCALARY ZONE.
• THIS ZONE IS PRESENT AT THE BASE OF CAPSULE.
• THIS IS CONSISTS OF MERISTEMATIC CELLS.
• THESE CELLS CONSTANTLY ADD NEW CELLS TO THE CAPSULE AT ITS BASE.
• THE PRESENCE OF THIS MERISTEM AT THE BASE GIVE CAPABILITY TO CAPSULE TO GROW FOR A LONG PERIOD.
• THIS IS THE UNIQUE FEATURE OF HORNWORTS SPOROPHYTE AND NOT FOUND IN ANY OTHER BRYOPHYTE.

(b) CAPSULE--

• IT FORM MAJOR AND IMPORTANT PARTS OF SPOROPHYTE.
• IT IS A LONG , SLENDER ,SMOOTH ,UPRIGHT AND CYLINDRICAL STRUCTURE.
• INTERNALLY CAPSULE IS DIVIDED INTO FOLLOWING PARTS--
  • (1) COLUMELLA - THE CENTRE OF CAPSULE IS OCCUPIED BY STERILE MASS OF TISSUE CALLED AS COLUMELLA .
  • (2) ARCHESPORIUM -- IT FOUND BETWEEN COLUMELLA AND CAPSULE WALL.IT EXTENDS FROM BASE TO THE TOP OF CAPSULE.SURROUNDING THE COLUMELLA THERE IS CYLINDER OF SPOROGENOUS TISSUE WHICH IS DIFFERENTIATED INTO ALTERNATIVE BLOCKS OF STERILE BRANCHED PSEUDOELATERS TOWARDS APEX.
  • (3) CAPSULE WALL ---- IT CONSIST MANY LAYER OF CELLS, ABOUT FOUR TO SIX LAYER OF CELLS.,THE OUTERMOST LAYER OF CAPSULE WALL IS EPIDERMIS.  

OTHER OPTION IS NOT FIT IN QUESTION SO ONLY OPTION A IS CORRECT.

FROM ABOVE EXPLANATION A IS CORRECT OPTION.