IGCSE Biology Paper-1: Specimen Questions with Answers 138 - 139 of 208

Question 138

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Question

MCQ▾

When we peel the skin of a potato tuber, we remove

Choices

Choice (4)
a.Periderm
b.Epidermis
c.Leaves
d.Cuticle

Answer

a.

Explanation

Periderm is a tissue of secondary origin that replaces damaged epidermis. Cork cambium or phellogen develops from outer layer of cortex. It produces secondary cortex or phelloderm on inner side and cork or phellum on outer side. The cells of phellum are dead, suberized, and impervious to water. Cells of phelloderm are thin walled, living and store food. Phellum, phellogen and phelloderm collectively called as periderm. Periderm is secondary protective tissue. Due to pressure of secondary xylem, epidermis raptures and cortex is lost after two or three years of secondary growth. In potato, a model for periderm studies, periderm replaces the epidermis early in tuber development and suberized phellum constitute tuber’s skin. Thus, when we peel off a potato tuber, we will remove periderm.

The Tubers Skin

The Tuber’s Skin

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Question 139

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Question

MCQ▾

Which of the following plant shown here is Not a pteridophytes?

A Pteridophytes

A Pteridophytes

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Choices

Choice (4)
a.Lopholea
b.Dryopteris
c.Asplenium
d.Pteridium

Answer

a.

Explanation

Features of Pteridophytes

  • The pteridophytes are found in cool, damp, shady places though some may flourish well in sandy-soil conditions.
  • Evolutionarily, they are the first terrestrial plants to possess vascular tissues – xylem and phloem. So, known as vascular cryptogams. They are flowerless and seedless plants.
  • The main plant body is a sporophyte which is differentiated into true root, stem, and leaves.
  • These organs possess well-differentiated vascular tissues. A cambium is altogether absent.
  • In xylem trachea are absent and in phloem companion cells are absent.
  • Primary root is short lived. It is replaced by adventitious roots.
  • The leaves in pteridophyta are small (microphylls) as in Selaginella or large (macrophylls) as in ferns.
  • Pteridophytes show origin and evolution of stele (i. e. , vascular tissue, pericycle and pith).
  • Stem is usually underground rhizome or an erect trunk as in tree ferns. Leaves are large (megaphyllous) and variously shaped.
  • The sporophytes bear sporangia that are subtended by leaf-like appendages called
  • sporophylls. In some cases, sporophylls may form distinct compact structures called strobili or cones (Selaginella, Equisetum).
  • The sporangia produce spores by meiosis in spore mother cells. Sporangia are borne on abaxial side of fertile leaves.
  • These sporangia are borne either singly or in groups, called sori (sing sorus). The spores germinate to give rise to inconspicuous, small but multicellular, free-living, mostly photosynthetic thalloid gametophytes called prothallus.

Examples of Pteridophytes: Rhynia, Homeophyton, Psilotum, Lycopodium, Lepidodendron, Lepidocarpon, Selaginella, Isoetes, Equisetum, Calamites, Ophioglossum, Angiopteris, Adiantum, Dryopteris, Lastraea, Nephrolepis, Polypodium, Pteridium, Marsilea, Salvinia, Azolla.