CIE IGCSE Biology: 复习笔记:1.1.5 Features of Organisms: Extended

CIE IGCSE Biology: 复习笔记:1.1.5 Features of Organisms: Extended

The Five Kingdoms: Extended

  • The first division of living things in the classification system is to put them into one of five kingdoms
  • They are:
    • Animals
    • Plants
    • Fungi
    • Protoctists
    • Prokaryotes
  • Main features of all fungi (e.g. moulds, mushrooms, yeast)
    • usually multicellular
    • cells have nuclei and cell walls not made from cellulose
    • do not photosynthesize but feed by saprophytic (on dead or decaying material) or parasitic (on live material) nutrition

A typical fungal cell

  • Main features of all Protoctists (e.g. Amoeba, Paramecium, Plasmodium)
    • most are unicellular but some are multicellular
    • all have a nucleus, some may have cell walls and chloroplasts
    • meaning some protoctists photosynthesise and some feed on organic substances made by other living things

Two examples of protoctist cells

  • Main features of all Prokaryotes (bacteria, blue-green algae)
    • often unicellular
    • cells have cell walls (not made of cellulose) and cytoplasm but no nucleus or mitochondria

A typical bacterial cell

The Plant Kingdom: Extended

  • At least some parts of any plant are green, caused by the presence of the pigment chlorophyll which absorbs energy from sunlight for the process of photosynthesis
  • The plant kingdom includes organisms such as ferns and flowering plants

 Ferns

  • Have leaves called fronds
  • Do not produce flowers but instead reproduce by spores produced on the underside of fronds

Ferns

Ferns reproduce by spores found in the underside of their fronds

Flowering plants

  • Reproduce sexually by means of flowers and seeds
  • Seeds are produced inside the ovary found at the base of the flower
  • Can be divided into two groups – monocotyledons and dicotyledons

Wheat plants are monocotyledons

Sunflowers are dicotyledons

How do you distinguish between monocotyledons and dicotyledons?

1) Flowers

  • Flowers from monocotyledons contain petals in multiples of 3
  • Flowers from dicotyledons contain petals in multiples of 4 or 5

2) Leaves

  • Leaves from monocotyledons have parallel leaf veins
  • Leaves from dicotyledons have reticulated leaf veins (meaning that they are all interconnected and form a web-like network throughout the leaf)

Comparing monocots and dicots

Exam Tip

Identification of monocotyledons and dicotyledons comes up fairly frequently in the multiple choice paper and so it is worth learning the two differences between their flowers and leaves.

Viruses: Extended

  • Viruses are not part of any classification system as they are not considered living things
  • They do not carry out the seven life processes for themselves, instead they take over a host cell’s metabolic pathways in order to make multiple copies of themselves
  • Virus structure is simply genetic material (RNA or DNA) inside a protein coat

Structure of a typical virus

转载自savemyexams

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