Features of Organisms: Extended (CIE IGCSE Biology)

• 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

• 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

• 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