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O-level Biology: Classification

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O-level Biology: Classification
« on: August 26, 2014, 11:58:55 AM »

Classification is the sorting out of living organisms  according to common features.

The classificatory system:
The biggest group is the Kingdom, Kingdoms are divided into  Phyla which are divided into Classes which are divided into orders which are divided into families which are divided into genera which are divided into  species.
Species: A group of living organisms having the same  characters and can breed together successfully producing a fertile offspring.
As we go down the classificatory system, organisms number  decrease. The system can be memorized by
the word  “KPCOF” but don’t forget get adding genus and  species at the end.
  The Binomial System: Each organism has two names written in Latin, the first name  is the name of the genus it belongs to and the second name is the name of its species. This is the binomial system
However, we don’t just write names as we do usually, there  are certain rules that must be followed to write the Latin name:
  • The name of the genus must begin with a capital letter.
  • The name of the species must begin with a small letter.
  • Both names must be written in Italics or if you can’t write  in italics just Underline the name.
For example, we humans belong to the genus Homo and our  species is sapiens. So the correct scientific name of humans is Homo sapiens,  Or H. sapiens for short.
 Other examples:
  • Wolf: Canis lupus
  • Zebra: Equus burchelli
  • Lion: Panthera Leo
Viruses: Viruses are not classified into a kingdom because it is not  considered a living organism because it cannot reproduce on its own. They are very small and measured in nm (nanometers), they  could only be seen through an electronic microscope.
A Virus has a protein coat around it, and genetic material  inside it (RNA or DNA).
Viruses are not considered a living organism because they  don’t have any of the seven characteristics, except that they reproduce by replication, but that only happens inside the host cell.
Viruses strike humans by the following steps:
  • A virus sticks its self to a cell and injects the genetic  material into the it
  • The virus reproduces more of its self by replication
  • The virus keeps on replicating until the cell bursts
  • The new viruses go out and kill other cells
   Kingdom Bacteria:  A  bacterium is a single-celled organism that lives everywhere on earth. It can  only be seen by a microscope

 Structure of bacteria:

Cell Wall: It’s made of a substance called peptidoglycan,  which contains glycogen and sugars.
Cell Membrane: It protects the bacterium from bursting when  too much water is present and gives it its shape.
Cytoplasm: It’s where the chromosomes are kept and it stores  granules of various materials.
Chromosome: A single DNA strand coiled up, it contains the  bacterium’s genes.
Slime Capsule: This is an extra feature that is not present  in all bacteria, it is created by the bacterium when the external conditions  are not favourable.

Flagellum: This is an extra feature that is not present in  all bacteria, it helps in moving and swimming.
   Adaptation: Bacteria have managed to adapt its self in order to survive  in various conditions. They obtain their food by various methods:
Autotrophic Bacteria: They make their own food by photosynthesis.
 Heterotrophic Bacteria: They feed on ready made food, they  are unable to create their own.

There are three types of heterotrophic bacteria, these are:

Saprophytic Bacteria: They secret enzymes which digest dead  organic matter to simple soluble substances which the bacterium feeds on, thus  causing Decomposition.
Mutualistic Bacteria: These live on the roots of plants,  they use Nitrogen in the airspaces between the soil to convert it to nitrate  ions which they feed on.
Pathogenic Bacteria: These are parasites, they cause  diseases to plants and animals.
Bacteria also reproduce extremely quickly by binary fission  producing numerous offspring in a short time.
Some bacteria has a flagellum which is very useful for  movement and swimming.
Some bacteria respire aerobically while others respire  anaerobically.
 Kingdom Fungi:  Fungi are Multicellular organisms, except for yeast which is  a unicellular fungus. Some fungi are not made of cells, but rather of microscopic threads called hyphae.

There are two types of hyphae:

 Reproductive hyphae: They form spores which carry out  reproduction.
Feeding hyphae: They form a network which grows over or  through the food materials, they are called mycelium.
Hyphae are tube like, microscopic structure,  it contains a cytoplasm which contains  glycogen granules, and several nuclei. It doesn’t contain chloroplasts neither  starch granules. In the center there is a vacuole, and the hyphae is surrounded  by a hyphae wall which is sometimes made of chitin. Large numbers of hyphae  grow together through whatever the fungus is feeding on making a branching  network called mycelium.

How Do Fungi Eat ?
 Fungi use a process called saprotrophic nutrition to feed  its self. The hyphae secretes enzymes which digests dead organic matter or  animal waste which is then absorbed by the hyphae to be used by the fungi.

Reproduction Of Fungi
 At some point the fungi produce a reproductive structure,  mushrooms for example, which produces thousands of tiny spores, these are then dispersed to other areas and grow into a new mycelium.

Adaptations Of Fungi
 Fungi are adapted to perform their functions easily by the  following ways:
 They grow long mycelium of hyphae on whatever they feed on,  these secret enzymes which digests what the fungi feeds on.
 They are able to grow tall mushrooms of toadstools so the  spores could be widely dispersed by wind or insects, thus they reproduce quickly.

Why Fungi Are Not Plants:
 Long ago, fungi were classified as plants, but in details,  fungi are actually different to plants, firstly, they do not contain  chloroplasts and they do not undergo photosynthesis. Secondly, Their cell walls
 (hyphae walls) are made of chitin not cellulose as in  plants. Thirdly, their extra supplies of sugar is stored as glycogen not starch. And lastly, they are heterotrophic eaters not autotrophic like plants.
 Kingdom Plant:  Plants are multicellular organisms. The main difference  between them and other organisms is they feed using photosynthesis, which is a process which involves making sugars out of water and carbon dioxide using the  sunlight energy. Plants are green because they contain a lot of chlorophyll  which is a green pigment which traps sunlight for photosynthesis, plants are  autotrophic organisms, they make their own food. Plant cells contain a large  vacuole, a nucleus, chloroplasts and a cell wall made of cellulose, cell walls  are not present in animal cells.
The Plants Kingdom contains several different phyla, but we  will discuss only one of them, which is flowering plants or Angiosperms.
There are two types of flowering plants, monocotyledonous  and dicotyledonous (monocots and dicots for short). The main difference between  both types is the number of cotyledons in their seeds, monocots contain only  one cotyledons in their seeds
 while dicots contain  two in theirs. Cotyledons are structures which grow into the first leaves after  germination.
One could differentiate between the two classes (monocots  and dicots) just by looking at their external features. Monocots have flowers  with number of parts divisible by three (three petals – six leaves etc.), while  dicots have number of parts of the flower divisible by 4 or 5 (4 petals – 10  leaves etc.)
A monocot flower,
 containing 6 petals
 (divisible by 3)
A dicot flower,
 containing 5 petals
 (divisible by 5 )
  The difference  could also be told by looking at the leaves of both flowers, you find that  monocots have long sharp leaves with parallel veins, and dicots have leaves  with branching veins.

 Kingdom Animal:  The animal kingdom is divided into two groups, vertebrates  and invertebrates. To study this kingdom study the following tables.
  Vertebrates Phylum: Chordata
Moist Skin
Dry Scales
 Of limbs
2 fins
 1 tail
4 limbs
4 limbs
4 limbs
4 limbs
Lay Eggs
Lay Eggs
Lay Eggs
Lay Eggs
Give Birth
Exta Info
Live in water
 Tail helps
 Moves frwrd
 Fins change
Live on land
 And water
Lay water-
 Proof shell
Lay eggs
 With hard
 Shell. Have
Have ear
 Young feed
 On mother
  • P.O.C = Points of comparison
  • Cold Blooded = Poikilothermic – Warm Blooded = Homeothermic.
 Invertebrates Phylum: Arthropoda 
  • All arthropods have jointed legs
  • All arthropods have a hard external skeleton called CUTICLE  or EXOSKELETON that encloses their body.
Many    body
 Eyes.    Pair
 Of    antenna
Simple    eyes
 No    antenna
Simple    eyes
 Two    pairs of
Simple    eyes
 Pair    of
 Present/    3
 Pairs    of legs
No    wings/
 4    pairs of
More    than 4
 Pairs    of legs/
 No    wings
No    wings/
 One    pair of
 Legs    on each
 Body    segment
Extra    Info
Wings    are
 Not    present
 In    all of them
Spiders    and
Live    in water/
 Through    gills
  Phylum: Molluscs:
  • They have a soft body and many  have a hard shell
   Phylum: Annelids:
  • Some have heads and antenna
  • They have legs like structures called chaetae which helps them moving
  • Their body is divided into many segments

Tube Worms
 Phylum: Nematodes:
  • They are worms like Annelids
  • Their body is not divided into segments
  • No obvious head or legs
  • No chaetae
  • Some are parasites that live in the digestive system
  • Some live in the soil
Nematodes under microscope[/t][/t][/t][/t][/t][/t][/t][/t]
« Last Edit: August 26, 2014, 12:07:17 PM by Mr Smart »


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