CHAPTER 1_Characteristics and Classification of living Organisms

Characteristics and Classification of living Organisms

• Movement

• Respiration

• Sensitivity

• Growth

• Reproduction

• Excretion: toxins in the body that gets rid of.

• Nutrition

→ How to Remember: MRS. H. GREN

How Organisms are Classified

• defined in a specific group

• can be classified by their features

• a species is defined as a group of organisms that can be reproduced to produce fertile offsprings

The Binominal System

Linnaeus (Swedish naturalist): Developed a system to classify organisms into increasingly specific groups.

Subdivision: The more subdivided → the more features’ organisms share.

• Naming (Binomial System):

  • Scientific name = 2 parts (Latin).

  • Genus (capital letter) + species (lowercase).

  • Example: Homo sapiens.

  • Typed names are always italicised (shows they are Latin).

• Classification hierarchy:
  Kingdom → Phylum → Class → Order → Family → Genus → Species

Exam Tip – Classification

• Mnemonic for order: King Philip Came Over For Gran’s Spaghetti
  (Kingdom → Phylum → Class → Order → Family → Genus → Species)

Dichotomous Keys

• Definition: Keys identify organisms by asking questions about their features.

• Dichotomous = “branching into two”:

  • At each step → given 2 possible descriptions.

  • Choose 1 → leads to the next pair of descriptions.

• Process:

  1. Pick one organism.

  2. Start at the beginning of the key.

  3. Follow choices until organism is named.

  4. Repeat from the start with the next organism.

Example – Dichotomous Key for Leaves

Question: The diagram shows a leaf. Use the key to identify the leaf.

Key:

1. Leaf with several small leaflets → go to 2
     Leaf with one large leaf blade → go to 3

2. Leaflets broad and flat → A
     Leaflets narrow and hair-like → B

3. Leaf with smooth edge → C
     Leaf with toothed edge → D

Reflecting Evolutionary Relationships

• Purpose of classification: Show evolutionary relationships between species.

• Traditional method: Grouped organisms by shared physical features.

  • More similar features → more closely related.

• Limitations:

  • Using physical traits (colour, shape, size) can be misleading.

  • Often led to incorrect classifications.

Using DNA to Classify Organisms

• Organisms share features due to common ancestry.

  • Example: mammals → hair, mammary glands, external ears (pinnae).

• Early classification: Morphology (form/shape) & anatomy (detailed structure).

• Modern methods: DNA sequencing, biochemistry, microscopes.

• DNA analysis:

  • More similar DNA sequences → more closely related species → more recent common ancestor.

  • Example: Brachinus armiger and B. hirsutus are closely related; DNA differs by only one base.

• Amino acid sequences (coded by DNA) can also show relatedness.

The Five Kingdoms

• First division in classification: Organisms are placed into one of five kingdoms:

  1. Animals

  2. Plants

  3. Fungi

  4. Protoctists

  5. Prokaryotes

A. Animals – Key Features

• Multicellular

• Eukaryotic cells (have a nucleus)

• No cell walls or chloroplasts

• Heterotrophic: feed on organic substances made by other living things

B. Plants – Key Features

• Multicellular

• Eukaryotic cells: contain a nucleus, chloroplasts, and cellulose cell walls

• Autotrophic: feed by photosynthesis

1. Animal Kingdom:

• Definition: All vertebrates have a backbone.

• Five classes of vertebrates:

I. Mammals

II. Birds

III. Reptiles

IV. Amphibians

V. Fish

✅ Exam Tip:

• Focus on skin covering, reproduction (eggs/milk), thermoregulation, and respiration.

• Comparing these features helps answer classification and identification questions.

2. Vertebrates:

I. Reptiles

II. Fish

III. Amphibians

IV. Birds

V. Mammals

3. Invertebrates:

• Definition: Animals without a backbone.

• Key classification feature: Presence or absence of legs.

• Arthropods: Invertebrates with jointed legs, divided into classes:

I. Myriapods

II. Insects

III. Arachnids

IV. Crustaceans

✅ Exam Tip:

• Focus on body segments, number of legs, wings, and antennae — these features often appear in identification questions.

4. Arthropods

1. Arachnids

2. Crustaceans

3. Insects

4. Myriapods

Fungi – Key Features

• Usually multicellular (except yeast)

• Eukaryotic cells: have nuclei, cell walls not made of cellulose

• Heterotrophic nutrition:

  • Saprophytic – feed on dead/decaying material

  • Parasitic – feed on living material

• Do not photosynthesize

A. Protoctists – Key Features

• Mostly unicellular, some multicellular

• Eukaryotic cells: all have a nucleus; some have cell walls and chloroplasts

• Nutrition:

  • Some photosynthesize

  • Some feed on organic substances (heterotrophic)

B. Prokaryotes – Key Features

• Usually unicellular

• Cells: have cell walls (not cellulose) and cytoplasm

• No nucleus and no mitochondria

Plants – Key Features (Extended)

• Green parts due to chlorophyll → absorbs sunlight for photosynthesis

• Includes ferns and flowering plants

Ferns:

• Leaves called fronds

• Reproduce by spores on the underside of fronds (no flowers)

Flowering Plants:

• Reproduction: Sexual via flowers → seeds

• Seeds develop inside the ovary at the base of the flower

• Two groups:

  1. Monocotyledons (monocots)

  2. Dicotyledons (dicots)

Monocotyledons vs Dicotyledons - how to distinguish

1. Flowers:

• Monocots → petals in multiples of 3

• Dicots → petals in multiples of 4 or 5

2. Leaves:

• Monocots → parallel veins

• Dicots → reticulated veins (web-like network throughout the leaf)

Viruses - extended

• Not classified in the Five Kingdoms → not considered living

• Do not carry out the seven life processes themselves

  • Take over a host cell’s metabolic pathways to reproduce

• Structure: Genetic material (DNA or RNA) inside a protein coat