Characteristics and Classification of Living Organisms Study Guide

Characteristics of Living Organisms

Movement: An action by an organism or part of an organism causing a change in position or place.
- Plants exhibit slow movement; for example, roots move downwards in response to gravity, and leaves grow towards light.
Respiration: Chemical reactions occurring in cells that break down nutrient molecules to release energy for metabolism. Metabolism refers to all chemical reactions taking place within cells.
Sensitivity: The ability to detect or sense stimuli in the internal or external environment and to produce an appropriate response.
- Animals possess sensory cells and specialized sense organs to detect light, sound, touch, pressure, and chemicals in the air or food.
Growth: A permanent increase in size and dry mass resulting from an increase in cell number.
- Growth includes both cell division and development.
- Development: Defined as an increase in complexity.
Reproduction: The biological process that produces more individuals of the same kind of organism.
Excretion: The removal from an organism of the waste products of metabolism, toxic materials, and substances that are in excess of requirements.
Nutrition: The intake of materials necessary for energy, growth, and development.
- In green plants, nutrition involves photosynthesis, where light energy is utilized to convert carbon dioxide ( $CO_2$ ) and water ( $H_2O$ ) into simple sugars.

Concept and Use of a Classification System

Classification: The scientific method of categorizing organisms into smaller and larger groups based on their similarities.
Hierarchical Levels: The largest classification group is the Kingdom, while the smallest is the species.
Importance of Classification:
- Identification of organisms most at risk of extinction to implement conservation strategies.
- Understanding the evolutionary relationships between various organisms.

The Binomial System

Definition: An internationally agreed-upon system where the scientific name of an organism consists of two parts indicating the genus and the species.
Species: A group of organisms capable of reproducing to produce fertile offspring.
Genus: A group of closely related species that do not interbreed with one another.
Naming Rules:
- The first name is the Genus (always starts with a capital letter).
- The second name is the species (always starts with a small letter).
Scientific Name Examples:
- Lion: Panthera leo
- Tiger: Panthera tigris
- Human: Homo sapien
- Cholera bacterium: Vibrio cholera
- Malaria parasite: Plasmodium malariae
- Grey wolf: Canis lupus
Example Analysis: The lion and tiger belong to the same genus (Panthera) but represent different species (leo and tigris respectively).

Methods of Classifying Organisms

1. Traditional Methods:
- Based on studies of morphology (outward appearance) and anatomy (internal structure).
- Organisms are categorized based on evolutionary relationships (phylogenetic classification).
- Organisms in the same phylogenetic group are believed to share a common ancestor.
- Disadvantages: This method is time-consuming and often lacks high accuracy.
2. Modern Methods:
- Involves analyzing sequences of bases in DNA and sequences of amino acids in proteins.
- DNA consists of a base sequence that dictates the order of amino acids in protein synthesis.
- Relationship Rule: The smaller the difference in the base sequence, the more closely related the species are.
- Each species possesses a distinct number of chromosomes and a unique sequence of DNA bases, making it identifiable from others.

DNA Evidence in Primate Classification

Genetic evidence reveals the following percentage differences in genetic material compared to humans:
- Chimpanzees: $1.2\%$ difference.
- Gorillas: $1.6\%$ difference.
- Orang-tans: $3.1\%$ difference.
Bonobos and chimpanzees share the same percentage difference ( $1.2\%$ ) with humans.
Conclusion: Organisms sharing a more recent ancestor show more similar base sequences. Chimpanzees and Bonobos share a recent ancestor, resulting in a small difference in DNA sequence and a closer relationship.
Advantages of DNA Classification:
- Higher accuracy compared to traditional systems.
- Faster, cheaper, and more efficient.
- Enables large-scale identification of many species simultaneously.
- Requires only trace samples for analysis.

Features of Organisms and the Five Kingdoms

Universal Cell Features: All living organisms have cells containing a cell membrane, cytoplasm, and DNA as genetic material.
Cytoplasmic Structures:
- Ribosomes: Small structures (free-floating or attached to the rough endoplasmic reticulum) that conduct protein synthesis.
- Enzymes: Speed up chemical reactions such as respiration.
Cell Types:
- Prokaryotic: No nucleus.
- Eukaryotic: Contains a nucleus.
The Five Kingdoms:
- Animal, Plant, Fungi, Protoctist, and Prokaryotes (Bacteria).
- Hierarchy within Kingdoms: A Kingdom is divided into Phyla, and a Phyla is divided into Classes.

The Animal Kingdom

General Characteristics:
- Multicellular bodies.
- Cells contain nuclei but lack cell walls and chloroplasts.
- Heterotrophic: Feed on organic substances produced by plants.
Classification: Divided into vertebrates (with backbones) and invertebrates (without backbones).

Classification of Vertebrates

1. Fish:
- Body covered in overlapping scales.
- Streamlined shape for low resistance in water.
- Gills protected by an operculum (bone plate).
- Possess fins for movement.
- Cold-blooded with external fertilization during sexual reproduction.
2. Amphibians:
- Moist skin without scales.
- Four limbs and ears.
- Cold-blooded.
- Lifecycle: Larvae (tadpoles) have gills; adults have lungs.
- Lay jelly-covered eggs.
3. Reptiles:
- Dry scales to minimize water loss.
- Four limbs (except for snakes).
- Cold-blooded.
- Lay eggs with tough, rubbery shells.
4. Birds:
- Feathers on the body; scales on the legs.
- Possess beaks.
- Warm-blooded (maintain constant body temperature).
- Lay hard-shelled eggs.
5. Mammals:
- Body covered with fur or hair; possess whiskers.
- Four different types of teeth.
- Give birth to live young.
- Mammary glands produce milk for young to suck from the teat.
- Warm-blooded (homoithermic).

Invertebrates: Arthropods

Arthropod Characteristics: Meaning "jointed limbs," all have jointed limbs, a hard exoskeleton, and segmented bodies (head, thorax, and abdomen).
1. Insects:
- Three pairs of legs ( $6$ total).
- Body divided into head, thorax, and abdomen.
- One pair of antennae and one pair of compound eyes.
- Usually possess two pairs of wings.
2. Arachnids:
- Four pairs of legs ( $8$ total).
- Body divided into cephalothorax and abdomen.
- Several pairs of simple eyes.
- Chelicerae used for biting and poisoning.
3. Crustacea:
- Five or more pairs of legs ( $\ge 10$ total).
- Body divided into cephalothorax and abdomen.
- Two pairs of antennae and one pair of compound eyes.
- Often have a calcified exoskeleton.
4. Myriapods:
- Ten or more pairs of legs (typically one pair per segment).
- Body not clearly divided into thorax and abdomen.
- One pair of antennae and simple eyes.

The Plant Kingdom

General Characteristics: Green color due to chlorophyll, which converts light energy to chemical energy. Multicellular with roots, stems, and leaves.
1. Ferns:
- Have roots and leaves called fronds (divided into leaflets).
- Do not produce flowers.
- Reproduce via spores developed in sporangia.
2. Flowering Plants:
- Reproduce via flowers; seeds are produced inside the ovary.
- Dicotyledonous (Dicots):
  - Veins: Branched.
  - Leaves: Broad with long stalks.
  - Roots: Tap root system.
  - Seeds: Two cotyledons.
  - Stem: Vascular bundles in a ring.
  - Flowers: Parts in multiples of $4$ or $5$ .
- Monocotyledonous (Monocots):
  - Veins: Parallel.
  - Leaves: Long with short stalks.
  - Roots: Fibrous roots.
  - Seeds: One cotyledon.
  - Stem: Vascular bundles scattered.
  - Flowers: Parts in multiples of $3$ .

Kingdom Fungi, Protoctista, and Prokaryotae

Fungi:
- Usually multicellular with nuclei.
- Cell wall made of chitin (a protein), not cellulose.
- Lack chlorophyll; feed saprophytically or parasitically.
- Structure: Often made of microscopic threads called hyphae. Sporangiophores grow vertically to hold the sporangium containing spores.
Protoctista:
- Single-celled organisms with nuclei.
- Algae (Plant-like): Have chloroplasts and cellulose cell walls (e.g., Chlamydomonas).
- Protozoa (Animal-like): No cell wall or chloroplasts (e.g., Paramecium, Plasmodium).
Prokaryotae (Bacteria):
- Single-celled; no nuclei.
- Cell wall made of murein (peptidoglycan).
- Circular DNA and smaller ribosomes; no mitochondria.
- May have flagella or a slime capsule.
- Reproduce via binary fission.

Characteristics of Viruses

Non-cellular structure.
Consist of a protein coat (capsid) surrounding genetic material (either DNA or RNA).
Only capable of reproduction inside a host cell.
Smaller in size than bacteria.

Dichotomous Keys

Function: Used to identify unfamiliar organisms.
Structure: Consists of pairs of contrasting features (dichotomous means "two branches") moving from general to specific traits.
Example Logic:
- 1. Has legs (Go to 2) / Has no legs (Go to 4).
- 2. Has 6 legs (Go to 3) / Has 8 legs (Spider).
- 3. 1 pair of wings (Housefly) / 2 pairs of wings (Wasp).
- 4. Has shell (Snail) / No shell (Earthworm).

Questions & Discussion

Question (Nov 2013 P23 Q1): Complete Table 1.1 with characteristics based on definitions.
- Note: Definitions provided were for movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition.
Question (J2011 P22 Q1): How can we test if mud from the sea bottom has living organisms?
- (i) Name a solution for testing carbon dioxide: Limewater (or bicarbonate indicator).
- (ii) If $CO_2$ is detected, which two characteristics are linked? Respiration and Nutrition (or Excretion).
Question (J2012 P21 Q1 - Car Analogy):
- (i) Burning fuel to release energy: Matches Respiration.
- (ii) Headlights switching on in dark: Matches Sensitivity.
- (iii) Filling the tank with fuel: Matches Nutrition.
- (iv) Release of waste gases: Matches Excretion.
- Identify a characteristic not carried out by a car: Growth or Reproduction.
Question (M 2015 P21 Q2): Given the name Falco peregrinus, to which species does it belong?
- The species name is peregrinus.
Question (NOV 2012 P12 Q4): What is the binomial name for an African lion?
- Panthera leo.
Question (M2017 P32 Q5): Define the term species.
- A group of organisms that can reproduce to produce fertile offspring.
Question (Nov 2017 P33 Q1): State two features characteristic of all birds.
- Feathers and beaks (or laying hard-shelled eggs).