Characteristics and Classification of Living Organisms Study Guide

Getting Started: Features of Living Organisms

Living organisms possess specific biological features that distinguish them from non-living things.
The following list explores potential features found in living organisms:
- Breathing
- Excretion
- Growth
- Reproduction
- A blood system
- Movement
- A nervous system
- Nutrition
- Respiration
- Sensitivity

The Case Study of the Platypus

Historical Background:
- In $1799$ , a dead specimen of an unusual animal was brought from Australia to England.
- The animal's morphology was confusing: it featured a beak and webbed feet (similar to a duck) but possessed fur (similar to a mole).
- Initial uncertainty existed regarding whether the creature laid eggs or gave birth to live young, leading to a debate over whether it was a bird or a mammal.
Scientific Investigation:
- Dr. George Shaw studied the specimen and initially suspected it was a hoax.
- He specifically looked for evidence of the beak being stitched onto the head, but confirmed the beak was a genuine part of the animal's anatomy.
Nomenclature History:
- Dr. Shaw originally named the animal Platypus anatinus.
- Etymology: 'Platypus' means 'flat-footed' and 'anatinus' means 'like a duck'.
- The name 'Platypus' was later found to be already assigned to a species of beetle.
- A second name was suggested: Ornithorhynchus paradoxus.
- Etymology: 'Ornithorhynchus' means 'nose like a bird' and 'paradoxus' means 'puzzling'.
- The name has since reverted to Platypus anatinus.
Classification Decision:
- Proof eventually confirmed that platypuses lay eggs.
- Despite egg-laying, they feed their young with milk, which is a defining mammalian characteristic.
- Consequently, scientists classified the platypus as a mammal in a specific group called monotremes, which also includes echidnas (spiny anteaters).

Characteristics of Organisms

Definition of Organism: An organism is a complete living thing, ranging from bacteria and trees to humans and platypuses.
All living organisms share seven fundamental characteristics, often remembered by the acronym MRS GREN.
Movement:
- Definition: An action by an organism or part of an organism causing a change of position or place.
- Animals generally move their whole bodies, while plants move parts of themselves slowly (e.g., turning toward light).
- Internal movement: Even in stationary plants, chloroplasts can be observed moving within cells under a microscope.
- Rapid plant movement: The Venus flytrap can close its leaves quickly to trap and digest insects for nutrients.
Respiration:
- Definition: The chemical reactions in cells that break down nutrient molecules (usually glucose) and release energy for metabolism.
- Note: This is explored in detail in Chapter $11$ .
Metabolism:
- Definition: The total sum of all chemical reactions that take place in living organisms.
Sensitivity:
- Definition: The ability to detect and respond to changes in the internal or external environment.
- Internal examples: Temperature of the blood.
- External examples: Intensity of sunlight, sound (e.g., using ears to detect speech).
- Defensive response: Pufferfish inflate by swallowing water when detecting a threat to deter predators.
Growth:
- Definition: A permanent increase in size and dry mass.
- Real growth vs. temporary change: A pufferfish inflating is not growth because it returns to its original size.
- Mechanism: Animals and plants grow by producing new cells (detailed in Chapter $16$ ).
- Dry Mass:
- Definition: The mass of an organism after it has been killed and all water has been removed.
- Measurement Process: An organism is killed and dried to find the mass of the body without water. This is repeated with several organisms of the same type over a period to observe the growth trend.
Reproduction:
- Definition: The processes that make more of the same kind of organism.
- While not every individual reproduces, at least some individuals of every kind must do so to ensure species survival (detailed in Chapters $14$ and $15$ ).
Excretion:
- Definition: The removal of the waste products of metabolism and substances in excess of requirements (such as extra water).
- Note: Human excretion is covered in Chapter $13$ .
Nutrition:
- Definition: Taking in materials for energy, growth, and development.
- Requirement: Organisms need chemicals to build cells and energy sources.
- Variation: Methods of nutrition differ significantly between plants and animals (detailed in Chapters $6$ and $7$ ).

The Biological Classification System

Basis of Classification: Classification involves putting organisms into groups based on how closely they are related.
Evolutionary Context:
- The first living organism, a single cell, appeared approximately $4.5 \times 10^9$ years ago.
- Complex life evolved from this ancestor.
- Common Ancestor: A species that lived in the past and is thought to have given rise to several different species alive today.
- Example: All mammals are thought to have descended from a common ancestor that lived more than $200 \times 10^6$ years ago.
Taxonomic Utility: Classification helps scientists understand an organism's function. If a newly discovered animal has hair and produces milk, it is immediately identified as a mammal with known baseline traits.

Species and the Binomial Naming System

Species:
- Definition: A group of organisms that can reproduce with each other to produce fertile offspring.
- Fertile: Able to reproduce.
- Infertile: Not able to reproduce.
- Note: The word 'species' is identical in both singular and plural forms.
Hybrids and Infertility:
- Horses (Equus caballus) and donkeys (Equus asinus) are different species.
- A male donkey and a female horse can produce a mule.
- Mules are strong and healthy but are infertile, proving their parents are separate species.
Binomial System:
- An internationally agreed system for naming species consisting of two parts.
- Genus: The first word; represents a group of species that share similar features and a common ancestor. It always starts with a capital letter.
- Species Identifier: The second word; starts with a lowercase letter.
- Formatting: The scientific name must be printed in italics or underlined if handwritten (e.g., Equus caballus).

Identification via Dichotomous Keys

Dichotomous Key: A method of identifying an organism by working through pairs of statements (branching into two) that eventually lead to the organism's name.
Example Key for Selected Organisms:
- $1$ : Has jointed limbs (Go to $2$ ); No jointed limbs (Earthworm).
- $2$ : More than $5$ pairs of jointed limbs (Centipede); $5$ or fewer pairs of jointed limbs (Go to $3$ ).
- $3$ : First pair of limbs form large claws (Crab); No large claws (Go to $4$ ).
- $4$ : $3$ pairs of limbs (Locust); $4$ pairs of limbs (Spider).

Questions & Discussion

Discussion Questions on Naming:
- Question: Scientists give every species a two-word name used worldwide. Is this a good idea? Why?
- Question: Scientific names are in Latin, a dead language invented for this system in the $18^{th}$ century. Is using Latin a good idea?
Activity $1.1$ : Matching Characteristics and Descriptions (Group Activity):
- Requirements: $14$ blank cards.
- Process: Write the $7$ characteristics on $7$ cards and their descriptions on the other $7$ . Shuffle and place face down in $2$ rows of $7$ . Players match names to descriptions memory-style.
Yak Classification Questions:
- Question: Yaks have the scientific name Bos grunniens. Explain what this tells us about their classification.
- Response: This tells us the yak belongs to the genus Bos and the species grunniens.
- Question: A yakolo is the offspring of a yak and a buffalo. Yakolos are unable to reproduce. Explain how this suggests they belong to different species.
- Response: Since the offspring (yakolo) is infertile, it satisfies the definition that the parents must belong to different species, as they cannot produce fertile offspring together.