Characteristics, Classification & Features Of Organisms

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Notes

Characteristics of Living Organisms (MRS GREN)

**Movement**: an action causing a change of position or place.
**Respiration**: chemical reactions breaking down nutrient molecules to release energy.
**Sensitivity**: ability to detect stimuli and make appropriate responses.
**Growth**: permanent increase in size and dry mass (cell number/size).
**Reproduction**: processes that make more of the same kind of organism.
**Excretion**: removal of toxic metabolic wastes and excess substances.
**Nutrition**: intake of materials for energy, growth and development.

Concept & Uses of Classification Systems

A **species** is a group of organisms that can reproduce to produce fertile offspring.
Linnaeus developed the **binomial system**: scientific name = **Genus** (capital) + **species** (lowercase), e.g.×Homo sapiens×.
Hierarchy: **Kingdom, Phylum, Class, Order, Family, Genus, Species** (mnemonic: King Philip Came Over For Grand's Spaghetti).
**Dichotomous keys** use paired statements to identify organisms by their features.
Modern classification uses **DNA sequencing**; more similar base sequences = more closely related.

The Five Kingdoms

**Animals**: multicellular, no cell walls/chloroplasts, feed on organic substances.
**Plants**: multicellular, cellulose cell walls, chloroplasts, feed by photosynthesis.
**Fungi**: usually multicellular, cell walls not cellulose, saprophytic/parasitic nutrition.
**Protoctists**: mostly unicellular, some have chloroplasts, varied nutrition.
**Prokaryotes** (bacteria): unicellular, cell walls not cellulose, no nucleus or mitochondria.

Features of Animals – Vertebrates

All vertebrates have a **backbone**.
**Fish**: scales, gills, lay eggs in water.
**Amphibians**: moist skin, gills as larvae/lungs as adults, lay eggs in water.
**Reptiles**: dry scaly skin, lungs, lay eggs on land.
**Birds**: feathers, wings, beak, lay eggs with hard shells.
**Mammals**: fur/hair, mammary glands, external ears (pinnas), give birth to live young.

Features of Animals – Invertebrates (Arthropods)

Invertebrates lack a backbone; arthropods have **jointed legs** and **segmented bodies**.
**Myriapods**: many body segments, 1 or 2 pairs of legs per segment.
**Insects**: 3 body parts, 3 pairs of legs, 1 pair of antennae, often 2 pairs of wings.
**Arachnids**: 2 body parts, 4 pairs of legs, no antennae.
**Crustaceans**: 2 pairs of antennae, variable legs, often have a carapace.

Features of Plants (Extended)

Plants contain **chlorophyll** for photosynthesis.
**Ferns**: leaves called fronds, reproduce by **spores** on underside of fronds.
**Flowering plants**: reproduce by flowers and seeds; seeds inside ovary.
**Monocotyledons**: petals in multiples of 3, **parallel leaf veins**, narrow grass-like leaves.
**Dicotyledons**: petals in multiples of 4 or 5, **reticulated leaf veins**, broad leaves.

Viruses (Extended)

Viruses are **not considered living**; they do not carry out MRS GREN.
They consist of **genetic material (RNA or DNA)** inside a **protein coat**.
They replicate by taking over a host cell's metabolic pathways.

Typical animal cell (eukaryotic) – no cell wall or chloroplasts.

Typical plant cell – has cellulose cell wall, chloroplasts and a large vacuole.

Prokaryotic cell (bacterium) – no nucleus or mitochondria.

Structure of a typical virus – genetic material inside a protein coat.

Practice questions

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1.Which characteristic of living organisms is defined as 'the chemical reactions that break down nutrient molecules in living cells to release energy for metabolism'?
Easy
- ARespiration
- BNutrition
- CExcretion
- DGrowth
2.What is the correct order of classification from the broadest to the most specific group?
Easy
- AKingdom, Phylum, Class, Order, Family, Genus, Species
- BKingdom, Class, Phylum, Order, Family, Genus, Species
- CSpecies, Genus, Family, Order, Class, Phylum, Kingdom
- DPhylum, Kingdom, Class, Order, Family, Genus, Species
3.The scientific name for the house mouse is Mus musculus. To which genus does it belong?
Medium
- AMus
- Bmusculus
- CMammal
- DVertebrate
4.Which of the following is NOT a characteristic of all living organisms?
Medium
- APhotosynthesis
- BMovement
- CExcretion
- DReproduction
5.A new organism is discovered. It is unicellular, has a nucleus, and feeds on organic matter. To which kingdom does it most likely belong?
Hard
- AProtoctista
- BProkaryotae
- CFungi
- DAnimalia
6.Which group of vertebrates has moist skin and spends part of its life in water?
Easy
- AAmphibians
- BReptiles
- CFish
- DMammals
7.Two species have very similar DNA base sequences. What does this indicate?
Hard
- AThey are closely related and share a recent common ancestor.
- BThey are not related at all.
- CThey belong to the same species.
- DThey have identical physical features.
8.Which of the following is a feature of all arthropods?
Medium
- ASegmented body
- BSix legs
- CTwo pairs of antennae
- DExoskeleton made of chitin

Slides

Characteristics of Living Organisms

All living organisms share seven life processes: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.
Remember them with the mnemonic MRS GREN.
Movement: a change of position or place. Respiration: chemical reactions releasing energy from nutrients. Sensitivity: detecting and responding to stimuli.
Growth: permanent increase in size and dry mass. Reproduction: making more of the same organism. Excretion: removal of waste products. Nutrition: taking in materials for energy and growth.

Which of the following is NOT a characteristic of all living organisms?

Respiration
Photosynthesis
Excretion
Sensitivity

Classification and the Binomial System

A species is a group of organisms that can reproduce to produce fertile offspring.
Organisms are classified into groups based on shared features. The hierarchy is: Kingdom, Phylum, Class, Order, Family, Genus, Species.
The binomial system gives each organism a two-part scientific name: Genus (capital) and species (lowercase), e.g. Homo sapiens.
Remember the order with: King Philip Came Over For Grand's Spaghetti.

The scientific name of humans is ____ sapiens.

Dichotomous Keys

A dichotomous key is a tool used to identify organisms based on a series of choices between two descriptions.
Each choice leads to another pair of descriptions until the organism is identified.
To use a key: start at the beginning, follow the statements that match your organism, and continue until you reach its name.

Using a dichotomous key, an organism has legs but no wings. Which group does it belong to?

Bird
Cat
Fish
Snake

The Five Kingdoms

Living organisms are divided into five kingdoms: Animals, Plants, Fungi, Protoctists, and Prokaryotes.
Animals: multicellular, no cell walls or chloroplasts, feed on organic substances.
Plants: multicellular, have cellulose cell walls and chloroplasts, feed by photosynthesis.
Fungi: usually multicellular, cell walls not made of cellulose, feed saprophytically or parasitically.
Protoctists: mostly unicellular, some have cell walls and chloroplasts.
Prokaryotes: unicellular, no nucleus or mitochondria, cell walls not made of cellulose.

Which of these are true about the five kingdoms?

All animals are multicellular.
Plant cells have cell walls made of cellulose.
Fungi can photosynthesise.
Prokaryotes have a nucleus.

Vertebrates and Invertebrates

Vertebrates have a backbone. There are five classes: fish, amphibians, reptiles, birds, mammals.
Mammals have fur/hair, feed young with milk, and have external ears (pinnas).
Invertebrates lack a backbone. Arthropods have jointed legs and segmented bodies.
Arthropod groups: myriapods (many legs), insects (3 pairs of legs, 3 body parts), arachnids (4 pairs of legs), crustaceans (2 pairs of antennae).

Which of the following is a defining feature of mammals?

They have scales
They lay eggs
They have fur or hair
They have gills

Monocotyledons and Dicotyledons

Flowering plants are divided into monocotyledons and dicotyledons.
Monocots: petals in multiples of 3, parallel leaf veins, narrow leaves.
Dicots: petals in multiples of 4 or 5, reticulated (net-like) leaf veins, broad leaves.

Monocotyledons have petals in multiples of ____, while dicotyledons have petals in multiples of 4 or 5.

Viruses (Extended)

Viruses are not considered living organisms and are not placed in any kingdom.
They do not carry out the seven life processes themselves.
They consist of genetic material (DNA or RNA) surrounded by a protein coat.
Viruses replicate by taking over a host cell's metabolic machinery.

Why are viruses not classified in any kingdom?

They are too small to see
They do not carry out all seven life processes
They have no genetic material
They are all harmful

Using DNA to Classify Organisms (Extended)

Modern classification uses DNA base sequences to determine evolutionary relationships.
The more similar the DNA sequences of two species, the more closely related they are.
DNA sequencing is more accurate than comparing physical features alone.
Amino acid sequences in proteins can also be used as they are coded by DNA.

Two species have very similar DNA base sequences. What does this suggest?

They are not related
They are closely related
They are the same species
They evolved from different ancestors

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