Characteristics of living organisms — Combined Science 0653 - Biology Revision Notes & Topical Questions

Section 1 of 20The seven characteristics of living organisms

The seven characteristics of living organisms

Movement

Movement an action by an organism or part of an organism causing a change of position or place.

Respiration

Respiration the chemical reactions in cells that break down nutrient molecules and release energy for metabolism.

Sensitivity

Sensitivity the ability to detect and respond to changes in the internal or external environment.

Growth

Growth a permanent increase in size and dry mass.

Reproduction

Reproduction the processes that make more of the same kind of organism.

Excretion

Excretion the removal of the waste products of metabolism and substances in excess of requirements.

Nutrition

Nutrition the taking in of materials for energy, growth and development.

Section 2 of 20Applying the characteristics

Applying the characteristics

Who shows them

• Who shows them all living organisms show all seven characteristics.
  • (animals, plants, fungi, protoctists and prokaryotes)
• Bacteria are prokaryotes and also show all seven.

Memory aid

• Memory aid the first letters spell MRS GREN.

Excretion and egestion

• Excretion and egestion excretion removes metabolic waste made in cells, whereas egestion removes undigested food as faeces.

Section 3 of 20Species and the binomial system

Species and the binomial system

Species

Species a group of organisms that can reproduce to produce fertile offspring.

Classification

• Classification species are grouped by the features that they share.
• Linnaeus, a Swedish naturalist, introduced a system that divides organisms into smaller and more specialised groups.

Binomial system

• Binomial system an internationally agreed system that gives each organism a Latin name of two parts, the genus and then the species.
• The genus name has a capital letter and the species name does not.
• Typed binomial names are written in italics, as in Homo sapiens.

Section 4 of 20Sequence of classification

1. Kingdom
2. Phylum
3. Class
4. Order
5. Family
6. Genus
7. Species

• Closeness of grouping
  • the more a group is subdivided, the more features its species have in common.

Section 5 of 20Dichotomous keys

Dichotomous key

• Dichotomous key a key that branches into two, giving two descriptions at a time that lead to the identity of an organism.

Using a key

• Using a key follow the statements from the beginning, using the specimen to answer each one, until no statements are left.
• Start from the beginning of the key again for each new organism.

Constructing a key

• Constructing a key write pairs of contrasting statements about visible features so that each choice leads to another pair or a name.

Section 6 of 20Classification and evolutionary relationships

Classification and evolutionary relationships

Aim

• Aim classification systems aim to reflect the evolutionary relationships between species.

Morphology and anatomy

• Morphology and anatomy organisms were first grouped by overall form and by body structure found by dissection,
• but physical features such as colour, shape and size can lead to wrong classification.

Common ancestor

• Common ancestor organisms share features because they descended from a common ancestor.

DNA sequencing

• DNA sequencing organisms that share a more recent ancestor have more similar base sequences in their DNA.
• The more similar the base sequences or amino acid sequences of two species, the more closely related they are.

Section 7 of 20The animal and plant kingdoms

Feature	Animals	Plants
Number of cells	Multicellular	Multicellular
Nucleus	Present	Present
Cell wall	Absent	Cellulose cell wall
Chloroplasts	Absent	Present
Nutrition	Feed on organic substances made by other living things	Feed by photosynthesis

Section 8 of 20More from the specification

1Seven Universal Life Processes

• All living organisms perform movement, respiration, sensitivity, growth, reproduction, excretion,
  • and nutrition (MRS GREN) to maintain thermodynamic order and reproductive continuity.

2Morphological Distinctions in Angiosperms

• Monocotyledonous plants feature single cotyledons, parallel leaf venation, fibrous roots, and floral parts in multiples of three,
• whereas dicots exhibit two cotyledons, reticulate leaf networks, taproots, and floral parts in fours or fives.

3Arthropod Classification by Anatomical Architecture

• Arthropods are classified by segmented bodies, chitinous exoskeletons,
  • and jointed appendages into insects, arachnids (eight legs), crustaceans,
    • (two pairs of antennae)
  • and myriapods.
  • (three body segments, six legs)

4Monocotyledon

• A flowering plant with parallel leaf veins and petals in threes.

5Dicotyledon

• A flowering plant with net veins and petals in fours or fives.

Section 9 of 20The five vertebrate classes

• Vertebrates = animals with a backbone, and there are five classes.
  • Features are used to place an animal in its class.

Section 10 of 20Vertebrate features compared

Class	Main features	Examples
Mammals	Fur or hair, a placenta, young fed on milk from mammary glands, external ears (pinnae), endothermic	Horse, dog, squirrel, human
Birds	Feathers, two legs and two wings, a beak, eggs with hard shells laid on land	Parrot, blue tit, eagle
Reptiles	Dry fixed scales on the skin, eggs with rubbery shells laid on land	Snake, turtle, iguana
Amphibians	Smooth moist skin, adults with lungs live on land, larvae with gills live in water, eggs without shells laid in water	Frog, toad, newt
Fish	Loose wet scales, gills for breathing, eggs without shells laid in water	Flounder, grouper

Section 11 of 20Invertebrates and arthropods

Invertebrates

• Invertebrates animals without a backbone.

Arthropods

Arthropods invertebrates with jointed legs.

• All arthropods have an exoskeleton, a segmented body and jointed legs.

Section 12 of 20Arthropod groups

Class	Main features	Example
Myriapods	Body of many segments, at least one pair of jointed legs on each segment, one pair of antennae	Centipede
Insects	Three-part body (head, thorax and abdomen), six jointed legs, two pairs of wings, one pair of antennae	Butterfly
Arachnids	Two-part body (cephalothorax and abdomen), four pairs of jointed legs, no antennae	Spider
Crustaceans	More than four pairs of jointed legs, chalky exoskeleton, gills, two pairs of antennae	Crab

Section 13 of 20Main and defining features

Main and defining features

Main features

• Main features the features a group has, and some are shared between groups.
• All vertebrates have a backbone and all arthropods have segmented bodies.

Defining feature

• Defining feature a visible feature that sets one group apart from the others.
• Mammals have fur and crustaceans have two pairs of antennae.

Section 14 of 20Fungi, protoctists and prokaryotes

1Five kingdoms

• Five kingdoms animals, plants, fungi, protoctists and prokaryotes.

2Fungi (moulds, mushrooms, yeast)

• Fungi (moulds, mushrooms, yeast) usually multicellular, with nuclei and cell walls that are not cellulose.
• They do not photosynthesise and feed saprophytically on dead matter or parasitically on living things.

3Protoctists (Amoeba, Paramecium, Plasmodium)

• Protoctists (Amoeba, Paramecium, Plasmodium) mostly single-celled, although some are multicellular, and all cells have a nucleus.
• Some have cell walls and chloroplasts, so some photosynthesise and others feed on organic matter.

4Prokaryotes (bacteria, cyanobacteria)

• Prokaryotes (bacteria, cyanobacteria) often single-celled, with a cell wall that is not cellulose and cytoplasm but no nucleus or mitochondria.

Section 15 of 20The plant kingdom

1Chlorophyll

• Chlorophyll at least some parts of any plant are green, and the pigment absorbs light for photosynthesis.

2Ferns

• Ferns have leaves called fronds, make no flowers and reproduce by spores on the underside of the fronds.

3Flowering plants

• Flowering plants reproduce sexually using flowers and seeds, and the seeds form in the ovary.
• They are divided into monocotyledons and dicotyledons.

Section 16 of 20Monocotyledons and dicotyledons

Feature	Monocotyledons	Dicotyledons
Petals	In multiples of three	In multiples of four or five
Leaf veins	Parallel	Reticulated (net-like)
Leaf shape	Narrow, grass-like	Broader, in a wide range of shapes
Example	Wheat	Sunflower

Section 17 of 20Viruses

Viruses

Not classified

• Not classified viruses are not part of any kingdom because they are not considered living organisms.

Reproduction

• Reproduction they cannot carry out the seven life processes, so they take over a host cell to make copies of themselves.

Structure

• Structure genetic material (RNA or DNA) inside a protein coat.

Section 18 of 20More from the specification

Binomial classification system

• Organisms are named using the binomial classification system, consisting of the genus name followed by the species epithet.
  • (e.g. Mus musculus)

Classification using DNA sequences

• Modern biological classification determines how closely related species are by comparing base sequences of DNA and amino acid sequences in shared proteins.

Hierarchical classification systems

• Living organisms are arranged into a hierarchical taxonomic system of ranks: domain, kingdom, phylum, class, order, family, genus,
• and species.

Characteristics of life

• Characteristics of life nutrition — Nutrition is a universal characteristic of living organisms, defined as the taking in of materials for energy, growth,
• and development.
  • (autotrophic in plants, heterotrophic in animals)

Binomial classification system

• Organisms are named using the binomial classification system, consisting of the genus name followed by the species epithet.
  • (e.g. Mus musculus)

Classification using DNA sequences

• Modern biological classification determines how closely related species are by comparing base sequences of DNA and amino acid sequences in shared proteins.

Hierarchical classification systems

• Living organisms are arranged into a hierarchical taxonomic system of ranks: domain, kingdom, phylum, class, order, family, genus,
• and species.

Characteristics of life

• Characteristics of life nutrition — Nutrition is a universal characteristic of living organisms, defined as the taking in of materials for energy, growth,
• and development.
  • (autotrophic in plants, heterotrophic in animals)

Binomial system

• Naming an organism with two Latin names, the genus and the species.

Species

• A group of organisms that can reproduce to produce fertile offspring.

System

• The object or group of objects chosen for study.

Nutrition

• Taking in or making food.

Dichotomous

• Branching into two.

Section 19 of 20Key terms

Term	Meaning
Respiration	The chemical reactions in cells that break down nutrient molecules and release energy.
Sensitivity	The ability to detect and respond to changes in the environment.
Excretion	Removal of the waste products of metabolism and substances in excess of requirements.
Species	A group of organisms that can reproduce to produce fertile offspring.
Binomial system	Naming an organism with two Latin names, the genus and the species.
Dichotomous key	A key that branches in two to identify an organism.
Nutrition	Taking in materials for energy, growth and development.
Growth	A permanent increase in size and dry mass.

Term	Meaning
Vertebrate	An animal with a backbone.
Arthropod	An invertebrate with an exoskeleton, jointed legs and a segmented body.
Protoctist	A mostly single-celled organism whose cells have a nucleus.
Prokaryote	An organism whose cells have no nucleus.
Monocotyledon	A flowering plant with parallel leaf veins and petals in threes.
Dicotyledon	A flowering plant with net veins and petals in fours or fives.
Saprophytic	Feeding on dead or decaying matter.
Virus	Genetic material in a protein coat that reproduces only inside a host cell.

Section 20 of 20Exam technique

1

Confusing excretion with egestion — excretion is removal of metabolic waste and egestion is removal of undigested food.

2

Thinking bacteria are not living — bacteria are prokaryotes and show all seven characteristics.

3

Saying growth is any increase in size — growth is a permanent increase in size and dry mass.

4

Writing the genus with a small letter or the species with a capital — the genus has a capital and the species does not.

1

Confusing arachnids with crustaceans — arachnids have four pairs of legs and no antennae, crustaceans have more than four pairs and two pairs of antennae.

2

Saying all protoctists photosynthesise — only some have chloroplasts.

3

Treating viruses as a kingdom — they are not classified as living.

4

Giving a backbone as a defining feature of mammals — all vertebrates have one, and fur is the defining feature.

5

Saying ferns reproduce by seeds — they reproduce by spores.