Complete revision notes for Topic 1 of the CIE IGCSE Biology course: Characteristics and classification of living organisms. Explanations with diagrams for every specification point. These notes are written for candidates taking the Extended paper.
Characteristics and classification of living organisms
1.1 Characteristics of living organisms
Describe the characteristics of living organisms by defining the terms:
MRS GREN
Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition
Movement as an action by an organism or part of an organism causing a change of position
or place
Physical movement by animals
Tropisms in plants
Amoeboid movement by changing shape of the cytoplasm
Etc.
Respiration as the chemical reactions in cells that break down nutrient molecules and
release energy for metabolism
Sensitivity as the ability to detect or sense stimuli in the internal or external environment
and to make appropriate responses
Growth as a permanent increase in size and dry mass by an increase in cell number or cell
size or both
Dry mass: the mass of a biological sample after the water content has been
removed, usually by placing the sample in an oven. The dry mass is used as a
measure of the biomass of a sample
Reproduction as the processes that make more of the same kind of organism
Excretion as removal from organisms of the waste products of metabolism (chemical
reactions in cells including respiration), toxic materials, and substances in excess of
requirements
Nutrition as taking in of materials for energy, growth and development; plants require light,
carbon dioxide, water and ions; animals need organic compounds and ions and usually need
water
,NOTE viruses are non-living according to these criteria:
Do not respire
Do not respond to stimuli
Do not grow
Do not reproduce independently
Produce no waste products
1.2 Concept and use of a classification system
Organisms can be classified into groups by the features that they share
Originally classification relied on observable physical characteristics, but today genetic
analysis is used for accuracy
Organisms were first classified by a Swedish naturalist called Linnaeus in a way that allows
the subdivision of living organisms into smaller and more specialised groups:
Define species as a group of organisms that can reproduce to produce fertile offspring
Define and describe the binomial system of naming species as an internationally agreed
system in which the scientific name of an organism is made up of two parts showing the
genus and species
Rules:
Each kind of organism has a Latin name made up of two words
The first part of the name is the genus that the organism belongs to. The second part
of the name is the species
The scientific names should be in italics if printed and separately underlined if
handwritten
, The genus names should always begin with a capital letter, but the species names
start with a small letter
Examples:
Homo sapiens (humans)
Canis lupus (wolves)
Elephas maximus (elephants)
Felis domesticus (cats)
Explain that classification systems aim to reflect evolutionary relationships
Organisms share features because they originally descend from a common ancestor. BUT
this is not the only reason organisms share features e.g. convergent evolution, so we need
to be careful.
Explain that classification is traditionally based on studies of morphology and anatomy
Morphology is the study of external appearance of living organisms
Anatomy deals with the study of internal structure of living organisms (this was studied
through dissection)
Explain that the sequences of bases in DNA and of amino acids in proteins are used as a
more accurate means of classification
The first organism to have its entire genome sequenced was Haemophilus influenzae in
1995. The first human genome sequence was completed in 2003 (Human Genome Project).
Why is this more accurate?
Convergent evolution makes distant species appear related
(independently evolve similar traits as a result of having to adapt to similar
environments or ecological niches rather than due to common phylogeny)
Mimicry (evolved resemblance between species e.g. to avoid predation)
Explain that organisms which share a more recent ancestor (are more closely related) have
base sequences in DNA that are more similar than those that share only a distant ancestor
1.3 Features of organisms
List the features in the cells of all living organisms, limited to cytoplasm, cell membrane,
DNA as genetic material, ribosomes for protein synthesis and enzymes involved in
respiration
Cytoplasm: the fluid inside a cell where reactions occur. Contains organelles
Cell membrane: a bilayer of phospholipids around the cell that controls the entry/exit of
substances
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller williambennett. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £2.99. You're not tied to anything after your purchase.
