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Summary IGCSE CAIE BIOLOGY (0610) NOTES AND TOPIC QUESTIONS
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IGCSE CAIE BIOLOGY (0610) NOTES AND TOPIC QUESTIONS COMPREHENSIVE SUMMARY AND TOPIC QUESTIONS WITH ANSWERS (CORE AND EXTENDED)
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IGCSE CAIE BIOLOGY (0610) 2023-2025 NOTESAND TOPIC QUESTIONS + ANSWERS
UNIT 1: Characteristics and classification of living
organisms
1.1 Characteristics of living organisms (MRS GREN)
- Movement: an action by an organism or part of an organism causing a change of position or place
- Respiration: the chemical reactions that break down nutrient molecules in living cells to release
energy for metabolism
- Sensitivity: the ability to detect or sense stimuli in the internal or external environment and to
make appropriate responses
- Growth: a permanent increase in size and dry mass by an increase in cell number or cell size or
both
- Reproduction: the processes that make more of the same kind of organism
- Excretion: the removal from organisms of toxic materials, the waste products of metabolism
(chemical reactions in cells including respiration) and substances in excess of requirements
- Nutrition: the taking in of materials for energy, growth and development; plants require light,
carbon dioxide, water and ions; animals need organic compounds, ions and usually need water
1.2 Concept and uses of classification systems
- A species is defined as a group of organisms that can reproduce to produce fertile offspring.
- These species can be classified into smaller, specialised
groups by the features that they share.
- The species in these groups have more and more features
in common the more subdivided they get.
- You can remember the order of classification using the
mnemonic: KING PHILIP CAME OVER FOR GRAN’S
SPAGHETTI
- An organism is given its scientific name using the binomial system. (‘binomial’ means that it is a
name made up of 2 parts)
- The binomial system of naming species is an internationally agreed system in which the
scientific name of an organism is made up of two parts showing the genus and species.
- The genus always starts with a capital letter and the species is always in lowercase.
, - The binomial name is always typed in italics.
Extended:
- Classification systems aim to reflect evolutionary relationships between species.
- Traditional biological classification systems grouped organisms based on the visible similar
features that they shared – specifically using morphology and anatomy.
- This caused many difficulties for scientists in the past because similarities in physical features
do not guarantee that organisms are closely related. (For example, both dolphins and sharks
have streamlined bodies and fins, but dolphins are
mammals, and sharks are fish)
- Organisms share features because they originally descend from a common ancestor.
- Originally, organisms were classified based on how they appeared. However, as technology
advanced, microscopes, knowledge of biochemistry and eventually DNA sequencing allowed us
to classify organisms more accurately.
- Studies of DNA sequences of different species show that the more similar the base sequences
in the DNA of two species, the more closely related those two species are (and the more
recent in time their common ancestor is)
- This means that, for example, the base
sequences in a mammal’s DNA are more
closely related to all other mammals than to
any other vertebrate groups.
- Groups of 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.
, Dichotomous keys: (In any dichotomous key, you’ll have to observe the features of the organisms
carefully and compare them to each statement to identify them)
Example of a dichotomous key question:
You may be asked to construct
your own dichotomous key, in
which case, you:
1. Select Organisms:
Choose the group to
classify.
2. List Characteristics:
Identify observable traits.
3. Start Broad: Use a broad
characteristic to divide
into two groups (e.g., "Has
wings? Yes/No").
4. Subdivide Groups:
Further split each group
with another
characteristic.
5. Continue Until Unique:
Keep dividing until each
organism is uniquely
identified.
6. Test the Key: Verify that it
correctly identifies all
organisms.
7. Format Clearly: Write the
key in a clear, step-by-step
format.
1.3 Features of organisms
- The first division of organisms in the classification system is the kingdom: Animals, Plants, Fungi,
Protoctists, Prokaryotes
- All animals:
o Are Multicellular
o Have cells which have a nucleus but no chloroplasts or cell wall (unlike plant cells)
o Feed on organic substances made by other living things (herbivores feed on plants,
carnivores feed on other animals)
, - All plants:
o Are multicellular
o Have cells which contain a nucleus, cell walls made of cellulose and chloroplasts
o Feed by photosynthesis
Extended
- All Fungi (molds, mushrooms, yeast):
o Are usually multicellular
o Have nuclei
o Have cell walls that are NOT MADE OF CELLULOSE
o Do NOT photosynthesise, instead they feed by saprophytic (on
dead or decaying material) or parasitic (on live material) nutrition
- Protoctists (Amoeba, Paramecium, Plasmodium):
o Most are unicellular, some are multicellular
o ALL have a nucleus, some have chloroplasts and cell walls
o So, some protoctists photosynthesise (like plants) and some
feed on organic matter (like animals).
- All Prokaryotes (Bacteria):
o (Most) Are Unicellular
o Have cell walls that are NOT MADE OF CELLULOSE as well
as cytoplasm but HAVE NO NUCLEUS OR
MITOCHONDRIA
, - Animals can be further classified into either vertebrates (with a backbone) or invertebrates
(without a backbone):
- There 5 classes of vertebrates:
o MAMMALS (humans, deer, bears):
▪ Have fur or hair on their skin
▪ young feed on milk from parents’ mammary glands
▪ have external ears (pinna).
o REPTILES (snakes, turtles):
▪ Have dry, scaly skin
▪ lay eggs with rubbery shells on land
▪ are cold blooded
o BIRDS (bluetit, pigeons):
▪ Have feathers, wings, beaks
▪ lay eggs with hard shells on land
▪ are warm blooded
o FISH (clownfish, grouper):
▪ Have scales on their bodies,
▪ have gills for breathing,
▪ lay eggs without shells in water
▪ are cold blooded
o AMPHIBIANES (frogs):
▪ Have smooth, moist skin
▪ lay eggs without shells in water.
▪ The larvae live in water so have gills to
breathe but develop lungs as they become
adults, allowing them to breathe on land.
- The other category is invertebrates, which can be further classified based on whether they have
legs or not.
- All invertebrates that have jointed legs are part of the arthropod phylum.
- There are 4 classes of arthropods include:
o MYRIAPODS (centipedes):
▪ Body consists of many segments
▪ Each segment contains at least 1 pair of
jointed legs
▪ Have 1 pair of antennae
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