IGCSE 0610 Biology (2026-2028) - Chapter 1 Classification

Chapter 1 Classification

7 characteristics of living organisms?

Movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition.

Movement

An action by an organism that causes a change in position or place.

Respiration

Chemical reactions in cells that break down nutrient molecules and release energy for metabolism.

Sensitivity

Ability to detect or sense stimuli in external or internal environment and make appropriate responses.

Growth

Permanent increase in size and dry mass by an increase in cell number or cell size or both.

Excretion

Removal from organisms of the waste products of metabolism, toxic materials and substances in excess of requirements.

Nutrition

Taking in of materials for energy, growth and development.

How are organisms classified?

They are classified into groups by the features they share.

Define species

Group of organisms that can reproduce and produce a fertile offspring.

Define binomial system

An internationally agreed system of naming species in which the scientific name of an organisms is made up of two parts, genus then species.

What are classification systems for?

To reflect evolutionary relationships.

How do scientists identify whether a species is closely related to one another?

By comparing the sequences of bases in the DNA of organisms from two different species. The more similar the base sequences, the more closely related a species is to one another. They have a more recent common ancestor than species with different DNA base sequences.

How can biologists identify that two organisms are closely related?

Two organisms can be identified as closely related if they belong to the same genus or are the same species (not same species name). FYI: Same species = same genus and same species name.

Characteristics of animals

• Multicellular.

• Cells have a nucleus

• No cell walls or chloroplasts.

• Feed on organic substances made by other living organisms.

Characteristics of plants

• Multicellular.

• Cells have nucleus

• Cell walls made of cellulose

• Have chloroplasts. Feed by photosynthesis. Usually have roots, stems and leaves.

Characteristics of fungi

• Usually multicellular, some are unicellular like yeast.

• Feed saprophytically or parasitically.

• Are usually decomposers.

• Cells have nuclei

• No chloroplasts

• Have cell walls made of chitin.

• Reproduce by spores.

Characteristics of Protoctista

• Multicellular or unicellular.

• May have plant-like cells and animal-like cells.

• Some feed by photosynthesis and some feed on organic substances made by other organisms.

Characteristics of Prokaryotes

• Usually unicellular.

• Cells have no nucleus.

• Often have plasmids.

• Does not have mitochondria.

• Have cell walls that are not made of cellulose

• Circular DNA that is free in the cytoplasm.

Describe the structure of a virus

A virus consists of genetic material (DNA or RNA) surrounded by a protein coat called a capsid

Explain why viruses are not considered living things

Viruses are not considered living because they do not show the seven characteristics of living organisms on their own. They can only reproduce inside a host cell and do not carry out metabolism independently.

How do viruses work

They take over a living host cell's machinery and make multiple copies of themselves. They then burst out of the cell and invade other cells, this process is repeated.

Define Vertebrates

Vertebrates are animals that have a backbone (vertebral column)

Describe the 3 main characteristics of fish

• Scaly skin

• Breathe through gills

• Have fins

Describe the 4 main characteristics of amphibians

• Smooth, moist, scale-less skin

• Live in water when young and on land when adult

• Soft eggs laid in water

• Larva has gills, adults have lungs

Describe the 2 main characteristics of reptiles

• Scaly skin

• Lay rubbery shelled eggs

Describe the 6 main characteristics of birds

• Have beaks

• Forelimbs modified into wings

• Vertebrates with feathers

• Lay hard-shelled eggs

• Endothermic

• Heart has 4 chambers

Describe the 8 main characteristics of mammals

• Give birth instead of laying eggs

• Endothermic

• Heart has 4 chambers

• Has placenta

• Young feed on milk from mammary glands

• Vertebrates with hair

• Have a diaphragm

• Have different types of teeth

Define arthropods

Animals with exoskeleton, several jointed legs but no backbone (invertebrates).

2 characteristics of arthropods

• Have exoskeleton

• Have several pairs of jointed legs

Give the 4 classes of arthropods

• Insects

• Crustaceans

• Myriapods

• Arachnids

Characteristics of insects

• Have 3 pairs of jointed legs

• Body is divided into head, thorax and abdomen

• One or two pairs of wings (one or both may be vestigial)

• Breathe through trachea

• One pair of antennae

Characteristics of crustaceans

• Have more than 4 pairs of jointed legs

• Breathe through gills

• Have an exoskeleton made of chitin, often hardened with calcium to form a tough shell

• 2 pairs of antennae

• 3 body segments (head, thorax, abdomen

Characteristics of arachnids

• Have 4 pairs of jointed legs

• Body divided into cephalothorax and abdomen

• Breathe through book lungs

• No antennae

Characteristics of myriapods

• Have several jointed legs

• Each body segment has a pair of jointed legs

• Body consists of many segments

• Centipedes and millipedes

• One pair of antennae

• Elongated body

What is the green colour in plants caused by?

A pigment called chlorophyll

Define photosynthesis

Photosynthesis is the process by which chlorophyll in plants absorbs energy from sunlight and uses it to convert carbon dioxide and water into glucose and oxygen.

Characteristics of ferns

• Plants with roots, stems and leaves

• Have leaves called fronds

• Reproduce by spores

• Spores are produced on the underside of the fronds

• Do not produce flowers

Characteristics of flowering plants

• Plants with roots, stems and leaves

• Reproduce sexually by means of flowers and seeds

• Seeds produced in ovary, in the flower

2 main groups of flowering plants

Monocotyledonous plants and dicotyledonous plants (monocots and dicots)

Feature of monocots

• Have one cotyledon in their seeds

• Strap-shaped leaves

• Branching root system

• Veins in leaves run parallel to one another

Features of dicots

• Two cotyledons in their seeds

• Tap root system

• Leaves are often broader

• Have network of branching veins

Formula for magnification

magnification = size of drawing divided by size of actual object OR size of real object = size of drawing x magnification

Define dichotomous key

A dichotomous key is a tool used to identify organisms by following a series of paired statements, where each choice leads to the next pair, until you end up with the name of your organism

Give the 5 main vertebrates

Fish, amphibians, reptiles, birds and mammals