Organisation of the Organism

2. Organisation of the Organism — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

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📚 Cambridge IGCSE Biology 0610 Hub / Topical Revision

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Lesson summary

2. Organisation of the Organism — IGCSE BIOLOGY notes: Describe the structures and functions of cell organelles, specialised cells and levels of organisation, and calculate magnification.StructureFunctionAnimalPlantNucleusContains the DNA that controls the activities of the cellY…

Chloroplasts
Carbohydrate store
Structures present
Genetic material
Light microscope
Electron microscope

Section 1 of 10Animal and plant cell structures

Structure	Function	Animal	Plant
Nucleus	Contains the DNA that controls the activities of the cell	Yes	Yes
Cytoplasm	Gel of water and solutes that supports organelles and is the site of many reactions, including anaerobic respiration	Yes	Yes
Cell membrane	Holds the cell together and controls which substances enter and leave	Yes	Yes
Ribosomes	Site of protein synthesis	Yes	Yes
Mitochondria	Site of aerobic respiration	Yes	Yes
Cell wall	Made of cellulose; gives support and defines the shape	No	Yes
Chloroplasts	Contain chlorophyll, which absorbs light energy for photosynthesis	No	Yes
Permanent vacuole	Holds cell sap (sugar and salt solution); stores materials and helps support the cell	No	Yes

Section 2 of 10Animal cells compared with plant cells

Nucleus

Nucleus both cell types have a nucleus with a distinct membrane.

Cell wall

Cell wall animal cells have no cellulose cell wall.

Chloroplasts

Chloroplasts animal cells have none, so they cannot photosynthesise.

Carbohydrate store

Carbohydrate store animal cells store glycogen, whereas plant cells store starch or sucrose.

Section 3 of 10Bacterial cells (prokaryotes)

Bacterial cells (prokaryotes)

Size

Size bacteria are microscopic single-celled organisms.

Structures present

Structures present a cell wall, cell membrane, cytoplasm and ribosomes.
- (made of peptidoglycan, not cellulose)

Genetic material

Genetic material there is no nucleus; a circular chromosome of DNA floats free in the cytoplasm.

Plasmids

Plasmids small extra rings of DNA that carry additional genes are sometimes present.
They also lack mitochondria, chloroplasts and other membrane-bound organelles.

Flagella

Flagella some bacteria have long whip-like tails used for movement.

Examples

Lactobacillus and Pneumococcus.
Lactobacillus is rod-shaped and used to make yoghurt; Pneumococcus is spherical and causes pneumonia.

Section 4 of 10Structures seen with different microscopes

Structures seen with different microscopes

Light microscope

Light microscope uses visible light and glass lenses, with a useful magnification of up to about ×1500.
It shows the nucleus, cytoplasm, cell membrane and, in plants, the cell wall, large vacuole and chloroplasts.

Electron microscope

Electron microscope uses a beam of electrons and gives far higher magnification and resolution.
It reveals ribosomes, vesicles, endoplasmic reticulum and the folded inner membranes of mitochondria.
Samples must be dead and in a vacuum, so living processes cannot be watched.

Rough endoplasmic reticulum

Rough endoplasmic reticulum membranes studded with ribosomes look rough under the electron microscope, giving this name.

Resolution

Resolution the ability to separate two points that are close together.

Section 5 of 10Specialised animal cells

Cell	Function	Adaptations
Ciliated cell	Moves mucus in the trachea and bronchi	Surface extensions called cilia beat to move mucus and trapped particles up to the throat
Nerve cell	Conducts impulses	Long to reach different parts of the body; branched extensions contact other cells; fatty sheath around the axon insulates it and speeds up impulses
Red blood cell	Transports oxygen	Biconcave disc gives a large surface area for diffusion; haemoglobin binds oxygen; no nucleus leaves more room for haemoglobin
Sperm cell	Fertilises the egg	Haploid nucleus in the head; acrosome with digestive enzymes to penetrate the egg; mid-piece packed with mitochondria; tail for swimming
Egg cell	Fertilisation and early embryo growth	Haploid nucleus; large amount of cytoplasm with nutrients; membrane changes after one sperm enters so no more can enter

Section 6 of 10Specialised plant cells

Cell	Function	Adaptations
Root hair cell	Absorbs water and mineral ions from soil	Root hair gives a large surface area; thin wall lets water pass quickly; no chloroplasts
Xylem vessel	Conducts water and supports the plant	No end walls, giving a continuous column of water; cells are dead with no organelles or cytoplasm; walls thickened with lignin
Palisade mesophyll cell	Photosynthesis	Column-shaped so many cells fit under the upper epidermis and absorb sunlight; packed with chloroplasts

Section 7 of 10Levels of organisation

Cell

Cell the basic functional and structural unit of all living organisms.

Tissue

Tissue a group of cells of similar structure working together to perform the same function.

Organ

Organ different tissues working together to perform a specific function.

Organ system

Organ system a group of organs with related functions working together to perform body functions.

Organism

Organism all the organ systems working together.

Animal examplesdigestive, circulatory, respiratory, excretory, nervous and reproductive systems.
Plant examplesthe shoot system (leaf, stem, flower) and the root system (xylem, phloem).

Leaf

Leaf an organ made of epidermis, palisade and spongy mesophyll, xylem and phloem tissue.

Tissue

Tissue always made of one type of cell only.

Section 8 of 10Magnification and units

Magnification

Magnification image size ÷ actual size, so actual size = image size ÷ magnification.

Units

Units convert to the same unit before dividing; magnification has no unit, only ×.

Length conversions

1 mm = 1000 µm and 1 cm = 10 mm.
To convert mm to µm multiply by 1000; to convert µm to mm divide by 1000.

Drawing

Drawing use sharp unshaded lines, label the drawing and write the magnification beside it.

Section 9 of 10Key terms

Term	Meaning
Organelle	A small structure inside a cell with a specific function.
Tissue	A group of similar cells that carry out the same function.
Organ	A structure made of several tissues working together.
Organ system	A group of organs working together to carry out a major function.
Differentiation	The process by which a cell develops the structure and features needed for its job.
Prokaryote	A cell with no nucleus, whose DNA floats free in the cytoplasm.
Magnification	Image size divided by actual size.

Section 10 of 10Exam technique

Saying the cell wall controls what enters the cell — it is fully permeable; the cell membrane controls entry and exit.

Thinking animal cells have no mitochondria — all cells that respire aerobically have them.

Confusing a tissue with an organ — an organ contains several different tissues.

Giving magnification a unit such as mm — magnification has no unit, only ×.

Last updated: 14 October 2026