Cells: The Basic Units of Life

Vocabulary-style flashcards covering cell theory, microscopy, levels of organisation, and the structure and function of animal and plant cells.

Cell

The smallest structural and functional unit of all living organisms and the basic unit of life.

Robert Hooke ($1665$)

The first scientist to observe and name ‘cells’ after looking at cork under a microscope.

Antonie van Leeuwenhoek ($1670\text{s}$)

Built powerful lenses and was the first to observe living cells, which he called ‘animalcules’, in pond water.

Matthias Schleiden ($1838$)

A scientist who concluded that all plants are made of cells.

Theodor Schwann ($1839$)

A scientist who concluded that all animals are made of cells, proposing that cells are universal.

Rudolf Virchow ($1855$)

Added to cell theory by stating that all cells come from pre-existing cells (‘omnis cellula e cellula’).

Tenet 1 of Cell Theory

All living things are made up of one or more cells.

Tenet 2 of Cell Theory

The cell is the basic unit of structure and function in living things.

Tenet 3 of Cell Theory

All cells arise from pre-existing cells through cell division.

Unicellular

An organism made of a single cell that performs all life functions, such as Bacteria or Amoeba.

Multicellular

An organism made of many cells that work together and specialise, such as humans or plants.

Levels of Organisation

The structural hierarchy of life: cell $\rightarrow$ tissue $\rightarrow$ organ $\rightarrow$ organ system $\rightarrow$ organism.

Tissue

A group of similar cells working together to perform a shared function, such as muscle tissue.

Organ

Two or more tissue types working together to perform a function, such as the heart.

Organ system

A group of organs working together for a broad function, such as the circulatory system.

Millimetre ($mm$)

$1 \text{ mm} = 1,000$ micrometres; a unit visible to the naked eye.

Micrometre ($\text{μm}$)

$1 \text{ μm} = 1,000$ nanometres; most cells are measured in this unit.

Nanometre ($nm$)

The smallest common unit of scale used for viruses and cell organelles.

Stereo (dissecting) microscope

A microscope with low power ($10\times$ to $40\times$) that provides a $3\text{D}$ image of large specimens.

Compound light microscope

A common classroom microscope with medium–high power ($1,000\times$ to $1,500\times$) used for thin, transparent specimens.

Electron microscope

An extremely high power microscope ($2,000,000\times$) used for fine organelle detail; specimens must be dead and in a vacuum.

Total magnification

The calculation involving Eyepiece magnification $\times$ objective lens magnification.

Field of view

The circular area visible through the eyepiece of a microscope.

Prokaryotic Cell

A small cell ($0.1$ to $5 \text{ μm}$) with no true nucleus where DNA floats freely, such as Bacteria.

Eukaryotic Cell

A larger cell ($10$ to $100 \text{ μm}$) with a true, membrane-bound nucleus and organelles, such as plants and animals.

Nucleus

The control centre of the cell that contains the cell's DNA.

Mitochondria

The organelles that supply energy to the cell; they are numerous in active cells like muscle cells.

Cell membrane

The flexible outer boundary of the cell that controls what substances enter and leave.

Cytoplasm

A jelly-like substance within the cell where many chemical reactions take place.

Muscle cells

Specialised animal cells packed with mitochondria and protein fibres that contract to create movement.

Nerve cells (neurons)

Specialised animal cells with long, thin extensions that carry electrical signals.

Red blood cells

Biconcave disc-shaped cells with no nucleus, used to maximise oxygen transport via haemoglobin.

Cell wall

A rigid layer made of cellulose surrounding plant cells that provides structure and support.

Chloroplasts

Organelles containing chlorophyll where photosynthesis occurs to produce glucose from sunlight.

Large central vacuole

A plant organelle that stores water and nutrients while maintaining turgor pressure for rigidity.

Guard cells

Pairs of cells that open and close stomata to control gas exchange and water loss.

Root hair cells

Specialised plant cells with long extensions that increase surface area for water and mineral absorption.

Xylem

Plant transport tissue made of dead, hollow cells that moves water and minerals upward from roots.

Phloem

Plant transport tissue made of living cells that moves glucose from the leaves to the rest of the plant.