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Cells form the basic units of life on Earth, and most cells are microscopic, needing a magnifier to see. It is estimated that there are 10^30 cells or 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 cells on Earth! There are more living cells on Earth than there are stars in the universe or grains of sand on our planet (Crockford et al., 2023)
What is a cell?
What is a cell?
Cells are the structural and functional unit of all living organisms
Some organisms are unicellular (the organism is 1 cell), some multicellular (the organism is many cells), and others are colonial (unicellular organisms connected and functioning together)
Some cells are prokaryotic, and some are eukaryotic
Robert Hooke discovered plant cells in 1665 while studying cork through a microscope
Subtopics
Subtopics
Cell Theory
Cell Theory
The Cell Theory says that all living things are made of cells
It states that cells are the basic units of life.
Lastly, cells come only from other cells.
Laboratory
Laboratory
Allium (onion) Root Tip: practice looking at cells
Selaginella (spike-moss) leaf: practice with microscope and live material
Questions for Thought
Questions for Thought
How are cells observed?
What magnifier(s) would you use to look small parts of a leaf? Why?
How are plant and animal cells similar/different?
Which magnifier should you use to view fresh, three-dimensional plant material?
Why don’t cells grow indefinitely large?
How do the cell organelles function like a city?
How are chloroplasts and mitochondria interconnected to create energy for a plant cell?
How can prokaryote biomass be so large?
Why are there so many more eukaryote species?
See also the propagation section for comparison questions
Additional Resources
Additional Resources
Scientists discover unknown organelle inside our cells (Phys.org 25Jun2025)
└Tavakoli et al. (2025) Hemifusomes and interacting proteolipid nanodroplets mediate multi-vesicular body formation
Plant cells decide their fate by listening to neighbors and sensing their size (Phys.org 26Jun2025)
└Fung et al. (2025) Multi-scale dynamics influence the division potential of stomatal lineage ground cells in Arabidopsis
AI tool reveals single-cell structure of chromosomes—in 3D (Phys.org 28May2025)
└Wang & Cheng (2025) Reconstructing 3D chromosome structures from single-cell Hi-C data with SO(3)-equivariant graph neural networks
Closely related plant proteins can control cell shape and growth in surprisingly distinct ways (Phys.org 21May2025)
└Brumm et al. (2025) Functional divergence of plant SCAR/WAVE proteins is determined by intrinsically disordered regions
The geologic history of primary productivity (Crockford et al., 2023)
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