Introduction to Cells (1.1)IB Diploma Biology

come only from existingcells.

4-cell stage of a sea biscuit by Bruno Vellutini on Flickr (CC) http://flic.kr/p/daWnnS

CELLS

Hooke’s Micrographia in full! http://lhldigital.lindahall.org/cdm/ref/collection/nat_hist/id/0

1665Hooke names “cells” in his book

“Micrographia” after observing cork under a lense.

All livin

g th

ing

s a

re ma

de o

f cells.

1676 van Leeuwenhoek, a master microscope maker identifies “animalcules” and becomes the father of microbiology.

All

livin

g t

hin

gs

are

m

ad

e o

f ce

lls.

http://en.wikipedia.org/wiki/Antonie_van_Leeuwenhoek

Robert Brown: http://en.wikipedia.org/wiki/Robert_Brown_(botanist)

1833 Robert Brown names the cell nucleus.

Cells are the smallest units of life.

He also discovered Brownian motion:

http://en.wikipedia.org/wiki/Brownian_motion

1837 German Botanist

Mathias Schleiden posits that all plants are made of cells

http://en.wikipedia.org/wiki/File:Matthias_Jacob_Schleiden.jpg

1839 German physiologist

Theodor Schwann, after a lovely dinner with his mate Schleiden and a chat about nuclei, realised that animals were comprised of cells too and stated: “All living things are composed of cells and cell products”

He was also responsible for the discovery of Schwann cells in the PNS, pepsin in the gut, the fact that yeast is organic… and he made up the word ‘metabolism’.

What a legend! Or, as they say in German, legende!

http://en.wikipedia.org/wiki/File:Schwann_Theodore.jpg

Robert Remak: http://en.wikipedia.org/wiki/Robert_Remak

1855 Robert Remak discovers cell division and confirms the existence

of the plasma membrane. Cells come only from pre-existing cells.

German doctor, pathologist and biologist Rudolf Virchow plagiarized Remak’s work and got most of the credit…

(A.K.A. the father of modern pathology)

Image from Amoeba Mike’s Blog (go read the original post): http://amoebamike.wordpress.com/2009/10/06/spontaneous-generation-a-brief-history-of-disproving-it

1864Pasteur disproves the prevailing theory of “spontaneous generation” with his swan-neck flask experiments.

Populations need to be seeded by existing populations: cells come only from pre-existing cells.

1.1.1 According to the cell theory, living organisms are composed of cells

Cells vary in many ways within and between organisms, but some things are common to all cells…

• Surrounded by a membrane

• Contain genetic material (DNA)

• Contain enzymes to catalyze chemical reactions within the cell

• Have an energy-release system (or metabolism)

1.1.2 Organisms consisting of only one cell carry out all functions of life in that cell

All cellular organisms carry out the following functions of life:

• Metabolism (chemical reactions that release energy for cellular use)

• Reproduction (either asexual or sexual)

• Homeostasis (maintain stable internal conditions)

• Growth• Response to the environment• Excretion (removal of waste)

• Nutrition (Obtaining food needed for energy & growth)

1.1.2 Organisms consisting of only one cell carry out all functions of life in that cell

Sugar Cubes by Uwe Hermann on Flickr (CC) http://flic.kr/p/cFMMc

Which dissolves faster: sugar cubes or sugar crystals? Why?

What will go cold faster: French fries or a baked potato? Why?

French Fries by Ian Britton on Flickr (CC) http://flic.kr/p/6RLQ8j

1.1.3 Surface are to volume ratio is important in the limitation of cell size

As the cell gets larger, it requires more resources to be imported and

produces more products (and waste) to be exported.

Therefore, a larger volume requires more exchange across the membrane.

http://commons.wikimedia.org/wiki/Sphere

http://commons.wikimedia.org/wiki/Sphere

As the cell gets larger…

http://commons.wikimedia.org/wiki/Sphere

As the cell gets larger……the surface area tovolume ratio actually gets smaller…

http://commons.wikimedia.org/wiki/Sphere

As the cell gets larger……the surface area tovolume ratio actually gets smaller……so the exchange processes become lessefficient with increasing size.

http://commons.wikimedia.org/wiki/Sphere

Diffusion Pathways

are shorter (and more efficient) in with a larger surface are to volume ratio.

Cells can get around this problem by growing projections, having a flattened form, or being long and thin.

Multicellular organisms have developed circulatory systems to deliver nutrients and oxygen and remove wastes. Exchange structures with large surface areas, such as the lungs and the gut, have evolved.

http://en.wikipedia.org/wiki/Caulerpa

Big Cell Exceptions

Caulerpa species of algae are one giant cell with many

nuclei distributed throughout.

Emergent Properties

Photo by Stephen Taylor: http://www.flickr.com/photos/gurustip/9668701965/in/photostream

the whole is

more than the sum

of its parts

1.1.4 Multicellular organisms have properties that emerge from the interaction of their cellular components

1.1.5 Specialized tissues can develop by cell differentiation in multicellular organisms

• 220 recognized, different highly-specialized cells types in humans

• EX: Rod cells in retina of the eye are light-sensitive

• EX: Red blood cells carrying oxygen and nutrients

• Groups of similar cells form tissues (epithelial, muscle, connective, and nervous)

Screenshot from this excellent tutorial: http://www.ns.umich.edu/stemcells/022706_Intro.html

Differentiation (specialization) of cells: All diploid (body) cells have the same chromosomes.

So they carry all the same genes and alleles.BUT

Not all genes are expressed (activated) in all cells.The cell receives a signal.

This signal activates or deactivates genes.Genes are expressed accordingly and the cell is committed.

Eventually the cell has become specialized to a function.

Key Concept: Structure v. FunctionHow do the structures of specialized cells reflect their

functions? How does differentiation lead to this?

1.1.6 Differentiation involves the expression of some genes and not others in the cell’s genome

1.1.8 Question the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae

• Exception #1: Muscle Fiber• Muscle fibers are much larger

than normal animal cells and may have as many as several hundred nuclei per “cell”

• Exception #2: Fungal Hyphae• In some fungi, each hypha is a single, long tube structure with

many nuclei

• Exception #3: Giant Algae• Can grow as large as 100mm (!)

yet only has one nucleus• An organism this size would be

expected to be made up of many cells…

1.1.9 Investigate functions of life in Paramecium and one named photosynthetic unicellular organism

• Nucleus replicates for asexual reproduction once cell grows large enough

• Membrane maintain homeostasis, takes in nutrients, and excretes wastes

• Metabolic reactions occur in the cytoplasm where enzymes are

• Contractile vacuoles maintain stable water levels in cell• Flagella and cilia allow for movement in response to

environment

Source: http://umanitoba.ca/Biology/BIOL1030/Lab1/biolab1_3.html#Ciliophora

Homeostasis – contractile vacuole fill up with water and expel I through the plasma membrane to manage the water content

Reproduction – The nucleus can divide to support cell division by mitosis, reproduction is often asexual

Metabolism –most metabolic pathways happen in the cytoplasm

Growth – after consuming and assimilating biomass from food the paramecium will get larger until it divides.

Response – the wave action of the cilia moves the paramecium in response to changes in the environment, e.g. towards food.

Excretion – the plasma membrane control the entry and exit of substances including expulsion of metabolic waste

Nutrition – food vacuoles contain organisms the parameium has consumed

1.1.9 Investigate functions of life in Paramecium and one named photosynthetic unicellular organism

Source: http://www.algae.info/Algaecomplete.aspx

Homeostasis –contractile vacuole fill up with water and expel I through the plasma membrane to manage the water content

Reproduction – The nucleus can divide to support cell division, by mitosis (these cells are undergoing cytokinesis)

Metabolism –most metabolic pathways happen in the cytoplasm

Growth – after consuming and assimilating biomass from food the algae will get larger until it divides.

Response – the wave action of the cilia moves the algae in response to changes in the environment, e.g. towards light.

Excretion – the plasma membrane control the entry and exit of substances including the difussion out of waste oxygen

Nutrition –photosynthesis happens inside the chloroplasts to provide the algae with food

1.1.9 Investigate functions of life in Paramecium and one named photosynthetic unicellular organism

1.1.12 Use a light microscope to investigate the structure of cells and tissues.

Modern Microscopy

Image: d2540-6 by USDA on Flickr (CC): http://flic.kr/p/dPqvvY

As we develop more and more sophisticated and precise imaging tools, we can see more detail of the cells and molecules that make us.

Scanning electron microscopes deliver high-resolution, 3D surface images of structures, whereas transmission electron microscopes give us a view inside cells and organelles.

Transmission electron micrograph of HIV particles.

HIV-1. Transmission electron micrograph, via wikimedia commons: http://commons.wikimedia.org/wiki/File%3AHIV-1_Transmission_electron_micrograph_AIDS02bbb_lores.jpg

120nm

False-coloured scanning electron micrograph of HIV (green) budding on a lymphicoyte (blue) http://en.wikipedia.org/wiki/File:HIV-budding-Color.jpg OR http://phil.cdc.gov/phil/details.asp?pid=10000

1μm

Scanning electron micrograph of HIV particles budding on a human lymphocyte.

1.1.13 Draw cell structures as seen with the light microscope.

• Draw in pencil• Make the drawing at least 1/3 page large• Label with straight lines with a ruler• Lines must exactly touch the structure which is named• Include a title• Size of parts must be correct in relation to the larger drawing• Print all labels horizontally on the drawing

1.1.14 Calculate the magnification of drawings and the actual size of structures shown in drawings or micrographs.

5μm

Scanning electron micrograph of human sperm and egg cells.

Image from wikimedia commons http://en.wikipedia.org/wiki/Spermatozoon

2.1.4 Compare the relative size of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using appropriate SI units

Use the

10xrule

of

thumb

http://www.flickr.com/photos/sanna_nixi/799023133/

Molecules ≈ 1nmCell Membrane ≈ 10nm thickVirus ≈ 100nmBacteria ≈ 1μm (1000nm)Eukaryotic animal cell ≈ 10μm Eukaryotic plant cell ≈ 100μm

http://www.flickr.com/photos/rogerss1/3520043134/ http://click4biology.info/c4b/2/cell2.1.htm#size

Of course, there are numerous egg-ceptions.For example, the yolk of an egg is a single animal cell

Bibliography / Acknowledgments

Jason de Nys

Chris Paine