1.1 Introduction to Cells
IB Biology HL 1
Mrs. Peters
Fall 2014
What is a Cell?

Cell: the basic structural
and functional unit of all
organisms
Cells

Discovered by Robert
Hooke in the late 1600’s

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Examined a piece of cork
with a home-made
microscope
Saw numerous box-shaped
structures
Named them “cells” after the
rooms or cells that Monks
lived in
www.history-of-the-microscope.org,
ucmp.berkeley.edu
U1. Cell Theory

The Cell Theory: When Schleiden and
Schwann proposed the cell theory in 1838,
cell biology research was forever changed.
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Schleiden was a botanist (studied plants)
Schwann was a zoologist (studied animals)
Shared notes and came up with the theory
together.
The cell theory also provides us with an
operational definition of "life."
U1. Cell Theory

The cell theory states that:
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All life forms are made from one or more
cells.
Cells only arise from pre-existing cells.
The cell is the smallest form of life.
Evidence for Cell Theory
All life forms are made from one or
more cells.
Evidence: since Robert Hooke, tissue
samples for many different organisms
have been examined using light and
electron microscopes and have been
found to consist of cells.
Evidence for Cell Theory
Cells only arise from pre-existing cells.
Evidence: Louis Pasteur’s experiments in the
1800’s
Education-portal.com
Evidence for Cell Theory
The cell is the smallest form of life.
Evidence: experiments can be done in
which cells are burst open and the
subunits (organelles) are separated
using a centrifuge, the subunits of cells
do not survive long by themselves.
A1. Atypical to Cell Theory

Striated muscles: skeletal muscles which
are made up of muscle fibers that are
longer than a “normal” cell and contain
several hundred nuclei
www.physioweb.org
A1. Atypical to Cell Theory

Mammalian red blood cells (erythrocytes)

Mature blood cells do not contain a nucleus
Macroevolution.net
A1. Atypical to Cell Theory

Giant algae: single cells that are
undifferentiated which are attached to
chains of identical cells or surrounded by
an outer layer that allows them to form
large structures
Oceana.org
A1. Atypical to Cell Theory

Aseptate fungal
hyphae: long threads
on fungi which have
many nuclei but are
not divided into
separate cells by cell
walls
Peer.tamu.edu, psmicrographs.co.uk
U2. Living Things

Living organisms can be multicellular (many
cells) or unicellular (one cell)

All living things need the following functions
to survive:

Metabolism, growth, response to environment,
homeostasis, nutrition, excretion, and
reproduction
U2. Living Things

Which of the following do you think is
considered non-living based on cell theory
and the needs of living things? Why?
A. bacteria B. plankton
C. viruses
U2. Living Things

Answer:
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Viruses because they are not made up of
cells
They reproduce by inserting their DNA into
the DNA of another organism.
Cells become little virus producing factories.
Aids Virus
www.healthoma.com
Influenza Virus
www.dreamstime.com
U2. Functions of Living Things

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Metabolism: the break down of organic
material to make chemicals needed to
sustain life
Growth: ability to grow and develop in
different stages (ex: infant to child to adult)
Response to environment: ability to
detect change in surroundings and
respond accordingly to survive
U2. Functions of Living Things

Homeostasis: the ability to control its
internal environment (this is why you
sweat or shiver)

Nutrition: must be able to obtain food
either by producing its own or consuming
other things
U2. Functions of Living Things

Excretion: the ability to dispose of waste
created from metabolism
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Reproduction: survival depends on
creating offspring either sexually or
asexually
TOK Discussion

There is a difference between the living
and non-living environment.

How are we able to know the difference?
U3. Surface Area to Volume Ratio
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Cells are very small, the size of the
organism does not change the size of cells

Elephant cells are the same size as mouse
cells
U3. Surface Area to Volume Ratio

The volume of a cell determines the level
of metabolic activity that takes place in it

The surface area of a cell determines the
rate of exchange of materials with the
outside environment
U3. Surface Area to Volume Ratio

As volume increases, so does surface
area, but not proportionately

If a cell is cube shaped, let’s see what
happens as the cube changes size

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SA = surface area
Vol = volume
U3. Surface Area to Volume Ratio
Side (mm)
SA (mm2)
Vol (mm3)
Ratio SA to Vol
1
6
1
6:1
2
24
8
3:1
3
54
27
2:1
The overall ratio gets smaller as cells increase in
size.
Surface Area to Volume Ratio

As a cell grows larger, it has less surface
area to obtain materials and the rate of
exchange becomes limiting; the cell can’t
keep up with its requirements
Surface Area to Volume Ratio

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Cells with thin projections or folds (microvilli)
on their surface, increase surface area
without increasing volume
Larger organisms don’t have larger cells,
they have more cells
Surface Area to Volume Ratio

Cell size is limited by surface area to
volume ratio
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The smaller the cell, the higher the surface
area to volume ratio
High surface area to volume ratio facilitates
the exchange of materials between the cell
and its environment more quickly
Cell Size


Most cells are too small to see
with the naked eye; light and
electron microscopes are
needed to see them
Virtual Field Trip Time!
 Write down relative size
comparisons for atoms,
molecules, bacteria, organelles,
eukaryotes (must use correct
units)
 Membrane thickness is ~7nm
Relative Size Review
Invisible:
• 0.04 nm Atom
• 0.05-1 nm small molecules
• 1.2-2 nm large molecules
Visible with electron microscope:
• 7nm Cell Membrane Thickness
• 50-90 nm Viruses
Relative Size Review
Visible with light microscope:
• 0.5-1 µm Bacteria
• 20 nm-1 µm Organelles
• 20 µm Animal cell
• 40 µm Plant cell
U4. Emergent Properties
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Emergent properties/characteristics are
Properties that arise from the interaction of
component parts
Different cell types interact with each other
to allow more complex functions to take
place
Ex: nerve cells interact with muscle cells to
stimulate movement
tissues
Main Types of Cells

Two main types of cells determined by
structure

Prokaryotes
• Greek meaning “before the nucleus”
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Eukaryotes
• Cells that have a nucleus
Prokaryotes

General Characteristics:
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Unicellular
No membrane bound
organelles
No true nucleus
Types:
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Bacteria
• Spirals, rods, spheres
Eukaryotes
 General
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Characteristics:
Unicellular or multicellular
Membrane bound
Organelles
True Nucleus
 Types:
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Plant
Animal
Fungi (don’t need to
worry about this one!)
Microscopes Part 2
 Draw
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the following from Prepared Slides:
Paramecium
Three types of bacteria
Frog Blood
Spirogyra
Start a new paper for this set of drawings,
remember:
• Use pencil or colored pencils
• Fill the box
• Label the box (what and magnification)
Surface Area to Volume Ratio
 Time
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to create!
Obtain a piece of clay and directions
Make each shape and record the surface area
and volume ratios
Compare surface area and volume for each
shape