A 2.

2 Cell structure

“What are the features common to all cells and the features that differ? ”
“How is microscopy used to investigate cell structure?”
 Students should be aware that deductive reason can be used to generate predictions from theories. Based on
Cells as the basic structural
A2.2.1 cell theory, a newly discovered organism can be predicted to consist of one or more cells.
unit of all living organisms

Students should have experience of making temporary mounts of cells and tissues, staining, measuring sizes
Microscopy skills &
A2.2.2 using an eyepiece graticule, focusing with coarse & fine adjustments, calculating actual size & magnification,
calculating magnification
producing a scale bar & taking photographs.
Developments in Include the advantages of electron microscopy, freeze fracture, cryogenic electron microscopy, and the use of
A2.2.3
microscopy fluorescent stains & immunofluorescence in light microscopy.
Structures common to cells Typical cells have DNA as genetic material and a cytoplasm composed mainly of water, which is enclosed by a
A2.2.4
in all living organisms plasma membrane composed of lipids. Students should understand the reasons for these structures.
Include these cell components: cell wall, plasma membrane, cytoplasm, naked DNA in a loop and 70S
ribosomes. The type of prokaryotic cell structure required is that of Gram-positive eubacteria such as Bacillus
A2.2.5 Prokaryote cell structures
and Staphylococcus. Students should appreciate that prokaryote cell structure varies. However, students are not
required to know details of the variations such as the lack of cell walls in phytoplasmas and mycoplasmas.
Students should be familiar with features common to eukaryote cells: a plasma membrane enclosing a
compartmentalized cytoplasm with 80S ribosomes; a nucleus with chromosomes made of DNA bound to
A2.2.6 Eukaryote cell structures histones, contained in a double membrane with pores; membrane-bound cytoplasmic organelles including
mitochondria, endoplasmic reticulum, Golgi apparatus and a variety of vesicles or vacuoles including lysosomes;
and a cytoskeleton of microtubules and microfilaments.
Processes of life in Include these functions: homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli
A2.2.7
unicellular organisms and reproduction.
Differences in eukaryotic Include presence and composition of cell walls, differences in size & function of vacuoles, presence of
A2.2.8 cell structure between chloroplasts and other plastids, and presence of centrioles, cilia and flagella.
animals, fungi and plants
Atypical cell structure in Use numbers of nuclei to illustrate one type of atypical cell structure in aseptate fungal hyphae, skeletal muscle,
A2.2.9
eukaryotes red blood cells and phloem sieve tube elements
Students should be able to identify cells in light or electron micrographs as prokaryote, plant or animal. In
Cell types and cell
electron micrographs, students should be able to identify these structures: nucleoid region, prokaryotic cell wall,
A2.2.10 structures viewed in light
nucleus, mitochondrion, chloroplast, sap vacuole, Golgi apparatus, rough and smooth endoplasmic reticulum,
and electron micrographs
chromosomes, ribosomes, cell wall, plasma membrane and microvilli.
Students should be able to draw and annotate diagrams of organelles (nucleus, mitochondria, chloroplasts, sap
Drawing and annotation
vacuole, Golgi apparatus, rough and smooth endoplasmic reticulum and chromosomes) as well as other cell
A2.2.11 based on electron
structures (cell wall, plasma membrane, secretory vesicles and microvilli) shown in electron micrographs.
micrographs
Students are required to include the functions in their annotations.
Cells as the basic structural unit of all living organisms

What do all these images have in common?

They are all called “cells”. But are they biological cells?

In biological sciences a cell is the basic

structural unit of all living organisms.
The first definition of a cell was
developed when Robert Hooke and
other biologists from the 17th century
used microscopes to look at structures
of living organisms. They concluded
that all organism are made of cells. https://www.quora.com/What-did-Robert-Hooke-see-in-the-cork-cell
Cells as the basic structural unit of all living organisms
Based on observations, scientists
have agreed on some key
principles for cells to be
biologically defined as cells.
These principles can be
summarized as the cell theory
and are based on 3 main pillars.

https://youtu.be/4OpBylwH9DU
Cells as the basic structural unit of all living organisms

What are some of the principles of the cell theory?

All living things are made out of cells
• Multicellular organism have a
number of specialized cells
• Unicellular cells are composed of
only one cell
Cells are the smallest units of life
• Organelles carry out various
metabolic functions in the cell
• Cell components cannot survive
alone
Cells come only from other cells
• Cells multiply by division
• All cells descended from
simpler common ancestors

https://i.ytimg.com/vi/q-DPfOgD1IQ/maxresdefault.jpg
Structures common to cells in all living organisms
In addition to these basic principles of life, there are some structures
which are common to cells in all living organisms.

https://www.preproom.org/info-library/default.aspx?t1=3&t2=7&t3=0&t4=0
Structures common to cells in all living organisms
Every cell is surrounded by a cell membrane
composed of lipids. Why is this important?

http://store.bioetch.com/sites/store.bioetch.com/files/imagecache/product_full/cell_membrane_02.jpg

All cells contain genetic material. What’s the significance?

http://www.blogcdn.com/www.engadget.com/media/2013/06/dna-619.jpg

All cells have a cytoplasm - an aqueous solution where chemical

and biological reactions can take place. What is the significance?
Microscopy skills & calculating magnification
Label the diagram
Microscopy skills & calculating magnification

http://www.progensci.co.uk/content/product_pictures/NOVEX/Novex%20Junior%20image%20JPEG.jpg
When using microscopes to measure cells sizes, there are two different magnifications to consider:

1. Magnification of the In order to

work out the
microscope, which is magnification
of the
the magnification of microscope,
the image when the values from
the eyepiece
viewed down a lens and the
microscope. objective lens
need to be
multiplied
together.

2. Magnification of a
drawing/image, which
is the one deduced
from directly
The eyepiece graticule is
measuring a specimen a transparent scale
using an eyepiece embedded within the
eyepiece lens. It usually
graticule. has 100 divisions. It is
superimposed on the
object to be measured.
Microscopy skills & calculating magnification
Measuring sizes of specimen

Eyepiece graticule We will not know the actual

scale in birds eye Eyepiece graticule scale over a size of the eyepiece units until
perspective when human cheek epithelial cell. the eyepiece graticule scale is
looking through The cell lies between 40 and 60 calibrated. To calibrate the
the microscope. on the scale. We therefore say eyepiece graticule scale, a
it measures 20 eyepiece units in miniature transparent ruler
diameter (the difference called a stage micrometer
between 60 and 40). scale is placed on the
microscope stage and is
brought into focus.
Microscopy skills & calculating magnification
On the image below, label the major and
minor divisions of the stage micrometer,
knowing that one major division on the stage
micrometer represents 0.1mm (= 100 μm) and
one minor/small division 0.01mm (= 10 μm).
Stage micrometer with the smallest increment being 0.01mm and 0.1 mm, respectively.

a. What is the total scale length of the eyepiece graticule shown above ? _______ μm
b. What is the length of one minor/small division of the eyepiece graticule?:_____ μm

1m = 100cm 1 cm = 10mm 1mm = 1000m 1m = 1000nm

Microscopy skills & calculating magnification
Microscopy skills & calculating magnification
Examples and how to draw biological specimen:
Microscopy skills & calculating magnification
Combining our knowledge of how to deduce the actual size of a specimen we
viewed under the microscope with our drawing skills of a biological sample, we
can now work out at which magnification we have actually drawn the image:
1. Using the image, you have just produced, draw a straight line below the cell to measure
the total length in cm or mm, just like shown in the example below.

2. Convert your measurement into µm (1mm = 1000µm).

3. Use the formula below and the actual (real) size of your specimen from previous
measurement with the eyepiece graticule and calculate the magnification of the drawing.
Microscopes – Calculating magnification
1. If a red blood cell has a diameter of 8 m and a student shows it with a diameter of 40 mm in
a drawing, what is the magnification of the drawing?

A. × 0.0002
B. × 0.2
C. ×5
D. × 5000 (Total 1 mark)

2. A student observes and draws an Amoeba, using the high power lens of a microscope. The
diameter of the drawing is 100 mm. The actual diameter of the Amoeba is 100 µm. What is the
magnification of the drawing?

A. 0.001
B. 100
C. 400
D. 1000 (Total 1 mark)

3. A sperm cell has a tail 50µm long. A student draws it 75mm long. What is the magnification?
Microscopes – Scale bars
What is the actual size of this weevil?
What is the magnification of the image?

A scale bar is like a little ruler that

provides a visual indication of the
specimen size. It can be used to
calculate magnification of an image 100 µm
or the actual size of a structure.
Microscopes: Calculating magnification using scale bars
What is the magnification of the image?

100 µm
Microscopes: Calculating magnification using scale bars

10 µm 500 nm
50 µm

How can these scale bars be used to calculate the magnification of the images?

Egg cell:

White blood cell:

Streptococcus bacteria:
Microscopes: Calculating specimen size using scale bars
What is the actual size of the weevil?

100 µm
Microscopes: Calculating specimen size magnification
Calculate the actual size of the cell if you
know the magnification of the image:

1. Measure the length of your cell

2. Re-arrange the formula

3. Divide the measured length (in the

most appropriate units) by the
magnification.
Microscopes: Calculating specimen size magnification
1. A student views an image of a cell magnified 350 times. The image is 250mm
long. What is the actual length of the sample in the image?

2. The image below shows a student’s drawing of a plant cell. Based on their
measurements with the eyepiece graticule the student calculated the
magnification of the drawing. Unfortunately they lost the calclulations showing
measured and actual sizes. Work out the real size of the plant cell.
Microscopes: Practice calculating specimen size
Calculate the size of these mitochondria Calculate the size of one of these skin cells

https://courses.candelalearning.com/biologynonmajorslakecountytwo/wp-content/uploads/sites/74/2014/08/Figure_03_01_03_new.jpg
https://courses.candelalearning.com/biononmajors2014fallmaster/wp-content/uploads/sites/70/2014/08/Figure_13_02_01.jpg

Calculate the size of the diatom Calculate the size of the diatom

X 1000 X 5000
Development in microscopy
Many of the most interesting biological events and structures are
smaller than the unaided human eye can see. In fact, human eyes have
a resolution of about 100 µm. On the chart below, notice that of all the
structures listed, only the plant cell is within our resolution--just barely.
Development in microscopy

1665 Robert Hooke 1670 Antony Van 19th century - modern light 20th century development of
discovers cells using Leeuwenhoek perfects microscope allowed discovery electron microscopes to increase
magnifying glasses microscopes by inventing of bacteria, chromosomes, the limit of resolution. Smaller
with a set focal point an adjustable knob to sex cell formation, structures (organelles such as
to view cork. bring images into focus. visualization of the ribosomes, mitochondria) could be
complexity of differnet cells. visiualized and magnified further.

Light microscopes only magnify images up to ca. 1000 times. This is due to the
wavelengths of light which only allow to distinguish between two points to a
certain limit. Electron microscopes can magnify images up to 1 000 000 times
because they use beams of electrons with shorter wavelengths. instead of light.
Development in microscopy - Resolution
Resolution is the ability to distinguish between two objects very close together. The
higher the resolution of an image, the greater the detail that can be seen.

Resolution is limited by the wavelength of too small to be seen

the radiation (the type of light or energy

source) used to view the sample.
Objects much smaller than the wavelength
of the radiation being used do not interrupt
the waves, and so are not detected.
Development in microscopy - Resolution

A microscope with a high

resolving power will allow 2 small
objects which are close together
to be seen as 2 distinct objects

A microscope with a more powerful magnification will not increase the

resolution any further. It will increase the size of the image, but objects
closer than about 200nm (0.2µm) will still only be seen as one point.
 Development in microscopy – Light microscope
0027006-Iris_root,_light_micrograph-SPL.jpg
http://www.sciencephoto.com/image/91252/350wm/C

Iris root (cross-section).

Light micrograph of a
section through the
root of an Iris plant (Iris
germanica) showing a
vascular cylinder.
Magnification: x100
when printed 10
centimeters wide

Thyroid gland,
yroid_gland_light_micrograph
http://www.visualphotos.com/image/1x6012955/th

light
micrograph.
Magnification
5000x

The light microscope doesn’t have a very high resolution and only allows cells or bigger
structures to be visualized. This limit is due to the wavelength of light (400-700nm). In other
words, optical microscopes can not resolve 2 points closer together than the wavelength of
light used, so cells which are smaller than. Cells observed under a light microscope can be
alive and show their natural composition and appearance. Magnification is ca. 1000 – 5000x.
Development in microscopy – Transmission electron
micrograph-of-a-myelinated-axon
edia/126491/Transmission-electron-
http://www.britannica.com/EBchecked/m
Transmission
electron
micrograph of a
myelinated axon.
en/image-gallery/electron/
http://www.vcbio.science.ru.nl/

Plant cell (root

tip cell) imaged
with a
Transmission
Electron
Microscope
(TEM)

The Transmission Electron Microscope (TEM) has a much higher resolution, which allows much higher
magnification than using light microscopes to visualize tiny structures (up to 2nm). However, images
produced would only be black or white, therefore sample material is usually stained using heavy metal ions.
This, together with the vacuum inside the microscope and the electron beams usually. In TEM electrons are
scattered as they pass through a thin section of the specimen, and then detected and projected onto an
image on a fluorescent screen. The transmission electron microscope magnifies objects up to 1 000 000x.
Development in microscopy – Scanning electron
ge-gallery/electron/
http://www.vcbio.science.ru.nl/en/ima

Gills of a fish, the mudskipper

(Periophthalmus argentilineatus)
taken with a Scanning Electron
Microscope (SEM)
chive/01689/flour-mite_1689997i.jpg
http://i.telegraph.co.uk/multimedia/ar

Coloured scanning electron micrograph

of a meal (or flour) mite (Acarus siro).
This species is a common pest of
granaries, mills and kitchens, feeding
particularly on grains and cereals
Like the TEM, the Scanning Electron Microscope (SEM) has a limit of resolution of about 2nm, which
allows very small structures to be visualized. With this technique, electrons are reflected off the surface
of the specimen. The objects also must be stained and fixed using harsh chemicals, as otherwise the
images produced are only black and white. Sample material is therefore dead or cells get killed in the
process. In contrast to the TEM, it produces images with a 3-dimensional appearance, which often are
processed in imaging software. The scanning microscope magnifies objects up to 1 000 000x.
Comparing light and electron microscopes:

Electron microscopes
Light (optical microscopes)
Transmission Scanning

Advantages

Disadvantages
Development in microscopy – Staining of samples
Molecules in cells are
colorless when fewed
under the electon
microscope, so stains
such as methylene blue
to bind DNA or RNA can
be used to visualize the
nucleus ot cytoplasm.

Often that is not

enough, and other
structures need to
be visualized.

Flourescent stains and

immunofluorescence
allow for that.
https://biotium.com/technology/cellular-stains/
Development in microscopy – Staining of samples

https://www.news-medical.net/news/20190111/Fluorescence-Microscopy-Choosing-the-Right-lllumination-System.aspx
Fluorescent
microscopy uses a
much higher intensity
light to illuminate the
sample, which then
excites flourescently
stained specimen.
This emits light at a
longer wavelength.

Immunofluorescence uses cells

of the immune system
(antibodies) which are equipped
with a flourescent marker. Upon
binding to a target a fluorescent
image can be produced.
Development in microscopy – Cryogenic
This preparation technique in microscopy is used
for researching the structure of proteins. The frozen
protein solution of interest is placed in an electron
microscope and patterns of many differently
orientated proteins are produced. Using computer
algorithms, a 3D image can be created.

https://bitesizebio.com/62839/history-of-cryo-electron-microscopy/
https://en.wikipedia.org/wiki/Cryogenic_electron_microscopy#/media/File:Cryogenic_electron_microscopy_workflow.svg
 Development in microscopy – Cryogenic
Cryo-EM analyses proteins at
the instant moment in time
when they freeze. This allows
https://www.jeolusa.com/NEWS-EVENTS/Blog/how-cryo-em-differs-from-tem

scientists to research the change

from one form to another as

ttps://en.wikipedia.org/wiki/Cryogenic_electron_microscopy#/media/File:CroV_TEM_(cropped).jpg
they carry out their function.

https://youtu.be/AzOFSolr0j8?si=64NgvALk-nTDl_jr
Development in microscopy – Freeze-fracture
Freeze-fracture electron microscopy is used to
produce images of surfaces within cells. Rapid
freezing of cells in liquified propane (-190°C) and
subsequent fracturing allows the cell to be
broken along lines of weakness, including the
centre of membranes. Any structures which
appeared globular are transmembrane proteins.

https://upload.wikimedia.org/wikibooks/en/5/51/FreezefractureMU.jpg
Development in microscopy – Freeze-fracture

The cell fractures at the weakest point of the

cell membrane (the hydrophobic interior of
the phospholipid bilayer) splitting it in two
layers. Proteins embedded with the
membrane remain with one of the two
layers. This procedure helps to visualize cell
structures three-dimensionally and to give
insight into the surface of cells..
Relative sizes of particles and cells
Prokaryotes & Eukaryotes
All cells can be divided into two types of cells – prokaryotes and eukaryotes.

Plant

Staphylococcus sp. Bacillus sp. Fungus Animal

Prokaryote cell structures

http://classes.midlandstech.edu/carterp/Courses/bio225/chap04/04-06_Prokaryotic_1.jpg
Prokaryotes were the first organism to evolve on Earth. They
have a simple cell structure and are very small in size (0.5 –
6µm). They are bacteria (e.g. Staphylococcus and bacillus)
which appear in many different forms and sometimes cause
diseases (strep throat, rashes etc). They lack a nucleus, have
a cell wall in addition to a cell membrane and smaller
protein producing ribosomes (70S) than in eukaryotes.
Prokaryote cell structures
Draw a diagram of the bacillus bacteria and outline cell structures such as plasma membrane, cell
wall, nucleoid, cytoplasm and 70S ribosomes, as shown in an electron micrograph:
Prokaryote cell structure & function
The table below summarizes the structures and functions of a prokaryotic cell:
Structure Features Function
• Semi-rigid structure • Maintains the shape (different shapes: coccus,
• Made from peptidoglycan (repeating bacillus, spirillum) of the cell
Cell Wall
disaccharides attached by polypeptides) • Protects the cell
• Prevents the cell from bursting
• Thin, partially permeable layer of • Controls the entry and exit of substances
Cell membrane
phospholipids • Pumps substances in and out by active transport
• Fluid (largely water) filled space inside the • Carries out chemical reactions of metabolism
plasma membrane using enzymes and biochemical molecules.
Cytoplasm • Contains many enzymes and ribosomes
• Does not contain any membrane bound
organelles
• 70S (smaller than eukaryotic ribosomes) • Synthesize (make or manufacture) proteins
Ribosomes
• granular appearance in the EM through transcription & translation
• Central region of the cytoplasm containing • The nucleoid is essential for controlling the
naked (not wrapped around a protein), activity of the cell and reproduction. It is where
Nucleoid single chromosomal DNA transcription and replication of DNA take place
• DNA in prokaryotes is circular
• Not surrounded by a membrane
Prokaryote cell structures – Practice question
This image shows an electron
micrograph of the gram-
positive bacterium Clostridium
botulinum. This bacterium
produces a neurotoxin that is
the most poisonous protein so
far discovered. This neurotoxin
is used in cosmetic treatments
under the brand name Botox®.

1. Identify the structures I, II, III and IV

2. What causes the cytoplasm of Clostridium to appear so dark in the electron micrograph?

3. This image is a longitudinal section: You can see a thin slice of the bacterium going from end
to end. What shape would you see in a transverse section (going from side to side)?

4. There is a scale bar on the micrograph. Use this to calculate the magnification of the
micrograph.

5. Use the magnification to calculate the actual length.

Eukaryote cell structures
Eukaryotic cells are very diverse in sizes
and shapes. They are more complex and
typically bigger in size (15 – 100µm) .
Their interior is compartmentalized, and
they have many membrane bound
organelles such as mitochondria,
chloroplasts, nucleus, Golgi apparatus and
Endoplasmic Reticulum. They also have
larger ribosomes (80S) than prokaryotes. https://www.youtube.com/watch?v=URUJD5NEXC8

Eukaryotes can be grouped into 4 categories

– 3 of which we will look at in more detail:
• Plants
• Animals
• Fungus

https://www.youtube.com/watch?v=-q82IrNWbKc
Eukaryotes: comparing animal, plant and fungal cells
Draw and annotate the structures of the three main types of eukaryotic cells:
Animal cell:

Animal cells have a boxy or spherical

shape, don’t contain chloroplasts or a
large vacuole, but instead many other
organelles in the cytoplasm. They have
centrioles composed of microtubules
and often have attachments such as
cilia or flagella used for locomotion.
Eukaryotes: comparing animal, plant and fungal cells
Draw and annotate the structures of the three main types of eukaryotic cells:
Plant cell:

Plant cells have a rectangular shape

and a cell wall in addition to the cell
membrane. The have chloroplasts for
photosynthesis and a large vacuole to
store food and water. They don’t have
centrioles and cilia or flagella.
Eukaryotes: comparing animal, plant and fungal cells
Draw and annotate the structures of the three main types of eukaryotic cells:
Fungal cell:

Fungal cells have a spherical shape and

a cell wall in addition to the cell
membrane. The don’t have chloroplasts
but often larger vacuolea to store food.
They don’t have centrioles and cilia or
flagella.
Eukaryotes: comparing animal, plant and fungal cells

Plant cells Animal cells Fungal cells

Plastids
A family of organelles with two outer
membranes and internal sacs

Cell wall
A rigid layer outside the plasma
membrane to strengthen and protect
the cell

Vacuole & Vesicles

Flexible, fluid filled compartment
surrounded by a single cell membrane

Centrioles
cylindrical organelles composed of
microtubules that organise the cell
during cell division

Attachments
Cilia and flagella used to generate
movement of a cell or movement of
fluid adjacent to cell
Nucleus & Nucleolus
• Spherical with double membrane
• Pores (holes) in the membrane
• Uncoiled chromosomes are referred
to as chromatin – stain dark.
• Nucleolus consists of RNA and
proteins, makes up 25% of nucleus

http://www.scienceclarified.com/images/uesc_03_img0119.jpg

Function:
• Stores genetic information in form of
chromosomes (DNA and associated histones)

• Nucleolus produces rRNA (ribosomal) which

combine with proteins for use outside the
cell to form ribosomes.
Free ribosomes

• 80 S (larger than in
prokaryotes), ca.20nm
• Composed of 2 subunits
• No exterior membrane
• Free in the cytoplasm or Free ribosomes
bound to ER
• Composed of ribosomal
RNA and protein
produced in the
nucleolus of the nucleus Bound ribosomes
• Appear as dark granules

http://iws.collin.edu/biopage/faculty/mcculloch/1406/outlines/chapter%207/rougher2.jpg

Function:
Produces proteins to function in the cytoplasm for use within the cell (enzymes)
 Mitochondrion

• Has a double membrane

• Outer membrane is smooth,
inner membrane is folded
• The folds are called “cristae”
• Variable in shape and number
(spherical or ovoid)

Function:
• Site of ATP production by
(aerobic) cell respiration.

• Fat digestion if it is used as an

energy source in the cell

http://emp.byui.edu/wellerg/The%20Cell%20Lab/Images/Eukaryotic%20Cell/mitochondria%2002.jpg
Endoplasmic Reticulum
• Two types: Smooth ER & Rough ER
• Made of flattened membrane sacs
called cisternae, attached to the
outside of the cisternae are
ribosomes (rER)
• Extensive network of tubules or
channels that extends almost
everywhere in the cell from the
nucleus to the plasma

Function:
• rER responsible for the production
of proteins which are then
transported by vesicles to the
Golgi apparatus for modification.

• Smooth ER produces
phospholipids and cellular lipids,
sex hormones. Also stores calcium
ions in muscle cells.
http://medcell.med.yale.edu/histology/cell_lab/images/smooth_er_proliferation.jpg
Golgi apparatus
• Consists of flattened sacs called cisternae, which
are stacked on top of one another
• Has a two sides: cis-side (receives products at
that site), and a trans-side (discharges products)
• Transport vesicles bud off
• Most of these are packaged into vesicles for
secretion through the plasma membrane
• Difference to rER:
• No attached ribosomes
• Often sited close to the plasma membrane http://www.tokresource.org/tok_classes/biobiobio/biomenu/eukaryotic_cells/Golgi.jpg

• The cisternae are shorter and more curved

than those of rER

Function:
• Processes proteins that arrive from the rER.
• This organelle functions in collection, packaging,
modification and distribution and transportation
of materials synthesized in the cell
Endoplasmic Reticulum and Golgi apparatus
Chloroplast
• Double membrane surrounding the chloroplast
• Stacks of thylakoids inside
• Each thylakoid is a disc composed of a flattened
membrane.
• Variable shape (spherical or ovoid)
Function:
• Production of glucose and other organic
compounds by photosynthesis

Lysosomes
• Formed from Golgi vesicles which bud off
• Spherical with single membrane
• High concentration of enzymes (proteins)
cause this organelle to stain heavily and
hence appears dark
• Only in animal cells (plants use vacuoles)
Function:
• Used for the breakdown of food or
unwanted, damaged substances
organelles using enzymes.
http://www.dematice.org/ressources/PCEM1/Histologie/P1_histo_009/Web/res/figure18.jpg
 Vacuoles & Vesicles

https://amit1b.files.wordpress.com/2009/12/vacuole-plant0.jpg
• Single membrane with fluid inside
• Plant cells: vacuoles are large and
permanent, often occupying the
majority or the cell
• Animal cells: Small and temporary
– typically referred to as vesicles.

Function:
• Vacuoles: In plant cells: Used for maintenance
http://ext.pimg.tw/geantsage/1381191097-978921997.jpg

of water balance and internal pressure.

• Vesicles: Used for transport of substances

within the cell – often from rER to Golgi
apparatus.

http://creationrev.wpengine.netdna-cdn.com/wp-content/uploads/2011/01/chloroplast_v1-300x229.gif
 microtubules
Flagellum & Cilia

• Whip-like structures projecting

from the cell surface
• Contain a ring of nine double
microtubules + 2 central ones
• Flagella are larger, and only one is
present, cilia are smaller and
many are present
• Have microtubules inside

Function:
• Cilia move liquid over surfaces
(e.g. particle-laden mucus
towards throat)

• For movement (sperm cells)

http://www.molbiolcell.org/content/20/1/F1.medium.gif
 microtubules
Microtubules
• Small cylindrical fibres
• Form core inside flagella or cilia
• Composed of the polymer tubulin

Centrioles
• Consist of 2 groups of 9 triple microtubules
• Only in animal cells

Cytoskeleton
• Constructed from protein fibers like
tubulin and actin, which are used to
make microtubules and microfilaments.
Function:
• Microtubules move chromosomes to
opposite sides of a cell during cell division
and help to construct cell walls.

• In animal cells, centrioles move towards the

poles of a cell and serve as anchor points for
microtubules during cell division.

• Cytoskeleton microfilaments help animal

cells to maintain shape. http://www.molbiolcell.org/content/20/1/F1.medium.gif
 https://www.ru.ac.za/media/rhodesuniversity/content/emu/images/LS%20bacterium%20copy-599x233.jpg

Cell wall
• An extracellular component, not an organelle
• All plant cells have a cell wall, but also fungi and some protists
• Consists of the polysaccharide cellulose

Function:
• Permeable – does not affect transport in and out of the cell
• Strong – gives support to the cell and prevents plasma membrane bursting when
under pressure
Game time: Who am I?
1. On 4 – 5 pieces of paper (or cards) write down any of the previously
learned structures found in eukaryotic or prokaryotic cells (or any key term
you have learned in this topic).
2. Turn over the cards.
3. Join with 2-3 other students to form a group.
4. Join all cards, mix them and form them into a stack in the middle of the
table.
5. The youngest student in the group picks up the first card from the top of
the stack and without checking the word, holds it up over their forehead.
6. The student with the card starts asking Yes-No questions to find out what
structure they are by describing the features or functions.
• You must not name the structure unless you are fairly certain that you
get it right.
• Once you name a structure and it is correct you win a point and it’s the
next student’s turn.
• Once you name a structure and you get it wrong, you don’t win a point
and it’s the next student’s turn.
7. The game is over once all the structures have been guessed.
Comparing prokaryotes and eukaryotes

Prokaryotic cells Eukaryotic cells

Complexity

Genetic material/ DNA

Size
Membrane enclosed
organelles
Uni/multicellular
Size of ribosomes
Compartmentalization
Examples
Comparing prokaryotes and eukaryotes

Prokaryotic cells Eukaryotic cells

Complexity

Genetic material/ DNA

Size
Membrane enclosed
organelles
Uni/multicellular
Size of ribosomes
Compartmentalization
Examples
Cell types and cell structures viewed in micrographs

https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/12-ultrastructure-of-cells/cell-micrographs.html
Cell types and cell structures viewed in micrographs
What structures can you identify?
What could be the function of this cell?
Suggest what type of cell this could be.

http://images.fineartamerica.com/images-medium-large/tem-of-liver-cell-science-source.jpg Liver cell

The characteristics & functions of life

https://jamboard.google.com/d/1ynaIcgFGVDee05V1qajVO8TzYnpQQyIuJbcGlBTxXAc/edit?usp=sharing
The characteristics & functions of life
The characteristics & functions of life
Try to identify the characteristics of life in paramecium
 Response: cilia allow to move
paramecium in response to
Reproduction: the nucleus changes in the environment
Excretion: the (e.g. toward food source).
can divide to support cell
plasma membrane
division. Often
controls entry and Metabolism: the
reproduction is asexual.
exit of substances cytoplasm allows for
metabolic reactions
to happen.

Nutrition: food
vacuoles contain
nutrients which
Growth: Assimilation Homeostasis: The contractile
paramecium has
of food will allow vacuoles at each end of the cell
consumed and which
paramecium to fill up with water and expel it to
are gradually digested.
become larger. manage water content.
http://images.fineartamerica.com/images-medium-large/1-paramecium-caudatum-lm-m-i-walker.jpg
The characteristics & functions of life
Chlamydomonas is a unicellular algae that lives in soil and freshwater habitats

Can you identify the functions of

life for this organism?
http://protist.i.hosei.ac.jp/pdb/images/chlorophyta/Chlamydomonas/Euchlamydomonas/sp_10.jpg
Atypical cell structure in eukaryotes: Striated muscle cell

Challenges the idea that all cells

have only one nucleus and that
they are small.

Muscle cells (fibers) are larger

than most animal cells (in
humans, ca. 30mm vs other
cells (0.03mm in length).

longer than most animal cells, contain more nuclei

They are surrounded by a

single plasma membrane but
are said to be multinucleated.
Atypical cell structure in eukaryotes: Aseptate fungal hyphae

Hyphae are very long thread like structures,

which have a cell membrane and a cell wall
made from chitin. The main purpose of
hyphae is to absorb nutrients from the soil
or substrate they grow on.

As a result of continued nucleus

division, each hyphae has many
nuclei and continuous
cytoplasm spread along it.

Challenges the idea that

a cell is a single unit
with only one nucleus.
Atypical cell structure in eukaryotes: Red blood cells

In mammals, red blood cells don’t have a

nucleus. During development in the bone
marrow the nucleus is pinched off and
digested by cells of the immune system.

This makes the cell smaller and more

flexible, but it cannot renew itself and
has a limited life span (ca. 120 days)

https://www.news-medical.net/health/The-Immunological-Function-of-Red-Blood-Cells.aspx
 Atypical cell structure in eukaryotes: Phloem sieve tube cells
Plant cells move sugary sap through
cylindrical cells shaped like tubes. To
allow for little resistance between
adjacent cells the neighboring walls
are perforated with pores and nuclei
https://search.library.wisc.edu/digital/ARVQJW564YVCSK83

or lager organelles are missing.

During development of the cell the

nucleus and other cell organelles
break down. The functions of the
cell are maintained by the
neighboring companion cell.