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UNIT 1 CELL STRUCTURE

AS Biology
by

Blanca Peris

on 19 April 2016

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Transcript of UNIT 1 CELL STRUCTURE

AS BIOLOGY
UNIT 1 CELL STRUCTURE

1 ANIMAL CELLS AND PLANT CELLS
General animal cell as seen under the light microscope
A MAGNIFICATION
Magnification is the number of times larger an image is compared with the real size of the object.
B RESOLUTION
Picture 1.9 page 8. Which photomicrograph has a greater reolution? And magnification?
C THE ELECTROMAGNETIC SPECTRUM
4 THE ELECTRON MICROSCOPE
1 ANIMAL CELLS AND PLANT CELLS
A FEATURES IN COMMON
CELL SURFACE MEMBRANE:
1 ANIMAL CELLS AND PLANT CELLS
A FEATURES IN COMMON
CYTOPLASM:
MITOCHONDRIA (sing. mitochondrion):
1 ANIMAL CELLS AND PLANT CELLS
B DIFFERENCES
1 ANIMAL CELLS AND PLANT CELLS
B DIFFERENCES
CENTRIOLES: only found in animal cells. They take part in nuclear division. Under the light microscope it appears as a small structure close to the nucleus.
CELL WALLS: made of cellulose so it is quite rigid keeping the shape and preventing the cells from bursting. They can be reinforced with lignin. They are freely permeable.
PLASMODESMATA (sing. plasmodesma): cytoplasm strands that link neighbouring plant cells
1 ANIMAL CELLS AND PLANT CELLS
B DIFFERENCES
LARGE CENTRAL VACUOLE: permanent structure surrounded by a membrane (TONOPLAST).
CHLOROPLASTS: green and large organelles that contain chlorophyll (mainly found in leave cells).
2 UNITS OF MEASUREMENT IN CELL STUDIES
nm
2 UNITS OF MEASUREMENT IN CELL STUDIES
MEAURING CELLS/SAMPLES (Explained in page 7)
Find the actual diameter of these NOT TO SCALE structures following the steps.
3 MAGNIFICATION AND RESOLUTION
Then A=? and I=?
What is the Magnification?

The bar measures 2.5 cm

Seven week human embryo

What is the magnification?

Actual length = 0.002 mm

Measured length = 12.8 cm

a bacterium

Measured length with your ruler = 14.2 cm

What is the P. caudatum actual length?

x600

Paramecium caudatum

What is their actual mean?

Mean measured length of the four largest chloroplasts = 3.92cm

x9000

Chloroplasts

WORKSHEETS
RESOLUTION: is the ability to distinguish between to separate points. The greater the resolution the greater the detail that can be seen.
The maximum resolution in a light microscope is 200 nm. If two structures are closer than 200 nm they cannot be distinguished as separate (e.g. centrioles)
Magnifying a picture does not improve resolution.
C THE ELECTROMAGNETIC SPECTRUM
The limit of resolution is about one half the wavelength of the radiation used to view the specimen.
Light microscopes use visible light so the best resolution that can be achieved is XXX nm (in practice corresponds to a maximum magnification of about 1500 times).
The transmission electron microscope [TEM].
To be able to see structures smaller than 200 nm other microscopes were built using other wavelengths:
Ultraviolet light: still in use. It uses light of 200 nm (so best resolution is?)
X-rays: little success because they are very difficult to focus.
Then, a beam of electrons was used, they were very suitable because:
1. Their wavelength is very short (as X-rays).
2. They negatively charged so easily focused by electromagnets
The maximum resolution that can be achieved is 0.5 nm. (x1 000 000 of magnification)
The scanning electron microscope [SEM].
The electron beam is projected onto a fluorescent screen giving bright areas and a final image in black and white.
Electrons need to be kept in a vacuum, along with the specimen and the fluorescent screen.
embedding
fixing & dehydration

sectioning

staining
mounting

Preparing a specimen for the TEM
5 ULTRASTRUCTURE OF AN ANIMAL CELL AND FUNCTIONS OF ORGANELLES
200 nm
0.5 nm
x1500
x1000000
Dead or alive, easy to prepare
Dead and in a vaccum, harsh preparation that can cause distortions
Affordable for individuals or schools
Affordable only for universities or research centres.
If stains are not used real colours can be observed.
Specimens have to be stained by metal dyes.
Images are b&w, indirect
Label the diagrams in your worksheets, highlight the structures that cannot be seen with the light microscope (p 13).
NUCLEUS
The nucleus contains chromatin (DNA + histones) (chromosomes), that contain DNA organised in genes. They control the cell's activities and inheritance.
Largest organelle. Roughly spherical.
During cellular division the nucleus is the first to divide.
ENDOPLASMIC RETICULUM AND RIBOSOMES
The ER is a system of membranes continuous with the outer membrane of the nuclear envelope.
There are two types: the rough ER and the smooth ER. (RER and SER)
The smooth ER (no ribosomes attached) makes lipids and steroids (e.g. cholesterol) and the reproductive hormones oestrogen and testosterone.
Golgi apparatus
A stack of membrane bound flattened sacs.
It constantly receives proteins packaged in vesicles from the ER and packages modified proteins into vesicles for transportation to other parts of the cells or to the cell surface membrane (secretion).
It modifies proteins e.g. by the addition of sugars (glycoproteins).
Spherical sacs surrounded by a single layer of membrane. (0.1- 0.5 µm of diameter)
The breakdown of cells/bacteria taken up by white blood cells.
Breakdown of old organelles.
The enzymes can be released outside the cell e.g replacement of cartilage with bone during development.

Golgi vesicles are also used to make lysosomes.
Lysosomes
Mitochondria (sing mitochondrion)
Cell surface membrane
Microvilli
Centrioles
6 ULTRASTRUCTURE OF A PLANT CELL
7 TWO TYPES OF CELL
Spherical or sausage-shaped organelle surrounded by two membranes. (1 µm of diameter approx).
Site of aerobic respiration as result of it they produce adenosine triphosphate (ATP).

Present in all living cells.
They are just outside the nucleus at right angles to each other.
They are used as a starting point for growing the spindle for nuclear division.
All the organelles described (except centrioles and microvilli) are also found in plant cells.
Cellulose cell wall
On the outside of the plant cells plasma membrane. Supports the cell and helps to maintain cell shape.
Large central vacuole
A large membrane bound sac containing water and solutes. It helps in the maintenance of cell turgidity.
The size of ribosomes is measured in S units (S for sedimentation). These ribosomes are 80 S.
The rough ER is covered with ribosomes (25 nm in diameter), organelles consisting in two subunits (a large and a small).
Proteins made by ribosomes on the ER enter and travel through it, then small vesicles break off and join with the Golgi apparatus.
The inner membrane is highly folded to form
cristae
. The interior solution is called
matrix
.
ENDOSYMBIONT THEORY OF MITOCHONDRIA AND CHLOROPLASTS
Mitochondria and chloroplasts contain like bacteria:
70S ribosomes.
Circular DNA molecules.
Both DNA and ribosomes are active and code for some proteins.
Finger-like extensions of the cell surface membrane that increase the cell surface area of the cell membrane.
Each centriole is a hollow cylinder formed from a ring of microtubules, made of a protein called tubulin.
7 TWO TYPES OF CELL
There are two types of cells: PROKAYOTIC (without nucleus) and EUKARYOTIC CELLS (with nucleus).
Eukaryotic organisms include animals, plants, fungi and protoctists (unicellular eukaryotes)
7 TWO TYPES OF CELL: comparison
PROKARYOTE CELL
EUKARYOTE CELL
SIZE
DNA
RIBOSOMES
ORGANELLES
CELL WALL
diameter: 1-5 µm
circular, free in cytoplasm and naked
Smaller (70S)
No ER, few organelles, none surrounded by 2 membranes
Present, made of murein (peptidoglycan)
diameter: up to 40µm;
larger volume
linear, in nucleus, associated with proteins
Larger (80S)
Sometimes present (plants and fungi)
ER present. Some organelles surrounded by 1 membrane (lisosomes, vacuoles, Golgi); some by 2 (nucleus,mitochondrion); some with no membrane (ribosomes)
9 TISSUES AND ORGANS
Different levels of organisation:
CELLS TISSUES ORGANS SYSTEMS ORGANISMS
Tissues: group of cells that are specialised to do one or more jobs. They may be of the same type (e.g parenchyma in plants) or mixed (e.g xylem and phloem)
Organ: part of the body which forms a structural and functional unit, it is composed of more than one tissue (e.g stem, leaves, roots)
System: is a collection of organs with a particular function (e.g. vascular system)
Examples of plant tissues found in roots, stems and leaves
END-OF-CHAPTER QUESTIONS 1-3, 7-8
END-OF-CHAPTER QUESTIONS
Examples of plant tissues found in roots, stems and leaves
EPIDERMIS
Protective layer, one cell thick.
In stems and leaves it might be covered with a waxy cuticle that prevents water loss.
In leaves it has pores called stomata which allow the exchange of gases.
In roots it may have extensions called root hairs to increase the surface for absorption of water and minerals
PARENCHYMA
Its cells may be used for many functions:
Storage of starch.
When they are turgid (full with water), they prevent wilting.
They allow gas exchange having air spaces between cells.
In roots and stems it forms the cortex (outer region).
In stems it forms the central region or pith.
In leaves it contains chloroplasts and forms the palisade and spongy mesophyll.
Examples of plant tissues found in roots, stems and leaves
ENDODERMIS
Layer of one cell thick surrounding the vascular tissue in stems and roots
Layer of cells inside the endodermis.
In roots it grows new roots.
In stems the pericycle is formed from a tissue called sclerenchyma a tissue made out of dead and lignified cells.
PERICYCLE
PARTS?
How to use it?
How to prepare a slide
1st drawing of cells
Hooke 1665
1 ANIMAL CELLS AND PLANT CELLS
General plant cell as seen under the light microscope
A FEATURES IN COMMON
NUCLEUS:
Transparent structures allow light to pass through and are not visible, they need to be stained.
Present in all living cells.
Too thin to be seen under the light microscope (5-9nm).
It is a selective barrier between the cells contents and the external environment.
1 ANIMAL CELLS AND PLANT CELLS
A FEATURES IN COMMON
NUCLEUS:
Transparent structures allow light to pass through and are not visible, they need to be stained.
NUCLEOLUS (pl nucleoli) - an even more stained area made of DNA from different chromosomes. In variable number.
CHROMATIN – mixture of DNA and associated proteins loosely coiled.
Quite a large structure easily seen after staining. It contains:
1 ANIMAL CELLS AND PLANT CELLS
A FEATURES IN COMMON
GOLGI APPARATUS (BODY):
They carry out aerobic respiration producing ATP
The space between the cell surface membrane and the nucleus.
Aqueous nature (from fluid to jelly-like consistency)
Structures that can move about, change shape and divide.
It packages modified proteins into vesicles for transportation to the cell surface membrane and secretion out of the cell.
A stack of membrane bound flattened sacs.
1 ANIMAL CELLS AND PLANT CELLS
A FEATURES IN COMMON
ORGANELLES:
Structures inside cells often surrounded by membranes and have specific functions.
This is described as compartmentalisation (=different compartments) and leads to the cells showing division of labour (= sharing of the work between specialised organells)
Animal cells might have small and temporary ones.
They help to regulate the osmotic pressure.
It contains a solution of mineral salts, sugars, oxygen, enzymes, pigments (e.g. beetroots) and some waste products.
Inside the chloroplasts there are GRANA (sing. granum) that consist of stacks of membrane-bound sacs called THYLAKOIDS. (light is absorbed there)
(SI Units)
1. Use the stage micrometer to find the value of each eyepiece unit (calibration)
2. Convert it to micrometers.
3. Calculate the actual length of the structure. (x number of units the structure occupies)
0.2
The whole range of different wavelengths is called the electromagnetic spectrum.
The light travels in waves (visible light= 400-700nm).
If the object is smaller it cannot interfere with the light waves and it cannot be separately from nearby objects.
Types of electron microscope:
A beam of electrons passes through the specimen and is dispersed by the structures there.
The transmitted electrons are then captured on a photographic plate.
The specimen is coated in a very thin layer of metal and a beam of electrons is reflected off the surface onto a photographic plate.
This allows 3-D images to be formed. Less resolution than TEM.
Water boils at r.t. in a vacuum so the specimen is dehydrated -so dead- before use (and stained with heavy metals) and need to be very thin.
The nucleolus makes ribosomes using information from its own DNA
Surrounded by a double membrane called the nuclear envelope with nuclear pores allowing exchange with the cytoplasm.
Outer membrane joins up to the endoplasmic reticulum
They build-up the proteins. They can be attached to the ER or free in the cytoplasm. They are made of RNA and protein.
Contain powerful hydrolytic enzymes for:
A bacterium is 0.9 microns in diameter. An electron micrograph of the bacterium shows it as 72 mm in diameter. What is the magnification of the electron micrograph?

Magnification=
x80000
From your Summer HW
TEM OR SEM?
SEM
SEM
SEM
TEM
TEM
TEM (RER)
6 ULTRASTRUCTURE OF A PLANT CELL
Chloroplasts
Two layers of membranes.
They are also involved in the synthesis of lipids.
ATP is used as the universal energy currency. It releases energy when hydrolysed.
They are ancient bacteria which now live inside animal and plant cells.
It is extremely thin (7 nm)
Provides a selective barrier between the cells contents and the external environment.
It is useful for absorption in the gut
Not found in plant cells.
They produce ATP as a result of the absorption of light.
They contain chlorophyll, 70S ribosomes and circular DNA.
The inner layer is continuous and forms flattened membrane sacs called thylakoids (site of photosynthesis).
8 VIRUSES
Copy Figure 1.31 in p22
Much smaller than bacteria (20-300nm).
They consist of:
Self-replicating molecule of DNA or RNA.
No cytoplasm, no ribosomes.
Not surrounded by membrane.
Always parasitic as they can only reproduce by using the replicative machinery of their host.
A protective protein coat (capsid).
Are viruses living organisms?
Question 7
a) organelles with no membrane
nucleolus, ribosome, centrioles, centrosome, microtubule
b) organelles with 1 membrane
lysosomes, rough ER, smooth ER, Golgi body
c) organelles with 2 membranes
nucleus, mitochondrion, chloroplast
Question 8
l ribosome / microtubule;
a Golgi body;
b nucleolus;
c ribosome;
d ER / rough ER;
e rough ER;
f mitochondrion;
h chloroplast;
g nucleus;
i centrosome/centriole;
j nucleus;
k membrane;
THE END
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