Chapter 1- Cell Structures

Question 1

Protoctista

Answer 1

-similar to protist (?)

Question 2

Organelle

Answer 2

A specialised part of a cell that performs a particular function

Question 3

Magnification

Answer 3

This is a measure of the ability of a lens or other optical instrument to magnify (enlarge) the size of something in an optical image.

Question 4

Resolution

Answer 4

This refers to the ability of a microscope to distinguish two adjacent points as separate from each other.
The resolution shows how close (in nanometers) two points can be and still be distinguishable.

Question 5

Nucleus

Answer 5

Has a double membrane
The membrane is known as nuclear envelope
It has nuclear pores which are protein complexes that contain channels through the centre
The nucleus consists of genetic material known as DNA; DNA controls the metabolic activities of the cell as many of these proteins are the enzymes necessary for metabolism to take place
DNA is only in form of chromosomes during cell division
Generally, it is spread loosely through the nucleus- this is known as chromatin. Chromatin, a complex, is formed by DNA and a protein called histone.
Also contains nucleolus which form ribosomes.
Ribosomes can escape the nucleus through its pores to reach the cytoplasm.

Question 6

Endoplasmic Reticulum

Answer 6

Transport system
Chemicals need to processed and transported. The endomembrane system is responsible for this.
The endomembrane system is the folded inner membrane of the cell which consists of the golgi apparatus and endoplasmic reticulum.
E.R is a network of membranes enclosing flattened sacs called Cisternae.
The E.R comes in two types: rough and smooth.
These membranes form channels through the cytoplasm and join with the outer nuclear membrane to form a continuous membrane.

Question 7

Rough Endoplasmic Reticulum

Answer 7

Ribosomes are embedded in the membrane
These ribosomes make proteins that are designed for transport and secretion.
(Ribosomes that are free in the cytoplasm make proteins for the cell’s own use)
These new proteins enter the lumen of the RER and combine with carbohydrates. Carbohydrates act as a seatbelt for the proteins.
This is transported to Golgi apparatus
Cells that produce a lot of proteins (ex:enzyme, hormone-producing cells) have extensive RER

Question 8

Smooth Endoplasmic Reticulum

Answer 8

Lack of ribosomes
Makes lipids, including phospholipids for cell membranes
Contains enzymes that detoxify lipid-soluble drugs and some harmful products of metabolism.

Question 9

Golgi apparatus

Answer 9

Has a series of membraneous flattened pile of sacs known as cisternae; these sacs are not interconnected
The body is divided into two sections as the cis face and the trans face
They modify proteins and lipids delivered to it by the RER and prepare them for secretion
The proteins (made by the RER) and the lipids (made by the SER) reach the cis face of the Golgi in the form of a vesicle (wrapped in a membrane); remember the carbohydrates only act as a seatbelt. 
They are modified and then transported out of the trans face. These vesicles then move to the cell membrane and fuse to it, releasing the contents to the outside by exocytosis.

Question 10

Mitochondria

Answer 10

These are membrane-bound and have double membranes
They are the final stage of cellular respiration. This where the energy stored in the bonds of complex organic molecules is made available for the cell to use by the production of the molecule ATP.
are most numerous in cells that are very active (e.g muscle cells and nerve cells)
The inner membrane is folded into a series of Cristae.
Consists of a fluid interior called matrix.
The inner membrane contains the enzyme used in aerobic respiration.
Also contains a small amount of DNA called (mt) DNA; they can produce their own enzymes and reproduce themselves
Also contains ribosomes

Question 11

Ribosomes

Answer 11

Usually present in large numbers
Manufactures proteins
Consist of two types of molecule: ribosomal ribonucleic acid (rRNA) and protein.
There are two subunits in a ribosome: large and small
These subunits are separate from each other but come together to form a complete ribosome by attaching to the mRNA when protein synthesis is about to begin.
Found in both eukaryotic and prokaryotic cells
The eukaryotic ones are larger

Question 12

Chloroplasts

Answer 12

Membrane-bound organelles only found in plant cells
Absorb light for photosynthesis
Has a double outer membrane and a complex arrangement of internal membrane that form thylakoids which are grouped into stacks called grana (a single stack is called granum) joined by intergranal lamellae.
Chlorophyll pigments are found in the thylakoids
Light independent reactions take place at the stroma.
The space between the grana is filled with a thick liquid called stroma.
Also contain ribosomes

Question 13

Lysosomes

Answer 13

Are special forms of vesicles that contain hydrolytic enzymes.
Concerned with the digestion of cellular material
Contains a variety of enzymes that break down proteins, nucleic acids, carbohydrates and lipids.
They can digest material that come from outside (ex:bacteria) and inside (ex: old or damaged organelles)
A single celled membrane separates the enzymes in lysosomes from the rest of the cytoplasm
Even if an enzyme escaped to the cytoplasm there will be relatively less damage as they work best in acidic conditions (which are present in the lysosome); cytoplasm are more or less neutral
Play an important important role in the immune system as they are responsible for breaking down pathogens ingested by phagocytic cells
Also play an important role in programmed death or apoptosis.

Question 14

Plasma Membrane

Answer 14

Eukaryotic cells are bound by plasma membrane
Controls what goes in and out- thus they have a different permeability to different biological molecules
Protein carriers can pump substances into or out of the cell according to need.
This membrane is made of phospholipids and proteins.

Question 15

Centrioles and Microtubules

Answer 15

Centrioles are present in most eukaryotic cells with the exception of flowering plants and most fungi.
Centrioles are constructed of microtubules arranged in 9 triplets forming a cylinder
During metaphase and anaphase, the spindle fibres that separate the chromosomes are organised by a system of microtubules.
Firstly it was thought that centrioles were responsible for this but now we know it is actually the centrosomes (two centrioles form the centrosome)which carry out this.
Centrioles occur in pairs near the nucleus

Question 16

Flagella and cilia

Answer 16

Flagella can be used as a sensory organelle detecting chemicals changes in the cell’s environment.
Structures composed of microtubules, found on the surface of cells, which move to create currents
The flagella and cilia may propel the cell along or (in the case of cilia only) move liquids across the surface of the cell
Mobile cilia beat in a rhythmic manner, creating a current
These are present in trachea to move mucus away from the lungs and also in the fallopian tubes to move egg cells from the ovary to the uterus.
Pairs of parallel microtubules slide over each other causing the cilia to move in a beating motion.
Stationary cilia are important in sensory organs such as nose.
Flagella are found in some single celled organisms where they move the cell around.
Flagella are the tail of sperm cells
It is usually found single but can come in pairs.
Cilia are generally present in large numbers but flagella are longer
Both have a structure of nine pairs of microtubules surrounding two central microtubules known as 9+2 arrangement.
Both are extensions of the cell membrane that surrounds them.
Although prokaryotic cells may have flagella, they are smaller and have simpler structures.

Question 17

Cell wall

Answer 17

Prevents the cell from bursting if water flows in
Cell walls are found in plant cells and in many members of the Protoctists (which are also eukaryotic cells) and fungi
The cell wall of plants and algae are made of cellulose
Fungal cell wall are made of chitin
In prokaryotic cells, cell wall is made of Murein which is a peptidoglycan made of sugars and amino acids.
Cellulose are chains of glucose molecule
Chitin is similar to cellulose but also contains nitrogen

Question 18

Cellulose Cell wall

Answer 18

Freely permeable
Give the plant a shape
The contents of the cell push against the cell wall which makes it rigid. This supports the individual cell as well as the plant
It also maintains the turgor pressure
Acts as a defence mechanism, protecting the contents of the cell against the invading pathogens.

Question 19

Vacuole

Answer 19

Membrane lined sacs in the cytoplasm containing cell sap. This is the solution that fills in the vacuole which contains sugars, amino acids, waste substances and mineral salts.
Many plants have permanent vacuoles which is important to maintain the turgor pressure. The contents of the cell push against the cell wall, which provides the rigid framework.
The membrane of the vacuole is called tonoplast. It is selectively permeable
Vacuoles in animal cells are smaller and transient (temporary).

Question 20

Light microscopes- bright field

Answer 20

Used for routinely examination; does not show internal structure of organelles
But using these, large cellular structures can be seen- ex: nuclei, cell walls, chloroplasts and vacuoles.
Compound Light microscope require two lens to view a specimen.
A typical compound light microscope can only magnify specimens which are thin and mostly transparent.
Light in focused up through the condenser and specimen.
The objective lens produces a magnified image, and then this is magnified again using eyepiece lens. This configuration allows for much higher magnification and reduced chromatic aberration. This is the failure of coloured rays to converge at one point because of a defect in a lens or mirror.

Question 21

Light microscopes - dissecting

Answer 21

Dissecting microscopes are a type of binocular microscopes used for observations at a low total magnification (x4 to x50)
Has two separate lens systems
These microscopes produce a 3D view of the specimen and are sometimes called stereo microscopes.

Question 22

Transmission Electron Microscope

Answer 22

Electrons pass through the material
Used to view extremely thin sections of material.
Magnetic lenses focus the image onto a fluorescent screen or photographic plate.
These extremely thin specimens need to be prepared using a machine called ultramicrotome which cuts a specimen to million bits.
Can see details inside the cell

Question 23

Scanning Electron Microscope

Answer 23

Primary Electrons knock electrons off the surface of the material.
These secondary electrons are picked up by a collector, amplified and transmitted onto a viewing screen or photographic plate, producing a 3D image.
Easily obtain clear pictures of organisms as small as bacteria and viruses.
Produces an detailed image of only the outside surface.

Question 24

Laser Scanning Confocal Microscope

Answer 24

A thick section of tissue (or even a small living organism) is scanned with a laser beam after the cells have been stained with fluorescent dyes.
The beam is scanned at different depths of section.
In fluorescent microscopes a higher light intensity is used to illuminate a specimen that has been treated with a fluorescent chemical (dye).
This microscope moves a single spot of focus light across a specimen (point illumination)
This causes fluorescence from the components labelled with a ‘dye’.
The emitted light from the specimen is filtered through a pinhole aperture to prevent blurring and maintain the high resolution.
Only light radiated from very close to the focal plane (the distance that gives the sharpest focus) is detected.
A laser is used instead of light to get higher intensities.

Question 25

LSCM benefits

Answer 25

The images are much clearer since the laser beam can be focused at a specific depth. This eliminates the blur seen in optical microscope that is caused by out-of-focus tissue above the focal point.
Images can be taken at successive depths and fed into a computer, which can reconstruct a 3D image of the tissue scanned.
Can see living specimens
Can observe cell processes by tracking the distribution of molecules
Non-invasive

Question 26

Why do electron microscopes have better resolutions?

Answer 26

Light microscope approx has a resolution of half the wavelength of visible light (400-700nm) used to illuminate on the specimen.
Electrons have a much shorter wavelength (0.005 nm) than light so electron microscopes have a higher resolutions.
Electrons beams are still diffracted but since they have shorter wavelength, they can be closer before they overlap.
This means that objects which are much smaller and closer together can be seen separately without diffraction blurring the image.

Question 27

Total Magnification

Answer 27

Magnification of eyepiece lens x magnification of objective lens

Question 28

Magnification and actual size formula

Answer 28

Magnification = image size / actual size

ALWAYS MEASURE THE BAR GIVEN NEXT TO THE DIAGRAM FOR THE IMAGE SIZE

Question 29

Units

Answer 29

1 metre - 1000mm
1mm- 1000um
1um- 1000 nm

Question 30

Cytoskeleton

Answer 30

In the cytoplasm, a series of thread proteins from the cytoskeleton
Microtubules and microfilaments

Question 31

Function of cytoskeleton

Answer 31

Cellular Movement- moving the cell or moving liquids across the surface of the cell; ex: flagella and cilia
Intracellular movement- the threads form a track along which organelles from one part of the cell to another.
Ex: movement of a vesicle; movement of a chromosome to either end of a cell during cell division.
Strengthening and support: supports the organelles and forms a ‘scaffolding’ that strengthens the cell and helps keep it in shape.

Question 32

What are microtubules and microfilaments made of

Answer 32

Microfilaments are solid strands but microtubules are tubular
Mostly actin (which is a protein) forms the filament and tubulin forms the microtubules

Question 33

Differences with animal and plant cells

Answer 33

Plant cells have a cellulose cell wall, chloroplasts and a large central vacuole containing cell sap.
Only animal cells have centrioles and flagella.
Cilia are very rare in plant cells, occurring only in one primitive group called the cycads.

Question 34

What is plasmodesmata

Answer 34

(Singular plasmodesma) are gaps in the cell wall through which cytoplasm connects the protoplast of one cell with an adjacent cell.
Protoplasts are cells of plants, bacteria, and fungi with removed cell walls. Since they lack cell wall, they are enclosed by plasmalemma.

Question 35

How to draw the optical image onto a paper

Answer 35

The picture should be smooth, non-shaded, continuous, labelled and clearly defined. It should be drawn using a sharp pencil and should take up most of the blank page. The magnification should be stated and the proportions should be accurate.
The label lines should be parallel to the top of the page and drawn using a ruler.

Question 36

What is an eyepiece graticule

Answer 36

This is a glass disc marked with a fine scale of 1 to 100.

This scale remains unchanged whichever objective lens is in place

Question 37

A stage micrometer

Answer 37

This is a microscope slide with a very accurate scale in micrometers engraved on it.

Question 38

How to calibrate an eyepiece graticule and a stage micrometer

Answer 38

Put the stage micrometer in place and the eyepiece graticule in the eyepiece.
Get the scale on the micrometer slide in clear focus,
Align the micrometer scale with the scale in the eyepiece. Take a reading from the two scales.
First you have to find the magnification factor. To do this, you need to make a certain number of graticule divisions equal to micrometer divisions.
If you know what each micrometer division equals to in millimetre then, you know what the total micrometer divisions (that fit into the certain graticule unit)
Then you known how many millimetres fit in a certain graticule unit .
To work out what a single graticule unit stand for, you can divide these values.
Next, you just convert this value to micrometers.

Question 39

How do you measure the size of a specimen

Answer 39

Remove the stage micrometer and place a prepared slide on the stage.
Measure the size of an object in graticule units and then multiply with the magnification factor.

Graticule divisions x magnification factor = measurement

Question 40

Ultrastructure

Answer 40

The optical image viewed from an electron microscope

Question 41

Disadvantages of electron microscopes

Answer 41

Expensive
Can only be used inside a carefully controlled environment
Specimens can also be damaged by the electron beam
Preparation process is complex; due to this there can be a problem with artefacts (structures that are produced due to the preparation process); sample preparation often distorts material
However, these can be eliminated as techniques improve.
The specimen has to be dead
Gives a monochrome micrograph
Large and needs to be installed
Vacuum is required

Question 42

Advantages of electron microscopes

Answer 42

It has a high magnification (500 000x for TEM) (x100 000 for SEM)
It has a high resolution (0.2 nm for TEM) (10nm for SEM)

Question 43

Disadvantages of optical microscopes

Answer 43

It has a lower magnification (1500x)

It has a low resolution ( 200nm)

Question 44

Advantages of optical microscopes

Answer 44

It is portable
It is cheap
The specimen can be living
Vacuum is not required
Simple sample preparation
Natural colour of sample is seen (or stains are used)

Question 45

What is an artefact?

Answer 45

An artefact is a visible structural detail caused by processing the specimen and not a feature of the specimen.
This appears in both microscopes
Ex: bubbles trapped under a cover slip when preparing a slide
Loss of continuity in membranes, distortion of organelles and empty spaces in the cytoplasm of cells.

Question 46

What is fluorescence?

Answer 46

Fluorescent is the absorption and re-radiation of light.
Light of a longer wavelength and lower energy is emitted after a shorter wavelength is absorbed. This is used to produce a magnified image.