2.2.1 Cell structure

Question 1

What are the 4 main types of sample preparation ?

Answer 1

Dry mounts, wet mounts, squash slide. smear slide

Question 2

what are dry mounts?

Answer 2

When thin slices or whole specimens are viewed, with just the coverslip placed on top e.g. plant tissue or hair.

Question 3

what is sectioning?

Answer 3

when the specimen is cut into very thin slices using a blade

Question 4

what are wet mounts

Answer 4

specimens are suspended in a liquid such as water or an immersion oil. Cover slip is placed on from an angle. aquatic organisms and other living samples can be viewed this way

Question 5

what are squash slides

Answer 5

first a wet mount is prepared. then a lens tissue is used to push down the cover slip. care must be taken so the cover slip is not broken. e.g. root tip squashes are used to look at cell division

Question 6

what are smear slides.

Answer 6

the edge of a slide is used to smear a sample, creating a thin, even coating on another slide. a cover slip is then placed on the sample. e.g. sample of blood

Question 7

why do we use stains

Answer 7

. the whole sample is illuminated at once, the images tend to have low contrast as most cells do not absorb a lot of light
.resolution is limited by the wavelength and diffraction of light as it passes through the sample
.the cytosol of cells and other structures are usually transparent
.stains increase contrast as different components in cells take up stains to different degrees so they become more visible

Question 8

how do you prepare a sample for staining

Answer 8

sample is paced on a slide and allowed to air dry. this is then heat fixed by passing through a flame. the specimen will adhere to microscope slide and will then take up stains

Question 9

crystal violet and methylene blue

Answer 9

they are positively charged dyes, which means they are attracted to negatively charged materials in the cytosplasm

Question 10

nigrosin and congo red

Answer 10

negatively charged so are repelled by negatively charged cytosol. These dyes stay outside the cell, leaving the cell unstained so they stand out against the unstained background

Question 11

iodine

Answer 11

stains carbohydrates in plant and animal specimens brown or blue-black. stains glycogen red

Question 12

what is differential staining

Answer 12

a technique which involves many chemical stains being used to stain different parts of the cell in different colours

Question 13

what are the four types of microscopes

Answer 13

light microscopes, transition electron microscope, laser scanning confocal microscope, scanning electron microscope

Question 14

electron microscopes can produce magnifications up to….

Answer 14

x500,000

Question 15

transmission electron microscope

Answer 15

a beam of electrons is transmitted through a specimen and focused to produce an image. best resolution. resulting power-0.5nm

Question 16

scanning electron microscope

Answer 16

a beam of electrons is sent across the surface of a specimen and the reflected electrons are collected. resolving power- 3 to 10nm. 3d images of surfaces produced

Question 17

Gram stain technique

Answer 17

used to separate bacteria into two groups: gram positive and gram negative bacteria. Crystal violet is first applied to the bacteria specimen on the slide. Then, iodine which fixes the dye. The slide is then washed with alcohol. The gram positive bacteria retain the

Question 18

Which bacteria are susceptible to the antibiotic penicillin

Answer 18

Gram positive bacteria are susceptible to the antibiotic penicillin, which inhibits the formation of cell walls. Gram-negative bacteria have much thinner cell walls that are not susceptible to penicillin,

Question 19

Acid fast technique

Answer 19

Used to differentiate species of the Mycobacterium from other bacteria. A lipid solvent is used to carry carbolfuchsin dye into the cells being studied. The cells are then washed with a dilute acid-alcohol solution. Mycobacterium are not affected by the acid-alcohol and retain the carbolfushsin stain which is bright red. Other bacteria lose the stain and are exposed to methylene blue stain, which is blue.

Question 20

What some of the stages involved in the production of slides

Answer 20

Fixing- chemicals like formaldehyde are used to press specimens in as near natural state as possible
Sectioning- specimens are dehydrated with alcohols and then place in a mould with wax or resin to form a hard black. This can then be sliced thinly with a knife called a microtome
Staining- specimens are often treated with separate stains to show different structures
Mounting- the specimens are secured to a microscope slide and a cover slip placed on top

Question 21

What is needed to produce a good scientific drawing

Answer 21

Title
State magnification
Use sharp pencil
White, unlined paper
Should be large
Smooth, continuous lines
No shading
Clearly defined structure
Ensure proportions are correct
Labels should not cross and should not have arrow heads
Labels drawn with a ruler

Question 22

What is magnification

Answer 22

How many times the image is than the actual side of the object being viewed

Question 23

What is resolution

Answer 23

The ability to distinguish between two objects that are close together

Question 24

Hey do electrons produce a higher resolution than light

Answer 24

They have a shorter wavelengths

Question 25

What is the magnification equation

Answer 25

Actual size= object size * magnification

Question 26

How to calibrate an eyepiece graticule

Answer 26

Identify a region where the divisions of the eyepiece graticule and the stage micrometer (sm) line up well
Count the divisions in the eyepiece graticule and sm in that region
In two columns write down:
The number of eyepiece graticule units in the region (EPGU)
The length of the sm in the region, including units
Divide the length of the sm region by the number of EPGUs in the region. The answer is the length that represents 1 EPGU

Question 27

Sample preparation for electron

Answer 27

Fixation using chemicals or freezing, staining with heavy metals and dehydration with solvents. Samples for a TEM will then be set in resin and may be stained agains. Samples for a SEM may be fractured to expose the inside and will then need to be coated with heavy metals.

Question 28

Why do samples for an electron microscopes need to processed in a specific way

Answer 28

The inside of an electron microscope is a vacuum to allow the electron beams to travel in a straight line

Question 29

Light microscopes produce magnifications and resolutions of …

Answer 29

X1500
200nm

Question 30

What is an artefact

Answer 30

A visible structural detail caused by processing the specimen and not a feature of the specimen. Artefacts appear in both electron and light microscopy. The bubbles that get trapped under the cover slip as you prepare a slide for light microscopy are artefacts. When preparing specimens for electron microscopy, changes in the ultra structure of cells are inevitable during the processing that samples must undergo.

Question 31

What is the cytoplasm made up of

Answer 31

Cytosol which is made up of water, salts and organic molecules

Question 32

What does metabolism include

Answer 32

The synthesis and breaking down of molecules

Question 33

Where do reactions take place

Answer 33

In the cytoplasm

Question 34

What do membranes do

Answer 34

They are selective permeable and control the movement of substances in and out of the cell and organelles

Question 35

The nucleus

Answer 35

Contains genetic information in the form of DNA molecules. Directs the synthesis of all proteins required by the cell, therefore the DNA controls the metabolic activities of the cell.

Question 37

DNA in the nucleus

Answer 37

DNA associates with proteins called histones to form a complex called chromatin. Chromatin coils and condenses to form structures called chromosomes which only become visible when cells are preparing to divide

Question 38

Nucleolus

Answer 38

Area within the nucleolus and is responsible for producing ribosomes. It is composed of proteins and RNA. RNA is used to produce ribosomal RNA (rRNA) which is then combined with proteins to form the ribosomes necessary for protein synthesis.

Question 39

Mitochondria

Answer 39

Site of the final stages of cellular respiration. Site of aerobic respiration. Produces the molecule ATP. Mitochondria have a double membrane. The inner membrane is highly folded to form structures called cristae and the fluid interior is called the matrix. Mitochondria contain a small amount of DNA called mitochondrial DNA and they can produce their own enzymes and reproduce themselves

Question 40

Vesicles

Answer 40

Membranous sacs that have storage and transport tiles. The consist of a single membrane with fluid inside. Vesicles are used to transport materials inside the cell

Question 41

Lysosomes

Answer 41

Specialised forms of vesicles that contain hydrolytic enzymes. Responsible for breaking down material in cells, including old organelles. They play an important role in the immune system as they are responsible for breaking down pathogens ingested by phagocytic cells. They also play an important role in programmed cell death or apoptosis

Question 42

What is the cytoskeleton

Answer 42

It is present throughout the cytoplasm of all eukaryotic cells. It is a network of fibres necessary for the shape and stability of a cell. Organelles are help in place by the cytoskeleton and it controls cell movement and the movement of organelles within cells

Question 43

What are the three components of the cytoskeleton

Answer 43

Microfilaments
Microtubules
Intermediate fibres

Question 44

Microfilaments

Answer 44

Contractile fibres formed from the protein actin. These are responsible for cell movement and also cell contraction during cytokinesis

Question 45

Microtubules

Answer 45

Globular tubulin proteins polymerise to form tubes that are used to form a scaffold-like structure that’s determines the shape of a cell. They also act as tracks for the movement of organelles, including vesicles around the cell. Spindle fibres which have a role in the physical segregation of chromosomes in cell division are composed of Microtubules

Question 46

Intermediate fibres

Answer 46

These fibres give mechanical strength to cells and help maintain their integrity

Question 47

Centrioles

Answer 47

A component of the cytoskeleton. Composed of Microtubules. Two associated centrioles form the centrosome which is involved in the assembly and organisation of the spindle fibres during cell division. Found in most eukaryotic cells apart from flowering plants and most fungi

Question 48

Cilia

Answer 48

Can be mobile or stationary.
Stationary cilia are present on the surface of many cells and have an important function in sensory organs such as the nose.
Mobile cilia beat in a rhythmic manner, creating a current and cause fluids and objects adjacent to the cell to move. Eg in the trachea to live mucus away form the lungs

Question 48

Flagella

Answer 48

Used primarily to enable cells mobility. In some cells they are used as a sensory organelle detecting chemical changes in the cell’s environment

Question 49

Endoplasmic reticulum

Answer 49

A network of membranes enclosing flattened sacs called cisternae. It is connected to the outer membrane of the nucleus

Question 50

Smooth ER

Answer 50

responsible for lipid and carbohydrate synthesis and storage

Question 51

Rough ER

Answer 51

Has ribosomes bound to the surface and is responsible for the synthesis and transport of proteins

Question 52

Ribosome

Answer 52

No membrane. Constructed of RNA molecules made in the nucleus. Site of protein synthesis. Mitochondria and chloroplasts also contain ribosomes

Question 53

Golgi apparatus

Answer 53

Compact structure formed of cisternae and doesn’t contain ribosomes. Has a role in modifying proteins and packaging them into vesicles.

Question 54

Protein production

Answer 54

Proteins are synthesised on the ribosomes bound to the endoplasmic reticulum. They then pass into its cisternae and are packaged into transport vesicles. Vesicles containing the newly synthesised protein move towards the Golgi apparatus via the transport function of the cytoskeleton. The vesicles fuse with the cis face of the Golgi apparatus and the proteins enter. The proteins are structurally modified before leaving the Golgi in vesicles form it’s trans face. Secretory vesicles carry proteins that’s are to be released from the cell. The vesicles move toward me and fuse with the cell surface membrane releasing their contents by exocytosis. Some vesicles form lysosomes, these contain enzymes for use in the cell.

Question 55

Cellulose cell wall

Answer 55

Cellulose is a complex carbohydrate. The cell walls are freely permeable so substances can pass in and out of the cell through the cell wall. The cell wall gives the cell its shape. Makes it rigid, prevents cell from bursting. Acts as a defence mechanism, protecting the contents of the cell against invading pathogens.

Question 56

Vacuoles

Answer 56

Membrane lined sacs contains cell sap. Large permanent vacuoles important in the maintenance of turgor, so that the contents of the cell push against the cell wall and maintain a rigid framework for the cell. Membrane of a vacuole is called the tonoplast. It is selectively permeable. If vacuoles appear in animal cells, they are small and not permanent

Question 57

Chloroplasts

Answer 57

Responsible for photosynthesis. Found in the green parts of cells like the leaves but not in the roots. Double membrane structure. Fluid enclosed in the choloroplast is called the strops. Chloroplasts can make their own proteins. The internal membranes provide a large surface area needed for the enzymes, proteins and pigment molecules necessary in the process of photosynthesis.

Question 58

DNA in prokaryotes

Answer 58

One molecule of DNA, a chromosome which is supercoiled to make it more compact. The genes on the chromosome are often grouped into operons, meaning a number of genes are switched on or off at the same time

Question 59

Ribosomes in prokaryotic cells

Answer 59

They are much smaller than those in eukaryotic cells. Eukaryotic cells have 80s ribosomes while prokaryotic cells have 70s ribosomes

Question 60

Cell wall in prokaryotes

Answer 60

Have a cell wall made from peptidoglycan. It is a complex polymer formed from amino acids and sugars

Question 61

What is fungi cell walls made of

Answer 61

Chitin