2.1.1 - Cell structure

Question 1

What is a microscope ?

Answer 1

A microscope is an instrument which enables you to magnify an object

Question 2

When was the first microscope discovered ?

Answer 2

The first microscopes developed were light microscope in the 16th and 17th century

Question 3

What is the cell theory ?

Answer 3

• Both plant and animal tissue is composed of cells
• Cells are the basic unit of all life
• Cells only develop from existing cells

Question 4

How does a light microscope work ?

Answer 4

A light microscope uses visible light and lenses to generate magnified images of small objects

Question 5

What are the two lenses in a light microscope ?

Answer 5

Objective lens and the eyepiece lens

Question 6

What do the two lenses in a light microscope allow ?

Answer 6

They allow for higher magnification

Question 7

Describe the sample preparation for a light microscope

Answer 7

• Samples are stained with coloured stains that bind to certain chemicals of cell structures
• Samples may also be sectioned and embedded in wax ; this helps with preserving structure whilst cutting

Question 8

What are the four main ways to prepare samples ?

Answer 8

• Dry mount
• Wet mount
• Squash slide
• Smear slide

Question 9

What is a dry mount ?

Answer 9

• Specimen is cut into very thin slices with a sharp blade

- Specimen is then placed on a slide with a cover slip on top

Question 10

What is a wet mount ?

Answer 10

• Specimens are suspended in a liquid
• A cover slip is placed at an angle
• It allows for aquatic samples to be viewed

Question 11

What are squash slides ?

Answer 11

A wet mount is prepared, then a lens tissue is used to gently press down the cover slip

Question 12

What are smear slides ?

Answer 12

The edge of a slide is used to smear the sample, creating a thin, even coating on another slide

Question 13

What is differential staining ?

Answer 13

It can distinguish between two types of organisms that would otherwise be hard to identify

Question 14

What are the two types of differential staining?

Answer 14

• Gram stain technique

- Acid fast technique

Question 15

What is Gram stain technique ?

Answer 15

• It is used to separate gram positive and gram negative bacteria.
• Crystal violet is applied to a bacterial specimen and then iodine, to fix the dye. The slide is then washed with alcohol.

Question 16

What would the results be for the gram stain technique ?

Answer 16

• Gram positive bacteria will appear blue/purple, they are susceptible to penicillin
• Gram negative bacteria will lose the stain because they have thinner cell walls, they are not susceptible to penicillin. They are then stained with safranin dye, which will make them appear red.

Question 17

What is Acid fast technique ?

Answer 17

• This technique is used to identify Mycobacterium, which have cell walls with a higher lipid content, this prevents dyes from readily binding to cells.
• A lipid solvent is used as a primary stain to carry Carbolfuchin dye into the cells.

Question 18

What would the results be for the acid fast technique ?

Answer 18

• Acid fast bacteria retain Carbolfuchin and appear pink

- Non Acid fast bacteria lose Carbolfuchin but retain methylene blue so they appear blue

Question 19

What is magnification ?

Answer 19

Magnification is how many times larger the image is seen compared to the actual size of the object being viewed

Question 20

How do you calculate magnification ?

Answer 20

• Magnification = Image size ÷ actual size

Question 21

What is Resolution ?

Answer 21

• Resolution is the ability to see individual objects as separate entities
• The higher the resolution the more details are visible

Question 22

What is electron microscopy ?

Answer 22

In electron microscopy, a beam of electrons with a wavelength of less than 1 nm is used to illuminate the specimen

Question 23

What are the advantages of electron microscopy ?

Answer 23

• It allows for more detail of the cells ultrastructure to be seen
• It can allow magnifications of up to x 500,000 and still have clear resolution

Question 24

What are the disadvantages of electron microscopy ?

Answer 24

• Very expensive
• Can only be used in a carefully controlled environment
• Specimens can become damaged by the electron beam
• The preparation process is very complicated and can lead to artefacts

Question 25

What is an Artefact ?

Answer 25

- Artefacts are structures that are produced due to the preparation process - Such as a bubble trapped under the cover slip - They appear in both light and electron microscopes

Question 26

What is Transmission Electron Microscopy ?

Answer 26

- A beam of electrons is transmitted through a specimen and focused to produce an image - It has the best resolution and a resolving power of 0.5 nm

Question 27

What is Scanning Electron Microscopy ?

Answer 27

- A beam of electrons is sent across the surface of a specimen and the reflected electrons are collected to create an image - It has a resolving power from 3-10 nm, so resolution isnt as good - Produces 3D images of surfaces

Question 28

What is fluorescent microscopy ?

Answer 28

In fluorescent microscopy, a higher light intensity is used to illuminate a specimen that has been treated with a fluorescent chemical

Question 29

What is fluorescence ?

Answer 29

- It is the absorption and radiation of light | - Light of a lower wavelength and lower energy is emitted and used to produce a magnified image

Question 30

What is Laser Scanning Confocal Microscopy ?

Answer 30

- A laser scanning confocal microscope moves a single spot of focused light across a specimen. This causes fluorescence from the components labelled with the fluorescent dye. The emitted light from the specimen is then fitted through a pinhole aperture. - Only light radiated from very close to the focal plane is detected - Unwanted radiation does not pass through the pinhole and is not detected

Question 31

Key points regarding LSCM

Answer 31

- A laser is used instead of light - Very high resolutions can be obtained - A 2D image is produced, 3D images can be produced by creating images at different focal planes - The beamsplitter is a dichroic mirror, which only reflects the wavelength from the laser but allows wavelengths from the sample to pass through - The positions of the two pinholes mean the light waves from the laser follow the same path as the light was radiated from the sample when it fluoresces. They both have the same focal plane, confocal.

Question 32

What are the key uses of LSCM ?

Answer 32

- Used in the diagnosis of the eye - Being developed for use in endoscopic procedures - Used in the development of new drugs

Question 33

Max resolutions

Answer 33

- Light microscope - 0.2 μm - TEM - 0.0005 μm - SEM - 0.003 - 0.01 μm

Question 34

Max magnifications

Answer 34

- Light microscope - x1500 - TEM - more than x1,000,000 - SEM - less than x1,000,000 but stunning 3-D images

Question 35

Name the two main types of organisms

Answer 35

Prokaryotes and eukaryotes

Question 36

What are prokaryotes ?

Answer 36

- Single celled organisms with a simple structure of just a single internal area called the cytoplasm, composed of cytosol. - Bacteria

Question 37

What are eukaryotes ?

Answer 37

- Make up multicellular organisms e.g. animals and plants - Have much more complicated internal structure, containing a membrane bound nucleus (nucleoplasm) and cytoplasm, which contains many membrane bound cellular components - Animal and plant cells

Question 38

What are bigger, prokaryotes or eukaryotes ?

Answer 38

Eukaryotes

Question 39

Define organelles

Answer 39

Membrane bound compartments within the cell, each providing distinct environments and therefore conditions for different cellular reactions

Question 40

What is the function of the cell-surface membrane ?

Answer 40

- It is a thin selectively permeable protein and phospholipid bilayer that controls the movement of materials in and out of the cell - It has receptor molecules to allow it to respond to chemicals

Question 41

What is the function of the nucleus ?

Answer 41

- It directs the synthesis of all proteins required by the cell and controls the metabolic activities of the cell - DNA molecules control the cell's activities; they associate with histone molecules to form chromatin. Chromatin coils tightly to form chromosomes. - The nuclear envelope protects it from damage - The nuclear pores allow substances such as RNA to move between the nucleus and cytoplasm.

Question 42

What is the function of the nucleolus ?

Answer 42

- The nucleolus is an area within the nucleus that is responsible for producing ribosomes - It is composed of proteins and RNA - RNA is used to produce ribosomal RNA which is then combined with proteins to form the ribosomes necessary for protein synthesis

Question 43

What is the function of mitochondria ?

Answer 43

- Mitochondria are the site of the final stages of cellular respiration, which is when energy is made available for the cell to use by the production of ATP - It has a double membrane; The inner membrane is highly folded to form cristae. The fluid inside the cristae is called the matrix. - They contain mitochondrial DNA, produce their own enzymes and can reproduce themselves.

Question 44

What is the function of vesicles ?

Answer 44

- Vesicles are small fluid filled sacs in the cytoplasm surrounded by a membrane - Their role is to transport substances in and out of the cell and between organelles

Question 45

What is the difference between a secretory vesicle and a transport vesicle ?

Answer 45

- A transport vesicle transports things inside the cells | - A secretory vesicle transports things outside of the cell

Question 46

What is the function of a lysosome ?

Answer 46

- Lysosome are specialised forms of vesicles that carry around hydrolytic enzymes which are used for digestion - These enzymes enable the lysosome to digest invading cells or break down worn out components of the cell. - They also play a role in programmed cell death which is known as apoptosis

Question 47

What is apoptosis ?

Answer 47

Programmed cell death

Question 48

What is the cytoskeleton ?

Answer 48

- The cytoskeleton is a network of fibres necessary for the shape and stability of a cell - Organelles are held in place by the cytoskeleton and it controls cell movement of organelles within the cell

Question 49

What are the three components of the cytoskeleton ?

Answer 49

- Microfilaments - contractile fibres formed from the protein actin. - Microtubules - globular tubulin proteins polymerised to form tubes that act as a scaffold structure determining the shape of a cell. Also act as tracks for the movements of organelles. - Intermediate fibre - fibres that give mechanical strength to cells and help maintain their integrity.

Question 50

What is the function of the microtubules and microfilaments ?

Answer 50

- Support the cell's organelles keeping them in position, strengthen the cell and help maintain its shape - They're responsible for the transport of organelles and materials within the cell.

Question 51

What is the function of centrioles ?

Answer 51

- Component of the cytoskeleton present in most eukaryotic cells. - Small hollow cylinders containing microtubules. - Two associated centrioles form the centrosome, which is involved in the assembly and organisation of the spindle fibres, and therefore the splitting chromosomes during cell division.

Question 52

What is the function of cilia ?

Answer 52

- Small hair-like structures found on the surface membrane of some animal cells. - Microtubules allow the cilia to move which is used to move substances along the cell surface e.g. In the trachea to sweep dust and dirt out of the lungs. - Cross section appears like a wheel with an outer membrane and nine pairs of microtubules arranged in a ring around two pairs in the centre

Question 53

What is the function of the flagella ?

Answer 53

- Long hair-like structures that stick out from the cell surface and are surrounded by the plasma membrane. - Used primarily to enable cell motility - In some cells, they are used as a sensory organelle detecting the chemical changes in the cells environment - Microtubules contract to make flagellum move, this is used to propel cells forward e.g. the tail of a sperm cell, this requires energy

Question 54

What is the function of a ribosome ?

Answer 54

- It is a small organelle that either floats free in the cytoplasm or is attached to the RER - It is where proteins are made during protein synthesis.

Question 55

What is the function of the smooth endoplasmic reticulum ?

Answer 55

- A system of membranes enclosing a fluid filled space | - It is used for synthesising and processing lipids and for storage

Question 56

What is the function of the rough endoplasmic reticulum ?

Answer 56

- A system of membranes enclosing a fluid filled space with its surface covered with ribosomes - It is responsible for the synthesis and transport of proteins

Question 57

What is the function of the Golgi apparatus ?

Answer 57

- The golgi body is a group of flat fluid filled sacs, sometimes seen with vesicles at the edge - It has a compact structure formed of cisternae and does not contain ribosomes - It processes and packages new lipids and proteins, it also makes lysosomes

Question 58

Where are proteins made ?

Answer 58

Mainly at the ribosomes attached to the RER. These proteins are stored in the RER until they can be processed and packaged at the golgi apparatus. Some ribosomes are free in the cytoplasm and the proteins they produce also stay in the cytoplasm.

Question 59

Making and secreting a protein (six marker)

Answer 59

- Transcription comes first. DNA is unzipped and mRNA copies the DNA strand. It copies it using complementary base pairing and is then transported out of the nucleus via the nuclear pores and to the ribosome. - Ribosomes in the rough endoplasmic reticulum make proteins to be secreted this is called translation. - Proteins are transported from the rough endoplasmic reticulum to the Golgi apparatus. It is transported to the cis face which then takes it in - Golgi body then processes and modifies proteins, it could also add glucose molecules. They then move to the trans face where they are released. - The secretory vesicles containing the proteins are then released and move towards the plasma membrane. They leave via the trans face. - Vesicles fuse with the plasma membrane, possible because they both have phospholipids and then the vesicle undergoes exocytosis, exocytosis is the process of the vesicle leaving the cell through the cell membrane

Question 60

What is the cellulose cell wall ?

Answer 60

A tough yet elastic wall of cellulose that surrounds and supports the cell wall

Question 61

What is the function of the cellulose cell wall ?

Answer 61

- The contents of the cell wall press against the cell wall, making it rigid - It is freely permeable - Defence mechanism against invading pathogens

Question 62

What is the vacuole ?

Answer 62

It is a membrane lined sac in plant cells containing cell sap

Question 63

What is the function of the vacuole ?

Answer 63

- Large permanent vacuoles are used to maintain turgor | - If vacuoles appear in animal cells they are small and transient

Question 64

What is the tonoplast ?

Answer 64

- The membrane of the vacuole is called the tonoplast | - It is selectively permeable

Question 65

What are chloroplasts ?

Answer 65

- Chloroplasts are found in plant cells, in the stems and leaves and not in the roots - They contain DNA and ribosomes, so they are able to make their own proteins

Question 66

What is the function of the chloroplast ?

Answer 66

The chloroplasts are the organelles responsible for photosynthesis in plant cells

Question 67

What is the structure of the chloroplast like ?

Answer 67

- They have a double membrane structure - The fluid enclosed in the chloroplasts is called the stroma - They have an internal network of membranes which form flattened sacs called Thylakoids - Several thylakoids stacked together are called a granum - The grana are joined by membranes called lamellae

Question 68

What do the grana contain ?

Answer 68

The grana contain the chlorophyll pigments, where light dependent reactions occur for photosynthesis