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A Level Biology > Cell Structure > Flashcards

Cell Structure Flashcards

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1
Q

Describe light microscopes

A

Poor resolution due to long wavelength of light
Living samples can be examined and a colour image obtained

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2
Q

Describe transmission electron microscope

A

High magnification and resolution
Electrons pass through the specimen to create an image

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3
Q

Describe scanning electron microscopes

A

High magnification and resolution
Electrons bounce off the surface of the specimen to create an image

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4
Q

Describe laser scanning confocal microscopes

A

High resolution and 3D imaging
Laser light used to create an image

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5
Q

What is resolution

A

Minimum distance between two objects in which they can still be viewed as separate

Optical microscope determined by wavelength of light

Electron microscope determined by the wavelength of the beams of electrons

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6
Q

What is magnification

A

Refers to how many times larger the image is compared to the object

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7
Q

What are the 4 main types of sample preparations?

A

Dry mount
Wet mount
Squash slide
Smear slide

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8
Q

Describe dry mount

A

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

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9
Q

Describe wet mounts

A

When water is added to the specimen before lowering the coverslip with a mounted needle to prevent air bubbles from forming. Aquatic organisms could be viewed this way

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10
Q

What are squash slides

A

Wet mounts which you then push down on the coverslip to squash the sample to ensure you have a thin layer to enable light to pass through. This is used when creating a root tip squash sample to view the chromosomes in mitosis

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11
Q

What are smear slides?

A

Created using the edge of another slide to smear the sample across another slide to create a smooth, thin even coated specimen. A cover slip is placed on top after smearing. This is used when examining blood cells in a blood sample

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12
Q

What is an eye piece graticule?

A

Scale on a glass disc which is called eyepiece graticule.

Used to measure the size of objects you are viewing under a microscope

Each time you change the objective lens and the magnification you have to calibrate the eyepiece

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13
Q

How to calibrate an eyepiece graticule

A

1) Line up the stage micrometer and eyepiece graticule whilst looking through the eyepiece

2) count how many divisions on he eyepiece graticule fit into one division on the micrometer scale

3) each division on the micrometer is 10μm so this can be used to calculate what one division on the eyepiece graticule is at the current magnification

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14
Q

What formula do we use for viewing structures under a microscope?

A

Magnification = size of image/ size of real object

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15
Q

What is differential staining?

A

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

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16
Q

How do crystal violet and methylene blue stain?

A

They are positively charged so they are attracted to and stain negatively charged material

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17
Q

How does nigrosin and Congo red stain?

A

Negatively charged so cannot enter cells as cytosol repels them. Creates a stained background, so unstained cells stand out

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18
Q

How is crystal violet used in gram staining

A

Crystal violet added, then iodine to fix the stain, alcohol is used to wash away any unbound stain. Gram positive bacteria appear blue/purple as the stain is retained to the thicker peptidoglycan cell wall later absorbing the dye.

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19
Q

How is safranin used in gram staining?

A

Gram negative bacteria cannot absorb methylene value as their peptidoglycan walls are too thin so they do not retain the stain. Safranin is used as a counterstain, turning them red

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20
Q

How does gram staining help medics?

A

Distinguishing between two different types of bacteria helps antibiotic diagnosis

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21
Q

What are electron microscopes

A

A beam of electrons have a very short wavelength = a high resolution so small organelles and internal structures can be visualised.

Image is created using an electromagnet to focus the beam of negatively charged electrons

Electrons are absorbed by air = EM must be in a vacuum
Only non living specimens can be examined

Image is black and white so samples must be stained

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22
Q

Outline process of transmission electron microscopes

A

Extremely thin specimens are stained and placed in a vacuum

Electron gun produces beam of electron that passes through the specimen

Some parts of the specimen absorb the electrons and this makes them appear darker

2D image produced and shows detailed images of internal structure of cells

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23
Q

Outline scanning electron microscopes

A

Specimens do not need to be thin as electrons are not transmitting through

Electrons are beamed onto the surface and the electrons are scattered in different ways

Produces a 3D image

24
Q

Outline laser scanning confocal microscope

A

Fluorescent microscope

Image created using high light intensity to illuminate the specimen stained with a fluorescent dye

Enables scientists to view sections of tiny structures that is challenging to physically section off and creates a 3D image

Microscope scan specimen point by point using a focused laser beam to create a 2D image of a 3D image in different focal planes is used,

25
Q

Structure of the nucleus?

A

Nuclear envelope - double membrane
Nuclear pores
Nucleoplasm- granular jelly like material
Chromosomes - protein bound, linear DNA
Nucleolus - smaller sphere inside which is the site of rRNA production - makes ribosomes

26
Q

Function of the nucleus

A

Site of DNA replication and transcription
Contains genetic code for each cell
Site of ribosome synthesis

27
Q

Structure of the flagella

A

Whip like structure

28
Q

Function of the flagella

A

For mobility and sometimes as sensory organelle for chemical stimuli

29
Q

What is the structure of cilia?

A

Hairlike projections out of cells

30
Q

Function of cilia

A

Mobile or stationary
Move substances in a sweeping motion
Stationary cilia are important in sensory organs such as the nose

31
Q

Structure of centrioles

A

Made of microtubules
Occurs in pairs to form a centrosome

32
Q

Function of centrioles

A

Involved in the production of spindle fibres and organisation of chromosomes in cell division

33
Q

Structure of the cytoskeleton

A

Network of fibres found within the cytoplasms all over a cell

Consists of microfilaments, microtubules and intermediate fibres

34
Q

Function of the cytoskeleton

A

Provides mechanical shape to cells - maintains shape and stability

Microfilaments are responsible for cell movement

Microtubules are responsible for creating a scaffold like structure

Intermediate fibres provide mechanical strength

35
Q

What is the endoplasmic reticulum

A

Rough and smooth ER have folded membranes called cisternae

Rough have ribosomes on the cisternae

36
Q

Function of the endoplasmic reticulum

A

RER - protein synthesis
SER - synthesis and store lipids and carbohydrates

37
Q

Structure of golf apparatus and vesicles

A

Folded membranes making cisternae

Secretary vesicles pinch off from the cisternae

38
Q

Function of Golgi apparatus and vesicles

A

Add carbohydrates to proteins to form glycoproteins

Produce secretory enzymes

Secrete carbohydrates

Transport modify and store lipids

Form lysosomes

Molecules are labelled with their destination

Finished produces are transported to cell surface in Golgi vesicles where they fuse with the membrane and the contents in released

39
Q

Structure of lysosomes

A

Bags of digestive enzymes - can contain 50 different enzymes

40
Q

Function of lysosomes

A

Hydrolyse phagocytic cells

Completely break down dead cells

Exocytosis - release enzymes to outside of cell to destroy material

Digest worn out organelles for reuse of material

41
Q

Structure of mitochondria

A

Double membrane
Inner membrane called Cristae
Fluid centre called mitochondrial matrix
Loop of mitochondria DNA

42
Q

Function of mitochondria

A

Site of aerobic respiration
Site of ATP production
DNA to code for enzymes needed in respiration

43
Q

Structure of ribosomes

A

Small, made up of two sub-units of protein and rNA

80s - large ribosome found in eukaryotic cells

70s - smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts

44
Q

Function of ribosomes

A

Site of protein synthesis

45
Q

Structure of chloroplasts

A

Surrounded by a double membrane
Contains thylakoids
Fluid filled stroma contains enzymes for photosynthesis found in plants

46
Q

Function of chloroplasts

A

Site of photosynthesis

47
Q

Structure of cell wall

A

Plants - made of microfibrils of the cellulose polymer

Fungi - made of chitin, a nitrogen-containing polysaccharide

48
Q

Function of cell wall

A

Provide structural strength to the cell

49
Q

Structure of plasma membrane

A

Found in all cells
Phospholipid bilayer - molecules embedded within and attached on the outside

50
Q

Function of the plasma membrane

A

Controls the entrance and exit of molecules

51
Q

Outline Protein synthesis

A
  1. Polypeptide chains are synthesised on the RER
  2. These polypeptide chains move to the cisternae in the RER and are packaged into vesicles to be sent to the Golgi apparatus via the cytoskeleton
  3. In the Golgi apparatus, the proteins are modified and packaged into vesicles
  4. Secretory vesicles carry the proteins to the cell surface membrane where it fuses and releases the protein by exocytosis
52
Q

Difference between prokaryotic and eukaryotic cells

A

Cells are much smaller
No membrane bound organelles
Smaller ribosomes
DNA is not contained within a nucleus
Cell wall made of murien

53
Q

Structure of prokaryotic cell genetic information

A

No nucleus - singular circular DNA molecule free in the cytoplasm which is not protein bound

54
Q

Structure of prokaryotic cell wall

A

Contains murein a glycoprotein

55
Q

Describe the capsule

A

Slimy layer made of protein
Prevents bacteria from desiccating (drying out) and protects the bacteria against the hosts immune system

A Level Biology (7 decks)

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