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BIOLOGY OCR > Cell structure and Microscopy > Flashcards

Cell structure and Microscopy Flashcards

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1
Q

What is the magnification of a light microscope, TEM and SEM?

A

Light - X1500

TEM - X500,000

SEM - X100,000

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2
Q

Define Magnification

A

The amount of times something is enlarged by, compared to the original object

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3
Q

What is the resolution of a light microscope TEM & SEM?

A 
light = 200nm
TEM = 0.2nm
SEM = 0.2nm
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4
Q

Define resolution

A

The ability to distinguish between two separate points with clarity.

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5
Q

How do you calculate magnification?

A

actual size

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6
Q

How many micrometres in a millimetre?

A

1000um

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7
Q

How many nano-metres in a micrometer?

A

1000nm

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8
Q

For a light microscope how do you prepare a slide (dry mount)?

A
  1. Take a thin slice of your specimen
  2. Using tweezers place your slice in the middle of a
    clean slide
  3. Place a cover slip on top of your slice
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9
Q

How do you prepare a slide for a light microscope (wet mount)?

A
  1. Pipette a small drop of water onto slide
  2. Using tweezers place slice, and the cover slip on top of water drop, ensuring there are no air bubbles under the cover slip
  3. Add the stain by placing a drop at one edge of the cover slip and a paper towel at the opposite edge to
    draw stain through
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10
Q

Name 4 similarities between Prokaryotic and Eukaryotic cell.

A

They both have:

  • Plasma membrane
  • Cytoplasm
  • Ribosomes
  • DNA and RNA
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11
Q

Name 4 differences between Prokaryotic and Eukaryotic cells.

A
  • much smaller (2µm in diameter vs eukaryotes that are 10-100 µm)
  • Free floating, circular DNA (nucleoid) not linear/straight and not contained within a nucleus
  • Less well-developed cytoskeleton
  • A cell wall made from peptidoglycan
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12
Q

Describe the function of the nucleus

A
  • Houses all of cell’s genetic material
  • Chromatin consists of DNA and proteins
  • Has instructions for making proteins
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13
Q

Describe the structure of the nucleus

A
  • Largest organelle
  • Contains chromatin
  • Surrounded by nuclear envelope
    and contains nucleolus
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14
Q

Describe the structure of the nucleolus

A
  • Dense spherical structure inside

nucleus

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15
Q

Describe the function of the nucleolus

A
  • Makes RNA and ribosomes
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16
Q

Describe the structure of the nuclear envelope

A
  • Surrounds nucleus
  • 2 membranes with fluid between them
  • Nuclear pores go through envelope
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17
Q

Describe the function of the nuclear envelope

A
  • Pores allow passage of relatively large molecules (e.g. hormones and mRNA)
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18
Q

Describe the structure of the RER

A
  • Flattened membrane sacs called cisternae
  • Continuous with outer nuclear membrane
  • Studded/littered with ribosomes
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19
Q

Describe the function of the RER

A
  • Modifies and transports proteins made on attached ribosomes
  • Some proteins are secreted from the cell
  • Some are placed on plasma membrane
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20
Q

Describe the structure of the SER

A
  • Flattened membrane sacs called cisternae

- No ribosomes

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21
Q

Describe the function of the SER

A
  • Involved in lipid production (e.g. cholesterols and steroid hormones)
  • Involved in lipid absorption from the gut
22
Q

Describe the structure of the golgi apparatus

A
  • Stack of membrane bound, flattened sacs

- Vesicles can often be seen around the edges

23
Q

Describe the function of the golgi apparatus

A
  • Modifies proteins (e.g. folding or adding sugar)

- Packages modified proteins into vesicles for transportation

24
Q

Describe the structure of the flagella

A
  • Extension sticking out from cell
  • Cylinder contains nine microtubules arranged in a circle and has 2 in the middle ‘9,2 formation’
  • Long
  • Usually present alone or in pairs
25
Q

Describe the function of the flagella

A
  • Enables movement
26
Q

Describe the structure of the mitochondria

A
  • Spherical or oval shaped and only 2-5 µm long
  • Enveloped in two membranes
  • Highly folded inner membrane forms cristae
  • Central part called matrix
27
Q

Describe the function of the mitochondria

A
  • Site of ATP (adenosine triphosphate) production and aerobic respiration
28
Q

Describe the structure of a lysosome

A
  • Small spherical sacs

- Surrounded by single membrane

29
Q

Describe the function of lysosomes

A
  • Keep damaging enzymes separate from the cell

- Can engulf old/worn out organelles and foreign substances, digesting them with their enzymes

30
Q

Describe the structure of chloroplast

A
  • Double membrane
  • Separated by fluid filled space
  • Continuous inner membrane
    with network of flattened membrane sacs called thylakoids
  • Stack of thylakoids = granum
31
Q

Describe the function of chloroplast

A
  • Site of photosynthesis
32
Q

Describe the structure of cilia

A
  • Hair-like extensions from the cell surrounded by the plasma membrane
  • contain microtubules from the cytoskeleton and are formed from centrioles
33
Q

Describe the function of cilia

A
  • Can act as antennae in cell signalling

- Or can act in large groups on a cell surface to move material around (e.g. cilia in airways wafting mucus)

34
Q

Describe the structure of the plasma membrane

A
  • Continuous outer membrane

- Contains a variety of molecules such as proteins and lipids

35
Q

Describe the function of the plasma membrane

A
  • Controls what goes in and out of cell

- Receptors on cell surface allow for endocytosis and exocytosis

36
Q

Describe the structure of the vacuole

A
  • A fluid filled sac within amembrane called a tonoplast
37
Q

Describe the function of the vacuole

A
  • The fluid contains water and a variety of solutes that helps plant cells regulate their water
38
Q

Describe the structure of ribosomes

A
  • No outer membrane
  • They are tiny organelles
  • Each consists of 2 sub-units
  • Some found in cytoplasm, some bound to RER
39
Q

Describe the function of ribosomes

A
  • Site of protein synthesis in the cell

- Act as an assembly line where mRNA is used to assemble proteins from amino acids

40
Q

Describe the structure of centrioles

A
  • Made of microtubules

- Small tubes of protein fibres

41
Q

Describe the function of centrioles

A
  • Take part in cell division

- Form spindle fibres, moving chromosomes in cell division

42
Q

What are the steps in protein synthesis?

A
  1. Genes are copied into messenger RNA (mRNA), which leaves the nucleus via nuclear pores and attaches to a ribosome
  2. Ribosomes read mRNA and assembles amino acids into a unique sequence
  3. Proteins produced by ribosomes on the rough ER are modified (e.g. sugars added and polypeptides folded) within the rough ER.
  4. The polypeptide(s) are transported to the Golgi apparatus in a vesicle.
  5. Further modified and packaged into a vesicle
  6. Vesicle transported to cell surface membrane and secreted (by exocytosis).
43
Q

What is the function of the cytoskeleton?

A
  • Helps maintain the shape of cell
  • Enables movement
  • Helps transport vesicles around cell
44
Q

What is the structure of the cytoskeleton?

A
  • A large network of protein fibres
45
Q

What are the two types of protein that the cytoskeleton consists of?

A
  • Actin filaments: Small microfilament strands 7nm in diameter help support the cell and give it mechanical strength. Intermediate filaments 10nm in diameter anchor the nucleus and can extend between some cells for communication.
  • microtubules: Stacks of protein cylinders, 18-30nm in diameter and made from a protein called tubulin.
    provides the cell with its shape and support. They form cilia, undulipodia and centrioles. Cytoskeletal motor proteins are present on microtubules. They use ATP to move the cell’s contents along the fibres.
46
Q

How do TEMs work?

A

Uses electromagnets to focus a beam of electrons which is transmitted through the specimen.

47
Q

Ho\w do SEMs work?

A

Scans a beam of electrons across the specimen. This knocks off electrons from the specimen and are gathered in a cathode ray tube.

48
Q

Do SEMs produce 2D or 3D images?

A

3D images

49
Q

Describe the structure of the cellulose cell wall

A
  • Made from cellulose fibres
  • Found on the outside
    of the plasma membrane of plants
50
Q

Describe the function of the cellulose cell wall

A
  • Supports the cell and maintains
    their shape - contributing to the shape of the whole plant
  • Prevents cells from bursting when they are swollen with water (turgid)
  • The cell wall is permeable to allow solutions to pass in and out
51
Q

Why do same parts of an image from a TEM look darker?

A

Denser parts of the specimen absorb more electrons making it look darker.

BIOLOGY OCR (12 decks)

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