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OCR BIOLOGY A LEVEL > Cell Structure > Flashcards

Cell Structure Flashcards

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1
Q

Define magnification

A

How much bigger an image is compared to a specimen

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2
Q

Define resolution

A

The ability to distinguish between two separate points

How detailed an image is

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3
Q

What is the maximum magnification of a light microscope

A

X1500

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4
Q

What is the maximum magnification of a TEM

A

X>1,000,000

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5
Q

What is the maximum magnification of a SEM

A

X<500,000

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6
Q

What is the maximum resolution of a light microscope

A

200nm/0.2um

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7
Q

What is the maximum resolution of a TEM

A

0.2nm/0.0002um

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8
Q

What is the maximum resolution of a SEM

A

20nm/0.002um

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9
Q

Advantages of light microscope

A

Relatively cheap
Can observe live specimens
Colour images

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10
Q

Disadvantages of light microscope

A

Low resolution (lower than electron microscopes)

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11
Q

Advantages of TEM

A

High resolution images to look at very small organelles eg ribosomes
Look at internal structures of organelles

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12
Q

Disadvantages of TEM

A

Specimens must be dead
Specimens must be thinly sliced
Images are black and white (colour can be added)
Produces 2D images

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13
Q

Advantages of SEM

A

Produces a 3D image

Shows the surface of an organism

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14
Q

Disadvantages of SEM

A

Specimens must be dead
Lower resolution than TEM
Images are black and white (colour can be added)

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15
Q

Advantages of scanning laser confocal

A

Pinhole prevents out of focus light reaching the detector so image is clearer
Can view thicker and living specimens at different depths

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16
Q

How does a light microscope work

A

Uses a number of lenses to produce an image that can be viewed directly at the eyepiece.
Light passes from a bulb under the stage, through a condenser lens and then through specimen.
This beam of light is passed through an objective lens (x4, x10, x40) and then the eyepiece lens (x10)

Looks at whole cells or tissues

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17
Q

How does a TEM work

A

Uses electromagnets to focus a beam of electrons, which is transmitted through the specimen.
Denser parts of the specimen absorb more electrons, which makes it look darker on the image, creating contrast

Produces 2D images

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18
Q

How does a SEM work

A

Scan a beam of electrons across the specimen

This knocks off the electrons across the specimen, which are gathered in a cathode ray tube to form an image

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19
Q

How are specimens treated before viewing with a SEM

A

Coated with a thin layer of gold particles

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20
Q

How are specimens treated before viewing with a LCSM

A

Tagged with fluorescent dye

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21
Q

What is the function of the pinhole in LSCM

A

Prevents out of focus light reaching the detector

22
Q

What does methylene blue stain and it’s colour

A

DNA

Blue

23
Q

What does giemsa stain and it’s colour

A

Blood cells
Red blood cells stain red
White blood cells stain purple

24
Q

What does eosin stain and it’s colour

A

Cytoplasm

Pink

25
Q

What does haemotoxylin stain and it’s colour

A

RNA purple

DNA blue

26
Q

Why are specimens often stained before viewing under a light microscope

A

Organelles are often transparent so it prevents object from appearing white

27
Q

How would you calculate actual size of a magnified object

A

Actual = image/ magnification

28
Q

How does a LSCM work

A

Uses laser beams to scan a specimen, tagged with fluorescent dye
Laser beam is focused through a lens which is aimed at a beam splitter
Beam splits and some light is directed to specimen
When the laser hits dye it gives off fluorescent light
Light if focused through pinhole onto a detector
Detector is hooked to a computer which generates the image

29
Q

How to prepare sample for use with electron microscopes

A

Treat it with heavy metals (like lead)

Metal ions scatter electrons foraged at the sample and give contrast between different structures

30
Q

How to prepare a dry mount

A

Use a thinly sliced specimen
Use tweezers to place specimen in the middle of a clean slide
Place a cover slip on top

31
Q

What can a dry mount be used for

A

Observing hairs,
Parts of insects
Pollen
Parts of a flower

32
Q

How to prepare a wet mount

A

Pipette a small drop of water onto the slide
Use tweezers to place specimen on water droplet
Stand cover slip upright near water droplet
Carefully tilt and lower slip so it covers the specimen
Try to avoid air bubbles
Add a stain to edge of cover slip, drawing the stain across the specimen

33
Q

What can a wet mount be used for

A

Living samples eg tiny aquatic organisms

34
Q

How to use a light microscope

A
  1. Clip the slide containing the specimen onto the stage
  2. Select lowest powered objective lens
  3. Use coarse adjustment knob to bring stage up to just below objective lens
  4. Look down eyepiece, using coarse adjustment knob to move stage until image is in focus
  5. Adjust focus with fine adjustment knob until you get a clear image
  6. Swap to higher powered objective lens if required
35
Q

What is an eyepiece graticule

A

It is fitted onto the eyepiece
Like a transparent ruler with numbers but no units
When you look through eyepiece you’ll see a scale

36
Q

What is the stage micrometer

A

Placed on the stage
It is a microscope slide with an accurate scale (has units)
Used to work out value of divisions on the eyepiece graticule at a particular magnification

37
Q

Why are a variety of stains used to stain samples

A

Different stains can be used to make different parts of cell show up

38
Q

Structure and function of nucleus

A

Large organelles surrounded by nuclear envelope (double membrane)
Contains many pores
Contains chromatin (made of DNA and proteins)
Contains a nucleolus

Controls cells activities by controlling transcription of DNA
DNA contains instructions to make proteins
Pores allow substances to move between nucleus and cytoplasm
Nucleolus makes ribosomes

39
Q

Structure and function of plasma membrane

A

Made of lipids and proteins

Regulates movement of substances in/out of cell
Has receptor molecules which allow it to respond to chemicals like hormones

40
Q

Structure and function of cell wall

A

Rigid structure that surrounds plant cells
Made of cellulose

Supports plant cells

41
Q

Structure and function of lysosome

A

Round organelle surrounded by a membrane with no clear internal structure

Contains digestive enzyme
To digest invading cells or break down worn out components
Transports hydrologic enzymes

42
Q

Structure and function of rough ER

A

System of membranes enclosing a fluid filled space
Surface is covered with ribosomes

Folds and processes proteins made at the ribosomes

43
Q

Structure and function of the smooth ER

A

System of membranes enclosing a fluid filled space

Synthesises and processes lipids and steroid hormones

44
Q

Structure and function of a vesicle

A

Small fluid filled sac in the cytoplasm surrounded by a membrane

Transports substances in/out of cell via plasma membrane
Some are formed by Golgi apparatus or ER and some at the cell surface

45
Q

Structure and function of Golgi apparatus

A

Group of fluid filled membrane bound flattened sacs
Vesicles at the edges of the sacs

Processes and packages new lipids and proteins
Makes lysosomes

46
Q

Structure and function of mitochondrion

A

Double membrane
Inner membrane folded to form cristae
Inside is the matrix which contains enzymes for respiration

Site of aerobic respiration where ATP is produced
Found in large numbers in cells that are active and require a lot of energy

47
Q

Structure and function of chloroplast

A

Small flattened structure found in plants
Surrounded by double membrane
Membranes inside called thylakoid membranes
Thylakoid are stacked up to form grana
Grana are linked together by lamellae - thin flat pieces of thylakoid membrane

Site of photosynthesis
Some photosynthesis happen in grana and other parts in the stroma (thick fluid in chloroplasts)

48
Q

Structure and function of a centriole

A

Small hollow cylinders made of microtubules (tiny protein cylinders)
Found in animal cells but only some plant cells

Involved in separation of chromosomes during cell division

49
Q

Structure and function of cilia

A

Small hair like structures found on the surface membrane of some animal cells

Cross section - outer membrane and a ring of 9 pairs of protein microtubules inside and a single pair in the middle

Microtubules allow cilia to move
Movement is used by the cell to move substances along the cell surface

50
Q

Structure and function of flagellum

A

Flagella on eukaryotic cells are like cilia but longer
Stick out from the cell surface
Surrounded by plasma membrane
Two microtubules in centre and 9 pairs around the edge

Microtubules contract to make flagellum move
Flagella propel cells forward (eg when sperm swims to egg)

OCR BIOLOGY A LEVEL (1 decks)

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