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A Level Biology Edexcel > Cells, Microscopy and DNA > Flashcards

Cells, Microscopy and DNA Flashcards

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1
Q

Two types of microscope

A
  1. Light microscope

2. Electron microscope

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2
Q

What is a light microscope

A

The kind of microscope found in homes and hospitals.
Magnifies up to 1000x
Can resolve items up to ~0.2uM apart.

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3
Q

What is an electron microscope?

A

Much greater magnification than light microscope

Can resolve items up to ~0.05nm apart.

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4
Q

Magnification equation

A

Length of image / Length of object

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5
Q

What does resolution mean?

A

The shortest distance between two points in the object for them to appear as two distant points in the image rather than merging into one larger point.

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6
Q

Key differences between light an electron microscope

A
  1. Electron microscope can only view dead cells because electrons require a vacuum to move
  2. The images produced on an electron microscope are monoochrome
  3. Staining for electron microscopy is achieved with heavy metals. Some cells take up the metals better than others, therefore the accept more electrons and appear darker in the final image.
  4. The wavelength for the electron microscopoe is much shorter than the light wavelength. Therefore there is a much higher resolution of the electron microscope.
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7
Q

Name the parts of a light microscope

A
  1. eye piece lense
  2. nosepiece
  3. objective lenses
  4. stage
  5. condenser lense
  6. coarse focus
  7. fine focus
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8
Q

What does the condenser lense do?

A

Focuses light before it hits the specimen.
Achieved with an iris diaphram - used to vsary the intesity of light hitting the speciemen.
This is where the built in light source comes from.

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9
Q

What is the eye peice lense for?

A

To focus light after it has passed through the specimen

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10
Q

What is the objective lense for?

A

CHange the magnification of the sample

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11
Q

The course and fine focus screws…

A

Move either the stage or the objective lenses up or down to find focus on the sample
The coarse lense move further with smaller rotations that the fine lense.

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12
Q

What is the stage for?

A

To place the glass cover slip containing the sample

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13
Q

Two types of preparation using a ligjt microscope

A
  1. temporary preparation

2. permanent preparation

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14
Q

What is used to help visualise cells under the microscope?

A

Stains

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15
Q

How many membranes does a nucleus have?

A

two

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16
Q

How big are the pores of the nuclear membrane?

A

~100nm

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17
Q

What is the function of the nuclei?

A

ribosome biogensis

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18
Q

Size of a mitochondria

A

0.5-1.5um in diameter

3-10um long

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19
Q

Number of membranes of the mitochondria

A

two

  • outer membrane is smooth
  • inner membrane is folded to form a cristae
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20
Q

What is the matrix of the mitochondria made of?

A

aqueous solution of metabolites and enzymes, and circular molecules of DNA.

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21
Q

What is hate mitochondrial crista

A

One of the many folds of the inner membrane of the mitochondria, where chemicals involved in ATP synthesis ring aerobic respiration are located.

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22
Q

What are choroplasts and what shape/size are they?

A

~ 4-10um long and 2-3um wide.
They occur in the mesophyll cells of plant leaves, where one cell may be packed with 50 chloroplasts.
Chloroplasts are the site of photosynthesis.

23
Q

What is a thylakoid?

A

The folded inner membrane of a chloroplast

24
Q

What is a stack of thylakoids called?

A

grana

25
Q

Describe the structure of the chloroplast

A

chloroplasts are double membrane bound organelles located in the mesophyll cells in the leaves of plants. The outer membrane is a smooth, continuous boundary but the inner membrane is tucked in to form branches called thylakoids. These thylakoids run parallel to one another and a bunch together is known as a grana. Chlorophyll is located in thte grana.
Between the grana, losely collected branched membranes can still be found in an aqueous solution which contains enzymes and starch grains. This is known was the stroma. Small circular molecular of DN are also located here.

26
Q

What is the larger group of organelles called that the chloroplast is from?

A

Plastids

27
Q

What are plastids?

A

a large group of organelles found only in plant cells and never in animal cells.
Members of this group are:
Chloroplasts - chlorophyll is stored
amyloplsts - starch is stored
chromoplasts - stores non-photosynthetic pigments such as carotene

28
Q

What are ribosomes?

A

The site of protein synthesis

29
Q

The size of ribosomes is recoded in…

A

Svedberg units: S units.

30
Q

What is a Svedberg unit?

A

he rate of sedimentation during centrifugation under standardized conditions,

31
Q

Ribosomes in the cytoplasm of eukaryotic cells are what S unit?

A

80 S.

Actual size of around 25nm

32
Q

Ribosomes have how many sub-units?

A

two

33
Q

How many membranes to ribosomes have/.

A

none

34
Q

What are ribosomes made of?

A

Protein and RNA

35
Q

Where do you find ribosomes?

A

floating freely in the cytoplasm or attached to the ER (to form rough ER)

36
Q

How many membranes does the ER have?

A

one

37
Q

What are the two types of ER?

A

smooth and rough

38
Q

Describe rough ER

A

has a continuous outer membrane which surrounds the nucleus. It is known as ‘rough’ because it has ribosomes attached to it.
In the lumen of the rough ER that protein structure takes place.
Sometimes proteins are transferred from the rough ER to the Golgi, either directly or via vesicles which pinch off from the edge of the ER.

39
Q

What is a vesicle?

A

A small single membraned, spherical organelle used to store and transport substances around the cell.
Much smaller than a vacuole, but strucurally the same.

40
Q

Describe the smooth ER

A

Completely separate from the rough ER, usually not found anywhere near the cell’s nucleus.
Called smooth because it has no ribosomes attached.
Synthesises lipids, phosphorus-lipids and steroids.
In the cytoplasm of voluntary muscle fibers a special type of smooth ER is the site of storage for calcium ions which are important for muscle contraction.

41
Q

Describe the Golgi apparatus?

A

consists of a stack of flattened membranous sacs, called cisternae
One side is produced by fusing vesicles from the rough ER. At the opposite side, vesicles are formed from swellings at the margins that become pinched off. Present in all cells but especially prominent in metabolically active cells.
The Golgi is responsible for sorting, modifying and packing polymers for secretion or use within the cell.

42
Q

Describe the lysosome

A

Small spherical vesicles bound by a single membrane
They contain a mixture of around 50 hydrolytic enzymes which are produced by the rough ER and modified at the Golgi.
They are necessary for the breakdown of food vacuoles, old organelles or harmful bacteria. Once engulfed into a larger vacuole, the lysosome releases all of its contents, including the hydrolytic enzymes. As a result, food, organelle or bacterium is digested and the products of digestion are released into the cytosol.

43
Q

What is autolysis?

A

When an organism dies and the hydrolytic enzymes normally found in the lysosome are released into the cell, digesting everything inside.

44
Q

What are centrioles?

A

Made up of microtubules of a globular protein called tubulin.
These microtubules form a network of unbranched, hollow cylinders that are important for cellular structure and moving organelles around the cytoplasm.

45
Q

Describe the centrioles.

A

Occur in pairs lying at right angles to one another
Each centriole is made of nine bundles of microtubules
During cell division they move apart to create the spindles.

46
Q

Describe the plant cell wall

A

It is not an organelle but instead it is the product of other organelles.
composed of long, straight fibers of cellulose eld together by hydrogen bonds. Because these structures are laid down at different angles the plant cell resists changes in shape, and also helps to prevent the plant cell bursting when placed in dilute solutions.
The spaces between the bundles of cellulose allow movement of water between cell wall to cell wall.

47
Q

What is plasmodesmata?

A

Cytoplasmic connections between plants cells ought gaps in their cell walls. Part of the symptomplast pathway.

48
Q

What is the permanent vacuole of the plant cell?

A

Fluid-filled organelle which takes up the majority of the plant cell. Bound by tonoplast - the barrier between the fluid in the vacuole and the cytoplasm of the plant cell.

49
Q

Main differences between a eukaryotic cell and a prokaryotic cell

A
  1. Size: prokaryotic cells are super small, about the size of a mitochondria.
  2. Absence of a nucleus: Prokaryotes lack a membrane-bound nucleus and instead have circular DNA in their cytoplasm referred to as a nucleoid.
  3. Presence of plasmid: Another type of circular DNA but generally only encodes for a few genes, and usually contains antibiotic resistance genes.
  4. 70S Ribosomes: Still used for protein synthesis, but smaller than eukaryotic ribosomes.
  5. Absence of membrane-bound organelles:
  6. Cell wall: prokaryotes all have a cell wall, like plant but not animals. However, made of peptidoglycan, not cellulose.
  7. Pili and flagella: Help prokaryotic cells attach to surfaces or to each other and flagella help it to move around.
50
Q

Describe the bacterial cell wall:

A

The rigid wall gives the cell a permanent shape and protects against bursting, similar to the plant cell wall.
However, it is made of peptidoglycan which is a polymer f amino acids and sugars. All bacterial cells have this cell wall.
Some bacterial cells also have other properties which makes staining them different.

51
Q

What is a gram positive bacterial stain?

A

Has a thick wall made almost entirely of peptidoglycan and will stain purple when stained with crystal violet.

52
Q

What is a gram negative bacteria?

A

Thin walls of peptidoglycan with additional outer membrane with high lipid content.
The high lipid contents prevents the crystal violet stain taking and does not turn purple.

53
Q

What are the important properties of gram positive and negative bacteria?

A

Gram negative bacteria are generally impermeable to antibiotics, including penicillin.
Gram positive bacteria are sensitive to penicillin.

A Level Biology Edexcel (5 decks)

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