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A-Level Biology - OCR A > 2.2 - Basic Components of Living Systems > Flashcards

2.2 - Basic Components of Living Systems Flashcards

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1
Q

What is the magnification equation?

A

Magnification = Image Size ÷ Actual Size

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2
Q

Define magnification

A

The number of times larger the image is compared with the size of the object

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3
Q

Define resolution

A

The ability to distinguish between two points on an image.

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4
Q

Describe a dry mount technique

A

Solid specimens are viewed whole or cut into very small, thin slices on a slide.

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5
Q

Describe a wet mount technique

A

Specimens are suspended in a liquid such as water or an immersion oil.

A cover slip is placed on at an angle to avoid ARTEFACTS such as air bubbles.

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6
Q

Describe a squash slides technique

A

A wet mount is first prepared and then a lens tissue is used to gently push down the cover slip.

Potential damage to cover slip can be avoided by squashing the specimen between two microscope slides
e.g. when viewing a xylem vessel in celery.

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7
Q

Describe a smear slides technique

A

The edge of a slide is used to smear the specimen creating a thin, even coating on another slide. A cover slip is then placed over the sample.

Usually used to look at blood, urine etc.

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8
Q

Name the four types of microscope

A

Light
Transmission Electron (TEM)
Scanning Electron (SEM)
Fluorescent

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9
Q

Detail the max. resolution and max. effective magnification of a light microscope

A

Max. resolution - 200nm

Max. effective magnification ≈ 1500x

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10
Q

Detail the max. resolution and max. effective magnification of a TEM

A

Max. resolution - 0.5nm

Max. effective magnification - over 500,000x

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11
Q

Detail the max. resolution and max. effective magnification of an SEM

A

Max. resolution - 3-10nm

Max. effective magnification - Over 100,000x

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12
Q

Which electron microscope is able to see a sectional view through the specimen?

A

Transmission Electron Microscope (TEM)

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13
Q

Define fluorescence

A

The absorption and re-radiation of light.

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14
Q

Name and describe the features of a laser scanning confocal microscope

A

Specimen is coated in a fluorescent chemical or dye.

Illumination pinhole - light is focussed onto the dichroic mirror through this.

Dichroic mirror - acts as a beam splitter. The mirror only reflects one wavelength of light (from the laser), other wavelengths (produced by the specimen) are transmitted through.

Objective lens - Focuses the light reflected from both the dichroic mirror and the specimen.

Confocal pinhole - Focuses the light from the specimen onto a detector.

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15
Q

Name the potential uses of laser scanning confocal microscopy

A
  • Currently used in diagnosis of eye diseases.
  • Being developed for endoscopic procedures
  • It can see the distribution of molecules, so it is used in drug development.
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16
Q

Describe a limitation of laser scanning confocal microscopy

A
  • Cannot be used in deep tissue imaging due to refractive index discontinuities.
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17
Q

Describe and explain what would be seen if you stain a cell with Methylene Blue

A

Entire cell would be stained a blue colour.

This is because methylene blue is a POSITIVE stain meaning it is attracted to the negative cytosol therefore staining all of its components.

Other positively charged stains include Crystal Violet which stains a cell purple (violet).

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18
Q

Describe and explain what would be seen if you stain a cell with Congo Red

A

The NEGATIVELY charged Congo Red stain would remain outside of the cell as it is repelled by the negatively charged cytosol. This stains its surroundings red, therefore increasing the contrast and making the cell stand out.

Other negatively charged stains include Nigrosin which stains black.

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19
Q

Name two differential staining techniques

A
  • Gram Staining technique

- Acid-Fast technique

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20
Q

Describe the Gram Staining technique

A

Used to separate bacteria into two groups: Gram-positive, and gram-negative.

  • Crystal violet stain is first applied to a bacterial specimen on a slide.
  • Iodine is then applied to ‘fix’ the first dye.
  • The slide is then washed with alcohol.

Gram-positive bacteria will retain the CV stain due to their thick cell walls and appear purple/blue under a microscope.
Gram-negative bacteria have thinner cell walls and will lose the stain.

  • The Gram-negative bacteria are then stained with Sarafin dye (aka Counterstain). The bacteria will then appear red.
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21
Q

Describe the Acid-Fast technique

A

Used to distinguish species of Mycobacterium from other bacteria.

  • A lipid solvent is used to carry Carbolfuschin dye (red) into the cells.
  • Cells are washed with a dilute acid-alcohol solution. Mycobacterium are not affected by the solution and retain the bright red stain.
  • Other bacteria lose the stain and are exposed to methylene blue.
22
Q

Name any other common stains

A

Iodine - stains starch blue/black

Acetic Orcein - stains chromosomes dark red and prevents mitosis from occurring by ‘fixing’ the cells

Eosin - stains cytoplasm, RBCs, collagen and muscle fibres fluorescent red.

23
Q

How long is a stage micrometer?

A

1000μm long

24
Q

What is a eukaryote?

A

An organism with a nucleus.

25
Q

What is a prokaryote?

A

An organism without a nucleus.

Pro- is no (nucleus)

26
Q

What is the nuclear envelope?

A

A double membrane which controls material entry and exit.

27
Q

What are nuclear pores?

A

Gaps in the nuclear envelope which allow large molecules, like mRNA, out of the nucleus.

28
Q

What is chromatin?

A

The material from which proteins and DNA is made up from.

29
Q

What is the nucleolus?

A

The largest part of the nucleus. It makes ribosomes.

30
Q

Detail the functions of the nucleus

A
  • Produces mRNA for protein synthesis
  • Retains genetic material in the form of DNA or a chromosome
  • Manufactures ribosomal RNA and ribosomes
31
Q

What are mitochondria?

A

The main organelles involved in respiration and are responsible for the production of ATP.

They are 2-5μm long.

32
Q

What is a vesicle?

A

A small sac-like membrane-bound organelle used for transport of substances.

33
Q

What are lysosomes and what is their function?

A

They are special vesicles which contain enzymes.

They:

  • break down pathogens
  • release enzymes to the outside of the cell
  • digest worn out organelles
  • break cells down when they die
34
Q

What are microtubules and what is their function?

A

They act like motorways in a cell. They connect organelles to keep them in place.

35
Q

What are centrioles?

A

They co-ordinate growth of microtubules, they are used in cell division.

36
Q

What is the rough ER?

A

A connected series of flattened sacs with ribosomes scattered on the surface. Used in protein synthesis and is used as a pathway to transport proteins out of the cell.

37
Q

What is the smooth ER?

A

Organelle which synthesises, stores and transports lipids and carbohydrates. It has no ribosomes on its surface.

38
Q

What is a ribosome?

A

Cell organelles which play an important role in protein synthesis. They are found in the cytoplasm or on RER. They have two subunits containing RNA and protein.

39
Q

What is the golgi apparatus?

A

A series of flat membrane-bound sacs. It does ‘modification and packaging’.
Proteins produced by the RER pass through the golgi apparatus to be modified.
Once modified, the proteins are packaged into vesicles.

40
Q

What is are flagella and cilia?

A

Protrusions on a cell, essential for locomotion and transport. Cilia are found only on eukaryotic cells.

Cilia also function to move fluid or materials past an immobile cell as well as moving a cell or groups of cells.

41
Q

What is the cytoskeleton?

A

A network of molecules which build an intracellular scaffolding within cell cytoplasm.

42
Q

What are the two types of ribosome?

A

80S - found in eukaryotic cells

70S - found in prokaryotic cells

43
Q

What is the function of the cytoskeleton?

A

It provides:

  • structural stability
  • keeps the cell in shape
  • helps organelles maintain their position
  • pathways for the movement of cell components
44
Q

Describe the structure of the cytoskeleton

A

It is made from two proteins: tubulin and actin. These aid the movement of organelles and vesicles within the cell.
Actin creates structures called actin filaments which have contractile properties. These are responsible for cell movement.
Globular tubulin proteins polymerise to form microtubules. These form the scaffold-like ultrastructure of the cell.

45
Q

Describe how the cytoskeleton functions

A

Microtubule motors (a protein) e.g. Kinesin, use microtubules as a ‘motorway’.

Movement of kinesin is regulated with a Microtubule Associated Protein (MAP). Kinesin (or other MAP) is specific to a certain receptor on a vesicle/organelle, so it ‘knows’ where to go.

Another enzyme, called MARK, can phosphorylate the MAP which then makes it unable to bind to the microtubule and therefore it is able to control the direction of movement.

The transport of substances via the cytoskeleton is an active process.

46
Q

What is transcription?

A

mRNA copies DNA code.

47
Q

What is translation on ribosomes?

A

When amino acids are assembled in the correct order using the code to make a protein.

48
Q

Define exocytosis

A

The process of a substance exiting a cell via a vesicle binding with the cell surface membrane and secreting the contents outside.

49
Q

Outline the stages of the production of insulin.

protein synthesis

A
  1. mRNA copy of the gene (instructions) for insulin is made in the nucleus.
  2. mRNA leaves the nucleus via a nuclear pore.
  3. mRNA attaches to a ribosome, in this case on the RER. Ribosome reads the instructions to make insulin.
  4. Insulin molecules are ‘pinched off’ in vesicles and travel towards the cis face of the golgi apparatus.
  5. Vesicle fuses with the cis golgi face.
  6. Golgi apparatus processes and packages insulin molecules.
  7. Packaged insulin molecules are ‘pinched off’ of the trans golgi face in vesicles and move towards the cell surface membrane.
  8. Vesicle fuses with cell surface membrane.
  9. Cell surface membrane opens to release insulin molecules outside.
50
Q

What is a plant cell wall made from?

A

Cellulose

51
Q

What is a bacteria cell wall made from?

A

Peptidoglycan

52
Q

What is a fungus cell wall made from?

A

Chitin

A-Level Biology - OCR A (16 decks)

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