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AQA A Level Biology Paper 1 > Topic 2.1 - Cells > Flashcards

Topic 2.1 - Cells Flashcards

Includes cell structure, microscopy, transport across membranes and mitosis

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1
Q

Describe how you convert cm → mm → μm → nm & vice versa

A
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2
Q

Define Magnification

A

How many times bigger the image is than the specimen (object)

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3
Q

Define Resolution

A

Minimum distance apart that two objects can be in order for them to appear as separate items

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4
Q

State the formula used to work out magnification

A
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5
Q

Describe how optical (light) microscopes work

A

Light from bulb travels through condenser lens, then specimen, up through objective lens and through eyepiece lens into your eye

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6
Q

State the maximum resolution for an optical microscope

A

0.2 µm

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7
Q

Name 2 pros of optical (light) microscopes

A
  • Easy and cheap to operate
  • Can have living specimens
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8
Q

Name 2 cons of optical (light) microscopes

A
  • Low resolution & magnification
    • Can’t see organelles smaller than 0.2 µm (e.g. ribosomes, endoplasmic reticulum and lysosomes)
  • Specimens often need staining to show specific organelles
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9
Q

Why do optical microscopes have a maximum resolution of 0.2 µm?

A

Due to the long wavelength of light rays

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10
Q

Name 2 Electron Microscopes

A
  • Transmission Electron Microscopes
  • Scanning Electron Microscopes
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11
Q

Describe how transmission electron microscopes work

A
  1. Use electromagnets to focus a beam of electrons which is then transmitted through the specimen
  2. Denser parts of specimen absorb more electrons = makes them look darker on image you end up with
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12
Q

State the maximum resolution for a transmission electron microscope

A

0.1 nm

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13
Q

Name a pro of transmission electron microscopes

A
  • Has highest resolutions & magnification
    • See internal structure of organelles e.g. chloroplasts
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14
Q

Name 4 cons of transmission electron microscopes

A
  • Non-living matter only
  • Image in black and white and 2D
  • Preparation may distort structure/give artefacts
  • Vacuum required
  • Elaborate preparation - staining is complex
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15
Q

Describe how scanning electron microscopes work

A
  • They scan a beam of electrons across specimen = knocks off electrons from specimens
  • Electrons gathered in cathode ray tube to form image
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16
Q

State the maximum magnification of SEMs

A

x 30,000

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17
Q

State the maximum resolution of SEMs

A

20 nm

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18
Q

Name 3 pros of SEMs

A
  • Can form complex 3D images of sample
  • Can be used on thick specimens
  • Magnifications & resolutions are higher than light microscopes
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19
Q

Name 3 cons of SEMs

A
  • Large and expensive & difficult to operate
  • Specimens has to be mounted in vacuum
  • Specimen has to be dead
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20
Q

What are 2 differences between fungal and plant cells?

A

In fungal cells:

Cell walls are made from of chitin & they don’t have chloroplasts

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21
Q

What is the function of the cell-surface (plasma) membrane?

A

Regulates movement of substances into and out of cells

(has receptor molecules on it and therefore responds to chemicals and other proteins )

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22
Q

What is the function of the nucleus?

A

Holds genetic information of cell

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23
Q

What is the function of the nucleolus?

A

Makes RNA and ribosomes

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24
Q

What is the function of nuclear pores?

A

Allow passages of large molecules (e.g. RNA)

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25
Q

What is the nucleoplasm?

A

Jelly-like material that makes up bulk of nucleus

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26
Q

What is the nuclear envelope?

A

Double membrane that surrounds nucleus

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27
Q

What is the function of the nuclear envelope?

A

Controls entry/exit of materials in and out of nucleus & reactions taking place within it

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28
Q

Where is chloroplast found?

A

Plant cells and some protoctists

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29
Q

Describe the structure of a chloroplast

A

Two membranes (chloroplast envelope) filled with fluid

  • Membranes stacked into layers known as thylakoids
  • A whole stack of thylakoid membranes is known as a granum
  • Fluid-filled matrix = stroma (starch grains are found there)
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30
Q

Where is chlorophyll found?

A

In thylakoids & lamellae

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31
Q

Name 3 adaptations of chloroplast

A
  • Granal membranes = large surface area for enzymes, etc (for 1st stage of photosynthesis)
  • Fluid of stroma = possess all enzymes (for 2nd stage of photosynthesis)
  • Chloroplasts contain DNA and ribosomes = can quickly manufacture some proteins for photosynthesis
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32
Q

What is the function of chloroplast?

A

Absorbs light for photosynthesis

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33
Q

Describe the structure of a mitochondrion

A
  • Have double membrane filled with fluid
    • Inner membrane is highly folded & called cristae
    • Inner section is called matrix
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34
Q

What does the matrix in mitochondria contain?

A

Enzymes involved in respiration

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35
Q

What is the function of a mitochondrion?

A

Site of aerobic respiration where ATP is produced/energy released

36
Q

Describe the structure of endoplasmic reticulum

A

Made up of flattened membrane bound sacs called cisternae

37
Q

What is the surface of the rough endoplasmic reticulum covered in?

A

Ribosomes

38
Q

What is the function of the rough endoplasmic reticulum?

A

Modifies and transports proteins made on ribosomes

39
Q

What is the function of the smooth endoplasmic reticulum?

A

Synthesises and processes lipids

40
Q

What is the function of the smooth endoplasmic reticulum in the liver cells?

A

Involved in breaking down toxins

41
Q

Describe the structure of the Golgi apparatus

A
  • Not a stable structure = constantly changing
  • Stacks of membrane-bound flattened sacs
42
Q

What is the function of a Golgi vesicle?

A

Stores lipids and proteins made by Golgi apparatus & transport them out of the cell

43
Q

Describe the function of the Golgi apparatus

A
  • Receives proteins from ER/moves to Golgi
  • Modifies proteins
  • Proceses/packages them into vesicles
  • Vesicle is moved to plasma membrane
  • Fuses with it/excoytosis
44
Q

What is the function of a cell wall?

A

Supports cell and prevents them from changing shape

(Cell wall is permeable to allow solutions to pass in and out)

45
Q

What is a lysosome?

A

Tiny bag of digestive enzymes, surrounded by a single membrane

46
Q

What is the function of lysosome?

A
  • Can digest invading cells or break down worn out components of cell
  • Keeps digestive enzymes away from cytoplasm
47
Q

Describe the structure of a ribosome

A
  • Has no outer membrane
  • Contains 2 sub-units
48
Q

What is the function of ribosome?

A

Site of protein synthesis

(mRNA used to assemble proteins from amino acids)

49
Q

Describe the structure of a cell vacuole

A
  • Membrane-bound organelle found in cytoplasm of plant cells
  • Surrounding membrane is called tonoplast
50
Q

What is the function of a vacuole?

A
  • Maintain pressure inside cell & keep them rigid (stops plants wilting)
  • Storage of waste
51
Q

Name 4 similarities between eukaryotes and prokaryotes

A
  • Plasma membrane
  • Cytoplasm
  • DNA & RNA
  • Ribosomes
52
Q

Name 4 structural differences between eukaryotes and prokaryotes

A

Prokaryotes have:

  • Smaller ribosomes (70s type)
  • No true nucleus (free, floating circular DNA)
  • No membrane-bound organelles
  • Cell wall made from the glycoprotein murein
53
Q

Name 3 additional features that prokaryotic cells can have

A
  • Flagella
  • Plasmids
  • Capsule
    *Pili
54
Q

What is a flagellum?

A

Hair-like structure that rotates to make prokaryotic cells move

55
Q

What are plasmids?

A

Small loops of DNA

(contain genes for things like antibiotic resistance)

56
Q

What is the function of a capsule?

A

Protects bacteria from attack by cells of immune system

57
Q

Viruses are …

A

Not cells = Acellular

58
Q

What are viruses essentially?

A

Just nucleic acids surround by protein = not alive

59
Q

What do viruses do?

A

Invade and reproduce inside the cells of other organisms

60
Q

Name 3 features of viruses

A
  • Contain core of genetic material - either DNA or RNA
  • Have protein coat around core called capsid
  • Have attachment proteins which stick out from edge of the caspid
61
Q

Why do the viruses have attachment proteins?

A

They allow them to cling on to a suitable host cell

62
Q

What is cell fractionation?

A

Process which cells are broken up and organelles they contain are separated out

63
Q

Name the 3 stages in cell fractionation

A
  1. Homogenisation - Breaking Up the Cells
  2. Filtration
  3. Ultracentrifugation - Separating the Organelles
64
Q

What happens in stage 1 (homogenisation) of cell fractionation?

A
  • Cells broken up by homogeniser (blender)
  • Added to solution
65
Q

Why do you break up the cells during fractionisation?

A

To breaks up the plasma membrane and release the organelles

66
Q

Name the 3 conditions of the solution used during cell fractionation and why they are used.

A
  • Isotonic - prevens organelles being damaged through osmosis.
  • Ice-cold - prevents enzyme activity so proteins are not brokens down.
  • Buffered- maintains a constant pH so proteins are not denatured
67
Q

What happens in stage 2 (filtration) of cell fractionation?

A

Homogenised cell solution is filtered through gauze to separate any large cell debris or tissue debris from organelles

(organelles = much smaller than debris)

68
Q

What happens in stage 3 (ultracentrifugation) of cell fractionation?

A
  1. Cell fragments poured into tube & put into centrifuge - spun at low speed
    1. Heaviest organelles (nuclei) at bottom of tube = form thick sediment called a pellet
    2. Rest of organelles stay suspended in fluid above pellet = called supernatant
  2. Supernatant is poured into another tube & spun in centrifuge at higher speed
    1. Heaviest organelles (mitochondria) form pellet at bottom
    2. Supernatant is spun at higher speed
  3. Process is repeated at higher speeds until organelles are separated out
69
Q

State the order of the organelles that are seperated in ultracentrifugation (from heaviest to lightest)

Nuclei to ribosomes

A

Nuclei, chloroplast, mitochondria, lysosomes, endoplasmic reticulum, ribosomes

70
Q

Describe how to prepare a ‘temporary mount’ of specimen on a slide

A
  1. Pipette drop of water onto slide
  2. Use tweezers to place thin section of your specimen on top of water drop
  3. Add drop of stain - iodine dissolved in potassium iodide solution
  4. Lower cover slip using a mounted needle
71
Q

Preparing a ‘temporary mount’ of specimen on a slide:

Why do you add a stain?

A

∵ Highlights objects in a cell

72
Q

Preparing a ‘temporary mount’ of specimen on a slide:

When adding the cover slip, describe what you should do to avoid getting air bubbles

A

When adding the cover slip:

  • Stand slip upright on slide, next to water droplet
  • Carefully tilt and lower it so it covers the specimen
73
Q

Preparing a ‘temporary mount’ of specimen on a slide:

Why do we try avoid getting air bubbles?

A

∵ they obstructs your view of specimen

74
Q

Define Exocytosis

A

Bulk transport of materials out of a cell from a vesicle

75
Q

Define Endocytosis

A

Bulk transport of materials into a cell by the formation of vesicle from the cell membrane

76
Q

Describe the stages of the cell cycle.

A
  1. Interphase - When DNA is replicated (also known as S phase)
  2. Mitosis - The cell divides through the stages of prophase to cytokinesis. (M phase)
  3. Growth - the cell produces proteins to use in processes, and may also get ready to divide again. (G phase)
77
Q

What are the stages of mitosis?

A

(Interphase)
Prophase
Metaphase
Anaphase
Telophase and cytokinesis

78
Q

Describe what occurs during prophase

A

Chromosomes condense after they have now been replicated (they become visible). The chromosomes consist of two identical chromosomes (sister chromatids) joined together at the centromere. The two centrioles (where the spindle fibres originate) move to opposite poles of the cell. Spindle fibres form and the nuclear envelope breaks down, releasing the chromosomes.

79
Q

Describe what occurs during metaphase

A

Spindle fibres continue to extend from the centrioles. The chromosomes line up along the equator of the cell and are attached to the centrioles from their centromeres by spindle fibres.

80
Q

Describe what occurs during anaphase

A

The sister chromatids seperate at the centromere (so they divide in two). Spindle fibres begin to shorten and the separated sister chromatids are pulled to opposite poles by the spindle fibres

81
Q

Describe what occurs during telophase and cytokinesis.

A

The chromosomes arrive at opposite poles and begin to decondense. The nuclear envelope begins to reform around each set of chromosomes. The spindle fibres break down. Once the nuclear envelope has been reformed, the cytoplasm splits, and the cell membrane reforms around the two new daughter cells.

82
Q

Match the image to the mitotic stage.

A

A - Anaphase
B - Telophase
C - Cytokinesis
D - Interphase
E - Metaphase
F - Prophase

83
Q

How do prokaryotic cells divide?

A

By binary fission, which occurs as follows:
1. The circular DNA replicates and both copies attach to the cell membrane
2. The cell membrane then begins to grow between the two DNA molecules and pinches inwards to divide the cytoplasm.
3. A new cell wall forms between the two DNA molecules, dividing the original cell.

84
Q

How do viruses replicate?

A

Viruses are not living, therefore they infect a host cell, and use the host’s replication machinery to replicate. (i.e. the viral DNA is combined with the host DNA so when it replicates its DNA, the viral DNA is also replicated).

85
Q
A

AQA A Level Biology Paper 1 (12 decks)

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