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Biology A-Level > Cell Structure > Flashcards

Cell Structure Flashcards

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1
Q

Define the terms eukaryotic and prokaryotic cell.

A

Eukaryotic: DNA is contained in a nucleus, contains membrane-bound specialised organelles.
Prokaryotic: DNA is free in cytoplasm no membrane bound organelles

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2
Q

State the relationship between a system and specialised cells.

A

Specialised cells —> tissues that perform specific function —> organs made of several tissue types —> organ systems

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3
Q

Describe the structure and function of the cell-surface membrane.

A

Fluid mosaic phospholipid bilayer.
- isolates cytoplasm from extracellular environment
- selectively permeable to regulate transport of substances
- involved in cell signalling / cell recognition

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4
Q

Explain the role of cholesterol, glycoproteins & glycoproteins in the cell-surface membrane.

A

Cholesterol: steroid molecule connects phospholipids & reduces fluidity.
Glycoproteins: cell signalling, cell recognition & binding cells together
Glycolipids: cell signalling & cell recognition

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5
Q

Describe the structure of the nucleus.

A
  • surrounded by nuclear envelope, a semi-permeable double membrane
  • nuclear pores allow substances to enter/exit
  • dense nucleolus made of RNA & proteins assembles ribosomes
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6
Q

Describe the function of the nucleus.

A
  • contains DNA coiled around chromatin into chromosomes
  • controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis and semi-conservative replication
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7
Q

Describe the structure of a mitochondrion.

A
  • surrounded by double membrane folded inner membrane form cristae: site of electron transport chain
  • fluid matrix: contains mitochondrial DNA, respitory enzymes, lipids, proteins
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8
Q

Describe the structure of a chloroplast.

A
  • vesicular plastid with double membrane
  • thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll
  • intergranal lamellae: tubes attach thylakoids in adjacent grana
  • stroma: fluid-filled matrix
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9
Q

State the function of mitochondria and chloroplasts.

A
  • mitochondria: site of aerobic respiration to produce ATP
  • chloroplasts: site of photosynthesis to convert solar energy to chemical energy
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10
Q

Describe the structure and function of the Golgi apparatus.

A

Planar stach of membrane-bound, flattened sacs cis face aligns with rER.
Molecules are processed in cisternae vesicles bud off trans face via exocytosis:
- modifies & packages proteins for export
- synthesises glycoproteins

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11
Q

Describe the structure and function of a lysosome.

A

Sac surrounded by single membrane embedded H+ pump maintains acidic conditions contains digestive hydrolase enzymes glycoprotein coat protects cell interior:
- digests contents of phagosome
- exocytosis of digestive enzymes

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12
Q

Describe the structure and function of a ribosome.

A

Formed of protein & rRNA free in cytoplasm or attached to ER
- site of protein synthesis via translate:
Large subunit: joins amino acids
Small subunit: contains mRNA binding site

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13
Q

Describe the structure and function of the endoplasmic reticulum (ER).

A

Cisternae: network of tubules & flattened sacs extends from cell membrane through cytoplasm & connects to nuclear encelope:
- rough ER: many ribosomes attached for protein synthesis & transport
- smooth ER: lipid synthesis

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14
Q

Describe the structure of the cell wall.

A
  • Bacteria: made of polysaccharide murein
  • Plants: made of cellulose microfibrils plasmodesmata allow molecules to pass between cells, middle lamella acts as boundary between adjacent cell walls.
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15
Q

State the functions of the cell wall.

A
  • mechanical strength and support
  • physical barrier against pathogens
  • part of apoplast pathway (plants) to enable easy diffusion of water
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16
Q

Describe the structure and function of the cell vacuole in plants.

A

Surrounded by single membrane: tonoplast contains cell sap: mineral ions, water , enzymes, soluble pigments
- controls turgor pressure
- absorbs and hydrolyse potentially harmful substances to detoxify cytoplasm

17
Q

Explain some common cell adaptations.

A
  • folded membrane or microvilli increase surface area
  • many mitochondria = large amounts of ATP for active transport
  • walls one cell thick to reduce distance of diffusion pathway
18
Q

State the role of plasmids in prokaryotes.

A
  • small ring of DNA that carries non-essential genes
  • can be exchanged between bacterial cells via conjugation
19
Q

State the role of flagella in prokaryotes.

A

Rotating tail propels organism

20
Q

State the role of the capsule in prokaryotes.

A

Polysaccharide layer:
- prevents desiccation
- acts as food reserve
- provides mechanical protection against phagocytosis & external chemicals
- sticks cells together

21
Q

Compare eukaryotic and prokaryotic cells.

A

Both have:
- cell membrane
- cytoplasm
- ribosome

22
Q

Contrast eukaryotic and prokaryotic cells.

A

Prokaryotic:
- small cells & always unicellular
- no membrane-bound organelles
- circular DNA not associated with proteins
- 70s ribosomes
- binary fission
- murein cell walls
- capsule
Eukaryotic:
- larger cells & often multicellular
- always have organelles & nucleus
- linear chromosomes associated with histones
- 80s ribosomes
- mitosis and meiosis
- cellulose cell wall
- no capsule

23
Q

Why are viruses referred to as ‘particles’ instead of cells?

A

Acellular & non-living: no cytoplasm cannot self-reproduce, no metabolism

24
Q

Describe the structure of a viral particle.

A
  • linear genetic material & viral enzymes
  • surrounded by capsid
  • no cytoplasm
25
Q

Describe the structure of an enveloped virus.

A
  • simple virus surrounded by matrix protein
  • matrix protein surrounded by envelope derived from cell membrane of host cell
  • attachment proteins on surface
26
Q

State the role of capsid on viral particles.

A
  • protect nucleic acid from degradation by restriction endonucleases
  • surface sites enable viral particle to bind to & enter host cells or inject their genetic material
27
Q

State the role of attachment proteins on viral particles.

A

Enable viral particles to bind to complementary sites on host cell: entry via endosymbiosis.

28
Q

Describe how optical microscopes work.

A
  1. Lenses focus rays of light and magnify the view of a thin slice of specimen.
  2. Different structures absorb different amounts and wavelengths of light.
  3. Reflected light is transmitted to the observer via the objective lens and eyepiece.
29
Q

Suggest the advantages and limitations of using an optical microscope.

A

+ colour image
+ can show living structures
+ affordable apparatus
- 2D image
- lower resolution than electron microscopes = cannot see ultrastructure

30
Q

Describe how a transmission electron microscope works.

A
  1. Pass a high energy beam of electrons through thin slice of specimen
  2. More dense structures appear darker since they absorb more electrons
  3. Focus image onto fluorescent screen or photographic plate using magnetic lenses
31
Q

Suggest the advantages and limitations of using a TEM.

A

+ electrons have shorter wavelength than light = high resolution, so ultrastructure visible
+ high magnification (500000)
- 2D image
- requires a vacuum = cannot show living structures
- extensive preparation may introduce artefacts
- no colour image

32
Q

Describe how a scanning electron microscope (SEM) works.

A
  1. Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses.
  2. Reflected electrons hit a collecting device and are amplified to produce an image on a photograph plate
33
Q

Suggest the advantages and limitations of using a SEM.

A

+ 3D image
+ electrons have shorter wavelength than light = high resolution
- requires a vacuum = cannot show living structures
- no colour image
- only shows outer surface

34
Q

Define magnification and resolution.

A

Magnification: factor by which the image is larger than the actual specimen
Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another

35
Q

Outline what happens during cell fractionation and ultracentrifugation.

A
  1. Homogenise tissue to break open cells & release organelles
  2. Filter homogenate to remove debris
  3. Perform differential centrifugation
    a) spin homogenate in centrifuge
    b) the most dense organelles in the mixture form a pellet
    c) filter off the supernatant and spin again at a high speed
36
Q

State the order of sedimentation of organelles during differential centrifugation.

A

Most dense —> least dense

Nucleus —> mitochondria —> lysosomes—> RER —> plasma membrane —> SER—> ribosomes

37
Q

Explain why fractionated cells are kept in a cold, buffered, isotonic solution.

A

Cold: slow action of hydrolase enzymes
Buffered: maintain constant pH
Isotonic: prevent osmotic lysis/ shrinking of organelles

Biology A-Level (20 decks)

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