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Biology > 2.1-Cell Structure > Flashcards

2.1-Cell Structure Flashcards

1
Q

Define Prokaryotic Cells.

A

DNA is ‘free’ in cytoplasm, no organelles e.g. bacteria & archaea.

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1
Q

Define Eukaryotic Cells

A

DNA is contained in a nucleus, contains membrane-bound specialised 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 with extrinsic and intrinsic proteins embedded.

  • 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 in the cell-surface membrane.

A

A steroid molecule that connects phospholipids and reduces fluidity.

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5
Q

Explain the role of glycoprotiens in the cell-surface membrane.

A

Cell signalling, cell recognition (antigens) and binding cells together.

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6
Q

Explain the role of glycolipids in the cell-surface membrane.

A

Cell signalling and cell recognition.

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7
Q

Describe 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 and proteins assembles ribosomes.
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8
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, semiconservative replication.`
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9
Q

Describe the structure of mitochondrion.

A
  • Surrounded by double membrane folded inner membrane forms cristae: site of electron transport chain.
  • Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins.
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10
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 with thylakoids in adjacent grana.
  • Stroma: fluid-filled matrix.
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11
Q

State the function of mitochondria.

A

Site of aerobic respiration to produce ATP.

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12
Q

State the function of chloroplasts.

A

Site of photosynthesis to convert solar energy to chemical energy.

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13
Q

Describe the structure and function of the Golgi Apparatus.

A
  • Planar stack of membrane-bound, flattened sacs cis face aligns with rER.
  • Molecules are processed cisternae vesicles bud off trans face via exocytosis:
    • Modifies & packages proteins for
      export
    • Synthesis glycoproteins
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14
Q

Describe the structure and function of a lysosome.

A

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

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15
Q

Describe the structure and function of a ribosome.

A

Formed of protein & rRNA. Free in cytoplasm or attached to ER.
- Site of protein syntheis via translation:
large subunit: joins amino acids
small subunit: contains mRNA binding site.

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16
Q

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

A

Cisternae: network of tubules & flattened sacs extends the cell membrane through cytoplasm & connects to nuclear envelope:
- Rough ER: many ribosomes attached for protein synthesis & transport.
- Smooth ER: lipid synthesis.

17
Q

Describe the structure of the Cell Wall.

A

Bacteria:
- Made of the polysaccharide murein.

Plants:
- Made of cellulose microfibrils plasmodesmata allow molecules to pass between cells, middle lamella acts as boundary between adjacent cell walls.

18
Q

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.
19
Q

Structure + 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 hydrolyses potentially harmful substances
    to detoxify cytoplasm.
20
Q

Explain some common cell adaptations.

A
  • Folded membrane or microvilli increase surface area
    e.g. for diffusion.
  • Many mitochondria = large amounts of ATP for active
    transport.
  • Walls one cell thick to reduce distance of diffusion
    pathway.
21
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.
22
Q

State the role of flagella in prokaryotes.

A
  • Rotating tail propels (usually unicellular) organism.
23
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.

24
Q

Compare eukaryotic and prokaryotic cells.

A

Both have:
- Cell membarane.
- Cytoplasm.
- Ribosomes (don’t count as an organelle since not
membrane-bound.

25
Q

Contrast eukaryotic and prokaryotic cells.

A

Prokaryotic:
- Small cells and always unicellular.
- No membrane-bound organelles & no nucleus.
- Circular DNA not associated with proteins.
- Small ribosomes (70s).
- Binary fusion - always asexual reproduction.
- Murein cell walls.
- Capsule, sometimes plasmids & cytoskeleton.

Eukaryotic:
- Larger cells and often multicellular.
- Always have organelles and nucleus.
- Linear chromosomes associated with histones.
- Larger ribosomes (80s).
- Mitosis & meiosis - sexual and/or asexual.
- Cellulose cell wall (plants)/ chitin (fungi).
- No capsule, no plasmids, always cytoskeleton.

26
Q

Why are viruses referred to as ‘particles’ and not cells?

A

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

27
Q

Describe the structure of a viral particle.

A
  • Linear genetic material (DNA or RNA) & viral
    enzymes e.g. reverse transcriptase.
  • Surrounded by capsid (protein coat made of
    capsomeres).
  • No cytoplasm.
28
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.
29
Q

State the role of the 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.
30
Q

State the role of attachment proteins on viral particles.

A

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

31
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.
32
Q

Outline how a student could prepare temporary mount of tissue for an optical microscope.

A
  1. Obtain thin section of tissue e.g. using ultratome
    or by maceration.
  2. Place plant tissue in a drop of water.
  3. Stain tissue on a slide to make structures visible.
  4. Avoid coverslip using mounted needle at 45* to
    avoid trapping air bubbles.
33
Q

Suggest the advantages and limitations of using an optical microscope.

A

+ Colour image
+ Can show living structures.
+ Affordable apparatus.
- 2D image
- Lower resolution that electron microscopes = c
cannot see ultrastructure.

34
Q

Describe how a Transmission Electron Microscope (TEM) works.

A
  1. Pass a high energy beam of electrons through thin
    slice of specimen.
  2. More dense structures appear darker since the
    absorb more electrons.
  3. Focus image onto fluorescent screen or
    photographic plate using magnetic lenses.
35
Q

Advantages and limitations of using a TEM.

A

+ Electrons have shorter wavelength than light = high resolution, so ultrastructure visible.
+ High magnification (x500000).
- 2D image.
- Requires a vacuum = cannot show living structures.
- Extensive preparation may introduce artefacts.
- No colour image.

36
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 photographic
    plate.
37
Q

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.

38
Q

Define magnification.

A

Factor by which the image is larger than the actual specimen.

39
Q
A

Biology (21 decks)

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