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Biology‎ A-level ♡ > Section 2- Cells > Flashcards

Section 2- Cells Flashcards

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1
Q

What is a Eukaryote?

A

These are (mostly) multicellular organisms made up of eukaryotic cells like animals, plants, fungi, and protists.

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2
Q

What is a Prokaryote?

A

These are single-celled organisms made up of prokaryotic cells like bacteria.

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3
Q

What are eukaryotic cells?

A

These cells are more complex, contain membrane-bound organelles and have DNA in the form of chromosomes within a nucleus.

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4
Q

What is in an animal cell?

A
  1. Nucleus
  2. nucleolus
  3. smooth endoplasmic reticulum
  4. rough endoplasmic reticulum
  5. Golgi apparatus
  6. golgi vessels
  7. Ribosomes
  8. Lyosomes
  9. Mitochondria
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5
Q

State the relationship between a system and specialised cells.

A

Specialised cells make up tissues that perform a specific function. These tissues then form organs, and these organs that carry out a specific function are organ systems.

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6
Q

Describe the structure of the cell-surface membranes.

A

The structure is a ‘Fluid mosaic’ phospholipid bilayer with extrinsic and intrinsic proteins embedded.

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7
Q

Describe the Function of the cell-surface membrane.

A
  1. isolates cytoplasm from the extracellular environment
  2. selectively permeable to regulate the transport of substances
  3. involved in cell signalling/cell recognition.
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8
Q

Explain the role of cholesterol, glycoproteins and glycolipids in the cell surface membrane.

A

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

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9
Q

Describe the structure of the nucleus.

A
  1. Surrounded by a nuclear envelope, a semi-permeable double membrane
  2. Nuclear pores allow substances to enter/ exit.
  3. Dense nucleolus made of RNA and proteins assembles ribosomes.
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10
Q

Describe the function of the nucleus.

A
  1. Contains DNA coiled around chromatin into chromosomes
  2. Controls cellular processes: Gene expression determines specialisation and site of mRNA transcription, mitosis, and semiconservative replication.
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11
Q

Describe the structure of a mitochondrion.

A
  1. Surrounded by a double membrane. The Folded inner membrane forms cristae which is the site of the electron transport chain.
  2. Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, and proteins.
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12
Q

Describe the structure of a chloroplast.

A
  1. Vesicular plastid with double membrane
  2. Thylakoids: flattened disks stacked to form grana; contain photosystems with chlorophyll.
    3: Intergrana Lamellae: tubes attach thylakoids in adjacent grana.
    Stroma: fluid-filled matrix.
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13
Q

State the function of mitochondria

A

Site of aerobic respiration to produce ATP

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14
Q

State the function of chloroplasts

A

Site of photosynthesis to convert solar energy to chemical energy.

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15
Q

Describe the structure of the Golgi apparatus.

A
  1. The planar stack of membrane-bound, flattened sac’s cis face aligns with the respiratory exchange ratio.
  2. Molecules are processed in cisternae vesicles bud off trans face via exocytosis.
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16
Q

Describe the function of the Golgi apparatus.

A
  1. modifies and packages proteins for export.
  2. synthesised glycoproteins
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17
Q

Describe the structure of a lysosome.

A
  1. Sac surrounded by a single membrane
  2. The embedded H+ pump maintains acidic conditions.
  3. Contains digestive hydrolase enzymes
  4. Glycoprotein coat protects cell interior.
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18
Q

Describe the Function of a lysosome

A
  1. Digest contents of phagosome
  2. exocytosis of digestive enzymes.
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19
Q

Describe the structure of a ribosome.

A
  1. Formed of protein and rRNA
  2. pree in cytoplasm or attached to Endoplasmic reticulum
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20
Q

Describe the function of a ribosome.

A
  1. site of protein synthesis via translation
  2. A large subunit joins amino acids
  3. small subunit contains mRNA binding site.
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21
Q

Describe the structure and function of the endoplasmic reticulum.

A
  1. Cisternae: a network of tubules and flattened sacs that extends from the cell membrane through the cytoplasm and connects to the nuclear envelope
  2. Rough ER: many ribosomes attached for protein synthesis and transport.
  3. Smooth ER: Lipid synthesis
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22
Q

Describe the structure of the cell wall.

A
  1. Bacteria: made of the polysaccharide murein
  2. Plants: Made of cellulose microfibrils. plasmodesmata allow molecules to pass between cells, middle lamella acts as a boundary between adjacent cell walls.
23
Q

State the functions of the cell wall

A
  1. mechanical strength and support
  2. Physical barrier against pathogens
  3. Part of apoplast pathway (plants) to enable easy diffusion of water
24
Q

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

A
  1. Surrounded by a single membrane: the tonoplast
  2. contains cell sap: mineral ions, water, enzymes, and soluble pigments.
    - Controls turgor pressure
    - Absorbs and hydrolysis potentially harmful substances to detoxify cytoplasm
25
Q

Explain some common cell adaptations.

A
  1. Folded membrane or microvilli increase surface e.g. for diffusion.
  2. Many mitochondria = large amounts of ATP for active transport.
  3. Walls one cell thick to reduce the distance of diffusion pathway.
26
Q

State the role of plasmids in prokaryotes.

A
  1. Small ring of DNA that carries non-essential genes.
  2. Can be exchanged between bacterial cells via conjugation
27
Q

State the role of flagella in prokaryotes.

A

Rotating cells (usually unicellular) organism

28
Q

State the role of the capsule in prokaryotes

A

!. Prevents desiccation
2. Acts as a food reserve.
3. Provides mechanical protection against phagocytosis and external chemicals.
4. sticks cells together

29
Q

similarities between eukaryotic and prokaryotic cells?

A

Both have:
1. cell membrane
2. Cytoplasm
3. Ribosomes (don’t count as an organelle as not membrane-bound)

30
Q

Contrast Eukaryotic and Prokaryotic cells.

A

Prokaryotic :
unicellular. no membrane-bound organelles. no nucleus
circular DNA not associated with proteins
Small ribosomes (70s)/ 80s ribosomes eukaryotic
Binary fission - always asexual reproduction. / mitosis and meiosis bot a/ sexusl
murein cell walls cellulose /chitin cell walls
Capsule, sometimes plasmids and cytoskeleton.

31
Q

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

A

Acellular and non-living: contain no cytoplasm and cannot self reproduce also no metabolism.

32
Q

Describe the structure of a viral particle

A
  1. Linear genetic material (DNA or RNA) and viral enzymes e.g. reverse transcriptase.
  2. surrounded by capsid (protein coat made of capsomeres
  3. no cytoplasm
33
Q

Describe the structure of an enveloped virus.

A
  1. Simple virus surrounded by matrix protein
  2. Matrix protein surrounded by envelope
  3. Attachment proteins on surface
34
Q

State the role of the capsid on viral particles

A
  1. protect nucleic acid from degradation by restricting endonucleases.
  2. surface sutes enable viral particle to bind to and enter host cells or inject their genetic material.
35
Q

State the role of attachment protein on viral particles

A

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

36
Q

Describe how optical microscopes work.

A
  1. lenses focus rays of light and magnify the view of a thin slice of the 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
37
Q

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

A
  1. obtain a thin section of tissue e.g. using ultratome or by maceration
  2. place plant tissue in a drop of water
  3. stain tissue on the slide to make structures visible
  4. add coverslip using a mounted needle at 45 degrees to avoid trapping air bubbles
38
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 = unable to see ultrastructures

39
Q

Describe how a transmission electron microscope works.

A
  1. pass a high beam of electrons through a thin slice of the specimen
  2. more dense structures appear darker since they absorb more electrons
  3. focus the image onto a fluorescent screen or photographic plate using magnetic lenses
40
Q

Suggest the advantages and limitations of using a TEM

A

+ electrons have a shorter wavelength than light= high resolution so visible ultrastructures
+ high magnification x500000
- 2d image
-requires a vacuum
-extensive preparation may introduce artefacts
- no color image

41
Q

Describe hoe 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
42
Q

Suggest the advantages and limitations of using an SEM

A

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

43
Q

Define magnification and resolution

A

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

44
Q

Explain how to use an eyepiece graticule and stage micrometre to measure the size of a structure.

A
  1. place on micrometer on stage to calibrate the eyepiece graticule
  2. line up scales on graticule micrometre. count how many graticule divisions are in 100um on the micrometre
  3. length of 1 eyepiece division = 100um / number of divisions
  4. use calibrated values to calculate the actual length of structures
45
Q

State an equation to calculate the actual size of a structure from microscopy.

A

actual size = image size/magnification

46
Q

Outline what happens during cell fractionation and ultracentrifugation.

A
  1. mince and homogenize tissue to break open cells and release organelles
  2. filter homogenate to remove debris
  3. perform differential centrifugation
    a) spin homogenate in a centrifuge
    b) the most dense organelles in the mixture form a pellet
    c) filter off the supernatant and spin again at a higher speed
47
Q

State the order of sedimentation of organelles during differential centrifugation

A

most dense—> least dense
nucleus–> mitochondria-> lysosomes -> RER-> plasma membrane -> SER-> ribosomes

48
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.

49
Q

State what the cell cycle is and outline its stages.

A

Cycle of division with intermediate growth periods.
1. interphase
2. mitosis or meiosis
3. cytokinesis.

50
Q

Explain why the cell cycle does not happen in some cells.

A

After differentiation, some types of cells in multicellular organisms (e.g. neurons) no longer can divide.

51
Q

What is the difference between the cell cycle and mitosis?

A

The cell cycle includes a growth period between divisions; mitosis is only 10% of the cycle and refers only to nuclear division.

52
Q

Outline what happens during interphase.

A

G1: cell makes proteins for replication and cell size doubles
S: Dna replicates chromosomes consist of 2 sister chromatids joined at a centromere
G2: organelles divide.

53
Q

What is the purpose of mitosis?

A

Produces 2 genetically identical daughter cells for growth, repair and aesexual reproduction.

54
Q
A

Biology‎ A-level ♡ (8 decks)

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