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BIOLOGY OCR A > Module 2 - Foundations in Biology > Flashcards

Module 2 - Foundations in Biology Flashcards

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1
Q

Cell structure:
Outline how a student could prepare a temporary mount of tissue for a light microscope.

A
  1. Obtain thin section of tissue
  2. Place plant tissue in a drop of water.
  3. Stain tissue on a slide to make structures visible.
  4. Add coverslip using mounted needle at 45° to avoid trapping air bubbles.
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2
Q

Cell structure:
Describe how light 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.
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3
Q

Cell structure:
Describe how a transmission electron microscope (TEM) works.

A
  1. Pass a high energy beam of electrons through a 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.
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4
Q

Cell structure:
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.
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5
Q

Cell structure:
How should the field of view in microscopy be recorded?

A

Draw a diagram with a sharp pencil. Do not use sketchy lines or shading.
Include a scale bar. Annotate visible structures.

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6
Q

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

A

actual size = image size / magnification

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7
Q

Cell structure:
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.

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8
Q

Cell structure:
Why do samples need to be stained for light microscopes?

A

Coloured dye binds to the structures.
Facilitates absorption of wavelengths of light to produce image. Differential staining: contrast between heavily & lightly stained areas distinguishes structures.

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9
Q

Cell structure:
State the magnification and resolution of a compound optical microscope.

A

magnification: x 2000
resolution: 200 nm

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10
Q

Cell structure:
State the magnification and resolution of a TEM.

A

magnification: x 500 000
resolution: 0.5 nm

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11
Q

Cell structure:
State the magnification and resolution of an SEM.

A

magnification: x 500 000
resolution: 3 - 10 nm

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12
Q

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

A
  1. Place micrometer on stage to calibrate eyepiece graticule.
  2. Line up scales on graticule and micrometer. Count how many graticule divisions are in 100μm on the micrometer.
  3. Length of 1 eyepiece division = 100μm / number of divisions.
  4. Use calibrated values to calculate actual length of structures.
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13
Q

Cell structure:
Describe the structure of the nucleus.

A

● Surrounded by a nuclear envelope, a semipermeable double membrane.

● Nuclear pores allow substances to enter/exit.

● Dense nucleolus made of RNA & proteins assembles ribosomes.

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14
Q

Cell structure:
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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15
Q

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

A

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

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16
Q

Cell structure:
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 in cisternae. Vesicles bud off trans face via exocytosis
● Modifies & packages proteins for export.
● Synthesises glycoproteins.

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17
Q

Cell structure:
Describe the structure and function of ribosomes.

A

Formed of protein & rRNA.
Have large subunit which joins amino acids & small subunit with mRNA binding site.
Protein synthesis

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18
Q

Cell structure:
Describe the relationship between the organelles involved in the production and synthesis of proteins

A

The ribosomes that synthesise proteins are attached to the rER. Vesicles transport proteins to the Golgi apparatus, which modifies proteins for secretion via vesicles

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19
Q

Cell structure:
Describe the structure of a 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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20
Q

Cell structure:
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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21
Q

Cell structure:
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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22
Q

Cell structure:
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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23
Q

Cell structure:
Describe the structure and function of a plant cell wall.

A

● Made of cellulose microfibrils for mechanical support.
● Plasmodesmata form part of apoplast pathway to allow molecules to pass between cells.
● Middle lamella separates adjacent cell walls.

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24
Q

Cell structure:
What are bacterial and fungal cell walls made of?

A

bacteria: peptidoglycan (murein)
fungi: chitin

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25
Q

Cell structure:
Describe the structure and function of centrioles.

A

● Spherical group of 9 microtubules arranged in triples. 9+2 arrangment
● Located in centrosomes.
● Migrate to opposite poles of cell during prophase & spindle fibres form between them.

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26
Q

Cell structure:
Describe the structure and function of the cell-surface plasma membrane.

A

‘Fluid mosaic’ phospholipid bilayer with extrinsic & 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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27
Q

Cell structure:
Explain the role of cholesterol, glycoproteins & glycolipids in the cell- surface membrane.

A

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

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28
Q

Cell structure:
Describe the structure and function of flagella.

A

● Hollow helical tube made of the protein flagellin.
● Rotates to propel (usually unicellular)
organism.

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29
Q

Cell structure:
Describe the structure and function of cilia.

A

● Hairlike protrusions on eukaryotic cells.
● Move back and forth rhythmically to sweep foreign substances e.g. dust or pathogens away / to enable the cell to move.

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30
Q

Cell structure:
Why is the cytoskeleton important?

A

● Provides mechanical strength.
● Aids transport within cells.
● Enables cell movement.

31
Q

Cell structure:
Compare eukaryotic and prokaryotic cells.

A

Both have:
● cell membrane
● cytoplasm
● ribosomes

32
Q

Cell structure:
Contrast eukaryotic and prokaryotic cells.

A

Prokaryotic:
0.5-5µm
DNA is circular with no proteins, in the cytoplasm
Cell division occurs by binary fission - no spindle involved
70s ribosomes
No membrane bound organelles
Cell wall is made from peptidoglycan and murein

Eukaryotic
100µm
DNA is associated with proteins, and formed into proteins
Cell division occurs by mitosis or meiosis involves spindle fibres (Separate chromosomes)
80s ribosomes
Membrane bound organelles, and not membrane bound organelles
Cell wall is present in plants (cellulose), fungi (chitin)

33
Q

Biological Molecules:
How do hydrogen bonds form between water molecules?

A

Water is polar: O more electronegative than H, so attracts electron density in covalent bond more strongly. Forms O 𝛿- (slightly negative) & H 𝛿+ (slightly positive).
There are intermolecular forces of attraction between a lone pair on O 𝛿- of one molecule & H 𝛿+ on an adjacent molecule.

34
Q

Biological Molecules:
State 7 biologically important properties of water.

A

● reaches maximum density at 4℃
● high surface tension
● incompressible
● metabolite/ solvent for chemical reactions in the body
● high specific heat capacity
● high latent heat of vaporisation
● cohesion between molecules

35
Q

Biological Molecules:
Why is the incompressible nature of water important for organisms?

A

Provides turgidity to plant cells.
Provides hydrostatic skeleton for some small animals e.g. earthworms.

36
Q

Biological Molecules:
Explain why ice floats on water. Why is this important for organisms?

A

Ice is less dense than water because H-bonds hold molecules in fixed positions further away from each other.
Insulates water in arctic climates so aquatic organisms can survive. Water acts as a habitat.

37
Q

Biological Molecules:
Why is the high surface tension of water important for organisms?

A

Slows water loss due to transpiration in plants.
Water rises unusually high in narrow tubes, lowering demand on root pressure.
Some insects can ‘skim’ across the surface of water.

38
Q

Biological Molecules:
Why is water an important solvent for organisms?

A

Polar universal solvent dissolves & transports charged particles involved in intra & extracellular reactions e.g. PO4 3- for DNA synthesis.

39
Q

Biological Molecules:
Why are the high specific heat capacity and latent of vapourisation of water important for organisms?

A

Acts as a temperature buffer which enables endotherms to resist fluctuations in core temperature to maintain optimum enzyme activity.
Cooling effect when water evaporates from skin surface as sweat/ from mouth when panting.

40
Q

Biological Molecules:
Define monomer and polymer. Give some examples.

A

monomer: smaller units that join together to form larger molecule
● monosaccharides (glucose, fructose, galactose, ribose)
● amino acids
● nucleotides
polymer: molecules formed when many monomers join together
● polysaccharides
● proteins
● DNA/ RNA

41
Q

Biological Molecules:
What happens in condensation and hydrolysis reactions?

A

Condensation: chemical bond forms between 2 molecules & a molecule of water is produced.

Hydrolysis: a water molecule is used to break a chemical bond between 2 molecules e.g. peptide bonds in proteins, ester bonds between fatty acids & glycerol in lipids.

42
Q

Biological Molecules:
Name the elements found in carbohydrates, lipids, proteins and nucleic acids.

A

carbohydrates & lipids: C, H, O
proteins: C, H, O, N, S
nucleic acids: C, H, O, N, P

43
Q

Biological Molecules:
Draw the structure of ⍺-glucose and 𝛽-glucose.

A

:)

44
Q

Biological Molecules:
Describe the properties of 𝛼 glucose.

A

● Small & water soluble = easily transported in bloodstream.
● Complementary shape to antiport for co-transport for absorption in gut.
● Complementary shape to enzymes for glycolysis = respiratory substrate.

45
Q

Biological Molecules:
Draw the structure of ribose.

A

:)

46
Q

Biological Molecules:
What type of bond forms when monosaccharides react?

A

(1,4 or 1,6) glycosidic bond
● 2 monomers = 1 chemical bond = disaccharide.
● Multiple monomers = many chemical bonds = polysaccharide.

47
Q

Biological Molecules:
Describe how disaccharides form.
Name 3 disaccharides.
Molecular formula

A

Condensation reaction forms glycosidic bond between 2 monosaccharides.
● maltose: glucose + glucose
● sucrose: glucose + fructose
● lactose: glucose + galactose
all have molecular formula C12H22O11

48
Q

Biological Molecules:
Describe the structure and functions of starch.

A

Storage polymer of 𝛼-glucose in plant cells:
● insoluble = no osmotic effect on cells
● large = does not diffuse out of cells
made from amylose:
● 1,4 glycosidic bonds
● helix with intermolecular H-bonds = compact
and amylopectin:
● 1,4 & 1,6 glycosidic bonds
● branched = many terminal ends for hydrolysis into glucose

49
Q

Biological Molecules:
Describe the structure and functions of glycogen.

A

Main storage polymer of 𝛼-glucose in animal cells (but also found in plant cells):
● 1,4 & 1,6 glycosidic bonds.
● Branched = many terminal ends for hydrolysis.
● Insoluble = no osmotic effect & does not diffuse out of cells.
● Compact.

50
Q

Biological Molecules:
Describe the structure and functions of cellulose.

A

Polymer of 𝛽-glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up).
● 1,4 glycosidic bonds.
● Straight-chain, unbranched molecule.
● Alternate glucose molecules are rotated 180°.
● H-bond crosslinks between parallel strands form microfibrils = high tensile strength.

51
Q

Biological Molecules:
How do triglyglcerides form?

A

Condensation reaction between 1 molecule of glycerol &
3 fatty acids which forms ester bonds.

52
Q

Biological Molecules:
Contrast saturated and unsaturated fatty acids.

A

Saturated:
● contain only single bonds
● straight-chain molecules have many contact points
● higher melting point = solid at room temperature
● found in animal fats
Unsaturated:
● contain C=C double bonds
● ‘kinked’ molecules have fewer contact points
● lower melting point = liquid at room temperature
● found in plant oils

53
Q

Biological Molecules:
Relate the structure of triglycerides to their functions.

A

● High energy:mass ratio = high calorific value from oxidation (energy storage).
● Insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing.
● Slow conductor of heat = thermal insulation e.g. adipose tissue.
● Less dense than water = buoyancy of aquatic animals.

54
Q

Biological Molecules:
Describe the structure and function of phospholipids.

A

Amphipathic: glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar
phosphate head.
● Forms phospholipid bilayer in water = component of membranes.
● Tails can splay outwards = waterproofing e.g. for skin.

55
Q

Biological Molecules:
Are phospholipids and triglycerides polymers?

A

No; they are not made from a small repeating unit. They are macromolecules.

56
Q

Biological Molecules:
Describe the structure and function of cholesterol.

A

Steroid structure of 4 hydrocarbon rings. Hydrocarbon tail on one side, hydroxyl group (-OH) on the other side.
Adds stability to cell surface phospholipid bilayer by connecting molecules & reducing fluidity.

57
Q

Biological Molecules:
What is the general structure of an amino acid? Draw it

A

-COOH carboxyl / carboxylic acid group.
-R variable side group consists of carbon chain & may include other functional groups e.g. benzene ring or -OH (alcohol).
-NH2 amine/ amino group.

58
Q

Biological Molecules:
How do polypeptides form?

A

Condensation reactions between amino acids form peptide bonds
(-CONH-).
There are 4 levels of protein structure.

59
Q

Biological Molecules:
Define ‘primary structure’ of a protein.

A

Primary: sequence, number & type of amino acids in the polypeptide, determined by sequence of codons on mRNA.
Secondary: hydrogen bonds form between O
𝛿- attached to ‒C=O & H 𝛿+ attached to ‒NH.

60
Q

Biological Molecules:
Describe the 2 types of secondary protein structure.

A

α-helix:
● All N-H bonds on same side of protein chain.
● Spiral shape.
● H-bonds parallel to helical axis.
β-pleated sheet:
● N-H & C=O groups alternate from one side to the other.

61
Q

Biological Molecules:
Define ‘tertiary structure’ of a protein. Describe the bonds present.

A

3D structure formed by further folding
● Disulfide bridges: strong covalent S-S bonds between molecules of the amino acid cysteine.
● Ionic bonds: relatively strong bonds between charged R groups (pH changes cause these bonds to break).
● Hydrogen bonds: numerous & easily broken.

62
Q

Biological Molecules:
Define ‘quaternary structure’ of a protein.

A

● Functional proteins may consist of more than one polypeptide.
● Precise 3D structure held together by the same types of bond as tertiary structure.
● May involve addition of prosthetic groups e.g metal ions or phosphate groups.

63
Q

Biological Molecules:
Describe the structure and function of globular proteins.

A

● Spherical & compact.
● Hydrophilic R groups face outwards & hydrophobic R groups face inwards = usually water-soluble.
● Involved in metabolic processes e.g. enzymes such as amylase, insulin (2 polypeptide chains linked by 2 disulfide bonds), haemoglobin.

64
Q

Biological Molecules:
Describe the structure of haemoglobin.

A

● Globular conjugated protein with prosthetic group.
● 2 𝛼-chains, 2 𝛽-chains, 4 prosthetic haem groups.
● Water-soluble so dissolves in plasma.
● Fe2+ haem group forms coordinate bond with O2.
● Tertiary structure changes so it is easier for subsequent O2 molecules to bind (cooperative binding).

65
Q

Biological Molecules:
Describe the structure and function of fibrous proteins.

A

● Can form long chains or fibres.
● Insoluble in water.
● Useful for structure and support e.g. collagen in skin.

66
Q

Biological Molecules:
List the functions of collagen, elastin and keratin.

A

Collagen: component of bones, cartilage, connective tissue, tendons.
Elastin: provides elasticity to connective tissue, arteries, skin, lungs, cartilage, ligaments.
Keratin: structural component of hair, nails, hooves/ claws, horns, epithelial cells of outer layer of skin.

67
Q

Biological Molecules:
Describe how to test for proteins in a sample.

A

Biuret test confirms presence of peptide bond
1. Add biurets regenat
3. Positive result: colour changes from blue to purple Negative result: solution remains blue.

68
Q

Biological Molecules:
Describe how to test for lipids in a sample.

A
  1. Dissolve solid samples in ethanol.
  2. Add an equal volume of water and shake.
  3. Positive result: milky white emulsion forms
69
Q

Biological Molecules:
Describe how to test for reducing sugars.

A
  1. Add an equal volume of Benedict’s reagent to a sample.
  2. Heat the mixture in an electric water bath at 100℃ for 5 mins.
  3. Positive result: colour changes from blue to orange & brick-red precipitate forms.
70
Q

Biological Molecules:
Describe the Benedict’s test for non-reducing sugars.

A
  1. Negative result: Benedict’s reagent remains blue.
  2. Add Hydrochloric acid
  3. Heat in a boiling water bath for 5 mins.
  4. Neutralise the mixture using sodium carbonate solution.
  5. Proceed with the Benedict’s test as usual - positive test means non-reducting sugar
71
Q

Biological Molecules:
Describe the test for starch.

A
  1. Add iodine solution.
  2. Positive result: colour changes from orange to blue-black.
72
Q

Biological Molecules:
How can the concentration of a solution be measured quantitatively?

A

● Use colorimetry to measure absorbance/%transmission. Interpolate a calibration curve from solutions of known concentration.

73
Q

Biological Molecules:
Outline the principles and process of paper/ thin-layer chromatography.

A
  1. Use capillary tube to spot solution onto pencil ‘start line’ (origin) 1 cm above bottom of paper.
  2. Place chromatography paper in solvent. (origin should be above solvent level).
  3. Allow solvent to run until it almost touches other end of the paper. Molecules in mixture move different distances based on relative solubility in solvent/attraction to paper.
74
Q

Biological Molecules:
What are Rf values? How can they be calculated?

A

Ratios that allow comparison of how far molecules have moved in chromatograms.
Rf value = distance between origin and centre of pigment spot / distance between origin and solvent front.

BIOLOGY OCR A (7 decks)

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