Bio 65 flashcard

Describe how you would test a solution for a reducing sugar and state the positive result. (3 marks)

• Add Benedict’s solution

• Heat in water bath at 80–100 °C

• Colour changes from blue → green / yellow / orange / red = positive

Explain how you would test for a non‑reducing sugar if the Benedict’s test was negative. (4 marks)

• Boil sample with dilute acid to hydrolyse glycosidic bonds

• Neutralise with alkali (e.g. sodium hydrogencarbonate)

• Repeat Benedict’s test

• Colour change = non‑reducing sugar present

Describe how to carry out the emulsion test for lipids and state the positive result. (3 marks)

• Add ethanol to sample and shake thoroughly

• Pour mixture into equal volume of water

• White / cloudy emulsion forms = positive

Explain how the structure of glycogen is related to its function. (4 marks)

• Polymer of α‑glucose; 1,4 and 1,6 glycosidic bonds → highly branched

• Many ends → rapid hydrolysis / fast energy release

• Compact → lots stored in small space

• Insoluble → no effect on water potential / no osmosis

Explain how the structure of cellulose makes it suitable for plant cell walls. (4 marks)

• Long, unbranched chains of β‑glucose; only 1,4 bonds

• Chains form straight, parallel strands

• Hydrogen bonds between chains → strong microfibrils

• High tensile strength → supports cell; prevents bursting; freely permeable

Compare and contrast triglycerides and phospholipids. (5 marks)

• Similar: glycerol + fatty acids; ester bonds; insoluble in water

• Triglyceride: 3 fatty acids; entirely hydrophobic → energy storage

• Phospholipid: 2 fatty acids + phosphate group; hydrophilic head + hydrophobic tails → forms membrane bilayer

• Phospholipids are amphipathic; triglycerides are not

Describe the induced‑fit model of enzyme action and explain how it lowers activation energy. (5 marks)

• Substrate enters active site → enzyme changes shape slightly → tighter fit

• Enzyme‑substrate complex forms

• Bonds in substrate strained / weakened

• Reacting groups brought close together

• Activation energy reduced → faster reaction; products leave; enzyme unchanged

Explain how temperature affects enzyme activity. (4 marks)

• Low temp: low kinetic energy → few collisions → few E‑S complexes → low rate

• Rising temp: more collisions → more E‑S → rate increases

• Optimum temp: maximum rate

• Above optimum: bonds break → tertiary structure changes → active site altered → denatured → rate falls

Explain how pH affects enzyme activity. (3 marks)

• H⁺ ions interfere with ionic and hydrogen bonds holding tertiary structure

• Active site shape changes → substrate no longer fits

• Fewer / no E‑S complexes → rate falls; extreme pH causes permanent denaturation

Compare competitive and non‑competitive inhibitors. (5 marks)

• Competitive: similar shape; binds active site; effect reversed by adding more substrate

• Non‑competitive: binds allosteric site; changes active site shape; effect NOT reversed

• Both reduce rate by preventing / reducing E‑S complex formation

Describe how DNA structure allows it to carry out its functions. (6 marks)

• Double helix → stable, protects genetic code

• Two strands → allows semi‑conservative replication

• Hydrogen bonds between bases → easy to separate strands

• Complementary base pairing → accurate replication / transcription

• Long molecule → stores large amount of information

• Base sequence → carries genetic code for protein synthesis

Describe semi‑conservative DNA replication. (5 marks)

• DNA helicase breaks hydrogen bonds → strands separate

• Each strand acts as template

• Free nucleotides align by complementary base pairing (A‑T, C‑G)

• DNA polymerase joins nucleotides → phosphodiester bonds; works 5’→3’

• New DNA = 1 original + 1 new strand → identical copies made

Compare DNA and RNA. (6 marks)

• Similar: nucleotides; phosphate + pentose + base; phosphodiester bonds

• DNA: deoxyribose; A,T,C,G; double‑stranded; long; stores information

• RNA: ribose; A,U,C,G; single‑stranded; shorter; transfers / translates information

Compare mRNA and tRNA. (5 marks)

• Similar: single‑stranded; ribose; A,U,C,G; involved in protein synthesis

• mRNA: long, linear, no folding; carries full gene code; codons; short‑lived

• tRNA: short, clover‑leaf shape, folded; anticodon + amino acid binding site; reusable

Explain why a mutation may result in a non‑functional protein. (4 marks)

• Base change → different codon → different amino acid

• Alters primary structure → changes folding

• Different bonds form → wrong tertiary structure

• Active site / binding site changed → protein cannot function

Compare prokaryotic and eukaryotic cells. (4 marks)

• Prokaryote: no nucleus; no membrane‑bound organelles; smaller; circular DNA; plasmids present

• Eukaryote: nucleus present; membrane organelles (mitochondria, ER etc.); larger; linear DNA; no plasmids

Explain how cell membrane structure controls movement of substances. (5 marks)

Explain why an electron microscope has higher resolution than an optical microscope. (3 marks)

🟢 Back:

• Resolution depends on wavelength of radiation used

• Light has long wavelength → cannot distinguish small objects

• Electrons have very short wavelength → much higher detail possible

22

🔵 Front: Describe what happens during each stage of mitosis. (6 marks)

🟢 Back:

• Prophase: chromosomes condense; nuclear envelope breaks down; centrioles move to poles

• Metaphase: chromosomes line up at equator; attach to spindle fibres by centromere

• Anaphase: centromeres split; sister chromatids pulled to opposite poles

• Telophase: chromosomes uncoil; nuclei reform; spindle breaks down

• Followed by cytokinesis → cytoplasm divides → 2 genetically identical cells

23

🔵 Front: Explain the importance of mitosis. (3 marks)

🟢 Back:

• Produces genetically identical cells

• Used for growth, repair of tissues and asexual reproduction

• Maintains the correct chromosome number

24

🔵 Front: Describe binary fission in prokaryotic cells. (3 marks)

🟢 Back:

• Circular DNA replicates; copies attach to cell membrane

• Plasmids replicate

• Cell elongates; membrane grows inward; cytoplasm divides → 2 identical cells

• Phospholipid bilayer → barrier to polar / water‑soluble substances

• Channel proteins → allow diffusion of specific ions / polar molecules

• Carrier proteins → allow facilitated diffusion or active transport (uses ATP)

• Cholesterol → regulates fluidity and permeability

• Glycoproteins / glycolipids → cell recognition / signalling

Describe osmosis. (3 marks)

• Net movement of water molecules

• From high water potential → low water potential

• Across a partially permeable membrane

Explain how active transport differs from facilitated diffusion. (4 marks)

• Active transport: low → high concentration; against gradient; needs ATP; carrier proteins only

• Facilitated diffusion: high → low; down gradient; no energy; channel or carrier proteins

• Both are specific; both use membrane proteins

Describe how you would use cell fractionation and ultracentrifugation to obtain mitochondria. (4 marks)

• Homogenise tissue in cold, isotonic, buffered solution → break cells; prevent damage / enzyme action

• Filter to remove debris

• Spin at low speed → pellet = nuclei; keep supernatant

• Spin supernatant at higher speed → pellet = mitochondria; resuspend

Explain why an electron microscope has higher resolution than an optical microscope. (3 marks)

• Resolution depends on wavelength of radiation used

• Light has long wavelength → cannot distinguish small objects

• Electrons have very short wavelength → much higher detail possible

Describe what happens during each stage of mitosis. (6 marks)

• Prophase: chromosomes condense; nuclear envelope breaks down; centrioles move to poles

• Metaphase: chromosomes line up at equator; attach to spindle fibres by centromere

• Anaphase: centromeres split; sister chromatids pulled to opposite poles

• Telophase: chromosomes uncoil; nuclei reform; spindle breaks down

• Followed by cytokinesis → cytoplasm divides → 2 genetically identical cells

Explain the importance of mitosis. (3 marks)

• Produces genetically identical cells

• Used for growth, repair of tissues and asexual reproduction

• Maintains the correct chromosome number

Describe binary fission in prokaryotic cells. (3 marks)

• Circular DNA replicates; copies attach to cell membrane

• Plasmids replicate

• Cell elongates; membrane grows inward; cytoplasm divides → 2 identical cells

Explain how the lungs are adapted for efficient gas exchange. (5 marks)

• Many alveoli → large surface area → fast diffusion

• Walls one cell thick → short diffusion distance

• Dense capillary network → good blood supply → maintains steep gradient

• Ventilation → refreshes air → keeps concentration difference high

• Moist surface → gases dissolve easily

Explain how counter‑current flow in fish gills increases oxygen uptake. (4 marks)

• Water flows opposite direction to blood in lamellae

• Concentration gradient maintained along whole length

• Oxygen diffuses into blood at every point; never reaches equilibrium

• Same direction flow would lose gradient halfway → less uptake

Explain how insects balance gas exchange and water loss. (4 marks)

• Tracheal system → efficient gas exchange

• Spiracles can close → reduce water loss

• Tracheoles highly branched → large surface area

• Waterproof cuticle → prevents evaporation

Explain how water moves from soil into xylem in roots. (5 marks)

• Enters root hair cells by osmosis → higher water potential in soil

• Moves across cortex: apoplast (cell walls), symplast (cytoplasm / plasmodesmata)

• Endodermis has Casparian strip → waterproof; blocks apoplast

• Water forced through cell membrane → controls movement

• Enters xylem down water potential gradient

Explain how water moves up the stem in xylem. (4 marks)

• Transpiration: water evaporates from mesophyll → creates tension / pull

• Cohesion: hydrogen bonds stick water molecules together → continuous column

• Adhesion: water sticks to xylem walls → helps support column

• Main force = transpiration pull; root pressure gives small push

Describe the mass‑flow hypothesis for translocation. (5 marks)

• At source (leaf): sucrose actively loaded into phloem sieve tubes

• Lowers water potential → water enters from xylem → high pressure

• Pressure drives mass flow of sap to sink (root / fruit)

• At sink: sucrose removed → water leaves → pressure falls

• Pressure difference between source and sink = driving force

Explain how xylem vessels are adapted for transport. (4 marks)

• Dead, hollow cells → no contents → no resistance to flow

• Thick walls with lignin → strong, waterproof → prevents collapse

• End walls broken down → continuous tubes from root to leaf

• Pits present → allow sideways movement to other tissues

Explain how phloem sieve tubes and companion cells are adapted for translocation. (4 marks)

• Sieve tubes: no nucleus / organelles → more space for flow; end walls have pores → easy movement

• Companion cells: many mitochondria → ATP for active loading of sucrose; connected by plasmodesmata

Front: Describe the pathway of oxygen from alveolus to red blood cell. (4 marks)

• Diffuses across alveolar epithelium

• Across capillary endothelium

• Into blood plasma

• Into red blood cell → binds to haemoglobin

Explain the oxygen‑haemoglobin dissociation curve. (4 marks)

• S‑shaped curve → loads easily at high pO₂ (lungs)

• Unloads easily at low pO₂ (tissues)

• Bohr effect: high CO₂ / low pH → curve shifts right → more O₂ released where respiration high

• Matches supply to demand

Explain how CO₂ affects oxygen binding to haemoglobin. (3 marks

• High CO₂ → lowers pH / increases acidity

• Changes shape of haemoglobin → lower affinity for oxygen

• Releases more oxygen to respiring tissues (Bohr effect)

Describe how tissue fluid is formed. (4 marks)

• At arterial end of capillary: high hydrostatic pressure from heart contraction

• Pressure forces water, small soluble molecules (glucose, ions, amino acids) out of blood

• Large molecules (proteins, blood cells) too big to pass through capillary walls → remain in blood

• Fluid formed = tissue fluid; surrounds cells, allows exchange of substances

Explain how tissue fluid is reabsorbed back into the blood. (4 marks)

• Hydrostatic pressure falls along capillary → lower at venous end

• Water potential inside capillary lower than in tissue fluid (due to plasma proteins remaining)

• Water re‑enters capillary by osmosis down water potential gradient

• Remaining excess fluid drained into lymph vessels → returns to blood via lymphatic system

Explain the role of hydrostatic pressure and water potential in the formation and return of tissue fluid. (5 marks)

• High hydrostatic pressure at arterial end pushes fluid out

• Low water potential in blood (from proteins) creates osmotic pull

• At venous end: hydrostatic pressure low; water potential gradient pulls water back in

• Balance between these two forces controls volume of tissue fluid

• Prevents too much fluid building up in tissues

Explain why tissue fluid does not contain large proteins or blood cells. (3 marks)

• Capillary walls have small pores / gaps

• Large proteins and cells are too big to fit through gaps

• Only small molecules and water pass out → composition different from blood plasma

Describe the function of tissue fluid. (2 marks)

• Supplies cells with oxygen, glucose and nutrients

• Removes waste products (CO₂, urea) from cells

Describe the structure of a nucleotide. (3 marks)

Pentose sugar (deoxyribose or ribose)

• Phosphate group

• Nitrogen‑containing base (A, T/U, C or G)

• Joined by condensation reactions / phosphodiester bonds

Describe how genes code for proteins. (4 marks)

• Base sequence of DNA determines amino acid sequence

• Each triplet of bases = 1 codon = 1 amino acid

• Code is degenerate, non‑overlapping and universal

• Sequence determines primary structure → determines shape/function

Describe transcription. (5 marks)

• DNA helicase breaks H‑bonds → strands separate

• Only one strand acts as template

• Free RNA nucleotides align by complementary base pairing (A‑U, C‑G)

• RNA polymerase joins nucleotides → mRNA formed

• mRNA leaves nucleus through nuclear pore

Describe translation. (5 marks)

• mRNA attaches to ribosome

• tRNA carries specific amino acid; anticodon binds to mRNA codon

• Ribosome moves along mRNA; reads code

• Peptide bonds form between amino acids (uses ATP)

• Polypeptide chain built until stop codon reached

Explain what is meant by the genetic code being degenerate and non‑overlapping. (3 marks)

• Degenerate: more than one codon codes for the same amino acid

• Reduces effect of mutations

• Non‑overlapping: each base is read only once; triplets separate

Describe the process of meiosis. (4 marks)

• Two divisions: meiosis I and meiosis II

• Homologous chromosomes pair; crossing over occurs

• Homologues separate in meiosis I; chromatids separate in meiosis II

• Produces 4 haploid genetically different cells

Explain how meiosis creates genetic variation. (3 marks)

• Crossing over between homologous chromosomes → new allele combinations

• Independent assortment of chromosomes → random alignment

• Random fertilisation further increases variation

Compare mitosis and meiosis. (4 marks)

• Mitosis: 1 division; 2 cells; diploid; genetically identical; growth/repair

• Meiosis: 2 divisions; 4 cells; haploid; genetically different; gamete production

• Both start with diploid parent cell; both have chromosome replication once

Explain what is meant by allele, genotype and phenotype. (3 marks)

• Allele: different version of a gene

• Genotype: genetic makeup / alleles present

• Phenotype: observable characteristics due to genotype + environment

Explain how natural selection leads to evolution. (4 marks)

• Variation exists within population due to mutation

• Selection pressure / change in environment occurs

• Individuals with advantageous alleles survive and reproduce

• Pass on alleles to next generation; frequency increases over time

Describe how stabilising selection occurs. (3 marks)

• Environment is stable / no change

• Individuals with average / most common phenotype favoured

• Extremes selected against; variation reduces; mean stays same

Describe how directional selection occurs. (3 marks)

• Environment changes

• Individuals with extreme phenotype favoured

• Mean phenotype shifts towards that extreme over generations

Explain how species are classified using the binomial system. (3 marks)

• Two names: Genus and species

• Genus starts with capital; species lowercase; italicised

• Universal system; avoids confusion from common names

Describe how hierarchy and classification work. (4 marks)

• Groups within larger groups; no overlap

• Order: Kingdom → Phylum → Class → Order → Family → Genus → Species

• Based on similarities in characteristics / DNA / proteins

• Reflects evolutionary relationships

Explain how DNA sequencing and protein structure help determine relationships between organisms. (4 marks)

• More similar base sequence → more closely related

• More similar amino acid sequence → more closely related

• Mutations accumulate over time; differences show how long ago they separated

• Used to build phylogenetic trees

Define antigen and explain its role in the immune response. (3 marks

• Antigen = protein / glycoprotein on cell surface

• Foreign to the body → triggers immune response

• Identifies pathogens, abnormal cells or foreign material; recognised by white blood cells

Describe the process of phagocytosis. (4 marks)

• Phagocyte recognises foreign antigens on pathogen

• Engulfs pathogen → encloses in phagosome

• Lysosomes fuse with phagosome → release digestive enzymes (lysozymes)

• Pathogen broken down; waste products removed; antigens presented on cell surface

Explain the role of T‑lymphocytes in the immune response. (4 marks)

• Specific receptors bind to complementary antigen (presented by phagocyte)

• Helper T‑cells activate B‑cells and cytotoxic T‑cells

• Cytotoxic T‑cells kill infected body cells by producing perforin

• Memory T‑cells formed → provide long‑term immunity

Explain the role of B‑lymphocytes and how they produce antibodies. (5 marks)

• Specific antibodies on surface bind to complementary antigen

• Activated by helper T‑cells

• Divide by mitosis → form clone of identical cells

• Most become plasma cells → secrete large amounts of specific antibody

• Some become memory cells → rapid response if same antigen returns

Describe the structure of an antibody and explain how it is adapted to its function. (5 marks)

• Quaternary protein; 4 polypeptide chains: 2 heavy, 2 light

• Variable regions = antigen‑binding sites → specific shape complementary to one antigen

• Constant region → binds to receptors on immune cells

• Disulfide bridges hold chains together

• Can bind to multiple antigens → clump pathogens together (agglutination)

Explain how antibodies lead to the destruction of pathogens. (4 marks)

• Agglutination: clump pathogens together → easier for phagocytes to engulf

• Neutralisation: bind to toxins / viral binding sites → prevent entry/harm

• Opsonisation: mark pathogen → attract phagocytes

• Activation of complement proteins → lyse (burst) cells

Compare and contrast active and passive immunity. (4 marks)

Active: body produces its own antibodies; long‑lasting; slow onset; memory cells formed

• Passive: antibodies received from outside source; short‑lived; immediate protection; no memory cells

• Both provide protection against specific pathogens

Compare natural and artificial immunity, giving examples. (4 marks)

• Natural active: get disease → make own antibodies (e.g. flu infection)

• Natural passive: antibodies passed from mother → baby (placenta / breast milk)

• Artificial active: vaccination → stimulate antibody production without disease

• Artificial passive: injection of ready‑made antibodies (e.g. anti‑venom)

Explain how a vaccination produces immunity. (4 marks)

• Contains dead / weakened / inactive pathogen or antigen

• Introduced into body → triggers immune response

• B‑cells activated → produce antibodies and memory cells

• If real pathogen enters later → memory cells respond rapidly → destroy before symptoms appear

Explain why vaccines may not work against all diseases, or why booster doses are needed. (3 marks)

• Pathogen mutates frequently → change in antigens → memory cells no longer recognise (e.g. influenza)

• Some pathogens have many different strains / antigen types

• Memory cells may decrease in number over time → booster increases count again

Explain how a vaccination produces immunity. (4 marks)

• Contains dead / weakened / inactive pathogen or antigen

• Introduced into body → triggers immune response

• B‑cells activated → produce antibodies and memory cells

• If real pathogen enters later → memory cells respond rapidly → destroy before symptoms appear

Explain how the structure of strach is related to its function. (4 marks)

• Made of α‑glucose; compact / coiled structure → large amount stored in small volume.

• Insoluble → does not lower water potential → no osmosis into cells.

• Large molecule → cannot leave cell.

• Branched structure → many ends → rapid hydrolysis / quick energy release when needed.

Test – PROTEINS / PEPTIDE BONDS

1. Add Biuret solution

2. Shake gently.

Result:

Positive: Blue → Purple / Lilac.

how do u test for starch

Add iodine solution directly to sample.

Result:

Positive: Orange‑brown → Blue‑Black.