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AS OCR Biology A
Terms in this set (155)
Describe the process of protein production.
1) Proteins synthesized on ribosomes bound to ER
2) Pass into cisternae
3) Packaged in transport vesicles
4) Move to Golgi via cytoskeleton
5) Fuse with cis face
7) Leave through trans face
Contractile fibres formed from actin.
Responsible for cell movement and contraction.
Globular tubulin proteins.
Scaffolding for cytoplasmic streaming.
Describe INTERMEDIATE fibres.
Give mechanical strength.
Give details of precursor enzymes.
apoenzyme + activator = holoenzyme
"proenzyme": precursor activated by change in conditions
Describe the process of active transport.
1) Molecule binds to receptors in carrier protein on outside
2) ATP binds to carrier on inside
3) ATP hydrolyzed to form ADP and phosphate
4) Phosphate changes shape of carrier
Large proportion of cysteine (containing sulfur).
Many strong disulfide bridges.
Fibrous protein in elastic fibres.
Made of small, soluble tropoelastin molecules linked together via interactions between hydrophobic areas.
Alternate hydrophobic and lysine-rich areas.
Cross-linking covalent bonds between lysine.
3 polypeptides wound in rope-like structure.
Every third amino acid in glycine (small).
R groups in proline and hydroxyproline repel each other.
Chondrocyte cells embedded in matrix containing fibres of elastin and collagen.
Give all components of lung volume.
1) Tidal volume
2) Vital capacity
3) Reserve volumes
4) Residual volume
What are "megakaryocytes"?
Platelets are fragments of large cells called megakaryocytes found in red bone marrow.
Describe the symplast pathway.
Describe the apoplast pathway.
Continuous cytoplasm connected by plasmodesmata.
Movement along cellulose inside cell wall.
What are aerenchyma cells?
Special parenchyma (packing) cells found in hydrophytes. Has large air spaces formed by apoptosis of parenchyma.
Define "homologous structure".
Appears superficially different and may perform different functions but has same underlying structure.
Define "divergent evolution".
Different species have evolved from a common ancestor with a different set of adaptive features.
Define "convergent evolution".
Unrelated species begin to share similar traits.
Define "analogous structure".
Adapted to perform the same function but have a different origin.
Define "gene flow".
Genes transferred between populations.
Define "genetic bottleneck."
Few individuals within a population survive an event.
Define "founder effect."
A small number of individuals create a new colony which is geographically isolated from the original.
Define "genetic drift".
Random change in allele frequency.
More than one allele for one gene.
Preservation and careful management of the environment and natural resources.
Describe the process of carrying out a student's t-test.
1) Identify null hypothesis
2) Calculate both means and standard deviations
3) Use formula to calculate t
4) Calculate degrees of freedom (n1 + n2 - 2)
5) Look up values for t in a table of critical values
How does callose help plants defend against pathogens?
Polysaccharide containing B1,3 and B1,6 glucose chains.
Between cell wall and membrane.
Lignin added for strength.
Blocks sieve plates and plasmodesmata.
What 2 chemicals do platelets secrete?
1) Thromboplastin: enzyme which triggers clotting
2) Serotonin: makes smooth muscle in vessel walls contract to reduce blood flow
What 2 chemicals do mast cells secrete?
1) Histamines: dilate blood vessels and make them more leaky, causing heat and swelling
2) Cytokines: attract phagocytes
Define "selective toxicity".
The ability to interfere with the metabolism of a pathogen without affecting host's cells.
How are individual nucleotides linked in a polynucleotide strand?
Phosphodiester bond between phosphate group at 5' and hydroxyl group at 3'
What are the 4 DNA bases?
Pyrimidines (smaller): Thymine and cytosine
Purines (larger): Guanine and adenine
2 hydrogen bonds between A and T
3 hydrogen bonds between C and G
Uracil replaces thymine in RNA
Describe the process of semi-conservative replication.
1) DNA polymerase moves from 3' to 5'
2) Leading strand unzipped from 3' end is continuously replicated
3) Lagging strand unzipped from 5' end discontinuous (polymerase waits until section of strand is unzipped and then works its way backwards)
4) Produced in sections called Okazaki fragments
Explain the triplet code.
Sequence of 3 bases called a codon.
Each codon codes for 1 amino acid.
'Start' codon would code for methionine.
Describe the process of transcription.
1) Section containing gene unwound and unzipped by helicase beginning at 'start' codon
2) Sense strand containing gene runs from 5' to 3'
3) Antisense strand runs from 3' to 5' and acts as template
4) Free RNA nucleotides pair with bases and bonded by polymerase
5) messenger RNA produced
Describe the process of translation.
1) mRNA binds to specific site on small ribosomal subunit at its start codon
2) tRNA folded in such a way that 3 bases making up an anticodon are all at one end of the molecule
3) Anticodon binds to complementary codon along mRNA
4) tRNA carries correct amino acids for primary sequence (added one at a time)
5) rRNA moves along the mRNA strand to catalyse the formation of peptide bonds until I reaches the 'stop' codon
What are the 3 main types of activity in cells?
Describe the structure of ATP.
Type of nucleotide.
Pentose sugar is ribose.
Nitrogenous base always adenine.
3 phosphate groups.
Universal energy currency.
Describe 3 disaccharides.
1) a-glucose + a-glucose = maltose
2) fructose + glucose = sucrose
3) glucose + galactose = lactose
1) Amylose: a-glucose joined by 1,4 bonds. Helix stabilized by H-bonding. Very compact.
2) Amylopectin: a-glucose joined by 1,4 bonds and 1,6 bonds. Branches every 25 subunits.
More branches than amylopectin so more compact.
Alternate B-glucose molecules upside-down. Unable to coil or form branches. 1,4 bonds. Cellulose molecules joined by H-bonds to form microfibrils, then macrofibrils, then fibres.
Describe the Benedict's test.
Alkaline solution of Copper(II)sulfate. Boil for 5 minutes. Reducing sugars reduce blue Cu2+ ions to red Cu+ ions. For non-reducing sugars, first boil with HCl to hydrolyze.
Why are lipids non-polar?
Electrons in outer orbitals that form bonds are more evenly distributed so there are no positive/negative areas.
Why are unsaturated fats healthier?
Double bonds cause molecules to kink, so cannot pack as tightly together.
Steroid alcohols. Four-ring carbon structure with a hydroxyl group at one end. Hydroxyl group is hydrophilic and rest of molecule is hydrophobic. Used to manufacture vitamin D, steroid hormones, and bile.
Describe the emulsion test.
1) Mix sample with ethanol
2) Mix with water
4) White emulsion indicates positive
What is the formula of a peptide bond?
What is the formula of an ester bond?
Describe the biuret test.
Peptide bonds form violet coloured complexes with copper ions in alkaline solutions.
1) Add sodium hydroxide
2) Add blue copper sulfate
3) Violet indicate positive
What is the difference between an anabolic and a catabolic reaction?
Anabolic reactions build up molecules. Catabolic reactions break down molecules.
Describe the induced-fit hypothesis.
R-groups within enzyme's active site form temporary bonds with substrate, putting strain on the substrate's bonds.
Describe the digestion of starch.
1) Broken into maltose by amylase
2) Broken into glucose by maltase
What is the temperature coefficient?
Measure of how much reaction rate increases with a 10 degree temp increase.
How does pH affect enzymes?
A return to optimum pH can result in renaturation. Hydrogen ions interact with polar and charged groups. The more hydrogen ions present, the less R-groups can interact with each other.
How is carbon dioxide converted into hydrogen carbonate ions?
CO2 + H2O <--> H2CO3 (carbonic acid)
Catalyzed by carbonic anhydrase.
H2CO3 <--> H+ + HCO3- (hydrogen carbonate)
Hydrogen carbonate ions move out of rbc and replaced by Cl-.
H+ ions bond with hemoglobin to form haemoglobinic acid as a pH buffer.
Define enzyme specificity.
Each enzyme catalyzes one biochemical reaction.
When are membranes partially permeable? When are they selectively permeable?
Without carrier proteins. With carrier proteins.
Define water potential.
Pressure exerted by water molecules as they collide with a membrane or container. Pure water has the highest potential water potential (zero). The more concentrated the solution, the more negative the water potential.
When an animal cell bursts because of high hydrostatic pressure.
Give examples of competitive inhibitors.
1) Statins: inhibit enzyme used in cholesterol synthesis. Reversible.
2) Aspirin: inhibits active site of COX enzymes, preventing synthesis of prostaglandins and thromboxane, the chemicals responsible for pain and fever. Non-reversible.
Give examples of non-competitive inhibitors.
1) Organophosphates: used as insecticides and herbicides. Inhibit an enzyme responsible for nerve impulse transmission. Non-reversible
2) Proton-pump inhibitors: block enzyme system responsible for secreting H+ ions into the stomach (non-reversible)
What is special about the enzyme (PFK) used for ATP synthesis?
ATP is an end-product inhibitor.
Inorganic. Help enzyme and substrate bind. Don't directly participate. Cl- is a cofactor for amylase. Minerals are sources.
Organic. Participate in reaction and are changed. Act as carriers; moving chemical groups between different enzymes. Vitamins are sources.
What ions make up the prosthetic group of carbonic anhydrase?
Describe light microscopy.
200 nm. x2000. Brightfield/widefield.
Laser scanning confocal: fluorescence, 3D, different depths, pinhole focus.
Describe transmission electron microscopy.
0.5 nm. x500 000. Electromagnets focus electrons. Denser = darker. Thin specimen.
Describe scanning electron microscopy.
3-10 nm. x500 000. Electron beams knock specimen electrons. Image on cathode ray tube. Surface. 3D.
Describe the preparation of a specimen for microscopy.
1) Fixing (use chemicals to preserve)
2) Sectioning (dehydrated with alcohol, placed in mold with wax resin, sliced thinly)
Describe the process of gram staining.
1) Add crystal-violet dye
2) Add iodine to fix
3) Wash with alcohol
4) Positive = thick wall (susceptible)
Negative = thin wall (counter-stain with safranin)
Describe the acid-fast technique.
Differentiates mycobacterium from other bacteria. Lipid solvent carries carbolfuchsin dye. Wash with acid-alcohol. Mycobacterium retain dye.
Describe prokaryotic DNA.
1 chromosome. Supercoiled. Genes groups in operons, so some switched on while others switched off.
Describe the ventilation system used by insects.
Spiracles can be opened and closed by sphincters. Tracheae lined with chitin spirals (chitin is relatively impermeable, so no exchange here). Each tracheole is a single elongated cell with no chitin. Tracheal fluid at the end of each tracheole limits oxygen diffusion. When lactic acid builds up, the tracheal fluid moves out of the tracheoles by osmosis. Mechanical ventilation may be used when muscular pumping of the thorax and abdomen help move air in and out. Air reservoirs may also be used.
Describe the structure of gills.
Gill plate (stack of gill filaments). Gill Filament (has lots of lamellae on it). Tips of adjacent filaments overlap to slow water. Counter current and buccal cavity vs. parallel and ram ventilation.
Describe the transport system in insects.
Open body cavity called haemocoel where fluid called haemolymph under low pressure.
What is important about the cross-sectional area of capillaries?
Total cross-sectional area of capillaries greater than arterioles supplying them so rate of blood flow falls.
Describe thin layer chromatography.
Stationary phase is silica gel and mobile phase is an organic solvent. Rate at which different amino acids move depends on H-bond interactions with silica and solubility in solvent. When finished, spray reacts with amino acids to produce purple spots. Retention value of amino acid = distance travelled by component / distance travelled by solvent.
Using a biological molecule to detect a chemical. Analyte = compound under investigation. Sensor contains molecule which binds to analyte (molecular recognition). Converts chemical signal to electrical signal (transduction). Signal processed into a display
Give the taxonomic groups in order.
(Domain), Kingdom, Phylum, Class, Order, Family, Genus, Species
Why classify organisms?
To identify species.
Find evolutionary links.
What form of naming did we used to use? What do we use now?
Common names. Binomial nomenclature.
Describe the five kingdoms.
1) Prokaryotae: Unicellular, no nucleus or membrane-bound organelles, small ribosomes
2) Protoctista: Unicellular eukaryotes, nucleus and membrane-bound organelles, may be sessile or move, autotrophic or heterotrophic
3) Fungi: Unicellular or multicellular, nucleus and membrane-bound organelles, mycelium body made or hyphae threads, saprotrophic, store food as glycogen
What are the 3 domains?
1) Eukarya: 80S ribosomes, 12 proteins in RNA polymerase, Protoctista, Animalia, Plantae, Fungi
2) Archaea: 70S ribosomes, 8-10 proteins in RNA polymerase, Archaebacteria (extremophiles similar to eukaryotes)
3) Eubacteria: 70S ribosomes, 5 proteins in RNA polymerase, EUbacteria (trUE bacteria with peptidoglycan cell wall)
What is phylogeny?
Study of evolutionary relationships between organisms.
What are 3 types of adaptation?
Anatomical, physiological, behavioural.
Variety of living organisms present in an area, including habitat biodiversity, species biodiversity (both species richness and species evenness), and genetic biodiversity.
What are the 3 types of non-random sampling?
Opportunistic, stratified, systematic.
What affects reliability?
Sampling bias and chance.
What are the advantages of abiotic factors?
Rapid changes detected. Human error reduced. High degree of precision. Data can be digitally stored.
How do you interpret Simpson's Index of Biodiversity?
0= no diversity. 1= infinite diversity.
Why maintain biodiversity?
Aesthetic reasons (e.g. tourism), economic reasons (e.g. monoculture causes soil depletion/ plants may be used for medicines), ecological reasons (e.g. keystone species have a disproportionately large effect on their environment compared to their abundance)
Give examples and advantages of in situ conservation.
Wildlife reserves, controlled grazing, restricted access, controlling poaching, feeding animals, reintroducing species, culling, halting succession (where early colonizing species replaced by woodland). Cheap, maintains genetic diversity and interdependent relationships within habitat.
Give examples of ex situ conservation.
Botanic gardens, seed banks, captive breeding.
What causes the heartbeat sound?
Blood rushing back against valves.
How do humans influence biodiversity?
Deforestation, monoculture caused by agriculture (removal of hedgerows and use of chemicals), climate change, pollution.
Give examples of conservation agreements.
Red List of endangered species, trade regulations, countryside stewardship.
How do you interpret the t-test?
If the value of t is greater than the critical value, you can state that the difference is significant.
Describe the mass flow hypothesis.
Solutes actively loaded into sieve tubes at source. Lowers water potential. Osmosis. Hydrostatic pressure. Water potential lowered at sink. Low pressure. Pressure gradient.
Explain the Bohr effect.
As partial pressure of CO2 rises, haemoglobin gives up oxygen more easily. This is because, in order for H+ ions to form haemoglobinic acid, oxyhaemoglobin must unload its oxygen.
Describe the structure of the xylem.
Xylem vessels (long, hollow columns of dead cells), parenchyma containing tannin (a protective chemical), and xylem fibres (long cells with lignified secondary walls for strength).
Describe the movement of water across the root.
1) Apoplast route: cohesion/tension as water pulled into xylem
2) Symplast route: root hair cells have higher water potential than next cell along
Describe the movement of water into the xylem.
1) Casparian strip contains suberin
2) Endodermal cells actively move minerals into xylem, causing root pressure
Describe the movement of water up the xylem.
1) Root pressure
2) Capillary action (apoplast): adhesion
3) Transpiration pull (apoplast): cohesion/tension theory, changes in tree diameter, air drawn into broken vessel
How does sucrose concentration vary between source and sink?
Higher near the source than the sink.
Describe the non-specific defense.
Barriers like skin, normal flora, sebum. Mucous membranes. Lysozymes. Stomach acid. Expulsive reflexes. Clotting.
Phagocytosis: cytokines released by mast cells attract phagocytes. Phagocytes recognize non-human protein on pathogen. Phagosome. Phagolysosome. Macrophages form MHC with glycoproteins.
How do plants recognize an attack?
Receptors respond to molecules or chemicals. Stimulates release of signaling molecules. Genes switched on. Chemical and physical defenses, and alarm signals activated.
What are opsonins?
Chemicals which bind to pathogens and tag them. Phagocyte receptors bind to opsonins.
Describe an antibody.
Glycoproteins called immunoglobulins. Have 2 heavy and 2 light chains joined by disulfide bridges. Variable regions act as binding sites. Can act as agglutinins or anti-toxins.
Describe the cell-mediated specific response.
1) Cells become damaged
2) Macrophages become APCs
3) CD4 receptors on some T-helper cells bind to antigens on APC. T-helper cell activated. Produces interleukins.
4) Interleukins stimulate T clonal expansion (T-memory, T-killer, T-helper)
5) Interleukins activate phagocytes
6) Interleukins bind to receptors on B-lymphocytes. B-lymphocyte activated (clonal selection). Stimulates clonal expansion (plasma, memory)
Describe the humoral response.
1) Free antigen in blood
2) B-lymphocyte with complementary antibody becomes APC
3) CD4 receptors on some T-helper cells bind to antigens on APC. T-helper cell activated. Produces interleukins
4) Interleukins bind to receptors on B-lymphocytes. B-lymphocyte activated (clonal selection). Stimulates clonal expansion (plasma, memory)
What are the 4 types of immunity?
Which enzyme catalyzes the synthesis of peptide bonds?
Why do solvents like alcohols dissolve cell membranes?
The solvent is less polar than water, so the membrane does not retain its bilayer structure.
Describe the process of endocytosis.
Phagocytosis for solids and pinocytosis for liquids.
1) Cell membrane bends inwards when it comes into contact with the molecule.
2) Membrane enfolds around the molecule until it fuses to form a vesicle.
3) Vesicle pinches off and transports the molecule inside the cell.
What are the three types of stem cell?
Totipotent: Can differentiate into any cell and could form a whole organism. Pluripotent: Can form all tissue types but not whole organisms. Multipotent: Can form a range of cells within a certain type of tissue.
Why is phylogeny better that Linnaean classification?
Does not require discrete taxonomical groups. Not misleading in terms of time scale.
How does paleontology support evolution?
Simplest organisms in oldest rock strata. Sequence of organisms matches ecological links. Can look at anatomical relationships between living and extinct organisms. Unfortunately, the fossil record is not complete and many are damaged.
How does comparative anatomy support evolution?
Analogous structures are evidence for convergent evolution. Homologous structures like the pendactyl limb are evidence for divergent evolution. Comparative embryology also used.
Which molecules are examined in comparative biochemistry?
Cytochrome c, rRNA, and DNA bases.
What is the Hypothesis of Neutral Evolution?
Most variability occurs outside the functional region. Neutral substitutions occur at a fairly regular rate; they are not affected by natural selection.
What causes discontinuous variation?
What causes continuous variation?
Polygenes and environmental factors.
Describe the physical aspect of non-specific defense.
Skin flora. Sebum inhibits pathogen growth. Tracheal mucous. Lysozymes in tear destroy cell walls. Stomach acid. Expulsive reflexes.
What do platelets secrete?
Serotonin (makes smooth muscle in blood vessel walls contract to reduce blood supply) and Thromboplastin. Thromboplastin sets off the coagulation cascade. Epidermal cells grow beneath the scab, and collagen fibres are deposited for strength.
What is the inflammatory response?
A localized response resulting in pain, heat, and swelling. Mast cells are activated in damages tissue and release histamines. These dilate blood vessels, raising the temperature and thus preventing pathogens from reproducing. They also make the blood vessels more leaky, causing swelling. Mast cells release cytokines, too, which attract phagocytes.
1) Pathogens produce chemicals that attract phagocytes.
2) Phagocytes recognize non-self antigens.
3) Engulfs pathogen in a vacuole called a phagosome.
4) Phagosome combines with a lysosome to become a phogolysosome. The enzymes digest the pathogen.
5) In macrophages, the pathogen's antigens are combined with glycoproteins in the cytoplasm called the major histocompatibility complex. They are moved to the surface. The macrophage is an antigen presenting cell.
What does a macrophage look like?
Simple, round nucleus.
What does a neutrophil look like?
What are cytokines?
Cell signaling molecules released by mast cells and phagocytes. Cytokines attract phagocytes and can increase body temperature.
What are opsonins?
Chemicals which bind to pathogens and 'tag' them. They are release by phagocytes. Phagocytes also have opsonin receptors so they can bind to them and engulf the pathogen.
What does a lymphocyte look like?
Very large nucleus which takes up most of cell.
What are antibodies?
Y-shaped glycoproteins called immunoglobulins which bind to a specific antigen on a pathogen or toxin.
Describe the structure of an antibody.
Constant region made of 2 heavy polypeptide chains and 2 light polypeptide chains. Chains held together by disulfide bridges. Variable region provides a binding site to form an antigen-antibody complex.
In what 3 ways do antibodies work?
1) Act like opsonins; the antibody attracts phagocytes and the antigen-antibody complex is engulfed.
2) Act as agglutinins (clumping pathogens).
3) Act as anti-toxins, binding to toxins and neutralizing them.
Describe the humoral specific response.
1) B effector cells with complementary antibodies on their cell surface membrane bind to pathogens, engulf it, and become APCs.
2) T helper cells have CD4 receptors which make them bind to the APC (clonal selection).
3) The T helper cell releases interleukins to activate other B effector cells to divide into plasma cells and B memory cells (clonal expansion).
This process is used for antigens found outside of cells, and produces antibodies that are soluble in blood.
Describe the cell-mediated specific response.
1) T helper cells have CD4 receptors which bind to macrophage APCs.
2) The T helper cell releases interleukins which have a variety of effects:
3) Clonal expansion of T memory cells.
4) Clonal expansion of T killer cells.
5) Production of interleukins to stimulate phagocytes and B cells.
This process responds to cells which have been changed in some way.
What are interleukins?
A type of cytokine released by T helper cells to stimulate clonal expansion.
What can T helper cells expand into?
T killer cells (release perforin which makes holes in pathogen's membrane) or T memory cells (can divide to form T killer cells).
What can B effector cells expand into?
Plasma cells (make antibodies) or B memory cells.
What types of direct transmission are there?
Direct contact; inoculation; ingestion.
What types of indirect transmission are there?
Fomites; inhalation; vectors; soil contamination.
How do plants use callose against pathogens?
Callose is a polysaccharide containing B1,3 and B1,6 linkages between glucose molecules. It is deposited between the cell wall and membrane in infected and neighboring cells, phloem sieve plates, and plasmodesmata. Lignin is then added for strength.
How do plants use chemicals against pathogens?
Insect repellent and insecticides; antibacterials; antiseptics; proteins which disrupt bacterial and fungal membranes; lysozymes; chitinases; cyanide.
What are the names of the different layers that make up veins and arteries?
Endothelium, elastic layer, muscle layer, collagen
How does tissue fluid move out of and back into the capillaries?
At the arteriole end of the capillaries, hydrostatic pressure is greater than oncotic pressure, so fluid is forced out. At the venous end, however, the oncotic pressure is greater, so the fluid is drawn back in by osmosis.
How does lymph differ from blood and tissue fluid?
Contains less oxygen, fewer nutrients, and some fatty acids from the intestine.
How is lymph transported in lymph vessels?
Through the contraction of skeletal muscles and the action of valves.
What is positive cooperativity?
As soon as one oxygen molecule binds to a haem group, the haemoglobin molecule changes shape, making it easier for the next molecules to bind.
Why does the oxygen dissociation curve level out at the top?
All the haem groups are bound to oxygen; they are saturated and cannot take up any more.
How does an oxygen dissociation curve look (A) when studying fetal haemoglobin, and (B) when looking at the Bohr effect, when there is a higher partial pressure of CO2?
for fetal haemoglobin, the curve is shifted to the left. For the Bohr effect, the curve is shifted to the right.
How is CO2 converted to hydrogen carbonate inside red blood cells?
CO2 + H2O => H2CO3 (carbonic acid)
H2CO3 => H+ + HCO3-
The reverse takes place in the lungs
What is the chloride shift?
HCO3- ions move out of red blood cells into the plasma down a concentration gradient. To maintain the electrical balance, Cl- ions take their place.
Why do red blood cells convert CO2 into hydrogen carbonate ions?
To maintain a steep CO2 concentration gradient.
How is haemoglobinic acid formed?
Haemoglobin accepts the H+ ions produced when carbonic acid is broken down into H+ and HCO3-. Haemoglobinic acid acts as a pH buffer.
Tissue which has its own intrinsic rhythm.
Why are open circulatory systems not very efficient?
Steep diffusion gradients cannot maintained, and the amount of haemolymph supplied to different tissues cannot be varied.
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