Paper 1 recall Flashcards
What is the test for reducing sugars and what are some examples of reducing sugars?
Add Benedict’s reagent (copper sulphate- blue) to 2cm^3 solution of food and heat for 5 minutes to form a red insoluble precipitate (copper oxide)
All monosaccharides and some disaccharides (maltose)
What is the test for a non-reducing sugar?
Carry out reducing sugar test and if negative: add 2cm^3 of food solution to dil HCl and boil for 5 minutes, add NaOH to neutralise and test pH with litmus paper (must be alkaline), re-test with Benedict’s and orange-brown solution should form for positive test
What is the test for starch?
Place 2cm^3 of the sample being tested into a test tube, add 2 drops of iodine solution and shake, positive test will show blue-black colour
What are the features of starch?
May be branched or unbranched
Unbranched are wound into tight coil
What are the features of glycogen?
Shorter chains than starch and more highly branched
Why is glycogen more suitable storage for animals than starch?
More highly branched for enzymes to act simultaneously for respiration and animals have a higher metabolic rate so need rapid glucose release
How does the cellulose cell wall prevent the cell from bursting?
Exerts an inward pressure that stops any further influx of water, the rigidity allows cells to align for larger surface areas for photosynthesis
What are the roles of lipids?
Cell membranes, source of energy, waterproofing, insulation and protection
What are the properties of triglycerides?
High ratio of energy storing carbon-hydrogen bonds to carbon atoms, low mass to energy ratio, large, non-polar, high ration of hydrogen to oxygen meaning the release water
What is the test for lipids?
2cm^3 of food solution add 5cm^3 of ethanol and shake thoroughly, add 5cm^3 water and allow shake gently, a milky-white emulsion appears for positive test
What is the secondary structure of proteins?
The positive charge of NH group and negative charge of C=O causes weak hydrogen bonds to form that create alpha helix or beta pleated sheet
How are ionic bonds formed in tertiary structure of proteins?
Formed between carboxyl and amino groups that aren’t involved in peptide bonds, they are relatively strong but easily broken by change in pH
What is the test for proteins?
Add Biuret reagent and a purple solution indicated positive test
What is the induced fit model for enzyme action?
The proximity of the substrate leads to a change in the enzyme shape that forms the functional active site, when the enzyme changes shape it puts a certain strain on bonds in the substrate, lowering the activation energy
What are the two ways changes in pH can alter how enzymes work?
Alters the charges on amino acids and breaking of ionic bonds in the tertiary structure
Why is DNA stable?
Phosphodiester backbone protects the more chemically reactive bases inside the double helix and hydrogen bonds between bases form bridges C-G forms 3 so the more C-G : A-T the more stable
How is ATP used by an organism?
Metabolic processes, movement, active transport, secretion and activation of molecules (glycolysis)
What are the features of water?
Dipole, hydrogen bonds, high specific heat capacity, high latent heat of vaporisation, high cohesion and surface tension in water
What are the importances of water?
Metabolite, raw material, hydrolysis, physiological solvent for O2, control of temperature, transparent for photosynthesis in water
What are some inorganic ions and what are their functions?
Fe2+ in haem, PO4 3- in ATP and DNA, H+ in determining pH and Na+ in co-transport
What are the 3 conditions for solutions used in cell fractionation?
Cold- reduce enzyme activity
Same water potential- prevent bursting organelles
Buffered- maintain pH for organelle structure
What are the steps in cell fractionation?
Homogenation: cell placed in homogeniser to release organelles, then the homogenate is filtered to remove debris and whole cells
Ultracentrifugation: spun in centrifuge at lowe speed and organelles form pellets from high to low mass as speed increases, supernatant removed and transferred to new tube before spinning again
What are the limitations of TEM?
Difficult to prepare specimen for resolution, may destroy the specimen, vacuum, must be dead, complex staining must be thin, artefacts may be present in the photomicrograph
How does SEM work?
All limitations of TEM, only it forms 3D images from computer analysis as the electron scatter and bounce of specimen surface, this has a lower resolving power then TEM
What does the nucleolus do?
Manufactures rRNA and assembles the ribosomes, there may be more than one nucleolus in each nucleus
What are the functions of RER?
Large SA for the synthesis of proteins and glycoproteins and provide a pathway for the transport of materials, especially proteins throughout the cell
What are the functions of the SER?
Synthesise, store and transport lipids and carbohydrates
What are the functions of the Golgi apparatus?
Add carbs to proteins to form glycoproteins, produce secretory enzymes, secrete carbohydrates for cell walls, transport, modify and store lipids and form lysosomes
When are lysosomes formed?
When Golgi apparatus vesicles contain proteases and lipases and lysozymes
What are the functions of lysosomes?
Hydrolyse ingested phagocytic material, release enzymes outside cell, digest worn-out organelles and autolysis
What are the cell walls of algae, fungi and bacteria made up of?
Algae- cellulose and/or glycoproteins
Fungi- chitin, glycan and glycoproteins
Bacteria- murein
What is the tonoplast and what does it contain?
The single membrane around a vacuole and a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments
What’s the structure of mitochondria?
Double membrane with the inner folding to form cristae, to provide a large SA for enzyme attachment, the matrix is the rest of the mitochondria and consists of the proteins, lipids, ribosomes, DNA and many respiration enzymes
What’s the structure of chloroplasts?
Double plasma membrane, grana are stacks of thylakoids containing chlorophyll, some are joined by extensions, the stroma is the fluid-filled matrix where the second stage of photosynthesis happens, starch grains can be found here
What are the features of prokaryotic cells?
No nucleus, no histones, may contain plasmids, no membrane-bound organelles, smaller ribosomes, murein cell wall, may contain outer mucilaginous layer called capsule
What’s the structure of general viruses?
Nucleic acids contained within a protein capsid
What happens in prophase of mitosis?
Centrioles move to opposite poles of the cell and spindle fibres develop, spanning the whole cell to form the spindle apparatus, nuclear envelope breaks down and chromosomes are left free and drawn to the equator by
spindle fibres attached to centromere
What happens in metaphase of mitosis?
Chromosomes are seen as two chromatids joined by centromere, they arrange across the equator of the cell
What happens in anaphase of mitosis?
Centromeres divide into two, spindle fibres pull the individual chromatids rapidly towards their respective poles and they’re now considered chromosomes
What happens in telophase and cytokinesis?
Chromosomes become longer and thinner, disappearing altogether, leaving chromatin, spindle fibres disintegrate and nuclear envelope and nucleolus reform, cytoplasm divides
Why may proteins be embedded in the membrane but not span across it?
To provide mechanical support, or act as cell receptors for molecules such as hormones
What are the functions of cholesterol in membranes?
Reduce lateral movement by pulling together fatty acid tails, make the membrane less fluid at high temp and prevent leakage of water and dissolved ions from the cell as they are very hydrophobic
What are the functions of glycolipids?
Act as recognition sites, help maintain the stability of the membrane and helps attach to other one and so form tissue
What are the functions of glycoproteins?
Act as recognition sites, help cells to attach to one another and form tissues and allows cells to recognise one another e.g. lymphocytes
How do protein channels control the entry and exit of substances?
Particular ions bond with the protein causing changes in shape, it is always open at one end and closed at the other
How can the rate of movement across membranes be increased?
Microvilli
Increase the number of protein channels and carrier proteins in a given area of membrane
Why is co-transport an indirect form of active transport?
The concentration gradient of sodium ions drives the movement, rather than ATP
What cells must an immune system be able to recognise?
Pathogens, non-self material, toxins and abnormal body cells such as cancer
How do lymphocytes recognise cells belonging to the body in foetus?
Foetus rarely become infected as they are protected by the placenta, lymphocytes within the foetus collide constantly with other cells, meaning they collide exclusively with own body cells, complimentary lymphocytes either die or are suppressed
How do lymphocytes recognise cells belonging to the body in adults?
Once produced in the bone marrow, they initially encounter self anit-gens and any that show immune response under controlled cell death (apoptosis) before they can differentiate
What are B lymphocytes?
Mature in the Bone marrow, associated with humoural immunity (antigens) in bodily fluids or ‘humour’ such as blood plasma
What are T lymphocytes?
Mature in the Thymus gland, associated with cell-mediated immunity
What cells can become APCs for cell-mediated immunity?
Phagocytes, cells infected by viruses, transplanted cells and cancer cells
Why is it called cell-mediated immunity?
T lymphocytes only respond to antigen presented on body cells rather than antigens in the body fluids
What do T cells do once they have been cloned?
Activate Tc cells, stimulate phagocytes, stimulate B cells and develop into memory cells
How do Tc cells kill infected cells?
Produce perforin which creates holes in the cell surface membrane
What’s the first stage in humoural immunity?
B cell matches to complimentary antigen, which is then taken up by endocytosis and the antigen is presented on B cell surface, Th cell then stimulates B cell to divide
What is the variable region of antibodies?
The binding sites
What are the advantages of monoclonal antibodies in medical treatments such as herceptin for breast cancer?
Non-toxic and highly specific leading to fewer side effects than the other treatments
What is passive immunity?
Introduction of antibodies from an outside source like anti-venom, no memory cells produced but fast working
What is active immunity?
Stimulating the production of antibodies either naturally from infection or artificially from vaccines
What factors influence the success of vaccination programmes?
Economic viability, side-effects, means of production, storage and transport, means of administering and herd immunity
Why may vaccination not eliminate disease?
Vaccine fails in individuals, develop disease immediately after vaccination, mutations, large number of varieties of the disease or individual objections to vaccines
What is the procedure for the ELISA test?
Apply the sample to a surface to which all the antigens in the sample will attach, wash, add antibody specific to antigen and leave, wash, add second antibody (with enzyme attached) that binds with first, add colourless substrate to create coloured products, the amount of antigen present is relative to the intensity of the colour
How do antibiotics act on bacteria?
Prevent the functioning of enzymes required for synthesis and assembly of peptide cross-linkages in cell wall, causing bursting by osmosis
What are the features of specialised exchange surfaces?
Large SA relative to volume, thin for short diffusion distance, selectively permeable for selected materials to cross, movement of the environmental medium (water flow or ventilation) and a transport system to maintain gradients
What’s the structure of insects gas exchange system?
Internal network of tubes called tracheae which divide into smaller dead-end tubes called tracheoles, these extend through the whole body of the insect bringing oxygen directly to respiring tissues, shortening diffusion distance
Spiracles on the body-surface are opened and closed by valves to prevent water loss, they lead into tracheae
How do respiratory gases move in and out of the tracheal system?
Along a diffusion gradient, mass transport (contraction of muscles to squeeze trachea) and the ends of tracheoles are filled with water
What’s the structure of the gills?
Stacked up with gill filaments with gill lamellae perpendicular to increase surface area
What features have insects evolved to limit water loss?
Small SA:V, waterproof coverings (rigid outer skeleton of chitin) and spiracles
How are some xerophytes adapted to minimise water loss?
A thick cuticle, rolling up of leaves, hairy leaves, stomata in pits or grooves and reduced SA:V ratio of leaves
What’s the structure of the alveoli?
Lined with epithelium with collagen and elastic fibres between them to stretch as they fill with air then spring back to expel the CO2
What lines the trachea walls of mammals?
Muscles, ciliated epithelium and goblet cells
What’s the full process of inspiration?
External intercostal muscles contract, internal intercostal muscles relax, ribs pulled up and outwards to increase thorax volume, diaphragm contracts and flattens to increase thorax volume, air pressure decreased meaning atmospheric pressure greater to air forced into lungs
Why is diffusion of gases between alveoli and blood rapid?
RBC slowed as they pass through pulmonary capillaries, distance between alveolar air and RBC reduced as RBC flattened against the wall, thin walls, large total SA, ventilation and rich blood supply
What enzymes are secreted by the pancreas?
Proteases, lipase and amylase
What do mineral salts in the saliva do?
Maintain pH neutral as this is optimum for amylase
What are triglycerides hydrolysed into by lipases?
Fatty acids and monoglyceride
What is emulsification?
Splitting of lipids into tiny droplets of micelles by bile salts produced in the liver to increase SA for lipases
How are micelles absorbed by the ileum?
They come into contact with the cell epithelium to break down releasing monoglycerides and fatty acids, these are non-polar so diffuse across the cell-surface membrane, they’re then transported to the ER of the epithelium cell to reform triglycerides, they then associate with cholesterol and lipoproteins to form chylomicrons, these exit epithelium cell by exocytosis and enter lymphatic capillaries into the blood system
What does it mean if haemoglobin has a high affinity for oxygen?
Takes up oxygen easily but releases it less easily
Why does the first oxygen molecule struggle to bind to haemoglobin?
The shape of haemoglobin has the polypeptide subunits closely united
How does CO2 impact haemoglobin affinity for oxygen?
Bohr shift to the right reduces the affinity causing unloading easier as pH is lowered causing haemoglobin to change shape
What are the features of a mammalian circulatory system?
Closed, double
Vessels confine blood
High body temp and metabolism
What happens during artial systole?
Contraction of the atrium walls, along with the recoil and relaxation of the ventricle walls, forces the remaining blood into the ventricles from the atria, throughout this stage the muscle of the ventricle walls remains relaxed
What happens during ventricular systole?
Ventricle walls contract simultaneously increasing pressure and forcing atrioventricular valves shut, causing further increase in pressure, once larger than the aorta and pulmonary artery blood is forced out,
How do artery and vein structures compare?
Arteries have a thicker muscular layer to allow constriction and dilation
Thicker elastic layer to allow stretch at systole and relaxation at diastole to maintain pressure
Greater overall thickness to resist bursting
No valves
How does relative structure of arteriole compare with arteries?
Thicker muscle wall as it need to constrict to control flow rate into capillaries and lower pressure
Thinner elastic layer as pressure is lower
Why are there spaces between the endothelial cells of capillaries?
To allow WBC to escape to deal with infections in tissues
What does tissue fluid contain?
Watery liquid containing glucose, amino acids, fatty acids, ions in solution and oxygen
How is tissue fluid formed?
High hydrostatic pressure at the arteriole end of capillaries forces tissue fluid out of the blood plasma, this is ultrafiltration as it leaves proteins and cells in the blood as they’re too large to pass
How does tissue fluid return to the circulatory system?
Low hydrostatic pressure in the capillaries and higher hydrostatic pressure of tissue fluid so forced back into the capillaries, also blood has lower water potential so water moves from tissue fluid in by osmosis
What happens to the remaining tissue fluid?
Carried back via the lymphatic system to larger vessels that drain into the blood via two ducts that join veins close to the heart
How are the contents of the lymphatic system moved?
Contraction of skeletal muscles applies pressure on the vessels and hydrostatic pressure
How does water move across the cells in a leaf?
Mesophyll cells lose water to the air spaces via evaporation from energy supplies by the sun, this lowers the water potential causing water to move in from neighbouring cells, this establishes a gradient that pulls water up from the xylem
How does water move up through the xylem?
Hydrogen bonds in water forms cohesion which creates a long column unbroken, this creates the transpiration pull which puts the xylem under tension as there’s a negative pressure in the xylem, hence cohesion-tension theory
What is some evidence for the cohesion-tension theory?
Trunk of the tree shrinks in the day as there is more transpiration so more tension, if the xylem vessel is broken and air enter, transpiration cannot occur and when xylem vessels are broken, water does not leak out, instead air is drawn in
What’s the process in the transfer of sucrose into sieve elements from photosynthesising tissue?
Sucrose is created at the SOURCE, which then diffuses by facilitated diffusion into companion cells, H+ are actively transported from companion cells into the spaces between cell walls, sucrose is then co-transported into the sieve tube elements
What’s the process for the mass flow of sucrose through sieve tube elements?
Sieve tube have a lower water potential causing osmosis from the xylem into sieve tube, creating high hydrostatic pressure, at respiring cells (SINK) sucrose is used or stored, causing active transport of sucrose into the cells and osmosis as water potential lower than sieve tube, lowering the hydrostatic pressure in the sieve tube
What’s the process for the transfer of sucrose from the sieve tube elements into storage or other sink cells?
The sucrose is actively transported by companion cells out of the sieve tube and into the sink cells
What do genes code for?
The amino acid sequence of polypeptides, rRNA and tRNA
What does the ‘degenerate code’ mean?
Most amino acids are coded for by more than one triplet
What are features of the genetic code?
Universal and non-overlapping
What is a codon?
The sequence of three bases on mRNA that codes for a single amino acid (are complimentary to a triplet on DNA)
What is the genome?
The complete set of genes in a cell
What is the proteome?
Full range of proteins produced by the genome
What is an anticodon?
Sequence of three organic bases on a tRNA molecule, which is complimentary to mRNA codons
Where does splicing occur and what does it remove?
Occurs in the nucleus to remove introns
What’s the process of translation?
Ribosome becomes attached at that starting codon on mRNA, tRNA with complimentary anticodon pairs up at the ribosome, a tRNA with complimentary anticodon pairs up with the next codon, the ribosome moves along the mRNA and the amino acids are joined by a peptide bond with enzyme and ATP, as it moves the first tRNA molecule is released to collect another amino acid and the third amino acid joins the chain, when the ribosome reaches the stop codon, the ribosome mRNA and tRNA all separate and the chain is complete
What are chromosome mutations?
Changes in the whole number or structure of chromosomes
What is polyploidy and where does it occur most common?
When organisms have three or more sets of chromosomes, rather than the usual two in homologous chromosomes, meaning they’re polyploid rather than diploid it occurs mostly in plants
What is non-disjunction?
Individual homologous chromosomes failing to separate during meiosis
What’s the summary for the first meiotic division?
Homologous chromosomes pair up and their chromatids wrap around each other to allow crossing over, then the homologous pairs separate
What’s the summary for the second meiotic division?
Chromatids move apart for division
How does meiosis improve genetic diversity?
Independent segregation and crossing over
What is independent segregation?
The arrangement of homologous chromosomes across the equator is random, meaning the combination of maternal/paternal chromosomes in the resulting daughter cells is a matter of chance, this also creates new genetic combinations, improving variety
What happens in crossing over?
The chromatid pair up and become twisted around one another, creating tension causing portions of chromatids to break off and rejoin the chromatid partner (recombination) causing exchange of alleles
How can we calculate the number of possible combinations of chromosomes in a fertilised cell?
(2^n)^2 where n= the number of homologous pairs of chromosomes in an organism
What is the phenotype?
The observable physical and biochemical characteristics of an organism
What type of adaptations can occur in natural selection?
Anatomical (short ears), physiological (chemical defence) and behavioural (migration of swallows from UK to Africa to avoid food shortages)
Why is courtship behaviour important?
Recognise members of their own species, identify mates that are capable of breeding, forms pair bonds, synchronise mating and become able to breed in physiological state
How does phylogenetic classification occur?
Based upon the evolutionary relationship between organisms and their ancestors, classifies species into groups with shared features and arranges the groups into hierarchy
What are the 3 domains?
Archaea, Bacteria and Eukarya
What is phylogeny?
The evolutionary relationships between organisms
What is ecosystem diversity?
The range of different habitats from a small local habitat to the whole earth
What is species richness?
The number of different species in an area at a given time
How can agriculture impact biodiversity?
Removal of hedgerows, monocultures, filling ponds and draining marsh, overgrazing, pesticides and fertilisers, effluent escape and lack of crop rotation and intercropping
How can genetic biodiversity be measured?
DNA base sequence comparison, mRNA base sequence comparison and amino acid sequence in proteins comparison
