Biology paper 1 questions and their verified answers, Exams of Biology

Download Biology paper 1 questions and their verified answers and more Exams Biology in PDF only on Docsity! Biology paper 1 questions and their verified answers Large molecules often contain carbon. Why? - Verified Answer they can readily form bonds with other carbon atoms. This forms a 'backbone'. Other atoms can then attach. Describe benedicts test for reducing sugars - Verified Answer add equal volumes of the sugar sample and benedicts reagent. Heat the mixture in a water bath for 5 minutes. Brick red precipitate will form. What is a reducing sugar? - Verified Answer a sugar that can reduce (give electrons to) another chemical. Describe the benedicts test for non-reducing sugars - Verified Answer with food sample, add an equal volume of dilute hydrochloric acid in a test tube. Place test tube in water bath for 5 mins. Add sodium hydrogen carbonate solution. Heat resulting solution with an equal volume of benedicts. Solution for 5 minutes. Turns orange/brown. What does dilute hydrochloric acid do in the benedicts test for non-reducing sugars? - Verified Answer it hydrolyses any disaccharide into monosaccharides, thus also forming reducing sugars. Describe the structure of starch - Verified Answer chains of alpha glucose Some chains are branched= amylopectin Some chains are coiled= amylose What purpose does the structure of amylose serve? - Verified Answer makes the molecule compact so it is stored more easily. What purpose does the structure of amylopectin serve? - Verified Answer more surface area for enzymes to work on, thus glucose molecules can be released at a much quicker rate. How is the structure of starch suited to its function? - Verified Answer 1. Starch is insoluble so it doesn’t affect water potential 2. It is large enough that it doesn’t diffuse out of cells 3. Compact enough so that a lot of it can be stored in a small space 4. Branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released How is the structure of glycogen suited to its function? - Verified Answer 1. Insoluble, so no effect on water potential of cell 2. Insoluble, so doesn’t diffuse out of cells 3. Compact, a lot of it can be stored in a small space 4. Very highly branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released Why do animals need highly branched glycogen? - Verified Answer because animal’s metabolic rate is faster than plants and so needs glucose to be released quicker. Describe the structure of cellulose - Verified Answer made up of straight chains of beta glucose The chains are parallel to each other, so H bonds form cross-linkages All the H bonds together strengthens the cellulose Forms micro fibrils Draw alpha and beta glucose - Verified Answer How does the structure of triglycerides relate to their properties? - Verified Answer 1. Triglycerides have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms, so it’s a good source of energy. 2. Low mass to energy ratio, so they’re good energy storage molecules. 3. Large and non-polar, therefore insoluble, therefore don't affect osmosis. 4. High ratio of hydrogen to oxygen atoms, so can release water when oxidized, hence provide a source of water What are the roles of lipids? - Verified Answer 1. Source of energy 2. Waterproofing 3. Insulation 4. Protection How does the structure of phospholipids relate to their properties? - Verified Answer 1. Polar, therefore will position itself to form a bilayer 2. The structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. These are important in cell recognition. Draw the structure of an amino acid - Verified Answer Draw how a dipeptide forms - Verified Answer What is meant by 'primary sequence' of a protein - Verified Answer The unique sequence of amino acids that make up a protein or polypeptide chain? What is the function of SER? - Verified Answer synthesises, stores and transports lipids and carbohydrates What is the function of RER? - Verified Answer provides a large surface area to synthesize proteins and glycoproteins Provides a transport pathway for materials throughout the cell What is the function of Golgi apparatus? - Verified Answer add carbs to proteins to form glycoproteins Produce secretory enzymes Secrete carbohydrates Transport, modify and store lipids Form lysosomes What is meant by 'organ'? - Verified Answer a combination of tissues that are coordinated to perform a variety of functions. Describe binary fission - Verified Answer the circular DNA molecule replicates and both copies attach to the cell membrane. Plasmids also replicate Cell membrane grows between the two DNA molecules, dividing the cytoplasm into two. A new cell wall forms between the two DNA molecules. Two daughter cells are produced, each with a single copy of circular DNA and a variable number of plasmids. How do viruses replicate? - Verified Answer they attach to their host cell with their attachment proteins. Nucleic acids are injected into host cell. The genetic info contains "instructions" for the host cells metabolic processes to start producing the viral components, which are assembled into new viruses. Describe cell mediated immunity - Verified Answer 1. Phagocytes inject pathogens. 2. The phagocyte places antigens from pathogen on its cell surface membrane, so it becomes an antigen presenting cell. 3. Receptors of T-helper cells have a complimentary fit to these antigens. 4. This attachment activates T cells to divide rapidly by mitosis and form a clone of genetically identical cells. 5. The cloned T cells: A. develop into memory cells B. stimulate phagocytosis C. stimulate B cells to divide and secret their antibody D. activate cytotoxic T cells. Describe humoral immunity - Verified Answer 1. The surface antigen of a pathogen is taken up by B cell 2. The B cell processes it and presents the antigen on its surface 3. T-helper cells attach to the processed antigens, thus activating the B cell 4. B cells divide by mitosis to produce a clone of plasma cells 5. These secrete the specific antibody that can bind to the pathogens antigen 6. The antigens destroy the pathogen 7. Some B cells develop into memory cells What is passive immunity and how is it produced? - Verified Answer produced by the introduction of antibodies into individuals from an outside source. Immunity is acquired immediately. No contact with pathogen/s needed. Short term immunity: antibodies aren't replaced when broken down, memory cells not formed. E.g. anti-venom What is active immunity and how is it produced? - Verified Answer produced by stimulating the production of antibodies by the individuals own immune system. Contact with pathogen/s needed. Immunity takes time to develop Natural active immunity - Verified Answer results from an individual becoming infected with a disease under normal circumstances. Long term Body produces its own antibodies Artificial active immunity - Verified Answer involves inducing an immune response in an individual WITHOUT them suffering the symptoms of the disease. E.g. vaccinations Memory cells produced What are the features of a successful vaccination programmer? - Verified Answer 1. Vaccine must be economically available in sufficient quantities 2. Must have few side effects 3. Available means of producing, storing and transporting the vaccine 4. Must be possible to produce herd immunity Why can vaccinations not be effective? - Verified Answer 1. Immunity may not be induced in people with defective immune systems 2. Individuals may develop disease after the vaccination but before their immunity levels are high enough to prevent it. 3. Pathogen may mutate frequently, so vaccines can’t prevent them from harming people 4. Certain pathogens conceal themselves from the body's immune system e.g. by hiding within cells 5. Individuals may object to vaccinations due to religious, ethical or medical reasons What are antibodies made up of? - Verified Answer 4 polypeptide chains: - 2 are 'heavy chains' - 2 are 'light chains' Variable (binding) region How does HIV replicate? - Verified Answer HIV attaches most commonly to T-helper cells The protein capsid fuses with the cell-surface membrane The RNA and enzymes of HIV enter T-helper cell Reverse transcriptase converts the viruses RNA to DNA The new DNA enters nucleus is inserted into T-h cell’s DNA HIV DNA in nucleus creates mRNA using the cells enzymes, which contains the instructions for making new viral proteins. The viral proteins are assembled into new HIV Features of specialized gas exchange surfaces - Verified Answer - a large surface area to volume ratio - Very thin therefore short diffusion pathway - Selectively permeable - A transport system How do insects carry out gas exchange? - Verified Answer 1. Insects contract their muscles, squeezing the trachea, enabling mass movement. 2. A diffusion gradient is established 3. The ends of tracheoles are in contact with individual cells, contain a small amount of fluid in which the gases are dissolved. The fluid is drawn into the muscle tissue during exercise. This increases the surface area of air in contact with the cells. Gases diffuse in through the spiracles and down the tracheae and tracheoles. Describe and explain the countercurrent exchange principle - Verified Answer -the blood and the water flow in opposite directions -blood that is loaded with O2 meets water, which already has maximum O2 -blood with little O2 meets with water with O2 removed -so, diffusion concentration gradient established and maintained across the entire width of the gill lamellae -so, 80% of O2 in water absorbed into fish blood How does the structure of a plant leaf link to gas exchange? - Verified Answer -all cells are close to stomata, and therefore surface, therefore a short diffusion pathway -inter-connecting air spaces in the mesophyll so that gases can readily contact mesophyll cells describe and explain why plant stomata links to gas exchange and its benefits - Verified Answer stomata are like minute pores, on the underside of leaves. Each has guard cells, which control the rate of gas exchange Apoplast pathway: water enters the root by entering the spaces in cell walls. Water moves up xylem due to H bonding in water. Water travels until it reaches the casparian strip, where water needs to travel via symplast pathway. What is plasmodesmata? - Verified Answer strands of cytoplasm linking one cell to another that passes through pores in cellulose cell walls Explain cohesion-tension theory - Verified Answer water is drawn from cell to cell by osmosis. It moves across the root cortex to keep a constant column of water. This creates 'tension' on the column of water in the xylem. Water shows cohesion due to its H bonding. This makes the column very strong. So, water is pulled up the xylem to replace the water lost by evaporation. Water moves between the cells of a leaf along the water potential gradient. What is the role of companion cells? - Verified Answer they load/unload organic solutes into the sieve tube Describe the transfer of sucrose into sieve elements - Verified Answer sucrose is manufactured from photosynthesizing cells. It diffuses by facilitated diffusion from photosynthesizing cells to companion cells, down a concentration gradient. H+ actively transported into the spaces between cell walls. H+ diffuses into sieve tube elements. Sucrose molecules also transported with them, through co-transport. What is a 'source' cell? - Verified Answer cells that photosynthesize and make sugars What is a 'sink' cell? - Verified Answer cells that use/store organic solutes Explain mass flow hypothesis - Verified Answer 1. Sugars build up at source, lowering water potential of source cells. 2. Water therefore enters cells by osmosis. 3. Sugars are then actively transported into sieve tubes by transfer cells 4. This lowers water potential in sieve tube, so water enters by osmosis. 5. This causes high pressure potential at source At sink, sugars are unloaded by companion cells 6. This raises water potential How can you investigate mass flow using aphids? - Verified Answer 1. Cut across their mouthparts. The mouthparts act as a sampling tube that they collect the phloem contents. 2. If the phloem is punctured with a hollow tube then the sap oozes out, showing that there is high pressure (compression) inside the phloem (this is how maple syrup is tapped). 3. If the xylem is punctured then air is sucked in, showing that there is low pressure (tension) inside the xylem. How can you investigate transport using radioactive tracers? - Verified Answer a plant is supplied with 14C, which becomes incorporated into organic substances in the plant. The plant is then frozen in liquid nitrogen to kill and fix it quickly, and placed onto photographic film in the dark. The resulting autoradiograph shows the location of compounds containing 14C. This shows that organic compounds (presumably sugars) are transported downwards from the leaf to the roots. Define genome - Verified Answer the complete set of genes in a cell Define proteome - Verified Answer the full range of proteins that a cell is able to produce Describe the process of transcription - Verified Answer DNA unwinds and separates (H bond between bases broken) Template strands form due to exposed bases Free RNA nucleotides align with template strand through complimentary base pairing RNA polymerase bonds the nucleotides together, forming a molecule of mRNA complimentary to the DNA MRNA leaves nucleus via nuclear pore Splicing occurs- introns removed Describe the process of translation - Verified Answer 1. MRNA associates with a ribosome in the cytoplasm 2. tRNAq molecules with complimentary anticodons align with the first 2 mRNA codons 3. Peptide bond forms between the amino acid molecules 4. The tRNA that bound to the first codon is free to leave the ribosome 5. The ribosome moves along the mRNA by one codon and now a new tRNA with a complimentary anticodon enters the ribosome 6. This continues until the ribosome reaches a stop codon The 2 mechanisms that mean that meiosis will result in genetic variation - Verified Answer independent segregation Crossing over What happens during independent segregation? - Verified Answer during meiosis 1 Each chromosome aligns with its homologous partner at the equator of the cell The combination of maternal/paternal chromosomes aligns randomly One chromosome of each pair goes to daughter cell- by chance What happens during crossing over? - Verified Answer when the chromosomes align, the chromatids of each pair become twisted around one another Tension is built and portions of chromatids are broken off, which rejoin with the chromatid of the homologous partner So, new genetic combinations of maternal and paternal alleles are produced What is ATP made up of? - Verified Answer adenine Ribose 3 phosphates How does ATP store energy? - Verified Answer has 3 phosphates, the bonds between these are unstable and so have a low activation energy, hence easily broke. When they break, they release energy. What does ATP synthase catalyze? - Verified Answer the formation of ATP from ADP In what scenarios is ATP reformed? - Verified Answer during photosynthesis, in chlorophyll containing plants During respiration (oxidative phosphorylation) Substrate level phosphorylation Why is ATP a good immediate energy source in a cell - Verified Answer the instability of the phosphate bonds? Each ATP molecule releases less energy than glucose molecule, and so is smaller and more manageable The hydrolysis of ATP to ADP is a single reaction that releases immediate energy What energy requiring processes need ATP? - Verified Answer metabolic processes Movement Active transport Secretion Activation of molecules Which has a longer wavelength: light or a beam of electrons? - Verified Answer light What are the two types of electron microscope? - Verified Answer transmission electron microscope Scanning electron microscope How does a transmission electron microscope work? - Verified Answer it has an electron gun which produces a beam of electrons This is focused onto a specimen by condenser electromagnets The beam passes through the specimen Some parts of the specimen absorb the electrons and appear dark and vice versa An image is produced Why can’t the highest resolution images not be produced by TEM? - Verified Answer there are difficulties preparing the specimen, which can limit resolution A higher energy electron beam may destroy the specimen How does a scanning electron microscope work? - Verified Answer it directs an electron beam onto a specimen surface rather than penetrating it.