Biology Long Answer Exam Questions
Explain the process in active transport.
- Active transport uses ATP to pump molecules from a lower concentration gradient to a higher concentration gradient - Large molecules and ions are transported - Particle enters pump from lower concentration - Phosphorylation occurs and adenosine triphosphate becomes adenosine diphosphate - Pump changes shape - Particle is released and pump returns to its original shape
Explain thermal properties of water.
- Hydrogen bonds between water resists change - High latent heat of vaporization (water to steam, vice versa) - High specific heat capacity (energy required to change temperature) - High latent heat of fusion (ice to water, vice versa) - Therefore, water provides a stable environment for aquatic organisms
Draw and label a cell membrane
- Phospholipid bilayer - Hydrophobic tail/ (non-polar) - Hydrophilic tail/ (polar) - Integral protein - Cholesterol - Peripheral protein - (bonus glycoprotein)
Describe the evidence supporting the endosymbiotic theory for mitochondria and chloroplasts.
- They have their own DNA (which is naked and circular) - They have ribosomes that are similar to prokaryotes (70s ribosomes) - They have a double membrane and the inner membrane has proteins similar to prokaryotes - They are roughly the same size as bacteria and are susceptible to antibiotic - They transcribe their DNA and use the mRNA to synthesize some of their own proteins - They can only be produced by division of pre-existing mitochondria and chloroplasts
Describe the function of lipids.
-Structure: Phospholipids are a main component of cell membranes -Hormonal signaling: Steroids are involved in hormonal signaling -Insulation: Fats in animals can serve as heat insulators -Protection: Triglycerides may form a tissue layer around many key internal organs and provide protection against physical injury -Storage of energy: Triglycerides can be used as long-term energy storage source
Distinguish between aerobic and anaerobic respiration.
Aerobic Respiration: -(fermentation)produces lactic acid in humans -(fermentation) produces ethanol and CO2 in yeast -occurs in cytoplasm of the cell -recycles NADH (NAD+) Anaerobic Respiration: Pyruvate transported to mitochondria Further oxidized to CO2 and water ( in krebs cycle) Produces a large amount of ATP compared to aerobic Can use other compounds/ lipids/ amino acids for energy
Distinguish between the structure of plant and animal cells.
Animal Cells Cell membrane Small vacuoles No chloroplast Lysosomes Stores glycogen Plant Cells Cell membrane and cell wall One large vacuole Chloroplast Stores starch
Describe the use of carbohydrates and lipids for energy storage in animals.
Carbohydrates: - Stored as glycogen (liver, muscle cells) - Short term energy storage - More soluble in water so transported easily - More easily digested in the body than lipids so energy is released faster Lipids: - Stored as fats in animals - Long term energy storage (x2) - More energy than carbohydrates - Insoluble in water, difficult to transport - Strong bonds in lipids make it harder to digest
Outline and illustrate the difference between cis and trans fatty acids.
Cis: - Common in nature - H-atoms on the same side of two C-atoms - Loosely packed - Cis-isomer triglycerides are liquid at room temp. Trans: - Rare in nature - H-atoms on the different side of two C-atoms - Closely packed - Trans-isomer triglycerides are solid at room temp.
Explain cohesive and adhesive properties of water.
Cohesive: - Hydrogen bonds between polar water molecules cause them to cohere - Negative dipole charge on O and positive on H - Water molecules stick to each other - Surface tension between molecules allows animals such as water striders to walk over the surface of ponds even though they are denser than water (optional) Adhesive: - Hydrogen bonds between polar water molecules and any other charged or ionic substance causes them to adhere - Allows for transport in an aqueous environment - Dipolarity of water makes them adhere to surfaces that are polar and therefore hydrophilic
Explain how the rate of photosynthesis can be measured directly and indirectly.
Direct measurement - CO2 uptake Placing the plant in a closed space with water CO2 then reacts with the water producing bicarbonate H+ ions which increases the acidity of the solution INcreased CO2 uptakes leads to an increase in pH and ultimately increases the rate of photosynthesis Direct measurement - Oxygen Production Aquatic plants can be submerged in water in a closed system or space with a gas syringe attached Alternatively, gas volume can be measured by displacing water in an inverted measuring cylinder or by simply counting bubbles Oxygen probes can be used with terrestrial plants kept in closed environments to measure increases in oxygen concentration Indirect measurement - change in biomass Glucose production can be indirectly measured by a plant's dry biomass Starch levels in a plant (glucose is stored as starch) Can be identified by staining with iodine solution = quantified using a colorimeter
Explain the difference between active transport and facilitated diffusion.
Facilitated Ions go from low to high concentration No energy required Presence of ion changes shape Active Ions go from high to low concentration Energy is required ATP is required to change shape
Outline the evidence for evolution produced by the fossil record, selective breeding of domesticated animals and homologous structures.
Fossils Fossils had similarities with existing organisms Showed over time organisms changed Selective breeding Domestic breeds share similar characteristics with wild breeds and still able to breed with them Selected wild species with desirable characteristics, were bred New species are created Shows that animals can evolve rapidly Homologous Structures Homologous structures within species Bones in limbs common with many species Shows that these bones evolved from one common ancestor
Complete the table to describe each of different functions that proteins have in and outside of cells.
Function Description Key examples Rubisco Tensile strengthening Some such as insulin, FSH, and LH are proteins, but hormones are chemically very diverse. Receptors Catalysis: Different enzymes to catalyse specific chemical reactions within the cell or outside it. Rubisco: Tensile strengthening Fibrous proteins give tensile strength needed in skin, tendons, and ligaments, and blood vessel walls. Collagen: Hormones Some such as insulin, FSH, and LH are proteins, but hormones are chemically very diverse. Insulin Receptors Binding sites in membranes and cytoplasm for hormones, neurotransmitters, tastes and smells, and also receptors for light in the eye and in plants. Rhodopsin Immunity Cells can make huge numbers of different antibodies. Immunoglobulins
Using examples, distinguish the difference between analogous and homologous characteristics.
Homologous characteristics Common ancestry [1] Pentadactyl limbs (lizard, bird, human, whale) [1] Analogous characteristics Convergent evolution [1] Both have similar structures to provide similar functions, but have evolved independently [1] The human and octopus eye [1]
Explain the effect of light intensity and temperature on the rate of photosynthesis.
Light intensity: - Rate will increase until it hits a maximum rate - Will eventually plateau because of other limiting factors - Different wavelengths will have different effects CO2 concentration: - Rate will increase until it hits a maximum rate - Will eventually plateau because of other limiting factors Temperature: - Rate will increase until all reagents are consumed - Enzymes responsible for photosynthesis denatures after it reaches an optimum temperature
Explain peat formation.
Peat is an accumulation of partially decayed vegetation or organic matter such as leaves and dead animals. As the peat accumulates, the peat retains water and this slowly creates wetter conditions that allow the area of the wetland to expand. In acidic and anaerobic conditions, such as in swamps or river beds, the saprotrophs who would usually decompose this dead organic matter cannot survive and will die off, leaving the matter only partially decomposed. As a result of the matter not being decomposed, the acidic conditions increase.
Describe the formation of polypeptides through condensation.
Polypeptides are chains of amino acids. [1] The amine group of one amino acid and the carboxyl group of another is linked. [1] This is a condensation reaction - water is released. [1] A peptide bond forms between the two amino acids. [1] The resulting molecule is a dipeptide (2 amino acids) or a polypeptide (≤2). [1] Diagram is also acceptable if it correctly outlines the process. [2]
Outline difference between prokaryotes and eukaryotes
Prokaryotes - Not compartmentalized - No cell wall - No nucleus (naked DNA) - 70s ribosomes - 1-10 um - No Golgi Apparatus - No endoplasmic reticulum - Binary fission - Pili - Flagella Eukaryotes - Compartmentalized cell structure - Plants cells have cell wall - Nucleus - 80s ribosomes - 2-1000 um - GA - ER - Mitosis - No Pili
Discuss the ethical implications of the therapeutic use of stem cells from specially created embryos.
Stem cells- multipotent (early stage of cell development) [1] Possible extraction from specially created embryos, from the umbilical cord blood of a baby, and from an adult's own tissues [1] Therapeutic Cloning - removal of a nucleus from virtually any cell of the body and its injection into an unfertilised egg [1] Ethical/beneficial: Can be used to treat patients with a variety of diseases, such as Stargardt's disease [1] Easier to obtain / more abundant compared to adult tissues - easier access / having more cells = able to treat more people [1] Cell from cloned embryo less likely to get rejected by body [1] Cells taken at a stage when embryo has no nervous system - can feel no pain [1] No "natural" human embryos need to be destroyed [1] Cells can be taken from embryos that have stopped developing and therefore would have died anyway [1] Stem cell research might pave way for future discoveries and beneficial technologies [1] Unethical: Involves creation and destruction of life (question: do we have the right to?) [1] Embryo is alive from moment the egg is fertilized, taking life is murder [1] Higher risk of developing into tumors compared to adult tissue or umbilical cord [1] Potential for human cloning technologies [1] More embryos are generally produced than needed, so excess embryos are killed [1] There is a better alternative we can invest in - iPS stem cells [1]
Explain why Urea is an example of a compound that is produced by living organism but can also be artificially synthesized.
Tov: It was thought that organisms composed of organic chemicals that could only be produced in living organism because of a 'vital force' was needed according to TOV it was predicted that urea could only be made in living organisms because it was an organic compound Urea was a organic compound discovered in human urine in the 18th century It was produced when there is an excess of amino acids in the body organic compound However, in 1828, german chemist wohler synthesized urea artificially using silver isocyanate and ammonium chloride Vitalism as a theory has since been disproven with the discovery that organic molecules can be artificially synthesised As a result, no vital force has been discovered, and what makes living organism different from nonliving matter is natural selection
Draw and annotate the molecular diagram of a generalised amino acid.
[1] Amino group correctly drawn and annotated [1] Carboxyl group (with two bonds for covalent) correctly drawn and annotated [1] R-group correctly drawn and annotated [1] Hydrogen correctly drawn and annotated
Describe the effects of removing rabbits from the following ecosystem
[1] Decrease in fox population [1] Increase in availability of carrots and grass [1] Increase in bird population [1] Increase in grasshopper population
Describe the evidences that falsified the Davison-Danielli model.
[1] Define the Davson-Danielli model (including; phospholipid bilayer between two layers of globular proteins.) [1 ]Misinterpretation of globular structures as transmembrane proteins. [1]Improvements in biochemical techniques allowed proper identification of membrane [1]Fluorescent antibody tagging showed that membrane proteins can freely move within the membrane
Compare the following graphs
[1] Denaturation of enzyme results in loss of efficiency [1] Denaturing occurs because of a change in shape [1] Some reference to lock and key or best fit theory [1] There is some optimum level of independent variable [1] Temperature graph drops off because enzymes become denatured at certain temperature [1] pH graph has optimum level of pH, and is affected similarly by changes in pH in both directions
Describe the process of simple diffusion.
[1] One of the methods of moving particles across membranes. [1] More particles move from an area of higher concentration than move in the opposite direction. [1] Higher to the lower concentration - a movement down the concentration gradient. [1] If the phospholipid bilayer is permeable, particles can pass between the phospholipids in the membrane. [1] Non-polar particles can pass through easily, while Ions with positive or negative charges cannot pass through easily [1] If the oxygen concentration in the cell is reduced do to anaerobic respiration and the concentration outside the cell is higher, oxygen will pass into the cell through the membrane by passive diffusion.
Compare the ways in which autotrophic, heterotrophic and saprotrophic organisms obtain energy.
autotrophs use an external / non-organic energy source (reject statements suggestion that energy is made) (some) autotrophs use light / (some) autotrophs use photosynthesis (some) autotrophs use inorganic chemical reactions / (some) autotrophs use chemosynthesis heterotrophs obtain energy from other organisms heterotrophs (usually) ingest food / consume food saprotrophs obtain energy from non-living matter / dead organisms saprotrophs digest organic matter extracellularly
Compare the induced fit model of enzyme activity with the lock and key model.
in both models substrate binds to active site substrate fits active site exactly in lock and key, whereas fit is not exact in induced fit substrate / active site changes shape in induced fit, whereas active site does not change shape in lock and key in both models an enzyme - substrate complex is formed in lock and key binding reduces activation energy, whereas in the induced fit change to substrate reduces activation energy lock and key model explains narrow specificity, whereas induced fit allows broader specificity induced fit explains competitive inhibition, whereas lock and key does not
Lactase is widely used in food processing. Explain three reasons for converting lactose to glucose and galactose during food processing.
it allows people who are lactose intolerant/have difficulty digesting lactose to consume milk (products); galactose and glucose taste sweeter than lactose reducing need for additional sweetener (in flavoured milk products); galactose and glucose are more soluble than lactose / gives smoother texture / reduces crystallization in ice cream; (bacteria) ferment glucose and galactose more rapidly (than lactose) shortening production time (of yoghurt/cottage cheese);
Simple laboratory experiments show that when the enzyme lactase is mixed with lactose, the initial rate of reaction is highest at 48 °C. In food processing, lactase is used at a much lower temperature, often at 5 °C. Suggest reasons for using lactase at relatively low temperatures.
less denaturation / enzymes last longer at lower temperatures; lower energy costs / less energy to achieve 5 °C compared to 48 °C; reduces bacterial growth / reduces (milk) spoilage; to form products more slowly / to control the rate of reaction;