biology as level paper questions

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How does HIV replicate?
1. The attachment protein attaches to a receptor molecule on the cell membrane of the host helper T-cell. 2. The capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cells cytoplasm.
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HIV replication continued?
3. Inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template. 4. From this. DNA is made + insrted into the human DNA. 5. Host cell enzymes are used to make viral proteins from the viral DNA.
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HIV CONTINUED?
6.The viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells
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Describe an ethical issue surrounding monoclonal antibody therapy?
Animals are used to produce the cells from which the monoclonal antibodies are produced.
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What are monoclonal antibodies?
Antibodies produced from a single group of genetically identical B cells.
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Describe how monoclonal antibodies can be used to target a drug to cancer cells?
Monoclonal antibodies are made against antigens specific to cancer cells. An anti-cancer drug is attached to the antibodies. The antibodies bind to the antigens on cancer cell as complementary. This delivers the anti cancer drug to the cells.
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Describe the Bohr effect?
1. When cells respire they produce carbon dioxide, which raises the pCO2. 2. This increases the rate of oxygen unloading so the dissociation curve shifts right.
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What is the difference between endopeptidases and exopeptidases?
Endopeptidases hydrolyse peptide bonds within a protein. Exopeptidases hydrolyse peptide bonds at the ends of proteins.
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What are dipeptidases?
Dipeptidases are exopeptidases that work specifically on dipeptides. They act to seperate the 2 amino acids that make a dipeptide by hydrolysing the peptide bond between them.
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What does lipase do?
Breaks down lipids into monoglycerides and fatty acids. Lipases are made in the pancreas. They work in the small intestine.
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What is the role of bile salts?
Bile salts emulsify lipids causing them to form small droplets. Several small droplets have a larger SA so increases the SA of lipid thats available for lipase to work on.
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What is the role of micelles?
Micelles help to move monoglycerides and fetty acids towrads the epithelium. Becasue micelles constantly break up and reform they can release monoglycerides and fatty acids, allowing them to be absorbed.
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What does amylase do?
Catalyses the conversion of starch into maltose.
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How is glucose absorbed? How is fructose absorbed?
Glucose is absorbed by active transport with sodium ions via a co-transporter protein. Fructose is absorbed via facilitated diffusion through a different transporter protein.
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Describe inspiration?
1.External intercostal + diaphragm muscles contract. 2. This causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity. 3. Lung pressure decreases. 4. Air will flow from high-low pressu
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Describe expiration?
1. The external intercostal muscles and diaphragm muscles relax. 2. The ribcage moves downwards and inwards and the diaphragm becomes curved again. 3. The volume of the thoracic cavity decreases, causing the air pressure to increase.
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Describe features of alveoli that speed up the rate of diffusion?
A thin exchange surface- The alveolar epithelium is only 1 cell thick. This means that there is a short diffusion pathway. 2. A large SA- The large number of alveoli mean there is a large SA.
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Describe xerophytic adaptations?
1. Stomata sunk in pits that trap moist air, reducing the concentration gradient. 2. Waxy waterproof cuticles on leaves and stems to reduce evaporation.
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What is meant by qualitative testing?
The process of determining whether or not a particular chemical is present in a sample.
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Describe the properties of triglycerides?
The long hydrocarbon tails of the fatty acids contain lots of chemical energy-a load of energy is released when they are broken down. They are insolubel so dont affect the water potential of the cell.
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Describe the properties of phospholipids?
Make up the bilayer of cell membranes, cell membranes control what enters and leaves a cell. Their heads are hydrophilic and their tails are hydrophobic, so they form a double layer. The centre of the bilayer is hydrophobic.
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Describe enzymes?
Enzymes are catalysts that lower the activation energy due to bending bonds. This allows reactions to take place at a lower temperature than normal.
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Explain why enzymes are effective in tiny quantities?
They are not used up in the reaction and so can be used repeatedly.
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Explain why changing certain amino acids that are not part of the active site prevents the enzyme from functioning?
The changed amino acis may be one that forms hydrogen bonds with other amino acids. If the new amino acid does not form hydrogen bonds the tertiary structure of the enzyme will change, including the active site.
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What is the primary structure of a protein determined by?
A gene. If a mutation occurs in that gene it could change the tertiary structure of the enzyme produced.
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What is the significance of DNA to an organism?
It carries an organisms genetic information.
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What is a gene?
A sequence of DNA bases that codes for a polypeptide.
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Describe the orle of DNA polymerase in semi-conservative replication of DNA?
DNA polymerase joins nucloetides together forming phosphodiester bonds.
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What are the functions of ATP?
Phosphorylate compounds making them more reactive. Provide energy to energy requiring cellular reactions.
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What is the role of hydrogen ions?
Hydrogen ions determine pH. The more hydrogen ions present, the lower the pH. Enzyme controlled reactions are affected by pH.
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What is the role of iron ions?
Iron ions are an important part of haemoglobin. Haemoglobin carries oxygen around the body in red blood cells. The iron ions bind to the oxygen in haemoglobin.
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What is the role of sodium ions?
Sodium ions help transport glucose and amino acids across membranes. -Co-Transport.
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What is the role of phosphate ions?
Phosphate ions are an essential component of ATP and DNA, It is the bonds between phosphate groups that store energy in ATP.
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Where is the energy in ATP stored?
It is stored in high energy bonds between the phosphate groups
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Explain why a log scale is used to record the number of cells?
Large range
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When should you use a students t-test?
When you have 2 sets of data that you want to compare. It tests whether there is a significant difference in the means of 2 sets of data.
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When should you use the chi squared test?
When you have categorical data and you want to compare whether your observed results are statistically different from your expected results.
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What 3 things do you need to think about when evaluating methods and results?
Repeatability/ Reproducibility/ Validity
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What is the function of the nucleus?
The nucleus controls the cells activities. Nuclear pores allow substances e.g. RNA to move between the nucleus and the cytoplasm. The nucleolus makes ribosomes.
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What is the function of receptor molecules on the cell surface membrane?
Allow it to respond to chemicals like hormones.
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What is the function of the RER?
Folds and processes proteins that have been made at the ribsomes.
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What is the function of the SER?
Synthesises and processes lipids.
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What is the function of a cell vacuole?
Helps to maintain pressure inside the cell and keep the cell rigid. This stops plants wilting. Also involved in the isolation of unwanted chemicals inside the cell.
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What is the difference between fungal cells and plant cells?
Fungal cell walls are made out of chitin, not cellulose. Fungal cells dont have chloroplasts because they dont photosynthesise.
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What is the function of capsules?
It helps to protect bacteria from attack by cells of the immune system.
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What is magnification?
How much bigger the image is than the specimen.
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How do TEMS work? How do SEMS work?
TEMS- Use electomagnets to focus a beam of electrons, which is then transmitted through the specimen. SEMS- Scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in a cathode ray tube form image
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Describe some aseptic techniques used to prevent contamination of cultures by unwanted microorganisms?
1. Regularly disinfect work surfaces to minimise contamination. 2. Use sterile equipment + discard safely after use. 3. Work near a bunsen flame as hot air rises. 4. Minimise the time spent with the lid off the agar plate. 5. Briefly flame the neck
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Describe the primary immune response compared to the secondary immune response
The primary response is slow becasue there arent many b-cells that can make the antibody needed to bind to it. The infected person will show symptoms. The secondary immune response is faster and gets rid of the pathogen before any symptoms.
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Why is glycogen more highly branched than starch?
It is more highly branched so has more ends that can be acted on simultaneously by enzymes. It is broken down more rapidly to form glucose monomers which are used in respiration. Animals have a higher metabolic rate + respiratory rate than plants.
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What is the effect of temperature on enzyme action?
A rise in temperature increases the kinetic energy of molecules. As a result the molecules move around more rapidly and collide with each other more often. This means that the enzyme + substrate molecule come together more often in a given time.
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What is the effect of a high temperature on enzyme action?
Cause hydrogen and other bonds in the enayme molecule to break. This results in the active site changing shape. At first the substrate fits less easily into this changed active site.
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Why is DNA a stable molecule?
1. The phosphodiester backbone protects the more chemically reactive organis bases inside the double helix. Hydrogen bonds link the organic pairs forming bridges.
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ATP is sometimes referred to as an immediate enrgy source, explain why?
ATP releases energy very rapidly. This energy is released in a single step and is transferred directly to the reaction requiring it.
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Explain how ATP can make an enzyme-catalysed reaction take place more readily?
ATP provides a phosphate that can attach to another molecule, making it more reactive and so lowering its activation energy. As enzymes work by lowering activation energy they have less work to do + function more readily.
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State 3 roles of ATP in plant cells?
Active Transport/ Formation of lysosomes/ Activation of molecules
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Compare and contrast the differences between prokaryotic and eukaryotic cells?
Prokaryotic cells have no true nucleus. DNA isnt associated with histones. DNA is in the form of plasmids. 70s ribosomes= smaller. Cell wall made of murein. Have a capsule
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What are the functions of proteins in the cell membrane?
Provide structural support/ Allow active transport across the membrane through carrier proteins/ act as receptors/ help cells to adhere together
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What are the functions of cholesterol in the membrane?
Reduce lateral movement of other molecules including phospholipids/ Make the membrane less fluid at high temperatures/ Prevent leakage of water and dissolved ions from the cell.
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What are the functions of glycolipids + glycoproteins in the membrane?
Act as recognition sites/ Help maintain the stability of the membrane/ Helps cells to attach to one another and so form tissues
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Describe the fluid-moaic model?
Fluid- The phospholipid molecules are constantly moving. Mosaic- Proteins embedded in the phospholipid bilayer like tiles of a mosaic.
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How do you work out species richness?
Taking random samples of a community and counting the number of different species.
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What is biodiversity? What is community? What is an ecosystem?
Biodiversity- The variety of living organisms in an area. Community- All the populations of different species in a habitat. Ecosystem- All the living and non living components of a particular area.
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What is a gene pool?
Gene pool- The total number of alleles in a particular population at a given time.
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Why is the genetic code described as non-overlapping and universal?
Non-overlapping- Each base triplet is read in sequence, base triplets do not share their bases. Universal- The same specific base triplets code for the same amino acids in all living things.
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Explain what a non dijunction event is and how they occur?
Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division. It usually results in a gamete having 1 more or fewer chromosome.
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Compare and contrast gene and chromosomal mutations?
gene mutation is an alteration of the nucleotide sequence of a gene whereas chromosomal mutation is an alteration of the structure or number of chromosomes.
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What is directional selection? What is stabilising selection?
Directional selection- Where individuals with the alleles for characteristics of an extreme type are more likely to survive and reproduce. Stabilising selection- Where individuals with alleles for characteristics towards the middle of the range.
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What is the founder effect?
The founder effect describes what happens when just a few organisms from a population start a new colony and there are only a small number of diferent alleles in the initial gene pool
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Describe the cohesion-tension theory?
1. Water evaporates from the leaves at the top of the xylem. 2. This creates tension, which pulls more water into the leave. 3. Water molecules are cohesive so when some are pulled into the leaf others follow. This means whole column moves upwards.
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Describe the cohesion tension theory step 4?
Water enters the stem through the roots.
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Card 2

Front

HIV replication continued?

Back

3. Inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template. 4. From this. DNA is made + insrted into the human DNA. 5. Host cell enzymes are used to make viral proteins from the viral DNA.

Card 3

Front

HIV CONTINUED?

Back

Preview of the front of card 3

Card 4

Front

Describe an ethical issue surrounding monoclonal antibody therapy?

Back

Preview of the front of card 4

Card 5

Front

What are monoclonal antibodies?

Back

Preview of the front of card 5
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