paper 1 biology

• Structure of HIV


  Attachment proteins

  Core of RNA and enzymes enclosed in capsid
• How HIV is replicated

  Attachment proteins attach on receptors on helper T cell

  RNA enters the cell

  Reverse transcriptase converts RNA into DNA

  Viral proteins are created

  Viral component assembled and released from cell
• Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells

  DNA is converted into RNA through reverse transcriptase

  Viral DNA is incorporated into cell's DNA

  DNA is transcribed and translated into HIVs RNA and creates viral proteins for assembly
• Describe phagocytosis


  Phagocyte detects debris and engulfs pathogen

  Phagosome vesicle forms around

  Lysosome fuses, releasing enzymes

  Enzymes hydrolyses pathogen

  Antigen is displaced on cell surface membrane (now an APC)
• Cells that stimulate immune response

  Abnormal cells, Transplants, Pathogens , Toxins(not a cell)
• Role of disulfide bridge in antibody

  holds together 2 polypeptide chains
• How HIV affects production of antobodies and causes AIDS

  1) HIV attaches to and destroys helper T cell

  2) Less B cells stimulated

  3) Less antibodies made
• Describe how the B lymphocytes of a frog would respond to vaccination against Ranavirus

  B cell binds to specific antigen

  B cell divides by mitosis

  Plasma cells produce antibodies

  B cells produce memory cells
• Monoclonal antibody


  antibodies with same tertiary stucture produced from plasma cells
• Difference between active and passive immunity

  1. Active involves memory cells, passive does not;

  2. Active involves production of antibody by plasma cells / memory cells

  3. Passive involves antibody introduced into body from outside

  4. Active long term, because antibody produced in response to antigen;

  5. Passive short term, because antibody (given) is broken down;

  6. Active takes time to develop, passive is fast acting.
• Name and describe five ways substances can move across the cell-surface membrane into a cell

  1) Simple diffusion of small/non-polar molecules down a concentration gradient

  2)Facilitated diffusion down a concentration gradient via protein carrier/channel

  3. Osmosis of water down a water potential gradient;

  4. Active transport against a concentration gradient via protein carrier using ATP

  5. Co-transport of 2 different substances using a carrier protein
• Describe and explain two features you would expect to find in a cell specialised for absorption.

  Microvilli - increases surface area

  Many carrier protein for co- transport so faster rate of absorption

  More mitochondria - for ATP for active transport
• The movement of substances across cell membranes is affected by membrane structure. Describe how

  1. Phospholipid bilayer allows diffusion of nonpolar/lipid-soluble substances;

  2. Phospholipid bilayer prevents diffusion of polar/ charged/lipid-insoluble substances

  3. Carrier proteins allow active transport

  4. Channel/carrier proteins allow facilitated diffusion/co-transport

  6. Number of channel proteins determines how much movement

  7. Membrane surface area determines how much diffusion

  8. Cholesterol affects fluidity/rigidity/permeability
• Disadvantage of optical microscope

  Lower resolution as light has too high a wavelength
• Describe how a sample of chloroplasts could be isolated from leaves

  Blend the sample and filter it

  Spin it at a high speed (in cold, same water potential and ph controlled solution) then take out first pellet of nucleus

  Spin at higher speed and take out pellet of chloroplast
• Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells (4)

  DNA in nucleus is code (for protein)

  Ribosomes - site of protein synthesis produces proteins

  Mitochondria- produce ATP for protein synthesis

  Golgi apparatus - packages and modifies proteins

  Vesicle - transports and fuses with cell surface membrane
• Give one advantage of viewing a biological specimen using a transmission electron microscope compared with using a scanning electron microscope


  can see internal structures/ higher resolution
• structure of chloroplast

  
• conditions for centrifugation


  ice cold - reduce enzyme activity

  ph controlled - so enzymes dont denature

  same water potential - prevents lysis of cell
• what are cell walls made of

  plants + algae - cellulose

  fungi - chitin

  prokaryotes - murein
• ELISA test


  1. First antibody binds to antigen as it is complementary

  2. Second antibody with enzyme attached is added

  3. Second antibody attaches to antigen

  4. Substrate added and colour changes;
• Describe binary fission in bacteria

  DNA and plasmids are replicated

  cytoplasm splits to produce daughter cells
• Name the fixed position occupied by a gene on a DNA molecule.

  Locus
• Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind. Explain why.

  Binding of first oxygen changes tertiary

  Uncovers another binding site
• Name the blood vessels that carry blood to the heart muscle

  coronary arteries
• When counting, cells that touch top or left lines are counted but cells that touch right or bottom lines are not counted. Suggest two reasons for this rule.

  To avoid counting same cells twice

  To be consistent and get comparable results

  To avoid dealing with parts of cells
• Explain a stain allowed a doctor to count the white blood cells amongst all the red blood cells.

  White blood cells have a nucleus (that stains but red cells do not)
• explain the role of the heart in the formation of tissue fluid.

  Contraction of ventricles produces high blood / hydrostatic pressure

  This forces water (and some dissolved substances) out of blood capillaries
• Suggest how a blockage in the lymphatic system could cause lymphoedema


  Excess tissue fluid cannot be (re)absorbed / builds up
• Describe advantage of dissociation curve being shifted to right

  lower affinity for O2 at low partial pressures

  Easier unloading of O2 for (aerobic) respiration
• Describe how the change in chromosome number was produced

  
  

  Explain why all the cells of the body will have this mutation

  In meiosis

  Homologous chromosomes / sister chromatids do not separate

  
  

  extra chromosome in gamete

  All cells derived (from a single cell / zygote) by mitosis

  Mitosis produces genetically identical cells
• Describe processes involved in absorption and transport of digested lipid molecules from ileum into lymph vessels

  Micelles contain bile salts, monoglycerides and fatty acids

  They make fatty acids more soluble in water

  Fatty acids are absorbed by diffusion at ileum

  Triglycerides reform in cells

  Vesicles move to cell membrane
• graph shape for normal distribution

  bell shaped curve and symmetrical
• How stabilizing selection affects mean and standard deviation

  Mean - stays the same

  Standard deviation - decreases

  Mode is favored and extremes decreases as selection pressure is against them
• Explain how crossing over can lead to genetic variation


  Sister chromatids exchange their alleles at the chiasmata

  Leads to more combinations of alleles
• 2 structural differences of DNA and RNA

  DNA - deoxyribose, double stranded, longer,has thymine

  RNA - ribose, has uracil
• How is a protein made

  DNA unwinds so hydrogen bonds between bases are broken, catalyzed by DNA helicase

  One DNA strand acts as template so free MRNA nucleotides line up to opposite complementary bases.

  Adjacent nucleotides form phosphodiester bonds catalyzed by RNA polymerase

  MRNA leaves nucleus and attaches to start codon at ribosome

  TRNA brings complimentary anticodon with specific amino acid

  Ribosome moves along MRNA until stop codon and process of TRNA repeated

  Amino acids join together to formpeptide bonds and polypeptide chain
• How to form scientific name of an animal

  Genus species
• What is a hierarchy


  Small groups within larger groups without any overlaps
• What is a species

  Organisms that can produce fertile offspring with one another and have similar characteristics/genes to eachother