Describe how the structures of starch and cellulose molecules are related to their functions.
Starch is helically coiled. This means it is compact. It also is branches, which means glucose is easily released for respiration. Starch is also insoluble. As a result, it is osmotically inactive and doesn’t affect water potential. It is also a large molecule, which means it can not leave the cell membrane.
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Describe the structure of proteins
Polymer chain of amino acids joined by peptide bonds from a condensation reaction. The primary structure is the number type and sequence of amino acids. The secondary structures are alpha helices and beta pleated sheets formed by hydrogen bonds. The tertiary structure is 3d folded amino acids by hydrogen and ionic bonding and disulphide bridges to form globular proteins. The quaternary structure has 2 or more polypeptide chains.
Describe competitive and non-competitive inhibition of an enzyme
Competitive
Inhibitors reduce binding of enzyme to substrates to prevent the formation of e-s complexes forming. Inhibitor is a similar shape to substrate. Binds to active sites can be overcome by more substrate
Non-competitive
Inhibitor binds to site on enzyme other than active. Prevents formation of active site. Cannot be overcome by adding more substrate.
Describe the appearance and behaviour of chromosomes during mitosis.
During prophase chromosomes coil and appear as chromatids joined at the centromere. during metaphase chromomsomes line up on the equator, and attach to spindle fibres by their centromere. During anaphase, the centromere splits, the sister chromatids are pulled to opposite poles of the cell. during telophase, chromatids uncoil and become thinner.
Describe the structure of DNA
A polymer of nucleotides formed from deoxyribose, a phosphate and a nitrogenous base. Phosphodiester bonds form between nucleotides. Double helix strands are held by hydrogen bonds between adenine, thymine and cytosine and guanine
Describe semi-conservative DNA replication
DNA helicase unwinds DNA, both strands act as templates, nucleotides line up in complementary pairs adenine- thymine and cytosine- guanine. DNA polymerase then joins nucleotides forming phosophodiester bonds. each new DNA molecule consists of one original strand and one new strand
Explain five properties that make water important for organisms.
A solvent so reactions can occur.
High specific heat capacity so buffers changes in temperature.
Large latent heat of vaporisation so provides a cooling effect.
Cohesion between water molecules so supports columns of water.
Cohesion between water molecules so produces surface tension supporting small organisms
Describe how bacteria are destroyed by phagocytes.
The phagocyte is attracted to the pathogen by chemical products of the pathogen up a concentration gradient. The phagocyte has several receptors on its cell surface membrane that attaches on to the surface of the pathogen. The pathogen is the engulfed by the phagocyte and contained in a membrane forming a phagosome. The lysosomes move towards the phagosome and join to the phagosomes. The lysosomes release their lysozymes into the phagosomes where they hydrolyse the bacterium. The hydrolysis products of the bacterium are absorbed by the phagocyte.
Optical Vs Transmission electron microscopes
- TEM uses electrons whereas optical uses light
- TEM allows a greater resolution so smaller organelles can be observed
- TEM view only dead specimens whereas optical can view live specimens
- TEM does not show colour optical can
- TEM require thinner specimens
- TEM requires a more complex preparation
- TEM focuses using magnets and optical uses lenses
Transcription
- Hydrogen bonds between bases break
- One DNA strand acts as a template
- Free DNA nucleotides align by complementary base paring
- In RNA uracil base, pairs with adenine on DNA
- RNA polymerase joins adjacent RNA nucleotides
- By phosphodiester bonds between adjacent nucleotides
- Pre-mRNA is spliced to form mRNA
Translation
- mRNA attaches to ribosomes
- tRNA anticodons bind to complementary mRNA codons
- tRNA brings a specific amino acid
- Amino acids join by peptide bonds
- Amino join together with the use of ATP
- tRNA released after amino acid joined to polypeptides
- the ribosomes move along the mRNA to form the polypeptide
Breathing in - Breathing out
Inhalation:
Exterior intercostal muscles contract moving the ribs upwards and out. The diaphragm also contracts. This increases the volume in the lungs decreasing the pressure. As a result air is sucked in as the atmospheric pressure is greater than inside the lungs
Exhalation:
Exterior intercostal muscles relax moving the ribs inwards and down. The diaphragm also relaxes. This decreases the volume and increases the pressure. As a result air is drawn out as the atmospheric pressure is now less than inside the lungs.
Vaccines
- contains antigen from pathogen
- macrophage presents antigen on its surface
- T-cell with complementary receptor protein binds to antigen
- T- cell stimulates B-cell with a complementary antibody on its surface
- B-cell secretes large amounts of antibodies
- B-cell divides to form clones all secreting/producing the same antibody
Describe the difference between active and passive immunity.
- Active involves memory cells, passive does not
- Active involves production of antibody by plasma cells
- Passive involves antibodies introduces into body from outside
- Active long term because antibody produced in response to antigen
- Passive short term, because antibody is broken down
- Active can take time to develop/work, passive is fast acting
Succession
Colonisation by a a pioneer species
Change of environment
Enables other species to colonise and survive
so there is a change in biodiveristy
so stability increases and the environment becomes less hostile
eventually climax communities form
