biology

• cross bw male donkey and female horse produce mule, why do scientist regard them as different species?

  mule has odd number of chromosomes, errors occur in meiosis, mule is not a fertile offspring
• why courtship song is an important part of species recognition?

  helps differentiate between species, a characteristic of a species,
• what is a gene?


  gene is a section of DNA that contains coded information for the formation of polypeptide and functional RNA
• how many bases coded for each amino acid?

  three
• why are only three bases coded for each amino acid?

  -only 20 different amino acids, -each amino acid has its own code of bases, -only four different bases of DNA, -if each base is coded for a different amino acid only four different amino acids could be coded for, -using a pair(4)^2=16 of bases different codes are possible but it's still inadequate, - three bases (4)^3=64 produce codes which are more than enough to satisfy the requirements of 20 amino acids
• code for each amino acid is called?

  a triplet
• features of genetic code?

  Universal, non-overlapping, and degenerate.
• degenerate means


  because most amino acids are coded for by more than one triplet
• non-overlapping means?


  each base in the sequence is read only once
• universal means?


  each triplet codes for the same amino acid in all organisms
• what are exons?


  exons are coding sequence that are translated to amino acids to form final polypeptide
• what are introns?


  introns are non-coding sequences that are not translated are removed during a process called splicing
• what are homologous chromosomes?


  Pairs of chromosomes that have the same genes at the same loci, but potentially different alleles.
• what is locus/loci?


  Position of a gene on the chromosome
• what is an allele?

  An allele is an alternative form of a gene that determines a specific trait or characteristic.
• what is mutation?


  A change in the DNA sequence of a gene that produces a new allele of that gene.
• function of mRNA?


  transfers DNA from nucleus to cytoplasm, acts as a messenger.
• what is a codon?


  A sequence of three bases on mRNA that code for one amino acid, are complementary to the triplet on DNA.
• what is a genome?

  The complete set of genes in an organism.
• what is a proteome?


  The complete set of proteins produced by a genome.
• messenger RNA

  1. long strand 2. single helix 3. the sequence of mRNA is the same as the sequence of bases on DNA in a process called transcription.
• tRNA

  1. small molecule 2. single stranded 3. folded into a clover leaf shape 4. one end of the chain is longer than the other it acts a binding site to which an amino acid can attach easily 5. has anticodons on the opposite end of tRNA
• what is anti codon?

  a sequence of three nucleotides forming a unit of genetic code in a transfer RNA molecule, corresponding to a complementary codon in messenger RNA.
• function of tRNA?


  1.during protein synthesis, anticodon on tRNA pairs up with a complementary codon on mRNA 2. the end chain attaches amino acids 3. it lines up amino acids on mRNA template during protein synthesis
• what is directional selection?

  Directional selection is a type of natural selection where individuals with traits that are more extreme in one direction have a higher fitness and are favored by the environment.
• what is stabilising selection?

  Stabilizing selection is a type of natural selection that favors the average phenotype and reduces variation in a population.
• what is phenotype?


  The observable characteristics or traits of an organism.
• what is genotype?


  The genetic makeup of an organism.
• how are proteins digested in human gut?

  1. proteins are hydrolysed by proteases 2. endopeptidases hydrolyse the bonds 'between' the amino acids, this produces a series of peptide molecules. 3. exopeptidases hydrolyse the peptide bonds at the terminal ends of the peptide molecules prepared earlier, this produces dipeptides. 4. dipeptidases hydrolyses the peptide bonds between two amino acids. these are membrane bound and a part of ileum.
• describe the complete digestion of starch by mammal?

  1. carbohydrates are hydrolysed by amylases 2. amylase hydrolyses the glycosidic bond of a starch molecule this produces a disaccharide, maltose. 3. maltose is hydrolysed by maltase which is a disaccharidase. 4. maltase is present inside the cell lining of ileum it is a membrane bound disaccharidase.
• describe how the structure of the insect gas exchange system provides with sufficient oxygen and limits water loss?

  1. the body of insect have small pores on the surface called spiracles. they are the site of gas exchange. 2. tracheoles are highly branched and increases the surface area. 3. the walls of tracheoles are very thin which shortens the diffusion pathway. 4. tracheoles are permeable to oxygen. 5. the spiracles can close so limits the water loss. 6. there is hair around spiracles which prevents water loss.
• describe how humans breathe in?

  1.the external intercostal muscles contract and internal intercostal muscles relax. 2. the ribs move outward and upward this increases the volume of thorax. 3. the diaphragm muscles contract and it flattens this increases the volume 4. the increases volume reduces the pressure inside the lungs. 5. the atmospheric pressure is higher than the lungs so air moves in.
• describe how humans breathe out?

  1. the internal intercostal muscles contract and external intercostal muscles relax. 2. the ribs move downward and in this decreases the volume of thorax. 3. the diaphragm muscles relax and move up this decreases the volume. 4. this increases pressure inside the lungs. 5. the pulmonary pressure is higher than the atmospheric pressure so air rushes out.
• how does cellulose give cotton its strength

  • The many hydrogen bonds found between the parallel chains of microfibrils
  • Cellulose fibres and other molecules (e.g. lignin) found in the cell wall form a matrix