Paper 1 A01 Practice Questions Flashcards
Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells [6 marks]
- TEM use electrons and optical use light
- TEM allows a greater resolution
- With TEM, smaller organelles can be observed
- TEM can only view dead/dehydrated specimens and optical can view living specimens
- TEM does not show colour and optical can
- TEM requires a more complex/time consuming preparation
- TEM focuses on magnets and optical uses glass lenses
An environmental scientist investigated a possible relationship between air
pollution and the size of seeds produced by one species of tree.
He was provided with a very large number of seeds collected from a population of
trees in the centre of a city and also a very large number of seeds collected from a
population of trees in the countryside.
Describe how he should collect and process data from these seeds to investigate
whether there is a difference in seed size between these two populations of trees.
[5 marks]
- Use random sample of seeds from each population
- Use large enough sample to be representative of the whole population
- Indication of what size was measured
- Calculate a mean and standard deviation for each population
- Use the student’s t test
- Analyse whether there’s a significant difference between the two populations
Explain five properties that make water important for organisms.
[5 marks]
- Metabolite in condensation/hydrolysis
- A solvent so metabolic reactions can occur and allows transport of substances
- High specific heat capacity so buffers changes in temperature
- Large latent heat of vaporisation so provides a cooling effect through evaporation
- Cohesive properties so supports columns of water e.g. xylem
Outline the similarities in, and the difference between the structures of DNA and RNA molecules [6 marks]
Similarities:
- Both polymers of nucleotides
- Cytosine, guanine and adenine
- Both have phosphodiester bonds
Differences:
- Deoxyribose vs ribose
- Thymine vs uracil
- Long vs short
- Double helix vs single stranded
Outline the similarities in, and the differences between, the structures of chloroplasts and mitochondria [4 marks]
Similarities:
- Double membrane
- Both contain DNA
- Both contain ribosomes
Differences:
- Thylakoids/grana vs cristae
- Stroma vs matrix
Describe how a quaternary protein is formed from its monomers [5 marks]
- Amino acids joined by peptide bonds
- By condensation reactions
- Secondary structure is formed by hydrogen bonding and causes alpha helix’s or beta pleating to occur
- Tertiary structure caused by interactions between R groups of amino acids
- Quaternary structure formed by bonds between polypeptides (>1)
Describe the structure of DNA and the structure of a chromosome [6 marks]
DNA:
- Polymer of nucleotides
- Nucleotides consist of deoxyribose sugar, nitrogenous base, and phosphate
- Phosphodiester bonds join adjacent nucleotides
- DNA double helix held by H bonds between A+T and C+G (complementary base pairs)
Chromosomes:
- Consist of two chromatids joined at a centromere
Apart from mutation, describe and explain the other processes that result in increases in genetic variation within a species [4 marks]
- Independent segregration of homologous chromosomes
- Crossing over between homologous chromosomes
- Random fertilisation of gametes
- Produces new combinations of alleles
Describe the mechanism for absorption of amino acids [4 marks]
- Facilitated diffusion of amino acid into the ilium (H—>L)
- Via co transport
- Sodium ions actively transported from cell to blood
- Creating sodium ion concentration gradient
- Facilitated diffusion of amino acid into blood
Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs [3 marks]
- Renal vein
- Vena cava and right atrium
- Right ventricle to pulmonary artery
Explain how water from tissue fluid is returned to the circulatory system [4 marks]
- Plasma proteins remain
- Creating water potential gradient with high hydrostatic pressure at arteriole end, plasma fluid moves out.
- Water moves to blood by osmosis
- Returns to blood by lymphatic system
Describe how mRNA is formed by transcription in eukaryotes [5 marks]
- DNA helicase breaks hydrogen bonds between complementary base pairs
- One DNA strand acts as a template
- Free RNA nucleotides align by complementary base pairing
- Uracil binds with adenine in place of thymine
- RNA polymerase joins adjacent nucleotides
- By phosphodiester bonds
- Introns are removed to form mRNA
Describe how a polypeptide is formed by translation of mRNA [6 marks]
-mRNA attaches to ribosomes
- tRNA anticodons bind to complementary mRNA codons
- tRNA brings a specific amino acid
- Amino acids join by peptide bonds
- With the use of ATP
- The ribosome moves along the mRNA to form the polypeptide
Define ‘gene mutation’ and explain how a gene mutation can have:
- No effect on an individual
- A positive effect on an individual
[4 marks]
- Change in base sequence of DNA
- Results in formation of new allele
- Genetic code is degenerate so amino acid sequence may not change (no effect on individual)
- Can change amino acid sequence to result in polypeptide that positively changes the properties of the protein
Describe how the process of meiosis results in haploid cells [4 marks]
- DNA replication
- 2 divisions
- Separation of homologous chromosomes in first division
- Separation of sister chromatids in second division
- Produces 4 haploid cells
