Questions at end of AS paper 2 Flashcards
Describe the roles of iron ions, sodium ions, and phosphate ions in a cell ( 5 marks )
Iron ions
- Haemoglobin binds with oxygen
Sodium ions
- Co-transport of glucose
- Because sodium moved out by
active transport
- Creates a sodium concentration
gradient
- Affects osmosis
Phosphate ions
- Affects osmosis
- Joins nucleotides
- Used to produce ATP
- Phosphorylates other
compounds
- Water soluble part of
phospholipid
The movement of substance across cell membranes is affected by membrane structure. Describe how (5 marks)
- Phospholipid bilayer allows movement of non-polar substances
- Phospholipid bilayer prevents movement of polar substances
- Carrier proteins allow active transport
- Channel/ carrier proteins allow faciliatated diffusion
- Shape of channel/ carrier determines which substances move
- Membrane surface area determines how much diffusion
- Cholesterol affects fluidity
Explain five properties that make water important for organisms (5 marks)
- A metabolite in condensation
- A solvent so metabolic reactions can occur
- High specific heat capacity so buffers changes in temperature
- Large latent heat of vapourisation so provides a cooling effect
- Cohesion between water molecules so supports columns of water
- Cohesion between water molecules so produces surface tension supporting small organims
Describe and explain how you would use cell fractionation and ultracentrifugation to obtain a sample of nuclei from muscle tissue (6 marks)
- Homogenise to break open cells
- Filter to remove debris
- Cold solution to prevent enzyme activity
- Solutions with equivalent water potential to prevent osmosis
- Buffered solution to stop enzyme denaturing
- Centrifuge at lower speed so nuclei in pellet move to bottom
Describe the role of organelles in the production and release of enzymes by animal cells (5 marks)
- DNA in nucleus codes for enzyme
- Ribosome produces enzyme
- Rough endoplasmic reticulum transports enzyme
- Mitochondria produce ATP
- Golgi apparatus modify enzymes
- Vesicles move to cell surface membrane
Describe the structure of ATP.
Outline how named enzymes break down and resynthesise ATP (4 marks)
- Ribose, Adenine, and 3 phosphates
- ATP to ADP + Pi by ATP hydrolase in hydrolysis
- ADP + Pi to ATP by ATP synthase
- In condensation reaction
Describe how the 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
- Tertiary structure formed by interactions between R groups
- Quaternary structure contains more than 1 polypeptide
Describe the structure of DNA and the structure of a chromosome (6 marks)
- Polymer of nucleotides
- Nucleotide consists of deoxyribose, phosphate, and a nitrogenous base
- Phosphodiester bonds between nucleotides
- DNA double helix held by hydrogen bonds
- Hydrogen bonds between adenine, thymine and cytosine and guanine
- DNA associated with histones
- Chromosome consists of 2 chromatids joined at a centromeme
Other than mutations, describe and explain the other processes that result in increase in genetic variation within a species (4 marks)
- Independent segregation of homologous chromosomes
- Crossing over between homologous chromosomes
- Random fertilisation of gametes
- Produces new combinations of alleles
Define gene mutation and explain how a gene mutation can have:
- No effect on an individual
- A positive effect on an individual (4 marks)
(Definition of gene mutation)
1. Change in the base/nucleotide (sequence of
chromosomes/DNA);
2. Results in the formation of new allele;
(Has no effect because)
3. Genetic code is degenerate (so amino acid
sequence may not change);
OR
Mutation is in an intron (so amino acid sequence
may not change);
4. Does change amino acid but no effect on tertiary
structure;
5. (New allele) is recessive so does not influence
phenotype;
(Has positive effect because)
6. Results in change in polypeptide that positively
changes the properties (of the protein)
OR
Results in change in polypeptide that positively
changes a named protein;
7. May result in increased reproductive success
OR
May result in increased survival (chances);
Compare and contrast the structure and properties of triglycerides and phospholipids (5 marks)
- Both contain ester bonds (between glycerol and
fatty acid); - Both contain glycerol;
- Fatty acids on both may be saturated or
unsaturated; - Both are insoluble in water;
- Both contain C, H and O but phospholipids also
contain P; - Triglyceride has three fatty acids and
phospholipid has two fatty acids plus phosphate
group; - Triglycerides are hydrophobic/non-polar and
phospholipids have hydrophilic and
hydrophobic region; - Phospholipids form monolayer (on
surface)/micelle/bilayer (in water) but
triglycerides don’t;
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein (4 marks)
- Glucose and galactose;
- Joined by condensation (reaction);
- Joined by glycosidic bond;
- Added to polypeptide in Golgi (apparatus);
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;
- (So with TEM) smaller organelles/named cell
structure can be observed
OR
greater detail in organelles/named cell structure
can be observed; - TEM view only dead/dehydrated specimens and
optical (can) view live specimens; - TEM does not show colour and optical (can);
- TEM requires thinner specimens;
- TEM requires a more complex/time consuming
preparation; - TEM focuses using 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 larger number of seed 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 2 populations of trees (5 marks)
- Use random sample of seeds (from each
population); - Use (large enough) sample to be representative
of whole population; - Indication of what size was measured eg mass;
- Calculate a mean and standard deviation (for
each population); - Use the (Student’s) t-test;
- Analyse whether there is a significant difference
between (the means of) the two populations;
