How are alveoli efficient gas exchange surfaces? (2)
- alveoli increase surface area of lungs
- alveolar walls create short diffusion pathways
How do alveoli affect rate of gas exchange in lungs? (2)
- allow more gas molecules to diffuse across the gas exchange surface.
- therefore, increasing rate of diffusion
Explain importance of capillaries in gas exchange. (2)
- transports deoxygenated blood to alveoli & oxygenated blood away from alveoli
- this creates a steep concentration gradient
Give a function of a channel protein. (1)
- transfer molecules across cell surface membrane by facilitated diffusion
Explain why it is called a fluid mosaic structure. (2)
- Fluid membrane: molecules can move within membrane via diffusion
- Mosaic: membrane contains proteins & phospholipids arranged in a scattered pattern that look like mosaic if viewed from above
State 3 functions of a phospholipid bilayer. (3)
- controls the exchange of substances across membrane
- enables membrane to fuse w/ other membranes
- provides flexibility to membrane
State 2 differences between facilitated diffusion and active transport. (2)
- Facilitated diff doesn’t use ATP, active transport does use ATP.
- Facilitated diff. takes place along conc. gradient , active transport only occurs against conc. gradient
Compare and contrast Davson-Danielli model to fluid mosaic model. (3)
Similarities:
- both contain phospholipid bilayer
- globular proteins present in both
Differences:
- fluid mosaic contains hydrophobic regions, Dav-Dan has none.
Explain a feature of DNA that helps stabilise its structure. (1)
- Hydrogen bonds b/w base pairs
Name 2 types of RNA. (2)
- mRNA
-tRNA
Compare and contrast the structure and functions of DNA & RNA. (5)
- DNA is double stranded, RNA is single.
- DNA has deoxyribose sugar, RNA has ribose sugar
- both contain pentose sugars
- both contain bases: adenine, guanine & cytosine
- both have sugar phosphate backbone
Describe the structure of DNA. (5)
- double helix
- polymer of nucleotides
- each nucleotide made up of deoxyribose, a phosphate group & a nitrogenous base
- phosphodiester bonds b/w nucleotides
- Hydrogen bonds b/w adenine-thymine & cytosine-guanine.
Explain importance of antiparallel nature of DNA strands. (3)
- DNA strands run in opposite directions
- DNA strands have a 3’ & 5’ end.
- Shapes of 5’ end & 3’ end are different
Contrast the structure of mRNA and tRNA. (3)
- mRNA is longer
- mRNA = straight molecule, tRNA is a folded molecule
- mRNA has no hydrogen bonds, tRNA has some.
Explain how mRNA controls translation. (3)
- contains start codon that acts as a signal to start translation
- RNA has stop codon at end of gene to signal end of translation
- to produce a complete polypeptide
Describe importance of tRNA in protein synthesis. (3)
- bind w/ their specific amino acid & bring them back to mRNA
- 2 tRNAs fit on ribose & bring their a.a side by side
- for a peptide bond to form
How does a globular protein enable performing its function. (3)
- haemoglobin
- orientation of R groups enables protein to be soluble
- their solubility allows them to perform roles in transport
Explain why one symptom of anaemia is fatigue. (3)
- insufficient iron = less haemoglobin produces
- therefore, decrease in oxygen transported to cells
- so rate of respiration decreases, causing fatigue
State the functions of enzymes used in DNA replication. (2)
- DNA helicase used to break hydrogen bonds b/w 2 DNA strands
- DNA polymerase used to join nucleotides together
Explain role of free DNA nucleotides. (1)
- to form complimentary base pairs
Why is DNA replication described as semiconservative. (2)
- each strand of DNA is copied
- therefore, half of the parent strand is conserved within the daughter strand
Explain why scientists use nitrogen isotopes. (2)
- Nitrogen is an essential chemical component of DNA
- therefore, every time DNA replicates it incorporates new Nitrogen atoms into the DNA.
