Aqa Biology AS unit 2 five/six markers

HideShow resource information

Q

Explain how water enters xylem from the endodermis

  • 6 MARKER
  • Casparian strip blocks the apoplastic pathway and only allows water to move through the symplastic pathway (1)
  • Active transport by endodermis of ions/salt into the xylem (2)
  • Lower water potential in the xylem so water moves by osmosis down a water potential gradient into the xylem (1)
  • Evaporation of water from the leaves results in a transpiration pull (2)
  • Water molecules bind to the xylem and create a continuous water column travelling up to the leaves (2)
1 of 8

Q

Describe how DNA is replicated.

  • 6 MARKER.
  • DNA strands separate and the H-bonds break (1)
  • DNA helicase is involved in this process (1)
  • Each strand acts as a template and free nucleotide bases attach (2)
  • Complementary base pairing occurs, e.g. AT, GC (1)
  • DNA polymerase joins the nucleotides onto the new strands (1)
  • H-bonds reform (1)
  • Semi-conservative replication (1)
2 of 8

Q

Describe how tissue fluid is formed and how it is returned

  • 6 MARKER.
  • Formation:
  • High hydrostatic pressures force water and fluid out (2)
  • Large proteins remain in the capillary (1)
  • Return:
  • Low water potential in capillary due to plasma proteins (2)
  • Water enters capillary by osmosis (2)
  • Some is returned via the lymphatic system (1)
3 of 8

Q

Explain how oxygen is loaded, transported and unloaded in the body.

  • 6 MARKER.
  • Haemoglobin has a high affinity for oxygen so carries it in red blood cells (2)
  • Loading/uptake in the lungs (1)
  • At high partial pressure (1)
  • Unloads/dissociates to respiring tissues (1)
  • At low partial pressure (1)
  • Unloading is linked to a higher carbon dioxide concentration (1)
4 of 8

Q

Describe how gene transmission and selection have led to antibiotics being less effective.

  • 6 MARKER.
  • Antibiotic resistant gene/allele is shared/spread through vertical gene transmission (2)
  • Resistant bacteria survive and reproduce (1)
  • Increase in frequency of resistant gene/allele in future generations (1)
  • Horizontal gene transmission (1)
  • Plasmid DNA cloned/spread through conjugation (2)
  • Can occur between bacteria of different species (1)
5 of 8

Q

Arteries and arterioles take blood away from the heart; how are their walls adapted to this function?

  • 6 MARKER.
  • Elastic tissue stretches under pressure when the heart beats (1)
  • Recoils after (1)
  • Evens out/maintains a smooth pressure flow (1)
  • Muscle contracts (1)
  • Reduces diameter of the lumen (1)
  • Changes flow/pressure (1)
  • Epithelium is smooth (1)
  • Reduces friction (1)
6 of 8

Q

Describe the processes that lead to a reduction in genetic variation.

  • 6 MARKER.
  • (General principle) - reduced variety/number of alleles in new population (1)
  • Founder effect: a few individuals from a population become isolated/form colonies (2)
  • Genetic bottlenecks: significant fall in the size of the population (2)
  • Selective breeding/artificial selection (1)
  • Using organisms with particular alleles/traits (1)
7 of 8

Q

Scientists studied two species of North American seahorses; how could they distinguish how closely related they are?

  • 6 MARKER.
  • Compare DNA/sequence of bases and nucleotides (2)
  • DNA hybridisation (1)
  • Separate DNA strands (1)
  • Mix DNA strands of different species (1)
  • Temperature requires to separate the strands indicates relationship (1)
  • Compare same/named protein (1)
  • Sequence of amino acids/primary structure (1)
8 of 8

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all DNA, genetics and evolution resources »