Biology Important Questions Flashcards
Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. (5 marks)
Micelle contains bile salts and fatty acids
Makes fatty acids soluble
Fatty acids absorbed by diffusion
Triglycerides form
Vesicles move to cell membrane
Describe how mRNA is formed by transcription in eukaryotes (5 marks)
Hydrogen bonds break by DNA helicase
One strand of DNA acts as a template
Free RNA nucleotides align by complementary base pairings
RNA polymerase joins nucleotides by phosphodiester bonds
Uracil instead of Thymine
Pre-mRNA is spliced
Describe how a polypeptide is formed by translation of mRNA (6 marks)
mRNA leaves via a nuclear pore to the ribosome
tRNA anticodon is complementary to the mRNA codon
tRNA brings specific amino acids
Joined by peptide bonds using ATP
Ribosome moves along the mRNA strand to form a polypeptide
tRNA released to collect another amino acid
Describe and explain 5 ways which substances are transported across cell membranes (5 marks)
Diffusion - small molecules down a concentration gradient
Facilitated diffusion - down a concentration gradient via protein carrier
Osmosis - water down a potential gradient
Active transport - against a concentration gradient using ATP and carrier protein
Co-transport - 2 substances using a carrier protein
Describe the structure of DNA (5 marks)
Polymer of nucleotides
Adenine, thymine, cytosine and guanine
Deoxyribose, phosphate and nitrogenous base
Double helix
Phosphodiester bonds
Explain how water from tissue fluid is returned to the circulatory system (4 marks)
Plasma proteins remain
Reduces the water potential in the capillaries
Water moves by osmosis
Water returns to the lymphatic system
Describe the light independent reaction (Calvin Cycle) (6 marks)
CO2 combines with RuBO (ribulose biphosphate) using the enzyme Rubisco
Produces 2 GP molecules (glycerate-3-phosphate)
GP reduced to 2 molecules of TP (triose phosphate)
Using reduced NADP
Using energy from ATP
TP converted into organic substances e.g glucose
During the light-independent reaction, carbon dioxide is converted into organic substances. Describe how.
Carbon dioxide combines with RuBP
Produces two glycerate-3-phosphate molecules
GP reduced to TP
Using reduced NADP
Using energy from ATP
Triose phosphate (TP) converted into glucose
Describe the cohesion-tension theory of water transport in the xylem (5 marks)
Evaporation of water from the levels
Lowers the water potential of leaf cells
Water pulled up the xylem
Water molecules stick together by hydrogen bonds
Forming continuous water column
Describe the mass flow hypothesis for the mechanism of translocation in plants (4 marks)
Leaf sugars actively transported into phloem
Lowers water potential of sieve cell
Increase in pressure causes mass movement
Sugars used for respiration
Describe the transport of carbohydrates in plants’ (5 marks)
Sucrose enters the phloem by active transport
By companion cells
Lowers water potential in the phloem, water enters via osmosis
Produces high hydrostatic pressure
Mass flow to respiring cells
What is glycolysis? (4 marks)
Glucose is phosphorylated using ATP
Turns into glucose phosphate
Triose phosphate (TP) is produced by splitting glucose phosphate
TP is oxidised to form 2 pyruvate molecules
NAD reduced to NADH
Net gain of ATP
Compare active and passive immunity
Active takes time to work whereas passive is fast-acting
Active is long term immunity, passive is short term
Memory cells are not made in passive, they are made in active
In passive antibodies are introduced whereas in active they are produced naturally
Allopatric Speciation 6 mark answer scheme
Allopatric speciation due to isolation
Geographical isolation occurs
No interbreeding can happen between the separated populations
Random mutations create new alleles leading to variation
There are different selection pressures in the two environments
Better adapted organisms survive and reproduce
Leads the allele frequency increasing
6 mark scheme for Sympatric Speciation
Occurs in the same population
Random mutations occur leading to variation
Reproductive isolation
Change in allele frequency
Disruptive selection causes Sympatric
Cannot interbreed and produce fertile offspring
