Key topics that haven't been assessed for a while (PAPER 3) Flashcards
(23 cards)
What is the cohesion-tension theory in xylem transport?
Water is pulled up xylem due to transpiration causing a loss in water potential in the leaves, cohesion between water molecules increases, and adhesion to xylem walls, more water is drawn up.
What is the mass flow hypothesis in phloem transport?
- Sources of sucrose actively transported between source cells, sieve tubes and phloem, aided by the companion cells providing ATP.
- Sucrose is transported to sink cells.
What enzyme breaks hydrogen bonds during DNA replication?
DNA helicase.
What enzyme synthesises new DNA strands in replication?
DNA polymerase.
What is transcription in protein synthesis?
RNA polymerase forms pre-mRNA using one DNA strand as template.
What is translation in protein synthesis?
mRNA is translated at ribosome; tRNA brings amino acids to form a polypeptide.
How does haemoglobin transport oxygen?
It binds O₂ in lungs (high pO₂) and releases it in tissues (low pO₂); affected by Bohr effect.
What happens in meiosis I?
Homologous chromosomes pair, crossing over occurs, and homologues separate.
How do fish perform gas exchange?
Via gill lamellae using counter-current flow to maintain O₂ gradient.
How do insects exchange gases?
Air enters via spiracles into tracheae; O₂ diffuses to cells.
Describe the role of phagocytosis in immunity.
Phagocytes engulf pathogens, digest them, and present antigens.
What is the function of B cells?
Produce antibodies and memory cells as part of humoral response.
What are the types of stem cells?
Totipotent, pluripotent, multipotent, and induced pluripotent (iPS).
How do transcription factors regulate gene expression?
They bind DNA at promoter regions to activate or repress transcription.
What is DNA methylation?
An epigenetic modification that silences genes.
Describe an action potential in a neuron.
Na⁺ influx causes depolarisation; K⁺ efflux causes repolarisation.
What happens at a synapse?
Neurotransmitter released from presynaptic neuron binds postsynaptic receptors.
Where does the light-dependent reaction occur?
In the thylakoid membranes of chloroplasts.
What enzyme fixes CO₂ in the Calvin cycle?
Rubisco.
What is the difference between GPP and NPP?
GPP is total energy from photosynthesis; NPP = GPP – respiration.
What is ecological succession?
Gradual change in species composition, from pioneer species to climax community.
How do farming practices increase energy efficiency?
By reducing movement, controlling temperature, using fertilisers and pesticides.
