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In a model experiment, bacteria initially use nitrogen-15, a heavier stable isotope, to make their DNA. They are transferred to a medium supplying only nitrogen-14, the lighter isotope. DNA extracted before transfer and after one and two cell divisions is…
The conceptual diagrams model changes in a developing neural network. (i) State two major changes visible between early development and later childhood. (ii) Outline the main change visible between later childhood and adolescence.
Neurons in the brain have a high metabolic demand. Suggest a major source of energy for this tissue.
Compare a bacterial cell with a typical animal cell. Which contrast is valid? A. Only the bacterium has ribosomes B. Only the animal cell contains hereditary DNA C. Both must have a cellulose cell wall D. The animal cell has membrane-bound internal…
A runner accelerates from a walk into a sustained run. Outline two internal mechanisms that can raise the runner’s heart rate.
Explain how platelets help prevent pathogens entering through a skin wound.
Specialized neurons develop early in an embryo. State the process by which cells initially become neurons.
(a) Outline the structure and properties of triglycerides. (b) Explain how energy moves through a photosynthetic ecosystem.
Mammals use olfactory receptor cells to detect odours. Describe two features these cells need for this role.
An odour provides information about the surrounding environment. Suggest two mammalian behaviours that could change when a particular odour is detected.