Biological Molecules
This monosaccharide is the main respiratory substrate in cells.
What is glucose?
This property of the cell-surface membrane allows some substances through but not others.
What is selective permeability?
This term describes the movement of molecules from high to low concentration.
What is diffusion?
Explain why independent segregation contributes to variation in gametes.
homologous chromosome pairs line up and separate independently, producing different combinations of maternal and paternal chromosomes in gametes.
The unit used to measure the amount of substance.
What is the mole?
This type of reaction joins monomers together by removing water.
What is a condensation reaction?
Explain why facilitated diffusion is still considered passive transport.
because substances move down a concentration gradient and no ATP is required, even though membrane proteins are involved.
The name of the tissue that transports sucrose in plants.
What is phloem?
This index is commonly used to measure biodiversity.
What is Simpson’s Index of Diversity?
Explain why momentum is always conserved in a closed system.
because the total external force is zero, so the total momentum before and after an interaction remains constant.
Explain why triglycerides are a good energy store.
they contain many C–H bonds, so they release a lot of energy when oxidised, and are also insoluble, so they do not affect water potential.
A student says, “All substances that cross membranes need transport proteins.” Explain why this is incorrect.
some small or non-polar molecules (such as oxygen) can pass directly through the phospholipid bilayer by simple diffusion.
Explain why mass flow in the xylem is faster than diffusion alone would be.
water molecules move together in a transpiration stream, pulled upward by cohesion and tension, rather than moving only by random diffusion.
A mutation occurs in DNA but does not alter the amino acid sequence of the protein. Explain how this is possible.
the genetic code is degenerate, so more than one codon can code for the same amino acid.
The reason why you see light and dark fringes using double slit
constructive and destructive interference
Explain why a change in pH can reduce enzyme activity.
pH changes can alter ionic and hydrogen bonds, changing the enzyme’s tertiary structure and active site, so fewer enzyme-substrate complexes form.
Explain why electron microscopes have transformed our understanding of cell ultrastructure.
they have much greater resolution than light microscopes, so they can distinguish much smaller structures such as ribosomes, ER, and membrane detail that light microscopes cannot resolve clearly.
Explain why haemoglobin is described as having a high affinity for oxygen in the lungs but a lower affinity in respiring tissues.
in the lungs, high oxygen concentration promotes oxygen loading; in respiring tissues, lower oxygen concentration promotes unloading, allowing oxygen to be delivered where needed.
Name two causes of genetic variation in a population.
What are:
This intermolecular force exists between all molecules, even non-polar ones, due to temporary fluctuations in electron density.
What are London forces (instantaneous dipole-induced dipole forces)?
A competitive inhibitor reduces the rate of an enzyme-controlled reaction. Explain why increasing substrate concentration may reduce the effect of the inhibitor.
the inhibitor competes with the substrate for the active site, so increasing substrate concentration increases the chance that substrate binds instead of inhibitor.
Explain why surface area to volume ratio becomes a problem as cells increase in size.
volume increases faster than surface area, so exchange becomes less efficient and diffusion distances become greater.
The term for the pressure created when water enters plant cells and pushes against the cell wall.
What is turgor pressure?
Explain why small populations are often more vulnerable to extinction than large populations.
they usually have less genetic diversity, so they are less likely to possess advantageous alleles, making them less able to adapt to environmental change or disease.
The value that related energy and frequency in photons
What is planks constant