Biology: The Dynamic Science Premium
Guide | Updated Exam Questions and In-
Depth Answers with Detailed Explanations
(Already Passed A+) 2026/2027
• phospholipids and sterols -✓✓two major types of lipids in a biological membrane
• polar -✓✓phospholipids have a ---- end containing a phosphate group linked to
one of several alcohols or amino acids
• nonpolar -✓✓phospholipids have a ---- end containing two fatty acid tails
• hydrophilic -✓✓the polar end of a phospholipid is ----
• hydrophobic -✓✓the nonpolar ends of a phospholipid are ----
• phospholipid hydrocarbon chains -✓✓the nonpolar part of sterols are packed in
with the -----
• hydrogen bonds -✓✓Membrane lipids only rarely flip-flop between the two
layers because their polar heads are attracted by ---------- to the water molecules of
the aqueous solutions on either side of the membrane. These attractions keep the
heads facing outward toward the aqueous solution, and make transitions between
layers of the membrane energetically unfavorable.
• transport proteins -✓✓transmembrane proteins that help a certain substance or
class of closely related substances to cross the membrane.
examples include channel proteins & ion pumps
• receptors -✓✓membrane proteins that recognize and bind specific molecules in
the EXTRAcellular environment
• enzymes -✓✓many of these proteins are membrane proteins, orientated in the
membrane so they act on extracellular molecules
, i.e. the smooth ER has these to catalyze lipid synthesis and metabolism
• passive transport -✓✓this transport depends on concentration differences on both
sides of the membrane. it moves molecules from high to low concentration. no
energy required.
• active transport -✓✓transport which moves substances against their concentration
gradients. it uses energy like ATP
• diffusion -✓✓a type of passive transport in cells in which molecules move from
areas where there are more of them to areas where there are fewer of them
• dynamic equilibrium -✓✓result of diffusion where there is continuous movement
of particles but no overall change in concentration
• simple diffusion -✓✓movement of a solute from an area of high concentration to
an area of low concentration
examples include nonpolar inorganic gases and nonpolar organic molecules like
hormones
• facilitated diffusion -✓✓process of diffusion in which molecules pass across the
membrane through cell membrane channels down their concentration gradient
examples include polar and charged molecules
• channel proteins -✓✓have a hydrophilic channel that certain molecules or ions
can use as a tunnel
• ion channels -✓✓a type of channel protein that allows certain ions to diffuse
across a plasma membrane down an electrochemical gradient
• gated channels -✓✓a type of ion channel that is a protein channel that opens and
closes in reaction to a stimulus (change in voltage or by binding signal molecules)
• change in shape -✓✓opening or closing of a gated channel involves a
________________
Guide | Updated Exam Questions and In-
Depth Answers with Detailed Explanations
(Already Passed A+) 2026/2027
• phospholipids and sterols -✓✓two major types of lipids in a biological membrane
• polar -✓✓phospholipids have a ---- end containing a phosphate group linked to
one of several alcohols or amino acids
• nonpolar -✓✓phospholipids have a ---- end containing two fatty acid tails
• hydrophilic -✓✓the polar end of a phospholipid is ----
• hydrophobic -✓✓the nonpolar ends of a phospholipid are ----
• phospholipid hydrocarbon chains -✓✓the nonpolar part of sterols are packed in
with the -----
• hydrogen bonds -✓✓Membrane lipids only rarely flip-flop between the two
layers because their polar heads are attracted by ---------- to the water molecules of
the aqueous solutions on either side of the membrane. These attractions keep the
heads facing outward toward the aqueous solution, and make transitions between
layers of the membrane energetically unfavorable.
• transport proteins -✓✓transmembrane proteins that help a certain substance or
class of closely related substances to cross the membrane.
examples include channel proteins & ion pumps
• receptors -✓✓membrane proteins that recognize and bind specific molecules in
the EXTRAcellular environment
• enzymes -✓✓many of these proteins are membrane proteins, orientated in the
membrane so they act on extracellular molecules
, i.e. the smooth ER has these to catalyze lipid synthesis and metabolism
• passive transport -✓✓this transport depends on concentration differences on both
sides of the membrane. it moves molecules from high to low concentration. no
energy required.
• active transport -✓✓transport which moves substances against their concentration
gradients. it uses energy like ATP
• diffusion -✓✓a type of passive transport in cells in which molecules move from
areas where there are more of them to areas where there are fewer of them
• dynamic equilibrium -✓✓result of diffusion where there is continuous movement
of particles but no overall change in concentration
• simple diffusion -✓✓movement of a solute from an area of high concentration to
an area of low concentration
examples include nonpolar inorganic gases and nonpolar organic molecules like
hormones
• facilitated diffusion -✓✓process of diffusion in which molecules pass across the
membrane through cell membrane channels down their concentration gradient
examples include polar and charged molecules
• channel proteins -✓✓have a hydrophilic channel that certain molecules or ions
can use as a tunnel
• ion channels -✓✓a type of channel protein that allows certain ions to diffuse
across a plasma membrane down an electrochemical gradient
• gated channels -✓✓a type of ion channel that is a protein channel that opens and
closes in reaction to a stimulus (change in voltage or by binding signal molecules)
• change in shape -✓✓opening or closing of a gated channel involves a
________________
