A-Level Biology - OCR
Antibodies are made by plasma cells. Explain how plasma cells are specialised for their role -
ANS-Plasma cells have a lot of ribosomes, rough endoplasmic reticulum, Golgi apparatus and
mitochondria.
\As more solute is added to a solution, what happens to the solute potential and hence the
water potential? - ANS-Solute potential decreases, hence water potential decreases
\Briefly outline the events of atrial systole - ANS-Left and right atria contract together; blood is
squeezed from the atria through the atrioventricular valves into the ventricles, down a pressure
gradient.
\Briefly outline the events of diastole - ANS-Once ventricular contraction is complete, heart
muscle starts to relax, heart starts to fill with blood again and semilunar valves close
\Briefly outline the events of ventricular systole - ANS-Ventricular blood pressure rises very
quickly to a level above the arteries; semilunar valves open and blood rushes out of ventricles
into the arteries
\Cacti are succulents. What does this mean? - ANS-They store water in their stems which
become fleshy and swollen
\Channel proteins and carrier proteins have what main role within the membrane? -
ANS-Transport
\Define and describe exocytosis - ANS-The bulk transport of particles too large to pass through
the membrane, out of the cell. It works like a reversal of pinocytosis. A vesicle containing the
substance fuses with the plasma membrane. The fused site opens, releasing the contents of the
secretory vesicle.
\Define and describe phagocytosis - ANS-The intake of solid particles into the cell by engulfing.
Pseudopodia surround the particles, the membrane fuses together, to form a vesicle.
\Define and describe pinocytosis - ANS-The intake of liquids into the cell by engulfing. The
plasma membrane invaginates, and the membrane fuses around the substance, forming a
vesicle.
\Define bulk transport and give two examples - ANS-The movement of large molecules that are
too big to pass across the plasma membrane. Endocytosis (phagocytosis or pinocytosis) brings
large molecules INTO the cell, enclosed in a vesicle. Exocytosis transports large molecules
OUT of cells.
\Define the term active transport - ANS-Movement of molecules, against their concentration
gradient (using energy liberated from ATP hydrolysis) using specific protein channels or carriers
\Define the term diffusion. - ANS-The net movement of a substance from an area of high
concentration to an area of low concentration. It is passive, does NOT require ATP.
\Define the term epidemic - ANS-A rapid spread of disease through a high proportion of a
population (usually within a country)
\Define the term facilitated diffusion - ANS-Movement of molecules from a high concentration to
a low concentration, across a partially permeable membrane, via specific channel or carrier
proteins. It is passive, does NOT require ATP
,\Define the term osmosis - ANS-The movement of water molecules from a region of higher
water potential to a region of lower water potential, across a partially permeable membrane
\Define the term tissue - ANS-A group of cells working together to perform a particular function
\Define the term translocation - ANS-Transport of assimilates from source to sink (tissue that
needs them)
\Describe 2 major pathways taken by water to move between cells - ANS-Apoplast - through
spaces in cell walls and between cells (mass flow...not osmosis); symplast - moves through
cytoplasm and between cells via plasmodesmata
\Describe 3 adaptations of marram grass (xerophyte) and explain their importance - ANS-Leaf
rolled longitudinally trapping air inside (air becomes humid and reduces water loss from the
leaf); thick waxy cuticle on upper epidermis (reduces evaporation); stomata on lower epidermis
inside rolled leaf (protected by enclosed air space); stomata are in pits in lower epidermis which
is folded and covered by hairs (reduces air movement and hence water loss); spongy mesophyll
very dense with few air spaces (less surface area for evaporation of water)
\Describe and explain how erythrocytes are adapted for their function - ANS-Very small so have
a large SA:vol (biconcave shape also ensures this) meaning oxygen can reach all regions inside
the cell; well-developed cytoskeleton allows the erythrocytes to change shape and move
through very narrow capillaries; no nucleus or organelles so more space for Hb molecules
\Describe and explain how sperm cells are adapted for their function - ANS-Acrosome in head
contains enzymes to penetrate the egg follicle during fertilisation; many mitochondria to
generate ATP for flagellar movement; large haploid nucleus in head to fertilise haploid ovum
\Describe and explain three features of a good exchange surface - ANS-Large SA (folded walls;
provides more space for relevant molecules to pass through); thin, permeable barriers (reduces
diffusion distance); good blood supply (keeps high concentration gradients for rapid diffusion)
\Describe how a microorganism can become resistant to an antibiotic - ANS-Bacteria that
survive a treatment will be slightly resistant to the antibiotic and the antibiotic acts as a selective
force which selects the resistant individuals. When they reproduce, some of their offspring may
be more resistant, thus resistance evolves.
\Describe how a root hair cell plasma membrane is adapted for transport of mineral ions -
ANS-Contains specialised carrier proteins to transport specific mineral ions in by active
transport
\Describe how agglutinins function - ANS-Agglutinins cross link pathogens by binding
specifically via their variable regions. Pathogens are clumped together (agglutinated), meaning
they cannot enter host cells and are easier to phagocytose
\Describe how an antigen presenting cell leads to large numbers of T helper cells - ANS-APC
binds specifically to a Th cell (clonal selection). This selected Th cell then proliferates by mitosis
(clonal expansion)
\Describe how antitoxins function - ANS-Neutralise toxin molecules released by a pathogen
through direct binding
\Describe how B lymphocytes are activated and the role of activated B lymphocytes - ANS-Th
cell binds specifically to B lymphocyte; B lymphocyte differentiates into a plasma cell. Plasma
cells release antibodies specific to the particular antigen
\Describe how capillaries are adapted for exchange - ANS-Narrow lumen (squeezes red blood
cells against walls so transfer of oxygen is better to the tissues); walls consist of single layer of
, endothelial cells (reduces diffusion distance); walls are permeable (allows blood plasma and
dissolved substances to leave the blood)
\Describe how carrier proteins are used in active transport - ANS-Molecule binds to specific site
in carrier protein; ATP binds to separate binding site; carrier protein changes shape
(conformational change) and transports molecule across membrane
\Describe how cartilage is adapted for its function - ANS-Connective tissue that contains elastin
and collagen fibres; prevents ends of bones from rubbing together
\Describe how cytokinesis differs between dividing animal cells and plant cells - ANS-Animal
cells - cleavage furrow forms and plasma membrane is pulled inwards, splitting the cytoplasm;
plant cells - vesicles assemble around metaphase plate and fuse; new plasma membrane and
cellulose cell wall are laid down
\Describe how guard cells open in sunny conditions - ANS-Light energy --> ATP; ATP used to
actively transport potassium ions from epidermal cells into guard cells; water potential of guard
cells lowered; water moves in by osmosis and guard cells become turgid
\Describe how human alveoli are adapted to reduce diffusion distances - ANS-Alveolus wall one
cell thick; capillary wall one cell thick; walls of alveoli/capillaries contain squamous (flattened)
cells; caoillaries are in close contact with alveoli walls; capillaries are narrow to restrict RBC
movement
\Describe how macrophages process antigens for presentation on their cell surface membrane -
ANS-Antigen fragments combined with MHC (special glycoproteins in cytoplasm)
\Describe how meiosis produces genetic variation in the gametes produced - ANS-Crossing
over in prophase I; independent assortment in metaphase I; independent assortment in
metaphase II
\Describe how neutrophils are specialised for their role - ANS-Plasma membrane contains
receptors for opsonins, well developed cytoskeleton for phagocytosis, many mitochondria for
respiration, many ribosomes to make enzymes, many lysosomes.
\Describe how opsonins function - ANS-Opsonins bind specifically to an antigen on a pathogen
(via the variable region), clearly marking the pathogen for destruction by a neutrophil. A
neutrophil will bind to the constant region of the opsonin and destroy the pathogen by
phagocytosis
\Describe how T killer cells destroy a virally infected cell - ANS-Release perforins which punch
holes in the membrane of the cell; Tk cell inserts channels through which it floods hydrogen
peroxide/nitric acid/hydrolytic enzymes
\Describe how the charge inside a RBC is maintained when hydreogencarbonate ions diffuse
into the plasma - ANS-Chloride ions move into the RBCs from the plasma (chloride shift)
\Describe how the nasal cavity is adapted for exchange - ANS-Large SA with a good blood
supply, warming air to body temperature; lined with hair (which secretes mucus) to trap dust and
MOs, protecting from infection; moist surfaces to increase the humidity of the incoming air,
reducing evaporation from exchange surfaces
\Describe how the pH inside a RBC is buffered as hydrogen ions build up inside, making the
RBC very acidic - ANS-Hydrogen ions are taken out of solution and combined with haemoglobin
to form haemoglobinic acid (HHb)
\Describe how the structure of an antibody enables it to perform its function - ANS-The variable
region is specific to the antigen - it has a shape that is complementary to the shape of the
Antibodies are made by plasma cells. Explain how plasma cells are specialised for their role -
ANS-Plasma cells have a lot of ribosomes, rough endoplasmic reticulum, Golgi apparatus and
mitochondria.
\As more solute is added to a solution, what happens to the solute potential and hence the
water potential? - ANS-Solute potential decreases, hence water potential decreases
\Briefly outline the events of atrial systole - ANS-Left and right atria contract together; blood is
squeezed from the atria through the atrioventricular valves into the ventricles, down a pressure
gradient.
\Briefly outline the events of diastole - ANS-Once ventricular contraction is complete, heart
muscle starts to relax, heart starts to fill with blood again and semilunar valves close
\Briefly outline the events of ventricular systole - ANS-Ventricular blood pressure rises very
quickly to a level above the arteries; semilunar valves open and blood rushes out of ventricles
into the arteries
\Cacti are succulents. What does this mean? - ANS-They store water in their stems which
become fleshy and swollen
\Channel proteins and carrier proteins have what main role within the membrane? -
ANS-Transport
\Define and describe exocytosis - ANS-The bulk transport of particles too large to pass through
the membrane, out of the cell. It works like a reversal of pinocytosis. A vesicle containing the
substance fuses with the plasma membrane. The fused site opens, releasing the contents of the
secretory vesicle.
\Define and describe phagocytosis - ANS-The intake of solid particles into the cell by engulfing.
Pseudopodia surround the particles, the membrane fuses together, to form a vesicle.
\Define and describe pinocytosis - ANS-The intake of liquids into the cell by engulfing. The
plasma membrane invaginates, and the membrane fuses around the substance, forming a
vesicle.
\Define bulk transport and give two examples - ANS-The movement of large molecules that are
too big to pass across the plasma membrane. Endocytosis (phagocytosis or pinocytosis) brings
large molecules INTO the cell, enclosed in a vesicle. Exocytosis transports large molecules
OUT of cells.
\Define the term active transport - ANS-Movement of molecules, against their concentration
gradient (using energy liberated from ATP hydrolysis) using specific protein channels or carriers
\Define the term diffusion. - ANS-The net movement of a substance from an area of high
concentration to an area of low concentration. It is passive, does NOT require ATP.
\Define the term epidemic - ANS-A rapid spread of disease through a high proportion of a
population (usually within a country)
\Define the term facilitated diffusion - ANS-Movement of molecules from a high concentration to
a low concentration, across a partially permeable membrane, via specific channel or carrier
proteins. It is passive, does NOT require ATP
,\Define the term osmosis - ANS-The movement of water molecules from a region of higher
water potential to a region of lower water potential, across a partially permeable membrane
\Define the term tissue - ANS-A group of cells working together to perform a particular function
\Define the term translocation - ANS-Transport of assimilates from source to sink (tissue that
needs them)
\Describe 2 major pathways taken by water to move between cells - ANS-Apoplast - through
spaces in cell walls and between cells (mass flow...not osmosis); symplast - moves through
cytoplasm and between cells via plasmodesmata
\Describe 3 adaptations of marram grass (xerophyte) and explain their importance - ANS-Leaf
rolled longitudinally trapping air inside (air becomes humid and reduces water loss from the
leaf); thick waxy cuticle on upper epidermis (reduces evaporation); stomata on lower epidermis
inside rolled leaf (protected by enclosed air space); stomata are in pits in lower epidermis which
is folded and covered by hairs (reduces air movement and hence water loss); spongy mesophyll
very dense with few air spaces (less surface area for evaporation of water)
\Describe and explain how erythrocytes are adapted for their function - ANS-Very small so have
a large SA:vol (biconcave shape also ensures this) meaning oxygen can reach all regions inside
the cell; well-developed cytoskeleton allows the erythrocytes to change shape and move
through very narrow capillaries; no nucleus or organelles so more space for Hb molecules
\Describe and explain how sperm cells are adapted for their function - ANS-Acrosome in head
contains enzymes to penetrate the egg follicle during fertilisation; many mitochondria to
generate ATP for flagellar movement; large haploid nucleus in head to fertilise haploid ovum
\Describe and explain three features of a good exchange surface - ANS-Large SA (folded walls;
provides more space for relevant molecules to pass through); thin, permeable barriers (reduces
diffusion distance); good blood supply (keeps high concentration gradients for rapid diffusion)
\Describe how a microorganism can become resistant to an antibiotic - ANS-Bacteria that
survive a treatment will be slightly resistant to the antibiotic and the antibiotic acts as a selective
force which selects the resistant individuals. When they reproduce, some of their offspring may
be more resistant, thus resistance evolves.
\Describe how a root hair cell plasma membrane is adapted for transport of mineral ions -
ANS-Contains specialised carrier proteins to transport specific mineral ions in by active
transport
\Describe how agglutinins function - ANS-Agglutinins cross link pathogens by binding
specifically via their variable regions. Pathogens are clumped together (agglutinated), meaning
they cannot enter host cells and are easier to phagocytose
\Describe how an antigen presenting cell leads to large numbers of T helper cells - ANS-APC
binds specifically to a Th cell (clonal selection). This selected Th cell then proliferates by mitosis
(clonal expansion)
\Describe how antitoxins function - ANS-Neutralise toxin molecules released by a pathogen
through direct binding
\Describe how B lymphocytes are activated and the role of activated B lymphocytes - ANS-Th
cell binds specifically to B lymphocyte; B lymphocyte differentiates into a plasma cell. Plasma
cells release antibodies specific to the particular antigen
\Describe how capillaries are adapted for exchange - ANS-Narrow lumen (squeezes red blood
cells against walls so transfer of oxygen is better to the tissues); walls consist of single layer of
, endothelial cells (reduces diffusion distance); walls are permeable (allows blood plasma and
dissolved substances to leave the blood)
\Describe how carrier proteins are used in active transport - ANS-Molecule binds to specific site
in carrier protein; ATP binds to separate binding site; carrier protein changes shape
(conformational change) and transports molecule across membrane
\Describe how cartilage is adapted for its function - ANS-Connective tissue that contains elastin
and collagen fibres; prevents ends of bones from rubbing together
\Describe how cytokinesis differs between dividing animal cells and plant cells - ANS-Animal
cells - cleavage furrow forms and plasma membrane is pulled inwards, splitting the cytoplasm;
plant cells - vesicles assemble around metaphase plate and fuse; new plasma membrane and
cellulose cell wall are laid down
\Describe how guard cells open in sunny conditions - ANS-Light energy --> ATP; ATP used to
actively transport potassium ions from epidermal cells into guard cells; water potential of guard
cells lowered; water moves in by osmosis and guard cells become turgid
\Describe how human alveoli are adapted to reduce diffusion distances - ANS-Alveolus wall one
cell thick; capillary wall one cell thick; walls of alveoli/capillaries contain squamous (flattened)
cells; caoillaries are in close contact with alveoli walls; capillaries are narrow to restrict RBC
movement
\Describe how macrophages process antigens for presentation on their cell surface membrane -
ANS-Antigen fragments combined with MHC (special glycoproteins in cytoplasm)
\Describe how meiosis produces genetic variation in the gametes produced - ANS-Crossing
over in prophase I; independent assortment in metaphase I; independent assortment in
metaphase II
\Describe how neutrophils are specialised for their role - ANS-Plasma membrane contains
receptors for opsonins, well developed cytoskeleton for phagocytosis, many mitochondria for
respiration, many ribosomes to make enzymes, many lysosomes.
\Describe how opsonins function - ANS-Opsonins bind specifically to an antigen on a pathogen
(via the variable region), clearly marking the pathogen for destruction by a neutrophil. A
neutrophil will bind to the constant region of the opsonin and destroy the pathogen by
phagocytosis
\Describe how T killer cells destroy a virally infected cell - ANS-Release perforins which punch
holes in the membrane of the cell; Tk cell inserts channels through which it floods hydrogen
peroxide/nitric acid/hydrolytic enzymes
\Describe how the charge inside a RBC is maintained when hydreogencarbonate ions diffuse
into the plasma - ANS-Chloride ions move into the RBCs from the plasma (chloride shift)
\Describe how the nasal cavity is adapted for exchange - ANS-Large SA with a good blood
supply, warming air to body temperature; lined with hair (which secretes mucus) to trap dust and
MOs, protecting from infection; moist surfaces to increase the humidity of the incoming air,
reducing evaporation from exchange surfaces
\Describe how the pH inside a RBC is buffered as hydrogen ions build up inside, making the
RBC very acidic - ANS-Hydrogen ions are taken out of solution and combined with haemoglobin
to form haemoglobinic acid (HHb)
\Describe how the structure of an antibody enables it to perform its function - ANS-The variable
region is specific to the antigen - it has a shape that is complementary to the shape of the
