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A LEVEL BIOLOGY OCR EXAM QUESTIONS
AND ANSWERS
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Contains
chromatin (DNA wound around histones)
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What is the structure and function of the nucleolus? - CorreCt Answers Made of RNA, produces ribosomes
...
Separates the nucleus from the rest of the cell
...


What is the structure and function of the rough endoplasmic reticulum
(RER)? - CorreCt Answers -A system of fluid filled membranes studded
with ribosomes
...
Large surface area
formed by folding, enables lots of protein synthesis
...


What is the structure and function of the smooth endoplasmic reticulum
(SER)? - CorreCt Answers -A system of fluid filled membranes
...
Contain enzymes for cholesterol, lipid and phospholipid
synthesis
...
Vesicles from the RER

join at the cis face
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Folding proteins into their
3D shape
...


What is the structure and function of the ribosomes? - CorreCt Answers -2
subunits, large and small
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Proteins synthesised here
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Inner membrane folded into cristae within a
fluid filled matrix
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Site of aerobic
respiration
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break
down old organelles and foreign matter for reuse
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Inner membrane forms flat discs filled with
chlorophyll called thylakoids, in stacks called granum
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Contain own DNA and 70s
ribosomes
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What is the structure and function of the plasma membrane? - CorreCt
Answers -Phospholipid bilayer, cholesterol, proteins, glycoproteins,
glycolipids
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Controls
what enters and leaves the cell
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Acts as a receptor for
various chemicals
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What is the structure and function of the centrioles? - CorreCt Answers Present in animals only
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Used
as an anchor point to separate chromosomes during cell division
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What is the structure and function of the cell wall? - CorreCt Answers Present in plants and fungi only
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Chitin
in fungi
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prevents the cell from bursting when turgid
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What is the structure and function of the flagella? - CorreCt Answers -9
pairs of microtubules surround 2 lone microtubules
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Used for moving unicellular organisms around
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A membrane covers the
whole thing
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Move together in a wafting pattern
to move single celled organisms
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Which structures are involved in the production of proteins? - CorreCt
Answers -Nucleus; RER; transport vesicle; Golgi apparatus

What is the structure and function of the cytoskeleton? - CorreCt Answers Microfilaments made of actin - allow cell movement and cytokinesis
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Intermediate fibres give mechanical strength, maintaining integrity
...

Prokaryotes also have: peptidoglycan cell wall; smaller ribosomes; naked
loop of DNA; plasmids
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Multicellular organisms therefore need transport systems

Describe and explain three features of a good exchange surface - CorreCt
Answers -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 human alveoli are adapted to reduce diffusion distances CorreCt Answers -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 the role of surfactant in alveoli - CorreCt Answers -Coats the
internal surface of the alveoli to reduce cohesive forces between water
molecules, preventing collapse

Describe the mechanism of inspiration - CorreCt Answers -Diaphragm
contracts (moves down and flattens); external intercostal muscles contract
to push ribcage up and out; volume of thorax increased and so pressure
decreases below atmospheric pressure; air rushes into lungs down a
pressure gradient

Why do alveolar walls contain elastic fibres? - CorreCt Answers -To stretch
during inspiration and recoil , pushing air out, during expiration

Which tissue type comprises alveolar walls? - CorreCt Answers -Squamous
epithelium

The trachea is lined with ciliated epithelial tissue and goblet cells
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- CorreCt Answers -Goblet cells produce mucus onto
the tracheal lining, trapping dust and microorganisms
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Describe why
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The C-shape allows food to pass down the oesophagus
behind the trachea

Describe how the nasal cavity is adapted for exchange - CorreCt Answers 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 the roles of smooth muscle and elastic tissue in the airways CorreCt Answers -Smooth muscle can contract to constrict airways (not
under conscious control, i
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involuntary); elastic fibres elongate smooth
muscle again, recoiling the airway to its original shape and size (dilates
airway)

Describe precautions that must be taken when using a spirometer - CorreCt
Answers -Subject should be free of asthma; there should be no air leaks in
the apparatus; mouthpiece should be sterilised; soda lime should be fresh
and functioning

Describe what is meant by the term vital capacity and state the factors that
it depends upon - CorreCt Answers -The maximum volume of air that can
be moved by the lungs in one breath; measured by taking one deep brearh
and expiring all the possible air from the lungs
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State the usual range for vital capacity - CorreCt Answers -2
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0 dm3

Describe what is meant by residual volume and state the standard volume CorreCt Answers -The volume of air that remains in the lungs even after
forced expiration, i
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the air that remains in the airways and alveoli
(usually 1
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A
normal value would be 0
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State the equation for ventilation rate - CorreCt Answers -Ventilation rate =
tidal volume x breathing rate (breaths per minute)

The normal breathing rate of a healthy 50 year old woman is 18 breaths per
minute and her tidal volume is 500 cm3
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Calculate her tidal volume during this exercise and state
how much higher than normal this figure is
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1 dm3 higher than normal

Most bony fish have 5 pairs of gills which are covered by a bony flap, known
as the
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Each gill filament is folded into
secondary lamellae providing a very large surface area

Describe ventilation in bony fish - CorreCt Answers -Buccal cavity (mouth)
can change volume; floor of mouth moves downwards, drawing water into
the buccal cavity; mouth closes and water is pushed through the gills
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What is the
function of this fluid? - CorreCt Answers -Gaseous exchange occurs
between air in tracheole and the tracheal fluid

When an insect is active, what changes occur in the insect to increase their
oxygen supply? - CorreCt Answers -Tracheal fluid can be withdrawn into
the body fluid to increase the surface area of the tracheole wall exposed to
air

What is the fluid mosaic model? - CorreCt Answers -The theory of the cell
membrane formed from a sea of phospholipids emmeded with proteins
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What is a glycoprotein? - CorreCt Answers -A protein with a carbohydrate
molecule attached
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g
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Also bonds to phospholipids, preventing it becoming too fluid
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- CorreCt Answers -The net movement of a
substance from an area of high concentration to an area of low
concentration
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Define the term facilitated diffusion - CorreCt Answers -Movement of
molecules from a high concentration to a low concentration, across a
partially permeable membrane, via specific channel or carrier proteins
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What is a carrier protein? - CorreCt Answers -A protein which changes
shape to allow larger molecules to pass through the membrane
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What types of molecules can diffuse directly across the phospholipid
bilayer? - CorreCt Answers -Small molecules such as oxygen and carbon
dioxide; lipid-soluble molecules such as steroid hormones and alcohol

Describe the movement of water across the phospholipid bilayer - CorreCt
Answers -Water is polar and insoluble in lipid, BUT because it is present in
such high quantities, significant direct, simple diffusion does occur
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g
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Describe the effects of temperature on membrane structure - CorreCt
Answers -As temperature increases, phospholipids will have more KE, so
move faster and more, making the bilayer more fluid and it begins to lose
its structure
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Carrier and channel proteins may become denatured, affecting membrane
transport
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Endocytosis (phagocytosis or pinocytosis) brings large
molecules INTO the cell, enclosed in a vesicle
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Define and describe phagocytosis - CorreCt Answers -The intake of solid
particles into the cell by engulfing
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Define and describe pinocytosis - CorreCt Answers -The intake of liquids
into the cell by engulfing
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Define and describe exocytosis - CorreCt Answers -The bulk transport of
particles too large to pass through the membrane, out of the cell
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A vesicle containing the substance fuses with
the plasma membrane
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Describe the role of ATP in bulk transport - CorreCt Answers -ATP is
required to provide energy for the movement of vesicles along microtubules
of cytoskeleton (via motor proteins); ATP is needed to fuse vesicle
membrane and plasma membrane together (PM is changing shape)

What is the main difference between active transport and facilitated
diffusion? - CorreCt Answers -Active transport requires ATP; facillitated
diffusion is passive

Define the term osmosis - CorreCt Answers -The movement of water
molecules from a region of higher water potential to a region of lower water
potential, across a partially permeable membrane

What is water potential? - CorreCt Answers -The tendancy of water
molecules to move from one region to another
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What is the purpose of semilunar valves? - CorreCt Answers -To prevent
backflow of blood from arteries to the ventricles

Why is the left ventricular wall so much thicker than the right ventricular
walls? - CorreCt Answers -Blood is pumped throught the aorta and needs
sufficient pressure to overcome the resistance of the systemic circulation

Why are there so many mitochondria in cardiac muscle? - CorreCt Answers
-Supply energy for contraction

What is the purpose of intercalated discs between adjacent muscle cells? CorreCt Answers -Ensures an even, synchronised contraction

Briefly outline the events of atrial systole - CorreCt Answers -Left and right
atria contract together; blood is squeezed from the atria through the
atrioventricular valves into the ventricles, down a pressure gradient
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Erythrocytes cannot change
shape as much

Describe the role of the lymph fluid - CorreCt Answers -A system of tubes
that returns excess tissue fluid to the blood system

How does tissue fluid facilitate exchange of substances to body cells? CorreCt Answers -Tissue fluid surrounds body cells so exchange occurs
across plasma membranes

Describe the simple structure of haemoglobin - CorreCt Answers -Four
subunits (each with a polypeptide chain and a haem group); haem groups
each contain an Fe2+ ion at the centre; iron ions can attract and hold an
oxygen molecule

What is the process known as by which oxyhaemoglobin releases its oxygen
to respiring cells? - CorreCt Answers -Dissociation

What is the main difference between foetal haemoglobin and adult
haemoglobin? - CorreCt Answers -It has a higher affinity for oxygen than
adult haemoglobin

Describe three ways in which carbon dioxide is transported - CorreCt
Answers -5% dissolved directly in the plasma; 10% directly with
haemoglobin in the form of carbaminohaemoglobin; 85% in the form of
hydrogencarbonate ions

Describe the formation of hydrogencarbonate ions - CorreCt Answers Carbon dioxide from the blood plasma diffuses into RBCs anf combines
with water to form carbonic acid (catalysed by carbonic anhydrase);
carbonic acid then dissociates into hydrogencarbonate ions and protons

Describe how the charge inside a RBC is maintained when
hydreogencarbonate ions diffuse into the plasma - CorreCt Answers Chloride ions move into the RBCs from the plasma (chloride shift)

Describe how the pH inside a RBC is buffered as hydrogen ions build up
inside, making the RBC very acidic - CorreCt Answers -Hydrogen ions are
taken out of solution and combined with haemoglobin to form
haemoglobinic acid (HHb)

What is the net result of the Bohr effect? - CorreCt Answers -More oxygen is
released where more carbon dioxide is produced in respiration

With reference to protein structure, explain how increasing hydrogen ion
levels affects haemoglobin - CorreCt Answers -More hydrogen ions -->
lower pH (more acidic cytoplasm); tertiary structure of Hb altered which
reduces its affinity for oxygen

State three events that occur in G1 phase of the cell cycle - CorreCt Answers
-Cells grow and increase in size; proteins from which organelles are made
are synthesised (transcribed and translated); organelles replicate

What happens during the S phase of the cell cycle? - CorreCt Answers -This
is the synthesis phase, DNA is replicated
...


Describe what may happen in G0 phase of the cell cycle - CorreCt Answers Cells may undergo apoptosis, differentiation or senescence

State three cell cycle checkpoints and briefly describe what is being checked
for at each - CorreCt Answers -G1/S - checks for size, growth factors,
nutrients, DNA damage; G2/M - checks DNA has been properly replicated;
spindle assembly - checks chromosomes have correctly attached to spindle
fibres

State three purpose of mitosis in life cycles - CorreCt Answers -Asexual
reproduction; growth; tissue repair; replacement of cells

Describe the main events of phophase - CorreCt Answers -Nuclear envelope
breaks down; chromatin condenses (DNA supercoils); nucleolus
disappears; spindle fibres start to form from centrioles

Describe the main events of metaphase - CorreCt Answers -Chromosomes
line up along equator (metaphase plate); spindle fibres attach through
centromeres

Describe the main events of anaphase - CorreCt Answers -Sister chromatids
pulled to opposite poles of the cell by shortening tubulin spindle fibres

Describe the main events of telophase - CorreCt Answers -Nuclear envelope
reforms around each set of chromosomes; chromatin relaxes; nucleolus
reappears

Describe how cytokinesis differs between dividing animal cells and plant
cells - CorreCt Answers -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

Why would we use the root tip for investigating mitosis? - CorreCt Answers
-It is the location of meristematic tissue (source of stem cells) in a plant, i
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cells are actively dividing

Explain why we warm the root tips in hydrochloric acid when preparing a
root tip squash - CorreCt Answers -To break the links between cellulose cell
walls in plant cells; this ensures the stain penetrates the cells and binds to
the chromosomes

Which stain would we use to stain chromosomes in a root tip squash? CorreCt Answers -Acetic orcein

What is differentiation? - CorreCt Answers -The process by which a cell
develops to become more distinct in form and function

Describe and explain how erythrocytes are adapted for their function CorreCt Answers -Very small so have a large SA:vol (biconcave shape also
ensures this) meaning oxygen can reach all regions inside the cell; welldeveloped cytoskeleton allows the erythrocytes to change shape and move
through very narrow capillaries; no nucleus or organelles so more space for
Hb molecules

Explain why a neutrophil contains many lysosomes - CorreCt Answers These contain hydrolytic enzymes which digest pathogens

Describe and explain how sperm cells are adapted for their function CorreCt Answers -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 how guard cells open in sunny conditions - CorreCt Answers 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 the purpose of cytoskeleton threads and motor proteins in
palisade cells - CorreCt Answers -Moves the chloroplasts to areas of
appropriate light intensity

Describe how a root hair cell plasma membrane is adapted for transport of
mineral ions - CorreCt Answers -Contains specialised carrier proteins to
transport specific mineral ions in by active transport

Describe how cartilage is adapted for its function - CorreCt Answers Connective tissue that contains elastin and collagen fibres; prevents ends of
bones from rubbing together

Define the term tissue - CorreCt Answers -A group of cells working together
to perform a particular function

State three types of muscle tissue, giving an example of where each is found
- CorreCt Answers -Skeletal - bicep/tricep etc
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g
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Genetically
unique with half the genetic information of a somatic cell
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Name these, state their transport material and the direction of transport CorreCt Answers -Xylem - water, soluble mineral ions (upwards); phloem assimilates (up or down)

What tissue is found in between the xylem and phloem? What is its
function? - CorreCt Answers -Meristematic tissue (source of stem cells)

What is the purpose of parenchyma cells in xylem tissue? - CorreCt
Answers -To separate and support the vessels (act as packing tissue)

What is the purpose of lignin in xylem vessels? - CorreCt Answers Strengthens vessel wall and prevents collapse

How do bordered pits form and what is their purpose? - CorreCt Answers Where lignification is incomplete, leaving gaps in the cell wall; the bordered
pits in 2 adjacent vessels are aligned to allow water to leave one vessel and
pass into the next, as well as leave the xylem

Describe three adaptations of xylem vessels that relate structure to function
- CorreCt Answers -1) Dead cells aligned end to end to form a continuous
column; (2) Tubes are narrow so water column doesn't break easily and

capillary action can be effective; (3) Bordered pits allow sideways
movement of water between vessels; (4) Lignin allows stretching of xylem
(spiral, annular or reticulate patterns) as plant grows

What two components of phloem tissue are concerned with transport? CorreCt Answers -Sieve-tube elements and companion cells

Why do sieve tube elements contain no nucleus and very little cytoplasm? CorreCt Answers -Allows space for mass flow of sap to occur

How are companion cells adapted for active loading? - CorreCt Answers Many mitochondria to produce ATP

Describe 2 major pathways taken by water to move between cells - CorreCt
Answers -Apoplast - through spaces in cell walls and between cells (mass
flow
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increased
rate as stomata more open); humidity (incr
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decr
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wind
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rate
as maintaining high water vapour potential gradient)

State two precautions that should be taken to ensure no air bubbles are in
the potometer setup - CorreCt Answers -Set up u/w; cut stem u/w to
prevent air entering xylem

The distance moved by the meniscus in a potometer is 45mm in 5 minutes
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5 mm
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- CorreCt Answers -7
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This puts water at the top of xylem under
tension
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What property of water causes cohesion? - CorreCt Answers -The polarity
of the water molecule, which produces hydrogen bonds between the
molecules

Describe 3 adaptations of marram grass (xerophyte) and explain their
importance - CorreCt Answers -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)

Cacti are succulents
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Define the term translocation - CorreCt Answers -Transport of assimilates
from source to sink (tissue that needs them)

State two sinks (for translocation) in a plant - CorreCt Answers -Roots
growing or active uptaking mineral ions; actively dividing meristematic
tissue; part plants that are laying down food stores (e
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developing seeds,
fruits etc)

What is the difference between active loading and active transport? CorreCt Answers -Active transport is the movement of particles against
their concentration gradient using metabolic energy (ATP)
...

In this case, active loading uses active transport to pump hydrogen ions out
of the companion cells
...


Describe the role of hydrogen ions in active loading - CorreCt Answers -The
hydrogen ions are pumped out of the companion cells, creating a hydrogen
ion concentration gradient across the cell membrane
...
8

State the kingdom of organism that causes each of the following diseases:
tuberculosis, Black Sigatoka, Athlete's foot, malaria - CorreCt Answers Bacteria, fungi, fungi, protoctists

State the kingdom of organism that causes each of the following diseases:
blight, ringworm, ring rot, bacterial meningitis - CorreCt Answers Protoctists, fungi, bacteria, bacteria

Give one plant disease caused by each of the following: viruses, bacteria and
fungi - CorreCt Answers -Tobacco mosaic virus, ring rot, black sigatoka

State three factors that would affect the speed of disease transmission in
plants - CorreCt Answers -Overcrowding; poor mineral nutrition; damp,
warm, humid conditions; climate change

State how the influenza virus is most likely to be transmitted between
different humans - CorreCt Answers -Respiratory droplets (inhalation)

State four different types of vector that can be used to transmit a
communicable disease - CorreCt Answers -Water (e
...
diarrhoeal diseases);
animals (e
...
mosquito transmits Plasmodium); wind (carries spores);
humans (hands, clothing etc
...


State three active physical defences a plant would employ against an
invading pathogen - CorreCt Answers -Callose synthesised and deposited
between plasma membrane and cell wall; callose blocks sieve plates in
phloem; callose deposited in plasmodesmata between infected cells and
their neighbours; lignin added to cell walls; tyloses block xylem vessels

State three chemical defences a plant would employ against an invading
pathogen - CorreCt Answers -Antibacterial compounds like phenols,
alkaloids; terpenes; hydrolytic enzymes like glucanases and chitinases;
caffeine; tannins etc
...


Opsonins are non-specific
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They must be non-specific, so
they can attach to many different pathogens
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This selected Th cell then proliferates by mitosis (clonal
expansion)

Describe how B lymphocytes are activated and the role of activated B
lymphocytes - CorreCt Answers -Th cell binds specifically to B lymphocyte;
B lymphocyte differentiates into a plasma cell
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Antibodies are made by plasma cells
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Describe how opsonins function - CorreCt Answers -Opsonins bind
specifically to an antigen on a pathogen (via the variable region), clearly
marking the pathogen for destruction by a neutrophil
...
Pathogens
are clumped together (agglutinated), meaning they cannot enter host cells
and are easier to phagocytose

Describe how antitoxins function - CorreCt Answers -Neutralise toxin
molecules released by a pathogen through direct binding

Describe how the structure of an antibody enables it to perform its function
- CorreCt Answers -The variable region is specific to the antigen - it has a
shape that is complementary to the shape of the antigen; the disulfide
bridges hold the four polypeptide chains together; the hinge region allows
some flexibility so that the molecule can bind to more than one antigen; the
constant region may have a shape that can be recognised by the
neutrophils
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Explain why a secondary immune response is so much faster than a
primary immune response - CorreCt Answers -B memory and T memory
cells are circulating in the blood
...
Plasma cells can
produce antibodies faster, sooner and in much greater quantity
...
They may
even act as antigens and be attacked by antibodies from our immune
system
...
Ring vaccination is vaccinating people around the site of the
outbreak, so that the pathogen will not be transmitted across that ring to
the whole population
...
When they reproduce, some of their offspring may be
more resistant, thus resistance evolves
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Domain; Kingdom;
Phyllum; Class; Order; Family; Genus; Species
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It uses two (bi) names
...

The genus has a capitalised first letter
...
Cons: Limited
magnification, poor resolution
...


What is a transmission electron microscope be used for? - CorreCt Answers
-Observing the internal ultrastructure of cells under high magnification and
resolution

What is a scanning electron microscope used for? - CorreCt Answers Viewing the surface of objets under high magnification and resolution

What are the pros and cons of an electron microscope? - CorreCt Answers Pros: Very high magnification and excellent resolution
...


What is the difference between a transmission and an scanning electron
microscope? - CorreCt Answers -TEM sends a beam of electrons through
the specimen, the SEM bounces electrons off the surface
...
Electron uses a beam of
electrons, focused by magnets
...
It must be calibrated using a stage micrometer
before being used to measure specimens
...
it has 100 divisions, each of 0
...

It is used to calibrate the eyepiece graticule

Why do we stain specimens? - CorreCt Answers -To provide more contrast,
and make it easier to distinguish certain parts
...


What is the formula to calculate magnification? - CorreCt Answers Magnification = Image size / Actual size

What is the formula to calculate actual object size? - CorreCt Answers Actual size = Image size / Magnification

How do we work out image size? - CorreCt Answers -Use a ruler and
measure the image
...


What are the maximum resolutions of the different microscopes? - CorreCt
Answers -Light: 200nm; SEM: 10nm; TEM: 0
...


What is the maximum magnification of the different microscopes? CorreCt Answers -Light: 1,500X; SEM: 100,000X; TEM: 500,000X
...

What is a light microscope used for? - CorreCt Answers -Observing living
and dead specimins

What are the pros and cons of a light microscope? - CorreCt Answers -Pros:
Cheap, portable, easy to use, can study living specimens
...


What is a laser scanning confocal microscope used for? - CorreCt Answers Creating a high resolution, high contrast image, at different depths of the
specimen
...
Cons: specimen has
to be dead, very expensive, very large, needs great skill and training to use
...


What is the difference between light and electron microscopes? - CorreCt
Answers -Light uses lenses to focus a beam of light
...


What is an eye piece graticule? - CorreCt Answers -A small ruler fitted to a
light microscope's eyepiece
...


What is a stage micrometer? - CorreCt Answers -A millimeter long ruler
etched onto a slide
...
01mm or 10 micrometers
...


What is differential staining? - CorreCt Answers -Using a stain to
distinguish between either 2 different orgaisms, or between organelles of a
specimin due to preferential absorbtion of stain
...


What is magnification? - CorreCt Answers -A measure of how much larger
the image of a specimen looks under the microscope

What is resolution? - CorreCt Answers -The ability to distinguish between
to adjacent individual points as separate
...
2nm
...


What are the main structures of all eukaryotic cells? - CorreCt Answers Nucleus; nucleolus; cytoplasm; cytoskeleton; plasma
membrane;mitochondria; Golgi apparatus; smooth endoplasmic reticulum;
rough endoplasmic reticulum; ribosomes
...




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