knowledge organisers unit 2 Flashcards
1
Q
How much oxygen an organism needs depends on its…
A
volume
2
Q
The rate that oxygen is absorbed at depends on the…
A
surface area available for gas exchange
3
Q
What does the surface area to volume ratio of an organism affect
A
- the surface adapted for use for gas exchange.
- the level of activity of the organism
4
Q
What happens to SA:V ratio as organisms increase in size
A
SA:V ratio decreases so specialized respiratory surfaces are needed
5
Q
Why can’t insects use their external surface for gas exchange?
A
As they’re covered in an impermeable cuticle to reduce water loss by evaporation.
6
Q
Gas exchange in insects
A
- Pairs of spiracles on segments of the thorax and abdomen.
- These holes lead to tubes called tracheae leading to tracheoles.
- Tracheoles enter muscle cells directly. They have fluid at the end for dissolving and diffusion of oxygen.
- During flight, when oxygen requirements increase, fluid in tracheoles decreases to shorten diffusion path and whole-body
contractions ventilate the tracheal system by speeding up air flow through spiracles.
7
Q
Why do fish require a specialised gas exchange surface?
A
- they have a smaller SA:V ratio
- relatively active and so have high metabolic rates, making oxygen requirements high.
- require a ventilation mechanism to maintain concentration gradients for gas exchange
8
Q
What does a fish ventilation mechanism do
A
Pushes water (a dense medium with low oxygen content) over the high surface area gill filaments
9
Q
What does removal of water do to gill filaments
A
Causes them to collapse, stick together and the gas exchange surface becomes too small for survival
10
Q
Steps of ventilation in fish
A
- Mouth opens, floor of buccal cavity lowers so volume increases, pressure decreases and water rushes in.
- Mouth closes, floor of buccal cavity raises, increasing pressure pushing water over the gills.
- Pressure in gill cavity increases and water forces operculum open and leaves through it.
11
Q
Structure of gills
A
Gills have gill filaments made of gill plates/lamellae (the gas exchange surface across which the water flows). Gill rakers prevent large particles entering and blocking the gills
12
Q
What must gas exchange surfaces be?
A
-Moist in terrestrial animals.
-Be thin for a short diffusion pathway.
-Have a large S.A.
-Be permeable to gases.
-Good blood supply to maintain concentration gradients (larger organisms only)
13
Q
What is a continuous flow
A
If water and blood flow in the same direction, equilibrium is reached and oxygen diffusion reaches no net movement halfway across the gill plate
14
Q
What is counter current flow
A
If water and blood flow in opposite directions across the gill plate, the concentration gradient is maintained and oxygen diffuses into the blood across the entire gill plate.
15
Q
How do amoeba adapt to gas exchange?
A
- single cell.
- large SA:V ratio.
- there is a short diffusion distance to the middle of the cell
16
Q
How do flatworms adapt to gas exchange?
A
- multicellular.
- smaller SA:V ratio.
- flattened body to reduce diffusion distance so rate of oxygen diffusion through body surface meets demand
17
Q
How do earthworms adapt to gas exchange?
A
- multicellular.
- small SA:V ratio.
- mucus secreted to moisten surface and slow moving to reduce oxygen demand.
18
Q
Steps of ventilation in humans INSPIRATION
A
- External intercostal muscles contract and pull the rib cage up and out.
- Outer pleural membrane is pulled out. This reduces pressure in the pleural cavity and the inner pleural membrane is pulled outward.
- This pulls on the surface of the lungs and causes an increase in the volume of the alveoli.
- Alveolar pressure decreases to below atmospheric pressure and air is drawn into the lungs.
19
Q
Why do amphibia have aquatic tadpoles with feathery gills
A
don’t ventilate like fish but movement of the gills through water maintains a concentration gradient
20
Q
Gas exchange in amphibia
A
have soft, moist skin and exchange gases over their surface at rest. Oxygen and carbon dioxide circulate through a closed circulation system containing haemoglobin. When active, movements of the buccal
cavity ventilate lungs, which are simple with few alveoli
21
Q
What does a cuticle do
A
Waxy transparent layer so allows light to pass through to the photosynthetic palisade mesophyll below, but reduces water lost by evaporation through the top surface of the lead
22
Q
What does the upper epidermis do
A
transparent for light to easily
penetrate to photosynthetic layers
23
Q
What does the palisade mesophyll do
A
Packed with chloroplasts
24
Q
What does the vascular bundle do
A
Contain xylem (carries water from roots), phloem (carry sucrose to other parts of the plant) and bundle sheath parenchyma
25
What does the stomata do
allow the exchange of gases down a concentration gradient. The gases diffuse through intracellular spaces to and from the photosynthetic cells where they dissolve in the moist lining and diffuse into the cells. Guard cells open and close the stomata. The opening of the stomata during the day allows carbon dioxide to enter the air spaces and then the cells to be used in photosynthesis. The closing of the stomata during the night reduces water loss.
26
What does the spongy mesophyll do
surrounded by air spaces for easy diffusion of gases. The mesophyll cell membranes are the site of gas
exchange.
27
How are leaves adapted for photosynthesis
- large S.A and orientate perpendicular to the sun for maximum light absorption.
- have palisade cells packed with chloroplasts
- thin with a transparent cuticle and upper epidermis for light to penetrate into the leaf, and for efficient diffusion of gases from the stomata up through the gas spaces to the photosynthetic layers.
28
How do stomata open
Turgid guard cells bend due to thickened inner walls, opening stomatal pore
29
How do stomata close
Flaccid guard cells meet in the middle, closing the stomatal pore
30
Opening and closing of stomata for gas exchange
1. In light, chloroplasts in guard cells photosynthesise and produce ATP.
2. The ATP is used for the active transport of potassium ions into guard cells.
3. Starch is converted to malate.
4. Malate and potassium ions lower water potential of guard cells and water is drawn in by
osmosis.
5. Uneven thickening of guard cell inner walls causes them to bend as they swell, opening the stomatal pore.
6. The opposite occurs when there is no light closing the pore
31
How do unicellular organisms get nutrition
1. Amoeba pseudopodia move around prey and enclose it in a food vacuole.
2. Enzymes are released from
lysosomes that fuse with the food
vacuole and the prey is digested.
3. Products of digestion are absorbed into the cytoplasm and the undissolved waste is egested by exocytosis.
32
What kind of gut does hydra (single food source) have
Undifferentiated, sac-like gut with a single opening.
33
What kind of gut does earthworms (varied foods) have
A tube gut with different openings for ingestion and egestion and specialised regions for the digestion of different food.
34
What kind of gut do humans (omnivorous diet) have
Specialised regions of gut. The wall of the gut contains serosa, muscle layers (longitudinal and circular), sub mucosa, mucosa, epithelium
35
Features of serosa
Tough outer coat of connective tissue
36
Features of muscle layers (circular and longitudinal)
Longitudinal muscle contracts to shorten the gut and circular muscle contracts to reduce diameter. These waves of
contraction called peristalsis force food along the gut.
37
Features of submucosa
Contains blood and lymph vessels to remove digested food
products.
38
Features of mucosa
Inner layer that secretes mucus for lubrication. In some areas it
secretes digestive juices; in others it absorbs products.
39
Features of epithelium
Layer of cells in contact with food
40
What is autotrophic nutrition
makes complex organic
molecules from
simple inorganic ones. E.g. photoautotrophic, chemoautotrophic
41
What is photoautotrophic nutrition
Use light as a source of energy for synthesis of food
42
What is chemoautotrophic nutrition
Oxidise inorganic molecules to provide energy for the synthesis of food.
43
What is heterotrophic nutrition
Consume complex organic food molecules e.g. saprophytic and holozoic
44
What is saprophytic nutrition
External digestion of food using secretion of enzymes followed by absorption of the products of digestion into the organism, e.g. fungi
45
What is holozoic nutrition
internal digestion of food. Involves ingestion, absorption, assimilation and egestion.
46
What do endopeptidases (proteases) do
Hydrolyse peptide bonds between specific amino acids in the middle of the polypeptide chain to form shorter polypeptide chains
47
What do exopeptidases (protease) do?
Hydrolyse peptide bonds on the end of peptides, from the free amino end or the free carboxyl end
48
What does the buccal cavity do
mechanical digestion of food. Tongue moves food to the cutting
and grinding surfaces of the teeth. Chemical digestion of starch and glycogen into maltose by the enzyme amylase. Saliva moistens food and also maintains the pH for the enzyme. The tongue then rolls the food into a bolus which is swallowed.
49
What does the liver do
Produces bile which emulsifies lipids to increase the S.A available
for lipase enzymes to digest them.
Neutralises stomach acid to create a slightly alkaline pH in the duodenum for the pancreatic
enzymes.
50
What does the gall bladder do
stores the bile before delivering it to the duodenum via the bile duct.
51
What does the duodenum do
further digestion occurs on
the epithelial cells of the villi.
- Sucrose digested by sucrase into glucose and fructose.
- Maltose digested by maltase into alpha glucose.
- Lactose digested by lactase into glucose and galactose.
- Further digestion of polypeptides by endopeptidases and exopeptidases.
52
What does the ileum do
- Amino acids are actively transported into the epithelial cells of the villi; facilitated diffusion then occurs into the capillaries in the villi.
- Glucose and other monosaccharides move into epithelial cells by co-transport with sodium ions; facilitated diffusion then occurs into the capillaries
in the villi.
- Fatty acids and glycerol diffuse into epithelial cells and are reassembled into triglycerides and carried by the lacteal to the lymphatic system.
53
What does the villus of the ileum do
Increase S.A in the small intestine for absorption of digested food into the blood
54
What does the pancreas do
produces enzymes that are
transported to the duodenum via the pancreatic duct. Carbohydrase = pancreatic amylase.
55
What do pancreatic lipase enzymes do
digest triglycerides into
monoglycerides and eventually glycerol and fatty acids
56
What does the stomach do
gastric glands in the mucosa
produce gastric juice. The Oxyntic cells produce hydrochloric acid (HCl) that kills bacteria and lowers the pH to 2. The chief cells produce pepsinogen, the inactive precursor of the endopeptidase
enzyme, pepsin. This is activated by the HCl. Finally, the goblet cells produce mucus to protect the stomach lining.
57
What does the oesophagus do
peristaltic waves of muscle
contraction push the bolus of food down to the stomach. Mucus lubricates the way.
58
How are the canines in carnivores adapted for a high protein/lipid diet
Long and pointed to pierce flesh and seize and kill prey
59
How are the incisors in carnivores adapted for a high protein/lipid diet
On upper and lower jaw grip and tear flesh
60
How are the carnassial teeth in carnivores adapted for a high protein/lipid diet
Act like shears, sliding past each other to rip muscle from bone
61
How are the premolars and molars in carnivores adapted for a high protein/lipid diet
Have sharp cusps that cut and crush. The jaw has strong muscles and moves in a vertical plane opening wide and strongly clamping down to hold prey.
62
How are the guts in carnivores adapted for a high protein/lipid diet
- relatively short gut.
- usually a large stomach for digestion of mostly protein diet.
- small caecum
63
How are the premolars and molars of herbivores adapted to a high cellulose diet
Jaw moves in a horizontal plane so these interlocking teeth grind food. Teeth have open, unrestricted roots and so grow throughout life
64
How are the diastema of herbivores adapted to a high cellulose diet
Space where tongue can push food to the grinding cheek teeth
65
How are the incisors of herbivores adapted to a high cellulose diet
Cut vegetation against a horny pad on upper jaw. Canines are absent or indistinguishable
66
How are the guts of herbivores adapted to a high cellulose diet
- very long gut for difficult process of cellulose digestion.
- large caecum containing bacteria that produce cellulase for cellulose digestion
67
What are parasites
Organisms which live on or in a host organism, obtaining their nutrition from the host and harming the host
68
What is an ectoparasite
Lives on the surface of another organism e.g. head lice (pediculus) which feeds by sucking blood from scalp
69
What is an endoparasite
Lives inside another organism e.g. adult pork tapeworm which lives in gut of humans
70
How are head louse adapted to feed on sucking blood from the scalp of the host
- has claws to hold onto the hairs.
- lays eggs which are glued to the base of hairs.
- transfer between hosts by direct contact as it can't jump
71
How are adult port tapeworms adapted to live in gut of humans
- thick cuticle produces anti-enzymes.
- scolex to attach to gut wall.
- reduced gut and feeds by absorbing pre-digested nutrients through its cuticle.
- produces large number of eggs that pass out in faeces.
72
Adult pork tapeworm life
1. primary host - a larval form develops in pigs.
2. secondary host - infection of humans occurs when a person eats pork containing live larval forms (tapeworm cysts in muscle tissue).
73
How is the gut a hostile environment
due to the presence of various secretions and peristalsis. The tapeworm has adapted to living in the gut as follows
74
Process of nutrition in ruminants
1. Grass mixed with saliva then chewed before being swallowed.
2. Cud enters rumen. Cellulose digesting bacteria produce cellulase; breaking down cellulose into glucose. Organic acids absorbed into bloodstream and CO2 and methane expelled.
3. Cud from rumen
enters reticulum. Cud back to mouth to be rechewed.
4. Cud swallowed to Omasum where water absorption occurs.
5. From the omasum, food enters the abomasum. Protein digestion occurs.
6. Products of digestion absorbed into the blood in small intestine
75
Pressure changes in heart in AORTA
- Contraction of the thick muscular wall (systole) increases pressure in the ventricle. When pressure in ventricle exceeds pressure in aorta, the semilunar valve is forced open and blood enters aorta; increasing pressure.
- As ventricle wall relaxes (diastole), pressure drops in both the ventricle and aorta. Semilunar valve closes, preventing blood flowing back into the ventricle.
- Elastic recoil of aorta walls
increases pressure momentarily.
76
Pressure changes in heart in LEFT VENTRICLE
- Pressure in atrium increases as it
contracts, forcing blood through
the atrio-ventricular valves into
the ventricles. As the atria empty,
the valves snap shut.
77
Pressure changes in heart in LEFT ATRIUM
As the ventricles fully relax,
contraction in the atria walls
causes the atrio-ventricular
valves to open and the ventricle
to refill with blood.
78
Pressure changes in the vessels of aorta
Pressure in the aorta is high due to contraction of the powerful left ventricle forcing blood into the vessel. It falls only slightly during ventricular diastole due to the elastic recoil of the arteries and the closing of the semi-lunar valves. Arterioles are further away from the heart, have a large surface area and are narrow, leading to a substantial drop in pressure. However, arterioles can adjust their diameter to control blood flow to the organs.
79
Pressure changes in vessels of arterioles
The huge cross-sectional surface area covered by the capillaries causes a dramatic decline in pressure. Slow-moving blood is essential for effective exchange between blood and cells. Low pressure requires valves and massaging effect of muscles to aid the transport of blood through the veins back to the heart.
80
Open circulatory system meaning
Blood is pumped into a haemocoel where it bathes organs and returns slowly to the heart
with little control over direction of flow. Blood is not contained in blood vessels.
81
Closed circulatory system meaning
Blood is pumped into a series of vessels; blood flow is rapid and direction is controlled. Organs are not bathed by blood but by tissue
fluid that leaks from capillaries.
82
Single circulatory system meaning
Blood passes through the heart once in each circulation
83
Double circulatory system meaning
Blood passes through the heart twice in each circulation – once in the pulmonary (lung) circulation and then again through the systemic (body) circulation.
84
Superior vena cava function
returns deoxygenated blood to the heart.
85
Aorta function
carries oxygenated blood from the left ventricle to the body.
86
Pulmonary artery function
takes deoxygenated blood to lungs from right ventricle.
87
Pulmonary (semilunar) valve function
They prevent blood flowing back
into the ventricles between heart
beats.
88
Right atrium function
contracts and pumps deoxygenated blood into the right ventricle.
89
Tricuspid valve function
pressure of the contraction of the
atrium opens this valve which then closes, preventing backflow
to the right atrium when the ventricles contract.
90
Right ventricle function
thinner muscular wall compared to the left ventricle as less
pressure is produced on
contraction.
91
Pulmonary veins function
return oxygenated blood from lungs to the left atrium
92
Bicuspid valve function
prevents backflow of blood
into the left atrium when the
ventricles contract.
93
Left ventricle function
comparatively thicker muscular wall to produce a higher pressure to push oxygenated blood rapidly
around the body.
94
Septum function
wall dividing oxygenated blood
(left) and deoxygenated blood (right) side of the heart.
95
Circulatory system of INSECTS
- Open circulatory system.
- Dorsal tube-shaped heart.
- No respiratory pigment in
blood as lack of respiratory
gases in blood due to tracheal gas exchange system.
96
Circulatory system of EARTHWORMS
- Closed circulatory.
- 5 pseudohearts.
- Respiratory pigment
haemoglobin carries
respiratory gases in blood.
97
Circulatory system of FISH
- Closed, single circulatory
system.
- Blood pumped to
and oxygenated in the gills
continues around body tissues. This means a lower pressure and slower flow around the body.
98
Circulatory system of MAMMALS
- Closed, double circulatory system.
- High blood pressure to body
delivers oxygen quickly.
- Lower pressure to lungs
prevents hydrostatic pressure
forcing tissue fluid into and
reducing efficiency of alveoli
99
Structure of artery
- Tough collagen outer coat to prevent overstretching.
- Small lumen surrounded by smooth endothelium to prevent friction.
- Thich layer of smooth muscle that contracts and relaxes to alter blood flow to different organs. Thick layer of elastic tissue recoils to propel blood forwards and even out flow
100
Structure of vein
- Larger lumen as blood is under lower pressure. This gives less resistance to blood flow.
- Less muscle and elastic
fibres. Instead, contain semilunar valves to prevent backflow of blood
101
Structure of capillary
A single layer of endothelium giving a short diffusion path.
102
Process of cardiac cycle
Atrial systole, ventricular systole, ventricular diastole, diastole
103
What is atrial systole
Atrial contracts, pressure opens atrio-ventricular valves, blood flows into ventricles
104
What is ventricular systole
Ventricles contract, atrio-ventricular valves close due to pressure in ventricles being higher than atria, semilunar valves in aorta and pulmonary artery open, blood flows into arteries
105
What is ventricular diastole
Ventricle muscle relaxes, semilunar valves close to prevent backflow of blood into ventricles
106
What is diastole
Heart muscle relaxes and atria begin to fill from vena cava and pulmonary veins.
107
Initiating the heartbeat
- The heartbeat is myogenic.
- The sinoatrial node acts as a pacemaker, sending waves of excitation across the atria causing them to contract simultaneously.
- A layer of connective tissue prevents the wave of excitation passing down to the
ventricles. The wave of excitation passes to the atrio-ventricular node where there is a delay to allow the atria to complete contraction.
- The atrio-ventricular node transmits impulses down the bundle of His to the apex of the heart.
- The impulse then travels up the branched Purkinje fibres, simulating ventricles to contract from the bottom up. This ensures all the blood is pumped out.
108
How can the electrical activity that spreads through the heart during the cardiac cycle be detected
Using electrodes placed on the skin and shown on a cathode ray oscilloscope - an ELECTROCARDIOGRAM (ECG)
109
What does each molecule of haemoglobin do
Haemoglobin has high affinity for oxygen so carries four oxygen molecules: forming oxyhaemoglobin.
110
Oxygen dissociation curve
A sigmoid curve that shows haemoglobin has a high affinity for oxygen at high partial pressures of oxygen (lungs) but releases it readily at lower partial pressures (respiring tissues)
111
What is the Bohr Shift
When CO2 is present, Bohr shift occurs which is the oxygen dissociation curve moving to the right; meaning haemoglobin has a lower affinity for oxygen, releasing it more readily. Helpful in respiring tissues
112
Myoglobin oxygen dissociation curve
Curve shifts to the left. It has a high affinity for O2 and holds on to it until partial pressures of O2 are really low, it then releases it
rapidly. It acts as a store of O2 in muscle
113
Foetal haemoglobin oxygen dissociation curve
Curve just to the left, a higher affinity for O2 than haemoglobin at all partial pressures so foetus can take O2 from the mothers blood.
114
What is chloride shift
Some CO2 is carried in the blood dissolved in plasma, while some is carried in the blood as carbaminohaemoglobin. However, most is carried as hydrogen carbonate ions as shown below.
115
Chloride shift steps
1. CO2 diffuses into a red blood cell (RBC).
2. CO2 combines with H2O catalysed by the enzyme carbonic
anhydrase, forming carbonic acid.
3. Carbonic acid dissociates into hydrogen ions (H+) and hydrogen carbonate ions (HCO3-) diffuse out of the RBC into the plasma.
4. Chloride ions (Cl-) diffuse (facilitated diffusion) into the RBC to maintain electrochemical neutrality – the chloride shift.
5. H+ bind to oxyhaemoglobin, reducing its affinity for
oxygen. This is the Bohr effect.
6. Oxygen is released from the haemoglobin.
7. Oxygen diffuses from the RBC into the plasma and body cells
116
What is the formation of tissue fluid
a link between blood and cells. This is important as plasma transports nutrients, hormones and excretory products and also distributes heat.
117
Steps of formation of tissue fluid
1. At the arterial end of the capillary bed, hydrostatic pressure is higher than osmotic pressure.
2. Water and small soluble molecules are forced through
the capillary walls, forming tissue fluid between the cells.
3. Proteins and cells in the plasma are too large to be forced out.
4. Due to reduced volume of blood and friction, blood pressure falls and it moves through the capillary.
5. At the venous end of the capillary bed, osmotic pressure
of the blood is higher than the hydrostatic pressure.
6. Most of the water from tissue fluid moves back into blood capillaries (down its water potential gradient). The
remainder of the tissue fluid is returned to the blood via lymph vessels
118
Structure of the root
Epidermis, exodermis, cortex (parenchyma), phloem, xylex, endodermis
119
Structure of stem
Epidermis, collenchyma and parenchyma (cortex), vascular bundle, pith, intervascular cambium
120
Why is the endodermis impregnated with areas of suberin called the casparian strip
Blocks the apoplast pathway, forcing water into the symplast pathway
121
What happens when minerals are selected to move into the symplast by active transport
Sets up a water potential gradient, with lower water potential in the xylem, so water moved in by osmosis resulting in a force called root pressure
122
Movement of water across the root cortex of Apoplast pathway
From cell wall to cell wall
123
Movement of water across the root cortex of Symplast pathway
From cytoplasm to cytoplasm through plasmodesmata
124
Movement of water across the root cortex of Vacuolar pathway
From vacuole to vacuole
125
Structure of xylem
Vessels, tracheids, fibres, parenchyma
126
What are xylem
Dead cells that transport water and minerals up the plant and provide mechanical strength and support as they are strengthened by waterproof lignin.
127
What is transpiration
The loss of water as water vapour by evaporation and diffusion out of the open stomata, from the leaves of plants. Leads to the transpiration stream
128
What is the transpiration stream
Water moves into the root and enters the xylem (root pressure). Cohesive forces between water molecules and adhesive forces between water molecules and the hydrophilic lining of the xylem create a transpiration pull as the water leaving the xylem into the leaf cells pulls on molecules below. This is cohesion–tension theory.
129
Factors increasing transpiration
Lower humidity, higher temperature
130
Adaptations of HYDROPHYTE plant to environment e.g. water plants
- Little/no waxy cuticle as no need to conserve water.
- Stomata on upper surface as lower surface submerged.
- Poorly developed xylem as no need to transport water.
- Large air spaces (aerenchyma) provide buoyancy and act as reservoirs of gas.
131
Adaptations of MESOPHYTE plant to environment e.g. live with some water
- Close stomata at night to decrease water loss.
- Shed leaves in unfavourable conditions, e.g. winter.
- Underground organs and dormant seeds survive winter.
132
Adaptations of XEROPHYTE plant to environment e.g. marram grass
- Thick waxy cuticle reducing water loss by evaporation from epidermal tissue.
- Sunken stomata increasing humidity in an air chamber above the stomata, reducing diffusion gradient and therefore water loss.
- Rolled leaves - reduces area of leaf exposed directly to air.
- Stiff interlocking hairs trap water vapour inside rolled leaf, reducing water potential gradient and therefore water loss.
133
What do phloem sieve tubes
Carry sucrose and amino acids
134
How are sieve elements in phloem adapted
End in sieve plates containing pores through which cytoplasmic filaments extend linking cells
135
How are companion cells in phloem adapted
Contain many mitochondria for ATP and the organelles for protein synthesis. Proteins and ATP passed to the sieve elements through plasmodesmata
136
What is translocation
The phloem transports the products of photosynthesis from the leaf to the area of use/storage.
137
Experimental evidence of translocation
1. Ringing experiments (removal of phloem) show accumulation of sucrose products on leaf side of the ring but none on root side. Movement of sucrose was blocked by removal of phloem. Therefore, phloem is the route of transport. Higher temperature
2. Using aphids to sample sap from the phloem. An aphid stylus
extends into sieve tube elements. If a laser is used to remove the
stylus from the body, the stylus then becomes a micropipette
and sap drips out. Can be analysed to show that sucrose and
amino acids are carried in phloem.
3. Radioactive labelling of carbon dioxide which will become incorporated into sucrose can be used in conjunction with the above technique to determine the rate of transport in the phloem.
4. Sources and sinks can be determined by autoradiography using radioactively labelled carbon dioxide.
138
FOR the theory of mass flow
Sucrose made at source lowers water potential. Water enters cells and sucrose is forced into phloem. This increases hydrostatic pressure and therefore mass flow occurs along the phloem to the root where sucrose is stored as starch, water potential is less negative and water moves into the xylem
139
AGAINST theory of mass flow
-Sieve plates impede flow.
-Translocation is faster than expected with diffusion.
-Doesn't explain bidirectional flow or different rates of flow of sucrose and amino acids.
-Doesn't explain companion cell mitochondria, high O2 intake or stopping of translocation by cyanide
140
Assessing biodiversity in field work
- Grid an area and use a random number generator to select co-ordinates where to place quadrats.
- Count the number of different species and the number of individuals of each species in the quadrat.
- Repeat 10 times to improve reliability.
- Calculate Simpson’s diversity index
141
What does Simpson's diversity index do
Reduces species richness and evenness to a single number so that different areas can be compared.
142
What is biodiversity
The number of different species (species richness) and numbers of individuals of each species (species evenness) in a given environment.
143
What does it meant that biodiversity varies SPATIALLY
The closer to the equator, the
more biodiversity there is.
144
What does it meant that biodiversity varies TEMPORALLY
Through time biodiversity has varied, e.g. mass extinctions reduce biodiversity.
145
How do human activities affect biodiversity
Through habitat destruction and climate change
146
What is polymorphism
The presence of more than one form or type of organism within a single species.
147
What is polymorphism a result of
Multiple alleles for a gene.
148
How is polymorphism assessed
By determining the number of alleles and proportion of individuals with that allele with Analysis of Base Sequences in DNA
149
How has biodiversity been generated
By the process of natural selection.
- All individuals in a species have genetic variation (through mutation) that can be inherited.
- Some variants have a selective advantage, e.g. if a selection pressure is predation, a better camouflaged individual has an advantage over a less well camouflaged one.
- These variants survive, reproduce and pass their advantageous alleles to their offspring.
150
What does natural selection lead to?
Leads to organisms being adapted to their environments. Adaptations can be morphological, physiological, or behaviour.
151
In a desert environment, what have the extreme temperature fluctuation and aridity lead a small rodent (jerboa) to have...
- large ears to aid heat loss (morphological adaption)
- a long loop of Henle to reabsorb the maximum volume of water from urine (physiological adaption)
- crepuscular activity (dawn and dusk), burrowing to avoid the heat of the day and cold nights (physiological adaption)
152
What is classification
The division of living organisms into groups based on their evolutionary relationships.
- It's hierarchical: large groups are split into groups of decreasing size.
- It's phylogenetic: organisms in the same group are more closely related.
153
What does it mean that classification groups are discrete
An organism cannot belong to more than one group at the same taxonomic level
154
What is a taxon
Each group of classification
155
What are the taxonomic groups
Kingdom, Phylum, Class, Order, Family, Genus, Species
156
What is a species
A group of similar organisms that can interbreed to produce fertile offspring
157
What is a binomial name
A name in two parts - genus and species. Organisms in genus more closely related. Avoids issues with language differences
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What does it mean that classification have a tentative nature
Classification is based on the CURRENT info available so subject to change when new info comes to light
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What are the five kingdoms
Prokaryotae, Animalia, Plantae, Fungi, Protoctista
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Characteristics of Prokaryotae
Lack a nucleus and membrane-bound organelles, have 70S ribosomes, circular DNA and a cell wall of peptidoglycan
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Characteristics of animalia
Multicellular eukaryotes, no cell wall, heterotrophic and have nervous co-ordination
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Characteristics of plantae
Multicellular eukaryotes, photosynthetic containing chloroplasts, have a cell wall of cellulose
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Characteristics of fungi
Heterotrophic eukaryotes with a cell wall made of chitin; most are composed of thin threads called hyphae, reproduce by spores
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Characteristics of protoctista
Mostly unicellular eukaryotes, algae have no tissue differentiation
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What are the three domains
Eubacteria, Archaea, Eukarya
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What are eubacteria
these are the ‘true’ bacteria
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What are archaea
these are also prokaryotic but are extremophiles
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What are eukarya
these are all the eukaryotic organisms.
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What are extemophiles
live where environmental conditions are harsh, e.g. in very high or low temperatures (thermophiles or psychrophiles), in acidic or very alkaline environments, and in areas with high salinity (halophiles) or high pressure.
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What does morphology mean
Looking at the shape and form of an organism
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Why do some organisms have similar morphology but are unrelated in evolutionary terms
Convergent evolution
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Advantage of using biochemical analysis e.g. DNA sequencing
Can overcome issues caused by convergent evolution
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What are homologous structures
Have the same structure but different functions e.g. pentadactyl limb which is the same in lots of animals but have different functions. Indicate they're related
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What are analogous structures
Function is the same, origin of structure is different. Arise through convergent evolution. E.g. wings of birds and insects.
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What are phylogenetic trees
Diagrams that represent the evolutionary pathways leading to different species. The axis is time, which moves forward the further up the tree branches you go. Each junction represents a common ancestor for the branches. The more recent a common ancestor, the more closely related the organisms are
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What are biological polymers
Have subunits which are different, like DNA, RNA or protein.
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How can biological polymers be used to establish relatedness
Sequences of subunits can be compared and number of differences counted. More differences in sequence; the less closely related the organisms are.
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What do mutations in DNA lead to
Lead to differences in the amino acid sequence of proteins. Use the differences to construct a molecular clock which shows how long ago the mutation occurred.
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How can DNA banding patterns/DNA fingerprint be produced
Fragments of DNA and proteins separated by gel electrophoresis. Banding pattern is produced, called DNA fingerprint, which can be used for comparison. Sequences of DNA and amino acids can be established.
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How does gel electrophoresis work
allows small fragments to move further and the electrical charge causes movement of the negatively charged fragments to the positive electrode
