Topic 3 Flashcards
1
Q
How are fish adapted to exchange gases?
A
- lower conc. of O2 in water than in air, so fish have adaptations to get enough. (to maintain concentration gradient and maintain diffusion)
- gills on each side of head
- gills made up of stacks of gill filaments which give large SA for gas exchange (so increase rate of diffusion)
- gill filaments have rows of lamellae, increasing SA
- lamellae have lots of blood capillaries and thin layer of cells to speed up diffusion, between water and blood.
- gills provide short diffusion pathway, large SA:Vol ratio and a maintained concentration gradient.
- counter current system
2
Q
What is the counter current system in the gills of fish?
A
- blood flows through lamellae in one direction and water flows over them in opposite direction.
- maintains a concentration gradient between water and blood
- concentration of oxygen in water always higher than in the blood so as much oxygen as possible diffuses from water into blood
3
Q
How does surface area to volume ratio differ by size of an organism?
A
- smaller organisms have a larger surface area to vulume ratio
- larger the organism, the smaller the surface area to volume ratio as volume increases faster than surface area.
4
Q
how are gasses exchanged in single celled organisms
A
- simple diffusion of substances across cell surface membranes
- large SA, thin surface and short diffusion pathway (O2 can take part in biochemical processes as soon as it diffuses into cell), so no need for specialised gas exchange system
5
Q
How are gasses exchanged in multicellular organisms?
A
- diffusion across outer membrane is too slow due to too long diffusion pathway and larger organisms have a low SA: Vol ratio (hard to exchange enough substances to supply a large volume of animal through a relatively small outer surface).
- need exchange organs and systems (mass transport) to exchange substances
6
Q
How does surface area to volume ratio affect metabolic rate?
A
- metabolic rate=amount of energy expended by organism in given time period
- during rest periods the organims’s body only requires energy for functioning of vital organs such as lungs, heart and brain
- metabolic rate increases with body mass
- metabolic rate high in those with larger surface area to volume ratio than in those with a small surface area to volume ratio because smaller organisms lose more heat so use more energy to maintain body temp
7
Q
How can metabolic rate be investigated
A
respirometres
oxygen/co2 probes
calorimeters
8
Q
How does body size of an organism affect heat exchange?
A
- organisms with low surface area to volume ratio lose heat less easily
- organisms with a larger surface area to volume ratio lose heat more easily
- smaller organisms need a high matabolic rate to generate enough heat to stay warm and alive
9
Q
How does body shape of an organism impact heat exchange?
A
- organisms with compact shape have small surface area to volume ratio which minimises heat loss from their surface
- organisms with less compact shape have a larger surface area to volume ratio so heat is lost more easily
- compactness depends on temp of environment organism lives in e.g. those in cold environments may have small ears and a round head to minimise heat loss by reducing surface area to volume ratio
10
Q
Explain some behavioural adaptations for exchange of substances
A
- organisms with small surface area to volume ratio that live in hot environments spend a lot of time in water such as hippos, as they don’t lose heat as easily as organisms with a high surface area to volume ratio so need to keep cool
- small mammals have high metabolic rates so if living in cold regions, need to eat large amounts of high energy foods
11
Q
Explain physiological adaptations that organisms may have for exchange of substances
A
- smaller mammals may have thick layers of fur or hibernate when it’s very cold
- some small desert animals have kidney structure adaptations so they produce less urine so they do not lose as much water if they have a high surface area to volume ratio, as water already evaporates more from their surface
12
Q
What properties do most gas exchange systems have?
A
- large surface area
- thin (often just one layer of epithelial cells), which provides a short diffusion distance across gas exchange surface
- maintained concentration gradient of gases across exchange surface
13
Q
A
14
Q
How are insects adapted for gas exchange?
A
- rigid exoskeleton with waxy coating that is impermeable to gases
- oxygen moves into traceae through spiracles on surface
- oxygen travels down it’s concentration gradient towards the cells
- traceae branch off into smaller trachioles with thin permeable walls and go to individual cells
- oxygen diffuses directly into respiring cells as the circulatory system of the insect does not transport oxygen
- carbon dioxide from cells moves down its own concentration gradient to spiracles to be released
- insects use rhythmic abdominal movements to move air in and out of spiracles
15
Q
How are dicotyledonous plants adapated for gas exchange?
A
- gases exchanged through stomata
- oxygen diffuses out of stomata
- carbon dioxide diffuses in through stomata
- concentration gradient maintained as lower concentration in spongy mesophyll compared to atmosphere
- high oxygen concentration in spongy mesophyll compared to atmosphere
- to reduce water loss by evaporation. stomata close at night when photosynthesis not occurring
16
Q
What structural and functional compromises exist between opposing needs for efficient gas exchange and the limitation of water loss in xerophytic plants?
A
- adapted to survive in environments with limited water
- curled leaves to trap moisture to increase local humidity (reduces water potential gradient from inside of plant to outside, further reducing evaporation/transpiration)
- hairs to trap moisture to increase local humidity, less evaporation
- sunken stomata to trap moisture to increase humidity, less evaporation
- thicker cuticle to reduce evaporation
- longer root network to reach more water
17
Q
What structural and functional compromises exist between opposing needs for efficient gas exchange and the limitation of water loss in terrestrial insects?
A
- gas exchange system has small surface area to volume ratio as water can only evaporate from small spiracles, reduces water loss
- insects have lipid layer on exoskeleton so is waterproof, so water cannot evaporate from all of body, only through spiracles
- have spiracles that gases enter and water evaporates from which can open and close to reduce water loss
18
Q
Describe the gross structure of the human gas exchange system
A
- air enters trachea
- trachea splits into 2 bronchi
- one bronchus leads to each lung
- bronchi branch off into smaller bronchioles
- many alveoli at end of each bronchiole
- alveoli are the site of gas exchange
19
Q
How is the Aveolar epithelium adapted for gas exchange?
A
- alveolar epithelium is a single layer of thin flat cells which provides a short diffusion pathway
- contain elastin which helps alveoli recoil to normal shape after exhilation
20
Q
How do Alveoli speed up rate of diffusion?
A
- thin exchange surface
- large surface area-lots of them
- steep concentration gradient of oxygen and carbon dioxide between alveoli and capillaries, which increases rate of diffusion. This is constantly maintained by blood flow and ventilation.
21
Q
How are gases exchanged in the alveoli?
A
- oxygen diffuses out of alveoli across alveolar epithelium and capillary endophelium into haemoglobin in blood (in capillary)
*carbon dioxide diffuses into alveoli from blood - oxygen moves down trachea, bronchi, bronchioles, into alveoli, down pressure gradient
- oxygen moves into blood down diffusion gradient
22
Q
Describe the process of Inspiration
A
- external intercostal and diaphragm muscles contract
- causes ribcage to move upwards and outwards and diaphragm to flattern which increases volume of thoracic cavity (space where lungs are)
- as volume of thoracic cavity increases, lung pressure decreases to below atmospheric pressure
- causes air to flow down a pressure gradient so air flows down trachea into lungs
- active process so requires energy from ATP
23
Q
Describe the process of normal Expiration
A
- external intercostal and diaphragm muscles relax
- ribcage moves downwards and inwards and diaphragm curves again
- causes volume of thoracic cavity to decrease (space where lungs are), causing lung/air pressure to increase to above atmospheric pressure
- means air forced down pressure gradient and out of lungs.
- passive process
24
Q
Describe process of forced expiration
e.g. blowing out candles
A
- external intercostal muscles relax and internal intercostal muscles contract
- pulls ribcage further down and in
- movement of 2 sets of intercostal muscles is antagonistic
- active process
25
how do lung diseases effect gas exchange and/or ventilation?
1. reduce rate of gas exchange in alveoli
2. less oxygen can diffuse into bloodstream, body cells receive less oxygen and rate or aerobic respiration reduced
3. less energy released so person often tired and weak
26
Define Tidal Volume
volume of air in each breath
27
Define Ventilation Rate
number of breaths per minute
28
Define Forced Expiratory volume (FEV1)
maximum volume of air that can be breathed out in one second
29
Define Forced Vital Capacity (FVC)
maximum volume of air possible to forcefully breathe out of lungs after breathing in
30
Define Digestion
Large insoluble biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes
31
Where are carbohydrates digested?
* begins in mouth
* continues in duodenum
* completed in ileum
32
What enzymes hydrolyse carbohydrates into monosaccharides?
1. amylases
2. membrane-bound disaccharidases
33
How are Carbohydrates digested?
1. amylase produced by pancreas and salivary glands. Amylase hydrolyses polysaccharides such as starch into the disaccharide maltose by hydrolysing the glycosidic bonds
2. Starting in duodenum and ending in ileum, membrane bound disaccharidases (sucrase, lactase, maltase), which are enzymes hydrolyse disaccharides into monosaccharides (fructose, galactose, maltose)
34
How are proteins digested?
1. endopeptidases hydrolyse peptide bonds between amino acids in the middle of a polymer chain
2. Exopeptidases hydrolyse peptide bonds between amino acids at end of a polymer chain
3. membrane bound dipeptidases hydrolyse peptide bonds between 2 amino acids (dipeptide)
35
Where does protein digestion occur?
starts in stomach, continues in duodenum and fully digested in ileum
36
How does lipase and bile salts digest lipids
* lipase produced in pancreas and can hydrolyse the ester bonds in triglycerides to form glycerol and fatty acids and some monoglycerides
* bile salts produced in liver and can emulsify lipids to form micelles that increase surface area for lipase to work on
37
Describe the process of the physical digestion of lipids
* lipids coated in bile salts (released from gallbladder and made in liver) to create emulsion
* many small droplets of lipids provides larger surface area to enable faster hydrolysis action by lipase
38
Describe the process of the chemical digestion of lipids
Lipase hydrolyses lipids into glycerol and fatty acids and some monoglycerides
39
What are Micelles?
* water soluble vesicles formed from fatty acids, glycerol, monoglycerides and bile salts
* deliver fatty acids, glycerol and monoglycerides to epithelial cells of ileum for absorption
(release fatty acids and glycerol so they can move into epithelial cell via diffusiom)
40
How is the ileum adapted for absorption?
* ilieum wall covered in villi
* villi have thin walls surrounded by network or capillaries
* walls have epithelial cells that line ileum that have very small microvilli
* features maximise absorption by increasing surface area, descreasing diffusion distance and maintaining a concentration gradient (by a capillary network)
41
How are Monosaccharides and amino acids absorbed?
*
42
How are monoglycerides and fatty acids absorbed?
| lipid absorption
* lipids digested into monoglycerides and fatty acids by action of lipase and bile salts, which form tiny structures called micelles
* micelles encounter ilieum epithelial cells and due to non polar nature of fatty acids and monoglycerides, they can simply diffuse across cell surface membrane to enter cells of epithelial cells.
* once in cell, they are modified back into triglycerides inside and golgi body
* when triglyceride combined with protein, forms a chylomicron
* chylomicron extruded via exocytosis from epithelial cell in a golgi vesicle and enter a lacteal (lympth capillary). Chylomicron absorbed inside lacteal
* lympth in lacteal transports chylomicron away from intestine
43
What are haemoglobins?
* group of chemically similar molecules found in many different organisms
* quartnernary structure structure, made up of 4 polypeptide chains
* each chain has a haem group, where oxygen binds
* each haemoglobin molecule can carry 4 oxygen molecules
* haemoglobin and red blood cells carry oxygen around body
44
What happens when an oxygen molecule binds to a haemoglobin molecule?
oxyhaemoglobin
- when O2 joins to Hb=association/loading
- when O2 leaves oxyHb=dissociation/unloading
45
What does affinity for oxygen refer to?
tendency to bind to oxygen
46
How does the affinity of haemoglobin for oxygen change with partial pressure of oxygen (po2) (higher pO2=greater oxygen conc.)
* higher pO2=greater affinity for oxygen. Oxygen loads onto Hb to form oxyhaemoglobin (lungs)
* oxyhaemoglobin unloads O2 with lower pO2 (respiring tissues/cells)
47
How is oxygen delivered to respiring tissues from alveoli by haemoglobin in blood?
* alveoli in lungs have HIGH O2 concentration, so a high pO2
* haemoglobin has a high affinity for oxygen
* haemoglobin loads oxygen and forms oxyhaemoglobin
* respiring tissues used oxygen, which lowers pO2
* haemoglobin has a low affinity for O2
* red blood cells deliver oxyhaemglobin to respiring tissues
* O2 unloads from oxyhaemglobin
48
What does the oxyhaemoglobin curve show?
* shows haemoglobin saturation with oxygen at any given partial pressure
* at high pO2, haemoglobin has a high affinity for oxygen, so haemoglobin has a high oxygen saturation. Haemoglobin loads oxygen/oxygen joins to haemoglobin. (In alveoli)
* at low pO2, haemoglobin has a low affinity fot oxygen, so haemoglobin has a low oxygen saturation. Oxygen unloads from oxyhaemoglobin/oxygen leaves oxyhaemoglobin. (in respiring tissues/cells)
49
What is the advantage of haemoglobin having a low affinity for oxygen at low pO2, in respiring tissues?
Haemoglobin unloads oxygen, where it is needed. It is needed in respiring tissues, where respiration is occuring
* oxygen unloaded, so aerobic respiration can continue so the maximum quantity of ATP produced so muscle contraction can continue
50
What is cooperative binding?
* the cooperative nature of oxygen binding to haemoglobin is due to the tertiary structure of the haemoglobin changing shape when first oxygen binds
* this makes it easier for further oxygen molecules to bind, as another binding site uncovered
* BUT if haemoglobin become too saturated with oxygen, then it's harder for more oxygen to join
51
what is the Bohr effect?
* when a high pCO2 causes the oxyhaemoglobin curve to shift to the right
* the affinity haemoglobin has for oxygen decreases because carbon dioxide lowers blood pH making iy acidic, which changes the shape of haemoglobin slightly
52
How does the oxyhaemoglobin curve change in alveoli and in respiring tissues due to pCO2?
* low pCO2 in alveoli, so curve shifts left, increased affinity and so uploads more oxygen
* high pCO2 at respiring tissues, so curve shifts right, decreased affinity and so unloads more oxygen
53
How are animals adapted to their environment in terms of their haemoglobin?
many animals have different types of haemoglobin which have different affinities for oxygen/ different oxygen transport properties, which is an apaptation to their environments
54
How does foetal haemoglobin differ to the haemoglobins of other organisms?
* oxygen dissociation curve shifts to the left of adults
* haemoglobin has a higher affinity for oxygen at the same pO2 than humans, so haemoglobin is more saturated with oxygen than human haemoglobin
* advantage as foetus cannot inhale/exhale so only receives oxygen through mother's haemoglobin in blood supply from placenta, so foetal haemoglobin must have a higher affinity for oxygen to load oxygen from mother's haemoglobin in blood
55
How does Llama haemoglobin differ to the haemoglobin of other organisms?
* llamas live at high altitiudes with low pO2
* oxygen dissociation curve shifts left, meaning llama heamoglobin has a high affinity for oxygen, so loads oxygen more readily and becomes more saturated with oxygen at the same pO2, compared to adult human haemoglobin
56
How does the haemoglobin of a dove differ to the haemoglobin of human haemoglobin?
* oxygen dissociation curve shifts to the right of humans
* at the same partial pressure, dove haemoglobin has a lower affinity for oxygen, so unloads it more reasily and becomes less saturated with oxygen, compared to human haemoglobin
* advantage as doves have a faster metabolism (due to high muscle contraction when flying) so needs more oxygen for respiration to provide energy for contracting muscles, by generating the maximum amount of ATP during aerobic respiration
57
How does the haemoglobin of an earthworm differ to human haemoglobin?
* live underground where there is a lower pO2
* oxygen dissociation curve shifts to the left of human
* haemoglobin of worm has a higher affinity for oxygen, so loads it more readily and becomes more saturated with oxygen, compared to human haemoglobin
* advantage as able to load enough oxygen that is required, when there is a low pO2
58
Describe the structure of the human circulatory system
* a closed, double circulatory system
* closed=the blood remains within the blood vessels
* double circulatory system=the blood passes through heart twice in each circuit. One circuit delivers blood to the lungs and another circuit delivers blood to rest of body
* in one complete cicuit of body, blood passes through heart twice.
* right side of heart pumps deoxygenated blood to lungs for gas exchange
* blood returns to left side of heart and oxygenated blood pumped around body
59
What is the need for a double circulatory system in mammals?
* to manage the pressure of blood flow
* blood flows through lungs at a lower pressure. This prevents damage to the capillaries in alveoli and reduces the speed at which the blood flows, enabling more time for gas exchange (pulmonary circuit)
* oxygenated blood from lungs then goes back through heart to be pumped out at a higher pressure to rest of body . This is important to ensure blood reaches respiring cells (systematic circuit)
60
Outline the key blood vessels in the circulatory system
* coronary arteries supply heart with own blood supply. Supply cardiac muscle with oxygenated blood so it can continuously contract
* vena cava carries blood from body to heart
* aorta carries blood from heart to body
* pulmonary artery carries blood from heart to lungs
* pulmonary vein carries blood from lungs to heart
* renal artery carries blood from body to kidneys
* renal vein carries blood from kidneys to vena cava
* these blood vessesl connected via arteries, arterioles, capillaries and veins
61
What unique properties does cardiac muscle have, in relation to heart structure?
* walls of heart have thick muscular layer (cardiac muscle)
* cardiac muscle is myogenic so can contract and relax without nervous or hormonal stimulation
* cardiac muscle never fatigues, as long as it has an oxygen supply
62
What is the role of the coronary arteries in relation to heart structure?
* supply the cardiac muscle with oxygenated blood
* branch off from aorta
63
What can result from blocked coronary arteries?
Myocardial Infarction (heart attack)
* if become blocked cardiac muscle will not receive oygen so will not respire and cells will die, resulting in myocardial infarction
64
Outline the 4 chambers in the heart
2 top=atria
2 bottom=ventricles
* left and right sides of heart separated by wall of muscular tissue (septum) that ensures blood does not mix between left and right sides
* Atria have thinner muscular as dont need to contract as hard as only pump blood to ventricles
* Atria have elastic walls to stretch when blood enters
* ventricles have thicker walls to enable bigger contraction. Creates higehr bloof pressure to enable blood to flow longer distances to lungs and rest of body
65
Outline the structure and function of the Right Ventricle in the Heart
* pumps blood to lungs at lower pressure SO has thinner muscular wall than left
* this is to prevent damage to capillaries in lungs and ensures slow blood flow to allow time for gas exchange
66
Outline the structure and function of the Left Ventricle in the Heart
* pumps blood to body at higher pressure
* this ensures blood reaches all cells in body
* SO have thicker muscular wall compared to right to enable larger contractions of muscle to create higher pressure
67
Describe the function of the Veins connected to the human heart
* 2 veins bring blood in to heart
* Vena Cava carries dexoygenated blood from body to right atrium
* Pulmonary Vein carries oxygenated blood from lungs to left atrium (pulmonary refers to lungs)
68
Describe the function of thr Arteries connected to the human heart
* Arteries carry blood away from heart
* Pulmonary Artery carries deoxygenated blood from right ventricle to lungs to become oxygenated
* Aorta carries oxygenated blood from left ventricle to rest of body
69
Describe the location and function of Valves in the human heart
1. Semi Lunar Valves link ventricles to pulmonary artery and aorta and stop backflow of blood back into heart after ventricles contract
2. Atrioventricular valves between atria and ventricles. Stop backflow of blood into atria when ventricles contract
Bicuspid (left side)
Tricuspid (right side)
* Valves open when pressure is higher behind the valve
* close when pressure is higher in front of valve
* prevents backflow of blood so flow of blood is unidirectional
70
Outline the function of the Septum in the human heart
* separates deoxygenated and oxygenated blood
* maintains high concentration of oxygen in oxygenated blood to maintain concentration gradient to enable diffusion at respiring cells
71
Describe and explain the first stage of the Cardiac Cycle, Diastole
Diastole
* atria and ventricular muscles relaxed
* blood enters atria via vena cava and pulmonary vein
* blood flowing into atria increases pressure in atria
72
Outline the second stage of the Cardiac Cycle, Atrial Systole
Atrial Systole
* atria muscular walls contract, decreasing volume of atria and so increasing pressure more. Ventruclar muscular walls relaxed (ventricular diastole
* causes atrioventricular (AV) valves open as atria pressure above ventricular pressure, so blood flows into ventricles
73
Describe the final stage of the Cardiac Cycle, Ventricular Systole
* walls of ventricles contract so ventricular volume decreases and pressure increases
* pressure in ventricles above stria so AV valves close which prevents backflow of blood
* Semi Lunar (SL) valves open as pressure in ventricles above aorta and pulmonary artery
* blood pushed out of ventrciles into arteries (pulmonary and aorta) and out of heart
* cycle begins again with Diastole, with blood entering atria
74
What is Cardic Output and how is it calculated?
volume of blood pumped by the heart per minute (cm3 min-1)
Cardiac Output=stroke volume X heart rate
Heart rate (number of beats per minute
Stroke Volume= volume of blood pumped suring each heartbeat (cm3)
75
When do Atrioventricular and semi-lunar Valves open and close?
* Atrioventricular (AV) valves open when pressure higher in atria compared to ventricles
* AV valves close when pressure higher in ventricles compared to atria
* Semi-Lunar (SL) Valves open when pressure higher in ventricle compared to arteries (pulmonary artery or aorta)
* SL valves close when pressure higher in arteries compared to ventricles
76
What is the function of Arteries?
transport blood away from heart at high pressure
77
What is the function of Veins?
transport blood to heart at low pressure
78
What is the function of Arterioles?
arteries branch into narrower arterioles which transport blood into capillaries
79
What is the structure of Arteries?
80
Outline the structural differences between arteries and veins
* Arteries have thicker muscular layer than veins so that constriction and dilation can occur to control volume of blood
* Veins have thinner muscular layer than arteries so it cannot control the blood flow
* Arteries have a thicker elastic layer than veins to help maintain blood pressure, as walls can stretch and recoil in response to heart beat
* veins have relatively thin elastic layer as pressure lower
* arteries have thicker walls than veins to help prevent vessels bursting due to high pressure. Narrower lumen to maintain high bloof pressure
* veins have thinner walls as pressure lower so low risk of bursting. Thinness means vessels easily falttened to help blood flow to heart. Wider lumen
* arteries do not have valves
* veins have valves to prevent backflow of blood, helping return blood to heart
81
Describe the structure and function of Capillaries
* arterioles branch into capillaries
* form capillary beds/capillary network as exchange surfaces (many branched capillaries)
* capillary beds have capillaries each with a narrow diameter to slow blood flow
* red blood cells can only just fir through capillaries and are squashed against walls to maimise diffusion
* no muscle layer
* no elastic layer
* one cell thick consisting only of a lining layer, providing a short diffusion distance for echanging materials between the blood and cells
* no valves
82
Outline the properties of Arterioles
* thicker muscular layer than arteries to contract and close lumen to help restrict blood flow into capillaries, as too much blood into capillaries could damage them
* thinner elastic layer than arteries as pressure lower
* thinner walls than arteries as pressure lower
* no valves
83
Outline the structure and function of Arteries
* thick muscular walls with elastic tissue to stretch and recoil as heart beats which helps maintain high pressure
* wall contains layers of collagen, smooth muscle and elastic fibres
* inner lining (endothelium) folded so artery can stretch to maintain high pressure
* narrow lumen to maintain high blood pressure
* elastic fibres mean artery wall can expand around blood surging through at high pressure when heart contracts. Fibres recoil when heart relaxes
84
What is Tissue fluid?
* fluid containing water, glucose, amino acids, fatty acids, dissolves ions and oxygen which surrounds body tissues,
* this is so body cells receive essential molecules needed for survival e.g. for respiration
85
How is tissue fluid formed?
* capillaries have small gaps in walls so liquid and small molecules can be forced out
* as blood enters capillaries from arterioles, the smaller diameter results in a high hydrostatic pressure so water, glucose, amino acids, ions and oxygen are forced out (larger molecules stay in capillary)
* this is ultrafiltration
* tissue fluid bathes/surround tissues
86
What molecules are forced out of capillary and form tissue fluid in ultrafiltration?
* water molecules
* dissolved minerals and salts
* glucose
* small proteins and amino acids
* fatty acids
* oxygen
87
What molecules remain in the capillary in ultrafiltration?
* molecules that are too large to be forced out of gaps in capillary walls which are
* red blood cells
* platelets
* large proteins
88
How is tissue fluid reabsorbed?
* large molecules remain in capilarries and so create a lowered water potential compared to tissue fluid
* towards venule end (nearest to veins) of capillaries, hydrostatic pressure is lowered due to the loss of liquid (so no moreliquid forced out) , but the water potential is very low
* water re enters capillaries by osmosis from higher to lower water potential gradient. Water will contain waste molecules from tissues such as carbon dioide, urea etc. Those molecules dissolve in water and reabsorbed. This is how waste enters blood to be removed from body
89
Why does tissue fluid get reabsorbed?
If tissue fluid never reabsorbed, then tissues would be surrounded by too much tissue fluid and areas of the body would become swolen.
90
What is the function of the lymphatic system in the reabsorption of tissue fluid?
* not all liquid will be reabsorbed by osmosis as equilibrium will be reached
* rest of tissue fluid absorbed into lymphatic system and eventually drains back into blood stream near heart
* lympahtic system has lymph vessels that surround blood vessels.
91
What is Transpiration?
The loss of water vapour by evaporation from Stomata by diffusion
92
What is the Transpiration Stream?
The movement of water from the roots to the leaves
93
What is the structure of the Xylem?
* xylem vessels part of xylem tissue. Xylem vessels are elongated tubes formed from dead cells (vessel elements joined end to end
* no end walls between cells so tube is continuous so water and mineral ions can pass through easily
* thick walls made of lignin
* gaps in cell wall
94
What is the function of the Xylem?
* Transports water and mineral ions in solution up the plant from the roots to leaves (transpiration stream)
* lignin that forms walls strong and prevents tube from collapsing. It's waterproof to prevent water from adhering too much to the surface
* gaps in lignin allow water to leave vessels and pass between them.
95
Why do plants need mineral ions (nitrates and phosphates)?
* Nitrates- in DNA, amino acids (proteins), chlorophyll
* Phosphates- in DNA and ATP
96
Why is Transpiration needed?
* provides a means of cooling the plant via evaporative cooling
* Transpiration stream important in uptake of mineral ions
* Turgor pressure of the cells (due to presence of water as it moves up the plant) provides support to leaves (enabling an increased SA of leaf blade) and stem of non woody plants
97
Outline the Cohesion Tension Theory
* Cohesion- water is non polar molecule which enables hydrogen bonds to form between hydrogen and oxygen of different water molecules. This creates cohesion between water molecules so water travels up xylem as a continuous collumn
* Capillarity (adhesion) of water means water adheres to xylem walls. The narrower the xylem, the bigger impact of capillarity
* As water moves into roots by osmosis, it increases volume of liquid inside root so root pressure increases. Root pressure forces water above it upwards
98
Describe the movement of water up the Xylem (cohesion tension theory)
1. water vapour evaporates out of stomata on leaves (transpiration), which creates a lower pressure
2. more water pulled up xylem to replace lost water vapour (water moves due to negative pressure)
3. collumn of water within the xylem created due to cohesive water molecules
4. water molecules adhere to xylem walls which helps to pull the water collumn upwards (less likely to fall back down due to force of gravity)
5. tension created as collumn of water pulled back up xylem, pulling the xylem in to become narrower. This increases adhesion/capillarity action.
99
What is the role of the Stomata in Transpiration?
* Stomata control how much water leaves in transpiration. Plants in drier environments have fewer stomata to help reduce water loss. Plants have to minimise water loss but still have to exchange gases
* Stomata opening cycles
- when plants have enough water, guard cells are turgid which keep the pores open
- when plants dehydrated, guard cells become flaccid because water moves out of vacuoles by osmosis causing the hole to close
- stomata close at night when little photosynthesis happening as less carbon dioxide and water needed so water loss and gas exchange reduced.
100
How are water and mineral ions obtained by plants?
* water absorbed from soil by osmosis and moves up the stem of the plant from roots to leaves
* mineral ions absorbed by active transport from the soil (including nitrates and phosphates) and are dissolved in the water
101
What has exchange adaptations exist in plants?
* gases exchanged with atmosphere in mesophyll layer of leaf which has a large SA due to large air spaces in spongy mesophyll
* thin leaves reduces diffusion distance for gases in and out of leaf
* gases move in and out of leaf through stomata (pores in lower epidermis of leaf)
102
What is the need for gas exchange in plants?
* plants need carbon dioxide for photosynthesis and oxygen for respiration. Both processes produce each other as a waste product
* dependent on time of day that balance of photosynthesis to respiration will create different concentration gradients which cause gases to diffuse in/out.
103
How do different factors affect the rate of Transpiration?
1. light intensity? positive correlation. More light causes more stomata to open so there is a larger SA for evaporation
2. Temperature? positive correlation. More heat means more kinetic energy, faster moving molecules, so more evaporation. This increases water potential gradient between inside and outside of leaf so water diffuses out of leaf faster
3. Wind? positive correlation. More wind will blow away humid air containing water vapour from stomata, therefore maintaining the water potential gradient
4. Humidity? Negative correlation. More water vapour in air will make water potential gradient positive outside of leaf, reducing water potential gradient
104
What is Translocation?
The movement of assimilates/solutes e.g. amino acids, sugars, from source to sink
- source= where assimilates are produced
- sink= where assimilates are used up
- e.g. source for sucrose is the leaves and the sinks are food storage organs, meristems, and other parts of plant
- enzymes maintain concentration gradient from source to sink by changing solutes (e.g. breaking them down/converting them). There is always a lower concentration at sink then at source.
105
What is the function of the Phloem?
Phloem tissue transports organic substances in plants
106
What is the structure of Phloem?
* sieve tube elements are living cells that form the tube for transporting solutes. They contain no nucleus and few organelles
* companion cell for each sieve tube element
* companion cells carry out living functions for sieve cells e.g. providing energy needed for active transport of solutes
107
Outline the Mass Flow Hypothesis
1. solutes actively transported from companion cell into sieve tubes at source. This lowers water potential inside sieve tubes, so water enters by osmosis from xylem and companion cells. This creates a high hydrostatic pressure inside sieve tubes at source at end of phloem
2. at sink end, solutes removed to be used up. This increases water potential inside sieve tubes so water leaves stubes by osmosis. This lowers hydrostatic pressure inside sieve tubes
3. There is a pressure gradient from source to sink, so solutes forced from source to sink. Solutes then used at sink.
108
What Mass Flow Evidence is there that supports the hypothesis?
* rings of bark removed from trees contain phloem BUT not xylem. A bulge forms above ring with fluid containing higher concentration of sugars that fluid below the ring. This is because sugars cannot move past area with removed bark, giving evidence of a downward flow of sugars
* translocation stops when a metabolic inhibitor (stops ATP production) is put into phloem. This is evidence active transport is involved and translocation is an active process
* radioactive tracer e.g. radioactive carbon (14C) can be used to track movement of organic substances in plant
109
What Mass Flow evidence is there that objects to the hypothesis?
* sugar travels to many sinks, not just the one with the highest water potential, so opposite of what model says
* sieve plates would be a barrier to mass flow due to the high pressure needed for solutes to pass through at a reasonable rate
110
Describe and Explain how ringing experiments are carried out to investigate transport in plants
1. ring of bark and phloem peeled and removed from a tree trunk
2. result from removing the phloem is the trunk swells above the removed section
3. analysis of the liquid in this swelling shows it contains sugar
4. this shows when phloem is removed, the sugars cannot be transported and therefore proves the phloem transports sugars
111
Describe and explain how Tracers can be used to investigate transport in plants
1. Plants are provided with only radioactively labelled carbon dioxide and over time this is absorbed into the plant and used in photosynthesis to create sugars which all contain radioactively labelled carbon
2. thin slices from stems are then cut and placed on x ray film that turns black when exposed to radioactive material
3. when stems are placed on the x ray film, the section of stem containing the sugars turn black and this highlights where the phloem are and shows sugars are transported in the phloem
