Organisms Exchange their Substances with their Environment Flashcards

(141 cards)

1
Q

why do organisms need to exchange substances with their environment?

A

cells need to take in oxygen (for aerobic respiration) and nutrients.
they also need to excrete waste products like carbon dioxide and urea.
most organisms need to stay at roughly the same temperature, so heat needs to be exchanged too.

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2
Q

what is the relationship between the size of animals and their surface area: volume ratio?

A

smaller animals have a higher surface area: volume ratio, whereas larger animals have a smaller surface area: volume ratio.

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3
Q

what two things affect heat exchange?

A

body size and body shape.

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4
Q

how does body size affect heat exchange?

A

the rate of heat loss from an organism depends on its surface area.
if an organism has a large volume, its surface area is relatively small. this makes it harder for it to lose heat from its body.
if an organism is small, its relative surface area is large, so heat is lost more easily. this means smaller organisms need a relatively high metabolic rate, in order to generate enough heat to stay warm.

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5
Q

how does body shape affect heat exchange?

A

animals with a compact shape have a small surface area relative to their volume; this minimises heat loss from their surface.
animals with a less compact shape (have sticky bits out/more gangly) have a larger surface area relative to their volume; this increases heat loss from their surface.

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6
Q

what behavioural and physiological adaptations do organisms have to aid exchange?

A

animals with a high SA: volume ratio tend to lose more water as it evaporates from their surface. some small desert mammals have kidney structure adaptations so that they produce less urine to compensate.
to support their high metabolic rates, small mammals living in cold region need to eat large amounts of high energy foods such as seeds and nuts.
smaller mammals may have thick layers of fur or hibernate when the weather gets really cold.
larger organisms living in hot regions find it hard to keep cool as their heat loss is relatively slow. elephants have developed large flat ears to increase their surface area, allowing them to lose more heat.

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7
Q

what two major adaptations to gas surface exchanges have?

A

they have a large surface area.
they are thin which provides a short diffusion pathway across the gas exchange surface.

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8
Q

how do single-celled organisms exchange gases across their body surface?

A

they absorb and release gases by diffusion through their outer surface.
they have a relatively large surface area, a thin surface and a short diffusion pathway, so there’s no need for a gas exchange system.

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9
Q

how does gas exchange occur in fish?

A

using a counter-current system.
there’s a lower conc. of oxygen in water than in air.
water, containing oxygen, enters the fish through its mouth and passes through the gills. each gill is made of lots of thin plates called gill filaments which give it a big surface area for exchange of gases.
the gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area even more.
the lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion.
blood flows through the lamellae in one direction and water flows over in the opposite direction. this counter-current system maintains a large concentration gradient between the water and the blood. the conc. of oxygen in the water is higher than that in the blood, so as much oxygen as possible diffuses from water into the blood.

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10
Q

how does gas exchange occur in insects?

A

insects have microscopic air-filled pipes called tracheae which they use for gas exchange.
air moves into the tracheae through pores on the surface called spiracles.
oxygen travels down the concentration gradient towards the cells.
the tracheae branch off into smaller tracheoles which have thin permeable walls and go to individual cells. this means that oxygen diffuses directly into the respiring cells; the insect’s circulatory system doesn’t transport oxygen.
carbon dioxide from the cells move down its own concentration gradient towards the spiracles to be released into the atmosphere.
insects use rhythmic abdominal movements to move air in and out of the spiracles.

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11
Q

how does gas exchange occur in dicotyledonous plants?

A

the main gas exchange surface is the surface of the mesophyll cells in the leaf. theyr’e well adapted for their function; they have a large surface area.
the mesophyll cells are inside the leaf. gases move in and out through special pores in the epidermis called stomata.
the stomata can open to allow exchange of gases, and close if the plant is losing too much water.
guard cells control the opening and closing of stomata.

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12
Q

how are insects and plants able to control water loss?

A

insects: if they lose too much water, they close their spiracles using their muscles. they also have waterproof, waxy cuticle all over their body and tiny hairs around their spiracles, both of which reduce evaporation.
plants: a plants’ stomata are usually kept open during the day to allow gaseous exchange. water enters the guard cells, making them turgid which opens the stomatal pore. if a plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore.

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13
Q

what are xerophytic plant adaptations when living in warm, dry or windy habitats where water loss is a problem?

A

stomata sunk in pits that trap moist air, reducing the concentration gradient of water between the leaf and the air. this reduces the amount of water diffusing out of the leaf and evaporating away.
a layer of hairs on the epidermis; which again traps the moist air around the stomata.
curled leaves with the stomata inside, protecting them from wind which helps to increase the rate of diffusion and evaporation.
a reduced number of stomata, so there are fewer places for water to escape.
waxy, waterproofed cuticles on leaves and stems to reduce evaporation.

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14
Q

explain the human gas exchange system.

A

lungs are used for gas exchange in humans.
as you breathe in, air enters the trachea (windpipe).
the trachea splits into two bronchi; one bronchus leading to each lung.
each bronchus then branches off into smaller tubes called bronchioles.
the bronchioles end in small ‘air sacs’ called alveoli.
the ribcage, intercostal muscles and diaphragm all work together to move air in and out.

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15
Q

what is ventilation?

A

this consists of inspiration and expiration.
its controlled by the movements of the diaphragm, internal and external intercostal muscles and ribcage.

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16
Q

explain inspiration.

A

the external intercostal and diaphragm muscles contract.
this causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic activity (the space where the lungs are).
as the volume of the thoracic cavity increases, the lung pressure decreases to below atmospheric pressure.
air will always flow from an area of higher pressure to an area of lower pressure so air flows down the trachea and into the lungs.
inspiration is an active process and so it requires energy.

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17
Q

explain expiration.

A

the external intercostal and diaphragm muscles relax.
the ribcage moves downwards and inwards and the diagram becomes curved again.
the volume of the thoracic cavity decreases, causing air pressure to increase to above atmospheric pressure.
air is forced down the pressure gradient and out of the lungs.
normal expiration is a passive process and so it doesn’t require energy.

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18
Q

what are two examples of forced expiration?

A

blowing out candles on your birthday cake.
coughing.

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19
Q

explain forced expiration.

A

the external intercostal muscles relax and the internal intercostal muscles contract, pulling the ribcage further down and in. this movement is said to be antagonistic.

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20
Q

where does human gaseous exchange occur?

A

in the alveoli.

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21
Q

what are alveoli made of?

A

a single layer of thin, flat cells called alveolar epithelium.

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22
Q

explain gas exchange in the alveoli.

A

there is a huge number of alveoli in the lungs, which means there’s a big surface area for exchanging oxygen and carbon dioxide.
the alveoli are surrounded by a network of capillaries.
oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium (forms the capillary wall) and into haemoglobin in the blood.
carbon dioxide diffuses into the alveoli from the blood, and is breathed out.

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23
Q

what features are present in the alveoli that speed up the rate of diffusion so gases can be exchanged quickly?

A

a thin exchange surface; the alveolar epithelium is only one cell thick and so there’s a short diffusion pathway.
a large surface area; a larger number of alveoli means a larger surface area for gas exchange.

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24
Q

what impact does a steep concentration gradient have on gas exchange in humans?

A

a steep conc. gradient of oxygen and carbon dioxide between the alveoli and the capillaries increases the rate of diffusion.
gases are able to be exchanged quickly.
the conc. gradient is maintained by the flow of blood and ventilation.

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25
what do lung diseases affect in the lungs?
they affect both ventilation and gas exchange in the lungs; how well the lungs function.
26
how can doctors diagnose lung diseases?
they can carry out tests to investigate lung function.
27
define tidal volume.
the volume of air in each breath; usually between 0.4 dm cubed and 0.5 dm cubed for adults.
28
define ventilation rate.
the number of breaths per minute, for a healthy person at rest it's about 15 breaths.
29
define forced expiratory volume1 (FEV1).
the maximum volume of air that can be breathed out in 1 second.
30
define forced vital capacity (FVC).
the maximum volume of air it is possible to breathe forcefully out of the lungs after a really deep breath in.
31
what equipment is used to measure tidal volume, ventilation rate, (FEV1) and (FVC)?
a spirometer.
32
how do we interpret data on risk factors of lung disease?
first we describe the data on the graphs, include values from the graph and use the appropriately. then we draw conclusions from the graph, we do this stating correlations and not causations. just because there's a correlation does not mean that factor caused the lung disease- there may be other factors. the look oat other things to consider from the graph; keep information points which can be useful in understanding the risk factors of lung disease.
33
how do we dissect fish gills in bony fish?
make sure you are wearing an apron or lab coat. place chosen fish in a dissection tray or on a cutting board. gills are located on either side of the fish's head. they're protected on each side by a bony flap called an operculum and supported by gill arches. to remove the gills, push back the operculum and use scissors to carefully remove the gills. cut out each gill arch through the bone at the top and bottom. looking closely you should see the gill filaments.
34
explain the basics of digestion.
the large biological molecules in food are too big to cross cell membranes. this means they can't be absorbed from the gut into the blood. during digestion, these large molecules are broken down into smaller molecules by hydrolysis, which can move across cell membranes. This means they can easily be absorbed from the gut into the blood, to be transported around the body for use by the body cells.
35
what is used to break down the biological molecules in food?
digestive enzymes.
36
what are digestive enzymes?
these are enzymes which are produced by specialised cells in the digestive systems of mammals. these enzymes are then released into the gut to mix with food.
37
explain the process of carbohydrate digestion.
carbohydrates are broken down by amylase and membrane-bound disaccharidases. amylase is a digestive enzyme that catalyses the conversion of starch into the smaller sugar maltose. this involves the hydrolysis of the glycosidic bonds in starch. membrane-bound disaccharidases are enzymes that are attached to the cell membranes of epithelial cells lining the ileum. they help to break down disaccharides into monosaccharides. this involves the hydrolysis of glycosidic bonds.
38
where is amylase produced and released into?
produced in the salivary glands, which release amylase into the mouth. and also in the pancreas, which releases amylase into the small intestine.
39
explain the process of lipid digestion.
lipids are broken down by lipase with the help of bile salts. lipase enzymes catalyse the breakdown of lipids into monglycerides and fatty acids. this involves the hydrolysis of the ester bonds in lipids. bile salts emuslify lipids; this causes the lipids to form small droplets. once the lipid has been broken down, the monoglycerides and fatty acids stick with the bile salts to form tiny structures called micelles.
40
why are bile salts important in the process of lipid digestion?
several small lipid droplets have a bigger surface area than a single large droplet. so the formation of small droplets greatly increases the surface area of lipid that's available for lipases to work on.
41
where are lipases made?
in the pancreas. they work in the small intestine.
42
how are bile salts produced?
produced by the liver.
43
what are proteins broken down by?
a combination of proteases. these are enzymes that catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids. these proteases are endopeptidases and exopeptidases.
44
define proteases
these are enzymes that catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids.
45
what are endopeptidases?
they act to hydrolyse peptide bonds within a protein.
46
name and give the functions of two examples of endopeptidases
trypsin is an example of an endopeptidase. it is synthesised in the pancreas and secreted into the small intestine. pepsin is another example. it's released into the stomach by cells in the stomach lining. pepsin only works in acidic conditions which are provided by hydrochloric acid in the stomach
47
what are exopeptidases?
they act to hydrolyse peptide bonds at the ends of protein molecules. they remove single amino acids from proteins.
48
name and give the function plus location of an exopeptidase
dipeptidases are exopeptidases that work specifically on dipeptides. they act to separate the two amino acids that make up a dipeptide by hydrolysing the peptide bond between them. dipeptidases after often located in the cell-surface membrane of epithelial cells in the small intestine.
49
what are the products of digestion?
monosaccharides monoglycerides and fatty acids amino acids
50
how are monosaccharides absorbed across the ileum epithelium into the bloodstream?
glucose is absorbed by active transport with sodium ions via a co-transporter protein. galactose is absorbed in the same way using the same co-transporter protein. fructose is absorbed via facilitated diffusion through a different transporter protein.
51
how are monoglycerides and fatty acids absorbed across the ileum epithelium into the bloodstream?
micelles help to move monoglycerides and fatty acids towards the epithelium. because micelles constantly break up and reform, they can 'release' monoglycerides and fatty acids, allowing them to be absorbed; whole micelles are not taken up to the epithelium. monoglycerides and fatty acids are lipid-soluble, so can diffuse directly across the epithelial cell membrane.
52
how are amino acids absorbed across the ileum epithelium into the bloodstream?
amino acids are absorbed via co-transport. sodium ions are actively transported out of the ileum epithelial cells into the blood. this creates a sodium ion concentration gradient. sodium ions can then diffuse from the lumen of the ileum into the epithelial cells through sodium-dependent transporter proteins, carrying the amino acids with them.
53
how is oxygen carried around the body?
by haemoglobin
54
what do red blood cells contain?
haemoglobin
55
what is haemoglobin?
haemoglobin is a large protein with a quaternary structure; its made up of more than one polypeptide chain (four). each chain has a haem group, which contains an iron ion and gives haemoglobin its red colour. haemoglobin has a high affinity for oxygen. oxygen joins to haemoglobin in red blood cells to form oxyhaemoglobin.
56
what is the partial pressure of oxygen?
it is the measure of oxygen concentration. the greater the concentration of dissolved oxygen in cells, the higher the partial pressure.
57
what is the partial pressure of carbon dioxide?
it is a measure of the concentration of CO2 in a cell.
58
explain how haemogblobin's affinity for oxygen varies.
it varies depending on the partial pressure of oxygen. oxygen loads onto haemoglobin to form oxyhaemoglobin where there's a high partial pressure of oxygen. oxyhaemoglobin unloads its oxygen where there's a lower partial pressure of oxygen. oxygen enters blood capillaries at the alveoli in the lungs. alveoli have a high partial pressure of oxygen so oxygen loads onto the haemoglobin to form oxyhaemoglobin. when cells respire, they use up oxygen; this lowers the partial pressure of oxygen. red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen. the haemoglobin then returns to the lungs to pick up more oxygen.
59
what does a dissociation curve show?
it shows how saturated the haemoglobin is with oxygen at any given partial pressure.
60
why is the dissociation curve 's-shaped'?
the graph is 's-shaped' because when haemoglobin (Hb) combines with the first O2 molecule, its shape alters in a way that makes it easier for other molecules to join too. but as the Hb starts to become saturated, it gets harder for more oxygen molecules to join. as a result, the curve has a steep bit in the middle where it's really easy for oxygen molecules to join, and shallow bits at each end where it's harder. when the curve is steep, a small change in pO2 causes a big change in the amount of oxygen carried by the Hb.
61
explain the Bohr effect
haemoglobin gives up its oxygen more readily at higher partial pressures of carbon dioxide. when cells respire they produce carbon dioxide, which raises the pCO2. this increases the rate of oxygen unloading — so the dissociation curve 'shifts' right. the saturation of blood with oxygen is lower for a given pO2, meaning that more oxygen is being released.
62
what is the benefit of having a particular type of haemoglobin?
it is an adaptation that helps organisms to survive in a particular environment.
63
how does haemoglobin differ in organisms living in low oxygen environments?
these organisms have haemoglobin with a higher affinity for oxygen than human haemoglobin.
64
what is the characteristic of the dissociation curve for organisms in low oxygen environments?
the dissociation curve is to the left of the human haemoglobin curve.
65
what type of haemoglobin do very active organisms have?
very active organisms have haemoglobin with a lower affinity for oxygen than human haemoglobin.
66
what is the characteristic of the dissociation curve for active organisms?
the dissociation curve is to the right of the human haemoglobin curve.
67
give an example of an organism living in a depleted oxygen environment.
an example is a lugworm. ## Footnote A = animal living in depleted oxygen environment, eg. a lugworm.
68
give an example of an organism living at high altitude.
an example is a llama in the Andes. ## Footnote B = animal living at high altitude where the partial pressure of oxygen is lower, e.g. a llama in the Andes.
69
give an example of an active animal with a high respiratory rate.
an example is a hawk. ## Footnote D = active animal with a high respiratory rate living where there's plenty of available oxygen, eg. a hawk.
70
what is the circulatory system?
the circulatory system is a mass transport system that carries raw materials from specialised exchange organs to body cells.
71
why do multicellular organisms need a specialised transport system?
multicellular organisms, like mammals, have a low surface area to volume ratio.
72
what are the main components of the circulatory system?
The circulatory system is made up of the heart and blood vessels.
73
what is the function of the heart in the circulatory system?
The heart pumps blood through blood vessels to reach different parts of the body.
74
what types of blood vessels are involved in the circulatory system?
The blood vessels include arteries, arterioles, veins, and capillaries.
75
what does blood transport in the body?
blood transports respiratory gases, products of digestion, metabolic wastes, and hormones.
76
what are the two circuits of the circulatory system?
one circuit takes blood from the heart to the lungs and back, while the other takes blood around the rest of the body.
77
what supplies blood to the heart?
The heart has its own blood supply via the left and right coronary arteries.
78
what is the role of the pulmonary artery?
The pulmonary artery carries deoxygenated blood to the lungs.
79
what is the role of the pulmonary vein?
The pulmonary vein carries oxygenated blood from the lungs to the heart.
80
what does the aorta do?
the aorta carries oxygenated blood to the body.
81
what is the function of the vena cava?
the vena cava carries deoxygenated blood to the heart.
82
what is the function of arteries?
arteries carry blood from the heart to the rest of the body. all arteries carry oxygenated blood except for the pulmonary arteries, which take deoxygenated blood to the lungs.
83
how does the structure of arteries help the functioning of the circulatory system?
artery walls are thick and muscular and have elastic tissue to stretch and recoil as the heart beats, which helps to maintain a high pressure. the inner lining of the artery (endothelium) is folded, allowing the artery to stretch — this also helps it to maintain high pressure.
84
what is the function of arterioles?
arteries divide into smaller vessels called arterioles. these form a network throughout the body. blood is directed to different areas of demand in the body by muscles inside the arterioles, which contract to restrict the blood flow or relax to allow full blood flow.
85
what is the function of veins?
veins take blood back to the heart under low pressure. all veins carry deoxygenated blood (because oxygen has been used up by body cells), except for pulmonary veins which carry oxygenated blood to the heart from the lungs.
86
how does the structure of veins help the functioning of the circulatory system?
veins have a wider lumen than equivalent arteries, with very little elastic or muscle tissue, therefore a low pressure is made. veins contain valves to stop the blood flowing backwards. blood flow through the veins is helped by contraction of the body muscles surrounding them.
87
what is the function of capillaries?
they're the smallest of blood vessels and act as a diffusion pathway for an exchanging of substances, e.g glucose and oxygen, between cells.
88
how does the structure of capillaries help the functioning of the circulatory system?
capillaries are always found very near cells in exchange tissues (e.g. alveoli in the lungs), so there's a short diffusion pathway. their walls are only one cell thick, which also shortens the diffusion pathway. there are a larger number of capillaries to increase surface area for exchange.
89
what are capillary beds?
networks of capillaries in tissue
90
what is tissue fluid and its function?
tissue fluid is the fluid that surrounds cells in tissues. it's made from small molecules that leave the blood plasma, e.g. oxygen, water and nutrients. cells take in oxygen and nutrients from the tissue fluid, and release metabolic waste into it.
91
how are substances able to move out of the capillaries, in the capillary bed, into the tissue fluid?
by pressure filtration.
92
how does pressure filtration work?
- at the start of the capillary bed, nearest the arteries, the hydrostatic (liquid) pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid. - this difference in hydrostatic pressure means an overall outward pressure forces fluid coming out of the capillaries and into the spaces around the cells, forming tissue fluid. - as fluid leaves, the hydrostatic pressure reduces in the capillaries — so the hydrostatic pressure ismuch lower at the venule end of the capillary bed (the end that's nearest to the veins). - due to the fluid loss, and an increasing concentration of plasma proteins (which don't leave the capillaries), the water potential at the venule end of the capillary bed is lower than the water potential in the tissue fluid. - this means that some water re-enters the capillaries from the tissue fluid at the venule end by osmosis.
93
what occurs if there is any excess tissue fluid?
any excess tissue fluid is drained into the lymphatic system ( a network of tubes that acts a bit like a drain), which transports this excess fluid from the tissues and dumps it back into the circulatory system.
94
what side of the heart does what in the circulatory system?
the right side pumps deoxygenated blood to the lungs and the left side pumps oxygenated blood to the whole body.
95
how is the left ventricle adapted to do its job effectively?
the left ventricle of the heart has thicker, more muscular walls than the right ventricle, because it needs to contract powerfully to pump blood all the way round the body. the right side only needs to get blood to the lungs, which are nearby.
96
how are the ventricles adapted to do their job effectively?
the ventricles have thicker walls than the atria, because they have to push blood out of the heart whereas the atria just need to push blood a short distance into the ventricles.
97
how are the atrioventricular (AV) valves adapted to do their job effectively?
the AV valves link the atria to the ventricles and stop blood flowing back into the atria when the ventricles contract.
98
how are the semi-lunar (SL) valves adapted to do their job effectively?
the SL valves link the ventricles to the pulmonary artery and aorta, and stops blood flowing back into the heart after the ventricles contract.
99
how are cords adapted to do their job effectively?
the cords attach the atrioventricular valves to the ventricles to stop them being forced up into the atria when the ventricles contract.
100
how are the valves adapted to do their job effectively?
the valves only open one way — whether they're open or closed depends on the relative pressure of the heart chambers. if there's higher pressure behind a valve, it's forced open, but if pressure is higher in front of the valve it's forced shut. this means blood only flows in one direction through the heart.
101
what is the cardiac cycle?
the cardiac cycle is an ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating round the body.
102
what are the three stages of the cardiac cycle?
ventricles relax, atria contract ventricles contract, atria relax ventricles relax, atria relax
103
explain the 'ventricles relax, atria contract' stage
the ventricles are relaxed. the atria contract, decreasing the volume of the chambers and increasing the pressure inside the chambers. this pushes the blood into the ventricles. there's a slight increase in ventricular pressure and chamber volume as the ventricles receive the ejected blood from the contracting atria. the semi-lunar valves are closed and the atrioventricular valves are open.
104
explain the 'ventricles contract, atria relax' stage
the atria relax. the ventricles contract (decreasing their volume), increasing their pressure. the pressure becomes higher than the atria, which forces the AV valves shut to prevent back-flow. the pressure in the ventricles is also higher than in the aorta and pulmonary artery, which forces open the SL valves and blood is forced out into these arteries.
105
explain the 'ventricles relax, atria relax' stage
the ventricles and atria both relax. the higher pressure in the pulmonary artery and aorta closes the SL valves to prevent back-flow into the ventricles. blood returns to the heart and the atria fill again due to the higher pressure in the vena cava and pulmonary vein. in turn this starts to increase the pressure of the atria. as the ventricles continue to relax, their pressure falls below the pressure of the atria and so the AV valves open. this allows blood to flow passively (without being pushed by atrial contraction) into the ventricles from the atria. the atria contract, and the whole process begins again.
106
what are the two types of data that we may have to interpret in the exam?
a graphical display of the 3 stages of the cardiac cycle a diagram of the heart showcasing open and closed valves.
107
what do most cardiovascular diseases start with?
atheroma formation
108
how are artheromas formed?
the wall of aqn artery is made up of several layers. the endothelium (inner lining) is usually smooth and unbroken. if damage occurs to the endothelium (e.g. by high blood pressure) white blood cells (mostly macrophages) and lipids from the blood, clump together under the lining to form fatty streaks. over time, more white blood cells, lipids and collective tissue build up and harden to form a fibrous plaque called an atheroma.
109
how do artheromas cause cardiovascular diseases?
artheromas partially block the lumen of the artery and restrict blood flow, which causes blood pressure to increase. coronary heart disease, a type of cardiovascular disease, occurs when the coronary arteries have lots of atheromas in them, which restricts blood flow to the heart muscle. it can lead to myocardial infarction.
110
what are the 2 types of diseases that affect the arteries?
aneurysm — a balloon-like swelling of the artery. thrombosis — formation of a blood clot.
111
how does an atheroma cause an aneurysm?
atheroma plaques damage and weaken arteries. they also narrow arteries, increasing blood pressure. when blood travels through a weakened artery at high pressure, it may push the inner layers of the artery through the outer elastic layer to form a balloon-like swelling — an aneurysm. this aneurysm may burst, causing a haemorrhage.
112
how does an atheroma cause thrombosis?
an atheroma plaque can rupture the endothelium of an artery. this damages the artery wall and leaves a rough surface. platelets and fibrin (a protein) accumulate at the site of damage and form a blood clot (a thrombus). this blood clot can cause a complete blockage of the artery, or it can become dislodged and block a blood vessel elsewhere in the body. debris from the rupture can cause another blood clot to form further down the artery.
113
how can interrupted blood flow to the heart cause a myocardial infarction?
the heart muscle is supplied with blood by the coronary arteries. this blood contains the oxygen needed by heart muscle cells to carry out respiration. if a coronary artery becomes completely blocked (e.g. a blood clot) an area of the heart muscle will be totally cut off from its blood supply, receiving no oxygen. this causes a myocardial infarction — commonly known as a heart attack. a heart attack can cause damage and death of the heart muscle. symptoms include pain in the chest and upper body, shortness of breath and sweating. if large areas of the heart are affected, complete heart failure can occur which is often fatal.
114
what are the 3 common risk factors for cardiovascular disease?
high blood cholesterol and poor diet cigarette smoking high blood pressure
115
explain how 'high blood cholesterol and poor diet' may cause cardiovascular disease
if the blood cholesterol is high (above 240mg per 100 cm cubed) then the risk of cardiovascular disease is increased. this is because cholesterol is one of the main constituents of the fatty deposits that form atheromas. atheromas can lead to increased blood pressure and blood clots. this could block the flow of blood to coronary arteries, which could cause a myocardial infarction. a diet high in saturated fat is associated with high blood cholesterol levels. a diet high in salt also increases the risk of cardiovascular disease because it increases the risk of high blood pressure.
116
explain how 'cigarette smoking' may cause cardiovascular disease
both nicotine and carbon monoxide, found in cigarette smoke, increase the risk of cardiovascular disease. nicotine increases the risk of high blood pressure. carbon monoxide combines with haemoglobin and reduces oxygen transported in the blood, and so reduces the amount of oxygen available to tissues. if the heart muscle doesn't receive enough oxygen it can lead to a heart attack. smoking also decreases the amount of antioxidants in the blood — these are important for protecting cells from damage. fewer antioxidants can lead to atheroma formation.
117
explain how 'high blood pressure' may cause cardiovascular disease
high blood pressure increases the risk of damage to the artery walls. damaged walls have an increased risk of atheroma formation, causing a further increase in blood pressure. atheromas can also cause blood clots to form. a blood clot could block flow of blood to the heart muscle, possibly resulting in myocardial infarction. so anything that increases blood pressure also increases the risk of cardiovascular disease, e.g. being overweight, not exercising and excessive alcohol consumption.
118
what are the two types of tissue involved in transport in plants?
xylem tissue phloem tissue
119
what is xylem tissue?
it is a mass transport system. xylem tissue transports water and mineral ions in solution. these substances move up the plant from the roots to the leaves.
120
what is phloem tissue?
it is a mass transport system, moving substances over large distances. phloem tissue transports organic substances like sugars (also in solution) both up and down the plant.
121
what are xylem vessels?
they are part of the xylem tissue that actually transports the water and ions. xylem vessels are very long, tube-like structures formed from dead cells (vessel elements) joined end to end. there are no end walls on these cells, making an uninterrupted tube that allows water to pass up through the middle easily.
122
explain the cohesion-tension theory of water transport within the xylem tissue
cohesion and tension help water move up plants, from roots to leaves, against the force of gravity. - water evaporates from the leaves at the top of the xylem. this is transpiration. - this creates tension (suction), which pulls more water into the leaf. - water molecules are cohesive (they stick together) due to their hydrogen bonds, so when some are pulled into the leaf others follow. this means the whole column of water in the xylem, from the leaves down to the roots, moves upward. - water enters the stem through the roots.
123
what is transpiration?
transpiration is the evaporation of water from a plant's surface, especially the leaves. water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf. when the stomata open, it moves out of the leaf down the concentration gradient (there's more water inside the leaf than in the air outside).
124
what are the 4 factors which affect the transpiration rate?
light temperature humidity wind
125
how does light affect the transpiration rate?
the lighter it is the faster the transpiration rate (i.e. there's a positive correlation between light intensity and transpiration rate). this is because the stomata open when it gets light to let in carbon dioxide for photosynthesis. when it's dark the stomata are usually closed, so there's a little transpiration.
126
how does temperature affect the transpiration rate?
the higher the temperature the faster the transpiration rate. warmer water molecules have more energy so they evaporate from the cells inside the leaf faster. this increases the concentration gradient between the inside and outside of the leaf, making water diffuse out of the leaf faster.
127
how does humidity affect the transpiration rate?
the lower the humidity, the faster the transpiration rate (i.e. there's a negative correlation between humidity and transpiration rate). if the air around the plant is dry, the concentration gradient between the leaf and the air is increased, which increases transpiration.
128
how does wind affect the transpiration rate?
the windier it is, the faster the transpiration rate. lots of air movement blows away water molecules from around the stomata. this increases the concentration gradient, which increases the rate of transpiration.
129
what is a potometer?
it is a special piece of apparatus used to estimate transpiration rates. it usually measures water uptake by a plant, but it's assumed that water uptake by the plant is directly related to water loss by the leaves. you can use a potometer to estimate how different factors affect the transpiration rate.
130
explain how a potometer is used to estimate how different factors affect the transpiration rate
cut a shoot underwater to prevent air from entering the xylem. cut it at a slant to increase the surface area available for water uptake. assemble the potometer in the water and insert the shoot underwater, so no air can enter. remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water. check that the apparatus is watertight and airtight. dry the leaves, allow time for the shoot to acclimatise, and then shut the tap. remove the end of the capillary tube from the beaker of water until one air bubble has formed, then put the end of the tube back into the water. record the starting position of the air bubble. start a stopwatch and record the distance moved by the bubble per unit time. the rate of air bubble movement is an estimate of the transpiration rate. only change one variable at a time. all other conditions must be kept constant.
131
what does the phloem tissue transport?
it transports solutes which are dissolved substances such as sucrose. it transports these solutes around plants
132
how is phloem tissue adapted for transporting solutes?
- the phloem tissue contains sieve tube elements and companion cells. - sieve tube elements are living cells that form the tube for transporting solutes. sieve tube elements have no nucleus and a few organelles and so there's a companion cell for each sieve tube element. they carry out living functions for sieve cells, e.g providing the energy needed for active transport of solutes.
133
what is translocation?
translocation is the movement of solutes to where they're needed in a plant. solutes are sometimes called assimilates. it's an energy-requiring process that happens in the phloem, translocation moves solutes from 'sources' to 'sinks'. the source of a solute is where it's made (so it's at a high conc. there). the sink is the area where it's used up (so it's at a lower conc. there). the higher the concentration of solutes at the source, the higher the rate of translocation.
134
what is the role of enzymes in regards to the sources and sinks?
enzymes maintain a conc. gradient from the source to the sink by changing the solutes at the sink (e.g. by breaking them down or making them into something else). this makes sure there's always a lower conc. at the sink rather than at the source.
135
what is the mass flow hypothesis?
this is the best supported theory that best explains phloem transport.
136
explain the first stage of the mass flow hypothesis
stage 1: - active transport is used to actively load the solutes (e.g. sucrose from photosynthesis) from companion cells into the sieve tubes of the phloem at the source (e.g. the leaves). - this lowers the water potential inside the sieve tubes, so water enters the tubes by osmosis from the xylem and companion cells. - this creates a high pressure inside the sieve tubes at the source end of the phloem.
137
explain the second stage of the mass flow hypothesis
- at the sink end, solutes are removed from the phloem to be used up. - this increases the water potential inside the sieve tubes, so water also leaves the tubes by osmosis. - this lowers the pressure inside the sieve tubes.
138
explain the final stage of the mass flow hypothesis
- the result is a pressure gradient from the source end to the sink end. - this gradient pushes solutes along the sieve tubes towards the sink. - when they reach the sink the solutes will be used (e.g. in respiration) or stored (e.g. as starch).
139
explain all 4 types of supporting evidence for mass flow
1. if a ring bark (which includes the phloem, but not the xylem) is removed from a woody stem, a bulge forms above the ring. the fluid from the bulge has a higher concentration of sugars than the fluid from below the ring — this is evidence that there's a downward flow of sugars. 2. a radioactive tracer such as radioactive carbon (carbon 14) can be used to track the movement or organic substances in a plant. 3. pressure in the phloem can be investigated using aphids (they pierce the phloem, then their bodies are removed leaving the mouthparts behind, which allows the sap to flow out). the sap flows out quicker nearer the leaves than further down the stem — this is evidence that there's a pressure gradient. 4. if a metabolic inhibitor (which stops ATP production) is put into the phloem, then translocation stops — this is evidence that active transport is involved.
140
what are the 2 objections of mass flow
1. sugar travels to many different sinks, not just one with the highest water potential, as the model would suggest. 2. the sieve plates would create a barrier to mass flow. a lot of pressure would be needed for the solutes to get through at a reasonable rate.
141
explain the experiment of the translocation of solutes using radioactive tracers
1) supply part of a plant (often a leaf) with an organic substance that has a radioactive label. one example is carbon dioxide containing the radioactive isotope, carbon 14. this radioactively-labelled CO, can be supplied to a single leaf by being pumped into a container which completely surrounds the leaf. 2) the radioactive carbon will then be incorporated into organic substances produced by the leaf (e.g, sugars produced by photosynthesis), which will be moved around the plant by translocation. 3) the movement of these substances can be tracked using a technique called autoradiography. to reveal where the radioactive tracer has spread to in a plant, the plant is killed (e.g. by freezing it using liquid nitrogen) and then the whole plant (or sections of it) is placed on photographic film — the radioactive substance is present wherever the film turns black. 4) the results demonstrate the translocation of substances from source to sink over time — for example, autoradiographs of plants killed at different times show an overall movement of solutes (e.g. products of photosynthesis) from the leaves towards the roots.