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Aqa a level biology > Topic 3: Organisms exchange substances with their environment > Flashcards

Topic 3: Organisms exchange substances with their environment Flashcards

1
Q

Describe the relationship between the size, surface area and volume ratio of organisms

A

As the size of an organism increases the surface area to volume ratio decreases

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2
Q

How do you calculate surface area to volume ratio

A

surface area / volume

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3
Q

Explain the position of mitochondria in large cells

A

-large cells have smaller surface area to volume ratio which means that without mitochondria being close to the cell surface membrane, diffusion pathway would be longer and less efficient

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4
Q

adaptations of gas exchange surfaces

A

Adaptations of gas exchange surfaces:

across the body surface of a single-celled organism

in the tracheal system of an insect (tracheae, tracheoles and spiracles)

across the gills of fish (gill lamellae and filaments including the counter-current principle)

by the leaves of dicotyledonous plants (mesophyll and stomata).

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5
Q

exchange and surface area

A

To survive, organisms transfer materials between the internal and external environments

-The environment around cells of multicellular organisms is tissue fluid

-Mass transport systems maintains diffusion gradient pathways

-the size and metabolic rate of an organism will affect the amount of material that is exchanged. Larger metabolic rate = larger surface area : volume ratio

-exchange can take place passively (diffusion or osmosis) or actively (active transport)

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6
Q

what do organisms need to exchange

A

oxygen, glucose, minerals, vitamins, amino acids, fatty acids, urea, carbon dioxide, heat

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7
Q

what is the importance of exchange

A

metabolic processes like respiration
homeostasis (heat)

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8
Q

how are things exchanged

A

Active transport –> requires metabolic energy e.g co transport

Passive processes –> no energy e,g simple diffusion

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9
Q

surface area to volume ratio

A

Larger animals have a smaller surface area to volume ratio

Smaller animals have a large surface area to volume ratio

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10
Q

what are the names for two tubes transporting gases to respiring tissues

A

trachea
tracheoles

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11
Q

Explain four ways in which an insects tracheal system is adapted for efficient gas exchange

A

1) has many tracheoles that are highly branched so increases surface area

2) Tracheoles also have thin walls which reduces diffusion pathway

3) Trachea has fluid/gas at the end of tracheoles that moves into tissues so faster diffusion

4) body can be moved by muscles so moves air which ensures a concentration gradient

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12
Q

Explain the movement of oxygen into the gas exchange system of an insect when it is at rest

A

-there is a high concentration of oxygen closest to the spiracle and lower concentration of oxygen in respiring tissues. This means that at rest oxygen diffuses down a concentration gradient to respiring tissues to be used in processes such as aerobic respiration

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13
Q

Describe an explain the results of abdominal pumping on gas exchange of insects

A

-as pressure increases the amount of CO2 released increases
-as tubes of gas exchange system are squeezed during abdominal pumping, volume decreases and thus pressure increases
-this means that more CO2 is released due to gases moving from high to low pressure

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14
Q

what stimulates the spiracle to open

A

high partial pressure of CO2

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15
Q

what causes the oxygen concentration in the trachea to fall when the spiracles are closed

A

-respiration causes oxygen conc to fall and no new oxygen can enter the spiracle through diffusion as it is closed

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16
Q

do insects have a large or small surface area to volume ratio

A

large

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17
Q

what gas exchange system do insects have

A

tracheal

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18
Q

what is the spiracle

A

opening in the surface of an insects gas exchange system

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19
Q

what does the exoskeleton do

A

provides protection
reduces water loss

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20
Q

what do cartilage rings around the trachea of an insect do

A

gives it structure and prevents it from collapsing

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21
Q

what are tracheoles

A

dead end tubes which are high gas in volume which increases the surface area. They also have thin walls which means a shorter diffusion pathway

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22
Q

how to gases move in an out an insects tracheal system (3 ways)

A

-down a diffusion gradient
-mass transport due to muscle contraction
-pressure changes due to changing water volume

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23
Q

how do gases move down a diffusion gradient in insects

A

-Oxygen –> high O2 concentration closest to the spiracle and lower closest to respiring tissues

-Carbon dioxide –> High CO2 concentration closest to the respiring tissues and lower closest to the spiracle

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24
Q

how does mass transport due to muscle contraction occur in insects

A

1) muscle contractions reduce the volume inside the trachea

2) this increases the gas pressure inside the insect

3) causing gases to move to an area of lower pressure in the atmosphere surrounding the insect.

–> moves out gas (CO2) during respiration from exercise

-Abdominal pumping is an example of muscle contraction (high pressure = more CO2 released due to volume decreasing)

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25
Q

how do pressure changes due to changing water volume occur in insects

A

-Lactate production from anaerobic respiration during high intensity exercise is soluble in water and reduces water potential in cells

-Water moves by osmosis into the surrounding tissue from the end of the tracheoles

-Increases the volume of tracheole filled with gas (in which gases diffusion quicker)

–> less water = more gas

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26
Q

what are limitations of gas exchange in insects

A

-Water vapor could evaporate out of the spiracle when open which increases dehydration. To mitigate against this insects have an exoskeleton and hairs on the spiracle

-mainly diffusion that occurs so molecules must be small

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27
Q

Describe and explain how the countercurrent system leads to efficient gas exchange across the gills of a fish

A

-Countercurrent flow is the movement of blood and water in opposing directions. This means that a favourable concentration gradient for oxygen by diffusion is maintained along the entire length of the lamellae. Equilibrium is not reached.

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28
Q

what is a fish

A

any member of a group of organisms that consist of all gill bearing aquatic craniate animals that lack limbs with digits

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29
Q

How do gills of fish work

A

The water passes through their mouth and over their gills. They are able to use diffusion to get oxygen from water when it passes over the surface of the gills

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30
Q

how do fish get oxygen

A

through dissolved oxygen in water

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31
Q

what are adaptations of fish

A

-has gill filaments that increase surface area and shortens diffusion pathway

-good blood supply –> maintains concentration gradient

-Has many lamella that increase surface area for exchange

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32
Q

what would happen in fish had parallel flow

A

-If oxygen and water had parallel flow diffusion would reach equilibrium which is an issue as oxygen will no longer diffuse as concentration gradient would not be maintained all the way along the lamellae.

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33
Q

how does diffusion occur in a fish

A

-Diffuse occurs in a counter current flow

-Water and blood flow in opposing directions

-Oxygen rich blood always comes into contact with oxygen rich water. This maintains a favorable concentration gradient for diffusion of oxygen along the entire length of the lamellae. This means that no equilibrium is reached

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34
Q

why do fish need a specialised exchange system

A

-impermeable membrane of skin so gases cannot easily diffuse
-small surface area to volume ratio

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35
Q

what are along an arch of a gill

A

Along each arch there are multiple projections called gill filaments, with
lamellae on them which participate in gas exchange.

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36
Q

how does ventilation occur in a fish

A

. Ventilation begins with
the fish opening its mouth followed by lowering the floor of buccal cavity. This enables water
to flow in. Afterwards, fish closes its mouth, causing the buccal cavity floor to raise, thus
increasing the pressure. The water is forced over the gill filaments by the difference in
pressure between the mouth cavity and opercular cavity. The operculum acts as a valve and
pump and lets water out and pumps it in.

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37
Q

Explain how the counter current mechanism in fish gills ensures the maximum amount of oxygen passes into the blood flowing through the gills

A

-water and blood flow in opposite directions
-this means that a favourable concentration gradient is maintained, The oxygen concentration is always higher in the water than in the blood
-diffusion is maintained throughout the entire length of the lamellae

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38
Q

where is oxygen concentration higher - the blood or water

A

water

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39
Q

Explain how the presence of gills adapts the damselfly to its way of life

A

-damselfly has larger metabolic rate and larger surface area to volume ratio
-this means that the damselfly needs more oxygen

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40
Q

describe the features of fish that give them a large surface area

A

gills have many filaments with lots of lamellae on them

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41
Q

explain the relationship between gill surface area and swimming speed

A

larger gill surface area means more oxygen is supplied so more respiration and thus more energy is provided

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42
Q

how are diffusion gradients maintained in and out of the leaf

A

-mitochondria carrying out respiration and chloroplasts carrying out photosynthesis

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43
Q

what are the adaptations in leaves for rapid gas exchange

A

-high stomatal density
-large surface area of mespohyll cells
-interconnecting air spaces
–large SA:vol ratio so greater SA for exchange
-densely packed stomata so short diffusion pathway

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44
Q

what is the gas exchange surface of a plant

A

leaf

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45
Q

what is the pore on the underside of a leaf

A

the stomata

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46
Q

describe a method for finding the surface area of a gas exchange surface

A

-trace an outline the leaf onto squared paper

-count the number of squares covered by the leaf

-mutliply by 2

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47
Q

what is the structure of a leaf

A

-waxy cuticle

-upper epidermis

-palisade mesophyll

-spongy mesophyll

-lower epidermis

-stomata and guard cells

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48
Q

how would you measure stomatal density

A

1) calculate magnification

2) find area of diagram

3) divide area by magnification to get actual size

4) total no of stomata divided by actual size total

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49
Q

why does a plant in a desert have a low stomatal density

A

due to dry atmospheric conditions. This means that there is a steep diffusion gradient for water vapour and thus less water loss.

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50
Q

what is a mesophyte

A

plant adapted to a habitat with adequate water

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51
Q

what is a xerophyte

A

plants adapted to a dry habitat

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52
Q

what is a halophyte

A

plants adapted to a salty habitat

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53
Q

what is a hydrophyte

A

plant adapted to a freshwater habitat

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54
Q

how are xerophytes adapted

A

Thick cuticle –> impermeable to water

Spines for leaves –> smaller surface area for water loss

Low stomatal density –> reduces surface area for water loss

Sunken stomata and stomatal hairs –> trap a layer of still moist air (keeps osmotic gradient at equilibrium)

Rolled leaves –> traps air very saturated with water

Extensive root system –> increases water uptake

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55
Q

what part of the exoskeleton of a terestial insects prevents water loss

A

lipid layer

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56
Q

what are insect adaptations to prevent water loss

A

-small surface area to volume ratio
-waterproof exoskeleton
-spiracles open and close
-hairs on the spiracle

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57
Q

how is water loss minimised in insects

A

-hairs on spiracles
-closing of spiracles
-waxy cuticle on body

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58
Q

why does a mouse have a high metabolic rate

A

-larger surface area to volume ratio
-this means more heat loss due to faster rate of metabolism

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59
Q

why is oxygen uptake a measure of metabolic rate in organisms

A

-oxygen is used in respiration which provides energy through ATP

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60
Q

structure of human gas exchange surface

A

trachea, bronchi, bronchioles, alveoli, diaphragm

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61
Q

eptihelium of the trachea

A

-Contains goblet cells and cilia

-Mucus is produced in the goblet cell which is then given to glandular tissue to secrete it

-Finger like projections that are able to move the layer of mucus

-Mucus traps dust and pathogens thus preventing it from reaching the lungs

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62
Q

adaptations of alveoli

A

-short diffusion pathway

-concentration gradient is maintained by bloodflow and ventilation

-larger surface area of alveoli

-Flattened epithelial cells of alveoli that are only one cell thick so reduces diffusion pathway

-high partial pressure of oxygen in alevoli

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63
Q

pathway for gas exchange in alevoli

A

-Alevolar endothelium –> Alevolar epithelium –> capillary epithelium/endothelium

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64
Q

process of inhalation

A

1) External intercostal muscles contract causing the ribs to move up and out

2) The diaphragm contract and flattens

3) This causes the volume of the thoracic cavity to increase subsequently reducing the gas pressure causing air to move into the lungs from outside the body, down a pressure gradient

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65
Q

process of exhalation

A

1) Internal intercostal muscles relax causing ribs to move down and in

2) The diaphragm relaxes thus returning back to its domed shape

3) This causes the thoracic volume to decrease and subsequently causes pressure to increase forcing air out of the lungs

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66
Q

define pulmonary ventilation

A

-the total volume of air that is moved into the lungs during 1 minute

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67
Q

define tidal volume

A

the volume of air normally taken in at each breath when body is at rest

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68
Q

define breathing volume

A

the number of breaths taken in one minute

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69
Q

how do you calculate pulmonary ventilation

A

tidal volume x breathing volume

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70
Q

describe and explain 2 features of the alevolar epithelium that makes the epithelium well adapted

A

-one cell thick and flattened which ensures short diffusion pathway
-permeable which allows diffusion of CO2 and O2

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71
Q

explain why the death of alveolar epithelium cells reduces gas exchange in human lungs

A

-surface area reduces
-longer diffusion pathway
-rate of gas exchange reduces

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72
Q

Describe the pathway taken by an oxygen molecule from an alveolus to the blood

A

oxygen molecules diffuse through the alveolar epithelium and into the epithelium of capillaries

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73
Q

when a person starts to breathe out, the percentage of oxygen in the air first exhaled is the same as the percentage of oxygen in the atmospheric air. Explain why

A

air from nose/mouth is not same as in alveoli

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74
Q

explain why it is important that the pieces of leaf tissue examined were very thin

A

-optical microscopes can only observe a single layer so light can pass through the sample

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75
Q

Give two reasons why it was important that the student counted the number of stomata

A

-so the sample is representative
-to collect a reliable study

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76
Q

state two reasons why the rate of water uptake by a plant may not be the same as rate of transpiration

A

-water is used in hydrolysis
-water used in photosynthesis

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77
Q

what do rolled leaves ensure

A

decrease in water potential gradient

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78
Q

explain the advantage of the stomata closing when the light s turned of

A

-closed stomata reduces rate of water loss which maintains the water content of cells

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79
Q

describe how the student could use an eyepiece graticule to determine the mean diameter of stomata

A

-measure each stomata using the eyepiece graticule
-calibrate eyepiece against stage ruler
-calculate mean

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80
Q

explain how you would use traces from this spirometer to compare the tidal volumes and breathing rates of male and female human subjects

A

-define tidal volume + breathing rate
-volume and time need to be calibrated
-tidal volume = pulmonary ventiliation / breathing rate
-one peak = one breath
-male and female groups should be standardised -> non-smoker/non-alcoholic
-traces should be taken at rest
-study should be replicated then a mean should be calculated

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81
Q

give one reason for the difference in PEF values between ages of 35 and 85 years

A

weakening of the muscles

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82
Q

what is a spirometer

A

a device used to measure lung volume

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83
Q

define affinity

A

attracted to bind

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84
Q

what is haemoglobin

A

haemoglobin is a water soluble, globular protein (quaternary structure)

-It consists of 2 beta polypeptide chains and 2 alpha helixes

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85
Q

why does haemoglobin carry oxygen in the blood

A

Haemoglobin carries oxygen in the blood as oxygen can bind to the haem (Fe2+) group. Each molecule can carry four oxygen molecules.

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86
Q

where is oxygen loaded and unloaded from red blood cells

A

-different organisms have different haemoglobin structures

-Oxygen is loaded into haemoglobin in the lungs and is unloaded in respiring tissues

-haemoglobin has a quaternary structure, formed by condensation reactions and contains nitrogen

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87
Q

what does the affinity of oxygen for haemoglobin depend on

A

depending on the partial pressure of oxygen (greater concentration of dissolved oxygen in cells = greater partial pressure)

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88
Q

what occurs during respiration in terms of oxygen and haemoglobin

A

During respiration, oxygen is used up and therefore the partial pressure decreases, thus decreasing the affinity of oxygen for haemoglobin. As a result of that, oxygen is released in respiring tissues where it is needed. After the unloading process, the haemoglobin returns to the lungs where it binds to oxygen again.

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89
Q

cooperative binding and oxygen dissociation

A

Lungs –> low PO2, high saturation levels, high affinity

Respiring tissues –> high PO2, low affinity, low saturation levels

1) Initially it is very difficult for first oxygen to bind

2) Once the first O2 binds there is a conformational change to the active site

3) This makes it easier for 2nd and 3rd oxygen to bind

4) It is then reliant on a high PO2 to bind the 4th oxygen molecule

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90
Q

what do disassociation curves show

A

-Dissociation curves illustrate the change in haemoglobin saturation as partial pressure changes. The saturation of haemoglobin is affected by its affinity for oxygen, therefore in the case where partial pressure is high, haemoglobin has high affinity for oxygen and is therefore highly saturated, and vice versa.

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91
Q

how does saturation affect affinity

A

-Saturation can also have an effect on affinity, as after binding to the first oxygen molecule, the affinity of haemoglobin for oxygen increases due to a change in shape, thus making it easier for the other oxygen molecules to bind.

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92
Q

positive cooperativity graph

A

Initially the curve is shallow because it is hard for the first oxygen molecule to bind. Once it has bound though it changes the shape making it easier for oxygen molecules two and three to bind, hence the steep increase. This is called positive cooperativity. Finally the gradient begins to flatten out because the likelihood of the fourth oxygen finding a binding site is low.

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93
Q

how does carbon dioxide affect affinity

A

Carbon dioxide is released by respiring cells which require oxygen for the process to occur. Therefore, in the presence of carbon dioxide, the affinity of haemoglobin for oxygen decreases, thus causing it to be released. This is known as the Bohr effect. It does this because carbon dioxide creates slightly acidic conditions which change the shape of the haemoglobin protein, thus making it easier for the oxygen to be released.

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94
Q

how many polypeptide chains does haemoglobin have

A

4

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95
Q

where is there a high partial pressure of carbon dioxide

A

respiring tissues due to decreased affinity which unloads more oxygen

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96
Q

does fetal haemoglobin have a higher or lower affinity

A

higher

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97
Q

why do xerophetic plants have slower rate of growth

A

lower stomatal density

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98
Q

Suggest one advantage of the change in affinity of haemoglobin for oxygen

A

facilitates the loading of oxygen in the lungs

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99
Q

Describe the advantage of the Bohr effect during intense exercise

A

-during intense exercise more oxygen is required for aerobic respiration
-This means that when there is high PCO2 the affinity reduces so oxygen dissociates

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100
Q

which way does the graph shift when there is a reduced affinity of haemologbin for oxygen

A

right

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101
Q

how many haem groups does haemolgobin have

A

4 (Fe2+)

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102
Q

how is the affinity of haemoglobin affected

A

-The affinity of haemoglobin is affected by its tertiary structure (3D)

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103
Q

difference between fetal haemoglobin and adult haemoglobin

A

-Fetal haemoglobin has a higher saturation at the same PO2 than adult haemoglobin. This is necessary to supply the fetus with oxygen from the mother

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104
Q

Bohr affect

A

-At the lungs there is a lower PCO2 so haemoglobin has a higher affinity to oxygen thus helping it associate
(graph shifts left)

-At the respiring tissues where there is a high PCO2 the curve shifts to the right which reduces its affinity and supports the disassociation of oxygen
(graph shifts right)

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105
Q

what stimulates the change in affinity of haemoglobin

A

PCO2 stimulates the change in affinity of haemoglobin

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106
Q

how does CO2 change affinity

A

-When in solution carbon dioxide is acidic. This lowered pH through more CO2 the more H+ ion concentration which causes a change in the tertiary (3D) structure of the protein due to hydrogen bonding being easily attracted to changes in pH. The change in shape causes a decreased affinity to oxygen

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107
Q

Haemoglobin in animals

A

-lives with lower PO2

-Lungworms live in an oxygen poor environment which means that haemoglobin has a higher affinity for oxygen at lower partial pressures. This means that it is able to more readily associate/load oxygen to be transported to respiring tissues for aerobic respiration

-llamas live in high altitude environments with a low PO2

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108
Q

why do smaller animals have larger metabolic rates

A

-larger surface area to volume ratio
-so more heat loss

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109
Q

explain the role of the cell cycle in maintaining efficient exchange of materials

A

-As cell size increases, surface area to volume ratio decreases
-so slower exchange of materials
-at a certain size cytokenesis occurs
-so faster exchange of materials

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110
Q

why do tadpoles not need lungs but a frog does

A

frogs have a smaller SA:vol
so has a slower diffusion pathway
lungs are a specialised exchange system to supply sufficient oxygen

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111
Q

how many molecules of oxygen can haemoglobin bind to

A

4 once fully saturated

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112
Q

how many bases are there for one amino acid

A

3

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113
Q

give two reasons why there would be more bases

A

1) stop/start sequence
2) addition of base my mutation

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114
Q

explain why llamas are better adapted to live in high mountains than horses

A

-llamas have low PCO2 in lungs
-greater affinity
-this means that oxygen is loaded from haemolgobin

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115
Q

Explain how the haemoglobin of species B allows a greater level of activity

A

-curve shifted to right so lower affinity
-more O2 unloads from haemoglobin into cells for greater respiration

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116
Q

Explain changes in shape of curve for dissociation of haemoglobin

A

-O2 binds causing shape to change

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117
Q

what does fetal haemoglobin mean

A

more oxygen is unloaded for easier respiration

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118
Q

give on use of amino acids

A

protein synthesis

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119
Q

explain why the binding of one molecule of oxygen makes it easier for a second oxygen molecule to bind

A

-binding of first oxygen molecule changes tertiary structure which creates another binding site

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120
Q

explain how the stain allowed the doctor to count white blood cells amongst all the red blood cells

A

-white blood cells have nucleus which is able to be stained whilst red blood cells dont

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121
Q

Explain the advantage of fetal haemoglobin

A

-greater affinity of O2 so more association
-this means that more oxygen moves from mother to foetus

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122
Q

explain the advantage of having more red blood cells for those living at higher altitudes

A

-more haemologbin
-loads more oxygen

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123
Q

what is meant by the term partial pressure

A

-a measure of the concentration of a gas

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124
Q

explain how the gills of fish are adapted for efficient gas exchange

A

-many lamellae increase SA for diffusion
-thin epithelium reduces diffusion pathway
-water and blood have countercurrent flow
-ventilation replaces water
-good blood supply maintains favourable concentration gradient

125
Q

Explain an advantage of the Bohr effect for aerobic respiration

A

-greater dissociation of oxygen from haemoglobin
-more oxygen for aerobic respiration in respiring tissues

126
Q

why do iron deficient plants have a low growth rate

A

-less thykaloid membrane
-less chlorophyll
-so slower rate of photosynthesis

127
Q

what do mineral salts do

A

keep pH neutral

128
Q

what is emulsification and what is its purpose

A

when lipids are split up into micelles by bile salts which are produced in the liver

This increases surface area of lipids for lipase

129
Q

Describe the complete digestion of starch by a mammal

A

-starch hydrolysed in salivary glands by amylase as alternating glycosidic bonds are broken thus forming maltose disaccharide
-As maltose reaches the ileum it is hydrolysed by the membrane bound dissacharidase maltase which hydrolyses maltose into alpha glucose

130
Q

explain what the results suggest about the effect of chewing on the digestion of starch in wheat

A

some starch already digested when chewing
-faster digestion of chewed starch
-same amount of digestion without chewing at end

131
Q

define digestion

A

when large insoluble molecules are hydrolysed into smaller soluble molecules so it can be absorbed

132
Q

what is the ileum

A

small intestine

133
Q

what is the duodenum

A

point between ileum and stomach

134
Q

types of digestion

A

-Mechanical and chemical

e.g mouth = mechanical –> provides large surface area for chemical digestion

e.g stomach = chemical due to HCL –> large insoluble into small soluble

135
Q

digestive enzymes

A

Amylase –> starch into glucose

Lipase –> fats into fatty acid and glycerol

Protease –> proteins into amino acids

136
Q

Digestion (key ideas)

A

Digestion of fat occurs in the ileum

Absorption of water into the blood occurs in the large intestine

Production of HCL in the stomach

137
Q

digestion of carbohydrates

A

-Amylase produced in the salivary glands hydrolyses alternating glycosidic bonds in starch which forms the disaccharide maltose

-maltose is then hydrolysed by maltase into alpha glucose

-maltase is produced in the ileum (membrane bound)

-optimum pH for amylase = 7

138
Q

membrane bound enzymes

A

-the membrane of the ileum is highly folded with many villi and microvilli and attached to this membrane are enzymes e.g membrane bound disaccharidases and dipeptidases

-membrane bound enzymes ensure shorter diffusion pathway

139
Q

dissaccharidases

A

maltase
sucrase
lactase

140
Q

dipeptidases

A

hydrolysis of dipeptide bonds between COOH and NH3 group of amino acids

141
Q

digestion of lipids

A

Digestion of lipids:

-lipids are hydrolysed by the enzyme lipase in the stomach (low acidic pH)

-monomers of a lipid are 3 fatty acids and 1 glycerol

-ester bond is hydrolysed (C-O)

Triglycerides –> fatty acids + monoglycerides

142
Q

what are monoglycerides

A

1 fatty acid and 1 glycerol

143
Q

bile salts

A

Micelles (lipid molecules) are more soluble in water

Fat globule –> bile salt (hydrophillic and hydrophobic side) –> emulsified fat droplets and micelles

-bile salts increases surface area for digestion by lipase

-bile is produced in liver and stored in the gallbladder

-Micelles are absorbed by diffusion

144
Q

physical and chemical lipid digestion

A

physical –> emulsification and micelle formation –> many small droplets of lipids provides larger surface area to enable faster hydrolysis action of lipase

chemical –> lipase (triglyceride –> fatty acid + monoglycerides)

145
Q

what are micelles

A

water soluble vesicles

deliver fatty acids, glycerol and monoglycerides to the epithelial cells of the ileum for absorption

146
Q

method of absorption

A

monosaccharides + amino acids –> co-transport

lipids –> diffusion due to non-polar nature

147
Q

protein digestion

A

-Lumen of the gut (endopeptidase + exopeptidase)

-inside cell surface membranes of epithelial cells (exopeptidase + dipeptidase)

148
Q

order of protein digestion

A

Protein –> polypeptides –> dipeptides –> amino acids

Endopeptidase –> Exopeptidase –> Dipeptidase

149
Q

endopeptidases

A

hydrolyse peptide bonds between amino acids in the central region of a protein molecule forming more ends of peptide molecules

150
Q

exopeptidases

A

hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases

151
Q

dipeptidases

A

hydrolyse the peptide bond between two amino acids of a dipeptide. Dipeptidases are membrane bound

152
Q

The action of endopeptidases and exopeptidases can increase the rate of protein digestion. Describe how

A

Endopeptidases hydrolyse the peptide bonds between amino acids inside the amino acid chain and exopeptidases hydrolyse the peptide bonds at the terminals of amino acid chains. This increases the surface area by providing more ends for exopeptidase

153
Q

suggest how a rabbit eating its own caecal droppings help a rabbits digestion and absorption of dietary protein

A

more undigested protein broken down so more amino acids absorbed in the stomach

154
Q

Standard deviations

A

for a difference to be significant, the standard deviations must not overlap

(no effect)

155
Q

membrane bound dissaccharidase found in the ileum

A

maltase + sucrase

156
Q

bond that lipase enzymes hydrolyse

A

ester bond

157
Q

suggest why co-transport cannot occur in the absence of oxygen

A

releases ATP required for active transport

158
Q

monomers in co-transport

A

-glucose + amino acids are the monomers in co-transport

-active transport, diffusion, facilitated diffusion

159
Q

steps for co-transport

A

1) sodium ions are actively pumped out of the epithelial cell by Na+-K+ pump using ATP

2) this lowers the concentration of sodium ions in the epithelium cell

3) this causes sodium ions to diffuse down their concentration gradient from the ileum into the epithelial cell via co-transporter protein

4) amino acids are co-transported into the epithelial cell with the sodium ions

5) this causes concentration of amino acids inside the epithelial cell to increase so they diffuse down their concentration gradient into the blood via a carrier protein

160
Q

digestion and absorption of fats

A

-triglycerides are hydrolysed by the enzyme lipase to release free fatty acids and monoglycerides

-lipids are hydrophobic so are soluble in the aqueous environment of the digestive tract

-lipase is water soluble so can only work at the surface of fat globules

-digestion is aided by emulsification due to smaller droplets produced preventing re-association (surface area increases to digest triglycerides)

161
Q

micelles and absorption

A

-monoglycerides and fatty acids associate with bile salts and phospholipids to form micelles

-micelles reduce diffusion distance so rate of absorption increases

-only dissolved monoglycerides and fatty acids can be absorbed because of their non-polar nature

162
Q

chlymicrons and cholesterol

A

Chlyomicrons:

-lipoproteins (particles designed for the transport of lipids in the circulation) –> fatty acids are combined with proteins

-released by exocytosis and they enter lacteals (lymphatic capillaries that poke up into the centre of each villi)

-deliver absorbed triglycerides into the bodies cells

Cholesterol absorption:

-absorbed in the small intestine

-cholesterol in bile

-drug ezetimibe blocks a protein that specifically mediates cholesterol transport

163
Q

Name process A,B,C and give evidence for each

A

A –> facilitated diffusion as using transporter protein
B –> active transport as ATP is used
C –> diffusion as neither is used

164
Q

explain how active transport creates the conditions for diffusion to occur

A

-A.T creates a low conc of Na+ ions inside the cell as it pumps Na+ ions out of the cell using sodium potassium pump which allows molecules to move down concentration gradient

165
Q

Describe the processes involved in the absorption of the products of starch digestion

A

-glucose moves with sodium via carrier protein
-Na removed from epithelial cell via active transport into blood
-this maintains low concentration of sodium in epithelial cell
-glucose moves into blood via facilitated diffusion

166
Q

direction for co-transport in the ileum

A

ileum –> blood –> cells

167
Q

Describe the role of micelles in the absorption of fats into the cells lining the ileum

A

-micelles are bile salts and fatty acids
-fatty acids absorbed by diffusion
-micelles make fatty acids more soluble in water
-micelles carry fatty acids to the lining of the ileum

168
Q

define the term double circulatory system

A

dexoygenated blood is pumped by the right side of the heart to the lungs and oxygenated blood is pumped by left side of the heart out of the heart to the rest of the body

-blood is confined to the vessels and passes twice through the heart

169
Q

Mammal double circulatory system

A

-two types of circulation; systemic circulation that pumps oxygenated blood around body and pulmonary circulation which pumps deoxygenated blood to lungs

170
Q

Capillary system

A

Pulmonary artery, Pulmonary vein (lungs)

Vena Cava, Aorta (heart)

Renal Vein, Renal artery (kidney)

171
Q

right vs left side of heart

A

right = deoxygenated
left = oxygenated

172
Q

movement of blood through heart

A

Body –> Vena cava –> tricuspid valve right atrium –> pulmonary valve –> right ventricle –> pulmonary artery –> lungs –> pulmonary vein –> left atrium –> mitral valve –> left ventricle –> aortic valve –> aorta –> body

173
Q

what is the septum

A

divides deoxygenated and oxygenated side of heart

174
Q

arteries

A

carry blood away from the heart

175
Q

Thickness of heart muscle

A

Heart muscle is thin and elastic which allows it to stretch and fill with blood

Left side of heart has a thicker muscular wall to pump oxygenated blood under high pressure around the body

176
Q

valves

A

Aortic / ventricular valves prevent backflow of blood

177
Q

relationship between body mass and metabolic rate

A

directly proportional

178
Q

why do bigger organisms require mass transport systems

A

Bigger organisms require mass transport systems as they have smaller surface area to volume ratios which cannot rely soley on diffusion. Mass transport requires respiration which requires oxygen which is delivered by the blood.

179
Q

transport in circulatory system

A

Our circulatory system provides mass transport of substances to and from exchange surfaces

Taken from exchange surfaces to cells –> oxygen, glucose, amino acids, fatty acids + glycerol, water, ions, minerals, vitamins

Taken from cells to exchange surfaces –> water, ions, CO2, urea

180
Q

features of a mass transport system

A

-suitable medium to carry nutrients and minerals around the body (blood)

-A form of mass transport to move the medium around the body in large volumes (circulatory system)

-A closed system of vessels that deliver the medium around the body (peripheral circulatory system)

-a mechanism to move the medium around the body and creates a pressure difference between one area and another (heart)

181
Q

how is blood moved around the body

A

-muscular contraction e.g contractions of heart tissue

-passive process e.g valves to control direction of flow or transpiration stream in plants etc

182
Q

the coronary artery

A

-The heart needs its own blood supply to supply the blood to all other parts of the body –> involves the contractions of muscles which require energy through ATP/respiration

-The coronary artery is connected to the aorta and spreads across the heart muscle

183
Q

calculating cardiac output

A

-cardiac output is a measure of the total volume of blood pumped out of the left ventricle every minute

-stroke volume = total volume of blood pumped out of left ventricle in one contraction

-cardiac output (dm3/min) = stroke volume (dm3) x heart rate (bpm)

-cardiac output can stay the same even if resting

184
Q

superior vs inferior vena cava

A

Superior vena cava –> blood returning from the top of the body

Inferior vena cava –> blood coming from bottom of the body

185
Q

valves

A

Mitral (bicuspid) valve = left side of heart

Aortic valve = left side of heart

Tricuspid valve –> right side of heart

pulmonary valve –> right side of heart

186
Q

Explain why having more red blood cells is an advantage to an athlete

A

-more haemoglobin
-more oxygen is carried for aerobic respiration

187
Q

artery vs vein

A

-veins have valves whilst arteries dont
-veins have a thinner layer of elastic than arteries
-arteries have a thicker layer of muscle

188
Q

pacemaker

A

-right atrium
-used to treat irregular heat beats/arrhythmia’s

189
Q

atrium vs ventricle

A

atrium –> thin walled and elastic and stretches as it collects the blood

ventricle –> thicker due to higher pressure and must contract strongly

190
Q

valves in the atrium

A

left = bicuspid valve

right = tricuspid valve

191
Q

what are vessels connecting the heart to the lungs called

A

pulmonary vessels

192
Q

what can blockage of coronary arteries lead to (coronary arteries branch of from the aorta)

A

myocardical infarction (heart attack) as muscle cells are unable to respire aerobically and thus die

193
Q

factors associated with cardiovascular disease

A

-high blood pressure
-smoking
-high blood cholesterol (LDH)
-diet

194
Q

where is the tricuspid valve located

A

right side

195
Q

what side is the renal vein and what side is the renal artery

A

renal vein = right side

renal artery = left side

196
Q

what does a closed circulatory system mean

A

blood remains within the vessels

197
Q

why do mammals have a double cirulatory system

A

to maintain/control pressure

198
Q

systemic vs pulmonary circulatory system

A

systemic –> pumps oxygenated blood

pulmonary –> pumps dexoygenated blood

199
Q

smoking

A

-tobacco and smoke increase likelihood of heart disease

-CO combines easily with hemoglobin in red blood cells to form carboxyhemoglobin. This reduces the oxygen carrying capacity of blood. To supply the equivalent volume of oxygen to tissues the heart works harder. This can lead to raised blood pressure that increases the risk of coronary heart disease and strokes. Reduction of oxygen means less oxygen supplied to muscles during exercise leading to a mycoardial infarction (heart attack)

-Nicotine from vapes also stimulates the production of the hormone adrenaline which increases heart rate and raises blood pressure and raises blood pressure. Nicotine also makes the platelets in the blood more sticky thus leading to higher risk of thrombosis (clots)

200
Q

high blood pressure

A

-your genes can cause you to have high blood pressure

-lifestyle factors such as stress, poor diet and lack of exercise there is an increased risk of high blood pressure.

-High blood pressure increases the risk of heart disease due to higher pressure in the arteries so heart must pump harder. Higher blood pressure within the arteries means that they are more likely to develop and aneurysm (swelling of artery). Walls of arteries become thickened and restrict flow of blood

201
Q

blood cholesterol

A

-high HDL remove cholesterol from tissues and transport it to the liver for excretion

-LDL cholesterol transports cholesterol from the liver to the tissues including artery walls

-High LDL cholesterol increases risk of cardiovascular disease

202
Q

diet

A

-High levels of salt raise blood pressure

-high levels of saturated fat increase LDL cholesterol and hence blood cholesterol concentration

-Vitamins however reduce risk for heart disease

203
Q

Explain what causes difference in pressure of blood vessles

A

left ventricle has thicker heart muscle
-oxygenated blood (contracts more)

204
Q

true or false - there is a higher pressure in aorta than ventricles

A

true - due to atrioventricular valves

205
Q

Give two ways in which blood passes through heart is achieved

A

-pressure gradient
-valves to stop backflow

206
Q

role of the sionatrial node

A

acts as a pacemaker by sending out electrical impulses

207
Q

atrioventricular valves

A

between atria and ventricles
-tricuspid and bisuspid valaves

208
Q

semi-lunar valves

A

located between ventricles and blood vessles leaving them (aorta and pulmonary artery)

209
Q

how is one-way flow of blood ensured

A

-valves
-pressure gradient maintained due to contraction

210
Q

which chamber of the heart has the highest pressure and why

A

left ventricle –> thick heart muscular wall

211
Q

what happens to ventricles during ventricular systole

A

right ventricle contracts at lower pressure than left ventricle

212
Q

explain why rate of blood flow has not yet started to increase in the aorta

A

-aortic and semi-lunar valves are closed as pressure in aorta is higher than in the ventricle

213
Q

explain how there is a small increase in pressure and rate of blood flow in the aorta

A

-elastic recoil of tissue smooths bloodflow

214
Q

Give on way in which an electrocardiogram could have produced more reliable results than counting the pulse

A

records every heartbeat

215
Q

true or false - the resting heart rate is the same as pulse rate

A

true

216
Q

explain how the elastic tissue in the wall helps even out pressure of blood flowing through artery

A

-elastic tissue stretches at high pressure and recoils during low pressure to maintain pressure of bloodflow

217
Q

Explain how the walls of arteries are related to their functions

A

-thick muscular walls and narrow lumen to withstand high pressure and controls blood flow
-elastin that recoils and stretches
-muscle contracts (vasoconstriction) that changes pressure
-folded endothelium lining removes friction

218
Q

explain why a vein can be described as an organ

A

comprised of two or more tissues working together

219
Q

two main stages of the cardiac cycle

A

The heart undergoes a sequence of events that is repeated in humans around 70 times each minute when at rest. This is known as the cardiac cycle. There are two main stages to the cardiac cycle; disastole (relaxation) and systole (contraction)

220
Q

diastole

A

-heart muscle is relaxed

-volume of atria and ventricles in increased and pressure is lower

-pressure is highest in the aorta and pulmonary artery as blood is being transported under high pressure

-semi-lunar valves are closed to prevent backflow

-due to low pressure in atria, blood is able to enter from vena cava and pulmonary vein so AV valves are slightly open allowing small volume of blood to move into the ventricles

221
Q

atrial systole

A

-atria contract

-reduced volume in atria and pressure increases

-blood moves down a pressure gradient into the ventricles

-AV valaves fully open

-semi-lunar valves are closed

222
Q

ventricular systole

A

-ventricles contract

-volume in ventricles reduces so pressure increases

-pressure in ventricles greater than pressure in aorta and pulmonary artery

-semi-lunar valves are open and blood moves up and out of heart down a pressure gradient

-AV valves close due to high pressure in ventricles

223
Q

order for cardiac cycle

A

atrial systole –> ventricular systole –> diastole

224
Q

blood vessels

A

-Arteries –> arterioles –> capillaries –> ventricles –> veins

225
Q

arteries

A

-carries blood away from the heart

-must be able to withstand high pressure

-thick walls contain collagen for strength and elastic tissue for stretch and recoil –> controls bloodflow

-folded endothelium that can unfold when stretched –> smooth to reduce friction

-contains elastin that maintain pressure and bloodflow (evens out)

-small lumen to maintain high pressure and blood flow

226
Q

veins

A

-contain valves to coordinate blood flow

-thin layers of collagen, smooth muscle and elastic tissue

-thin walls that can be flattened by skeletal system

-carry blood back to the heart

-wide lumen due to less muscular tissue and elastin

-lower pressure blood flow

Endothelium reduces friction

227
Q

capillaries

A

-single layer of endothelium cells

-very narrow lumen –allow for exchange of material between blood and cells

-narrow = short diffusion pathway

-slow blood flow = increased time for diffusion

-one cell thick

-fenestrations between endothelium allow for larger molecules to pass through

228
Q

4 components of blood

A

red blood cells
white blood cells
platlets
plasma

229
Q

Water potential outcomes

A

-as water leaves the ateriole end and into the tissue via filtration, down the pressure gradient, the water potential in the capillary decreases
-this causes water potential of the tissue fluid to increase
-cellular respiration also results in the production of water which further increases the water potential of the tissue fluid
-water moves back into capillary via osmosis down the water potential gradient and down its pressure gradient

230
Q

what is tissue fluid

A

liquid containing dissolved oxygen and nutrients which serves as a means of supplying tissues with essential solutes in exchange of waste products

230
Q

what is hydrostatic pressure

A

Hydrostatic pressure is created when blood is pumped along the arteries, into arterioles and
then capillaries.

231
Q

does tissue fluid or blood have a more negative water potential

A

blood

232
Q

what happens to the remaining tissue fluid which is not forced back into the capillaries

A

carried back via the lymphatic system
(contains lymph fluid that contains less oxygen and nutrients as its main purpose is the carry waste products)

233
Q

the hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why

A

water is forced out of capillaries through fenestrations down a pressure gradient.

or

As friction increases, pressure decreases

234
Q

Explain the role of the heart in the formation of tissue fluid

A

-during systole of the left ventricle a high hydrostatic pressure is created. This causes water to be forced out of capillaries down a pressure gradient

235
Q

The water potential of the blood plasma is more negative at the venule of the capillary than at the arteriole end of the capillary. Explain why

A

-water moves out of the capillary at the arteriol end via filtration down a pressure gradient
-proteins remain in the capillary causing it to be more concentrated and therefore have a lower water potential

236
Q

Explain how water from tissue fluid is returned to the circulatory system

A

-proteins remain in the blood
-water potential gradient is created
-water moves to blood by osmosis
-tissue fluid returns to blood by lymphatic system

237
Q

Explain how higher absorption of salt from the diet can result in build up of tissue fluid

A

higher salt = lower water potential so less water in capillaries

or

salt increases blood pressure in blood vessels which means water is forced out capillaries due to high hydrostatic pressure

238
Q

suggest how widening of blood vessels can reduce ventiruclar blood pressure

A

larger lumen reduces blood pressure in blood vessels
less friction

239
Q

suggest how a blockage in the lymphatic system could cause lymphoedema

A

excess tissue fluid cannot be reabsorbed

240
Q

tissue fluid, lymph and blood

A

-the contraction of the left ventricle pumps blood under high pressure around the body

-This transports blood containing oxygen, glucose, dissolved ions and water to tissues of the body

-The high pressure means that some of these substances leave the blood through the walls of the capillary

241
Q

model of ultrafiltration

A

1) Tissue fluid formation –> left ventricular systole (contraction) creates a high hydrostatic pressure. Water is forced out through fenestrations in capillaries. Movement down a pressure gradient

2) Tissue fluid reabsorption –> water travels down pressure gradient, tissue fluid returns by osmosis

242
Q

what happens as friction increases

A

pressure decreases

243
Q

water potential outcomes

A

Arteriole end –> water potential of tissue fluid increases because water moves out of the arteriole end. Water is a bi-product of cellular respiration. At the arteriole end the water potential is higher in the capillary so water moves out via osmosis.

Venule end –> Water moves into the capillary down a water potential gradient which has a lower water potential due to high concentration of proteins. CO2, urea and dissolved ions also diffuse into the capillaries

244
Q

where is water potential highest and lowest

A

Water potential highest is at the arteriole end

Water potential lowest at the venule end

This is caused by water moving out of the capillaries but large proteins remain (capillary is selectively permeable)

245
Q

hydrostatic pressure

A

Hydrostatic pressure is highest and water potential is highest at the arteriole end

Large proteins/molecules remain in the capillaries during tissue fluid formation

Higher blood pressure = more tissue fluid formed

246
Q

lymphatic drainage

A

-more tissue fluid leaves the capillaries than returns

-The lymphatic system is there to drain excess fluid into larger vessels which rejoin the blood system in the chest cavity

-Composition of lymphatic fluid will differ as there may be more CO2/urea

-Tissue fluid if moved by both hydrostatic pressure and muscular contractions surrounding the tissues/muscles

247
Q

lymphetic system

A

Lymphatic system also contains lymph nodes which filter out bacteria and foreign material from the tissue fluid with the help of lymphocytes which destroy pathogens

248
Q

true or false - all blood vessles have an endothelium to reduce friction

A

true

249
Q

give two other ways in which the total oxygen supplied to muscles during exercise is increased

A

-increased ventiliation
-increased stroke volume

250
Q

name the blood vessels that carry blood to the heart muscle

A

coronary arteries

251
Q

how is the volume of water lost from the leaves controlled

A

guard cells open and close the stomata

252
Q

explain one reason for the difference in water loss

A

-one plant has higher stomatal density

253
Q

Describe the cohesion-tension theory of water transport in the xylem

A

-water is lost from leaves bc of transpiration
-this lowers the water potential in the leaf
-water is pulled up the xylem creating tension
-water molecules stick together by hydrogen bonds forming continuous water column
-adhesion of water molecules to walls of xylem

254
Q

explain the relationship between humidity and transpiration rate

A

-as humidity increases the rate of transpiration decreases
-increased humidity increases water in atmosphere so lower water potential gradient in leaf for transpiration

255
Q

Explain why the diameter of the trunk is smallest at midday

A

-stomata is open when light intensity is greater so more water loss + photosynthesis rate increases
-Increase in temperature = more kinetic energy = increased diffusion/evaporation = creation of water potential gradient
-faster movement of water = narrower due to cohesion
-water is pulled up xylem creating transpiration stream
-adhesion between molecules and walls of xylem vessels

256
Q

Explain change in rate of water movement through xylem when light intensity increases

A

-as light intensity increases, rate of water moving through xylem increases due to increased photosynthesis rate
-stomata opens which means more water pulled due to cohesion as light intensity is greater

257
Q

explain why the diameter of the trunk decreased

A

-adhesion between water molecules and walls of xylem causes water to move up at a fast rate under tension

258
Q

adaptations of the xylem

A

-hollow lumen = no organelles to obstruct the flow of water

-cellulose cell wall of lignin = strength

-no end walls = constant stream of water

-pits in walls = travel between xylem to xylem

259
Q

movement of water

A

1) water is absorbed in the roots

2) water travels up the xylem

3) evaporates from the leaves

4) water leaves through the stomata

260
Q

how can plants control their rate of transpiration

A

changing size of stomatal pores

261
Q

movement of water across cells of leaves

A

-water is lost from mesophyll cells by evaporation from cell walls to air spaces of the leaf. This is replaced by water reaching mesophyll cells from xylem or other cells

cytoplasmic route occurs bc lower water potential, mesophyll cells lose water to air spaces

262
Q

cohesion

A

water molecules from hydrogen bonds between one another and hence tend to stick to eachother

263
Q

size of tree trunks (diameter)

A

increase transpiration = more tension = adhesion so xylem walls pulled inwards = smaller diameter of trunk

264
Q

what happens if a xylem vessel is broken

A

air enters
tree can no longer draw up water
water molecules not longer stick as continious column is broken

265
Q

explain what causes transpiration and results in a transpiration stream

A

1) water vapour diffuses from an area of high conc inside leaf to area of low conc in the atmosphere

2) this means that the water potential inside the leaf reduces causing tension so water moves from high w.p in xylem to the leaf

3) due to cohesion the loss of water molecules from top of xylem pulls the other molecules up thus generating a transpiration steam and a column of water in the xylem

4) This lowers the w.p of the cells at the base of the xylem meaning water moves from and area of high w.p in the soil to low w.p in root hair cells

266
Q

factors affecting transpiration

A

-humidity –> increased humidity increases water in the atmosphere so lower water potential gradient and thus transpiration rate decreases

-wind –> increased wind increases rate of transpiration as a steep concentration gradient is created

-temperature –> increased temp = more kinetic energy = more diffusion/evaporation

-light intensity –> increased light = stomata open or more photosynthesis = increased rate of transpiration

267
Q

Explain why translocation is important to plants

A

allows sugars to get from the leaf to respiring in the plant e.g roots or meristems

268
Q

explain why active transport is necessary in root hair cells

A

-to transport nitrate ions against concentration gradient into the root hair cells

269
Q

describe how a high pressure is produced in the leaves

A

-sucrose is co-transported into the sieve tube element
-this decreases the water potential in the sieve tube element
-water moves by osmosis from the xylem to the phloem creating a high pressure at the source due to increased water volume in the phloem

270
Q

describe the mass flow hypothesis for the mechanism of translocation in plants

A

-In source/leaf sugars actively transported into phloem
by companion cells
-Lowers water potential of sieve cell/tube and water enters by osmosis
-Increase in pressure causes mass movement (towards sink/root)
-Sugars used/converted in root for respiration for storage

271
Q

sucrose

A

-non-reducing sugar
-less reactive than glucose
-sugar used in translocation
-moves by facilitated diffusion
-high conc in phloem

272
Q

structure of the phloem

A

-sieve tube element

-companion cell next to phloem

-narrow rim of cytoplasm remaining in sieve tube element

-sieve plate pore (not hollow so transport can occur up and down plant)

273
Q

define translocation

A

transport of organic substances through phloem from source to sink

274
Q

source vs sink

A

Source = photosynthesising cells within leaves (site of sugar production)

Sink = growing regions/storage –> sugars can be stored or used

275
Q

mass flow hypothesis

A

1) Sucrose is produced at the source and enters companion cells via facilitated diffusion

2) sucrose needs to be loaded into the phloem sieve tubes via active transport. To do this H+ ions are actively pumped out of the sieve tubes into the cell wall of the sieve tube elements. This develops a proton gradient and results in H+ ions diffusing back into the sieve tube via a co-transporter. Co-transporter allows sucrose to move against conc gradient.

3) water moves from high water potential in xylem to low water potential in the phloem near source (leaf). This creates high pressure in phloem and thus pressure gradient

4) Solution then flows down the phloem to the sink where sucrose moved by facilitated diffusion down a concentration gradient into the sink cell. This increases water potential causing water to return to xylem by osmosis

276
Q

what is the role of companion cells

A

provides ATP for active transport of organic substances

277
Q

use ur understanding of the mass flow hypothesis to explain how pressure is generated inside this phloem

A

-sucrose actively transported into phloem
-this reduces water potential
-water moves into phloem by osmosis from xylem

278
Q

why is phloem pressure reduced during the hottest part of the day

A

-high rate of transpiration means increased water loss through the stomata
-less movement from xylem to phloem

279
Q

suggest two reasons why rate of water uptake by plant might not be same as rate of transpiration

A

-water used in hydrolysis
-water used in photosyntehsis

280
Q

how to return air bubble

A

open the tap

281
Q

effect of smoking

A

-smoking causes fatty deposits to build up
-narrowing of coronary arteries
-limits blood supply to the heart muscle

282
Q

sunken stomata

A

increased diffusion distance so reduced water loss

283
Q

waxy cuticle

A

impermeable to water

284
Q

rolled leaves

A

trap humid air = reduced water potential gradient = less evaporation of water vapor

285
Q

microsopic hairs

A

trap humid air = reduced air flow = reduced conc gradient

286
Q

very few stomata

A

reduced S.A for evaporation

287
Q

suggest an explanation for decrease in diameter of the trunk

A

-adhesion of water molecules to walls of xylem results in tension as water is pulled up the stem

288
Q

Describe how the anti-toxin antibody would be digested

A

-peptide bonds hydrolysed
-endopeptidases break peptide bonds in middle of chain
-exopeptidases break terminal peptide bonds
-dipeptidases break peptide bonds between 2 molecules

289
Q

bile salts and lipid droplets

A

-bile salts adsorb onto fat droplets
-lipid droplets are emulsified into smaller ones

290
Q

explain the importance of the xylem being kept open as a continuous tube

A

-unbroken water column means cohesion of H bonds between all water molecules
-evaporation creates tension in the column

291
Q

name the substance which hydrolyses fats into micelles

A

bile salts

292
Q

glucose and amino acids

A

two monomers used in co-transport

293
Q

Process of co-transport

A

1) Na+ ions activley transported out of epithelial cells via Na+-K+ pump into capillaries. This creates a concentration gradient between the ileum and epithelial cells

2) With new conc gradient Na+ ions diffuse into epithelial cells via glucose-Na co-transporter proteins

3) as glucose moves into epithelial cells using co-transporter protein a high conc of glucose is etablished in the cell. This causes glucose to move by facilitated diffusion into the capillaries via specific glucose channel proteins

294
Q

explain how the movement of Na+ ions out of the cell allows the absorption of glucose into the cell lining the ileum

A

Na+ ions moving out of the cell creates a concentration gradient between the ileum and blood for the diffusion of glucose into epithelial cells using a co-transporter protein

295
Q

describe and explain 2 features you would expect fo find in a cell specialised for absorption

A

-many microvilli
-many channel and carrier proteins

296
Q

describe the role of micelles in the absorption of fats and cells lining the ileum

A

-micelles are triglycerides combined with bile salts
-micelles increase the solutbility of lipids in water allowing for hydrolysis by lipase enzymes
-maintains diffusion gradient between fatty acids and ileum

297
Q

explain how sucrose-transport proteins in leaf cells enable the production of a pressure gradient in the phloem

A

-phloem activeley transported into phloem
-this decreases water potential inside the phloem
-water moves by osmosis into the phloem

298
Q

give 2 reasons why glucose uptake by muscle cells increases significantly during exercise

A

-increase rate of respiration to produce more ATP for contraction
-more glucose used so concentration gradient formed for facilitated diffusion

299
Q

greater affinity =

A

allows aerobic respiration at lower pCO2

300
Q

CO2 =

A

acidic = greater dissociation

301
Q

explain how an asthma attack caused the drop in the mean FEV shown in the figure above

A

-The bronchi muscle walls contract. The walls of bronchi secrete more mucus. The diameter of the airways is reduced so the air flow is reduced.

302
Q

suggest an explanation for the effect of temperature on the rate of CO2 release

A

-enzymes work faster
-higher rate of respiration and CO2 production
-spiracles open more often so more CO2 is released

303
Q

how did the scientists ensure they could make a valid comparison between leaves from different species

A

-use fully grown leaves

304
Q

describe a method you could use to find the surface area of a leaf

A

-draw around leaf on graph paper
-count squares
-multiply by 2

305
Q

why should the scientists use fully grown leaves

A

-younger leaves may have different number of stomata

306
Q

suggest 3 other adaptations that the leaves might have that enable the plants to grow well in dry conditions

A

-thick waxy cuticle
-hairy leaves
-small S.A of leaves

307
Q

describe how the arteriole can reduce blood flow into capillaries

A

-muscle contracts
-narrows lumen

Aqa a level biology (6 decks)

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