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Biology AS > Exchange and Transport > Flashcards

Exchange and Transport Flashcards

1
Q

4 features of an efficient gas exchange surface

A
  1. Large surface area
  2. Thin surface - eg squamous epithelial cells, for a short diffusion distance
  3. Moist surfaces for oxygen to dissolve in
  4. Good blood supply- network of blood capillaries in order to carry gases to and from the exchange surface
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2
Q

Why do large, active organisms need specialised exchange surfaces?

A

they have a smaller surface area : volume ratio, so cannot rely on diffusion across their surfaces as the distances are too large so diffusion would be too slow to supply oxygen/remove CO2 at the rate needed. Thus they rely on specialised exchange surfaces.

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3
Q

Where in the gas exchange system are rings of cartilage found? What is the role of the cartilage?

A

walls of the trachea, bronchi and some bronchioles.
Structural role: prevents collapse when the air pressure inside is low during inhalation, supports and holds open trachea and bronchi.

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4
Q

Where is smooth muscle found? What is its role?

A

Found in the walls of all the air passageways.
Contracts, narrowing the lumen of the airway and restricting the flow of air (e.g. to and from the alveoli in the bronchioles - important if there are harmful substances in the air)

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5
Q

Where are elastic fibres found? Function?

A

wherever there is smooth muscle - recoil to their original shape after smooth muscle constricts them, dilating the airway. Also stretch during inspiration.

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6
Q

Whee are goblet cells found? Function?

A

Trachea, bronchi and larger bronchioles.

Secrete mucus to trap dust/pollen/bacteria for removal. Prevents infection/damage to the exchange surfaces.

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7
Q

Function of ciliated epithelium? Where are they found?

A

Found lining the trachea, bronchi and bronchioles.

Cilia move in a synchronised pattern and waft mucus up the airway to the back of the throat where it is swallowed.

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8
Q

Describe the mechanism of inspiration

A
  1. Diaphragm contracts and flattens.
  2. Intercostal muscles contact, pulling the ribcage upwards and outwards
  3. These movements increase the volume inside the thorax, decreasing the pressure within the lungs.
  4. Higher atmospheric pressure pushes air into the lungs and they expand, stretching the elastic fibres.
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9
Q

Describe the mechanism of expiration

A
  1. diaphragm relaxes, returns to its domed shape
  2. intercostal muscles relax, ribcage falls
  3. These movements decrease the volume of the thorax, increasing the pressure in the thorax
  4. elastic fibres recoil and air is forced out of the lungs until the pressure is equal to atmospheric pressure
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10
Q

What is tidal volume? How can it be measured on a spirometer tracing?

A

the amount of air entering and leaving the lungs in each breath at rest.
Peak to trough on a spirometer tracing

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11
Q

What is vital capacity? How can it be measured on a spirometer tracing?

A

Maximum amount of air that can be taken in with a deep breath and then forced out of the lungs.
Measured from the highest peak to the deepest trough on a spirometer tracing.

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12
Q

Define ‘breathing rate’. How is this measured on a spirometer tracing?

A

breaths taken per minute, measured by counting the number of peaks (or troughs) in a set time e.g. 15secs and then multiplying to give a rate per minute

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13
Q

What is placed in the spirometer to absorb CO2?

A

soda lime

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14
Q

How can the volume of oxygen consumed be measured on a spirometer tracing?

A

by measuring the distance between the position if the first peak and the last peak on the VERTICal scale (the tracing slopes downwards)

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15
Q

why do multicellular animals need transport systems?

A

they are large with several layers of cells and very active, with a small surface area:volume ratio - it would take to long to supply nutrients/remove waste in the volume required by diffusion (used by sing-celled organisms)

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16
Q

What is an open circulatory system? what kind of animals have them>

A

blood is not contained in vessels but fills the central body cavity (haemocoel).
Found in insects

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17
Q

What is a closed circulatory system? what kind of animals have it? advantages?

A

blood is contained inside vessels. E.g. in fish and mammals.
Advantages: more efficient - allows for higher pressure reaching farther distances between the organs - higher pressure means faster speed, so essential nutrients can be supplied/waste removed more quickly e.g. to muscle tissues that have high metabolic rates.

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18
Q

What is a single circulatory system? give an example and describe the route the blood takes.

A

Blood travels through the heart once with each circuit. E.g. in fish blood flows from heart —> gills —> rest of body —-> back to heart

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19
Q

What is a double circulatory system? Name the 2 circuits and describe the route the blood takes through them.

A

Blood passes through the heart twice on each complete circuit.
1st circuit: pulmonary circulation, blood from heart —>lungs
2nd circuit: systemic circulation, blood from heart —> rest of body —> back to heart

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20
Q

Describe the journey of the blood through vessels in the mammalian circulatory system

A

Heart –> arteries –> arterioles –> capillaries –> veins –> venules –> back to heart

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21
Q

Describe the tunica externa of arteries in relation to function.

A

Thick tunica externa containing collagen, elastic fibres, connective tissue to prevent the wall rupturing under high blood pressure

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22
Q

describe the tunica media of arteries in relation to function.

A

Thick layer of smooth muscle to withstand high blood pressure. Elastic fibres allow expansion and recoil as the heart beats and relaxes, helping to MAINTAIN high pressure.

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23
Q

What is the function of circular and longitudinal smooth muscle in the tunica media of arterioles?

A

Circular: contracts to constrict the lumen and decrease blood flow to certain tissues (e.g. in vasoconstriction)
Longitudinal: contracts to dilate lumen and increase blood flow (e.g. in vasodilation)

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24
Q

How is the tunica intima of arteries adapted to function?

A

epithelium folded, so can expand without rupturing, withstanding high pressure.

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25
Q

<p>How do the lumens of veins and arteries compare and why are they different?</p>

A

<p>Veins have a larger lumen to reduce friction and aid blood flow, arteries have a narrow lumen to maintain high blood pressure.</p>

<p>Veins have valves</p>

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26
Q

Why do veins/venules have thinner layers of smooth muscle than arteries/arterioles?

A

Blood pressure is lower in veins so they do not have to be able to withstand/maintain high pressures. Blood is instead forced towards the heart by the construction of skeletal muscles.

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27
Q

How are capillary walls adapted to their function (3)

A
  1. Permeable walls allow exchange of materials between body cells and blood.
  2. Thin walls (squamous epithelium) allow rapid exchange of materials
  3. Pores/slits allow phagocytic white blood cells to squeeze through
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28
Q

How is blood plasma forces through the walls of the blood capillaries? what is it then called having left the capillaries?

A

By the high hydrostatic pressure created at the arteriole end. Liquid is then called tissue fluid.

29
Q

What is the function of tissue fluid?

A

provides a medium for exchange of nutrients, gases and wastes between blood and the body cells

30
Q

How is excess tissue fluid absorbed?

A

By blind-ending lymph capillaries, which have walls which are more permeable than capillary walls, with larger pores, Liquid is now called lymph.

31
Q

How is lymph returned to the blood?

A

Main lymph vessels join into veins

32
Q

What causes water from tissue fluid to move back into the blood at the venous end of the capillaries?

A

Plasma proteins remain in the blood (too big to leave via pores), lowering the water potential gradient. Water thus moves by osmosis from the tissue fluid back to the blood.

33
Q

Describe the sequence of events that control the heart beat - myogenic

A
  1. The sino-atrial node generates a wave of electrical stimulation that spreads across the 2 atria causing atrial systole
  2. The wave of electrical stimulation passes to the atria-vertricular node (the only place in the horizontal septum that is conductive)
  3. The atrio-ventricular node passes the electrical impulses to the bundle of His in the vertical septum between the ventricles.
  4. The bundle of His contains Purkyne tussle, which carries the excitation rapidly to the base of the ventricles (apex)
  5. the Purkyne tissue cause contraction of the ventricle walls from the base upwards, pushing the blood up the arteries
34
Q

Describe the structure of haemoglobin

A
  • conjugated protein with 4 prothetic team groups (contain iron)
  • wuaternary structure of 2 alpha and 2 beta polypeptide chains
  • globular tertiary structure - soluble
35
Q

In what three forms is CO2 carried in the blood?

A

85% as hydrogen carbonate ions, HCO3-, in the plasma

10 %as carbaminohaemoglobin inside red blood cells

5% as carbonic acid in plasma

36
Q

How do high concentrations of Co2 inhibit the affinity of haemoglobin for oxygen?

A

Some CO2 takes the place of O2 on the haemoglobin

The low pH caused by carbonic acid distorts the tertiary structure of the haemoglobin

37
Q

Describe the structure of haemoglobin

A
  • conjugated protein with 4 prosthetic haem groups (contain iron)
  • quaternary structure of 2 alpha and 2 beta polypeptide chains
  • globular tertiary structure - soluble
38
Q

Why is the rate of oxygen uptake (seen by reading the dissociation curve from left to right) slow initially, then rapid, then slow again?
(at rest)

A

The first O2 molecule binding onto haemoglobin causes a conformational change in its tertiary structure, making the uptake of the next two O2 molecules more rapid.
The final molecule of O2 binds more slowly as there is only 1 remaining binding site.

39
Q

What happens to the dissociation curve when there is a high concentration of CO2 (e.g. during exercise)? what is the name given to this change why is it beneficial

A

The whole dissociation curve is shifted to the right - the Bohr shift. This stimulates the release of oxygen to respiring tissues because the uptake of O2 in the lungs is inhibited due to the high CO2 concentration (cO2 binds to haemoglobin, taking up space for oxygen, and lowers pH damaging its tertiary structure)

40
Q

How does the dissociation curve for fetal haemoglobin differ from that for adult haemoglobin? Why is this important

A

Has a dissociation curve well to the left of that of adult haemoglobin.
This is because it has a much higher affinity for oxygen than adult haemoglobin and takes up oxygen at a lower partial pressure of oxygen/becomes more saturated at low pO2. The placenta has low partial pressure of oxygen, stimulating adult haemoglobin to dissociate/release its oxygen which the fetal haemoglobin will associate with.
The oxygen is then available for fetal respiration to release ATP energy for protein synthesis and growth.

41
Q

Describe the distribution of xylem and phloem in a root?

A

xylem in centre in a cross-shaped region, phloem is between the points of the xylem

42
Q

Describe the distribution of xylem and phloem in stems

A

In vascular bundles around the edge, with xylem towards the centre or the stem and phloem towards the outside

43
Q

Describe the distribution of xylem and phloem in leaves

A

xylem and phloem in veins, with xylem towards the top of the leaf and phloem towards the bottom

44
Q

How do ions and water respectively enter the root hair cells from the soil?

A

Ions: actively transported into the root hair cells using ATP energy made via respiration in the mitochondria
Water: enter by osmosis thanks to the lowered water potential of the cell caused by the presence of the ions

45
Q

What are the three possible pathways water can take across the root cortex?
By what process do ions travel through these pathways?

A
  1. The apoplastic pathway - through the cell walls by diffusion
  2. The symplastic pathway - through the cell walls, cell membranes and cytoplasm by osmosis
  3. the vacuolar pathway - cell to cell via the vacuoles by osmosis
    Ions move in solution by diffusion
46
Q

<p>How is water forced to enter the xylem vessels from the apoplastic route?</p>

A

<p>- The pathway is blocked by the waxy Caspian strip surrounding endodermal cell walls which is impermeable to water MADE OF SUBERIN - Water and ions are this forced to enter the endodermal cells, allowing them to control the movement of the ions - ions are actively transported by the endodermal cells into the xylem vessels - this lowers the water potential in the xylem so water can enter by osmosis, causing an upwards force of water towards the leaves</p>

47
Q

How is water forced up the xylem vessels in a column of water?

A

By capillary action (the tendency of water to rise up narrow tubes) due to the following properties:

  • adhesion: hydrogen bonding of water molecules to other molecules in the sides of the tubes (e.g. cellulose and lignin)
  • cohesion: the hydrogen bonding of water molecules to each other
48
Q

What is transpiration?

A

the loss of water vapour by evaporation from the leaf surfaces

49
Q

Explain the water potential gradient from the roots to the leaves in terms of the transpiration stream

A

Spongy mesophyll cells lose water by diffusion into the surrounding open air spaces (stomata), lowering their water potential and drawing in water from adjacent cells by osmosis.
This is repeated cell to cell until water is drawn from the xylem vessels by osmosis, creating a water potential gradient that is higher in the roots due to the uptake of water, and lower in the leaves due to the loss of water.

50
Q

Potometers assume that the rate of water uptake is directly proportional to the rate of transpiration. Why might this not always be the case?

A

A small amount of water is used in photosynthesis

51
Q

what are 3 precautions to take when setting up a photometer and why?

A
  1. Leafy shoot is cut under water so that no bubbles enter and block the xylem vessels
  2. the shoot is allowed to acclimatise to any new conditions before measurements are made and other conditions are kept constant
  3. the leaves are dried to prevent water blocking the stomata
  4. joints are made waterproof using vaseline - airtight to prevent bubbles entering and blocking the xylem vessels
52
Q

How does humidity affect the rate of transpiration and why?

A

High humidity slows the rate of transpiration - less steep diffusion gradient between the water vapour inside the leaf and that in the air

53
Q

How do air currents/wind affect the rate of transpiration and why?

A

increased air currents/wind = higher rate of transpiration because humid air is removed from around the leaf and replaced with drier air, increasing the diffusion gradient.

54
Q

How does temperature affect the rate of transpiration and why?

A

higher temp = increased rate of transpiration as there is more kinetic energy causing water molecules to move faster and therefore diffuse faster

55
Q

How does light intensity affect the rate of transpiration and why?

A

high light intensity = high rate of transpiration’s the rate of photosynthesis increases causing stomata to open wider to allow greater uptake of CO2 and simultaneously allowing more water to leave

56
Q

What are 4 adaptations of xylem vessels for transport?

A
  1. lignified walls for waterproofing and strengthening
  2. hollow lumen - no cell contents so no impedance to flow of water/ions
  3. end walls are broken down to a single perforation plate for rapid vertical flow
  4. pits (undignified regions) allow lateral movement to adjacent vessels/body cells
57
Q

what is the basic structure of phloem?

A

sieve tube elements and companion cells

58
Q

What are three adaptations of the sieve tube elements of phloem for transport?

A
  1. thin, permeable cellulose cell walls for exchange of materials
  2. little cytoplasm, few organelles and no nuclei - little impedance to flow of materials
  3. sieve plates with pores to allow vertical flow
  4. plasmodesmata through cell walls to allow passage of materials such as ATP from companion cells
59
Q

What are 2 adaptations of companion cells for transport in the phloem?

A
  1. nucleus to control translocation via enzyme/carrier protein production
  2. many mitochondria to produce ATP for active transport in the sieve tube elements
60
Q

what is a source? example?

A

Sites where sucrose is produced e.g. by photosynthesis in leaves/hydrolysis of food stores in roots

61
Q

what is a sink? example?

A

Sites where sucrose are used e.g. in respiration for growth in shoot tips/production of stores in roots

62
Q

In what direction is the main flow of phloem sap in summer and why?

A

Downwards - during high sunlight the main source areas are the photosynthetic leaves and the main sink areas are the storage areas in the roots

63
Q

In what direction is the main flow of phloem sap in the spring?

A

Upwards - main source areas are the food stores in the roots and the main sink areas are the growing (respiring) shoot tips

64
Q

Describe the sequence of events in translocation?

A
  1. sugars are actively transported into the sieve tubes from source areas
  2. This lowers the water potential and so water enters by osmosis
  3. This increases the hydrostatic pressure inside the sieve tubes
  4. this creates a mass flow of water and solutes towards the sink areas
  5. in the sink areas sugars etc are actively transported out of the sieve tubes into the body cells
  6. this lowers the water potential of the body cells and so water follows by osmosis
  7. This decreases the hydrostatic pressure in the sieve tubes in the sink areas
65
Q

What are three pieces of evidence for the mass-flow theory of translocation?

A
  1. companion cells contain many mitochondria, and phloem sap contains ATP
  2. Aphids feed on phloem sap via the proboscis - if their heads are cut off while feeding, phloem sap drips out
  3. Movement of phloem sap is about 20x faster than diffusion
  4. Ringing of a tree (removing bark and phloem) results in bulging above the ring as sugars accumulate (suggesting flow is downwards), especially in the summer
  5. metabolic inhibitors e.g. cyanide slow translocation
66
Q

way to improve accuracy of any experiment?

A

take more intermediate readings for independent variable

67
Q

way to improve reliability of experiment?

A

take more, readings at each temperature / repetitions

68
Q

what are bordered pits in the xylem vessels? role?

A

Unlignified regions which allow lateral movement of water/mineral ions to adjacent vessels/body cells

Biology AS (5 decks)

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