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Biology > Chapter 7 - Mass Transport > Flashcards

Chapter 7 - Mass Transport Flashcards

1
Q

What is mass transport?

A

When all substances move in the same direction at the same speed

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2
Q

What does the blood contain? And what is in that?

A
  • contains red blood cells
  • these also contain a protein called HAEMOGLOBIN which is used to transport oxygen in the blood
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3
Q

What are the 3 main adaptations of red blood cells?

A
  1. Large SA:V ratio- speeds up diffusion of oxygen into and out of the cell
  2. Flat - biconcave disc shape so short diffusion pathways
  3. No nucleus - more space for haemoglobin
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4
Q

Why is red blood cells having no mitochondria an advantage?

A
  • aerobic respiration by mitochondria would use up oxygen in the red blood cells
  • enables more space for haemoglobin
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5
Q

What sort of structure does haemoglobin have? And what does this mean?

A

QUATERNARY STRUCTURE
Contains more than one polypeptide chain

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6
Q

Describe the structure of haemoglobin.

A
  • made of 4 polypeptide chains (subunits): 2 alpha and 2 beta polypeptide chains
  • each subunit has one non protein haem group embedded in it
  • each haem group contains an iron ion (Fe2+)
  • each haem group can bind one oxygen molecule
  • so haemoglobin can bind 4 oxygen molecules in total
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7
Q

What is the cooperative nature of haemoglobin?

A

-Binding of the first oxygen molecule changes the tertiary structure of haemoglobin;
-This creates another binding site for oxygen and a second oxygen molecule binds;
-This changes the tertiary structure of haemoglobin again and a third binding site is created;
- so the change in shape of haemoglobin caused by binding of the first oxygens makes the binding of further oxygens easier.

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8
Q

What is meant by partial pressure, what is its symbol and what increases is?

A
  • The pressure exerted by an individual gas in a mixture of gases
  • pO2 is the symbol for “partial pressure of oxygen”.
  • Higher concentrations of a particular gas will increase the partial pressure for that gas.
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9
Q

What is meant by the terms:
1. Oxygen loading
2. Oxygen unloading
3. Oxyhaemoglobin
4. Deoxyhaemglobin

A
  1. Oxygen loading: haemoglobin associating with/picking up oxygen;
  2. Oxygen unloading: haemoglobin dissociating from/releasing oxygen;
  3. Oxyhaemoglobin: haemoglobin that has oxygen bound to it;
  4. Deoxyhaemoglobin: haemoglobin that does not have oxygen bound to it.
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10
Q

With reference to the oxygen dissociation curve, why is the S shape important?

A
  • In the lungs, haemoglobin can become fully saturated at a lower pO2 than if the relationship was linear

The steep part means that:
1. for a small decrease in the pO2 there will be a large decrease in the % saturation of haemoglobin with O2.
2. So more O2 will be unloaded to the tissues for aerobic respiration.

  • the more the curve shifts to the RIGHT, the lower the AFFINITY of oxygen by haemoglobin
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11
Q

What is the general meaning of the Bohr effect?

A

A higher carbon dioxide concentration will help oxygen to unload

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12
Q

Describe the Bohr effect [4].

A
  1. Respiring tissues release CO2 as waste;
  2. CO2 accumulates in the blood and lowers its pH;
  3. This is due CO2 dissolving in blood to form acid, which increases the hydrogen ion concentration of the blood;
  4. The drop in pH changes the tertiary structure of haemoglobin so oxygen is more easily released;
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13
Q

What occurs in the lungs during mass transport in humans?

A
  1. CO2 diffuses down its concentration gradient from blood to the alveoli to be exhaled;
  2. This lowers the concentration of CO2 in the blood and raises blood pH;
  3. This changes the tertiary structure of haemoglobin back to a shape that can more readily bind oxygen;
  4. The high pO2 in the lungs means that haemoglobin is rapidly saturated with oxygen
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14
Q

Why does the left side of the heart have thicker walls than the right side?

A

Left (ventricle) pumps blood to the BODY rather than to just the lungs
Therefore… a more forceful contraction is needed

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15
Q

What do coronary arteries do?

A

Provide the heart muscle with oxygen and glucose

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16
Q

How does the heart maintain a unidirectional flow of blood?
- refer to pressure and volume changes and valve movements.
STEP 1

A

Atria + ventricles relaxed so fill with blood

  1. Blood enters the atria and ventricles from pulmonary veins (left) and vena cava (right)
    - semi lunar valves = closed
    - left and right atrioventricular valves open
    - relaxation of ventricles allows blood to enter from atria
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17
Q

How does the heart maintain a unidirectional flow of blood?
- refer to pressure and volume changes and valve movements.
STEP 2

A

Atria contract (tops up ventricles with blood), ventricles still relaxed

  1. Atria contract to push remaining blood into ventricles
    - semi lunar valves closed
    - left and right atrioventricular valves open
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18
Q

How does the heart maintain a unidirectional flow of blood?
- refer to pressure and volume changes and valve movements.
STEP 3

A

Atria relax, ventricles contract so blood moves into pulmonary artery and aorta

  1. Blood is pumped into pulmonary artery and aorta
    - semi lunar valves open
    - left and right atrioventricular valves close
    - ventricles contract
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19
Q

What do valves do and how do they work?

A

Prevent the back flow of blood
- when pressure is GREATER IN FRONT of the valves it closes
- when pressure is GREATER BEHIND the valve it opens

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20
Q

Exam tip - unidirectional flow of blood

A

Talk about the pressure of blood in the chambers and whether this is higher IN FRONT OF or BEHIND the valve causing the valve to either open or close

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21
Q

What does the term myogenic mean?

A

Muscle contraction is initiated from the muscle itself rather than from a nerve

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22
Q

Describe how the cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN) [5]

A
  1. SAN: sends impulse across atria causing atrial contraction
  2. Non conducting tissue prevents immediate contraction of ventricles
  3. AVN: delays impulse whilst blood leaves atria
  4. AVN sends impulse down Bundle of His
  5. This causes ventricles to contract from base up
23
Q

What do arteries, arterioles and veins do?

A

Arteries + arterioles = carry blood AWAY from the heart under high pressure

Veins = carry blood BACK to the heart under low pressure

24
Q

Describe the structure of the arteries.
Refer to the lumen, endothelium, elastic tissue and muscle

A
  • small lumen
  • smooth endothelium to reduce friction of blood

Elastic tissue: STRETCHES due to high blood pressure when ventricle contracts, then RECOILS when ventricle relaxes
- the recoil = maintains blood pressure and smooth blood flow

Muscle: contracts to constrict lumen (vasoconstriction)
- reduces blood flow so can be diverted to where it is needed.

25
Q

What are the differences with arterioles to arteries? [3]

A
  1. Arterioles are smaller
  2. Muscle layer makes up higher proportion of wall (important role in vasoconstriction) - maintain temp
  3. Elastic layer makes up smaller proportion of wall as blood pressure is lower
26
Q

What is the structure of veins?
Refer to muscle layer, elastic layer, thickness of wall, valves and lumen

A

Muscle layer: thin as cannot control vasoconstriction/ dilation due to bringing blood back to heart

Elastic layer: thin as cannot burst due to low blood pressure + is too low to create the recoil

Thin walls: too low blood pressure so no risk of bursting + allows them to be flattened easily = aids blood flow

Valves: prevent back flow of blood especially under low blood pressure

Lumen: wider than arteries so can carry LARGER volume of blood more slowly

27
Q

List and describe the adaptations of the capillaries. [5]
2 are the same feature

A
  1. Single cell thick endothelium = short diffusion pathway
  2. Narrow lumen = increases the % of blood in contact with endothelium, increasing friction and reducing speed of blood flow
  3. Narrow lumen = shorter diffusion pathway as blood cells pass singly in close contact with endothelium
  4. Capillary is narrow overall = short diffusion pathways
  5. Pores between endothelial cells = fluid can leak out of blood to form tissue fluid
28
Q

What is tissue fluid?

A

Found in spaces around the cells - it is formed from substances that are filtered out of blood capillaries.

29
Q

How is tissue fluid formed?

A
  1. Ventricles contract which produces a high blood pressure
  2. At the arteriole end of the capillary, this high pressure forces water and some dissolved substances out of the capillary
  3. endothelium has pores so leakage can occur
  4. Red blood cells and large proteins are too large to leave
30
Q

How does tissue fluid return to the circulatory system?

A
  1. Due to friction and water loss, the blood pressure at the venule end of the capillary is lower than at the arteriole end.
  2. Blood also has low water potential due to proteins left behind
  3. Water from tissue fluid return to the venule end of the capillary by osmosis down a water potential gradient
  4. Remaining tissue fluid drains into lymphatic system whereby the lymph eventually drains back into blood
31
Q

What does the term hydrostatic pressure mean?

A

The pressure of a fluid
Blood pressure is a type of hydrostatic pressure

32
Q

What is cardiovascular disease? List an example and explain it

A

Refers to both the heart (cardio) and blood vessels (vascular)

  • coronary heart disease - fatty deposits block up the coronary arteries, reducing flow of oxygenated blood to heart muscle
33
Q

What is the xylem?

A

The tissue that transports water passively in the roots, stem and leaves of plants

34
Q

What are the adaptations of xylem?

A
  1. Long cells with no end walls: enables continuous water columns
  2. No cytoplasm/ organelles (dead tissue): nothing to obstruct water flow
  3. Cellulose cell walls thickened with lignin: withstand tension
  4. Pits in walls: unlignified (so not waterproof) allowing lateral movement of water out of the xylem.
    - can be important to allow water to bypass blocked xylem vessels
35
Q

Describe the cohesion tension theory [7]

A
  1. Water evaporates from leaf mesophyll cells + is lost from leaf because of transpiration
  2. This lowers the water potential of leaf mesophyll cells
  3. Water moves by osmosis down a water potential gradient from the xylem to replace water lost at mesophyll cells by evaporation
  4. Water molecules display cohesion: stick together by hydrogen bonds
  5. This means more water is pulled up the xylem to replace water leaving xylem - pull is known as ‘tension’
  6. So a continuous water column in formed up the xylem
  7. Adhesion of water molecules to walls of xylem via hydrogen bonds helps to support the water column
36
Q

Why do xylem vessels have a very narrow diameter?

A

Reduces the weight of the water column so it doesn’t collapse under gravity
- also maximises the adhesion relative to the volume of water carried

37
Q

Why does the diameter of a tree trunk reduce during the day?

APPLY YOUR KNOWLEDGE

A

Transpiration is greatest during the day so there is more tension in the xylem. This pulled the walls of the xylem vessels inwards (shrinking the diameter of tree trunk)

38
Q

Why do air bubbles in the xylem stop water flow through the vessels?

APPLY YOUR KNOWLEDGE

A

If a xylem vessels is broken and air enters it, the tree can no longer draw up water
- this is because the continuous water column is broken so water molecules can’t stick together

39
Q

When a xylem vessel ruptures, does air come in or does water leak?

A

If a xylem vessel is broken, water does not leak out, instead air is drawn in which is consistent with it being under tension

40
Q

Can water place a limit on tree height? - 2 points

A

Gravity: eventually the columns of water will weigh to much to be supported
Beyond a certain height there isn’t enough water e.g. it is used in respiration/ photosynthesis/ turgidity/ hydrolysis

41
Q

What factors speed up the rate of transpiration?

A

Light intensity: stomata open during the day so plants can take up CO2 for photosynthesis
Temperature: water molecules have more kinetic energy
Air movement: higher wind speed will blow water vapour away quicker so water potential gradient is steeper
Humidity: less water vapour in air will make water potential gradients steeper

42
Q

What is the source for mass transport in plants?

A

The leaves
- this is where organic compounds are synthesised during photosynthesis

43
Q

What is the sink for mass transports in plants?

A

The actively growing parts of the plant (shoot tips, root tips, new leaves), to storage organs (carrots, potatoes) or to seeds

44
Q

How are organic compounds moved from the source to the sink?

A

Occurs in the phloem tissue - via translocation

45
Q

What does the phloem tissue consist of?

A

Companion cells
Sieve tube elements

46
Q

How are sieve tube elements adapted for mass transport?

A
  1. They are stacked on top of one another (to form sieve tube)
  2. Their end walls (sieve plates) have large pores through which their cytoplasm can flow
47
Q

What do companion cells do?

A

-Synthesise carrier proteins (through nucleus and rER)
- produce lots of ATP for active transport (through many mitochondria)

48
Q

Describe the mass flow hypothesis. [6]

A
  1. At source companion cells actively transport sucrose into the sieve tube elements
  2. This lowers the water potential in the sieve tube elements and water enters them from the xylem by osmosis
  3. This produces a high hydrostatic pressure in the sieve tube
  4. This pressure gradient leads to the mass flow of fluid towards the sink
  5. At sink sucrose is unloaded
  6. Water potential is now higher in sieve tube so water moves back to the xylem. This means the hydrostatic pressure decreases in the sieve tube
49
Q

How is sucrose used by the sink?

A

It is hydrolysed (sucrose) into glucose and fructose then:
- can be respired to make ATP
- can be converted to amino acids or lipids
- glucose can be converted to starch for storage

50
Q

Why is carbohydrate translocated as sucrose and not glucose?

A

Sucrose - non reducing sugar so it is quite unreactive - needs to be hydrolysed by sucrase which is rare in phloem
Glucose - involved in a range of reactions (photosynthesis) so don’t want it to be used before it gets to the sink

51
Q

How does a tracer experiment work?

A
  • tracer (radioactive carbon dioxide) used to label organic compounds by putting it in a bag with some leaves of a plant
  • as CO2 is needed for photosynthesis it results in the production of radioactive SUCROSE.
  • then AUTORADIOGRAPH whereby X-ray film will turn black if radiation is released
52
Q

How do ringing experiments work?

A
  • remove ring of bark from tree (as this is where phloem is found)
    -the area above the cut acts as a sink where sugar collects (bulges)
  • therefore no sugar goes to the original sink (roots) so tree dies
53
Q

How does using aphids act as evidence?

A

Aphids are sap sucking insects that can penetrate phloem and feed on the sap
- if you cut away insect and leave mouth piece (stylet) - you can sample phloem sap
- sap comes out under high hydrostatic pressure

54
Q

What is the effect of low and high temperature on translocation?

A

LOW temperature: slows down translocation because enzyme activity of respiration slows down so less ATP available for loading of sucrose by companion cells

HIGH temperature: slows down translocation because more water is lost from the plant by transpiration through stomata so less water moves from xylem to phloem to create high hydrostatic pressure

Biology (22 decks)

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