Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biology AS > 3.4 Mass transport > Flashcards

3.4 Mass transport Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

What is the structure of haemoglobin?

A
  • Haemoglobin is a protein making up 95% of the dry mass of a red blood cell. It is the means of transport of oxygen around the body
  • Haemoglobin is made up of four polypeptide chains, each bound to one haem group
  • Each haem group can combine with one oxygen molecule, so that one molecule of haemoglobin can combine with a maximum of four oxygen molecules. This forms oxyhaemoglobin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the shape of the curve in the oxygen dissociation graph?

A
  • An oxygen dissociation curve is an S shape curve.
  • The curve is this shape because the first oxygen finds it difficult to bind to one of the sites on its 4 polypeptide subunits because they are closely united.
  • Therefore at low oxygen concentrations, little oxygen binds to haemoglobin - the gradient of the curve is shallow initially
  • Once the first one has bound it changes the shape of the haemoglobin so the next 3 oxygens find it easier to bind.
  • This is sometimes called a conformational change
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does the curve shifted to the right mean in an oxygen dissociation graph?

A
  • Any curve that is shifted to the right is an animal with haemoglobin with a low affinity for oxygen
  • Animals with a large surface area:volume ratio are in danger of losing body heat
  • They need to maintain body temperature by having a high respiratory rate to generate heat respiration requires oxygen
  • Active animals have a high respiratial rate to release energy for muscle contraction
  • The further to the right the curve, the lower is the affinity of haemoglobin for oxygen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the BOHR shift?

A
  • High concentrations of CO2 causes a shift to the right. This is knows as the Bohr shift. It means oxygen is more readily released to tissues
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does the curves shifted to the left mean on an oxygen dissociation graph?

A
  • The llama and foetal haemoglobin have a curve that has been shifted to the left of the human haemoglobin
  • Organisms on the left of the curve for humans can pick up oxygen easily if there is not much available
  • The further to the left the curve, the greater is the affinity of haemoglobin for oxygen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the structure and function of veins?

A
  • Walls are thin and contain 4 layers of tissue: epithelium, muscle layer, elastic tissue and collagen
  • Carries blood at low pressure (10 to 20mmHg)
  • Leads towards the heart
  • Contains valves to stop backflow
  • Mostly under the surface of the skin
  • Lumen diameter very large - many RBCs flow at once
  • Wall thin because pressure is low
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the structure and function of arteries?

A
  • Walls are very thick and contain 4 layers: epithelium, muscle layer, elastic tissue and collagen
  • Carries blood at systolic pressure (120mmHg)
  • Leads away from the heart
  • Contains no valves
  • Mostly deep beneath the skin
  • Lumen diameter fairly large - many RBCs flow, but closely packed together
  • Wall contains thick muscle layer to cope with very high internal pressure
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the structure and function of the capillaries?

A
  • Walls are made from one layer of epithelium cells
  • Carries blood at very low pressure (1 to 2mmHg)
  • Not connected to the heart
  • Contains no valves
  • Found throughout all tissue
  • Lumen diameter small - one RBC passes through at a time
  • Wall bursts under pressure changes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does oxygenated mean?

A

Blood with oxygen (usually coloured red on a diagram)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does deoxygenated mean?

A

Blood with low oxygen (usually coloured blue on a diagram)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a pulmonary vein?

A

Blood vessel which returns with oxygenated blood from the lungs to the left atrium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is a pulmonary artery?

A

Blood vessel which leaves the right ventricle transporting deoxygenated blood to the lungs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the aorta?

A

The major blood vessel, which carries, oxygenated blood from the heart to the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the ventricle?

A

One of the bottom two chambers of the heart

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the atrium?

A

One of the top two chambers of the heart

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the atrioventricular valve?

A

The valve which prevent backflow from the ventricles to the atria

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the vena cava?

A

The major blood vessel which returns deoxygenated blood to the heart from the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the semi lunar valves?

A

The valves which prevent backflow from the arteries to the ventricles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the septum?

A

Separates the two sides of the heart, keeping oxygenated and deoxygenated blood apart

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the coronary arteries?

A

Blood vessels on the surface of the heart, which supply the heart itself with blood

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is mass flow?

A

Mass flow essentially means the transport of lots and lots of substances through the circulatory system. The continual movement is caused by the heart pumping

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the first stage of the cardiac cycle?

A
  • Blood enters atria and ventricles from pulmonary veins and vena cava
  • Semi-lunar valves closed
  • Left and right atrioventricular valves open
  • Relaxation of ventricles allows blood to enter from atria
  • Relaxation of heart (diastole)
  • Atria are relaxed and fill with blood. Ventricles are also relaxed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the second stage of the cardiac cycle?

A
  • Atria contract to push remaining blood into ventricles
  • Semi-lunar valves closed
  • Left and right atrioventricular valves open
  • Blood pumped from atria to ventricles
  • Contraction of atria (atria systole)
  • Atria contract, pushing blood into the ventricles. Ventricles remain relaxed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the third stage of the cardiac cycle?

A
  • Blood pumped into pulmonary arteries and the aorta
  • Semi-lunar valves open
  • Left and right atrioventricular valves closed
  • Ventricles contract and walls thicken
  • Contraction of ventricles (ventricular systole)
  • Atria relax. Ventricles contract, pushing blood away from heart through pulmonary arteries and the aorta
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is relaxation of the heart?

A
  • Blood returns to the atria of the heart through the pulmonary vein and the vena cava.
  • As the atria fill, the pressure in them rises.
  • When this pressure exceeds that in the ventricles, the atrioventricular valves open, allowing the blood to pass into the ventricles.
  • The passage of blood is aided by gravity.
  • The muscular walls of the atria and ventricles are relaxed, which causes them to recoil and reduces the pressure within the ventricles.
  • This causes the pressure to be lower than that in the aorta and the pulmonary artery, and so the semi-lunar vales in the aorta and pulmonary artery close.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the contraction of the atria (atrial systole)?

A

The contraction of the atrial walls, along with the recoil of the relaxed ventricle walls, forces the remaining blood into the ventricles from the atria.
Throughout this stage the muscle of the ventricle walls remains relaxed.
The semi lunar valves stay closed and the atrioventricular valves open.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the contraction of the ventricles (ventricular systole)?

A

After a short delay to allow the ventricles to fill with blood, their walls contract simultaneously.
This increases the blood pressure within them, forcing shut the atrioventricular valves and preventing backflow of blood into the atria.
The pressure in the ventricles rises further, once it exceeds that in the aorta and pulmonary artery, blood is forced from the ventricles into these vessels.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are pocket valves?

A

In veins that occur throughout the venous system.
These ensure that when the veins are squeezed, e.g. when skeletal muscles contract, blood flows back towards the heart rather than away from it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the structure of a haemoglobin molecule?

A
  • Primary structure - Sequence of amino acids in the four polypeptide chains
  • Secondary structure - in which each of these polypeptide chains is coiled into a helix
  • Tertiary structure - in which each polypeptide chain is folded into a precise shape - an important factor in its ability to carry oxygen
  • Quaternary structure - in which all four polypeptide are linked together to form an almost spherical molecule. Each polypeptide is associated with a haem group - which contains a ferrous ion. Each ion can combine with a single oxygen molecule, making a total of four oxygen molecules that can be carried by a single haemoglobin molecule in humans
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What are haemoglobins?

A

Protein molecules with a quaternary structure that has evolved to make it efficient at loading oxygen under one set of conditions but unloading it under a different set of conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Explain loading and unloading oxygen.

A
  • The process by which haemoglobin binds with oxygen is called loading, or associating. In humans this takes place in the lungs
  • The process by which haemoglobin releases its oxygen is called unloading, or dissociating. In humans this takes place in the tissues
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What does having a high affinity mean for haemoglobin?

A

Haemoglobins with a high affinity for oxygen take up oxygen more easily, but release it less easily

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What does having a low affinity mean for haemoglobin?

A

Haemoglobins with a low affinity for oxygen take up oxygen less easily , but release it more easily

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is the role of haemoglobin?

A
  • The role of haemoglobin is to transport oxygen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What does haemoglobin need to do to be efficient at transporting oxygen?

A
  • Readily associate with oxygen at the surface where gas exchange takes place
  • Readily dissociate from oxygen at those tissues requiring it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Why are there different haemoglobins?

A
  • Scientists observed that many organisms possessed haemoglobin
  • They proposed that it carried oxygen from the gas-exchange surface to the tissues that required it for respiration - this meant that it must readily combine with oxygen
  • Consequently they investigated the ability of haemoglobin from different organisms to combine with oxygen
  • Results showed that there were different types of haemoglobins
  • These exhibited different properties relating to the way they took up and released oxygen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Why do different haemoglobins have different affinities for oxygen?

A
  • Each species produces a haemoglobin with a slightly different amino acid sequence
  • The haemoglobin of each species therefore has a slightly different tertiary and quaternary structure and hence different oxygen binding properties
  • Depending on its structure haemoglobin molecules range from those that have a high affinity for oxygen to those that have a low affinity for oxygen
38
Q

What happens when the first molecule binds on a oxygen dissociation curve?

A
  • The binding of the first oxygen molecule changes the quaternary structure of the haemoglobin molecule, causing it to change shape
  • This change makes it easier for the other subunits to bind to an oxygen molecule
  • In other words, the binding of the first oxygen molecule induces the other subunits to bind to an oxygen molecule
39
Q

What happens when the second molecule binds on a oxygen dissociation curve?

A
  • It therefore takes a smaller increase in the partial pressure of oxygen to bind the second oxygen molecule than it did to bind the first one
  • This is known as a positive cooperativity because binding of the first molecule makes binding of the second easier and so on.
  • The gradient of the curve steepens
40
Q

What happens when the third molecule binds on a oxygen dissociation curve?

A
  • The situation changes, however, after the binding of the third molecule
  • While in theory it is easier for haemoglobin to bind the fourth oxygen molecule, in practise it is harder
  • This is simply due to probability
  • With the majority of the binding site occupied, it is less likely that a single oxygen molecule will find an empty site to bind to
  • The gradient of the curve reduces and the graph flattens off
41
Q

Describe the loading, transport and unloading of oxygen.

A
  • At the gas-exchange surface CO2 is constantly being removed
  • The pH is slightly raised due to the low concentration of carbon dioxide
  • The higher pH changes the shape of haemoglobin into one that enables it to load oxygen rapidly
  • This shape also increases the affinity of haemoglobin for oxygen, so it is not released while being transported in the blood to the tissues
  • In the tissues, carbon dioxide is produced by respiring cells
  • Carbon dioxide is acidic in solution, so the pH of the blood within the tissues is lowered
  • The lower pH changes the shape of haemoglobin into one with a lower affinity for oxygen
  • Haemoglobin releases its oxygen into the respiring tissues
42
Q

How does ‘the more active a tissue, the more oxygen is unloaded’ work?

A

The higher the rate of respiration -> the more carbon dioxide the tissues produce -> the lower the pH -> the greater the haemoglobin shape change -> the more readily oxygen is unloaded -> the more oxygen is available for respiration

43
Q

What is the effect of carbon dioxide concentration on haemoglobin?

A
  • Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide
  • The greater the concentration of carbon dioxide, the more readily the haemoglobin releases its oxygen
44
Q

What effect does carbon dioxide have at the gas-exchange surface?

A
  • At the gas exchange surface, e.g. lungs, the concentration of CO2 is low because it diffuses across the exchange surface and is excreted from the organism.
  • The affinity of haemoglobin for oxygen is increased, which, coupled with the high concentration of oxygen in the lungs, means that oxygen is readily loaded by haemoglobin.
  • The reduced carbon dioxide concentration has shifted the oxygen dissociation curve to the left.
45
Q

What effect does carbon dioxide have in rapidly respiring tissues?

A
  • In rapidly respiring tissues, e.g. muscles, the concentration of CO2 is high.
  • The affinity of haemoglobin for oxygen is reduced, which, coupled with the low concentration of oxygen in the muscles, means that oxygen is readily unloaded from the haemoglobin into the muscles cells.
  • This increased CO2 concentration has shifted the oxygen dissociation curve to the right
46
Q

What effect does oxygen have on haemoglobin?

A
  • In humans, haemoglobin normally becomes saturated with oxygen as it passes through the lungs
  • In practise not all haemoglobin molecules are loaded with their maximum 4 oxygen molecules
  • As a consequence, the overall saturation of haemoglobin at atmospheric pressure is normally around 97%
  • When this haemoglobin reaches a tissue with a low respiratory rate, only one of these molecules will normally be released
  • The blood returning to the lungs will therefore contain haemoglobin that is still 75% saturated with oxygen
  • If a tissue is very active then 3 oxygen molecules will usually be unloaded from each haemoglobin molecule.
47
Q

How have different types of species adapted to different environments and conditions?

A
  • Different species have different types of haemoglobin, each with its own oxygen dissociation curve
  • For example, species of animals that live in an environment with a lower partial pressure of oxygen have evolved haemoglobin that has a higher affinity for oxygen than the haemoglobin of animals that live where the partial pressure of oxygen is higher
48
Q

Describe the haemoglobin in a llama.

A
  • Its an animal that lives at high altitudes
  • At these altitudes the atmospheric pressure is lower and so the partial pressure of oxygen is also lower
  • It is therefore difficult to load haemoglobin with oxygen
  • Llamas also have a type of haemoglobin that has a higher affinity for oxygen than human haemoglobin
  • In other words it is shifted to the left of that of a human haemoglobin
49
Q

What is a lugworm?

A
  • An animal that lives on the seashore
  • Its not very active
  • Spends most of its life in a U-shaped burrow
  • Most of the time the lugworm is covered by seawater, which it circulates through its burrow
50
Q

Describe the lugworms position on a oxygen dissociation curve.

A
  • The oxygen dissociation curve is shifted far to the left of that of a human
  • This means that the haemoglobin of the lugworm is fully loaded with oxygen even when there is little available in its environment
51
Q

How does a lugworm get its oxygen?

A
  • Oxygen diffuses into the lugworms blood from the water and it uses haemoglobin to transport oxygen to its tissues
  • When the tide goes out, the lugworm can no longer circulate a fresh supply of oxygenated water through its burrow
  • So, the water in the burrow contains progressively less oxygen as the lugworm uses it up
  • The lugworm has to extract as much oxygen as possible from the water in the burrow if it is to survive until the tide covers it again
52
Q

Why do large organisms have a transport system?

A
  • All organisms exchange materials between themselves and their environment
  • In small organisms exchange takes place over the surface of the body, however, with increasing size the surface area to volume ratio decreases to a point where the needs of the organism cannot be met by the body surface alone
  • Specialist exchange surfaces are therefore required
53
Q

Why are specialist exchange surfaces required in large organisms?

A
  • To absorb nutrients and respiratory gases, and remove excretory products
  • These exchange surfaces are located in specific regions of the organism
54
Q

Why is the transport system required in large organisms?

A
  • To take materials from cells to exchange surfaces and from exchange surfaces to cells, materials have to be transported between exchange surfaces and the environment
  • They also need to be transported between different parts of the organism
  • As organisms have evolved into larger and more complex structures, the tissues and organs of which they are made have become more specialised and dependant upon one another
  • This makes a transport system all the more essential
55
Q

What 2 factors depend on whether or not there is a specialised transport medium, and whether or not it is circulated by a pump?

A
  • The surface area to volume ratio
  • How active the organism is
  • The lower the surface area to volume ratio, and the more active the organism, the greater is the need for a specialised transport system with a pump
56
Q

What are the common features of the transport system?

A
  • A suitable medium in which to carry materials, for example blood. This is normally a liquid based on water because water readily dissolves substances and can be moved around easily, but can be a gas such as air breathed in and out of the lungs
  • A form of mass transport in which the transport medium is moved around in bulk over large distances - more rapid than diffusion
  • A closed system of tubular vessels that contains the transport medium and forms a branching network to distribute it to all parts of the organism
  • A mechanism for moving the transport medium within vessels. This requires a pressure difference between one part of the system and another
57
Q

How is the transport system achieved?

A

a. Animals use muscular contraction either of the body muscles or of a specialised pumping organ such as the heart
b. Plants rely on natural, passive process such as the evaporation of water
- a mechanism to maintain the mass flow movement in one direction, e.g. valves
- A means of controlling the flow of the transport medium to suit the changing needs of different parts of the organism
- A mechanism for the mass flow of water or gases, e.g. intercostal muscles and diaphragm during breathing in mammals

58
Q

What circulatory system do mammals have?

A
  • a closed, double circulatory system in which blood is confined to vessels and passes twice through the heart for each complete circuit of the body
59
Q

Why do mammals have a closed, double circulatory system?

A
  • Because when blood is passed through the lungs, its pressure is reduced.
  • If it were to pass immediately to the rest of the body its low pressure would make circulation very slow
  • Blood is therefore returned to the heart to boost its pressure before being circulated to the rest of the tissues
60
Q

What is the result of the blood returning to the heart in mammals?

A
  • Substances are delivered to the rest of the body quickly, which is necessary as mammals have a high body temperature and hence a high rate of metabolism
  • The vessels that make up the circulatory system of a mammal are divided into 3 types
61
Q

What are the 3 types of vessels in mammals?

A
  • Arteries
  • Veins
  • Capillaries
62
Q

What is the last part of the transport system in mammals?

A
  • Although a transport system is used to move substances longer distances, the final part of the journey to cells is by diffusion
  • The final exchange from blood vessels into cells is rapid because it takes place over a large surface area, across a short distance and there is a steep diffusion gradient
63
Q

What is the structure of the human heart?

A

It is two separate pumps, lying side by side.
The pump on the left deals with oxygenated blood from the lungs, while the right deals with deoxygenated blood from the body.

64
Q

Why does the heart need two separate pumps?

A

Blood has to pass through tiny capillaries in the lungs in order to present a large surface area for the exchange of gases.
In doing so, there is a very large drop in pressure and so the blood flow to the rest of the body would be very slow.
Mammals therefore have a system in which the blood is returned to the heart to increase its pressure before it is distributed to the rest of the body.
It is essential to keep the oxygenated blood in the pump on the left side separate from the deoxygenated blood in the pump on the right.

65
Q

What are the atrium and ventricle?

A

The atrium is thin-walled and elastic and stretches as it collects blood.
It receives blood from the veins.
The ventricle has a much thicker muscular wall as it has to contract strongly to pump blood some distance, either to the lungs or to the rest of the body.
They pump blood away from the heart and into the arteries.

66
Q

How do the atria and ventricles work together?

A

The right ventricle pumps blood only to the lungs, and it has a thinner muscular wall than the left ventricle.
The left ventricle has a thick muscular wall, enabling it to contract to create enough pressure to pump blood to the rest of the body.
While they are separate, and after birth there is no mixing of the blood in each of them, they pump in time with each other.
Both atria contract together and then both ventricles, pumping the same volume of blood.

67
Q

What happens if the coronary arteries get blocked?

A

Blockage of these arteries, for example by blood clot, leads to myocardial infarction, or heart attack, because an area of the heart muscle is deprived of blood and therefore oxygen.
The muscle cells in this region are unable to respire and so die.

68
Q

How does partial pressure of oxygen affect oxygen-haemoglobin binding?

A

As partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin. When partial pressure is low, oxygen is released from haemoglobin

69
Q

How does partial pressure of carbon dioxide affect oxygen haemoglobin binding?

A

As partial pressure of CO2 increases, the conditions become acidic causing haemoglobin to change shape. The affinity for haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. This is known as the Bohr effect

70
Q

How does saturation of haemoglobin with oxygen affect oxygen haemoglobin binding?

A

Its hard for the first molecule to bind. Once it does, it changes the shape to make it easier for the second and third molecules to bind, known as positive cooperativity. It is then slightly harder for the fourth oxygen molecule to bind because there is a low chance of finding a binding site

71
Q

Explain why oxygen is released from haemoglobin in respiring tissues.

A

• Partial pressure of oxygen is low
• high concentration of CO2 in respiring tissues, so affinity decreases

72
Q

What happens during cardia diastole?

A

The heart is relaxed. Blood enters the atria, increasing the pressure and pushing open the atrioventricular valves. This allows blood to flow into the ventricles. Pressure in the heart is lower than in the arteries, so semilunar valves remain closed

73
Q

Name the nodes involved in heart contraction and where they are situated.

A

• sinoatrial node (SAN) = wall of right atrium
• atrioventricular node (AVN) = in between the two atria

74
Q

What does myogenic mean?

A

the hearts contraction is initiated from within the muscle itself, rather than by nerve impulses

75
Q

How is water transported in plants?

A

through the xylem vessels; long, continuous columns that also provide structural support to the stem

76
Q

What is the cohesion-tension theory?

A

water molecules form hydrogen bonds with each other, causing them to ‘stick’ together. The surface tension of the water also creates this sticking effect. Therefore as water is lost through transpiration, more can be drawn up the stem

77
Q

What are the 3 components of phloem vessels?

A

• sieve tube elements - form a tube to transport sucrose in the dissolved form of sap
• companion cells - involved in ATP production for active loading of sucrose into sieve tubes
• plasmodesmata - gaps between cell walls where the cytoplasm links, allowing substances to flow

78
Q

How does sucrose in the leaf move into the cytoplasm?

A

sucrose enters companion cells of the phloem vessels by active loading, which uses ATP and a diffusion gradient of hydrogen ions. Sucrose then diffuses from companion cells into the sieve tube elements through the plasmodesmata

79
Q

How do phloem vessels transport sucrose around the plant?

A

as sucrose moves into the tube elements, water potential inside the phloem is reduced. This causes water to enter via osmosis from the xylem and increases hydrostatic pressure. Water moves along the sieve tube towards areas of lower hydrostatic pressure. Sucrose diffuses into surrounding cells where it is needed

80
Q

Give evidence for the mass flow hypothesis of translocation.

A

• sap is released when a stem is cut, therefore there must be pressure in the phloem
• there is a higher sucrose concentration in the leaves than the roots
• increasing sucrose levels in the leaves results in increased sucroses in the phloem

81
Q

Give evidence against the mass flow hypothesis of translocation

A

• the structure of sieve tubes seems to hinder mass flow
• not all solutes move at the same speed, as they would in mass flow
•sucrose is delivered at the same rate throughout the plant, rather than to areas with the lowest sucrose concentration first

82
Q

How can riniging experiments be used to investigate transport in plants?

A

the bark and phloem of a tree are removed in a ring, leaving behind the xylem. Eventually the tissues above the missing ring swells due to accumulation of sucrose as the tissue below begins to die. Therefore sucrose must be transported in the phloem

83
Q

How can tracing experiments be used to investigate transport in plants?

A

Plants grown in the presence of radioactive CO2, which will be incorporated into the plants sugars. Using autoradiography, we can see that the areas exposed to radiation correspond to where the phloem is

84
Q

What is transpiration?

A

the loss of water vapour from the stomata. This is evaporation and it mainly occurs on the leaves, as this is where stomata is located

85
Q

What is the rate of transpiration affected by?

A
  • temperature
  • light intensity
  • humidity
  • air movement/wind
86
Q

How does light intensity affect the rate of transpiration?

A
  • Positive correlation
  • more light causes more stomata to open = larger surface area for evaporation
87
Q

How does temperature affect the rate of transpiration?

A
  • positive correlation
  • more heat means more kinetic energy, faster moving molecules and therefore more evaporation
88
Q

How does humidity affect the rate of transpiration?

A
  • negative correlation
  • more water vapour in the air will make the water potential more positive outside of the leaf, therefore reduces the water potential gradient
89
Q

How does wind/air movement affect the rate of transpiration?

A
  • positive correlation
  • more wind will blow away humid air containing water vapour, therefore maintaining the water potential gradient
90
Q

How does water move up the xylem?

A
  1. water vapour evaporates out of the stomata on leaves. This loss in water volume creates a lower pressure
  2. When this water is lost by transpiration more water is pulled up the xylem to replace it (moves due to negative pressure)
  3. due to the hydrogen bonds between water molecules, they are cohesive. This creates a column of water within the xylem
  4. water molecules also adhere to the walls of the xylem, helping to pull the water column upwards
  5. as this column of water is pulled up the xylem it creates tension, pulling the xylem in to become narrower
91
Q

What does cohesion between water molecules create?

A

a continuous water column in the xylem

92
Q

What is adhesion?

A

the sticking of water molecules to the xylem wall and causes capillarity

Biology AS (36 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions