Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Biology > 3.3.4 Mass Transport > Flashcards

3.3.4 Mass Transport Flashcards

(128 cards)

Start Studying
1
Q

What is the function of a red blood cell?

A

To transport oxygen around the body to respiring cells via the blood.

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

What is the protein found in red blood cells?

A

Haemoglobin

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

What is Haemoglobin?

A

A quaternary structure protein that is found in red blood cells. It is a group of chemically similar molecules that are found in many different organisms.

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

What is a quaternary protein?

A

Has more than one polypeptide (Haemoglobin has 4)

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

Describe the structure of Haemoglobin?

A

It is a quaternary protein with 4 polypeptide chains
It has 2 alpha polypeptide chains and 2 beta polypeptide chains
Each polypeptide is bound to one heme group
Heme groups have iron within them so is where oxygen binds to
This means Haemoglobin can bind to 4 oxygen molecules to form oxyhemoglobin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why are Haemoglobin different in different organisms?

A

Because Haemoglobin is a group of proteins of different types, which differ slightly across different organisms (eg. Based on their environment).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is affinity?

A

The ability of Haemoglobin to attract or bind to oxygen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Where in the body does Haemoglobin have a high affinity/low affinity or oxygen?

A

High affinity in the lungs- to load oxygen to transport it around the body
Low affinity at respiring cells- to unload oxygen needed for respiration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How does Haemoglobin change its affinity?

A

By altering its tertiary structure depending on its location in the body eg. Due to a change in pH

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

What is saturation?

A

When Haemoglobin is holding the maximum amount of oxygen it can bind to.

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

What is association/loading?

A

The binding of oxygen to Haemoglobin

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

Describe association of oxygen and Haemoglobin?

A

Each heme group picks up one oxygen molecule so Haemoglobin can carry 4 oxygen molecules at a time.
It occurs when oxygen concentration is high and carbon dioxide concentration is low, as this increases Haemoglobin’s affinity for oxygen.
This results in association to form oxygen and Haemoglobin.

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

What is dissociation/unloading?

A

The detaching or unbinding of oxygen from Haemoglobin

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

Describe dissociation of oxyhaemoglobin?

A

Occurs when oxygen concentration is low and carbon dioxide concentration is high
Haemoglobin has a low affinity for oxygen
Results in dissociation to form oxygen and Haemoglobin

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

What is partial pressure?

A

Refers to the measure of oxygen concentration (pressure exerted by oxygen molecules).

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

Where is partial pressure of oxygen high/low and how does this affect the saturation of Haemoglobin?

A

Partial pressure of oxygen is high in the lungs due to a high concentration of oxygen. This means haemoglobin is unsaturated.
Partial pressure of oxygen is low in respiring tissues due to a low concentration of oxygen. This means haemoglobin is unsaturated.

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

What units is partial pressure measured in?

A

KPa

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

Describe how DNA changes haemoglobins affinity for oxygen?

A

DNA base sequence determines amino acid sequence of the polypeptide in the primary structure.
This changes the secondary structure depending on amino acids present, and so whether a-helix or b-sheets form.
Tertiary structure changes based on R groups of the amino acids in the primary sequence, and therefore determines how the polypeptide folds.
This determines how it conjugates with other polypeptides in the quaternary structure.
The different shaped quaternary structure proteins form different types of haemoglobin that each have a different affinity for oxygen.

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

What does the oxyhaemoglobin dissociation curve show?

A

The relationship between partial pressure of oxygen and percentage saturation of haemoglobin.

Haemoglobin is unsaturated at low partial pressure of oxygen as oxygen is unloaded.
Respiring tissues have a low partial pressure of oxygen as oxygen is used up in respiration.
Haemoglobin is saturated at high partial pressure of oxygen as oxygen is loaded.
Lungs have a high partial pressure of oxygen as it is inhaled there.

The graph shows how a small change in partial pressure of oxygen results in a large change in saturation (it has a sigmoidal/s-shape)

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

Describe co-operative binding/positive co-operativity?

A

Oxygen molecules do not all bind at the same time.
When the first oxygen molecule binds, haemoglobin changes shape (undergoes conformational changes).
This makes it easier for subsequent oxygens to bind as it uncovers new binding sites for oxygen.
When the third oxygen molecule binds, haemoglobin changes shape again.
This makes it more difficult for the 4th oxygen to bind.
It is also more difficult due to a lower partial pressure of oxygen than at first.

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

What is the Bohr effect?

A

The effect of carbon dioxide concentration on the oxygen dissociation curve for adult human haemoglobin.

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

What is the effect of a high carbon dioxide concentration on the oxyhaemoglobin curve and affinity?

A

It causes it to shift to the right, and affinity of haemoglobin for oxygen to decrease.
With carbon dioxide, haemoglobin is less saturated at a given partial pressure of oxygen, which shows it has a lower affinity for oxygen as it unloads more readily.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Explain the Bohr effect?

A

When respiration rate increases, a higher concentration of carbon dioxide is produced.
When carbon dioxide dissolves in the water in blood, it forms carbonic acid.
This means blood becomes acidic (decrease in blood pH).
Carbonic acid dissociates to produce H+ ions which decreases the pH of the blood plasma.
This changes the bonds in the tertiary structure of haemoglobin, and therefore its affinity for oxygen.
It means it has a lower affinity for oxygen at respiring cells to provide oxygen (and even lower during exercise due to faster rate of respiration during exercise).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Application of the Bohr effect in the human body?

A

At respiring cells, there is a high concentration of carbon dioxide.
This means haemoglobin has a low affinity for oxygen.
Therefore it unloads oxygen readily for respiration.
This means the curve shifts right.

At the alveoli/lungs, there is a low concentration of carbon dioxide.
This means haemoglobin has a high affinity for oxygen.
Therefore it loads oxygen readily to be transported to respiring cells.
This means the curve shifts left.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Explain why different organisms have different types of haemoglobin?
Because different types of haemoglobin have different affinities for oxygen. Organisms with a lower oxygen concentration in their environment eg. At high altitude, need haemoglobin with a high affinity for oxygen. This means it can load easily despite partial pressure of oxygen being low. Organisms with a high metabolic rate need haemoglobins with a low affinity for oxygen, as the rate of respiration is fast. This means oxygen can be more easily unloaded at respiring cells.
26
Compare fetal haemoglobin to adult haemoglobin and explain the difference?
Fetal haemoglobin has a higher affinity for oxygen. The foetus cannot inhale or exhale so only source of oxygen is maternal blood in the placenta. This means foetal haemoglobin has a higher affinity for oxygen in order to pull it away from the mother’s haemoglobin.
27
For what organisms would the oxyhaemoglobin dissociation curve shift left?
Foetuses Underground habitats High altitude habitats
28
For what organisms would the oxyhaemoglobin dissociation curve shift to the right?
Those with a fast metabolism Lower altitude habitats
29
What are the 2 features of the mammalian circulatory system?
It is a double circulatory system It is a closed circulatory system
30
What is meant by a double circulatory system?
The blood passes through the heart twice per circuit: once when blood is delivered to the lungs and again when blood is delivered to the rest of the body.
31
What is meant by a closed circulatory system?
The blood remains within the blood vessels and all are connected within a circuit.
32
Explain why mammals have a double circulatory system?
To manage the pressure of blood flow Blood flows through lungs at a lower pressure to prevent damage to capillaries in alveoli and reduces speed at which blood flows to allow more time for gas exchange. Blood flows through to the body at a higher pressure to ensure that blood reaches allow respiring cells to provide oxygen for respiration.
33
What are the 5 key blood vessels in the heart and what do they each transport?
Coronary arteries- supply oxygenated blood to heart muscle Pulmonary artery- deoxygenated blood to the lungs from the heart Pulmonary vein- oxygenated blood from the lungs to the heart Vena cava- deoxygenated blood from the body to the heart Aorta- oxygenated blood from the body to the heart
34
What are the blood vessels associated with the kidney?
Renal artery and renal vein
35
How are the key blood vessels connected?
Within the circulatory system by arteries, veins, capillaries and arterioles.
36
What is the cardiac muscle?
The walls of the heart made up of a thick muscular layer called cardiac muscle.
37
What are the two features of the cardiac muscle?
It is myogenic, meaning it can contract and relax without nervous or hormonal stimulation. It never fatigues as long as it is supplied with oxygen and glucose.
38
What supplies the cardiac muscle with oxygenated blood?
Coronary arteries
39
What are coronary arteries?
Blood vessels surrounding the heart that supply the cardiac muscle with oxygenated blood.
40
What happens if a coronary artery is blocked?
If they become blocked due to buildup of a fatty deposit, the cardiac muscle will not receive oxyegn. It will not be able to respire so cannot contract to pump blood around the body. This is a heart attack (myocardial infarction).
41
What are atria?
Heart chambers- left and right atrium
42
Describe the structure of the atria?
Made up of thinner muscular walls as they do not need to contract as hard as they only pump blood to ventricles. They have elastic walls to stretch when blood enters.
43
What are ventricles?
Heart chambers- left and right ventricles
44
Describe the structure of the ventricles?
Made up of thick muscular walls to enable larger contractions with greater force. This creates a higher blood pressure to enable blood to flow to the lungs and the rest of the body.
45
What is the difference between the left and right ventricles?
The right ventricle has a thinner muscular walls than the left ventricle as blood only needs to be pumped to the lungs rather than the entire body. Means that blood flows at a lower pressure to prevent damage to the capillaries in lungs, and to allow time for gas exchange.
46
Where do arteries transport blood?
Away from the heart
47
What is the aorta?
Artery that transports oxygenated blood from the left ventricle to the rest of the body (respiring cells).
48
What is the pulmonary artery?
Artery that transports deoxygenated blood from the right ventricle to the lungs to become oxygenated.
49
Describe the structure of arteries?
Thicker wall and narrow lumen to withstand and maintain blood flow at a high pressure. Thick elastic layer to stretch and recoil in response to the heart beat. Thick muscular walls enable arteries to constrict and dilate to control volume of blood flowing through. No valves
50
Where do veins transport blood?
Into the heart of
51
What is the vena cava?
Vein that transports deoxygenated blood from the body into the right atrium.
52
What is the pulmonary vein?
Vein that carries oxygenated blood from the lungs into the left atrium.
53
Describe the structure of a vein?
Thin muscular layer and wide lumen cannot control blood flow, but pressure is lower so there is less risk of bursting. Thin elastic layer as don’t need to be able to withstand high pressures. Has valves to prevent the back-flow of blood at low pressures.
54
What are capillaries?
Blood vessels that connect arterioles to the veins
55
Describe the structure of capillaries?
They form many branched capillaries called capillary beds at exchange surfaces. Very narrow lumen to slow down blood flow to allow more time to maximise diffusion/gas exchange. Walls are only one cell thick to provide a short diffusion distance to maximise the rate of diffusion. Have no muscle layer or elastic layer. No valves.
56
What are arterioles?
Blood vessels that are smaller than arteries to help restrict blood flow into the capillaries.
57
Describe the structure of arterioles?
Thicker muscular layer than the arteries to help restrict blood flow into the capillaries. Elastic layer is thinner than in the arteries as the pressure is much lower. Walls are thinner as pressure is lower than in arteries. No valves.
58
What does each layer of a blood vessel do?
Outer layer protects vessel by restricting pressure changes. Muscle layer contracts to control the flow of blood. The elastic layer stretches and recoils to maintain blood pressure. Thin inner lining is smooth to reduce friction and allow diffusion. Lumen is the central cavity through which blood flows.
59
What is the role of valves?
To prevent the backflow of blood.
60
What are the two types of heart valves?
Semi-lunar valves Atrioventricular valves
61
Where are the semi-lunar valves?
Between ventricles and arteries (aorta or pulmonary artery)
62
Where are the atrioventricular valves?
Between atria and ventricles
63
When do the valves open and close?
Open when the pressure is higher behind the valve. Close when the pressure is higher in front of the valve.
64
What is the septum?
The cardiac muscle in the middle of the heart that separates oxygenated and deoxygenated blood. It maintains a high concentration of oxygen in oxygenated blood to maintain the concentration gradient for diffusion at respiring cells.
65
What is the cardiac cycle?
The pressure and volume changes within the heart and how that controls the opening and closing of valves and therefore the flow of blood.
66
What are the 3 stages of the cardiac cycle?
Diastole Atrial systole Ventricular systole
67
What is the relationship between pressure and volume?
If volume decreases pressure increases.
68
When does pressure in a heart chamber increase?
When it contracts
69
Which direction on the pressure gradient does blood flow?
From high to low pressure
70
Describe the distole stage of the cardiac cycle?
Atria and ventricle muscles are both relaxed. Blood enters the heart via the vena cava and pulmonary vein into the atria. The pressure in the atria increases. Atrioventricular valves open. Pressure in the pulmonary artery and aorta is higher than in the ventricles. Semi-lunar valves close.
71
Describe the atrial systole stage of the cardiac cycle?
Atria contracts. Atria muscle walls contract which increases the pressure further due to decreased volume. Atrioventricular valves are open so blood flows into the ventricles. (Ventricle walls are relaxed)
72
Describe the ventricular systole stage of the cardiac cycle?
Ventricle’s muscular walls contract (from bottom upwards) so volume in ventricles decreases. Pressure in the ventricles increases beyond that of the atria. Atrioventricular valves close. Pressure in the ventricles is higher than in the arteries so semi-lunar valves open. Blood flows from ventricles into the pulmonary arteries and aorta.
73
What does diastole mean?
Relax
74
What does systole mean?
Contract
75
What is cardiac output?
The volume of blood which leaves one ventricle in one minute (dm3min-1).
76
Equation for cardiac output
Cardiac output = heart rate x stroke volume Heart rate- beats of the heart per minute (min-1) Stroke volume- volume of blood which leaves the heart in each beat (dm3)
77
When do the atrioventricular valves close?
When ventricular pressure is higher than atrial pressure.
78
When do semi-lunar valves open?
When ventricular pressure is higher than pressure in arteries.
79
When do semi-lunar valves close?
When ventricular pressure falls below pressure in arteries.
80
When do atrioventricular valves open?
When pressure in atria is higher than ventricular pressure.
81
Why is the pressure change in the ventricles larger than that of the atria?
The ventricles have a thicker muscular walls than the atria so can contract with a greater force to generate a higher blood pressure.
82
What is tissue fluid and what does it contain?
The fluid in which tissues are bathed in. It contains glucose, amino acids, fatty acids, ions in solution and oxygen which it delivers to cells. It removes carbon dioxide and other waste products from cells. It surrounds the cells and tissues that surround capillaries to transport material to and from each cell and the capillary.
83
What is hydrostatic pressure?
The pressure exerted by water molecules.
84
What is osmotic pressure?
The pressure due to movement of water molecules (water potential).
85
Explain how tissue fluid is formed?
Capillaries have small gaps in their walls so that liquid and small molecules can be forced out. As blood enters the capillaries from arterioles, the smaller diameter causes a higher hydrostatic pressure. This forces water, glucose, amino acids, fatty acids, ions and oxygen into the tissue fluid (ultrafiltration). Plasma proteins are too large so remain in the capillaries, decreasing water potential of blood at the venous end (can’t fit through gaps in the capillary endothelium cells). Due to water moving out, hydrostatic pressure decrease further, and water potential decreases lower than that of the tissue fluid. Water re-enters the capillary by osmosis down the water potential gradient. Waste molecules like carbon dioxide and urea dissolve in water to re-enter the capillary and be removed.
86
What is the lymph vessel and its role?
Not all liquid will be reabsorbed by osmosis into the capillaries as an equilibrium will be reached. The rest of the tissue fluid is drained by the lymph vessel into the lymphatic system and eventually drains back into the bloodstream near the heart.
87
What are 4 types of heart disesase?
Atheroma Thrombosis Aneurysm Myocardial infarction
88
What is an atheroma?
Damage to the endothelium of artery causes white blood cells and lipids to clump together under the lining which builds up to block the lumen.
89
What is thrombosis?
Formation of a blood clot or atheroma that dislodges and blocks blood vessels elsewhere.
90
What is an aneurysm?
Swelling of the artery due to atheroma that cause high blood pressure. This pushes inner layers of artery out to from an aneurysm which may burst to cause a hemorraghe.
91
What is myocardial infarction?
Heart attack Coronary arteries blocked by a fatty deposit so heart muscle can’t receive oxygen for respiration so cannot beat.
92
What are the risk factors for cardiovascular disease and why?
High blood pressure- damages the walls of the blood vessels so fatty deposits or blood clots may form.; Smoking- chemicals narrow blood vessels and increase blood pressure. Stress- raises heart rate and increases blood pressure Diet- high in saturated fat and cholesterol increases risk of fatty deposit forming in blood vessels. Genetic factors- predisposed to develop CVD
93
What is transpiration?
The loss of water through the stomata by evaporation. It occurs in plants.
94
What are stomata?
Stomata are pores/holes on the underside of a plants leaves that water vapour evaporates out of.
95
What is the transpiration stream?
The movement of water continuously through the xylem (More water pulled up to replace water that evaporates out of the stomata)
96
What are guard cells?
Cells present on the lower side on a plants leaves that control the opening and closing of the stomata and therefore the rate of transpiration.
97
Describe the effect of light intensity on the rate of transpiration
Increased light intensity increases the rate of transpiration Higher light intensity means photosynthesis is taking place. More stomata are open so carbon dioxide diffuses into leaves for photosynthesis. Larger surface area in which water can evaporate out of.
98
Describe the effect of temperature on the rate of transpiration?
Increased temperature increases the rate of transpiration. More heat means water molecules have more kinetic energy. Therefore they move faster so more evaporation out of the stomata.
99
Describe the effect of humidity on the rate of transpiration?
Increased humidity decreases the rate of transpiration. More water molecules in air so higher water potential in the air outside of the leaf. Decreases the water potential gradient so less evaporation out of stomata.
100
Describe the effects of wind speed on the rate of transpiration?
Increased wind increases the rate of transpiration Wind will blow away humid air surrounding leaves containing water vapour. Helps to maintain water potential gradient so more water can evaporate out of stomata.
101
What is osmosis?
The net movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane.
102
Describe how water moves into root hair cells?
There is a higher water potential in the soil than in the root hair cell. Water moves down the water potential gradient into the root hair cell by osmosis. Water potential of root hair cell increases so water moves along a row of root hair cells by osmosis until it reaches the xylem.
103
Describe how the root hair cell is adapted for efficient absorption?
Long projection provides a large surface area for a faster rate of absorption of water by osmosis, and mineral ions by active transport. Many mitochondria to respire and produce ATP to absorb mineral ions by active transport. Lots of ribosomes to make specific carrier proteins for the active transport of mineral ions into the root hair cell. Thin membrane to provide a short diffusion distance which increases the rate of absorption of mineral ions and water.
104
Why is cohesion-tension important in the xylem?
Water moves up a plant through the xylem which goes against the force of gravity. This is able to occur due to cohesion tension theory.
105
What are the elements of cohesion tension theory?
Cohesion Adhesion Root pressure
106
Describe cohesion in the xylem?
Water is a dipole molecule (slightly negative oxygen and slightly positive hydrogen). This enables hydrogen bonds to form between the hydrogen and oxygen atoms of different water molecules. This creates a cohesion between water molecules (they stick together). Therefore, water travels up the xylem in a continuous column of water that is unbroken.
107
Describe adhesion in the xylem?
When water molecules adhere/stick to the xylem walls. This creates tension as it pulls the walls of the xylem inwards which causes water to move upwards. Therefore narrower the xylem, the larger the impact of adhesion. Adhesion makes water molecules less likely to fall back down the xylem due to the force of gravity.
108
Describe how root pressure affects water movement in the xylem?
Root pressure is an increase in pressure in the roots that forces water above it upwards, known as positive pressure. Water moves into the roots by osmosis, which increases the volume of liquid inside the roots and therefore the pressure inside the root increases (known as root pressure). This positive pressure pushes water above it upwards in a column up the xylem.
109
Describe the movement of water up the xylem?
THE TRANSPIRATION STREAM: Water vapour evaporates out of stomata on leaves, which creates a loss of water volume and so a lower pressure. When this water is lost by transpiration, more water is pulled up the xylem to replace it (moves due to pull of negative pressure on the water column behind it). Water moves down the pressure gradient from high pressure in the roots to low pressure in the leaves. Due to the hydrogen bonds between water molecules, they are cohesive, so stick together to create a continuous column of water within the xylem. Water molecules also adhere and stick to the walls of the xylem, which helps to pull the water column upwards. As this column of water is pulled up the xylem, it creates tension, which pulls the xylem inwards to become narrower, which increases the impact of adhesion further.
110
Describe how the xylem is adapted for efficient transpiration?
Xylem cells form hollow tubes with no end walls to allow the continuous flow of water. Lignin provides waterproofing to prevent loss of water by evaporation. Lignin provides strength to the xylem to reduce breakages.
111
What is a potometer and why is it useful?
A potometer measures the rate of uptake of water from a plant. It is near impossible to measure transpiration, so as water uptake is proportional to transpiration, this is used to indicate the rate or transpiration. They are used to investigate the effect of a named variable on the rate of transpiration eg. Light intensity, humidity, temperature, wind.
112
Describe how to use a potometer?
A sample is cut from a plant underwater to prevent any air from entering the xylem and breaking the water column. Potometer is filled with water and all air bubbles are removed. Plant attached to potometer using rubber seals and petroleum jelly to make the equipment airtight so no air can get in or water can leak out. One air bubble is introduced into the equipment and the distance that this air bubble has moved towards the plant is recorded. The rate of transpiration is equal to the distance the bubble moved (used to work out volume)
113
What are control variables needed when using a potometer?
Surface area of leaves of different plant species
114
What is translocation?
The process by which organic substances (sugars) are transported to all cells in a plant, via the phloem.
115
Where does translocation occur?
In the phloem
116
What is transported in the phloem?
Sugars made in photosynthesis are transported to other non-photosynthesising cells in the plant for respiration.
117
What direction is transport in the phloem?
Both directions- up and down the plant
118
What direction is transport in the xylem?
One direction- up the plant from roots to leaves
119
In what form are sugars transported in the phloem?
Sugars are transported as sucrose because it is less reactive than glucose (produced by photosynthesis).
120
What are the two key cells that make up the phloem?
Sieve tube elements Companion cells
121
What are the features of the sieve tube elements?
Living cells Contain no nucleus Contain very few organelles Have perforated ends to enable a continuous flow of sugar solution
122
What are the features of companion cells?
Provide ATP required for active transport of organic substances (sugars).
123
What is mass flow hypothesis?
Mass flow hypothesis describes the movement of organic substances in a plant. It describes how sugars move from a source cell to a sink cell. The source cell is the photosynthesising leaf cells, and the sink cell is the respiring cells throughout the plant. The sugars move through the phloem
124
What is the source cell?
Photosynthesising leaf cells Where the organic substances is created Glucose created in the leaves during photosynthesis and converted to sucrose.
125
What is the sink cell?
Respiring cell Where the organic substance is transported to and used Sucrose is transported to and used by respiring cells
126
Describe how sucrose is transported in the phloem?
Photosynthesis occurs in the chloroplasts of leaf cells (source cell) to create organic substances- glucose which is converted to sucrose. Sucrose moves into the sieve tube elements using the companion cell by active transport (it is co-transported with H+ ions but this is not on the specification). The increase in sucrose in the sieve tube element lowers the water potential. This causes water to enter the sieve tube element from xylem vessels by osmosis, and the increase in volume in the sieve tube element increases the hydrostatic pressure, so liquid is forced towards respiring cells (the sink). Sucrose is used up in respiration or stored as insoluble starch at the sink cells, so more sucrose is actively transported into the sink cell. This causes the water potential of the sink cells to decrease. This results in osmosis of water from the sieve tube element into the sink cell (and some water returns to the xylem) The removal of water decreases the volume in the sieve tube element so the hydrostatic pressure decreases. Movement of sucrose occurs due to the difference in hydrostatic pressure between the source and the sink end of the sieve tube element.
127
Describe how tracers can be used to investigate translocation?
Plants provided with only radioactive carbon dioxide which is absorbed into the plant and used in photosynthesis to create sugars. Slices from stems placed in x-ray machines that turns black when exposed to radioactive material. Highlights where sugars are and shows they are transported in the phloem to other parts of the plant.
128
Describe how ringing can be used to investigate translocation?
Ring of bark and phloem are peeled and removed off a tree trunk. Leads to swelling above the removed section and analysis of the liquid in this swelling shows it contains sugar. Shows that when phloem is removed, the sugars can’t be transported and therefore proves that the phloem transports sugars.

Biology (24 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions