chapter 7 - mass transport

Question 1

what is translocation?

Answer 1

Translocation is the movement of sugars and assimilate (amino acids and sucrose) through the phloem in both directions.

Question 2

What is transpiration?

Answer 2

Transpiration is the movement of water in a plant through the xylem vessels in only One Direction

Question 3

What is the structure of mature xylem

Answer 3

mature xylem or made of dead cells called vessel elements. They do not have end walls or living contents therefore they are hollow. This allows unrestricted unrestricted flow of water through the vessel. At certain points in the xylem walls there are pits (bordered pits) these are undignified regions and allow movement of water between xylem vessels. Xylem vessels are stacked end to end

Question 4

What is the function of lignin in the xylem

Answer 4

xylem cells are lined with a waterproof coat made of the polysaccharide ligament. Lignin provides the strength and support to the cell walls of the xylem and it prevents water from escaping the tube. The xylem can also withstand pressure changes due to the movement of water with the support of lignin.

Question 5

what is the function of vessels being being hollow in the xylem.

Answer 5

It provides minimum resistance to the flow of water up the xylem vessel.

Question 6

What is the function of bordered pits in this xylem

Answer 6

they allow the flow of water and mineral ions from one element to another linking water uptake in roots with transpiration in leaves.

Question 7

how are xylem vessels formed

Answer 7

Immature xylem vessels are waterproofed When lignin is deposited on the inside of their cell walls. This process of lignification kills the cells and allows for maximum flow of water through the hollow tubes.

Question 8

describe the cohesion tension theory for when water moves up the xylem of plants

Answer 8

water from the soil travels by osmosis into the root hair cells [large surface area] as there is more volume of water in the root there is now a high pressure in the root. This high pressure pushes water upwards from The xylem to the leaves where there is a negative pressure due to water being lost from evaporation (from exchange surfaces). hydrogen bonds between water molecules causes the column of water to not break [cohesion] water molecules are attracted to the walls of the xylem vessels (adhesion). As the column of water is pulled up the xylem it creates tension pulling in the xylem in to become narrower this increases capillary action.

Question 9

What are the four factors affecting the rate of transpiration

Answer 9

temperature -As the temperature increases the rate of transpiration increases as more water is being evaporated.

humidity- a lower humidity increases transpiration rate. as spaces are normally saturated with water where is outside the leaf it is less humid the greater the difference in humidity the faster the water vapor will diffuse out of the leaf.

air movement-greater air movement will increase transpiration rate. increases evaporation.

light intensity-higher light intensity will increase transpiration rate. stomata open in light and close in dark.

Question 10

What is a potometer

Answer 10

A potometer is a device used for measuring the rate of water uptake from a leafy plant shoot the main reason for water uptake is transpiration. By changing the the surrounding atmospheric conditions the effects of transpiration of wind, heat, humidity and light can be measured. Potometers are difficult to set up because air bubbles in the xylem of the plant or in the apparatus itself will prevent the device from working properly

Question 11

Describe the symplastic pathway

Answer 11

The movement of water between the cytoplasm and the vacuoles through the plasma membrane ‘s. This process is slow or compared to the Apoplasic pathway.

Question 12

Describe the apoplastic pathway

Answer 12

water and minerals are transported through the cell walls this is a faster process compared to the symplastic pathway.

Question 13

what two structures is the phloem made out of

Answer 13

companion cells

sieve tube elements

Question 14

Where is the xylem located and where is the flow am located in vascular bundles

Answer 14

The xylem is located on the inner side of the vascular bundle and the phloem is located on the outside of the vascular bundle

Question 15

Describe the structure of phloem tissue

Answer 15

Sieve tube elements are lined up end to end to allow the flow of sap. Sieve tube elements have little cytoplasm and no nucleus to maximize space for sap. However the cell is still alive. Between the ends of sieve tubes are sieve plates.

Companion cells control transport in the sieve tube elements. Companion sells may contain mitochondria because the phloem requires active transport to move sap in translocation.

Question 16

What is a source

Answer 16

A source is a region of the plant where sucrose is loaded into the phloem, this could be the leaf as this is where photosynthesis takes place, producing glucose / sucrose. However it could also be a storage or getting West starch is stored/hydrolyzed and sugars are released.

Question 17

What is a sink

Answer 17

A region of the plant where sucrose is removed from the phloem. This could be the root tip or bud [growth points] storage organs or where sugar is used in respiration or converted into starch for storage.

Question 18

how does the process work at the source

Answer 18

Sucrose is actively loaded into the sieve tube elements this requires a companion cell to transport H+ ions and sucrose into the STE. This lowers the water potential in the STE therefore water moves into the STE by osmosis from the xylem from a less negative to a more negative water potential. This generates a high hydrostatic pressure causing mass flow towards the sink cells.

Question 19

describe the process at the sink

Answer 19

sucrose is unloaded and enters the sink cells. This lowers the water potential of the sink cells. Water followed by osmosis from the sieve tube down a water potential gradient. A lower hydrostatic pressure is produced

Question 20

describe active loading at the source

Answer 20

H+ ions are pumped out from the companion cells to the surrounding leaf tissue creating a diffusion gradient of H+ using active transport. H+ ions diffuse back into the companion cells through co-transporter proteins bringing sucrose with them. High concentrations of sugar in companion cells cause sucrose to defuse into the STE.

Question 21

Describe the radioactive tracer method for evidence of translocation

Answer 21

radioactive carbon 14 [C14] can be used to follow the path of organic substances in a plant. The plant is supplied with CO2 and is allowed to photosynthesize. The sucrose produced will contain radioactive carbon as the sucrose moves to other parts of the plant it can be detected using autoRadiography. The sample is exposed to photographic/x-ray film and any radioactive areas will produce a dark shadow on the film showing where sucrose has been transported to.

Question 22

Describe the ringing experiment for evidence of translocation

Answer 22

Ringing a plant means to remove a ring of phloem tissue around the circumference of a plant [the xylem is left in tact] this will mean that sucrose cannot be transported past at this point. When phloem tube is cut the flow in sap oozes and this is simple evidence to suggest that the contents of the tube or under pressure. [This is usually studied in conjunction with a radioactive tracer]

Question 23

Describe the structure of a hemoglobin molecule and how it is formed

Answer 23

primary structure-Sequence of amino acids in four polypeptide chains.
Secondary structure-in which each of these polypeptide chains is coiled into a helix.
tertiary structure-each polypeptide chain is folded into a precise shape for the ability to carry oxygen. Quaternary structure-for polypeptides are linked together to form an almost safari cool molecule each polypeptide [4] is associated with a haem group. which contains a FE2+ ion. each ion can combine with a single oxygen molecule. Making a total of four oxygen molecules that can be carried by a single hemoglobin molecule in humans.

Question 24

Describe the process in which oxygen binds to hemoglobin

Answer 24

The process is called loading or association. in humans this takes place in the lungs.

When there is a high partial pressure of oxygen there is high affinity and oxygen associates

Question 25

Describe the process of hemoglobin releasing oxygen

Answer 25

This process is called unloading or disassociating. In humans this takes place in the tissues or muscles.

When there is a low partial pressure of oxygen there is a lower affinity and oxygen disassociates

Question 26

What does hemoglobin with a high affinity for oxygen mean

Answer 26

hemoglobin with a high affinity for oxygen takes up oxygen more easily but releases it less easily

When there is a high partial pressure of oxygen that is a higher Finity and oxygen associates

Question 27

what does hemoglobin with a low affinity for oxygen mean

Answer 27

hemoglobin with a low affinity of oxygen means that it takes up oxygen less easily and releases it more easily

When there is a low partial pressure of oxygen that is a low affinity and oxygen disassociate

Question 28

How many Beta chains and how many alpha chains are in a single molecule of hemoglobin

Answer 28

They are two Beta chains and two alpha chains in a single molecule of hemoglobin

Question 29

What is formed when hemoglobin is combined with oxygen

Answer 29

Oxyhemoglobin

Form via a condensation reaction

Question 30

What does partial pressure of oxygen mean

Answer 30

It is a measure of how much oxygen is available to hemoglobin

Question 31

Describe the oxygen disassociation curve for adult hemoglobin

Answer 31

The code is an S shape due to the behavior of hemoglobin in different partial pressures

The first oxygen molecule combines with hemoglobin and slightly distorts it the joining of the first molecule is quite slow. After the first molecule has joined the quaternary structure of hemoglobin has changed making it easier for the second and third oxygen to join. this is shown by the curve becoming steeper. joining the fourth Oxygen molecule is more difficult as the majority of the binding sites are occupied so it is less likely that the oxygen molecule can reach an empty site.

This is called positive Cooperativity As the binding of the first molecule made the binding of the second easier

Question 32

describe the oxygen disassociation curve with the effects of carbon dioxide

Answer 32

In the presence of carbon dioxide hemoglobin has a reduced affinity for oxygen. The greater the concentration of carbon dioxide the more readily the hemoglobin releases its oxygen [bohr affect] When red blood cells reach a capillarity in a muscle the tissue will have a low partial pressure of oxygen because the tissues have been using oxygen for respiration. Oxyhemoglobin will unload completely in the presence of carbon dioxide [from respiring muscles]. This releases oxygen more readily for respiration and the dissolved carbon dioxide is acidic on the low pH cause the hemoglobin to change shape.

Question 33

Describe the three factors affecting hemoglobin saturation

Answer 33

Blood pH-lowering blood pH causes the presence of H+ ions from lactic acid or carbonic acid to reduce the affinity for hemoglobin so more oxygen is delivered to acidic sites which are aspiring more.

Blood temperature-and increased blood temperature reduces hemoglobin affinity hence more oxygen is delivered to warmed up tissue

Carbon dioxide concentration-the higher the carbon dioxide concentration in tissue the less affinity of hemoglobin for oxygen so the higher the rate of respiration the more oxygen is released.

Question 34

Comparing fetal and maternal hemoglobin

Answer 34

Fetal hemoglobin has a much greater affinity for oxygen because it binds too oxygen from the mothers blood stream.

The fetal hemoglobin can combine with a much higher percent of oxygen it will combine until it is 60% saturated. This allows the fetus to obtain oxygen from the Mum’s blood at low partial pressures

Question 35

Why do large organisms have a transport system

Answer 35

Large organisms have a transport system because diffusion is fast enough for transport over short distances however the efficient supply of materials over larger distances requires a mass transport system.

Question 36

What happens to the surface area to volume ratio when an organism increases in mass [size]

Answer 36

The surface area to volume ratio decreases

Question 37

Features of transport systems

Answer 37

• A suitable medium to carry materials [blood] this is usually a liquid because water dissolves in substances and can be moved around easily but it can also be a gas such as a breathed in and out of the Lungs.
• A closed system of tubular vessels that contain the transport medium and form a branching network to distribute it to all parts of the organism
• A mechanism for transporting medium within the vessels [pressure difference]

Question 38

Features of a transport system in plants

Answer 38

• Mechanism to maintain the mass flow of movement in one direction [valves]
• A way of controlling the flow of the transport medium to suit the changing needs of the different parts of the organism
• Mechanism for the mass flow of water or gas is for example intercostal muscles and die from during breathing in mammles

Question 39

Circulatory systems in mammals

Answer 39

mammals have a closed double circulatory system in which blood is confined to vessels and passes twice through the hot for each complete sack of the body. The vessels make up the circulatory system of a mammal which is divided into three parts [arteries, veins, capillaries]

Question 40

Describe the structure of the heart

Answer 40

aorta-connected to the left ventricle I’m carries oxygenated blood to all parts of the body accept the Lungs.
Atrium-thin walled, above ventricles, collects blood
Ventricle-has a much thicker muscular wall and has to contract strongly to pump blood either to the Lungs or the rest of the body
Atrioventricular valves-prevent the backflow of blood into the atria when ventricles contract.
vena cava- brings deoxygenated blood back from the tissues to the heart. connected to RV.
Pulmonary artery-connected to the RV I’m carries deoxygenated blood to the lungs.
Pulmonary vein-connected to the LA and brings oxygenated blood back from the lungs.

Question 41

What is the equation for cardiac output

Answer 41

Cardiac output = heart rate X stroke volume

Question 42

explain diastole

Answer 42

The atria and ventricular muscles are relaxed. blood will enter the atria via the vena cava and pulmonary vein. The blood flowing into the atria increases the pressure in the atria.

Question 43

explain atrial systole

Answer 43

The atrial muscular walls contract increasing the pressure, this causes the atrioventricular valves to open and blood to flow into the ventricles and the ventricular walls remain relax

Question 44

explain ventricular systole

Answer 44

The ventricle muscular walls contract increasing the pressure further than the pressure of the atria. This causes the atrioventricular valves to close and the semi lunar valves to open. The blood is pushed out of the ventricles into the arteries.

Question 45

What is the function of the atrioventricular valves

Answer 45

The atrioventricular valves separate the atria from the ventricles on each side of the heart. They prevent the backflow of blood from the ventricles into the atria during systole

Question 46

what is the function of the semi lunar valve‘s

Answer 46

They prevent the backflow of blood from the main artery back into the associated ventricle during ventricular diastole

Question 47

What are the different types of blood vessel

Answer 47

Arteries carry blood away from the heart into arterioles. arterioles are smaller arteries that control blood flow from the arteries to capillaries

capillaries are tiny vessels that link arterioles to veins

Veins carry blood from capillaries back to the heart.

Question 48

what is the main structure of arteries, arterioles and veins

Answer 48

A tough fibrous outer layer-resists pressure changes from both within and outside

Muscle layer- that can contract and control the flow of blood

Elastic Layer- Helps to maintain blood pressure by stretching and springing back [recoiling]

Thin inner lining endothelium - Smooth to reduce friction and thin to allow for diffusion

Lumen-central cavity of the blood vessel where the blood flows

Question 49

Structure of an artery related to its function

Answer 49

The muscle layer is thick compared to veins, the elastic Leah is thick compared to veins because the pressure in the arteries is high. Helps to resist the vessel busting under Pressure.

Question 50

Structure of arterioles related to its function

Answer 50

The muscle layer is relatively thicker than arteries, the contraction of this muscle allows construction of the lumen, controls blood movement into the capillaries that supply tissues with blood. The elastic layer is relatively thinner than in arteries, Because the blood pressure is lower

Question 51

Structure and function of veins

Answer 51

The muscle layer is relatively thin the construction and dilation cannot control the blood flow two tissues. The elastic layer is relatively thin, that is a low pressure of blood within the walls and this won’t cause the veins to burst. The overall thickness of the wall is small, it allows the veins to flatten easily, This aids the flow of blood within them. The valves are at intervals throughout, ensuring that blood doesn’t flow backwards as the pressure is low, valves make sure blood is flowing in one direction only [towards the heart]

Question 52

Structure and function of capillaries

Answer 52

Capillaries have thin walls-making them extremely thin so the distance over diffusion is short and allows for rapid diffusion. They are highly branched for a large surface area for exchange. They have a narrow diameter for a short diffusion pathway. They have a narrow lumen for a short diffusion pathway

Question 53

What is tissue fluid

Answer 53

Tissue fluid is a Substance well material is exchanged between blood and cells. It’s supplies fatty acids, ions, amino acids, glucose to the tissues. It’s receives carbon dioxide and other waste materials from tissues also.

Question 54

How is tissue fluid formed

Answer 54

Tissue fluid is formed in the blood plasma. at the arteriole ends of the capillaries. hydrostatic pressure causes tissue fluid to move out of the blood plasma. The pressure is only high enough to force small molecules out of capillaries leaving the rest in the blood because these are too large to cross the membrane. This type of filtration is called ultra filtration

Question 55

The return of tissue fluid to the circulatory system

Answer 55

Most tissue fluid returns to the blood plasma directly via the capillaries. not all the tissue fluid can return to the capillaries the remainder is Carried back via the lymphatic system

Question 56

Risk factors associated with cardiovascular disease smoking

Answer 56

Carbon monoxide combines easily with hemoglobin in red blood cells to form carboxyhemoglobin. This reduces the oxygen capacity of the blood. making the heart work faster increasing blood pressure, increasing CHD and stroke.

Nicotine stimulates the production of the hormone adrenaline which increases heart rate and raises blood pressure this increases the risk of smokers suffering CHD or a stroke. Nicotine also makes platelets in the blood more sticky and this leads to a higher risk of thrombosis.

Question 57

Risk factors associated with cardiovascular disease high blood cholesterol

Answer 57

High density lipoprotein [HDLs]remove cholesterol from the tissues and transport it to the liver for excretion they help to protect arteries against heart disease

Low density lipoprotein’s [LDLs] transport cholesterol from the liver to the tissues including the artery walls, leading to the development of atheroma which may lead to heart disease

Question 58

Risk factors associated with cardiovascular disease diet

Answer 58

There’s a number of aspects of diet that increase the risk of heart disease

High levels of salt raise blood pressure
High levels of saturated fats increase low density lipoprotein levels and hence blood cholesterol concentration

Question 59

What is myoglobin

Answer 59

It is a version of haemoglobin that is found in foetuses. It is also a protein found in striated muscles and heart muscles. It’s supplies oxygen to cells in the muscles and heart.

Question 60

What way does the oxyhaemoglobin curve shift in the presence of carbon dioxide/the Bohr effect

Answer 60

it’s just to the right. The affinity for oxygen decreases because of the acidic carbon dioxide which changes the shape of haemoglobin slightly. In the presence of carbon dioxide partial pressure of oxygen decreases meaning that there is a lower affinity for oxygen therefore more oxygen disassociates

even at the same partial pressure. more O2 dissociates

Question 61

Give an example of where there would be a low partial pressure of carbon dioxide

Answer 61

in the alveoli

there is a low partial pressure of carbon dioxide
therefore there is a low affinity for carbon dioxide
there is a high dissociation for carbon dioxide
Therefore there is an increased affinity of oxygen

Question 62

Give an example of where there are high partial pressure of carbon dioxide

Answer 62

in respiring tissues

there is a high partial pressure of carbon dioxide
there is a high affinity for carbon dioxide
there is low disassociation of carbon dioxide
there is a low affinity for oxygen
there is a high dissociation for oxygen

So oxygen unloads more often

Question 63

Why is it advantageous that fetal haemoglobin has a higher affinity for oxygen at the same partial pressure

Answer 63

Fetal haemoglobin/myoglobin having a higher affinity means that oxygen loads more easily from the mothers haemoglobin

Question 64

Llamas live in high altitude conditions. Why is it advantageous that llamas have a high affinity for oxygen even at lower partial pressures

Answer 64

This means that at a lower partial pressure a high affinity for oxygen means that oxygen loads more easily onto the haemoglobin. haemoglobin is still able to load even when there is not much oxygen available at high altitudes

Question 65

doves fly a lot therefore have a fast metabolism. They need more oxygen for respiration and to provide energy for contracting muscles. The curve for the doge shift to the right meaning that there is a lower affinity for oxygen even at the same partial pressure of oxygen explain why

Answer 65

lower affinity for oxygen means that oxygen loads less easily but oxygen disassociate more easily to respire in muscles and tissues. This provides energy for respiration and contracting muscles. oxygen unloads more readily

Question 66

Earthworms live underground explain why they have a higher affinity for oxygen even at the same or lower partial pressures for oxygen

Answer 66

Underground there is less oxygen therefore a lower partial pressure of oxygen. Having a higher affinity for oxygen means that more oxygen loads onto haemoglobin.

Question 67

Why do mammals have a double circulatory system

Answer 67

mammals require a double circulatory system to manage the pressure of blood flow.

The blood flows through the lungs at a lower pressure. This prevents damage to the capillaries in the alveoli and also reduces the speed at which the blood flow is enabling more time for gas exchange.

The oxygenated blood from the lungs then goes back through the heart to be pumped out at a higher pressure to the rest of the body this is important to ensure that all of the blood reaches all of the respiring cells in the body.

Question 68

What are the coronary arteries

Answer 68

they surround the heart muscle and tissue itself. The coronary arteries supply the cardiac muscle/heart muscle with oxygenated blood. 

Coronary arteries branch off from the aorta. Supply the cardiac muscle with oxygenated blood and glucose

Question 69

What does the superior vena cava do

Answer 69

carries blood from the head, neck, arms and chest to the heart

Question 70

What does the inferior vena cava do

Answer 70

It’s carries blood from the legs, feet, abdomen and pelvis back to the heart

Question 71

What does the aorta do

Answer 71

Carries blood from the heart to the rest of the body at high-pressure

Question 72

What does the pulmonary artery do

Answer 72

Carries blood from the right side of the heart to the lungs

Question 73

What does the pulmonary vein do

Answer 73

Carries oxygenated blood from the lungs back to the heart

Question 74

What does the renal artery do

Answer 74

Carries blood from the heart to the kidneys

Question 75

What does the renal vein do

Answer 75

Carries blood from the kidneys to the heart

Question 76

What is the advantage of the cardiac muscle/the heart being myogenic

Answer 76

it’s can contract and relax without nervous or hormonal stimulation. 

it never fatigues as long it has a constant supply of oxygen and glucose it will be able to respite aerobically.

Question 77

What is the advantage of the cardiac muscle and the walls of the heart having a thick muscle layer

Answer 77

It’s kind contract and relax. Eight ton contract with a high force which delivers oxygenated blood to the whole body. Contracting with a high force causes/creates high pressure

Question 78

what happens when the Coronary arteries become blocked

Answer 78

if they become blocked the cardiac muscle won’t receive oxygen therefore it will not be able to respire and the cells will die. This results in myocardial infarction (a heart attack)

Question 79

Why do the atria have thinner muscular walls and elastic walls

Answer 79

having thinner muscular walls means that the atria do not need to contract as hard as they are not pumping blood far

The atria having elastic walls enables it to stretch when blood enters

Question 80

Why did the ventricles have thicker muscular walls

Answer 80

Enables it to have a larger contraction, this creates a high blood pressure to enable blood to flow longer distances to the lungs and the rest of the body

Question 81

Why does the right Ventricle have a thicker muscular wall compared to the left ventricle

Answer 81

The right ventricle pumps blood to the lungs therefore it has a thinner muscular wall as you don’t want to damage the lungs with a higher pressure

Question 82

Why does the left ventricle have a thicker muscular wall than the right ventricle

Answer 82

The left ventricle pumps blood to the body does needs to be at a higher pressure to ensure blood reaches all of the cells in the body.

Question 83

What is the name for the atrioventricular valve on the left

Answer 83

bicuspid

Question 84

What is the name for the atrioventricular valve on the right

Answer 84

Tricuspid

Question 85

How do valves enable blood to flow in One Direction

Answer 85

valves only open when the pressure is higher behind the valve.  if the pressure is greater in front of the valve the valves close/shut to prevent the backflow of blood

Question 86

What is the function of a septum in the

Answer 86

The septum separates deoxygenated blood and oxygenated blood

This maintains a high concentration of oxygen in the oxygenated blood. This maintains a high concentration gradient when diffusion occurs at respiring cells

Question 87

Why is there a thick muscle layer in the arteries

Answer 87

So that constriction and dilation can occur to control the volume of blood therefore controlling the pressure. Blood pressure in the arteries is high therefore having a muscle layer allows the arteries to change its diameter maintaining Blood pressure and controlling blood flow

Question 88

Why is there a thick elastic layer in the Arteries

Answer 88

To help maintain blood pressure. The walls can stretch and recoil in response to the heartbeat

Question 89

Why the walls thicker in arteries

Answer 89

To help prevent the vessels busting during high pressure

Question 90

What is tissue fluid

Answer 90

Tissue containing water, glucose, amino acids, fatty acids, ions an oxygen which makes up the tissue

Question 91

How is tissue fluid formed

Answer 91

as blood enters the capillaries from the arterial is the smaller diameter in the capillaries result in a high hydrostatic pressure

Water, glucose, amino acids, fatty acids, ions and oxygen of forced out. ultrafiltration

 Red blood cells, platelets, large proteins remain in the capillary

At the venule end of the capillary, large molecules remain in the capillaries creating a lowered water potential. Hydrostatic pressure is also lowered due to the loss of liquid

water enters the capillaries by osmosis.

waste that has dissolved in the tissue fluid is carried into the capillaries by osmosis as well when water is reabsorbed. eg CO2 and urea.

Question 92

What happens to the excess liquid that is not reabsorbed by osmosis once equilibrium is reached

Answer 92

The rest of the tissue fluid is absorbed into the lymphatic system. This eventually drains back into the bloodstream near the heart

Question 93

How does root pressure in the roots of a plant help in the cohesion tension theory

Answer 93

as water moves into the roots by osmosis it increases the volume of liquid inside the route and therefore the pressure inside the route increases. This is known as root pressure. This Increase in pressure in the roots forces Water upwards. (Positive pressure)

Question 94

What is a source

Answer 94

Why the glucose is made e.g. photosynthesising leaf cell

Question 95

What is a sink cell

Answer 95

A respiring cells/where the glucose is delivered

Question 96

Describe the source to sink Explanation

Answer 96

in the source cells glucose that is being made by photosynthesis will lower the water potential in the source cells. Sucrose lower the water potential. Water enters by osmosis via surrounding cells.

where we have respiring sink cells sucrose is being used up by respiration. Therefore there is a more positive water potential. Water leaves the sink cells by osmosis.

there is an increase in the hydrostatic pressure at the source cells and a decrease in hydrostatic pressure at the sink cells. The solution at the source is forced towards the sink via the phloem. 



Question 97

What are some ways that you can look at biodiversity/measure biodiversity

Answer 97

species diversity – the number of different species and individuals within each species in a community

genetic diversity-variety of genes amongst all the individuals in a population of one species

Ecosystem diversity-the range of different habitats