B3.2 Transport

What is the cause of transpiration pull?

Cell walls of leaf drawing out water via the xylem. This generates tension.

What is the consequence of transpiration pull?

if there is a continuous water stream the tensions are transmitted all the way down to the root moving water upwards to the top of a tree/plant

Where does the energy for transpiration come from ?

It is a passive process but all the ebay required comes from the thermal energy that causes it.

Why does water transport rely on cohesion between molecules?

Because water has to resist the low pressures in the xylem vessels to ensure that the water column wouldnt break. Without cohesion this column would break.

Cavitation

column of liquid breaking due to lack of cohesion.

How are the xylem vessels adapted for water transport under low pressure?

They are formed of columns of cells

how is the xylem able to maintain rigidity under low pressure?

The vessel walls are thickened with a polymer

function of xylem in stems

transport of water from roots to leaves

function of phloem in stems

transport of sugars from leaves to roots

function of cambium in stem

production of more xylem and phloem

function of cortex in stem

support and photosynthesis

function of pith in stem

bulking out the stem

function of epidermis in stem

waterproofing and protection

how can xylem and phloem differentiate in cross-sections of stem?

Xylem is usually on the inner side of a vascular bundle and phloem on the outer side (cambium with stem cells is inbetween)

Function of epidermis in roots

absorbs water and mineral ions from soil using root hairs

Role of xylem in roots

transports water from the roots up to the stem and leaves

Role of the phloem in roots

transports sucrose from the leaves to the roots

Role of the cortex in the roots

unspecialised cells that bulk out the root to strengthen it and increase its surface area

Role of the endodermis in the root

consists of an inner skin of cells that water must pass through to reach the xylem.

How can the xylem and phloem differentiate in cross-sections of a root?

Xylem forms a star in the centre of a root and the phloem forms cicles in between the star points

List components of blood plasma

• water

• glucose

• amino acids

• mineral ions

• vitamins

• hormones

• plasma proteins

define tissue fluid

fluid that leaks out of capillaries

what is the cause of diffusion of plasma into the capillary network?

capillaries close to arteries tend to release fluid as blood supplied by arteries are at a high pressure

When does reuptake happen in capillaries ?

capillaries that are close to veins where the blood pressure is significantly lower

Compare the substances found in blood plasma and tissue plasma

Tissue fluid contains oxygen glucose and all other substances in blood plasma except from large proteins as they cannot pass through the capillary walls.

Describe the direction of transport of substances that are exchanged between tissue fluid and cells

the fluid flows between cells in a tissue which allows the cells to absorb useful substances.

How is oxygen absorbed from tissue fluid?

Via diffusion because o2 concentration in cells is lower due to aerobic respiration

How is carbon dioxide absorbed ?

It diffuses out of cells into tissue fluid along with other waste products of metabolism.

How is glucose absorbed?

Absorbed by sodium glucose co-transporters

How are waste products removed from the body?

As the tissue fluid flows between tissue cells it accumulates waste products. The tissue fluid then re enters the capillary network and the waste products from into venules to be taken out of the tissue. Co2 is removed by the lungs and other waste products are detoxified by the liver or excreted by the kidneys.

Why is there a need to drain excess tissue fluid into lymph ducts?

prevents oedema (swelling)

what is the structure of lymph ducts?

narrow blind ended vessels with permeable walls. There are an array of narrow vessels that join up to form wider lymphatic vessels creating the right and left lymphatic ducts.

How is lymph returned to the blood circulation?

Right and left lymphatic ducts merge with the subclavian veins so lymph is returned to the blood system.

What is the function of the heart and lungs or gills in blood circulation?

The heart pumps blood around the body while the lungs and gills act to oxygenate the blood

Why must the mammalian heart function as a double pump?

It contains both pulmonary and systemic circulation. The pulmonary circulation receives deoxygenated blood to oxygenate it at the lungs whilst the systemic circluation pumps blood around the body

Ventricles

Chambers of a strong muscular wall that can generate high blood pressure when it contracts

Atria

Chambers with a thinner muscular wall that collects blood from the veins and pumps it onto the ventricle

Atrioventricular valves

valves between the atria and ventricles that prevent backflow of blood to the atrial when the ventricles contract

Semilunar valves

between the ventricle and the artery. they closed to prevent the backflow of blood to the ventricles when ventricles are relaxed

Cardiac muscle

specialised muscle tissue that forms the war between the ventricles and the atria

Pacemaker

sinoatrial node in right atrium wall that initiates each heartbeat by sending an electrical signal into the atria

Septum

wall between the left and right ventricles and atrium. it prevents oxygenated and deoxygenated blood mixing

Coronary vessels

coronary arteries and veins in the wall of the heart

define myogenic contraction

generated in the heart muscle itself

define cardiac cycle

sequence of action that the heart follows

What is the role of pacemaker cells?

initiates each turn of the cycle by sending out an electrical signal that spreads through atria walls

What is the propagation of the electrical signal from the SA node through the atria and ventricles?

Causes left and right atria to contract. There is then a 0.1 second delay before this signal is conveyed to the ventricles. This allows the ventricles to fill up with blood. The signal is then sent through the ventricles causing them to contract and push blood into arteries

Explain the flow of blood during systole and diastole

during systole the heart muscle is contracting causing pressure increase as blood is transported to the next ‘part’. In diastole the heart is relaxing and filling a chamber with blood causeing a pressure drop.

Define systolic blood pressure

represents the pressure in your arteries when your heart contracts and pumps blood out to your body

define diastolic blood pressure

represents the pressure in your arteries when your heart muscle is relaxed and filling with blood between beats

What Conditions May a plant generate root pressure to transport water?

• high atmospheric humidity dreventing diffusion of water vapour through stomata to air

• At night stomata is closed preventing transpiration which may allow xylem to become air filled as sap sinks to roots

• Decidious trees that are leafless in winter → xylem is air fille debut has to refill with sap before new leaves are grown

What is root pressure?

mechanism used to refill xylem with sap when they have been airfilled.

How do roots maintain positive pressure potential when evaporation is insufficient to move water through the plant?

Root cells adjacent to xylem vessels load mineral ions into the vessels by active transport. Pump proteins that carry out active transport are in the plasma membrane of living cells. Active transport makes sap hypertonic compared to cytoplasm of adjacent cells so water moves from them to xylem vessels via osmosis. This raises the pressure in the vessels pushing the sap upwards.

define translocation

process where dissolved substances are moved from sources to sinks through phloem

define phloem sap

Solution of sucrose and other compounds being transported

define source

tissues of the plant where compounds are being produced by photosynthesis or are being unloaded from a store

define sink

tissues that need to be supplied with substrates for cell respiration or anabolic reactions for growth.

list example source tissues

Leaves because they produce carbon compounds by photosynthesis

List example sink tissues

roots because they need substrates for cellular respiration

outline the structure of sieve tube elements

they develop from columns of cells. Adjacent cells become connected by large perforations in the end walls

outline the function of Sieve tube elements

they load and unload sucrose (via active transport)

Outline the structure of companion cells

they have many mitochondria and fine cytoplasmic connections.

Plasmodesmata

fine cytoplasmic connections

outlines function of companion cells

Supply mitochondria to sieve tube elements

How is hydrostatic pressure created?

high solute concentrations develop in the sieve tubes of the leaf which draws in water by osmosis

Describe how the structure of capillaries are adapted to it’s function

• Layer of endothelium cells

• Basement membrane

• Pores

• Tissue fluid

Endothelium cells

these cells have a coating of extracellular fibrous proteins which are crosslinked to form a gel

Pores

allow blood plasma through but not red blood cells

Basement membrane

acts as a filter that allows small or medium particles to pass through

Tissue fluid

contains oxygen, glucose and other substances in plasma except large protein molecules

• flows between cells in a tissue allowing them to absorb and excrete waste products

Fenestrated capillaries

greater number of large pores in the walls

• allow larger volumes of tissue fluid to be produced which speeds up exchange between the tissue cells and the blood

diameter of capillaries

10um (micrometres)

Compare the function of arteries and veins

Arteries carry high pressure blood away from the heart while veins carry a low pressure stream of low pressure blood from organs to the heart

What are the 3 artery walls?

• tunica externa

• tunica media

• tunica intima

Tunica externa structure

tough outer layer of connective tissue with collagen fibres

Tunica media structure

thick layer containing smooth muscle and elastic fibres made of the protein elastin

Tunica intima structure

a smooth endothelium forming the lining of the artery.

How is the artery adapted to withstand high pressure ?

it has a thick muscular wall containing elastic fibres and collagen and narrow lumens

How do elastic fibres help to reduce energy expediture ?

they stretch and store potential energy as blood enters the artery and when the pressure falls at the end of each heart beat the stretched fibres return the energy by recoiling and squeezing the blood in the lumen

Unit of measurement of pulse rates

beats per minute

Two methods for determining heart rate:

Wrist and neck pulse measurements or using digital metres

How are veins adapted to help blood flow ?

contains valves to prevent backflow

How does the valve mechanism work ?

If blood starts to flow backwards it will get caught in flaps of the pocket valve which fill with blood and close the valve to block the lumen. if blood is flowing to the heart the flaps are pushed against the wall allowing flow

Function of coronary arteries:

supply the muscular heart walls with blood

• 3 main arteries - branches from aorta to create right coronary artery and left coronary artery which further splits into 2 to supply the left anterior and left posterior heart regions

Cause of coronary occlusion

fatty deposits build up in the arteries, containing lipids such as cholesterol

Consequence of coronary occlusion

restrict blood flow to downstream region of heart wall causing chest pain or shortness of breath

Causes of a heart attack

fatty deposits harden as they become impregnated with calcium slats, triggers formation of blood clot (thrombosis) which blocks blood flow to muscular wall of heart

Myocardial infarction

tissue death in the heart muscle due to inadequate blood supply

Coronary heart disease

conditions associated with narrowed or blocked coronary arteries

What factors are correlated with an increased risk of heart attacks or coronary occlusions ?

• hypertension

• smoking

• eating too much fat or cholesterol

• obesity

• high salt intake

• excessive alcohol consumption

• sedentary lifestyles

• genetic predisposition

• old age

What is the xylem used for ?

tissue used to transport water in plants

Role of cellulose in water transport

cellulose is in the cell walls which creates adhesion between the wall and water molecules. Water can then be drawn into the pores created in between cellulose molecules.