topic 4 Flashcards
Why is transport needed in cells?
- cells require supply of chemicals (glucose + oxygen for cellular respiration = must be transported from outside the organism into the cell.
- waste products such as CO2 must be transported out of the cell before it causes damage.
- cells need to transport substances made in one area to another or out of cell completely
The fluid mosaic model of the cell membrane
cell surface membrane controls transport of materials in/out of cells
- Fluid - phospholipid molecules can move around within each layer freely = membrane is flexible and can change shape.
- Mosaic - protein molecules are scattered around the membrane
Phospholipid bilayer with hydrophobic polar tails facing inwards on themselves and hydrophilic heads facing out.
Glycoproteins ( proteins with carbohydrate added)
- act as antigens on outer surface acting as receptors and important for cell recognition
Integral proteins
- can form pores / channels = allow specific molecules to move through (gated channels open + shut depending on conditions of cell) or simple gaps in lipid bilayer that allow ionic substances to move through in both direction
Peripheral proteins (can be enzymes)
- Form temporary bonds with the cell membrane, allowing them to detach + reattach at specific times - involved in regulating transport by eg cell signalling.
2 Main types of transport in cells?
Passive transport - involves no energy from cell, takes place due to concentration / pressure
Active transport - involves moving substances in or out cell up a conc gradient using ATP produced from cellular respiration.
3 Passive transport mechanisms?
-
Diffusion - movement of particles in liquid/gas down a concentration gradient from area of high conc to low conc as a result of random movements, until they reach a uniform distribution.
[after that equal numbers of particles move in all directions= doesn’t change conc]
- the phospholipids in bilayer just simply move apart to allow it pass through - Facilitated diffusion - diffusion that takes place through carrier proteins or protein channels
-
Osmosis - movement of water molecules down a conc gradient through a partially permeable membrane.
- water passes through channel protein to avoid the hydrophobic centre of phospholipid bilayer
3 Active transport mechanisms
-
Endocytosis - movement of large molecules into cells through vesicle formations.
[cell extensions (pili) engulf material to form a vesicle = which enters the cytoplasm] -
Exocytosis - movement of large molecule out of cells by the fusing of a vesicle containing the molecule with the surface cell membrane.
[Vesicles fuse with cell membrane to release the contents from cell] - Active transport - Movement of substances across membrane of cells directly using ATP (often up a conc gradient)
Facilitated diffusion through gated channels and carrier proteins
which type of substances use this?
- gated channels - open only when a specific molecule is present or there is an electrical change across membrane, and then close afterwards.
- Carrier proteins are specific for particular molecules, depending on the shape of the protein and the substance being carried.
- once the protein carrier of specific shape picks up substance from area of high conc, it changes shape
=allowing the molecules to get passed into the cell/area of low conc
- protein carrier then returns to its original shape - to allow more molecules to enter and then repeat.
it can only work when conc gradient is in the right direction as it does not use ATP (its passive)
Used by charged substances (eg glucose) because the cell membrane repels them.
Factors that affect rate of diffusion?
- surface area ( large SA = higher rate, as more particles can be exchanges at same time due to larger surface available)
- temperature (higher temp = move faster = higher rate)
- concentration (steeper conc gradient = the faster the particles move = higher rate)
- membrane thickness ( the distance they have to travel = shorter diffusion distance/thinner membrane = faster diffusion)
How might certain properties of a molecule affect how it’s transported?
- solubility = lipid-soluble molecules pass through membranes more easily.
- size = smaller molecules diffuse faster
- charge = charged molecules cannot diffuse by simple diffusion as membrane repels them so have to use facilitated
Osmotic concentration
- isotonic solution?
- hypotonic solution?
- hypertonic solution?
Isotonic solution - osmotic concentration of the solutes in the solution is the same as that in the cells
Hypotonic solution - Osmotic concentration of solutes in solution is LOWER than in cytoplasm of cells.
Hypertonic - Osmotic concentration of solutes in solution is HIGHER than in cytoplasm of cells.
Osmosis in :
-animal cells
-plant cells
animal cells:
- too much water moves out = cell shrivels as concentrated cytoplasm loses its internal structure and the chemical reactions stop working
- too much water moves in = cell burst
plant cells:
- too much water moves out = turgor is lost + cell membrane begins to pull away from cell wall as the protoplasm shrinks = called incipient plasmolysis + vacuole will be reduced
- too much water moves in = cytoplasm swells and presses on cell walls = becomes rigid = turgor = this state supports the stems + leaves of plant
[this is because the pressure of cytoplasm on cell wall is cancelled out by the inwards pressure of the cell wall on the cytoplasm (pressure potential) to stop water ]
in plants they do not swell/burst , only the contents change.
- Water potential?
Water potential - measure of the tendency of water to move by osmosis.
-pure water has highest water potential of 0.
-osmosis occurs from high water potential to low.
- Turgor pressure?
Measure of the inwards pressure exerted by the cell wall on the protoplasm of the cell as cell components expand + press outwards
-this force opposes/stops entry of water by osmosis
- turgor pressure has a positive value
- Osmotic potential?
Measure of the potential of a solution to cause water to move into the cell across a partially permeable membrane from high conc to low conc
-pure water has highest (least negative) osmotic potential
-solution with dissolves solute =lower (more negative)
-the greater solute cocn = the more negative
-osmotic potential has a negative charge
How can water potential be calculated?
Water potential = turgor pressure + osmotic potential
ψ = P + π
usually negative = usually positive + always negative
When turgor pressure is balanced with osmotic potential the cell is …
At turgor
How does active transport work
best example of active transport is sodium pump that actively moves potassium ions into cell and sodium ions out.
- Protein carrier of specific shape picks up glucose molecule of specifc shape
- Protein carrier changes shape to allow glucose molecules into the cell -this requires energy from the hydrolysis of ATP into ADP + P
- Glucose molecules are carried across membrane in protein carrier of matching shape from low conc to high conc
- Glucose molecules released and protein carrier returns passively to original shape to allow more glucose molecules to enter.
Explain the role of ATP in active transport
ATP binds to the carrier protein, providing enough energy for the protein to change shape, which carries the molecule in/out of cell.
Hydrolysis of ATP into ADP + P
How does ATP release energy?
When ADP is phosphorylated to form ATP, this requires energy which is then stored in the molecule.
Therefore when ATP is hydrolysed, the energy stored is released to be used were required.
Evidence for active transport using ATP?
- active transport takes place only in living , respiring cells
- The rate of active transport depends on temp + O2 conc. These also affect rate of respiration and so ATP production as well
- Many cells that are known to carry out active transport, have lots of mitochondria -site of aerobic respiration and ATP production
- Poisons that stop respiration or prevent ATPase from working, also stops active transport.
What is SA : V ratio and how does it affect gas exchange?
The relationship between the SA of an organism and its volume.
the larger the SA is compared to Volume =the more particles can be exchanged at same time = faster gas exchange
Gas exchange in small organisms?
why does it work like that?
For single-celled organisms (eg amoeba) nutrients/o2 can diffuse directly into cell from external environment + waste products directly out.
This works because:
- diffusion distance from outside to inside is very small
- SA:V ration is very large = there is big SA = more substances can diffuse in/out
- metabolic demands are low = don’t regulate own temp/ don’t use much o2 and produce much co2 etc = don’t need gas exchange to happen rapidly
= don’t need specialised gas exchange/ transport systems as diffusion is enough to supply their needs.
Gas exchange in larger organisms
Larger organisms made up of billions of cells = substances need to travel long distance from outside to reach cytoplasm of cells.
Metabolic rate is also higher as they control own body temp and are more active = demand for O2 + food and CO2 + waste produced is much higher than smaller organisms.
= have evolved specialised systems to exchange gases they need in and need to remove.
humans - in lungs
fish - in gills
insects - in tracheal system
plants - in leaves
What features make a gas exchange system effective?
- A large SA : V
- thin layers =minimise diffusion distance
- rich blood supply to maintain a steep concentration gradient
- Moist surfaces to allow gases to dissolve in it
- Permeable surfaces = allow free passage of respiratory gases
Nasal cavity in humans
main entrance for gases into the body
-the lining secretes mucus and is covered in hairs = external air is ‘filtered’ from dust /small particles and pathogens such as bacteria breathed in
-rich blood supply raises temp of air if needed
-moist surfaces increase level of water vapour in air
=all means that air entering lungs has little effect on internal environment.
Functions of parts involved in gas exchange in mammals
-Nasal cavity
-mouth
-Epiglottis
-Trachea
Nasal cavity - main route air enters gas exchange system.
Mouth - air can enter but it misses out on the cleaning of the nasal system
Epiglottis - Flap of tissue that closes over glottis when food is swallowed to stop food from entering gas exchange system
Trachea - Airway to bronchi lined with mucus secreting cells and cilia to move mucus / dust / microorganisms away from lungs.
-incomplete rings of cartilage
-left and right bronchus
-Lung
-Bronchioles
-Alveoli
incomplete rings of cartilage - prevent trachea + bronchi from collapsing + allow food to be swallowed and move to oesophagus
Left + Right bronchus - Tubes leading to lungs ( similar to trachea structure but narrower and divide to form bronchioles)
Lung - organ where gas exchange takes place
Bronchioles - small tubes that spread through lungs and end up in alveoli. (no cartilage and collapse easily)
Alveoli - Main site of gas exchange in lungs (tiny air sacs)
-Ribs
-Intercoastal muscles
-pleural membranes
-pleural cavity
-Diaphragm
Ribs - protective bony cage around the gas exchange system
Intercoastal muscles - found between ribs and important in breathing
Pleural membranes - surround the lungs and + line the chest cavity
Pleural cavity - space between the pleural membranes usually filled with lubricating fluid that allows membrane to slide easily with breathing movements
Diaphragm - broad sheet of tissue that forms the floor of chest cavity + important in breathing movements
Alveoli structure w capillaries
- Made of single layer of flattened epithelial cells
- capillaries run close also one cell thick wall
- layer of elastic connective tissue between alveoli + capillaries
- hold everything together and help force air out lungs which are stretched when u breath in = elastic recoil of lungs
- Lung surfactant (phospholipids) coats alveoli - preventing alveoli from collapsing = makes breathing easier
Gas exchange in alveoli
Alveoili has high conc of O2 + blood has high conc of CO2
02 diffuses into deoxygenated blood’s red blood cells and makes it oxygenated where its then carried to rest of body to use.
CO2 diffuses into alveoli and is then breathed out.
Adaptations of gas exchange system
(mammals)
- Large SA:V - Many (480-500) alveoli in lungs
- walls of alveoli + capillaries are one cell thick = short diffusion pathway
- Continuous flow of blood in capillaries that maintains conc gradient
- Moist walls for gases to dissolve in
What is Breathing / ventilation?
The process in which physical movements of the chest change the pressure so that air is moved in or out.
Process of inhalation ?
inhalation - taking air into the chest
[active, energy-using process]
-muscles around diaphragm contract = lowered + flattened
-intercostal muscles between ribs contracts = raising rib cage upwards + outwards
Process of inhalation ?
inhalation - taking air into the chest
[active, energy-using process]
-muscles around diaphragm contract = lowered + flattened
-intercostal muscles between ribs contracts = raising rib cage upwards + outwards
= volume pf chest cavity increases
=reduces pressure in cavity
=pressure within chest < pressure atmospheric air outside
=air moves in through trachea - bronchi - bronchioles - lungs to equalise the pressure inside and out
process of exhalation
Takin air out lungs - breathing air out
[passive process]
-muscles surrounding diaphragm relax
=moves up into resting domed shape
-intercostal muscles relax = ribs move down + in
-volume of chest cavity decreases
=increase in pressure
=pressure inside . pressure outside
=air moves out of lungs through bronchioles - bronchi - trachea - out
How your lungs are protected from pathogens and other harmful particles we may breath in?
-we breath in lots of tiny particles/dust/pollen/smoke particles/pathogens (cause disease)
-respiratory system produces loads of mucus that lines airways + traps these little particles / organisms
-moved up the airway by cilia that sweeps up the back of throat
=mucus swallowed
-acid in stomach + digestive enzymes digest the mucus and what its carrying.
Gas exchange in insects
have high o2 requirement - their respiratory system evolved to deliver o2 directly to the cells and remove co2 same way.
spiracles - along the abdomen of most insect
- They are site of entry/exit of respiratory gases
- Opened/closed by sphincters (these also control water loss)
Tracheae - largest tubes that carry air directly into body for gas exchange with cells
- supported by spirals of chitin - hold the trachea open if they are squished
- Chitin makes trachea impermeable to gases = little gas exchange takes place in these vessels
- Trachea divides to form narrower tubes - tracheoles
Tracheoles - narrow tube - a single elongated cell
- no chitin = freely permeable to gases
- spread through the tissues of insect
- so small = run between and even penetrate into cells
=most gas exchange occurs in tracheoles.
Spiracles and sphincters
-air enters through them
-major site of water loss
-sphincters kept closed as much as possible to prevent water loss
-one or two pairs open occasionally to allow enough air in for gas exchange
-when insects active = more spiracles open due to higher demand for O2
-opening + closing of spiracles coordinated by respiratory centres in nervous system which are stimulated by increase of CO2 or lactic acid build up in active tissue due to lack of O2.
Adaptation in respiratory system
[insects]
air moves along trachea + tracheoles by diffusion alone.
- huge network of tiny tracheoles gives large SA = most gas exchange occurs here
- moist walls = gas dissolve
- tracheoles may contain water towards end = limits penetration of gases for diffusion
-when insect very active + needs more O2 = lactic acid builds up in muscle tissues = these affects osmotic conc of cells = so water moves off tracheoles into cell by osmosis = exposes more SA in tracheoles for gas exchange.
Some insects have very active lifestyles + very high energy demands.
How do they get extra O2 supplied?
[dragonflies/butterflies/moths/bees/wasps/flies]
Have evolved ways of ventilating:
- Mechanical ventilation
- air actively pumped into tracheal system.
- when spiracles open = insects make muscular pumping movements of thorax/abdomen
- changes volume + pressure inside body
=drawing air in + out trachea + tracheoles
- Collapsible tracheae / air sacs that act as air reservoirs
- increase volume of air moved through respiratory system
- the ventilating movements of abdomen/thorax inflate/deflate them or some by general body movement
why would lungs not work as gas exchange organs in fish?
water is a lot dense and thick than air
air is 20% o2 whilst water has a lot less dissolved o2
=lungs - would use up enormous amount energy to move water in and out.
-so gills used instead - water flows over them in 1 direction only
=more effective + efficient in terms of energy for fast moving active animals living in water
Gas exchange in bony fish
have high o2 demand due to high active but cannot gas exchange through their scaly external as its not vry permeable to gases = use gills instead
- gills contained in a gill cavity + covered by a protective bony flap called the operculum
- operculum is important in maintaining flow of water over the gills, even when fish is stationary.
Structure of the gills
- gill filaments (lamellae) occur in large stacks
- gill filaments - main site of gas exchange
- need water to keep them apart = to keep large SA needed
- out of water, gill filaments stick together due to lack of water = exposed SA not enough for effective gas exchange + not enough water + o2 can enter
- have a rich blood supply
- blood leaving gills flows in opposite direction to incoming water
(counter current exchange system)
= steep conc gradient maintained
Process of Ventilating the gills in bony fish that have a o……. ?
-sharks + rays do not have an operculum
=have to swim all the time to keep water flowing in through their mouths + out over their gills.
-bony fish have operculum = can ventilate their gills even when not moving
- The floor of the mouth opens, and the operculum (gill flap) closes.
- The floor of the mouth is then raised to increase the pressure but a valve stops water from leaving.
- The increased pressure forces the operculum open which forces water over the gills.
Adaptations in gas exchange system ?
[ in fish]
- Large SA due to gills ligaments being kept apart by water
- Rich blood supply
- thin walls (short diffusion distance)
-
Countercurrent exchange system - blood in gill filaments flow in different direction than the water moving over the gills
= steep conc gradient maintained - Overlapping gill filaments - tips of adjacent gill filaments overlap = increases resistance to flow of water = slows down the flow of water over gills surface = gives more time for exchange of gases to occur.
Plants respire + photosynthesise and they’re opposite?
how’s it balanced?
- respiration - need O2 + release CO2
- photosynthesis - need CO2 + release O2
-during day photosynthesising tissue (green leaves + stems) need to take in MORE CO2 than is produced in respiration
-they also make MORE O2 than is needed in respiration = release it into air
-at day + night, plants take in 02 and release CO2 in respiration.
Main site of gas exchange is leaves
-different parts of leaf?
- Impermeable waxy cuticle (prevents water loss through evaporation/diffusion of gases)
- Upper epidermis (is transparent to allow maximum light through to cells with chloroplasts)
- Palisade mesophyll layer (cells are stacked vertically to fit in as many cells as possible. These cells contain the most chloroplasts - needed for photosynthesis)
- Spongy mesophyll layer (air spaces provide an increased surface area for gas exchange and allow gases to diffuse)
- Lower epidermis, guard cells, stomata (guard cells open and close stomata to control water loss = entry/exit of gases. Walls of guard cells are thicker on the side adjacent to the stomata to enable opening and closing)
Why is the spongy mesophyll layer important?
The spongy mesophyll cells inside have irregular shapes increasing SA.
-arranged with large air spaces between them
-Surfaces of spongy mesophyll cells are moist = gas exchange occurs freely between cells of the leaf + air spaces by diffusion.
how is a conc gradient maintained?
Gases move in + out leaf, maintaining a conc gradient so that gas exchange continues within the leaf.
the gases move in and out of leaf through diffusion through the stomata
What happens when conditions for photosynthesis are favourable?
During the day, when conditions are favourable for photosynthesis…
the stomata opens (this allows water loss to be balanced).
This allows carbon dioxide to diffuse in and oxygen (as a waste product of photosynthesis) to diffuse out.
Opening of stomata?
-a turgor-driven process
-guard cells respond to lowered CO2 levels in leaf
When CO2 needed in cells for photosynthesis in favourable conditions…
- Ions (mostly potassium) move into the guard cells by active transport
- = causes water to move in by osmosis as water potential is decreased
- = makes the guard cells swell + become turgid
- = causes the stomata to open
(due to the uneven bending due to arrangement of cellulose in cell wall)
Walls of guard cells are thicker + less flexible on the side adjacent to the stomata to enable opening and closing
Closing of stomata?
When conditions are less favourable for photosynthesis / when its dark.
- the active pumping of potassium ions into the cell stops = potassium ions are excreted
=water leaves the cell by osmosis - so turgor is reduced + guard cells become flaccid
=closing the stomata
where are stomata found?
most stomata are found on the underside of leaves
they are also present in stems to allow gas exchange to take place
What happens to the stomata on green stems when plants become thickened + woody?
When plants become thickened + woody, there are no stomata on surface anymore.
tissues underneath layers of cork + bark still need to take up O2 + remove CO2 for respiration, so..
special spongy areas called lenticels develop - which are made of loosely arranged cells with many air spaces.
they link the inner tissues of trunk or woody stem with them outside world so gas exchange can take place.
Lenticels can also form on roots for exchange of gases with the air in soil.
What are Lenticels?
Spongy areas with loosely packed cells that are site of gas exchange in woody stems and roots.
What are mass transport systems?
Why is transport in organisms important/needed?
Mass transport system - substances are transported in the flow of a fluid with a mechanism for moving it around the body
- for delivering O2 + nutrients and removing waste = so cells can carry out function efficiently
- transporting substances made internally around the body to where they are needed.
Features of an effective mass transport system
- A system of vessels that carry substances
- A way of making sure substances are moved in right direction
- A mean of moving material fast enough to supply needs of organism
- A suitable transport medium
Open vs Closed circulatory system
Open circulatory system (fish) :
- blood circulating in large open space.
Closed circulatory system (larger animals-mammals) :
- blood is contained within tubes, and makes a continuous journey out to distant part of body and back to heart.
Single circulation system:
Fish (bony fish)
- heart pumps deoxygenate blood to gills
- gas exchange occurs and it becomes oxygenated (at gills)
- blood travels on around rest of body giving up O2 to body cells
- returns to heart + repeat process
Double circulatory system
Involves 2 circulatory systems.
Systemic circulation :
- carries oxygenated blood from heart to cells where O2 is given used. - carries the now deoxygenated blood back to heart.
Pulmonary circulation :
- carries deoxygenated blood from heart to lungs for gas exchange to become oxygenated. - carries now oxygenated blood back to heart.
Why do birds and mammals need a double circulatory system instead?
- need far more O2 than fish
- maintain a constant body temp that’s usually higher than surrounding
=takes a lot of resources = cells need lots of O2 + glucose + produce lots of waste products that need to be removed quickly
Advantages of a double circulatory system in mammals:
- The separate circuits make sure that oxygenated and deoxygenated blood do not mix.
-so tissues can get as much O2 as possible - The oxygenated blood can be delivered quickly to the body tissues at high pressure.
-at lungs blood go through tiny vessels that allow gas exchange to occur effectively.
-if this oxygenated blood carried on to rest of body at low pressure, it would move very slowly
-as it returns to heart it can be pumped at high pressure around body = reaches all capillaries between body cell quick - supplying O2.
What does it mean that the mass transport system is the cardiovascular system?
What does this system do?
The mass transport system of the body made up of a series of vessels with a pump (the heart) to move blood through the vessels.
- delivers materials needed by cells of body + carries away waste products of their metabolism.
- carries hormones (chemical messages) from one part of body to another
- forming part of the defence system of the body
- distributing heat
main categories of the functions of blood?
The components of the blood?
- transport hormones
- defence
- distribution of heat
- formation of tissue fluid + lymph
Blood is made up of plasma and blood cells (erythrocytes, leukocytes and platelets).
Components:
-plasma
-Erythrocytes (red blood cells)
-Leucocytes (white blood cells)
-Platelets
Plasma
The water solution of your blood carrying other components in it
- Transports digested food products (e.g. glucose, amino acids from small intestine to rest of body)
- nutrient molecules
- hormones
- excretory products (e.g. carbon dioxide, urea).
- Transfers heat around the body to maintain steady body temp
Erythrocytes ( red blood cells)
- contain haemoglobin (red pigment that carries O2 + gives them their colour)
- formed in bone marrow
- transport oxygen from lungs to cells.
- well adapted through biconcave disc shape = large SA:V for O2 to diffuse in/out rapidly
- have no nucleus = more space for haemoglobin to carry O2
-each red blood cell contains 250-300 million molecules o haemoglobin = carry A LOT of O2.
-Haemoglobin can sometimes also carry CO2 produced in respiration back to lungs - the rest transported in plasma.
Platelets
- tiny fragments of large cells called megakaryocytes
[which are found in bone marrow] - Involved in blood clotting
Leucocytes (white blood cell)
- formed in bone marrow
- defend body against infections.
- all contain nucleus + have colourless cytoplasm - some can be stained / some can’t
- Lots of different types of leucocytes
What are the 2 main categories of leucocytes and the types in each one?
- Granulocytes: Leucocytes that have granules in cytoplasm that takes up stain + is obvious under microscope. They have lobed nuclei.
[Non-specific immune system]
-Neutrophils
-Eosinophils
-Basophils
- Agranulocytes: Leucocytes that do not have granules in cytoplasm to take up stain + have unlobed nuclei.
[Specific immune system]
-Monocytes
-Lymphocytes
Granulocytes
[non-specific immune system]
- Neutrophils - engulf + digest pathogens through phagocytosis
Multi lobed nuclei.
[70% leucocytes] - Eosinophils - respond to parasites, allergic reactions, inflammation, developing immunity to disease
[stained red by eosin stain] - Basophils - produce histamines involved in inflammation/allergic reactions.
[have two-lobed nucleus]
Agranulocytes
[specific immune system]
- Monocytes - move out of blood into tissue to form macrophages –> engulf pathogen by phagocytosis.
[largest leucocytes] - Lymphocytes - vital in specific immune response of the body.
[Small leucocytes with very large nuclei]
Can be B or T lymphocytes
How do substance move between the plasma/RBC and the body cells?
Through diffusion / active transport.
- tiniest blood vessels have walls only one cell thick - short diffusion distance
- each cell in body is close to one of these small vessels
Transport of Oxygen:
When haemoglobin picks up O2?
formula?
-Haemoglobin molecules packed in RBC transport O2.
-Each haemoglobin molecule is a large globular protein made up of 4 peptide chains, each with an iron containing prosthetic group (haem group) which can pick up 4 molecules of O2 in a reversible reaction to form oxyhaemoglobin.
- Hb + 4O2 ⇌ Hb4O2
haemoglobin + oxygen ⇌ oxyhaemoglobin
-1st O2 molecule that binds to haemoglobin alters arrangement of molecule = makes it easier for following O2 to bind
-final O2 molecule binds A LOT faster than first.
[same happens in reverse when removing O2 from Hb4O2, gets harder progressively]
-The conc of O2 in RBC when blood enters lungs is low = O2 moves into RBC from air in lungs by diffusion + picked up by haemoglobin = free O2 conc in red blood cell cytoplasm stays low = maintaining conc gradient = more O2 diffuses in an loads onto haemoglobin
Transport of oxygen:
-when oxyhaemoglobin removes oxygen?
-in tissues - O2 conc low - conc in cytoplasm of RBC higher than surroundings = O2 moves out into body cells by diffusion down conc gradient.
-Haemoglobin molecules gives up some of its O2. the rest is reserve in the transport system for when ur very active.
-In tissues, O2 saturation of environment falls = O2 released rapidly.
opposite formula since its reversible
Oxygen dissociation curve for haemoglobin
-check diagram (page 251)
What’s the Bohr effect?
- changes in the O2 dissociation curve of haemoglobin that occurs due to a rise in CO2 levels + a reduction of the affinity of haemoglobin for O2
- presence of carbon dioxide = affinity of haemoglobin for oxygen decreases = causing it to be released.
This means that oxygen dissociate from haemoglobin and can be used in respiring tissues.
=Haemoglobin needs higher levels of O2 to become saturated + gives up O2 much easier.
=so in active tissue with high CO2 levels = Haemoglobin releases O2 much more readily.
-in lungs capillaries, CO2 low = easier for O2 to bind to haemoglobin.
Haemoglobin has highest / lowest affinity where?
Lungs - haemoglobin has highest affinity for O2 so picks up O2 most
Tissues - Haemoglobin has lowest affinity for O2 so releases O2
What are the 2 other respiratory pigments?
- Fetal haemoglobin
- Myoglobin
Fetal Haemoglobin
- Found only in developing fetus
- When fetus is in uterus it depends on its mother to supply it O2
- Oxygenated blood from mother runs through placenta close to deoxygenated fetal blood.
- Fetal haemoglobin has a higher affinity for O2 than the mother = can remove O2 from the maternal blood
- Maternal + Fetal blood run in opposite directions =counter current exchange system = maximises O2 transfer to blood of fetus.
Myoglobin
structure?
- Respiratory pigment found in muscle tissues of vertebrates
[small bright red protein = gives red meat its strong colour] - similar structure to haemoglobin - contains haem group which binds with O2
- Much higher affinity for O2 than haemoglobin = easily becomes saturated with O2
[affinity not affected by partial pressure of O2 in tissues] - once Myoglobin binds to 02 molecule - it does not give up the O2 easily = acts as an O2 store
-When O2 levels in very active tissues gets really low + CO2 are very high =myoglobin releases its store of 02 when its most needed
Transport of carbon dioxide
What happens when CO2 goes into blood?
equation?
- Waste CO2 diffuses from respiring cells of the body cells into blood along conc gradient
- dissolves in blood it reacts with water slowly to form Carbonic acid which is catalysed by enzyme Carbonic anhydrase
- The carbonic acid separates to form the ions H+ and HCO3-
[hydrogen + Hyrogencarbonate]
CO2 + H20 ⇌ H2CO3 ⇌ HCO3- + H+
- Some of the CO2 carries in solution in plasma (5%)
- some combines w haemoglobin to form carbaminohaemoglobin (10-20%)
- Most is transported in cytoplasm of RBC as hydrogencarbonate ions
What does the enzyme Carbonic anhydrase do?
-Carbonic anhydrase controls the rate of the reaction between CO2 and water to form carbonic acid
-In body tissues there’s high conc of CO2 in blood = carbonic anhydrase catalyses formation of carbonic acid
-in lungs the CO2 conc is low = carbonic anhydrase catalyses the reverse reaction + free CO2 diffuses out of blood into lungs.
What is the chloride shift?
When the hydrogeincarbonate ions pass out of red blood cells by diffusion, and chloride ions move in.
How is the pH of the blood maintained/controlled?
Haemoglobin acts as a buffer in plasma
- accepting the hydrogen ions to form haemoglobinic acid to avoid changing the pH of the blood.
Why is clotting of blood important?
- A minor cut can make you lose lots of blood = could die if blood volume falls a lot
- Pathogens can get into your body through an open wound
- clotting mechanism seals up damaged blood vessels to minimise blood loss + prevent pathogens getting in
2 main substances involved in blood clotting?
Plasma, blood cells, platelets flow from cut vessels.
- contact between platelets + components of tissue causes platelets to break open in large numbers to release substances
- Serotonin : causes smooth muscle of blood vessel to contract = narrows the blood vessels = cutting of blood flow to damaged area
- Thromboplastin : enzyme that sets in progress a cascade of events that leads to formation of a clot
What happens in the blood clotting casade?
- Thromboplastin catalyses large soluble proteins prothrombin (in plasma) into thrombin (soluble protein, enzyme)
- happens at large scale at wound
- calcium ions needed in blood at right conc + vitamin K for this reaction to happen
- Thrombin acts on soluble fibrinogen - converting it to insoluble fibrin
= forms mesh of fibres to cover wound - platelets + blood cells pouring from wound get trapped in fibrin mesh = forms a clot
- Special proteins in structure of the platelets contract - making clot tighter + tougher to form a scab
- protects the skin + vessels underneath as they heal
What can happen if a clot forms in the wrong place?
Can lead to serious problems in blood vessels.
- clot in the vessels that supply your heart with blood can cause a heart attack
- clot in the brain can cause a stroke
Arteries function
- carry oxygenated blood away from heart towards cells of body
-2 exceptions (carry deoxygenated blood)
- pulmonary artery - carry deoxygenated blood from heart to lungs
-umbilical artery - during pregnancy carry deoxygenated blood from foetus to placenta
-arteries leaving heart branch of every direction + diameter of lumen (central space inside blood vessel) gets smaller the further from the heart
-smallest branches of arterial system - furthest from heart = arterioles
Structure of arteries
- narrow / small lumen = maintains high BP
-
thick walls with elastic fibres - to withstand blood pressure
+ smooth muscles - to withstand pressure
[arteries nearer to heart have more elastic fibres + furthest away have greater proportion of muscle tissue] - smooth lining =allow easy flow of blood
What happens to arteries with each heartbeat?
does lumen change?
- each heartbeat sends high-pressure surge of blood into arteries
-arteries close to heart must withstand these pressure surges - walls contain a lot of elastic fibres so they can stretch to accommodate the greater volume of blood without being damaged
- blood pressure in arteries high, but falls in arteries further away from heart - known as the peripheral arteries
-in peripheral arteries - muscle fibres in vessel walls contract or relax to change size of lumen = controlling blood flow
-makes the lumen smaller = harder for blood to flow through vessel - controls amount of blood flowing to an organ = regulating its activity.
Capillaries function
-arterioles feed into network of capillaries.
- small vessels that spread through tissues of body
- link arterioles + venules (smallest branches of venous system - furthest from heart)
- branch between cells - no cell is far from capillaries
=substances can diffuse between cells + blood quickly - blood flows slow through them due to small size = giving more opportunity for diffusion to occur
Capillaries structure
- walls one cell thick = very thin + permeable (don’t contain any elastic fibres/smooth muscle/collagen) = helps them fit between individual cells + allows for rapid diffusion through short dd
- narrow lumen = Red blood cells need to pass through the capillaries in single file = slow flow of blood = more opportunity for diffusion
- capillary wall made of single layer of epithelial cells
Veins function
- Carry deoxygenated blood towards heart
-expect for:
1. Pulmonary vein - carry oxygenated blood from lungs back to heart for circulation
2. The umbilical vein - in pregnancy, carries oxygenated blood from placenta to foetus
- receive blood that has passed through capillary networks, so the blood pressure is very low
Veins structure
- Large lumen - helps to ensure that blood returns to the heart at an adequate speed+ reduces friction between the blood and the endothelium of the vein
- rate of blood flow is slower in veins but larger lumen = volume of blood delivered per unit of time is = to that of arteries
- thin layer of smooth muscle with few elastic fibres
- Veins contain valves - prevent the backflow of blood, helping return blood to the heart
- A pulse is absent in veins due to the increased distance from the heart
Which 2 veins carry the returning blood into the heart ?
Inferior vena cava - from the lower parts of the body
Superior vena cava - from upper parts of the body
Veins hold a large volume of blood - they act as blood reservoirs.
How is blood returned to heart to be oxygenated again despite low blood pressure?
- One way Semilunar valves (due to half-moon shape) at frequent intervals throughout venous system.
- formed from infoldings of the inner wall of veins
- blood can pass towards heart, but if start to flow backwards, valves close preventing backflow. - Larger veins situated between large muscle particularly in arms + legs
- when muscles contract during physical activity = squeeze these veins = with valves keeping flow in 1 direction , the squeezing helps return blood to heart fast
Overall structure of heart
2 muscular pumps joined + working together in perfect synchrony
- right side receives blood from body + pumps to lungs
- Left side receives blood from lungs + pumps to rest of body
-2 sides separated by thick, muscular septum to stop mixing of oxygenated + deoxygenated blood
- top 2 chambers : atria (left + right atrium)
- bottom 2 chambers: ventricles (left + right ventricles)
What’s the heart’s muscle?
It’s properties?
- Heart made from cardiac muscle
special properties of cardiac muscle:
- carry on contracting regularly without resting / getting fatigued
- Myogenic - no external nerve impulses needed to contract heart
- has a good blood supply - the coronary arteries bring oxygenated blood to tissues
- Contains lots of myoglobin - stores oxygen for respiration needed to keep hearty contracting regularly
Label parts of heart on diagram -
-why does atrium have muscular walls?
-what are the sounds of ur heartbeat from?
As it receives blood at low pressure from the 2 venae cavae + needs to exert little pressure to move blood into ventricles.
-sounds of heart beat produced from blood hitting the heart valves.
Flow of blood around heart-
Superior v inferior vena cava?
right atrium to right ventricle?
Inferior vena cava - collects deoxygenated blood from lower parts of body
superior vena cava - receives deoxygenated blood from upper parts of body (head/neck/arms/chest)
[ valves at entrance of atrium stops backflow of blood back into veins]
–> blood delivered to the right atrium
- right atrium fills with blood - pressure builds up = opens tricuspid valve so right ventricle starts to fill with blood too.
- when R atrium is full - contracts - forcing blood into R ventricle
- Tricuspid valve made up of 3 flaps - separates R atrium from R ventricle + prevents backflow of blood back into atrium when ventricle contracts
Blood flow
-from right ventricle on -
-what are the tendinous cords?
-tendinous cords (valve tendons/ heartstrings) make sure valves are not turned inside out by pressure exerted when ventricles contract.
- R ventricle filled w blood + contracts. It’s muscular walls produce pressure to force blood out of heart into pulmonary artery through semilunar valve
- carries deoxygenated blood to capillary in lungs for gas exchange to become oxygenated.
Blood returning from lungs to heart -
- oxygenated blood returns from lungs to left side of heart in pulmonary vein
- Low pressure due to capillaries of lungs
- returns to L atrium - it contracts to force blood into L ventricle - fills with blood under pressure
- Backflow is prevented by bicuspid valve
Blood moving out of Left ventricle -
- L ventricle pumps blood out of heart and into aorta - major artery of body
- carries blood away from heart at high pressure to rest of body
- semilunar valves prevent backflow of blood from aorta back to L ventricle
Why is muscular wall of left side of heart thicker?
- Muscular walls of left side of heart is thicker as right side only pumps blood to lungs - close to heart
- whilst left side has to produce more force to pump blood under pressure to whole body + overcome the elastic recoil of arteries
What is the cardiac cycle?
The cardiac cycle is the series of events that take place in one heartbeat, including muscle contraction and relaxation
-The contraction of the heart is called = systole
-The relaxation of the heart is called = diastole
-Systole divided into atrial + ventricular systole
- atrial systole - when atria contract together forcing blood into ventricles
- ventricle systole - when ventricles contract, forcing blood out of ventricle and into pulmonary artery / aorta.
- relaxation stage - diastole
- One cycle of systole + diastole makes up a single heartbeat
Atrial systole ?
The walls of the atria contract :
= Atrial volume decreases
= Atrial pressure increases
- The pressure in the atria rises above that in the ventricles, forcing valves open = Blood is forced into the ventricles
- The ventricles are relaxed at this point; ventricular diastole coincides with atrial systole
[summary: Atrial systole + Ventricular Diastole - Atria contracts, pushing blood into ventricle. ]
Ventricular systole?
The walls of the ventricles contract
= Ventricular volume decreases
= Ventricular pressure increases
-The pressure in the ventricles rises above that in the atria
= forces valves to close, preventing back flow of blood
- The pressure in the ventricles rises above that in the aorta + pulmonary artery
= forces the semilunar (SL) valves open so blood is forced out of the heart (aorta / pulmonary artery) - During this period the atria are relaxing; atrial diastole coincides with ventricular systole
[summary : Atrial diastole + ventricular systole - ventricles contract after atria relaxes, pushing blood out of heart. ]
Diastole?
The ventricles and atria are both relaxed
Pressure in ventricles drops below that in the aorta and pulmonary artery, forcing the SL valves to close = atria continue to fill with blood
-Blood returns to the heart via the vena cava and pulmonary vein
- Pressure in the atria rises above that in the ventricles, forcing the AV valves open = Blood flows passively into the ventricles without need of atrial systole
-The cycle then begins again with atrial systole
[summary: cardiac diastole - all chambers are relaxed + blood flows into the heart. ]
The control of the heartbeat
Control of the basic heartbeat is myogenic, which means the heart will beat without any external stimulus.
This intrinsic rhythm means the heart beats at around 60 times per minute - maintained by a wave of electrical excitement similar to a nerve impulse that spreads through special tissue in heart muscle
Explain the steps involved in the process of controlling ur heartbeats
(natural pacemaker)
-The sinoatrial node = SAN (in atrial wall)
- The SAN initiates a wave of depolarisation that causes the atrium to contract
- There is a region of non-conducting tissue (annulus fibrosus) which prevents the depolarisation spreading straight to the ventricles
- Instead, the depolarisation is carried to the atrioventricular node (AVN)
-This is a region of conducting tissue between atria + ventricles. - After a slight delay the AVN is stimulated and passes the stimulation along the bundle of His ( a group of conducting fibres in septum of heart)
=This delay ensures that the atria has stopped contracting before ventricle starts. - The bundle of His divides into 2 branches, called Purkinje tissue = which carries the wave of excitation along them
- Contain Purkinje fibres that penetrates down septum and spread around the ventricles
- As depolarisation travels through tissues it sets of the contraction of the ventricles - starting at the apex (bottom) +
=blood is forced out of the ventricles into the pulmonary artery + aorta
What do the changes in the electrical excitation of the heart cause?
What are the electrical changes measured with?
changes in electrical excitation of heart causes the repeating cardiac cycle.
-electrical changes are measured in an electrocardiogram (ECG)
- monitor + investigate the electrical activity of the heart
- shows distinctive electrical waves produced by activity of heart
- A healthy heart produces a distinctive shape in an ECG
- used to indicate different heart conditions = monitor ps with heart disease
- readings produce diagram showing how electrical activity recorded in ECG + pressure changes measured in different chambers of heart work together during cardiac cycle
Look at different diagrams and interpret data showing ECG traces
Pages 261-262
What are cardiovascular diseases? ( biggest cause of death)
Cardiovascular diseases linked to atherosclerosis - what is that?
Cardiovascular diseases are diseases of the heart + circulatory system, many of which are linked to atherosclerosis.
Atherosclerosis - hardening of the arteries, caused by the build up of yellow fatty deposit on the lining of arteries causing them to be narrowed + resulting in many different health problems.
The formation of atherosclerosis ?
- The endothelium arteries lining is slightly damaged (by high cholesterol levels, smoking or high blood pressure)
- This leads to an inflammatory response, causing white blood cells to move to the site of damage
- WBC accumulate deposit of cholesterol = leads to a plaque (atheroma) forming on the lining of artery
- Fibrous tissue + calcium salts build up around plaque - turning it into hardened plaque
- Hardened area = parts of artery wall hardens = less elastic than it should be + clot can block artery = atherosclerosis.
- The build-up of fibrous plaque leads to narrowing of the artery’s lumen = restricts blood flow = increasing the blood pressure = damages the endothelial lining and the process is repeated.
Why does Atherosclerosis mostly occur in arteries not veins?
- blood pressure in arteries flows fast under high pressure = more strain on lining of vessel + can cause small areas of damage = which lead to the Atherosclerosis developing.
- In veins, the pressure is lower = damage less likely
Effects of Atherosclerosis on health?
- Aneurysms
- Raised blood pressure
- Heart disease ( Angina / myocardial infarction [heart attack])
- Strokes
Aneurysms
-in areas of artery narrowed by plaque - blood tends to build up behind blockage.
-The artery bulges + wall is put under more pressure = weakened ( known as aneurysm)
-weakened artery wall may split open = massive internal bleeding = drop in blood pressure =fatal
-can be treated by surgery before they burst if diagnosed
Raised blood pressure
-Narrowed arteries due to plaques on wall = causes high blood pressure
= can cause serious damage to tiny blood vessels in kidneys = become narrowed = proteins forced out through walls.
=Damage retina of eyes = blocked / leak = retina cells starved of O2 = can cause blindness
2 types of Heart disease it can cause?
Angina and Myocardial infarction (heart attack)
Angina ( heart disease )
-plaques built up slowly in coronary arteries = reducing blood flow to parts of heart muscles beyond plaques
-first noticed during exercise when cardiac muscle working harder + needing more O2
-narrowed coronary arteries cannot supply enough Oxygenated blood = heart muscle resorts to anaerobic respiration
=causes gripping pain in chest + arms + jaw
-usually stops after exercise + reduced by losing weight, regular exercise + not smoking
- drugs to dilate blood vessel + reduce heart rate
- stent may be inserted in coronary arteries to hold them open = allow easier blood flow
Myocardial infarction ( heart attack)
- a branch of coronary artery becomes completed blocked = part of heart muscle is permanently starved of O2
-Clot that forms in blood vessels knows as thrombosis can rapidly block whole blood vessel esp if its already narrowed by plaque = starves heart muscles beyond that point of O2 = heart attack
- chest pain more severe than angina = death may occur rapidly or occur after several days if not treated
Strokes
- Caused by an interruption to normal blood supply to an area of the brain.
-Due to bleeding from damaged capillaries / blockage cutting off blood supply to brain by blood clot caused somewhere else and carried in bloodstream until it gets stuck in an artery in the brain.
- blockage in main artery leading to brain = stroke = may lead to death
-dizziness / confusion / slurred speech / numbness / paralysis down one side of body.
Atherosclerosis is a multifactorial disease - many things influence their chance of being affected.
What are the 2 main groups these factors are broken into?
Modifiable risk factors - you can do something about it
Non - modifiable risk factors - you can’t do anything about it
Non - modifiable risk factors for Atherosclerosis
-
Gene: genetic tendency in some ethnic groups to develop Atherosclerosis or the CVDs.
- arteries may be more easily damaged / cholesterol metabolism may be faulty - Age: Older u get = blood vessels lose their elasticity + narrow slightly = more likely to suffer from Atherosclerosis + CVDs (esp heart disease)
-
Sex: under 50, men more likely to suffer from Atherosclerosis
- As oestrogen hormone in females reduces build-up of plaque - give women some protection against Atherosclerosis until menopause.
Modifiable (lifestyle) risk factors
- smoking
- exercise
- weight
- stress
- diet
Modifiable risk factors
- Smoking
- smokers more likely to develop Atherosclerosis
- chemicals in tobacco smoke can damage artery lining - making build-up of plaque more likely
- cause arteries to narrow = raising Blood pressure + increasing risk
Modifiable risk factors
- Exercise
- regular exercise = lowers blood pressure, prevent obesity, diabetes, lower blood cholesterol levels + reduces stress = all these also lower ur risk of developing Atherosclerosis
- exercise reduces formation of plaques in arteries + keeps plaques that are present more stable + less likely to rupture
Modifiable risk factors
- Weight
- does not directly affect risk of developing it, but very important indicator of risk
- has affect on other factors that increase risk of Atherosclerosis
- High blood pressure - exercise reduced blood pressure = reduces risk of damage to blood vessels + therefore plaque formation
- Type 2 diabetes - reduces chance of Type 2 diabetes which can result in damage to lining of blood vessels increasing risk of plaque formation
Modifiable risk factors
- stress
- high stress = releases cytokines
= that triggers inflammatory response to blood vessels = leading to plaque formation
+ tends to cause high blood pressure = symptom + cause of Atherosclerosis
Modifiable risk factors
- Diet
- diet linked to Atherosclerosis
- high intake of saturated fats associated with high blood cholesterol levels = involved in plaque formation
= The balance of lipoproteins in blood is recognised as a indicator of ur risk of developing Atherosclerosis + CVDs
Preventing Atherosclerosis
-balanced diet w variety of fats + lots of fruit + vegetables
-not smoking
-maintaining healthy weight to avoid high blood pressure + type 2 diabetes
-reducing stress
-getting plenty of exercise
Tissue Fluid?
How’s the composition of tissue fluid similar / different from plasma?
- Tissue fluid is the fluid that surrounds all cells in body.
- As blood passes through capillaries, some plasma leaks out through gaps in the walls of the capillary to surround the cells of the body
= This results in the formation of tissue fluid. - Composition of plasma + tissue fluid = virtually the same, although tissue fluid contains far fewer proteins
= Proteins are too large to fit through gaps in the capillary walls and so remain in the blood
Why does the tissue fluid bath all cells of body?
- Tissue fluid bathes almost all the cells of the body outside of the circulatory system
=Exchange of substances between cells and the blood occurs via the tissue fluid
- EG: carbon dioxide produced in aerobic respiration will leave a cell, dissolve into the tissue fluid surrounding it, and then diffuse into the capillary
mark scheme:
- supplies o2, glucose, amino acids, hormones = allow respiration + growth - removes CO2 + urea = pH controlled + cells not poisoned
How much liquid leaves the plasma to form tissue fluid depends on two opposing forces - which?
Tissue fluid forms due to hydrostatic pressure + oncotic pressure in capillaries:
- Hydrostatic pressure : pressure due to heart contracting contracting / pumping
- Oncotic pressure : pressure exerted by the proteins in the blood plasma (causes tendency for water to move into capillaries by osmosis)
- as there is movement of fluid out of capillaries due to hydrostatic pressure but proteins remain in blood = increased blood content = creates water potential between capillaries + tissue fluid = water potential of the capillaries becomes more negative (although oncotic pressure is relatively constant).
-However, overall movement of water is out from the capillaries into the tissue fluid
What happens at the arterial end of capillaries?
- how tissue fluid is formed:
- Hydrostatic pressure forcing water out is higher > than oncotic pressure moving water in
=fluid is squeezed out of capillary + forms tissue fluid around cells
-this is where diffusion between blood + cells takes place
What happens at the Venous end of capillaries?
- how tissue fluid is reabsorbed into cappilaries:
- Hydrostatic pressure forcing water out is lower< than oncotic pressure moving water in
= fluid moves into capillaries = most of the tissue fluid is lost
Why does the hydrostatic pressure decrease as blood moves through the capillary system towards the venous end ?
Hydrostatic pressure falls due to:
- The pressure from the pulse is completely lost
- When the fluid moves out of capillaries to form tissue fluid = volume of blood in capillaries lowered
= hydrostatic pressure becomes less than the oncotic pressure, which remains same
The formation of lymph?
- the tissue fluid constantly formed must also be constantly removed so our tissues don’t swell up
= most tissue fluid returns to capillaries - but around 10% of tissue fluid goes to lymph capillaries instead + becomes lymph
[Larger molecules that are not able to pass through the capillary wall enter the lymphatic system as lymph]
- Lymph capillaries join up to form larger vessels
= lymph vessels
How are Lymph vessels similar to veins?
(past EQ)
-lymph vessels are similar to veins 2 ways:
- Have one-way valves to prevent backflow of lymph
- Lymph moved through vessels by contraction of muscles
What is lymph?
What are lymph capillaries?
Lymph - the excessive tissue fluid which travels in the lymphatic system
Lymph capillaries - the blind tubes that carry the lymph away from the tissues
How is lymph similar / different from tissue fluid?
- Lymph has fewer nutrients + less oxygen as these have been taken up by cells from the tissue fluid
- Lymph has higher level of fatty acids that are absorbed directly into lymph system in the villi of the small intestines
- Lymph contains lymphocytes that produce anbodies which are emped into the blood along with the lymph
What are lymph glands?
why are they important?
- Lymph glands are found at intervals along the lymph vessels
-where lymphocytes accumulate = which produce antibodies
-antibodies used by body to fight disease
- Lymph glands also remove bacteria + other pathogens to be taken in + destroyed by phagocytes
- doctors look for enlarged lymph glands = indicate that body is fighting infection.
(in neck/armpit/stomach/groin : as that’s where the lymph nodes are found in body)
How are these antibodies emptied into blood?
- The lymph eventually re-enters the bloodstream through veins located close to the heart ( subclavian veins )
- antibodies are emptied into the blood along with the lymph
Transportation system in plants
What’s a xylem?
function?
Xylem - main tissue transporting water around a plant
Functions:
- Transports dissolved minerals and water from roots to the photosynthetic parts of plant - movement in upwards only.
[move water as part of transpiration stream] - provide Structural support - withstand compression forces from weight of plant pressing down on it.
Structure of Xylem
● Long hollow cylinders made of dead tissue with open ends , therefore they can form a continuous column (no end walls)
= do not contain any cytoplasm or organelles that could slow down the flow of water
● They are thickened with a tough substance called lignin , which is deposited in spiral patterns to enable the plant to remain flexible.
● contain pits - holes - (small regions in the walls that are not lignified) = enable water to move sideways between the vessels.
How does xylem vessels develop + change from living cells to non-living tubes of lignin?
-xylem starts as living tissue - protoxylem.
=walls not fully lignified = capable of stretching + growing
-cellulose microfibres laid down vertically in stem = increases strength to withstand compression forces from the weight of plant
-As stem ages + cell stops growing = increases amount of lignin laid down in cell walls = cell become impermeable to water + other substances
=tissue becomes stronger + more supportive but contents of cell die
=lignified tissue - metaxylem.
-end walls between cells break down = xylem form hollow tube running from roots to tips of stem + leaves
How do the lignified xylem vessels play an important supportive role in stems of plants?
-in small non woody plants - support comes from turgid parenchyma cells in centre and the sclerenchyma + collenchyma cells.
-woody plants = more xylem tissue lignified to increase support
-new ring of vascular tissue formed each year - tree rings show xylem produced in each growing season.
Evidence for movement of water through xylem?
- if cut end of shoot placed in solution of dye = dye can be seen carried into transport system through xylem tissues = they get stained + phloem don’t
- Ringing experiment - remove complete ring of bark - destroys living phloem cells but not xylem cells - dye placed in water shows upward movement of water through the plant unaffected = xylem
- Autoradiography - water with radioactive isotope is shown travelling up xylem as it can be traced by autoradiography as when plant against photographic film - shadowed areas = shows which organelles have incorporated radioactive substance = xylem
What’s phloem?
Function of phloem?
phloem - main tissue for transporting dissolved solutes around the plant
Function :
- involved in translocation
- Transport food in form of organic solutes around plant from leaves where they’re made by photosynthesis to tissues where they’re needed
Plants convert the glucose they make in photosynthesis into sucrose to be transported by phloem to leaves where its needed for growth or storage as starch
- flow can go both up + down phloem
Structure of Phloem?
● They’re tubes made of living cells as they do not become lignified = contents remain living
● Consist of phloem sieve tube elements and companion cells
● Sieve tube elements have no organelles = no barriers to transport
= form a tube to transport sugars such as sucrose, in the dissolved form of sap.
● Walls between cells pierced with holes in it = sieve plates = phloem contents flow through the holes
-formation of the gaps in sieve plate causes nucleus, tonoplast + some organelles to break down
=can survive with no nucleus as they have closely associated companion cells.
● Companion cells have many mitochondria to supply ATP needed for active transport - such as loading sucrose into sieve tubes.
-they have many infolding to increase SA - to transport sucrose into cell cytoplasm
● Plasmodesmata - gaps between cell walls to allow communication + flow of substances between cytoplasm of sieve tube elements and companion cells.
Water from soil into roots?
Water moves from soil to roots through root hair cells down a conc gradient via osmosis.
-root hair cells = fine, hair-like extensions of the membranes with a large surface area for absorption + allow close contact with soil particles.
-Water moves through the root by osmosis to replace water removed from the xylem
It can move through the symplast pathway or the apoplast pathway:
a. Symplast = water moves through the cytoplasm via the plasmodesmata.
b. Apoplast = water moves through cell walls and intercellular spaces which are permeable.
Symplast pathway?
-water diffuses down conc gradient from root hair cells to xylem through interconnected cytoplasm ( symplast) of cells of root
- moves through cytoplasm / plasmodesmata - gap in cellulose cell wal
- Symplastic Living (mark scheme)
Apoplast pathway?
-water pulled by the attraction between water molecules across adjacent cell walls (the apoplast) from root hair cell to xylem
-as water drawn into xylem - attraction between molecules ensures more water is pulled across from adjacent cell wall..
- water moves across cells of root in cell wall until reaches endodermis which contains a waterproof layer called the Casparian strip
- reaches Casparian strip = has to travel via the symplast pathway to xylem
- across cellulose cell wal and then enters symplast way when reaches endodermis
- Apoplastic non-living (mark scheme)
PMT Question
compare symplastic + apoplast pathway:
Apoplast:
- non-living
- faster
- uses cell wall
- through diffusion
- blocked by casparian strip
Symplast:
- living
- slower
- cytoplasm + plasmodesmata
- osmosis
- does not have to cross casparian strip
Translocation of water + mineral ions VS translocation of sucrose?
Translocation - movement of substances around plant
Translocation of water + mineral ions
- occur in xylem
- passive process
Translocation of organic solutes (eg sucrose)
-occurs in phloem
-active process
Movement of water in xylem depends on transpiration -
define transpiration?
define transpiration stream?
Transpiration - loss of water vapour from surface of plant that’s evaporated from surface of spongy mesophyll cells
Transpiration stream - movement of water + minerals up from soil through root hair cells and across the roots to xylem, then up xylem across leaf until its lost by evaporation from spongy mesophyll cells + diffuses out of stomata down conc gradient.
What’s the cohesion-tension theory?
Adhesion ?
- when molecules of water leave Xylem to enter cell by osmosis - creates tension in column of water in xylem - which is transmitted all way down to roots.
- Cohesion of water molecules - due to their polar nature and H+ bonds between them = water molecules ‘stick together’ = column of water is under tension as water evaporates
(giving column of water high tensile strength) - Adhesion of water molecules to xylem walls
= more water pulled up to xylem due to cohesion of water molecules, to replace what is lost.
= cohesion-tension theory
How does cohesion-tension model contribute to transpiration stream?
(from roots to shoots)
- Water evaporated/lost from leaves (stomata)
- Therefore leaf cells have low water potential (waterpotential gradient created)
- Column of water is under tension
- Because of cohesion of water molecules
- Due to their polar nature + forming H+ bonds
- Adhesion of water molecules to xylem wall
- More water pulled up to xylem to replace what is lost
How can you demonstrate water loss in a plant?
- seal pot of potted plant in plastic bag - prevents evaporation from soil surface interfering experiment
- Seal plant in bell jar - water lost - colourless liquid collects on the glass of jar
[can show this is water by using cobalt chloride / copper sulfate paper]
What can u use to demonstrate transpiration?
- can measure uptake of water by plant as most water taken up is used for transpiration
-uptake of water demonstrated using a protometer
Which factors affect rate of transpiration?
- light
- temperature
- air movement
- air humidity
LIght
- Stomata open in light for photosynthetic gas exchange + closed in dark
= transpiration rates increase with light intensity until all stomata are open = after that plateau as maximum reached + wont be affected more by light
- other factor is limiting it
Temperature
- increase temp =increased rate of movement of molecules = increases rate of diffusion of water vapour out of leaf = increasing transpiration
- also increase amount of evaporation from surface of spongy mesophyll
- eventually another factor will become limiting
Air movement / wind
- reduces amount of still air around stomata = increases diffusion gradient between inside + outside leaf = increasing rate of transpiration
Air humidity
- the conc of water vapours in air
- high air humidity = lowers rate of transpiration as reduced conc gradient between inside of leaf + air
- low air humidity = dry air - increases transpiration rate due to big conc gradient = more diffusion
What’s root pressure?
- during night when transpiration rates very low = drops of water may be forced out of leaves in process = guttation as result of root pressure.
-root pressure + pressure that results when salts are actively secreted from root cells into xylem sap, increasing conc across root + moving more water into xylem by osmosis
Substances transported in phloem are called?
travels from a to b ?
is phloem loading + translocation a active or passive process?
Substances transported in phloem are called assimilates - main assimilate is sucrose
transport of assimilated in phloem is from sources to sinks
sources - areas of plants high in sucrose + loads sucrose into the phloem + low water potential
= green parts (leaves + stems)
sinks - areas of plant low in sucrose + removes sucrose from phloem
= actively dividing cells in meristems / storage organs (roots/sjoots) + high water potential
- Phloem loading + translocation is an active process, using ATP from respiration.
Phloem loading
- sucrose is loaded into phloem sieve elements from surrounding cells
2 main loading routes into phloem sap:
- symplast pathway
- Apoplast pathway
Symplast pathway for sucrose loading?
a) Sucrose moves by diffusion from leaf cell to companion cell of phloem into the phloem sieve tube.
b) This decreases the water potential of the phloem so water moves into the phloem from the xylem by osmosis.
c) This generates a hydrostatic pressure in the phloem so water moves down the sieve tube towards the sink down the pressure gradient.
Apoplast pathway for sucrose loading?
a) Sucrose moves by diffusion from leaf cell to companion cell wall.
b) Sucrose is moved via active transport across the companion cell wall into the cytoplasm.
c) It moves through the plasmodesmata via diffusion into the sieve tube.
d) Osmosis, hydrostatic pressure, movement towards the sink.
Phloem unloading?
The phloem is unloaded passively :
a) Sucrose moves into sink cells by diffusion down conc gradient from sieve tubes to surrounding cells tubes
b) The sucrose is removed (e.g. stored or used ) which maintains the concentration gradient.
c) As sucrose moves out of the phloem the water potential of the phloem increases and water moves out by osmosis e.g. back to the xylem.
What’s the mass flow / pressure flow hypothesis?
Transport of materials using a transport medium and pressure/force is known as the mass flow or pressure flow hypothesis.
= explaining movements of solutes in phloem of plants
- The hypothesis which outlines how assimilates are transported in the phloem of plants from source to sink
- Sugars are actively transported into the phloem + water moves into the phloem down the osmotic gradient in response.
- This increases hydrostatic pressure which causes mass sugar movement movement towards sink
the hydrostatic pressure forces water out
Strengths of the Mass flow hypothesis in explaining movement of sugars through phloem tissues
Evidences for translocation:
a) You can use radioactive isotopes available to leaves = glucose made is radioactive = path it takes traced with autoradiography = sucrose found in the phloem.
b) If steam is used to kill a ring of bark on a tree then it stops movement of solutes in the phloem (and not the xylem).
c) Aphids feed off phloem tubes and sometimes pressure of fluid in phloem is so great that it moves right through alphids’ digestive system + appears as a droplet on other end of body =
evidence for high hydrostatic pressure in the phloem +can be used to analyse components of phloem for both content + rate of flow
Limitations of the Mass flow hypothesis in explaining movement of sugars through phloem tissues
- Doesn’t explain why there can be bidirectional movement in the sieve tube.
- different solutes move at different speeds in the sieve tube = this assumes all move at same speed
- sieve plates should acc slow movements of solutes rather than helping
A modified version of mass flow hypothesis = knows as the pressure flow hypothesis is better idea of how assimilates are transported at phloem.
- Sucrose is active;y loaded into sieve tube elements
- Osmotic gradient generated causes water to move into sieve tube elements
- turgor increases in sieve tube walls
- Mass flow of water takes place down turgor pressure gradient
- Sucrose moves with water
- Sucrose + water removed from sieve tube elements.
