Chapter 7: Mass transport Flashcards
Learn all about haemoglobin, the circulatory system, the heart and the cardiac cycle, blood vessels, water transport in xylem and transport in the phloem
What is haemoglobin?
A large protein found in red blood cells
structure of haemoglobin
- quaternary structure of 4 polypeptide chains
- each with a haem group which contains an iron ion
Haemoglobin has a high affinity for oxygen. What does this mean?
It means that each molecule of haemoglobin can carry 4 oxygen molecules
When there is a high partial pressure of oxygen what happens?
Haemoglobin’s affinity to oxygen increase so oxygen readily loads onto it to form oxyhaemoglobin. The opposite happens when there is a low partial pressure of oxygen.
Why does haemoglobin unload its oxygen at respiring cells?
respiring cells use up oxygen which decreases the partial pressure of oxygen (pO2) so that haemoglobin has a lower affinity for oxygen and releases oxygen which can be used up by the cell
When there is a high partial pressure of carbon dioxide what happens?
Haemoglobin’s affinity to oxygen decreases and it readily unloads its oxygen
Why do multicellular organisms such as mammals need a specialised transport system to supply their cells with raw materials
because they have a low surface area to volume ratio
What is the circulatory system?
The circulatory system is a specialised transport system made up of the heart and blood vessels that carries raw materials from specialised exchange organs to the body cells
The heart has its own blood supply. Which vessels supply the heart itself with blood?
The left and right coronary arteries supply the heart with blood.
there are two circuits to the circulatory system. describe them
one circuit takes blood from the heart to the lungs and then back to the heart
the other circuit supplies blood to the rest of the body
Xylem tissue transports…
water and mineral ions up from the roots to the leaves
Phloem tissue transport…
organic substances in solution up and down the plant
Xylem and phloem are both mass transport systems. What does this mean?
They transport substances over long distances
Structure of xylem vessels
parts of the xylem tissue that actually move the water and ions very long tube-like structures made up of dead cells joined end to end with no end walls so uninterrupted/unbroken tube
What is the cohesion-tension theory of water transport
water evaporates from the leaves
due to heat from the sun
this creates tension (suction)
which pulls more water into the leaf
cohesion
where water molecules form hydrogen bonds between themselves
means that water molecules stick together
so that a column of water is pulled up the xylem
transpiration
Transpiration is the evaporation of water from a plant’s surface esp. leaves
It is a side effect of photosynthesis:
plants need to open their stomata to let in CO2 which is needed for glucose production
but this also lets water out
Name the 4 main factors that affect transpiration rate.
light
humidity
temperature
wind
Explain how light affects transpiration rate.
more light = faster transpiration rate positive correlation stomata open to let in CO2 when light is present usually close at night
Explain how humidity affects transpiration rate.
less humidity = faster transpiration rate
negative correlation
air around the plant is dry
increases concentration gradient
Explain how temperature affects transpiration rate.
higher temp = faster transpiration rate positive correlation water evaporates from cells faster increases concentration gradient diffusion is faster
Explain how wind affects transpiration rate.
more wind = faster transpiration rate
positive correlation
more water vapour being removed
steeper diffusion gradient/increases conc. gradient
Describe how transpiration works.
water evaporates from the moist cell walls
accumulates in the spaces between cells in the leaf
when the stomata open
water vapour moves out of the leaf
down a concentration gradient
translocation
Translocation is the process by which organic molecules such as sugars like sucrose, and amino acids and some mineral ions are transported from one part of a plant to another
The Mass Flow Hypothesis
The best supported theory that explains how solutes are transported around a plant by translocation
Structure of the phloem
Phloem tissue is made up of sieve tube elements and companion cells
Sieve tube elements: living cells no nucleus few organelles arranged end to end ends walls are perforated form sieve plates
Companion cells:
carry out the living functions for sieve tube elements
e.g. providing energy ATP needed for active transport
one for each sieve tube element
Is transpiration a passive process. Explain why?
Yes, transpiration is a passive process because the only energy required is heat energy to evaporate water at the surface of leaves - it does not require metabolic energy.
sources
Sources are locations where sugars are made i.e. sucrose is made in the leaves via photosynthesis
sinks
Sinks are locations where the sugar will be used directly or stored for later
Give 2 objections against the Mass Flow hypothesis of translocation.
The sieve plates would create a barrier to mass flow
Sugar travels to lots of different sinks not just the ones with the highest water potential
Briefly describe the stages of the mass flow hypothesis of translocation.
Sucrose is actively transported into the sieve tubes using hydrogen ions/protons and co-transport proteins
Mass flow of sucrose through sieve tube elements occurs down a hydrostatic pressure gradient
Sucrose is then transferred from the sieve tubes into the sink cells
Describe how sucrose is transferred into the sieve tube elements.
sucrose is produced in photosynthesising cells
it diffuses down a conc. gradient into companion cells
via facilitated diffusion
hydrogen ions are actively transported from companion cells into the spaces within cell walls using ATP
H+ ions diffuse down their conc. gradient through carrier proteins in the sieve tube elements
sucrose molecule are transported along with the H+ ions by co-transport using co-transport proteins
Describe the mass flow of sucrose.
at the sources
sucrose produced during photosynthesis is actively transported into the sieve tubes
this lowers the water potential in the sieve tubes
the xylem has a higher water potential
so water moves from the xylem into the sieve tubes via osmosis
this creates a high hydrostatic pressure inside the sieve tubes
at respiring cells (sinks)
sucrose is either used or converted into starch
the respiring cells therefore have a lower conc. of sucrose
so sucrose is actively transported into the cells from the sieve tubes
this lowers the water potential of the cells
so that water moves into them from the sieve tubes via osmosis
the hydrostatic pressure inside the sieve tubes is lowered
the hydrostatic pressure at the source is higher than at the sink
sucrose solution moves down the hydrostatic gradient in the sieve tube at once
so there is mass flow of sucrose down the sieve tube
Describe how sucrose is transferred from the sieve tubes into sink cells.
Sucrose is actively transported out of the sieve tubes and into the sink cells by the companion cells
