Mass Transport

Moloney content

What are haemoglobins?

• large proteins found in red blood cells with a quaternary structure (4 polypeptide chains) that carry oxygen to tissues

• group of chemically similar molecules found in many different organisms

What is association/loading?

when an oxygen molecule joins to haemoglobin to form oxyhaemoglobin

What is dissociation/unloading?

when oxygen leaves oxyhaemoglobin to form haemoglobin

What does an oxygen dissociation curve show?

How saturated the haemoglobin is with oxygen at any given partial pressure

Meaning of affinity for oxygen

the tendency of a molecule to bind with oxygen

What is partial pressure (pO₂)?

a measure of oxygen concentration

Describe and explain the general shape of a dissociation curve

• when haemoglobin first binds with oxygen, its shape alters to make it easier for other oxygen molecules to join too

• As haemoglobin becomes more saturated, difficulty for more oxygen molecules o join increases

• this is shown by the shallow→steep→shallow dissociation curve

Describe the loading and unlading of oxygen in relation to the oxyhaemoglobin dissociation curve

What is partial pressure of carbon dioxide (pCO₂)?

What happens to haemoglobin at higher pCO₂?

A measure of the concentration of CO₂ in a cell

Haemoglobin gives up oxygen more readily at higher pCO₂ - gets more O₂ to cells during activity

Describe the effects of carbon dioxide concentration on the dissociation of oxyhaemoglobin (The Bohr Effect)

• carbon dioxide is produced from cell respiration (pCO₂ raises)

• rate of oxygen unloading increases

• so dissociation curve shifts right but stays the same shape

• saturation of blood with oxygen is lower for given pO₂, meaning more oxygen is released

Give three environments that have low oxygen concentration

• underground

• high altitudes

  • close to seabed

Describe the difference of the haemoglobin of organisms that live in low oxygen environments compared to human haemoglobin and its dissociation curve

• low concentration of oxygen - haemoglobin has higher affinity of oxygen

• due to low O₂ concentrations, haemoglobin must be good at loading O₂

• dissociation curve is to left of human

Describe the difference of the haemoglobin of organisms that have higher activity levels compared to human haemoglobin and its dissociation curve

• high oxygen demand - haemoglobin has low affinity for oxygen

• because haemoglobin must unload oxygen easily so it’s available

• Dissociation curve is to right of human

Describe the difference of the haemoglobin of organisms that are small compared to human haemoglobin and its dissociation curve

• small mammals have higher surface area : volume ratio than larger mammals

• they lose heat quickly so have a higher metabolic rate to keep warm

• meaning they have high oxygen demand

• small mammal haemoglobin have lower affinity for oxygen than human haemoglobin because their oxygen needs to unload easily to meet high oxygen demand

heart, cariovascular stuff

check class notes and compare with textbook

What are causal relationships?

Where a change in one variable causes a change in the other

What is the xylem?

tissue that transports water and mineral ions in solution in the stem and leaves of the plant (up from roots to leaves)

What is the phloem?

tissue that transports organic substances/solutes like sugars in solution both up and down the plant

Describe the structure of the xylem

• xylem vessels are part of xylem tissue that transports water and ions

• they are long, tube-like structures formed from dead cells joing end-to-end

• no end walls which makes uninterrupted tube allowing water to pass up through middle easily

Explain the cohesion-tension theory of water transport in the xylem [5 marks]

1. water lost from leaf because of transpiration/evaporation of water (molecules)

2. this lowers water potential of the mesophyll/leaf cells

3. water pulled up the xylem which creates tension

4. water molecules cohere/’stick’ together by hydrogen bonds

5. this forms continuous water column

6. adhesion of water molecules to walls of xylem vessel

What is transpiration?

the evaporation of water from a plant’s surface, especially the leaves

(water evaporates and leaves cells and leaves via stomata down water potential gradient)

What factors affect transpiration rate?

• light intensity

  • stomata open when it’s light to let CO₂ in for photosynthesis

  • they close in the dark - little transpiration

• temperature

  • warmer molecules = more energy = evaporate from cell faster

• humidity

  • lower humidity = faster transpiration rate (water potential)

• wind

  • windier = fast transpiration rate (water potential)

• estimating transpiration rate - potometers

• plant mass transport dissection (require practical 5)

do

Describe the structure of the phloem

• formed from cells arranged in tubes

• sieve tube elements are living cells that form the tube for transporting solutes, and have no nucleus and few organelles so

• there are companion cells for each sieve tube element to carry out living functions for sieve cells e.g. energy for active transport of solutes

What is translocation?

The movement of solutes to where they are needed in the plant

(solutes sometimes called assimilates

Explain the mass flow hypothesis for the mechanism of translocation in plants

Source (where assimilates/solutes produced)

• active transport used to actively load solutes from companion cells into sieve tubes of phloem at source

• water potential in sieve tube lowers, so water enters from xylem and companion cells via osmosis

• high pressure created at source end of phloem

Sink (where assimilates used up)

• at sink end, solutes are removed from phloem to be used up

• water potential increased inside sieve tube so water leaves via osmosis , lowering pressure

Flow

• results in pressure gradient from source end to sink end

• gradient pushes solutes along sieve tubes towards sink to be used

• higher concentration of sucrose at source = higher rate of translocation

finish flashcards - add evidence for mass transport hypothesis stuff

duh