Topic 3.1 - Gas Exchange Flashcards
Why do organisms need to exchange substances with their environment?
- Cells need to take in oxygen and nutrients
- Cells need to excrete waste products (e.g. carbon dioxide and urea)
- Most organisms need to stay same temperature = heat needs to exchanged
Smaller animals have a _____ SA : Volume Ratio
Higher
Why do multicellular organisms need exchange organs and mass transport systems?
Because diffusion across the multiple layers of cells would be too slow
Why don’t single-celled organisms need exchange organs or mass transport systems?
Because substances can diffuse directly into (or out of) cells across cell-surface membrane (diffusion rate is quick)
Name 2 things that cause diffusion across outer membrane to be too slow in multicellular organisms
- Cells deep within body
- Big distance between them & outside environment
- Larger animals = low SA:volume ratio
What is tissue fluid?
Liquid environment around cells of multicellular organisms
Name 2 factors that affect heat exchange
- Shape
- Size
Animals with compact shape have a ___ surface area relative to their volume which _____ heat loss from their surface
Animals with compact shape have a SMALL surface area relative to their volume which MINIMISIES heat loss from their surface
What do small animals (with a large surface area) need to stay warm and why?
High metabolic rate to generate enough heat to stay warm therefore they lose heat easily
Name 3 gas exchange surfaces adaptations
- Large SA
- Thin = short diffusion pathway
- Steep concentration gradient
Name 2 ways organisms maintain a steep concentration gradient
- Via movement of environmental medium e.g. air
- Via transport system to ensure movement of internal medium
Name 2 features that single-celled organisms have that allow gases to diffuse through their outer surface
Have large surface area, thin surface & short diffusion pathways
Name the main gas exchange surface in dicotyledonous plants
Surface of mesophyll cells in leaf
In dicotyledonous plants, how does gas move in and out of the plant?
Through stomata in the leaves
What do insects use for gas exchange?
Tracheae (microscopic air-filled pipes)
What are spiracles?
Pores on insects’ surface
Describe and explain the movement of oxygen into the gas exchange system of an insect when it is at rest
- Oxygen is used in aerobic respiration
- So oxygen concentration gradient established
- Oxygen diffuses in through spiracles, then tracheae & then through tracheoles which go into individual cells
How is carbon dioxide removed from insects?
Carbon dioxide from the cells diffuses (down its own concentration gradient) into tracheal tubes and through the spiracles
Why do insects have to be small in size?
Because insects mainly rely on diffusion to exchange gases
What are the tracheae supported by to prevent them from collapsing?
Strengthened rings of cartilage
Name 4 adaptations of dicotyledonous plants that enable efficent gas exchange
- Many stomata
- Thin, flat shape which provides large SA:volume ratio
- Numerous interconnection air spaces throughout mesophyll
- Leaf is flattened so no living cell is far form external air
Why do stomata have the ability to open and close?
To balance gas exchange with water loss.
Name 2 adaptations that insects have to minimise water loss (without reducing gas exchange too much)
- If insects are losing too much water, their close their spiracles using muscles
- Have waterproof, waxy cuticle over their body & tiny hair around their spiracles which reduce evaporation by trapping moist air.
Name an adaptation of dicotyledonous plants to minimise water loss without reducing gas exchange too much
If plants gets dehydrated, guard cells lose water & become flaccid to close stomata
How are plants’ stomata kept open during day (for gaseous exchange)?
Water enters guard cells, making them turgid which opens stomatal pore
What type of process is inspiration (breathing in)?
Active process – uses energy
What type of process is expiration (breathing out)?
Passive process
Describe the process of inspiration
Describe the process of expiration
Describe what happens during forced expiration (e.g. when you want to blow out candles)
- External intercostal muscles relax & internal intercostal muscles contract = pulling ribcage further down and in
- During this time, movement of 2 sets of intercostal muscles is said to be antagonistic (opposing)
What mainly causes the air to be forced out during normal quiet breathing (e.g. sleeping)?
Recoil of the elastic lungs
Describe how oxygen gets from the alveoli to the blood
Oxygen diffuses out of alveoli, across the alveolar epithelium and capillary endothelium (type of epithelium that forms the capillary wall) & into haemoglobin in blood via a diffusion gradient.
How does oxygen travel from outside to the body to the alveoli?
Oxygen from the air moves down the trachea, bronchi and bronchioles into the alveoli down a pressure gradient
Name 3 adaptations alveoli have for gaseous exchange
- Thin exchange surface:
Alveolar epithelium, and capillary endothelium is once cell thick which = short diffusion pathway - Large surface area and a large no. of alveoli = large SA for gas exchange
- Steep concentration gradient of oxygen and carbon dioxide between alveoli and capillaries which is maintained by flow of blood and ventilation
Name 2 things red blood cells do to enable efficent gas exchange
- Red blood cells are slowed as they pass through pulmonary capillaries which allow more time for diffusion
- Red blood cells are flattened against capillary walls which reduces diffusion distance
Describe the structure of haemoglobin
Haemoglobin is a large protein with quaternary structure, made up of 4 polypeptide chains. Chains linked together to form spherical molecule. Each chain contains a haem group which contains a iron ion for an oxygen molecule to bind to.
How many oxygen molecules can each haem group combine with?
1 oxygen molecule
How many molecules of oxygen can each haemoglobin carry?
4 oxygen molecules
What happens to haemoglobin in the lungs?
Oxygen joins to haemoglobin in RBCs to form oxyhaemoglobin
What happens to oxyhaemoglobin when it nears body cells?
Oxygen leaves oxyhaemoglobin (dissociates from it) & turns back to haemoglobin
What is partial pressure of oxygen?
A measure of oxygen concentration
The greater the concentration of dissolved oxygen in the cells is, the _____ the partial pressure is
Higher
Haemoglobin’s affinity for oxygen varies depending on…
The partial pressure of oxygen.
What happens to haemoglobin when there is low partial pressure of oxygen?
- Oxyhaemoglobin unloads its oxygen because haemoglobin has a low affinity for oxygen. This means it releases oxygen rather than combines with it
What happens to haemoglobin when there is high partial pressure of oxygen?
Oxygen loads onto haemoglobin to form oxyhaemoglobin because haemoglobin has a high affinity for oxygen. This means it will readily combine with oxygen rather than release it
What happens to oxygen when it enters the blood capillaries at the alveoli in the lungs & why?
Alveoli have high partial pressure of oxygen. Therefore oxygen loads onto haemoglobin to form oxyhaemoglobin
What happens to oxygen at respiring cells & why?
When cells respire they use up oxygen. Therefore, the partial pressure of oxygen decreases. So, red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen
What do dissociation curves show?
How saturated haemoglobin is with oxygen at any given partial pressure
Why is that when the partial pressure of oxygen is high, haemoglobin has a high saturation of oxygen?
Because haemoglobin has a high affinity for oxygen so it’ll readily combine with oxygen
Why is that when the partial pressure of oxygen is low, haemoglobin has a low saturation of oxygen?
Because haemoglobin has a low affinity for oxygen so it releases oxygen rather than combines with it
Why is it difficult for the haemoglobin to absorb the last oxygen
molecule?
Because the 4 polypeptides of the haemoglobin molecule are closely united
Why is the dissociation curve ‘S-shaped’?
- When haemoglobin combines with one oxygen molecule, it causes a conformational change (its shape alters), exposing more subunits to oxygen which makes it easier for other oxygen molecules to join. But as haemoglobin becomes saturated it is harder for more oxygen molecules to join. Therefore the curve has steep bit in middle where it’s really easy for oxygen molecules to join & shallow bits at each end where it’s harder.
Why does haemoglobin rarely achieves 100% saturation of oxygen?
Because it’s very difficult for 4 oxygen molecule to bind.
Why do different haemoglobin molecules have different affinities for oxygen? (structure wise)
Because different haemoglobin molecules have slightly different sequences of amino acids & therefore slightly different shapes
Haemoglobin gives up its oxygen more readily at a _____ partial pressures of carbon dioxide
HIGHER
What is the purpose of haemoglobin having a lower affinity for oxygen at higher partial pressure of carbon dioxide?
So more oxygen will dissociate into respiring tissues
Describe the Bohr Effect
- Respiring tissues produce carbon dioxide.
- Carbon dioxide dissociates into many hydrogen ions
- hydrogen ions bind to haemoglobin & changes its shape causing more oxygen to be released which lowers affinity for oxygen
Therefore, the dissociation curve ‘shifts’ to right
Left of the dissociation curve = …
Greater affinity of haemoglobin for oxygen
Right of the dissociation curve = …
lower affinity of haemoglobin for oxygen
What type of haemoglobin do organisms that live in environments with low concentration of oxygen have?
Haemoglobin with higher affinity for oxygen than human haemoglobin
(Dissociation curve is to the left of ours)
What type of haemoglobin do organisms who are very active & have a high oxygen demand have?
Haemoglobin with a lower affinity for oxygen than human haemoglobin
(Curve is to right of human one)
Name 2 factors (other than partial pressure of oxygen/carbon dioxide) that affect the affinity of haemoglobin for oxygen.
- Increasing temperature
- Decrease in pH (more acidic solution)
What happens to haemoglobin’s affinity for oxygen when there’s an increase in temperature and why is this beneficial?
Lowers affinity of hameoglobin for Oxygen. This is beneficial because temp. increases during exercise, when you need more oxygen for respiration
What happens to haemoglobin’s affinity for oxygen when there’s a decrease in pH and why does this occur?
Lowers affinity of hameoglobin for oxygen. Therefore a more acidic solution = the more hydrogen ions there will be to bind with hameoglobin. So more oxygen is released when carbon dioxide is present
What is foetal hameoglobin like (i.e. its affinity for oxygen)?
Has higher affinity for oxygen than adult haemoglobin
Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf
Carbon dioxide enters via stomata. Stomata are opened by guard cells. So carbon dioxide diffuses through air spaces down diffusion gradient
Describe and explain how the countercurrent system leads to efficient gas exchanges across the gills of a fish.
Water and blood flow in opposite directions. This maintains aconcentration gradient along whole of gill/lamellae
Name 4 common symptoms of lung disease
- Less elastic recoil
- Harder to remove air from the alveoli (when breathing out)
- (The walls of the alveoli are damaged) so reduced surface area (for gas exchange)
- (Inflammation of alveoli/thicker walls) so increased diffusion distance
- (More carbon dioxide/less oxygen in the alveoli) so reduced concentration gradients (for diffusion/gas exchange)
