3.2 Gas exchange (Plants and Animals) Flashcards
(28 cards)
What are the 3 key features of every gas exchange surface
- Large surface area to volume ratio
- Short diffusion distance
- Maintained a conc grad
Explain how the body surface of a single celled organism is adapted for gas exchange
- Thin flat shape and large SA:V
- Short diffusion distance to all parts of cells–>rapid diffusion e.g. of O2 and CO2
Where does gas exchange occur in plants/leaves (4)
- Gas exchange occurs through the stomata where
- Oxygen diffuses out of the stomata
- Carbon Dioxide diffuses in through the stomata
- To reduce water loss by evaporation, Stomata close at night when photosynthesis wont be occuring
Explain how leaves of dicotyledonous plants are adapted for gas exchange (3)
● Many stomata (high density) → large surface area for gas exchange (when opened by guard cells)
● Spongy mesophyll contains air spaces → large surface area for gases to diffuse through
● Thin → short diffusion distance
What is a xerophyte
Plant adapted to live in very dry conditions e.g. cacti and marram grass
Explain structural and functional comproimises in xerophytic pants that allow efficient gas echange while limiitgng water loss (4)
● Thicker waxy cuticle
○ Increases diffusion distance so less evaporation
● Sunken stomata in pits / rolled leaves / hairs
○ ‘Trap’ water vapour / protect stomata from wind
○ So reduced water potential gradient between leaf / air
○ So less evaporation
● Spines / needles
○ Reduces surface area to volume ratio
* Longer root netwrok to reach for more water
Describe the gross structre of the human gas exchange system
Trachea-
Bronchi
Bronchioles
Capilary network - capillary network
Alveoli - air sacs
Explain the essential features of the alveolar epithelium that makes it adapted as a surface for gas exchange (5)
- Flattened cells/1 cell thick–> Short diffusion distances
- Folded–>Large surface area
- Permeable–>Allows diffusion of O2 and CO2
- Moist–> Gases can dissolve for diffusion
- Good blood supply from large network of capilaries–>Maintains conc hgradient
Explain the importance of ventilation
● Brings in air containing higher conc. of oxygen & removes air with lower conc. of oxygen
● Maintaining concentration gradients
Describe how gas exchange occurs in the lungs
- Oxygen diffuses from alveolar air spiace into blood down its conc gradient
- Across alveolar epithelium then across capillary endothelium
Explain how humans beathe in (4)
Inspiration
- Diaphragm muscles contract- flattens and External intercostal muscles contarct
- Increasing volume and decreasing pressure (below atmospheric) in thoracic cavity
- Air moves into lungs down pressure gradient
Explain how human breathe out (4)
Expiration
- Diaphragm relaxes–> moves upwards External intercostal muscles relax, internal intercostal muscles may contract
- Decreasing volume and increasing pressure abover atmospheric in thoracic cavity
- Air moves out of lungs down pressure gradient
Suggest why expiration is normally passive at rest
- Internal intercostal muscles do not normally need to contract
- Expiration aided by elastic recoil in alveoli
Suggest how different lung diseases reduce the rate of gas exchange
● Thickened alveolar tissue (eg. fibrosis) → increases diffusion distance
● Alveolar wall breakdown → reduces surface area
● Reduce lung elasticity → lungs expand / recoil less → reduces concentration gradients of O2 / CO2
Suggest how different lung diseases affect ventilation
● Reduce lung elasticity (eg. fibrosis - build-up of scar tissue) → lungs expand / recoil less
○ Reducing volume of air in each breath (tidal volume)
○ Reducing maximum volume of air breathed out in one breath (forced vital capacity)
● Narrow airways / reduce airflow in & out of lungs (eg. asthma - inflamed bronchi)
○ Reducing maximum volume of air breathed out in 1 second (forced expiratory volume)
● Reduced rate of gas exchange → increased ventilation rate to compensate for reduced oxygen in blood
Suggest why people with lung disease experinece fatgiue
Cells receive less oxygen—>rate of aerobic respiration reduced—>less ATP made
Suggest how you can analyse and interpret data to the effects of pollution smoking and other risks faqctors on the incidence of lung idsease
● Describe overall trend → eg. positive / negative correlation between risk factor and incidence of disease
● Manipulate data → eg. calculate percentage change
● Interpret standard deviations → overlap suggests differences in means are likely to be due to chance
● Use statistical tests → identify whether difference / correlation is significant or due to chance
○ Correlation coefficient → examining an association between 2 sets of data
○ Student’s t test → comparing means of 2 sets of data
○ Chi-squared test → for categorical data
Suggest how you can evaluate the way in which experimental data led to statutory restrictions on the sources of risk factors
● Analyse and interpret data as above and identify what does and doesn’t support statement
● Evaluate method of collecting data
○ Sample size → large enough to be representative of population?
○ Participant diversity eg. age, sex, ethnicity and health status → representative of population?
○ Control groups → used to enable comparison?
○ Control variables eg. health, previous medications → valid?
○ Duration of study → long enough to show long-term effects?
● Evaluate context → has a broad generalisation been made from a specific set of data?
● Other risk factors that could have affected results?
Explain the difference between correlations and casual relationships
● Correlation = change in one variable reflected by a change in another - identified on a scatter diagram
● Causation = change in one variable causes a change in another variable
● Correlation does not mean causation → may be other factors involved
What is Fick’s Law
Diffusion is directly proportional to: Surface area x difference in concentration/Length of diffusion path
Structure of a Dicotyledonous leaf
- TOP TOP layer is waxy cuticle
- Top layer is upper eperdmis and below that is Palisade mesophyll
- Below that is Spongey mesophyll
- Below that is the stoma/stomata and the lower epidermis
- Also has air spaces and Vascular bundles(xylem and phloem vessels
State two similiarites and differneces betwene gas exchange in a plant and insect
Similarities:
No living cell is far from the external air
Air is diffused through pores in their outer covering ( can control the opening and closing of them)
Differences:
Insects have a smaller SA:V ratio
Insects have special structures (trachea) along which gases can diffuse-plants do not
Some herbicides cuase the stomata of plants to close. Suggest how these herbicides may lead to the death of a leaf
There is little to no gas exchange with the environment
There will be some interchange of CO2 and O2 by respiration and photosynthesis however neither process can continue relying on each other as some gases need to be obtaine dby the external enviornment
Features of bronchi
Two dividisions of the trachea each leading to one lung
Produces mucas to trap dirt particles and have cillia that move the dirt laden mucus towards the tghroat
The larger brinchi are supported by cartillage although th eamount of cartillage decreases as the bronchi gets smaller
