Unit 3 - Organisms exchange substances with their environment
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Summary AQA A Level Biology - Cornell Style Notes - Unit 3 - Exchange and Transport
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Unit 3 - Organisms exchange substances with their environment
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AQA
Clear and concise Cornell styled notes for Unit 3 Biology A Level - Exchange and Transport. The notes include diagrams and colours to make revision more visually appealing. The whole course is covered by my notes and is written in a detailed way that is still easily understandable, and each page in...
Unit 3 - Organisms exchange substances with their environment
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Adaptation to Facilitate Exchange Eve Holland
Key Points: Notes:
- Small organisms = higher Small Organism Exchange:
- Small, singer celled organisms have a high SA:V ratio
SA:V
- large surface area allows for maximum absorption of
- Small organism can use
nutrients and gases and secretion of waste products
simple diffusion for - This means they can exchange substances via simple
exchange diffusion
Adaptations Of Larger Organisms That Facilitates Diffusion:
- As organisms increase in size their SA:V ratio decreases, the
- As size increases SA:V increase in their volume means that the diffusion distance
decreases increases
- As Volume increases - Large multicellular animals and plants have evolved
diffusion does also adaptations to facilitate the exchange of substances
- Large multicellular organism - They have a large variety of specialised cells, tissues, organs
have had to adapt for and systems - Eg. gas exchange system, circulatory system,
lymphatic system, urinary system, xylem and phloem
exchange
- To survive these organisms
- These multicellular organisms need ATP to carry out
need ATP which relies on processes for survival - this ATP generated via respiration.
gas exchange system. - A specialised gas exchange system is used to supply the
oxygen needed for this respiration and release the CO2
generated by this process.
SA:V Ratio & Metabolic Rate:
- BMR = Basal Metabolic Rate - BMR = Basal Metabolic Rate
- Metabolic rate - BMR is significantly lower than the metabolic rate of an
measurement: Oxygen organism when it is moving
consumption, Carbon - The metabolic rate of an organism can be measured/
dioxide production, Heat estimate using different methods: Oxygen consumption,
Carbon dioxide production, Heat production
production
- Studies show that the larger the mass of an organism the
- Higher overall mass = higher
higher the metabolic rate - e.g a single rhino consumes
metabolic rate more oxygen within a given period of time compared to a
- However, per unit of mass single mouse
smaller organisms have a - Although metabolic rate increases with body mass the BMR
higher BMR as they have a per unit of body mass is higher in smaller animals as they
larger SA:V to lose heat. have a greater SA:V ratio so they lose more heat
Summary:
,Gas Exchange - Insects and Fish Eve Holland
Key Points: Notes:
Factors That Make A Good Gas Exchange Surface:
Good gas exchange surface:
- Large surface area
- Large surface area
- Short diffusion distance
- Short diffusion distance - Concentration gradient maintained
- Concentration gradient
maintained Tracheal System Of Insects:
- Insects have a waxy exoskeleton which is impermeable to gas
thus they have to have system for gas exchange
Insects can't absorb gas through - Breathing system = Spiracle → trachea → tracheoles →
their body as the have a waxy muscle fibres (site of gas exchange)
exoskeleton - Spiracles = opening in exoskeleton that allows gas in
Instead the has a gras exchange - Trachea = large tubes
system: Spiracle → trachea → - Tracheoles = narrower tubes (walls have reinforcement that
tracheoles → muscle fibres keeps them open as the air pressure fluctuates )
- For smaller insects, this system provides sufficient oxygen via
diffusion
- Very active, flying insects need a more rapid supply/intake of
oxygen. They create a mass flow of air into the tracheal
Some larger insects also news mass system by: Closing the spiracles and using muscles for a
flow system - pump movement and pumping movement for ventilation.
movement of water in tracheoles - Also, during flight the water found at the narrow ends of the
to aid diffusion tracheoles is drawn into the respiring muscle so gas diffuses
across quicker.
Gas Exchange In Fish:
Fish get their oxygen from water - There is a lower conc of oxygen in water than air so fish have
passing through the mouth and out had to adapt to get sufficient oxygen
- For fish, water passes into the mouth and out of the gills
the gills
- Each gill has thin plates called gill filaments which increase
SA for diffusion
Adaptations of gills: - Filaments are also covered in lamellae, also increasing SA.
- Gill filaments - Fish also have the counter-current system in the gills, blood
- Lamellae flows from lower oxygen conc to higher conc and then water
flowing towards lamellae with a higher oxygen conc to a
Both increase SA for diffusion lower one in the opposite direction.
- This maintains a steep conc gradient to maximise diffusion
Summary:
, Gas Exchange - plants and water Loss Reduction Eve Holland
Key Points: Notes:
Plants main gas exchange surface is Gas Exchange In Plants:
the mesophyll cells found mostly - Plants need to exchange oxygen and CO2 for
on the lower epidermis respiration and photosynthesis
- The main gas exchange surface is the mesophyll cells (in
Mesophyll cells have a large SA leaf)
- Mesophyll are well adapted as they have a large SA
Gas moves in out of the plant - Gas moves in and out of these cells through pores
through stomata called stomata which are located in the (lower)
epidermis
Stomata are opened and closed by - Stomata can open and close to control gas exchange
guard cells and water loss - guard cells control this opening and
closing.
Control Of Water Loss:
- Plants and insects have to balance exchanging gases
Control of water loss: and minimising water loss
Insects - can close spiracles, have Insects - muscles can close spiracles and they have a waxy
waxy cuticle and hairs to stop cuticle over their body & hairs around the spiracles to reduce
water escaping evaporation.
Plants - stomata are kept open in the day and are shut at
Plants - stomata can be opened night, water enters guard cells, making the turgid which
and closed opens stomata, but when dehydrated guard cells become
flaccid and close stomata
Xerophytic Plants - sunken stomata Xerophytic Plants - stomata are sunk in pits to trap
surrounded by hairs, curled leaves, evaporated water to reduce conc gradient of water in plant vs
fewer stomata, waxy cuticle air, hairs on epidermis to trap water vapour around stomata,
curled leaves to protect stomata from wind, fewer stomata,
waxy waterproof cuticles.
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