Gas exchange Flashcards

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1
Q

Gas exchange in single celled organisms?

A

By diffusion through their cell surface membrane

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2
Q

Why are microorganisms able to perform exchange via their surfaces?

A
  1. Large surface area (surface area to volume ratio)
  2. Thin surface
  3. Short diffusion pathway/distance
  4. Low demands

(therefore no specialised gas exchange system required)

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3
Q

Why do fish have specialised gas exchange systems?

A

Fish are multicellular so

  1. Small surface area to volume ratio
  2. Large diffusion distance
  3. High demand
  4. Body surface is impermeable (waterproof)

(Fish specialised gas exchange system = gills

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4
Q

Structure of gills in fish?

A
  • Each gill is made up of lots of thin plates called gill filaments
  • which give a large surface area for exchange of gases and therefore, increase the rate of diffusion
  • The gill filaments are covered in lots of tiny structures called lamellae which increases the surface area even more
  • gill lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion between the water and blood
  • they are also permeable, short diffusion distance
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5
Q

Counter current system?

A
  • ventilation brings in pure water (high oxygen, low carbon dioxide) and
  • circulation brings in deoxygenated blood (low oxygen, high carbon dioxide),
  • the water and blood pass over in opposite directions (counter-current flow),
  • which maintains concentration gradient all the way along the gill lamellae
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6
Q

Why do insects have specialised gas exchange systems?

A
  • High demand
  • Large diffusion distance
  • Body surface made of exoskeleton which is an impermeable barrier
  • Multicellular so has a relatively small surface area to volume ratio
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7
Q

Gas exchange in insects?

Structure of tracheal system

A
  • Air moves into the trachea through pores on the surface called spiracles
  • Oxygen travels down concentration gradient towards the cells
  • The trachea branch off into smaller tracheoles which have thin permeable walls and go to individual cells
  • Oxygen moves directly into the respiring cells
  • Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere
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8
Q

Control of water loss in insects?

A
  • They close their spiracles using muscles
  • They have a waterproof waxy cuticle all over their body
  • Tiny hairs around their spiracles

(these all reduce water loss)

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9
Q

Gas exchange by the leaves of dicotyledonous plants?

A
  • Mesophyll cells
  • Mesophyll cells have a large surface area
  • Gases move in and out through pores in the epidermis called stomata
  • The stomata can open to allow exchange of gases and close if the plant is losing too much water
  • Guard cells control the opening and closing of stomata
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10
Q

Adaptions of xerophytic plants?

A
  1. Stomata sunk in pits to trap water vapour reducing the concentration gradient of water between the leaf and air. This reduces evaporation of water from the leaf.
  2. A layer of ‘hairs’ on the epidermis to trap water vapor around the stomata
  3. Curled leaves with the stomata inside, protecting them from wind. (windy conditions increase the rate of diffusion and evaporation)
  4. A reduced number of stomata, so there are fewer places for water to escape
  5. Thicker waxy, waterproof cuticles on leaves and stem to reduce evaporation
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11
Q

Why can’t animals/plants perform exchange via their surfaces?

A
  • have a small surface area to volume ratio
  • multicellular (large diffusion distance and high demand)
  • impermeable surface (prevent pathogens entering and reduce water loss)
  • therefore, require specialised Exchange & Transport systems

(exchange system = increases rate of diffusion of nutrients in and wastes out)
(transport system = deliver nutrients and remove waste from all cells)

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12
Q

Why does gas exchange need to occur in humans?

A
  • Humans need to get oxygen into the blood (for respiration) and need to get rid of carbon dioxide (made by respiring cells)
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13
Q

Structure of the gas exchange system in humans?

A
  • As you breathe in, air enters the trachea (windpipe)
  • The trachea splits into two bronchi - one bronchus leading to each lung
  • Each bronchus then branches off into smaller tubes called bronchioles
  • The bronchioles end in small ‘air sacs’ called alveoli
  • This is where gases are exchanged
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14
Q

Adaptations of alveoli?

A
  • millions of tiny alveoli that are folded (large surface area)
  • thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
  • elastic tissue in wall (stretches when breathing in to increase surface area, recoils when breathing out to push the air out)
  • ventilation maintains concentration gradient (high oxygen, low carbon dioxide)
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15
Q

Adaptations of capillaries?

A
  • millions of tiny capillaries (large surface area)
  • thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
  • narrow lumen (increases diffusion time, decreases diffusion distance)
  • circulation maintains concentration gradient (low oxygen, high carbon dioxide)
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16
Q

Movement of carbon dioxide and oxygen in the gas exchange system?

A
  • Air (containing oxygen) moves down the trachea, bronchi and bronchioles into alveoli
  • This movement happens down a pressure gradient
  • Oxygen then moves into the blood where it can be transported round the body - this movement happens down a diffusion gradient

(Carbon dioxide moves down its own pressure and diffusion gradients, but in the opposite directions to oxygen so it can be breathed out)

17
Q

How oxygen moves from the alveoli to the capillaries?

A
  • Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary epithelium into haemoglobin/blood
18
Q

How carbon dioxide move from the capillaries to the alveoli?

A
  • Carbon dioxide diffuses into the alveoli into the blood
19
Q

Describe the process of breathing in/inspiration?

A
  • The external intercostal muscles contract
  • The diaphragm contracts
  • This causes the ribcage to move upwards and outwards and the diaphragm to flatten
  • increasing the volume of the thoracic cavity
  • as the volume of the thoracic cavity increases , the lung pressure decreases to below atmospheric pressure
  • so air flows down the trachea into the lunge
20
Q

Describe the process of breathing out/expiration?

A
  • The external intercostal and diaphragm muscles relax
  • the ribcage moves downwards and inwards
  • the diaphragm curves upwards again (becomes dome-shaped)
  • The volume of the thoracic cavity decreases
  • causing the air pressure to increase above atmospheric pressure
  • air is forced down the pressure gradient and out of the lungs