T3: Exchanging substances Flashcards
Describe the relationship between size and surface area to volume ratio of organisms. (1)
The larger the organism , the smaller the surface area to volume ratio
How does an organism’s surface area to volume ratio relate to their metabolic rate.
- The higher the surface area to volume ratio, the higher the metabolic rate.
Mammals such as a mouse and a horse are able to maintain a constant body temperature.
Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse. (3)
Mouse is :
1. Smaller so larger surface area to volume ratio;
2. More/faster heat loss (per gram/in relation to body size);
3. (Faster rate of) respiration/metabolism releases heat;
Must be comparative.
Ignore heat lost more easily/readily.
Explain why oxygen uptake is a measure of metabolic rate in organisms. (1)
- (Oxygen used in) respiration,
- which provides energy / ATP;
OR - which is a metabolic process /
chemical reaction;
Why do multicellular organisms require specialised gas exchange surfaces?
- smaller SA:V ratio means the diffusion distance is greater
- Thus substances cannot as easily enter the cells
Name four features of an efficient gas exchange surface.
- large surface area e.g folded membranes in mitochondria
- Thin / small so short diffusion pathway *
- Steep concentration gradient maintained by blood supply or ventilation e.g alveoli
- Flat /long/small so large SA:V ratio **
Give two reasons why insects can’t use their bodies as an exchange surface
- they have a water insoluble chitin exoskeleton
- a smaller surface area to volume ratio
Name and describe the three main features of an insect’s gas transport system.
• Spiracles= holes on the body’s surface which may be opened or closed by a valve for gas or water exchange.
• Tracheae= large tubes extending through all body tissues, supported by rings to prevent collapse.
• Tracheoles= smaller branches dividing off the tracheae.
Explain the process of gas exchange in insects.
- Air diffuses into tracheae through spiracles.
- O2 diffuses down concentration gradient towards the ends of the tracheoles to respiring cells
- CO2 produced by respiring cells move down concentration gradient along tracheoles, into tracheae, towards spiracles to be released into the atmosphere.
- Insects use rhythmic abdominal movements to move air in and out of spiracles - increasing rate of gas exchange.
Give 4 ways insects reduce water loss from their gas exchange system
5
- Waterproof/waxy cuticle all over their body surfaces = reduce evaporation.
- Small SA:V ratio = minimise area over which water is lost.
- When spiracles open, water may evaporate from the insect. spiracles closed to prevent this water loss.
- Tiny hairs around spiracles = reduces evaporation.
- Cuticle/chitin in tracheae impermeable so reduce water loss;
Describe how the structure of the insect gas exchange system:
* provides cells with sufficient oxygen
* limits water loss.
Explain your answers.
(4)
- Spiracles (lead) to tracheae (that lead) to tracheoles;
- Open spiracles allow diffusion of oxygen from air
- Tracheoles are highly branched so large surface area (for exchange);
- Tracheole (walls) thin so short diffusion distance (to cells)
- Tracheole walls are permeable to oxygen;
- Cuticle/chitin in tracheae impermeable so reduce water loss;
- Spiracles close (eg.during inactivity) preventing water loss;
Describe anaerobic respiration in insects
- During intense activity, cells around the tracheae undergo anaerobic respiration, producing lactic acid.
- This lowers the water potential of the cells, causing water in the tracheal fluid to move into the cells.
- This reduces the volume of tracheal fluid, drawing air down into the tracheae and making more tracheal surface available for the diffusion of oxygen and carbon dioxide.
Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange. (3)
- Tracheoles have thin walls so short diffusion distance to cells;
- Highly branched so large number of tracheoles so short diffusion
distance to cells; - Highly branched / large number of tracheoles so large surface area (for gas exchange);
- Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas
exchange surface; - Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;
Why can’t fish use their bodies as an exchange surface
- they have a waterproof, impermeable outer membrane
- a small surface area to volume ratio.
Describe how gills provide a large surface area for gas exchange in fish.
- gills have many filaments ; each filament have many lamellae increasing SA for faster diffusion.
- thin lamella which shortens diffusion distance
- Each lamella has a dense capillary network, which allows oxygenated blood to move rapidly steepening the diffusion gradient.
Explain the process of ventilation in fish.
- when the fish opens its mouth , the buccal cavity volume increases so the pressure decreases
- this forces water across the gill filaments and lamella across the gills
- oxygen from the water diffuses into the blood stream through a countercurrent exchange system.
Explain the countercurrent exchange system. (4)
- water and blood flow in opposite directions
- blood always passing water with a higher oxygen concentration
- diffusion gradient maintained throughout whole length of gill
- if water and blood flowed in same direction , equilibrium would be reached.
Explain how the counter current mechanism in fish gills ensures the max amount of oxygen passes into the blood flowing through the gills. (3)
- Water and blood flow in opposite directions;
- Blood always passing water with a higher oxygen concentration;
- Diffusion gradient maintained throughout length (of gill)
Explain two ways in which the structure of fish gills is adapted for efficient gas exchange (2)
- many lamellae / filaments so large surface area
- thin (surface) so short diffusion pathway
Name and describe 5 adaptations of a leaf that allow efficient gas exchange
- Thin and flat to provide short diffusion pathway and large surface area to volume ratio
- air spaces in the mesophyll allow diffusion of carbon dioxide and oxygen , facilitating photosynthesis
- arrangement of leaves minimises shadowing to allow maximum light absorption.
- transparent cuticle and epidermis that let light through to the photosynthetic mesophyll cells.
- guard cells: control opening of stomata in response to changes in light intensity.
- waxy cuticle which reduces evaporation and water loss.
Use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow slowly (2)
- Stomata close*
- Less carbon dioxide (uptake) for less photosynthesis/glucose
production;
stomata close to prevent water evaporation - cos theres already little water
Give 5 adaptations of xerophytic plants
- ( sunken) stomata in pits: traps a layer of moist air. The water vapour in the air reduces the water potential gradient reducing water loss
- Thick waxy cuticle to reduce water evaporation from the surface
- less stomata = less water loss
- rolled leaves: traps a layer of humid-insulating air
- Hairs on leaf (trichomes) : trap moist air reducing the water vapour potential.
Describe xerophytic plants.
a plant which is adapted for survival in hot dry environments
Describe the pathway taken by air as it enters the mammalian gaseous exchange system.
- nasal cavity
- trachea
- bronchi
- bronchioles
- alveoli