Exchange: Gas Exchange In Organisms Flashcards
(31 cards)
What is the definition of the term ‘surface area’?
The total area of the organism that is exposed to the external environment.
As the surface area and volume of an organism increases, the surface area to volume ratio decreases. This is because volume increases much more rapidly than surface area as size increases.
What is the surface area of like in small organisms?
Small organisms, i.e amoeba, have a very large surface area in comparison to their volume. This means there is a large SA for exchange of substances, but also there is a smaller distance from the outside of the organism to the middle of it. As a result, organisms can simply exchange substances across their surface.
What is the definition of the term ‘volume’?
The total internal volume of the organism (total amount of space inside the organism)
What is the surface area like in large organisms?
The larger the organism is the smaller its SA:V ratio, the larger the distance from the middle to the outside. Larger organisms will typically have a higher metabolic rate too, which demands efficient transport of waste out of cells and reactants into the cell. As a result, they have adaptations that help make the exchange across surfaces more efficient.
What is a ‘metabolic rate’?
The amount of energy expended by that organism in a time period e.g daily
What is ‘metabolic demand’?
How much oxygen and nutrients an organism needs to take on daily to respire enough to maintain the metabolic rate.
As a general rule, the greater the mass of an organism, the higher that organisms metabolic rate. This is because organisms with high metabolic rates require more efficient delivery of oxygen to cells.
What is the metabolic rate like in smaller organisms?
They have a lower metabolic rate due to a greater SA:V ratio. However, this also means they lose heat more easily and need greater amounts of energy to maintain a constant internal temperature: so, per unit of body mass, small organisms actually have a higher metabolic rate than larger organisms.
What do most gas exchange surfaces have in common?
Most gas exchange surfaces have two things in common that increase the rate of diffusion:
1. They have a large surface area.
2. They’re thin (often just one layer of epithelial cells) – this provides a short diffusion pathway across the gas exchange surface.
The organism also maintains a steep concentration gradient of gases across the exchange surface, which increases the rate of diffusion.
How do single-celled organisms absorb and release gases?
Single-celled organisms absorb and release gases by diffusion through their cell-surface membranes. They have a relatively large surface area, a thin surface and a short diffusion pathway (oxygen can take part in biochemical reactions as soon as it diffuses into the cell) - so there’s no need for a specialised gas exchange system.
What is the structure of the gills?
- Water, containing oxygen, enters the fish through its mouth and passes out through the gills. Each gill is made of lots of thin plates called gill filaments, which give a large surface area for exchange of gases (and so increase the rate of diffusion). The gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area even more.
- The lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion, between the water and the blood.
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What is the counter-current system?
In the gills of a fish, blood flows through the lamellae in one direction and water flows over them in the opposite direction. This is called a counter-current system. The counter-current system means that the water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen. This in turn means that a steep concentration gradient is maintained between the water and the blood — so as much oxygen as possible diffuses from the water into the blood.
How does gas exchange work in dicotyledonous plants?
- Plants need CO2 for photosynthesis, which produces O2 as a waste gas.
- They need O2 for respiration, which produces CO2 as a waste gas. The main gas exchange surface is the surface of the mesophyll cells in the leaf.
- They’re well adapted for their function - they have a large surface area.
- The mesophyll cells are inside the leaf. Gases move in and out through special pores in the epidermis (mostly the lower epidermis) called stomata (singular = stoma). 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.
How does gas exchange work in insects?
- Terrestrial insects have microscopic air-filled pipes called tracheae which they use for gas exchange.
- Air moves into the tracheae through pores on the surface called spiracles. Oxygen travels down the concentration gradient towards the cells. The tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells.
- This means that oxygen diffuses directly into the respiring cells — the insect’s circulatory system doesn’t transport O2 - Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere. Insects use rhythmic abdominal movements to move air in and out of the spiracles.
How are insects and plants equipped to reduce water loss?
- If insects are losing too much water, they close their spiracles using muscles. They also have a waterproof, waxy cuticle all over their body and tiny hairs around their spiracles, both of which reduce evaporation.
- Plants’ stomata are usually kept open during the day to allow gaseous exchange. Water enters the guard cells, making them turgid, which opens the stomatal pore. If the plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore.
How does having sunken stomata help reduce water loss?
Stomata sunk in pits to trap water vapour, reducing the concentration gradient of water between the leaf and the air. This reduces evaporation of water from the leaf.
How does having a layer of hairs help reduce water loss?
A layer of ‘hairs’ on the epidermis to trap water vapour round the stomata.
How does having curled leaves help reduce water loss?
Curled leaves with the stomata inside, protecting them from wind (windy conditions increase the rate of diffusion and evaporation).
How does having fewer stomata help to reduce water loss?
A reduced number of stomata, so there are fewer places for water to escape.
How does having a waxy cuticle help reduce water loss?
Thicker waxy, waterproof cuticles on leaves and stems to reduce evaporation.
What is the structure of the human gas exchange system?
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. The ribcage, intercostal muscles and diaphragm all work together to move air in and out.
What are intercostal muscles?
The intercostal muscles are found between the ribs. There are actually three layers of intercostal muscles, two of which you need to know about for your exams: the internal and external intercostal muscles. Unsurprisingly, the internal intercostal muscles are on the inside of the external intercostal muscles.
What is ventilation?
Ventilation consists of inspiration (breathing in) and expiration (breathing out). Its controlled by the movements of the diaphragm, internal and external intercostal muscles and ribcage.
What happens during inspiration?
During inspiration the external intercostal and diaphragm muscles contract. This causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity (the space where the lungs are). As the volume of the thoracic cavity increases, the lung pressure decreases to below atmospheric pressure. Air flows down the trachea and into the lungs - inspiration requires energy.
What is inspiration?
The process of inhalation.
