Module 3 Flashcards
Exchange surface
Explain why large, multicellular organisms need specialized exchange surfaces. (4marks)
- Large multicellular organisms have small SA:V ratio, so diffusion alone is insufficient to meet the need of the organism .
- Specialised exchange surfaces increase the SA for efficient gas exchange.
- Transport systems are required to carry substances to/from the cells.
Describe the features of the human alveoli that make them efficient for gas exchange. (6marks).
-lungs have large SA due to many alveoli present.
-moist surface allows to dissolve gases.
- alveoli are one cell thick, so shorter diffusion distance.
- alveoli are elastic, so they can expand and contract for efficient gas exchange.
- alveoli have good supply of blood (capillaries) so it maintains conc. gradient.
-the ventilation maintains the conc. gradient by removing air (exhalation) and bringing fresh air (inhalation).
Describe how the structure of the gills in fish is adapted for efficient gas exchange.( 6 marks )
- Gills have many filaments and lamellae to increase surface area.
- Thin epithelial cells on the gill filaments provide a short diffusion distance.
- Countercurrent flow of water and blood ensures a concentration gradient is maintained.
- Water flows continuously over the gills to remove waste gases and bring in oxygen.
- The large surface area and the constant movement of water provide efficient gas exchange.
Compare the features of an insect’s tracheal system and the human respiratory system that enable them to carry out gas exchange efficiently. (6marks)
Insects: Tracheae have many branches, increasing surface area for gas exchange. Humans: Alveoli have large surface area and are surrounded by capillaries for gas exchange.
Insects: Tracheoles provide a direct route to cells for oxygen and removal of CO2. Humans: Capillaries carry gases to/from cells via the bloodstream.
Insects: Spiracles can open and close to control water loss and air intake. Humans: The diaphragm and intercostal muscles assist in ventilation to maintain a concentration gradient.
Insects: No circulatory system for gas exchange, gases move directly in/out of cells. Humans: Circulatory system (blood) carries gases to/from tissues and maintains the concentration gradient.
Explain how the structure of the villi in the small intestine aids the absorption of nutrients. (3marks)
Villi provide a large surface area for absorption of nutrients.
The epithelial cells are one cell thick, providing a short diffusion distance.
Villi have a rich blood supply to carry absorbed nutrients away, maintaining concentration gradients.
Describe how the structure of a leaf is adapted for efficient gas exchange. (5marks)
Large surface area due to the broad shape of the leaf.
The leaf has many stomata to allow gas exchange.
The stomata can open and close to regulate gas exchange and water loss.
Mesophyll cells have air spaces to allow gases to move freely inside the leaf.
The thin leaf structure reduces the distance gases need to diffuse.
Explain the importance of maintaining a concentration gradient in the process of gas exchange. (4marks)
A concentration gradient allows gases to diffuse from an area of high concentration to an area of low concentration.
In the lungs, oxygen diffuses from the alveoli (high concentration) to the blood (low concentration).
Carbon dioxide diffuses from the blood (high concentration) to the alveoli (low concentration).
Maintaining this gradient ensures continuous and efficient gas exchange.
Compare the mechanisms of gas exchange in fish and in humans. (5marks)
Fish: Gills provide a large surface area for gas exchange. Humans: Alveoli provide a large surface area for gas exchange.
Fish: Countercurrent flow of water and blood maintains a concentration gradient. Humans: Ventilation and a good blood supply maintain concentration gradients.
Fish: Oxygen in water diffuses into blood via gill filaments. Humans: Oxygen in air diffuses into blood via alveolar walls.
Fish: Water passes over gills in one direction, ensuring continuous oxygen supply. Humans: Air is ventilated into the lungs to maintain oxygen supply.
Describe how the structure of the tracheal system in insects is adapted to facilitate gas exchange. (4marks)
Tracheae are tubes that carry air directly to tissues and cells.
Tracheoles have a large surface area for gas exchange.
The tracheal system is open to the outside via spiracles, allowing air to enter.
The thin walls of the tracheoles provide a short diffusion distance for gases.
Explain why a larger organism requires a specialized transport system for gas exchange. (3marks)
As organisms become larger, they have a smaller surface area to volume ratio.
Diffusion alone cannot transport gases to all cells in sufficient quantities.
A specialized transport system (e.g., circulatory system) allows for the efficient delivery and removal of gases.
