Gas Exchange UNIT 2 Flashcards
Single celled organisms exchange gases across their……
Body surface
They absorb and release gases by diffusion through their outer surface
They have large surface area, thin surface, short diffusion pathway, so no need for gas exchange system
Two major adaptations of gas exchange surfaces
Large surface area
Thin diffusion pathway
What system do fish use for gas exchange
The counter-current system
How does the counter current system work
Water containing oxygen enters fish mouth, passes out through gills. Each gill made up of lots of thin plates called gill filaments, which give a big surface area for exchange of gases. The filaments 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. Blood flows thorough lamellae in one direction and water flows over in the opposite direction. Maintains a large concentration gradient between water and blood, so as much oxygen as possible diffuses form water into blood
What do insects use for gas exchange
Tracheae
How do the tracheae work
Insects have microscopic air filled pipes called tracheae. Air moves into the tracheae through pores on the surface called spiracles. Oxygen travels down the conc gradient towards cells. Carbon dioxide from the cells moves down its own conc gradient towards the spiracles to be released into the atmosphere. 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 insects circulatory system doesn’t transport oxygen. Insects use rhythmic abdominal movements to move air in and out of the spiracles
Explain gas exchange in dicotyledonous plants
Plants need carbon dioxide for photosynthesis, which produces oxygen as a waste gas. They need oxygen for respiration, which produces carbon dioxide 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 as they have a large surface area. The mesophyll cells are inside the leaf. Gases move in and out through special pores in the epidermis called stomata. These 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 do insects control water loss
They close their spiracles using muscles. Also have waterproof waxy cuticle all over body and tiny hairs around their spiracles, both of which reduce evaporation
How do plants control water loss
The stomata are usually kept open during the day to allow gas exchange. Water enters the guard cells making them turgid which opens stomatal pore. If plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore.
What are xerophytes
Plants that are adapted for living in warm dry windy places where water loss is a problem
Examples of xerophytes adaptations
Stomata sunk in pits which trap moist air, reducing evaporation. Curled leaves with the stomata inside, protecting them from wind. A layer of ‘hairs’ on the epidermis to trap moist air round the stomata, reducing the concentration gradient of water. A reduced number of stomata, so there are fewer places for water to escape. Waxy, thick waterproof cuticles on leaves and stems to reduce evaporation
Suggest how a student could use a microscope slide to find the number of stomata per cm2
Determine field of view
Count number of stomata in field of view
Repeat and calculate a mean
