6.2 Gas Exchange in Single-celled organisms, Insects and Fish

Question 1

Name 3 adaptations of gas exchange surfaces

Answer 1

1. Thin so short diffusion distance
2. Large surface area
3. Maintained concentration gradient

Question 2

Describe how single-celled organisms exchange gases across their body

Answer 2

• absorb and release gases by diffusion through their outer surface
• have a large SA, thin surface and short diffusion pathway ~ don’t need a gas exchange system

Question 3

How do fish use counter-current system for gas exchange?

Answer 3

• water enters fish through its mouth and passes out through the gills
• each gill is made of lots of gill filaments ~ provide a large surface area for gas exchange
• gill filaments are covered in lamellae which also increase surface area
• lamellae have loads of blood capillaries and a thin layer of cells to increase rate of diffusion
• blood flows through the lamellae in one direction and water flows over in the opposite direction = counter-current system
• maintains a large concentration gradient between water and blood
• concentration of oxygen is always higher than in blood

Question 4

Why do fish use the specialised counter-current gas exchange system?

Answer 4

Lower concentration of oxygen in water than air

Question 5

How do insects use the trachea to exchange gases?

Answer 5

• insects have microscopic air-filled pipes called trachea
• air moves into the trachea through pores on the surface = spiracles
• oxygen travels down the concentration gradient towards the cells
• trachea branch off into smaller tracheoles which have thin, permeable walls and go to individual cells = oxygen diffuses directly into the respiring cells
• carbon dioxide from cells moves down its own concentration gradient towards spiracles to be released into the atmosphere
• insects use rhythmic abdominal movements to move air in and out of spiracles

Question 6

How do xerophytes such as dicotyledonous plants exchange gases?

Answer 6

• carbon dioxide for photosynthesis which produces oxygen
• oxygen for respiration which produces carbon dioxide
• main surface is surface of mesophyll cells as they are large
• the cells are inside the leaf o gases move in and out of stomata in the epidermis
• stomata can open to allow exchange of gases and close to stop plant using water
• stomata is controlled by guard cells

Question 7

How are insects adapted to prevent water loss during gas exchange?

Answer 7

• close their spiracles using muscles
• have a waterproof waxy cuticle all over their body
• tiny hairs that reduce evaporation

Question 8

How are plants adapted to prevent water loss during gas exchange?

Answer 8

• water enters the cell = making guard cells turgid so stomata is open
• dehydrated = guard cells lose water and become flaccid so stomata closes

Question 9

Name 5 adaptations of xerophytes

Answer 9

1. Stomata are sunk in pits so moist are is trapped = reducing concentration gradient of water between leaf and air = less water diffuses out of the leaf or evaporates away
2. Layers of hairs on the epidermis that trap most air around the stomata
3. Curled leaves with stomata inside are protected from wind
4. Reduced number of stomata = fewer spaces for water to escape
5. Waxy, waterproof cuticles on leaves and stems = reduces evaporation