Exchaning Substances

Question 1

Examples of organisms exchanging substances

Answer 1

• gas exchange - oxygen and carbon dioxide exchanged
• humans - urea diffuses from cells into the blood plasma for removal by kidneys

Question 2

What is SA:V?

Answer 2

• surface area to volume ratio
• indicates how easy/difficult it is for an organism to exchange substances with its environment

Question 3

Exchange surfaces in single-celled organisms?

Answer 3

• gases and dissolved substances can can diffuse directly into/out of the cell across the cell membrane
• because large SA compared to V
• enough substances can be exchanged across the membrane to supply volume of cell

Question 4

Multi-cellular organisms - exchange surfaces

Answer 4

• smaller SA:V ratio
• not enough substances can tissues from their outside surface to supply their entire volume
• need exchange surface for efficient diffusion

Question 5

Adaptions of the multi-cellular exchange surfaces

Answer 5

• thin membrane - short distance to diffuse
• large surface area so lots of a substance can diffuse at once
• exchange surfaces in animals have lots of blood vessels - get stuff in and out of blood quickly
• gas exchange surfaces in animals (eg alveoli ) are ventilated

Question 6

Job of lungs

Answer 6

• transfer oxygen to the blood and to remove water carbon dioxide
• to do this, contain millions of little air sacs called alveoli where gas exchange takes place

Question 7

Alveoli adaptations

Answer 7

• enormous surface area (to maximise)
• moist lining for dissolving gases
• very thin walls
• good blood supply

Question 8

Villi adaptations

Answer 8

• small intestine are covered in millions
• increase SA so digested food is absorbed much more quickly into the blood
• single layer of surface cells
• very good blood to assist quick absorption

Question 9

Exchanging substances - plants

Answer 9

• CO2 diffuses into the air spaces within the lead and diffuses into the cells where photosynthesis happened
Adaptations
• underneath leaf is an exchange surface
• this is covered in stomata for gases to diffuse through
• oxygen and water vapour diffuse out of stomata
• guards cells - control opening/closing of stomata so water is not lost
• flat shape of the leaf increases the area of this exchange surface (and air spaces increase SA too) more chance of CO2 getting in

Question 10

Exchanging substances - gills

Answer 10

• gills are gas exchange surfaces for fish
• water enters through the mouth and passes out through the gills - oxygen diffuses from the water into the blood and CO2 diffuses from the blood into the water
• each gill made of thin plates called gill filaments which give a big SA for gas exchange
• filaments covered in lamellae, which increase SA even more
• lamellae have lots of blood capillaries to speed up diffusion
• thin surface layer of cells to minimise distance gas has to diffuse
• blood flows through lamellae in one direction and water flows over in the opposite direction - maintains large concentration gradient between blood and water
• conc of oxygen is always higher than in the blood
• so as much oxygen as possible diffuses from the water into the blood