Exchanging substances

Question 1

how do organisms exchange substances with their environment?

Answer 1

• cells can use diffusion to take in substances, such as oxygen
• also use diffusion to get rid of waste products

Question 2

how is diffusion used to get rid of waste products?

Answer 2

through:
- carbon dioxide (from respiration)
- urea (from the breakdown of proteins)

Question 3

what is urea?

Answer 3

diffuses from cells into the blood plasma, then removed from the body by the kidneys

Question 4

how do you calculate an organism’s surface area to volume ratio?

Answer 4

SURFACE AREA:
length x width (area of square or rectangle)
total surface area: L x W x (height) + l x w x (sides)
VOLUME:
length x width x height
SA TO V RATIO:
divide both sides of the ration by the volume

Question 5

why do multicellular organisms need exchange surfaces?

Answer 5

• single celled organisms have a large SA compared to their volume
• multicellular organisms have a smaller SA compared to their volume
• MCO have specialised exchange surfaces and transport systems that carry substances to and from

Question 6

how does Gas exchange happen in the Lungs?

Answer 6

oxygen and carbon dioxide are exchanged in the lungs

Question 7

what is Alveoli?

Answer 7

millions of little air sacs that are contained in the lungs, this is where gas exchange happens

Question 8

what does alveoli have?

Answer 8

• a large surface area
• very thin walls, so gases don’t have far to diffuse
• a good blood supply

Question 9

how does the Villi provide a big surface area?

Answer 9

• the inside of the small intestine is covered in millions of villi
• they increase the surface area so that digested food is absorbed more quickly into the blood
• they have a single layer of surface cells and a good blood supply

Question 10

how does the structure of leaves let gases diffuse in and out of cells?

Answer 10

• plant leaves need to take in CO2 for photosynthesis and get rid of oxygen and water vapour
• underneath of the leaf is an exchange surface, its covered in small holes called stomata

Question 11

how is stomata used in this?

Answer 11

• CO2 diffuses through the stomata into the leaf, oxygen and water vapour diffuse out through the stomata
• the size of the stama are controlled by guard cells

Question 12

explain how Gills have large surface area?

Answer 12

• the gills are the gas exchange surface in fish
• water flows into the fish’s mouth and passes through the gills
• in the gills, oxygen diffuses from the water into the blood
• carbon dioxide diffuses from the blood into the water

Question 13

explain how Gills have large surface area for gas exchange?

Answer 13

• the gills are made up of lots of thin plates, this gives them a large surface area for gases to be exchanged
• the plates have lots of blood capillaries, so they have a good blood supply to speed up diffusion
• they have a thin layer of surface cells, so the gases only have to diffuse a short distance