topic 3 - size and surface area

Question 1

give three examples of what organisms need to exchange thing with it’s environment

Answer 1

(1) cells need to take in oxygen (for aerobic respiration) and nutrients
(2) they need to excrete waste products like carbon dioxide and urea
(3) most organisms need to stay at roughly the same temperature, so heat needs to be exchanged too

Question 2

what does how easily the exchange of substances depend on

Answer 2

the organism’s surface area to volume ratio

Question 3

why is the diffusion rate in single celled organisms quick

Answer 3

in single celled organisms these substances can diffuse directly into (or out of) the cell across the cell surface membrane - the diffusion rate is quick because of the small distances the substances have to travel

Question 4

what are the two reasons why in multicellular animals diffusion across the outer membrane is too slow

Answer 4

(1) some cells are deep within the body - there’s a big distance between them and the outside environment
(2) larger animals have a low surface area to volume ratio - it’s difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface

Question 5

what do multicellular animals use to absorb and excrete substances

Answer 5

specialised exchange organs

Question 6

what is mass transport

Answer 6

an efficient system to carry substances to and from their individual cells

Question 7

what does mass transport usually refer to in mammals

Answer 7

the circulatory system - which uses blood to carry glucose and oxygen around the body - it also carries hormones, antibodies and waste like CO2

Question 8

what does mass transport usually refer to in plants

Answer 8

involves the transport of water and solutes in the xylem and phloem

Question 9

what does the rate of heat loss form an organism depend on

Answer 9

its surface area

Question 10

what do smaller organisms have in order to generate enough heat to stay warm

Answer 10

a high metabolic rate

Question 11

how does whether an animal has a compact shape or not impact heat loss

Answer 11

animals with a compact shape have a small surface area to volume ratio - minimising heat loss from their surface
animals with a less compact shape have a larger surface area to volume ratio - increasing heat loss from their surface

Question 12

what are three adaptions small animals have to suit their climate

Answer 12

(1) animals with high SA:V tend to lose more water as it evaporates from their surface - some small desert mammals have kidney structure adaptions so that they produce less urine to compensate
(2) to support high metabolic rates small mammals living in cold regions need to eat large amounts of high energy foods such as seeds / nuts
(3) smaller mammals may have thick layers of fur and hibernate when the weather gets cold

Question 13

give two examples of how two large organisms living in hot regions have adapted to keep cool

Answer 13

larger organisms living in hot regions find it hard to keep cool as their heat loss is relatively slow
(1) elephants have developed large flat ears to increase their surface area, allowing them to lose more heat
(2) hippos spend much of the day in the water - a behavioural adaption to help them loose heat