unit 3A - exchange and transport systems

Question 1

not every animal have a body size/ shape to suit their climate. name 4 adaptions instead…

Answer 1

1) animals with a high SA:V tend to loose more water as it evaporates from its surface. some small desert animals have kidney structure adaptions so they produce less urine to compensate.

2) to support their high metabolic rates, small animals living in cold regions eat at lot of high energy foods like seeds and nuts.

3) smaller mammals may have thick layers of fur or hibernate when weather gets too cold.

4) larger organisms in hot areas, e.g. elephants have a slow heat loss so they have big ears to increase their SA. hippos spend a lot of time in water (behavioural adaption).

Question 2

how do single celled organisms exchange gases across their body surface?

Answer 2

1) single celled organisms absorb and release gases by diffusion through their outer surface
2) they have a relatively larger surface area, a thin surface and a short diffusion pathway (oxygen can take part in biochemical reactions as soon as it diffuses into the cell) so there’s no need for a gas exchange system.

Question 3

how does the counter current system for gas exchange in fish work?

Answer 3

there’s a lower concentration of oxygen in the water then the air. so fish have special adaptions to get enough of it.
1) water, containing oxygen, enters the fish through its mouth and passes out through the gills.
2) each gill is made of lots of thin plates called gill filaments, which gives a big surface area for exchange of gases
3) the gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area even more.
4) The lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion.
5) blood flows through the lamellae in one direction and water flows over in the opposite direction. this is called a counter- current system. it maintains a large concentration gradient between the water and the blood. the concentration of oxygen in the water is always higher that that is in the blood, so as much oxygen as possible diffuses from the water into the blood.

Question 4

how does insects use tracheae to exchange gases?

Answer 4

1) insects have microscopic air filled pipes called tracheae which they use for gas exchange
2) air moves into the tracheae through pores on the surface called spiracles
3) oxygen travels down the concentration gradient towards the cells.
4) 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.
5) carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.
6) insects use rhythmic abdominal movements to move air in and out of the spiracles.

Question 5

how do dicotyledonous plants exchange gases at the surface of the mesophyll cells?

Question 6

how do insects and plants control water loss?

Question 7

what are examples of xerophytic adaptions?