chapter 5 Flashcards
the volume of a living organism is proportional to the number of cells in its body. Each cell needs oxygen & nutrients to get rid of products such as carbon dioxide. The smallest organisms can absorb nutrients and get rid of waste by diffusion through their outer membranes. Do you think larger organisms can do the same? Why?
No. It would take longer to completely diffuse as the diffusion distance is too big.
What are some adaptations of exchange surfaces?
1- Large SA
2- Moist surface - acts as a solvent for diffusion
3- short diffusion distance (usually one cell thick)
4- can maintain a steep concentration gradient (by having a good blood supply)
Why do we need specialized exchange surfaces?
- Small SA:V because surface is too small to provide sufficient passage across
- Diffusion distance is too large
- Active process so it requires more O2 and glucose for respiration
Why do unicellular organisms have a large SA:V ratio?
Because they can achieve exchange of substances by diffusion across the cell membrane
What does it mean when large multicellular organisms have a small SA:V ratio?
It means that their outer surface is not big enough to exchange substances fast enough to keep them alive. Hence, they have specialized exchange surfaces.
Name four general things that need to be exchanged between organisms and their environment.
Respiratory gases, nutrients, excretory products and heat
Name four factors that affect the rate of diffusion of substances into cells.
Temperature, size of substances, size of diffusion surface, & the diffusion gradient
How do insects reduce water loss?
- Waterproof coverings over their body surfaces.
- Small SA:V ratio to minimize the area over which water is lost
What are tracheae?
An internal network of tubes that insects use to diffuse respiratory gases. They are supported by strengthened rings to prevent them from collapsing.
What do the tracheae divide into?
Smaller tubes called tracheoles. These extend throughout all the body tissues of the insect. Atmospheric air, with the oxygen it contains, is therefore brought directly to the respiring tissues.
What are the two ways in which respiratory gases move in and out of the tracheal system?
- Down a diffusion gradient.
- Ventilation
How do gases enter and leave the tracheae?
Through tiny pores on the body surface called spiracles which open and close by a valve.
What are the limitations of the insect tracheal system?
It relies mostly on diffusion to exchange gases between the environment and the cells.
What adaptations do the leaves show for gas exchange?
- a thin, flat shape that provides a large SA & a short diffusion pathway
- Many small pores (stomata) mostly in the lower epidermis
- numerous interconnecting air spaces that occur throughout the mesophyll
What are stomata?
Stomata are minute pores that occur mainly on the leaves.
