B2.2.1 - Exchange and Transport Flashcards
What is a surface area to volume ratio?
It is the surface area per unit volume of a substance
What happens when an organism has a large surface are : volume ratio?
Nutrients can diffuse directly into the organism quickly enough to sustain life, as diffusion distances are small
What happens when the organism gets larger?
The surface are : volume ratio decreases
Why can’t most multicellular organisms use simple diffusion to survive?
Diffusion over a greater distance cannot occur fast enough to meet the cells’ demands
What do multicellular organisms do then?
They have developed different adaptations to increase the surface area : volume ratio at exchange surfaces
What happens in the lungs?
The lungs contain many alveoli. These increase the surface area of the lungs in order to maximise the rate of diffusion of oxygen into the bloodstream
How does gas exchange work?
Ventilation (breathing) moves fair in and out and helps maintain a steep diffusion gradient
Oxygen diffuses into the blood
Carbon Dioxide diffuses out of the blood
What are adaptations made by the alveolus to improve this process?
The alveoli have very thin walls so there is a short distance making diffusion easy.
There are many alveoli which gives a relatively large surface area for diffusion
What happens in the small intestine?
The small intestine has fingerlike villi which increases the surface area of the intestine wall, maximising the diffusion rate
Why are transport systems needed?
Once a required substance has entered your body, it must be transported to where it is needed.
What is the main transport system in animals?
The circulatory system
What is the transport system in plants?
They have a system of tubes called Xylem and phloem. Xylem tubes carry water and mineral ions around a plant and phloem tubes transport sugars and amino acids
