3.1.1 Exchange Surfaces Flashcards
What is the need for exchange surfaces?
Organisms need to exchange things with their internal and external environments
What substances do organisms need?
Oxygen - for aerobic respiration.
Glucose - for energy (respiration).
Protein - for growth and repair.
Fats - for the production of membranes and an energy store.
Water.
Minerals.
What do organisms need to get rid of?
Waste products (e.g. ammonia, urea and carbon dioxide).
What factors affect the need for an exchange surface?
Size.
Surface area to volume ratio.
Amount of activity.
Do unicellular organisms need exchange surfaces?
No
Why don’t unicellular organisms need exchange surfaces?
They have a small size and a large surface area to volume ratio. They aren’t very active organisms so diffusion alone is enough to meet the needs
Do multicellular organisms need exchange surfaces?
Yes
Why do multicellular organisms need exchange surfaces?
They have a small surface area to volume ratio due to their large size. They have high metabolic activity so have a high demand for reasorces. Diffusion alone is not sufficiant.
What is the formula for volume?
Volume = base x height x depth
What is the formula for surface area?
Sum of the area of all the sides.
How do you calculate SA:V ratio?
Do the surface area divided by the volume so that the volume is equal to 1.
How does SA:V ratio change with the size of the organism?
The larger the organism typically the smaller the SA:V ratio.
What effect does a small SA:V ratio have?
Makes it harder for organisms to supply substances as there’s a larger distance to cover (volume) but less surface to enter (surface area)
How can some organisms change their SA:V ratio?
`By changing their shape
What are the features of a good exchange surface?
Large Surface Area.
Thin Barrier.
Good Blood Supply.
How does a large surface area make a good exchange surface?
Provides a large space for molecules to pass through.
How are some cells adapted to increase surface area?
Grow long ‘hairs’ or folds in the cell walls/membranes.
e.g. Root hair cells or alveoli
How does a thin barrier make a good exchange surface?
Reduces the distance the substance has to diffuse. As long as the membrane is permeable.
How does a good blood supply make a good exchange surface?
Brings a large supply of substances to one side, this keeps the concentration high. Also removes molecules on the demand side, keeping the concentration low. This maintains a steep concentration that helps to aid diffusion.
How does air enter the human gas exchange system?
Air enters through the nostrils or the mouth.
How is the nose adapted for gaseous exchange?
A border of hairs that trap and filter particles out of the system. Good blood supply.
Warms and moistens the air.
How is the mouth adapted for human gas exchange?
There is a pharynx at the back of the neck where the air mixes with the air from the nasal passage.
Where does air pass from the mouth and nose?
The trachea then the bronchi
What is the structure of the trachea and bronchi?
There is an outer layer of C shaped cartilage which provides support and prevents collapsing with low air pressure.
There is a glandular layer that is responsible for mucus production.
A layer of smooth muscle allows the lumen to contract - typically in response to harmful chemicals (asthma). Elastic fibers allow the lumen to dilate after contraction and relaxed.
The inner lining is made of ciliated endothelium containing goblet cells for mucus production.
Why does the trachea have C shaped cartilage?
To prevent it crushing the esophagus