Biology: Middle School: Grades 6, 7 and 8 Quiz - Exchange Surface and Diffusion (Questions)

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Getting essential materials to where they are needed in an organism requires specialized tissues and organs. In animals, the transport is taken care of by blood. In plants it is the sap, which is a mixture of water and nutrients. But when the materials arrive at the place they are required, how do they move out of the blood or the sap? The answer is by diffusion through exchange surfaces.

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An exchange surface is the place that substances are moved across membranes in an organism, for example the lungs of birds or mammals and the gills of fish. An example of exchange of materials is the gaseous exchange of oxygen and carbon dioxide between the organism and the air. Other exchange surfaces include the villi in the small intestine, root hair cells and leaves of plants.

In plants, the main exchange surfaces are the leaves and roots. Leaves have evolved to allow the efficient gaseous exchange of oxygen and carbon dioxide with the air during photosynthesis. Molecules of carbon dioxide enter the leaves through tiny pores called stomata. Once inside the leaf, these carbon dioxide molecules can diffuse through the cell membrane and into the cell. Oxygen is the waste product from photosynthesis and it is eliminated from the plant in the opposite direction to the carbon dioxide. A plant also needs water and mineral ions. These are absorbed from the soil by osmosis (water) and active transport (mineral ions) via specialized cells called root hair cells.

In animals, the common examples of exchange surfaces are in the lungs (where gaseous exchange takes place across the alveoli) and in the small intestine (where nutrients are absorbed into the bloodstream via the villi). As well as the factors above that make these two exchange surfaces efficient, they are supplied with very dense networks of capillaries. The capillaries have very thin walls that allow substances to diffuse easily in both directions to ensure that the material are efficiently exchanged with the blood.

For tests and exams at this level, you need to know the appearance of an alveolus and a villus and to be able to say how these are adapted to their function. You also need to know that an efficient exchange surface must be thin, have a steep concentration gradient and have a very large surface area. That applies to both plants and animals.

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1. Exchange surfaces are generally involved in the...
[ ] transfer of materials across a membrane
[ ] removal of waste
[ ] uptake of nutrients
[ ] respiration
2. Exchange surfaces are usually very...
[ ] thin
[ ] thick
[ ] wide
[ ] tall
3. These are found in large numbers in the lining of the small intestine.
[ ] Alveoli
[ ] Ville
[ ] Villi
[ ] Arteries
4. Alveoli are found in the...
[ ] gills
[ ] lungs
[ ] liver
[ ] brain
5. During gaseous exchange, which two gasses are involved?
[ ] Oxygen and hydrogen
[ ] Nitrogen and oxygen
[ ] Carbon dioxide and oxygen
[ ] Ammonia and oxygen
6. Carbon dioxide enters plants mainly through the...
[ ] roots
[ ] leaves
[ ] flowers
[ ] stem
7. Mineral ions enter the plant by active transport through the...
[ ] stem
[ ] leaves
[ ] roots
[ ] flowers
8. Within leaves, the gasses enter and leave through specialized pores called...
[ ] stomata
[ ] stoma
[ ] holes
[ ] gaps
9. Diffusion is faster across an exchange surface if the concentration gradient is...
[ ] less
[ ] increased
[ ] the same
[ ] moved
10. In animals, uptake of materials is quicker if there is a rich network of...
[ ] capillaries
[ ] villi
[ ] lungs
[ ] arteries
Biology: Middle School: Grades 6, 7 and 8 Quiz - Exchange Surface and Diffusion (Answers)
1. Exchange surfaces are generally involved in the...
[x] transfer of materials across a membrane
[ ] removal of waste
[ ] uptake of nutrients
[ ] respiration
This happens where there is a difference in concentration (a concentration gradient) of the materials being exchanged on the two sides of the membrane
2. Exchange surfaces are usually very...
[x] thin
[ ] thick
[ ] wide
[ ] tall
If the structure is thin, materials get through more quickly
3. These are found in large numbers in the lining of the small intestine.
[ ] Alveoli
[ ] Ville
[x] Villi
[ ] Arteries
These create a very large surface area within the small intestine
4. Alveoli are found in the...
[ ] gills
[x] lungs
[ ] liver
[ ] brain
They are also known as air sacs
5. During gaseous exchange, which two gasses are involved?
[ ] Oxygen and hydrogen
[ ] Nitrogen and oxygen
[x] Carbon dioxide and oxygen
[ ] Ammonia and oxygen
Oxygen is taken in and carbon dioxide is given out. Plants do the opposite during photosynthesis.
6. Carbon dioxide enters plants mainly through the...
[ ] roots
[x] leaves
[ ] flowers
[ ] stem
Leaves are thin and flat which helps to make gaseous exchange more efficient.
7. Mineral ions enter the plant by active transport through the...
[ ] stem
[ ] leaves
[x] roots
[ ] flowers
Mineral ions, such as nitrate ions, enter the plant through specialized cells in the roots called root hair cells. These have a lot of mitochondria to supply the energy required for the active transport of the mineral ions
8. Within leaves, the gasses enter and leave through specialized pores called...
[x] stomata
[ ] stoma
[ ] holes
[ ] gaps
These are found on the underside of the leaves
9. Diffusion is faster across an exchange surface if the concentration gradient is...
[ ] less
[x] increased
[ ] the same
[ ] moved
Think of it like a hill. If a hill is steeper (has a greater gradient), an object will roll down it better
10. In animals, uptake of materials is quicker if there is a rich network of...
[x] capillaries
[ ] villi
[ ] lungs
[ ] arteries
Lungs, gills and the villi all have a dense capillary network which takes up the materials quickly, thus maintaining a steep concentration gradient for maximal uptake