Specialised Exchange System

Question 1

What does every organism need to do?

Answer 1

No matter what the size is, every organisms need to exchange stuff with the environment

Question 2

What do cells need to take in? and excrete?

Answer 2

They need to take things like oxygen & glucose for aerobic respiration and other metabolic respiration. They also need to excrete waste products like carbon dioxide and urea.

Question 3

Formula for volume of cylinder

Answer 3

(pie)(radius^2)(height)

Question 4

Formula for volume of hemisphere

Answer 4

4/3 (pie)(radius^3)

Question 5

Formula for sphere surface area

Answer 5

4(pie)(radius^2)

Question 6

Why does it need to remove waste products from every cell?

Answer 6

To avoid damaging itself

Question 7

How do substances diffuse in single-celled organisms?

Answer 7

Substances can diffuse directly into or out of the cell across the plasma membrane. The diffusion rate is quick because of the short distance the substances have to travel and because they have a high surface area : volume ratio

Question 8

Why is the diffusion across the outer membrane in multicellular organisms slow?

Answer 8

> Some cells are deep within the body - there’s a big distance between them and the environments
Low surface area to volume ratio - its difficult to exchange enough substances to supply a large volume of animal through the small outer surface
They also have a higher metabolic rate, so they use up oxygen and glucose faster

Question 9

What do multicellular organism use to absorb and excrete substances?

Answer 9

They use specialised exchange surfaces (like the alveioli in the lungs)

Question 10

What are the three special feature that exchange surfaces have? and why do they have them?

Answer 10

> A large surface area
They’re thin
A good blood supply and ventilation
To improve their efficiency

Question 11

Why do most exchange surfaces have a large surface are: volume ratio?

Answer 11

To overcome limitations of sa:v ratio of large organism and to improve their efficiency

Question 12

Describe the root as having a high surface area

Answer 12

The cells on plants root grow into long ‘hairs’ which stick out into the soil. Each branch of a root will be covered in millions of these microscopic hairs.

This gives the roots a large surface area, which helps to increase the rate of absorptions of water (by osmosis) and mineral ions (by active transport) from the soil.

Question 13

Why are most exchange surfaces thin?

Answer 13

Exchange surfaces are usually thin to decrease the distance that the substances being exchanged have to travel over, and so improve efficiency and making the process fast

Question 14

Describe alveoli as being thin

Answer 14

The alveoli are the gas exchange surfaces in the lungs. Each alveolus is made from a single layer of thin, flat cells called the alveolar epithelium.

O2 diffuses out of the alveolar space into the blood. CO2 diffuses in the opposite directions.

The thin alveolar epithelium helps to decrease the distance over which O2, and CO2 diffusion takes place, which increases the rate of diffusion.

Question 15

Why do most exchange surfaces have a good blood supply or are well ventilated ?

Answer 15

> They have a good blood supply so substances are constantly delivered to and removed from exchange surfaces which maintain a steep concentration gradient for diffusion
Ventilations maintains conc gradients and makes the process more efficient

Question 16

Describe alveoli as being a good blood supply or well ventilated

Answer 16

The alveoli are surrounded by a large capillary network, giving each alveolus its own blood supply. The blood constantly takes O2 away from the alveoli, and brings more CO2.

The lungs are also ventilated (you breath in and out) so the air in each alveolus is constantly replaced.

These features help to maintain concentration gradient of O2 and CO2.

Question 17

Describe the gills as being a good blood supply or well ventilated

Answer 17

The gills are the gas exchange surface in fish. In the gills, O2 and CO2 are exchanged between the fish’s blood and the surrounding water.

Fish contain a large network of capillaries - this keeps them well-supplied with blood. They’re also well-ventilated - fish water constantly passes over them.

These features help to maintain a concentration gradient of |O2 - increasing the rate at which O2 diffuses into the blood

Question 18

Why do larger organism need a specialised surface for gas exchange?

Answer 18

Because in larger organism with more than two layers of cells, the body surface is no longer sufficient