5.1 Surface Area to Volume ratio

Question 1

What do single-celled organisms need to absorb? (3)

Answer 1

• Oxygen
• Glucose
• Amino acids

Question 2

What do single-celled organisms get rid of as waste?

Answer 2

Carbon Dioxide

Question 3

Cells need oxygen for aerobic respiration, which produces carbon dioxide as a waste product. How do these cells move between cells and the environment?

Answer 3

By diffusion

Question 4

Water is needed for many chemical reactions. It’s taken up by cells by osmosis. Dissolved food molecules (the products of digestion, e.g. glucose and amino acids) What type of reactions are these used in?

Answer 4

Synthesis reactions

Question 5

What is urea?

Answer 5

A waste product from the breakdown of proteins in the liver

Question 6

How is urea excreted from the body?

Answer 6

Urea diffuses from cells into the blood plasma. It is then filtered out of the blood by the kidneys and excreted as urine.

Question 7

Why do multicellular organisms need specialised exchange surfaces?

Answer 7

Multicellular organisms have relatively small surface area to volume ratios, which makes diffusion to and from cells deep within their bodies slow. This makes it difficult to exchange enough substances to supply their entire volume across their outside surface alone. To get around this, multicellular usually have specialised exchange surfaces to increase their surface area : volume ratio and therefore the rate at which substances are able to diffuse.

Question 8

Why do multicellular organisms tend to have a mass transport system?

Answer 8

To move things around the body - this shortens the distance these substances have to diffuse to and from cells.

Question 9

All of the movement into, out of and around the human body is dependent on the g_______ ________, c___________, d__________ and e_________ s_________ all working together.

Answer 9

gaseous exchange, circulatory, digestive and excretory systems

Question 10

Give 2 examples of exchange surfaces in humans and describe their function

Answer 10

1) Alveoli - allows oxygen and carbon dioxide to diffuse in and out of the body/bloodstream.
2) Villi - allows nutrients such as glucose, amino acids, mineral ions etc. to be absorbed from the small intestines into the bloodstream.