(U2) T&EM - Principals Of Exchange And Transport

Question 1

What is mass flow? (2)

Where does it occur? Also give examples (4)

Answer 1

• The transport of all molecules (bulk movement)
• from an area of high pressure to an area of low pressure

2. Larger organisms. E.g:

• xylem system
• phloem system
• ventilation system
• blood circulatory system

Question 2

What is the relationship between increasing size of an organism and its SA/V ratio?

Why is this an issue?

Answer 2

• Increased size = decreased SA/V ratio
• larger size means the organism is more metabolically active, SA is not large enough to meet these demands

SA increases less than volume

Question 3

What is surface area? (2)

biology

Answer 3

• the total number of cells
• in direct contact with the surrounding environment

Question 4

Why does increased volume of metabolically active tissue increase metabolic demand?

Answer 4

• increased vol = more cells
• more cells require glucose and oxygen for aerobic respiration & ATP production

Question 5

What is volume (2)

Biology

Answer 5

• the total 3D space
• occupied by metabolically active tissues

Question 6

Why do flowering plants and mammals need a mass flow system?

Answer 6

To transport water, hormones, nutrients etc around the body to all cells

Question 7

Why, for large organisms, is their large SA not viable for meeting metabolic demands? (2)

Answer 7

• majority of their cells not in contact with surrounding environment (thus cannot take in gases or nutrients)
• there is far more volume of cells in large organisms

Question 8

Relatively speaking, what is the difference between the SA/V ratio in small and large organisms?

Answer 8

• large organisms = small SA/V ratio
• small organisms = large SA/V ratio

Question 9

What are the features of exchange surfaces that aid passive and active transport? (4)

Give examples and explain briefly.

Answer 9

• optimised surface area via a flattened shape, e.g. red blood cells (increases SA/V ratio, allows gases to diffuse through epidermal surface)
• specialised exchange surfaces, e.g. external gills, internal lungs or root hair cells (increase SA for gas exchange or passive/active uptake)
• thin separating surface e.g. only 2 cells between gas in alveoli and blood (shortened diffusion distance, faster rate)
• concentration gradients e.g. in leaf mesophyll or ventilation - low conc of O₂ in blood (due to respiration), high in lungs or CO₂ low in mesophyll cells due to photosynthesis etc.

Question 10

Explain how the following systems of mass flow work:

• xylem system (basic)
• phloem system
• ventilation system
• circulatory system

Answer 10

1. xylem:

• transpiration causes tension
• water and minerals are pulled from roots to leaves

2. Phloem:

• ATP used to move sucrose from companion cells to phloem sieve tube
• two-way flow of organic solutes like sucrose around the plant

3.

Question 11

Why are mass flow systems so important?

Answer 11

Allow transport of substances over long distances