Biology As2 The Principles Of Exhange And Transport

Front 1

Define surface area.

Back 1

The total number of cells in direct contact with the surrounding environment. It affects the rate of exchange of materials at exchange surfaces and influences the rate of supply of metabolites to tissues.

Front 2

Define volume.

Back 2

The total three dimensional space occupied by metabolically active tissue. This volume affects the demand for metabolites.

Front 3

Define surface area-to-volume ratio.

Back 3

As an organism's size increases, its surface area increases less than its volume so not as many cells are in direct contact with the surrounding environment. Large organisms will have a small surface area-to-volume ratio, small organisms will have a large surface area-to-volume ratio.

Front 4

How can an organism's surface area be increased?

Back 4

Invagination (infolding) of the surface.

Evagination (outfolding) of the surface.

Flattening of the organism.

Front 5

Give examples of absorbtive surfaces.

Back 5

Leaf mesophyll, root hairs, capillaries, alveoli, erythrocytes.

Front 6

What are the features of exhange surfaces which aid transport?

Back 6

Large surface area, moist surface area, thin surface area, diffusion gradient.

Front 7

What is the structure and function of the leaf mesophyll?

Back 7

Structure

The leaf is a flattened structure (its thinness ensures a short diffusion distance) with a tightly packed upper palisade mesophyll layer and a loosely packed lower spongy mesophyll layer.

Function

The wide expanse of palisade tissue is efficient at trapping light, the loose arrangement of the spongy layer provides an air space system through the leaf and creates a huge surface for gas exchange.

Front 8

What is the structure and function of root hairs?

Back 8

Structure

Tubular extensions of the epidermal cells of the young root.

Function

Increase greatly the surface area for the uptake of oxygen, water and ions.

Front 9

What is the structure and function of alveoli?

Back 9

Structure

Small sacs occurring in clusters, and in vast numbers, within the mammalian lung. 0.2mm diameter, 700million, 70m^2.

Function

Huge, moist surface area provides for efficient gas exhange. The alveolar walls are thin (0.1-1μm) so the diffusion distance is short.

Front 10

What is the structure and function of capillaries?

Back 10

Structure

Small, thin walled blood vessels with a total length of 100,000km and total area of 1000m^2.

Function

Extensive network throughout the body provides for a huge surface area for the exchange of molecules between the body and the blood. No cell is further than 50μm from a capillary ie diffusion distance is minute.

Front 11

What is the structure and function of erythrocytes?

Back 11

Structure

Small, flexible biconcave discs, flattened and depressed at the centre, with a dumb-bell shaped cross section.

Function

The biconcave disc shape greatly increases the surface area-to-volume ratio allowing for efficient uptake of oxygen. Its thinness, especially where it is depressed at the centre, allows oxygen to diffuse to all the haemoglobin packed into the cell.

Front 12

Why may an organism require an absorbtive surface area?

Back 12

Terrestrial, high metabolic rate, impermeable skin, large, small surface area-to-volume ratio.

Front 13

Define diffusion.

Back 13

The net movement of molecules from an area of higher concentration to an area of lower concentration so that the molecules are evenly distributed.

Front 14

Define mass flow and why is it brought about?

Back 14

Mass flow is the movement of substances in bulk from one part of an organism to another. All molecules are swept along in the same direction. Mass flow is brought about by a pressure difference.

Front 15

Give examples of mass flow systems.

Back 15

The xylem, phloem, ventilation and blood circulatory system.

Front 16

Explain the pressure difference and function of the xylem system.

Back 16

Pressure difference

Tension in the leaf xylem is brought about by the transpirational loss of water from the leaves.

Function

One way flow of water and ions from roots to leaves in a flowering plant.

Front 17

Explain the pressure difference and function of the phloem system.

Back 17

Pressure difference

Movement is driving by energy from the plant.

Function

Two way flow of organic solutes (sucrose) in a flowering plant.

Front 18

Explain the pressure difference and function of the breathing (ventilation) system.

Back 18

Pressure difference

Pressure in the thorax ars alternately decreased and increased.

Function

Ventilation of the mammalian lung. Air is alternately drawn in and forced out.

Front 19

Explain the pressure difference and function of the blood circulatory system.

Back 19

Pressure difference

High pressure generated by the muscular heart.

Function

Circulation of blood carrying oxygen, carbon dioxide, glucose, urea, amino acids, fats and other substances in a mammal.