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19 Cards in this Set

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Define surface area.

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.

Define volume.

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

Define surface area-to-volume ratio.

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.

How can an organism's surface area be increased?

Invagination (infolding) of the surface.


Evagination (outfolding) of the surface.


Flattening of the organism.

Give examples of absorbtive surfaces.

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

What are the features of exhange surfaces which aid transport?

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

What is the structure and function of the leaf mesophyll?

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.

What is the structure and function of root hairs?

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.

What is the structure and function of alveoli?

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.

What is the structure and function of capillaries?

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.

What is the structure and function of erythrocytes?

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.

Why may an organism require an absorbtive surface area?

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

Define diffusion.

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

Define mass flow and why is it brought about?

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.

Give examples of mass flow systems.

The xylem, phloem, ventilation and blood circulatory system.

Explain the pressure difference and function of the xylem system.

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.

Explain the pressure difference and function of the phloem system.

Pressure difference


Movement is driving by energy from the plant.


Function


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

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

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.

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

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.