As 2 CCEA GCE Biology - Principles of exchange and transport

Inspiration

ACTIVE PROCESS _ REQUIRES ENERGY

External intercostal muscles contract and internal intercostal muscles relax.

Pulls the ribcage up and out

Same time diaphragm muscles contract and this flattens diaphragm.

Both actions increase the volume of the thorax and pressure in the thorax and lungs is reduced.

Air enters lungs inflating alveoli until pressure in lungs is = to the atmosphere outside

Expiration

PASSIVE PROCESS _ REQUIRES ENERGY

External intercostal muscles relax and internal intercostal muscles contract.

Ribs move down and in due to own weight

Same time diaphragm relaxes, drops the rib cage forcing the diaphragm into domed shape - pushing up into the thoracic cavity.

Reduced volume of the thorax as a result.

Pressure in the lungs decreases until it is above the atmosphere outside. Air forced out of lungs.

Exercise on expiration

Expiration becomes an active energy-requiring process as more muscles are used and breathing becomes forced.

Internal intercostal muscles contract more strongly, ribs move down, and abdominal muscles contract strongly, so the diaphragm moves up quickly.

Surface area

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

Affects the rate of exchange of materials - metabolites. Influences rate of supply to tissues.

Volume

Total 3-dimensional space occupied by metabolically active tissue.

Influences the demand for metabolites

Plant exchange adaptions - leaf mesophyll cells

Thin, short diffusion distance for gases.

Tightly packed upper palisade mesophyll layer - wide expanse = increased efficency at trapping light and a loosely packed spongy mesophyll layer = air space system - huge SA for gas exchange.

Plant exchange adaptions - root hair cells

Tubular extensions of epidermal cells.

Large Surface area to volume ratio - provide roots with O2 by diffusion. Take up minerals and water.

Animal exchange adaptions - Capillaries

Walls are very thin - one cell thick.

Large surface area for exchange of substances between the blood and body tissues.

Short diffusion distance - one cell thick, every body cell is very close to a capillary.

Animal exchange adaptions - Alveoli

Small sacs in clusters and vast numbers in the mammalian lung.

Folded = large surface area - allows the diffusion of increased volumes of oxygen.

Membrane = thin, so diffusion distances are short.

moist so they are permeable to gases

Animal exchange adaptions - Erythrocytes

Red blood cells - small biconcave discs which contain haemoglobin. Flattened and depressed in the centre.

Thin membrane = short diffusion distance

Biconcave shape increases the surface area to volume ratio for effective O2 uptake.

Depressed centre allows O2 to diffuse to haemoglobin.

Mass flow

All molecules move in the same direction from a high pressure area to a low pressure area.

Mass transport mechanism - Xylem Vessels - Plant

One way transport of water and ions from the roots to the leaves.

Tension is generated by the transpirational loss of water. Water moves up - the more water is drawn leads to a continuous stream.

Mass transport mechanism - Phloem Tubes - Plant

Two way flow of organic solutes in a flowering plant. Sugar from photosynthesis is transported as sucrose to growth and storage centres in the roots and shoots by translocation.

Mass transport mechanism - Breathing/Ventilation System - Animals

Ventilation of the mammalian lungs whereby air is alternatively drawn in and out. Pressure in the thorax is increased and decreased.

Mass transport mechanism - Circulatory System - Animals

Circulation of the blood carrying oxygen, glucose, amino acids, fats, CO2 and urea in a mammal. High pressure generated by muscular heart.

Adaptions to maximise rate of gas exchange in plants

Large surface area

Moist surface

Short diffusion path - very thin

Permeable

Diffusion gradient

Fick’s law equation

Rate of diffusion ∝

(surface area x difference in concentration)———————————————————

thickness of membrane

ROD is directly proportional to surface area and difference in conc

ROD is inversely proportional to the thickness of the membrane.

Respiration

Uses O2, Gives out CO2

Produces energy

Takes place in both day and night

Photosynthesis

Uses CO2, Gives out O2

Takes place in palisade mesophyll layer

Takes place during the day - requires light energy

Low light levels

Rate of photosynthesis = Rate of respiration at the compensation point.

Rate of CO2 used in photosynthesis is equal to the rate of CO2 produced in respiration.

High light levels

Rate of photosynthesis in photosynthesising cells is much greater than the rate of respiration - there is a net movement of CO2 into the leaves and O2 out of the leaves.

No light levels

Only respiration takes place as photosynthesis requires light energy.

O2 diffuses into cells and CO2 diffuses out.

Leaf adaptions - Thin

Ensures a high surface area to volume ratio.

Provides a short diffusion distance

Leaf adaptions - Spongy mesophyll

Large moist exchange surface - the cell membrane forms metabolic contact through air spaces.

Loose arrangement allows for a large surface area.

The positioning of the layer makes it easy for gases to diffuse. Close to the stomata.

Leaf adaptions - Intercellular air spaces

Found in spongy mesophyll.

Facilitates diffusion.

Leaf adaptions - Stomata

Pores allow gases to diffuse in and out of the leaf easily.

Open during the day and closed at night - reduces the water loss by transpiration

Opening and closing is controlled by the guard cells.

Guard cells change shape, e.g. when turgid, the stomata are open.

Leaf adaptions - Waxy cuticle

Stops too much water loss form occurring - cuticular transpiration of water.

Waterproof

Water can only leave by stomata down a water potential gradient - high to low.

Root adaptions for gas exchange

Energy is used from cell division and active transport of ions from soil.

Increased surface area to volume ratio.

Surrounded by air spaces between soil particles so they are not waterlogged.

Stem adaptions for gas exchange

Small pores here that allow O2 to enter and CO2 to leave.

RQ value equation

RQ =

Carbon dioxide produced ——————————————

Oxygen consumed

Respirometer to find oxygen consumption.

Concentrated potassium hydroxide solution is added to the tube where the organisms are present - absorbs CO2, so any changes in manometer levels are due to oxygen consumption only.

Respirometer to find CO2 output

Measured directly with any change in the manometer due to the net difference between O2 taken up and CO2 given out

Respirometer - control

Use the same organisms

Use the same apparatus for calculating O2 and CO2.

Temperature - use water bath

RQ Values meaning

Glucose = 1.0

Lipid = 0.7

Protein = 0.9

Gas exchange process in the lungs

Oxygen enters the alveolus and dissolves in fill of water on wall and moves by diffusion across cell into the blood

The blood flowing to the alveolus has a higher concentration of CO2 and a lower concentration of O2 than alveolar air.

O2 and CO2 diffuse down their respective concentration gradients - O2 diffuses into the blood and CO2 diffuses into the alveoli.

Effect of smoking - Cilla damage

nicotine paralysis

Build up in the air passage - restricts airflow - coughing, phlegm production and breathlessness.

Effect of smoking - emphysema

Gradual breakdown of the thin walls of the alveoli - larger air spaces and so the total surface area decreases. Loss of elastic fibres occurs and exhalation as a result is more difficult as it is harder to recoil after inhalation.

Effect of smoking - bronchitis

Inflammation of the lining of the air passages causing the narrowing of bronchi and bronchioles caused by tar.

Effect of smoking - lung cancer

Caused by tar = carcinogen that forms tumours.

Lung cancer starts in the epithelium of bronchioles.

Septal cells in alveoli

Release surfactant

• kills bacteria which may have entered from outside.

• reduces surface tension in moisture coating of alveoli - preventing collapse which would reduce the surface area for gas exchange

Alveoli thin walls

One cell thick made up of squamous epithelial cells.

Form an efficient exchange surface = allows a rapid rate of diffusion due to the reduced distance.

Upper respiratory track

Air enters and is filters, moistened and warmed by different parts of the upper respiratory track.

Nostrills

Lined with small hairs which act as filters preventing large airborn objects from penetrating the lungs.

Nasal cavities

Warm and moisten air and collects any airborn particles on mucous layer.

Cilla

Stick out from epithelial cells and line the nasal cavities. Sweep mucus and trapped particles back towards the throat.

Pharynx

chamber behind the tongue in which air, liquids and food passes through

Trachea

Muscular tube leading to the lungs.

The inner surface is lined with ciliated epithelial cells - goblet cells which produce mucus.

The outer wall contains c-rings of cartilage that keep the trachea open at all times - this divides into two bronchi.

Bronchus

Supported by plates of cartilage.

Lined with ciliated epithelia which provide protection against micro-organisms.

Divide into bronchioles

Bronchioles

No cartilage - held open by elasticity of surrounding smooth muscles so the diameter is controlled.

Leads to alveolar ducts and then alveoli

Alveoli

Walls have numerous capillaries where they receive blood form the pulmonary arteries and then drain it into the pulmonary veins.

Rich and constant blood supply maintains diffusion gradients.