gaseous exchange

14
GASEOUS EXCHANGE A S BIOLOGY LIGHT ACADEMY 11 M.R.NJOROGE

Upload: richard-njoroge

Post on 15-Jul-2015

91 views

Category:

Environment


4 download

TRANSCRIPT

GASEOUS

EXCHANGE

A S BIOLOGY

LIGHT ACADEMY 11M.R.NJOROGE

LIGHT ACADEMYM.R.NJOROGE 2

LUNG FUNCTION

• Humans need to get oxygen into the blood for respiration and get

rid of carbon dioxide made by respiring cells. This is where

breathing(or ventilation its sometimes called)and the lung.s come

in

LIGHT ACADEMY 3M.R.NJOROGE

Lungs are specialized organs for gaseous exchange

Fig 1.0 Lung structure

• As you breathe in the air enters the trachea (wind pipe)

• The trachea splits into two bronchi-one bronchus leading to each lung.

• Each bronchus,then branches off into smaller tubes called bronchioles.

• The bronchioles end in small air sacs called alveoli-this is where gases are exchanged.

• The rib cage,intercostal muscles and diaphragm all work together to move air in and out.

LIGHT ACADEMYM.R.NJOROGE 4

LIGHT ACADEMYM.R.NJOROGE 5

Identify the parts labeled A-G,below?

In humans gaseous exchange happens in the

alveoli

About alveolus• Lungs contain millions of

alveoli-the gas exchange surface.

• Each alveoli is made from a single layer of thin ,flat cells called alveolar epithelium.

• Alveoli are arranged in bunches and the end of bronchioles

• They are surrounded by network of capillaries, giving each alveolus its own blood supply.

Structure of alveolus

LIGHT ACADEMYM.R.NJOROGE 6

• Oxygen diffuses out of the alveoli,across the alveolar

epithelium and the capillary endothelium.(a type of

epithelium that forms the capillary wall),and into

haemoglobin in the blood.

• Carbon dioxide diffuses into the alveoli from the blood

,crossing the capillary endothelium then the alveolar

epithelium. After entering the alveolar space its breathed

out.

LIGHT ACADEMYM.R.NJOROGE 7

Epithelial tissue is

pretty common in

the body. Its

usually found on

exchange

surfaces

ADAPTATIONS OF ALVEOLI TO GASEOUS

EXCHANGEAlveolus have features that speeds up the rate of diffusion so gases can be exchanged quickly.

• A thin exchange surface-the alveolar epithelium is only one cell thick. This means there's is a short diffusion distance.(which speeds up diffusion)

• A large surface area –the numerous alveoli means there's large surface area for gas exchange.

• Alveoli are highly vascularised to increase the rate of blood flow to and from alveoli.

LIGHT ACADEMYM.R.NJOROGE© 8

Gaseous exchange has different parts with different

functions

The respiratory system has other parts that help it to exchange gases efficiently.

• Goblet cells secrete mucus. The mucus trapsmicroorganisms and dust particles in the inhaled air stopping them from reaching the alveoli.

• Cilia on the surface of the cells beat the mucus ,which move it (plus trapped microorganisms and dust) upwards away from the alveoli towrads the throat ,where its swalloowed.thishelps prevent lung infection.

• Elastic fibres in the walls of

the trachbronchi

,bronchioles and alveoli

help in the process of

breathing out.on breathing

in ,the klungs inflate and the

elastic fibres are strethed

,then the fibres recoilto help

push the air out when

exhaling.

• Smooth muscle

LIGHT ACADEMYM.R.NJOROGE 9

Review question

LIGHT ACADEMYM.R.NJOROGE 10

1. Fig. 6.1 is a section through lung tissue showing an alveolus and its blood

supply.(a) (i) Name the type of epithelial cell shown by

label lines A and B.[1] squamous / pavement

(epithelial) ;

(ii) Describe how the elastic fibres of the alveoli

contribute to the healthy functioning of

the lungs.[2] )

stretch / expand, on inspiration and recoil on

expiration ;R contraction (stretch) to increases,

surface area / volume of air, for, diffusion / gas

exchange ;

(recoil) to help, expel air / force air out ;

A carbon dioxide A if destroyed then cannot expel

air

prevent alveoli, bursting / breaking / AW ;ref. to

emphysema if elastic fibres destroyed ; (b) The actual diameter of the alveolus along

the line X–Y is 220 micrometres (μm).

Calculate the magnification of Fig. 6.1.

Show your working and give your answer to the

nearest whole number.

answer × [2]

(c) Outline two features of a gas exchange surface

that are shown on Fig. 6.1.[2]

LIGHT ACADEMYM.R.NJOROGE 11

b) award two marks if correct answer (anything in range 336–346)

allow +/– 1 mm in reading the line (74–76 mm)

75000 μm / 220 μm = 341 ;;if answer incorrect, award one mark for

correct measurement with unit and division by 220

award one mark if correct answer given to one or more decimal

places[2]

(c) look for two ideas – follow usual rules for marking numbered

answer lines

thin, alveolar wall / epithelial lining / AW ;

Ashort diffusion distance (between air in alveolus and blood in

capillary)

Asquamous cells are thin Rthin, membrane / cell membrane R large

surface area surrounded by, capillaries

/ capillary network ;A close contact with, capillaries / blood (vessels /

cells) A many capillaries A large area of alveolus in contact with,

capillaries / blood

LIGHT ACADEMYM.R.NJOROGE 12

(d) max 3 if no ref. to diffusion

(named) gas(es), diffuse

down, pressure gradients / concentration gradient / AW ;

A from high(er) partial pressure to low(er) partial pressure

A high(er) concentration to low(er) concentration ignore

‘along a concentration gradient’

in the answers accept the following AWs

capillaries / haemoglobin for blood

lungs for alveoli body for tissues

lungs valid statement linking information in table below – 1 mark for each row

comparison in partial pressure may be ‘higher / lower’ not both or high and

low, but if not then figures have to be given

LIGHT ACADEMYM.R.NJOROGE 13

(d) Fig. 6.2 is a simplified diagram of the circulatory system of a human, showing gas

exchange in the lungs and in respiring tissue. The partial pressures of oxygen

(pO2) andcarbon dioxide (pCO2) at four locations are also shown.

With reference to Fig. 6.2, explain

how the differences in pO2 and pCO2 in the alveolus and in blood

enable gas exchange in the lungs

and respiring tissue……………………..[4]

LIGHT ACADEMY M.R.NJOROGE 14