ocr alevel biology module 3

3 main factors that affect need for transport system

size, surface area to volume ratio, levels of activity

levels of activity

size (in very small organisms)

cytoplasm is very close to the environment in which they live

so diffusion supplies enough oxygen and nutrients to keep the cells alive and active

size (in very multicellular organisms)

have several layers of cells

oxygen or nutrients diffusing in from the outside have a longer diffusion pathway

diffusion is too slow to enable a sufficient supply

surface area to volume ratio

small organisms have a large SA:V ratio that supplies their cells with sufficient oxygen

as size increases volume increases quicker than SA

so large organisms have a small SA:V ratio

how to increase SA:V ratio

increase SA by adopting different shapes

e.g. a flatworm has a very thin, flat body

giving it a larger SA:V ratio

levels of activity

metabolic activity

uses energy from food and requires oxygen to release the energy in aerobic respiration

nutrients and oxygen needed for energy for movement

more energy needed for animals that keep themselves warm (e.g. mammals)

good exchange surfaces have..

1. large surface area - to provide more space for molecules to pass through

e.g. root hair in plants

2. thin barrier to reduce diffusion distance - must be permeable to the substances being exchanged

e.g. alveoli in lungs

3. good blood supply bringing fresh supplies of molecules to one side

keeping concentration high one one side

may remove molecules on the other keeping that side low concentration

e.g. gills in fish

alveoli

tiny folds of the lung epithelium to increase the surface area

bronchi and bronchioles

Smaller airways leading into the lungs

diaphragm

a layer of muscle beneath the lungs

intercostal muscles

muscles between the ribs

contraction of the external intercostal muscles raises the ribcage

trachea

the main airway leading from the back of the mouth to the lungs

ventilation

the refreshing of air in the lungs so that there is a higher oxygen concentration than in the blood

and a lower carbon dioxide concentration

gas exchange in the lungs

• gases pass by diffusion through the thin walls of the alveoli

• oxygen passes from the air in the alveoli to the blood in the capillaries

• carbon dioxide passes from the blood to the alveoli

• the lungs must maintain a steep concentration gradient in each direction to ensure diffusion can happen

alveoli structure

air filled sacs

small but there are many of them making them have a large surface area

lined by a thin layer of moisture

adaptions to reduce the diffusion distance

• alveoli wall is one cell thick

-capillaries are one cell thick

• both consist of squamous cells - flatten and very thin

• capillaries in close contact with alveoli

• capillaries are so narrow red blood cells are squeezed against the capillary wall

inspiration (inhaling)

1. diaphragm contracts - moving down and becoming flatter

2. external intercostal muscles contract

3. rib cage moves up and out

4. volume increases therefore pressure decreases below the atmospheric pressure

5. air moves into the lungs

expiration (exhaling)

1. The diaphragm relaxes.

2. external muscles relax and ribs fall

(intercostal muscles can contract to help push air out forcefully)

4. volume decreases so pressure increases more than atmospheric pressure

5. air move out of the lungs

cartilage

a form of connective tissue

ciliated epithelium

A layer of cells that have many hair-like extensions called cilia

elastic fibres

Protein fibres that can deform and then recoil to their original size

goblet cells

cells that secrete mucus

smooth muscle

involuntary muscle that contracts without the need for conscious thought

lung tissue

alveoli comprised of squamous capillaries

surrounded by capillaries

so diffusion distance is short

alveoli walls contain elastic fibres

that stretch during inspiration

recoil to help push air out in expiration

the airways to be effective must

• be large enough to allow sufficient air to flow without obstruction

• be supported to precent collapse when air pressure is low

• be flexible in order to allow movement

• lined with ciliated epithelium

• goblet cells release mucus which traps pathogens

• cilia move the mucus to the top of the airway to be swallowed

trachea and bronchi

• bronchi narrower than the trachea

• supported by cartilage which prevent collapse during inspiration

• rings of trachea are C shaped to allow flexibility

Bronchioles

• narrower than bronchi

• larger bronchioles may have some cartilage but smaller ones have none

• comprised of mainly smooth muscle and elastic fibres

smooth muscle and elastic tissue

• smooth muscle can contract

• this makes lumen narrower

• involuntary acts

• as muscle relaxed elastic fibre recoiled to their original size and shape

breathing rate

number of breaths per minute

oxygen uptake

the volume of oxygen absorbed by the lungs in one minute

tidal volume

volume of air inhaled or exhales in one breath

usually measured at rest

spirometer

a device that can measure the movement of air into and out of the lungs

vital capacity

the greatest volume of air that can be expelled from the lungs after taking the deepest possible breathe

vital capacity is usually in the region of..

2.5-5 dm3

using a spirometer

measures lung volume - movement of air in and out of the lungs

consists of a chamber of air floating on a tank of water

carbon dioxide air expelled passes through soda lime with absorbs the carbon dioxide

during inspiration air is drawn from the chamber. moving the lid down

during expiration air returns to chamber raising the lid

movement recorded on a data logger