Exchange and Transport Systems

Organisms need oxygen and carbon dioxide to diffuse as quickly as possibly;

>large surface areas help to increase rate of diffusion.

>they're thin (one cell thick) to provide a short diffusion pathway across the gas exchange surface.

>steep concentration gradient maintained.

Fish - single celled organisms

Water, (containing oxygen) enters the fish through the mouth and passes out through the gills. Each gill is made of lots of thin plates called gill filaments which increase surface area. The gill filamenta are covered in lamellae which inceases the surface area even more. They also have blood capillaries and a thin surface layer of cells to speed up diffusion between the water and blood.

Counter-Current System means that blood flows in one direction and water flows over them in the opposite direction, This helps water with a relatively high oxygen concentration always flow next to blood with a lower concentration of oxygen and maintains a steep concentration gradient.

Plants need carbon dioxide for photosynthesis which produces oxygen as a waste gas.

They need oxygen for respiration which produces carbon dioxide as a waste gas.

The main gas exchange surface is in the mesophyll cells in the leaf which are well adapted and have a large surface area.

Gases move in and out through special pores in the epidermis called stomata.

This can open to allow exchange of gases and close if the plant is losing too much water.

Guard cells control the opening and closing of the stomata.

Insects have microscopic air-filled pipes called tracheae which they use for gas exchange.

Air moves into the tracheae through pores on the surface called spiracles.

Oxygen travels down the concentration gradient towards the cells.

The tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells.

This means that oxygen diffuses directly into the respiring cells.

Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.

Insects use rhythmic abdominal movement to move air in and out of the spiracles.

If insects are losing too much water, they close their spiracles using muscles. They also have waterproof, waxy cuticles all over their body and tiny hairs around their spiracles, both of which reduce evaporation.

Xerophytic adaptations;

> Stomata sunk in pits to trap water vapour, reducing the concentration gradient of water between the leaf and the air, reducing evaporation of water from the leaf.

> A layer of 'hairs' on the epidermis to trap water vapour round the stomata.

> Curled leaves with the stomata inside, protecting them from wind.

> A reduced number of stomata, so there are fewer places for water to escape.

> Thicker waxy, waterproof cuticles on leaves and stems to reduce evaporation.

Ventilation consists of inspiration (breathing in) and expiration (breathing out) which is controlled by the movements of the diaphragm, internal and external intercostal muscles and ribcage.

Inspiration - during inspiration, the external intercostal and diaphragm muscles contract which causes the ribcage to move upwards and outwards and the diaphragm to flatten which increases the volume of the thoracic cavity. This makes the lung pressure decrease below atmospheric pressure and always air to flow from an area of higher pressure to an area of lower pressure.

ACTIVE PROCESS AND REQUIRES ENERGY

Expiration - during expiration, the external intercostal and diaphragm muslces relax which means the ribcage moves downwards and inwards. The diaphragm curves upwards again and the volume of the thoracic cavity decreases, causing air pressure to increase to above atmospheric pressure. Air is forced down the pressure gradient and out of the lungs.

PASSIVE PROCESS UNLESS FORCED.

Lungs contain millions of microscopic air sacs where gas exchange occurs called alveoli.

The alveoli are surrounded by a network of capillaries.

The wall of each alveolus is made from a single layer of thin, flat cells called alveolar epithelium.

The walls of the capillaries are made from capillary endothelium.

The walls of the alveoli contain a protein called elastin which helps the alveoli return to their normal shape after inhaling and exhaling.

Lung diseases affects both ventilation and gas exchange in the lungs.

> Tidal volume is the volume of air in each breath.

> Ventilation rate is the number of breaths per minute.

> Forced expiration is the maximum volume of air that can be breathed out in 1 second.

> Forced vital capacity is the maximum volume of air it is possible to breathe forcefully out of the lungs after a really deep breath in.

TB, fibrosis, asthma and emphysema all reduce the rate of gas exchange in the alveoli.

Less oxygen is able to diffuse into the bloodstream, the body cells receive less oxygen and the rate of aerobic respiration is reduced.

This means less energy is released and sufferers often feel tired and weak.

Body size - Smaller organisms need a relatively high metabolic rate in order to generate enough heat to stay warm and the rate of heat loss depends on the animal's size.

E.g, a mouse has a relatively large surface area so heat is lost more easily.

Body Shape - Animals with a compact shape have a small surface area relative to their volume which minimises heat loss from their surface.

E.g. animals which are a bit gangly have a larger surface area relative to their volume which increases heat loss from their surface.