Biology, gas exchange in humans and plants

Diffusion=
When molecules move from a region of high concentration to a region of low concentration. Oxygen into the cells then it is used up in respiration. Carbon dioxide diffuses out of cells.  

Flowering plants
Carbon dioxide + Water à Glucose + oxygen
To do this photosynthesis needs light (Occurs only when there is sun light)
If the light intensity is increased during the day then the rate of photosynthesis will increase. Net effect would be oxygen production when there is high intensity.

Glucose + OxygenàCarbon dioxide + Water
If you reverse this is is called respiration (occurs all the time)
Photosynthesis is not occuring so there is a net production of carbon dioxide. The stomata pores are closed so there is not much carbon dioxide given off by the plant.

Carbon dioxide passes from the athmosphere through the stomata pores in to the palisade cells for the process of photosynthesis.  Oxygen is given of during the dat through the stomata pores.

Adaptations of the leaf for gas exchange

• The thickness of the leaf, so thin that the diffusion distance is very small and then there wiill be faster diffusion time.
• The stomata pores formed by two gaurd cells which can open and close. this gives the plant control over gas exchange.

The role of the stomata in gas exchange
In the lower epidermis of the leaf are pores known as stomata. Each pore is formed by two gaurd cells.

During the day when there is light the gaurd cells become turgid and the pores are open for gas exchange.
At night in the dark the gaurd cells are flassid and so the pores close and stop gas exchange.

Humans
The thorax is a cage of bones called the ribs which extend from a bone in the front called the sternum. The ribs come out of this and curve around towards the backbone. In between the ribs are two sheets of muscles called the intercostal muscle these are responsible for the movement for the chest cavity up and down in the breathing process.

Air enters the thorax through the trachea which contains cartlidge present to support the tissue and stop it from collapsing when we breath out.  The trachea devides into two which are known as the bronchi. The bronchi the devides into brocnhioles. The dead end structure called the alveoli which is the site of gas exchange.

That on the surface on the lung tissue is a membrane which is called the inner pleural membrane. Then there is another membrane on top and in between is a fluid called pleural fluid.  This membrane is known as the outer pleural membrane. This membrane is attached to the rib cage. 

Ventillation
Alveoli is the site of gas exchange. Between alveoli´s there would be protein molecules which are called elastin which streches.

Diaphragm is a sheet of muscle from the front of the rib cage to the back.

Inhaling
 When we inhale there is a contraction of the diaphragm which then shortens. Then the diaphragm moves down which increases the volume in the thorax and then lungs. The pressure falling in the alveoli and air moves into the lungs.

Exhaling
The diaphragm move up intothe thorax. The streching force is removed and we have the recoil of the elastin protein molecules. This reduces the volume of the alveoli which the in turn increases pressure in the alveoli. This forces the alveoli gas out of the lung

Ventillation 
Alveoli is the site of gas exchange. Between alveoli´s there would be protein molecules which are called elastin which streches.

Intercostal muscle are between the backbone and the sternum.

Inhaling
A contraction of the external inter costal muscles. Then the thorax risea and moves outward. The volume in thorax increases. This streches the lung tissue. The pressure decreases and air moves in.

Exhaling
The internal costal muscle contracts. The rib cage moves down and in. Reduced volume of thorax  this compresses the alveoli tissue. Then the pressure increases and are moves out.

Alveoli adaptations to gas exchange

• Large surface area
• Dense network of blood vessel
• Thin alveoli walls, so fast diffusion
• Moist for the fast dissolving of gases 

Effects of smoking on the lungs

• Tars which cause lung cancer another one is bronchitis which damages the cilia cells also infamation, muscus and a common feature is the smokers caugh.
• Nicotine causes increase in blood pressure, clotting and heart damage.
• Carbon monoxide reduces the oxygen carried, also can reduce oxygen taken to the foetus.