Gaseous Exchange In Plants.
Plants obtain the gases they need through their leaves.
They require oxygen for cellular respiration and carbon dioxide for photosynthesis.
Taking in O2 and giving out CO2 is termed as Gaseous Exchange.. 

Gaseous Exchange In Plants.

The Epidermis of a leaf.

The gases diffuse into the intercellular spaces of the leaf through pores, which are normally on the underside of the leaf – stomata. From these spaces they will diffuse into the cells that require them.

The Epidermis of a leaf

Lenticels – pores in the bark of stems

Gaseous Exchange In Humans

Gaseous Exchange In Humans is carried out by respiratory system.

It is divided into two parts:

1. The Air Passage Way.

2. The Lungs.

The air passage way consists of parts through which air

comes in lungs and after exchange of gases it goes out.

It consists of following:

Gaseous Exchange In Humans is carried out by respiratory system

A pair of lungs are present in thoracic cavity, with 12 pair of ribs, rib muscles also called as (Intercoastal muscles) and a thick muscular structure, called diaphragm, present below lungs.

Left lung is smaller in size with two lobes, while Right lung having three lobes is larger.
Lungs have blood vessels that are branches of pulmonary arteries and veins.

Each lung encloses two membranes, the outer pleural membrane & inner pleural membrane.  

Mechanism of Breathing:


  Rib muscles contract and ribs are raised.                  Dome-Shape diaphragm contracts and is lowered, reducing the pressure on lungs, resulting in air flow in lungs from out side to equalize the pressure.


    The impure air is expelled out in exhalation. Rib muscles relax, raising the dome shape which increase pressure on lungs and air is expelled out.

Humans breathe 16 - 20 times / min in normal (at rest). During Exercise up to 30 - 40 times / min.  

Mechanism of Breathing

Respiratory Disorders:


  It is inflammation of bronchi, resulted by excessive secretions of mucus into the tubes, leading to swelling and blocking of tubes. It is caused by Virus, Bacteria or exposure to chemical irritants (e.g. tobacco smoke).

  There are two major types of bronchitis. Acute and Chronic.


    Cough, mild wheezing, fever, chills and shortness of breath.


    It is the destruction of walls of alveoli, resulting in larger sacs but with less surface area for gaseous exchange. Lung tissue breakdown, so air cannot be pushed out. Symptoms:

  Shortness of breath, fatigue, recurrent respiratory infection and weight loss. Symptoms appear after 50-70% damage.


  It is a lung infection caused by a bacterium, Streptococcus pneumonia. Some viral (Influenza) or fungal infections may also lead to pneumonia.                


    It is a form of allergy, with inflammation of bronchi, more mucous production and narrowing of airways.


  They vary from person to person. Major symptoms include shortness of breath, wheezing, cough and chest tightness.

Lung Cancer:

  It is a uncontrolled cell division in tissue of lungs, forming tumor. It is mostly caused by carcinogens (cigarette smoke), ionization radiation and viral infection.

Bad Effects of Smoking:

Cigarette smoke effects the whole body.
It may cause cancer in kidneys.
It has effect on circulatory system.
It may increase  the risk of tuberculosis.
It is responsible for weakening of teeth and bones.
It may damage the air pathway, leading to respiratory disorders.


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