Gaseous Exchange in plants and human

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 Gaseous Exchange between plants and human

It might sound obvious, but have you ever actually thought about what happens every time you breathe?

 Whenever you breathe in, your body takes in oxygen. Then, after using it to produce energy, it gets rid of carbon dioxide by breathing it out.

Now you might be wondering... where does all this oxygen come from? And where does the carbon dioxide go?

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This is where plants play a really important role. They take in the carbon dioxide that we breathe out and use it to make their own food through photosynthesis. In return, they release oxygen back into the atmosphere, the same oxygen that we breathe in.

So, in a way, humans and plants work as a team. We depend on plants for oxygen, and plants depend on the carbon dioxide we release. It's a beautiful cycle that keeps life on Earth going.


I. Fundamental Definitions

Cellular Respiration: The process where C-H bonds in food are broken by oxidation-reduction reactions, and the released energy is transformed into ATP.

Gaseous Exchange: The process of taking in oxygen and giving out carbon dioxide.

Breathing: The physical/mechanical process through which animals move air in and out of their bodies to facilitate gas exchange.

Difference between Breathing and Respiration: Respiration involves both mechanical and biochemical processes (energy release), while breathing is purely the mechanical movement of air.

II. Gaseous Exchange in Plants

Plants do not have specialized organs like human beings have nose, lungs etc.; instead, every cell exchanges gases with the environment independently.

Important Terms

Stomata: Microscopic pores in the epidermis of leaves and young stems through which gaseous exchange and water vapor movement occur.

Mesophyll Cells: Inner leaf cells that have large air spaces to facilitate gas movement.

Lenticels: Raised pores in the bark of woody stems and mature roots that allow air to pass through the otherwise impervious bark.

Cuticle: A thin layer over the epidermis of young stems and leaves through which some gas exchange can occur.

Day vs. Night Mechanisms

Daytime: Mesophyll cells perform photosynthesis and respiration simultaneously. The oxygen from photosynthesis is used for respiration, and the carbon dioxide from respiration is used for photosynthesis.

Nighttime: Since no photosynthesis occurs, cells take oxygen from the environment and release carbon dioxide via stomata.

Key Diagrams to Study

  • Figure 10.1: Gaseous exchange in a leaf showing stomata and mesophyll cells.
  • Figure 10.2: Internal and external view of lenticels on a stem.

III. Gaseous Exchange in Humans

The human respiratory system is divided into the air passageway and the lungs.

1. The Air Passageway

Path of Air:

Nasal Cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveolar Ducts → Alveoli

Nasal Cavity: Lined with hair and mucus to filter dust and warm/moisten incoming air.

Pharynx: A muscular passage common to both food and air.

Glottis: A narrow opening at the floor of the pharynx leading to the larynx, guarded by the epiglottis.

Larynx: Known as the "voice box", it is made of cartilage and contains vocal cords that vibrate to produce sound.

Trachea: The "windpipe", approximately 12 cm long, containing C-shaped cartilaginous rings to prevent it from collapsing.

Alveoli: Sac-like structures that form the respiratory surface. They are lined by a single layer of epithelial cells and surrounded by a network of capillaries for gas exchange.

2. The Lungs and Breathing Mechanism

Structure: A pair of spongy, elastic organs in the thoracic cavity. The left lung has two lobes, and the right lung has three.

Pleural Membranes: Two membranes (inner and outer) enclosing a lubricating fluid that allows the lungs to expand and contract freely.

Diaphragm: A thick muscular structure below the lungs that facilitates breathing.

The Phases of Breathing

  1. Inhalation (Inspiration): Rib muscles contract (raising ribs) and the diaphragm contracts (lowers). This increases thoracic volume, decreases pressure, and air rushes in.
  2. Exhalation (Expiration): Rib muscles and diaphragm relax. The ribs lower, the diaphragm becomes dome-shaped, thoracic space reduces, and air is expelled.


IV. Respiratory Disorders

Bronchitis: Inflammation of the bronchi or bronchioles, leading to excessive mucus and narrowing of tubes. It can be acute (short-term) or chronic (long-term).

Emphysema: Destruction of the alveolar walls, resulting in larger sacs with less surface area for exchange. Air becomes trapped in the lungs, making exhalation difficult.

Pneumonia: An infection of the lungs (usually by Streptococcus pneumoniae) where alveoli fill with fluid and pus.

Asthma: An allergy-driven inflammation of the bronchi, characterized by airway constriction in response to allergens such as dust, smoke, or pollen.

Lung Cancer: Uncontrolled cell division in lung tissues, primarily caused by carcinogens in cigarette smoke.

V. Effects of Smoking

  • Tobacco smoke contains over 4,000 chemicals, including at least 50 carcinogens.
  • Nicotine: A powerful poison that hardens artery walls and damages brain tissues.
  • Carbon Monoxide: Reduces the oxygen-carrying capacity of hemoglobin in the blood.
  • Social and Physical Impacts: Smoking increases the risk of tuberculosis and pneumonia, stains teeth, and leads to social unacceptance due to passive smoking risks.

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