Human Circulatory System

Gaseous Exchange in Plants

• Gases move by diffusion through stomata in leaves.

• Duringphotosynthesis: CO₂ enters, O₂ exits.

• During respiration: O₂ enters, CO₂ exits.

• Respiration occurs 24 hours a day. Photosynthesis requires sunlight.

Investigating the effect of light on net gas exchange

• Uses hydrogen-carbonate indicator to measure CO₂ levels.

• Test Tube 1 (Control): No leaf, CO₂ stable → Orange.

• Test Tube 2 (No Light): Leaf respires, no photosynthesis, CO₂ increases → Yellow.

• Test Tube 3 (Full Light): Photosynthesis > Respiration, CO₂ decreases → Purple.

• Test Tube 4 (Partial Light): Photosynthesis ≈ Respiration, CO₂ stable → Orange.

Gaseous Exchange in Humans

• Lungs are adapted organs for gas exchange between environment and blood.

Structures Involved in Gaseous Exchange (Respiratory System)

Ventilation / Breathing

• Movement of air into/out of lungs,requires pressure difference and airtight thoracic cavity.

• Driven by intercostal muscles and diaphragm changing lung volume/pressure.

Alveoli

• Approx. 700 million tiny air sacs, surrounded by blood capillaries.

• Diffusion occurs based on concentration gradients.

• CO₂ diffuses from blood into alveoli for exhalation.

• O₂ diffuses into red blood cells (forming oxyhaemoglobin) to be pumped around the body.

Adaptations of theAlveoli for Efficient Gaseous Exchange

1. Large surface area to volume ratio: Increases diffusion rate.

2. Moist surfaces: Helps gases dissolve, increases diffusion rate.

3. Fine network of blood capillaries: Rich blood supply, maintains steep diffusion gradient.

4. Walls are one cell thick (alveoli and capillaries): Short diffusion distance, increases rate.

5. Walls are permeable.

Breathing and Exercise

• Breathing rate increases with exercise to:

  • Supply muscles with more oxygen for aerobic respiration.

  • Remove extra carbon dioxide produced by aerobic respiration.

• Rate remains high after exercise to remove waste products.

The Effect of Smoking on the Breathing System and Circulation

• Smoking contributes to: Lung cancer, Chronic bronchitis, Emphysema.

Lung Cancer

• Carcinogens (cancer-causing chemicals) in tobacco smoke and tar cause cell mutation.

Chronic Bronchitis

• Healthy lungs: Cilia on bronchi/bronchioles, goblet cells secretemucus (traps microbes). Cilia waft mucus to throat.

• Smoking: Tar damages/paralyses cilia, leading to bacteria buildup and chest infections.

• Tar irritates airways, increasingmucus production that cannot be cleared → "smoker's cough".

Emphysema

• Cigarette smoke damages alveoli walls, causing them to burst and fuse.

• Reduces surface area forgas exchange.

• Leads to lack of oxygen, severely restricting physical activity. No cure.

Smoking and CVD (Cardio Vascular Disease)

• Damages circulatory system, increases risk of coronary heart disease.

• Fatty deposits in coronary arteries → Blockage → Lack of oxygen to heart → Heart attack.

• Carbon monoxide in smoke binds to haemoglobin (instead of O₂) → Heart works harder, higherblood pressure → Damages artery walls, increases clot risk.

• Nicotine makes blood cells "sticky" and narrows blood vessels (vasoconstriction).

Transport in Plants

• Vascular bundle: Network of veins from roots to leaves.

• Xylem: Transports water and dissolved mineral ions.

• Phloem: Transports sugars and amino acids.

• Water absorbed by roots via osmosis.

Transportin Humans

• Large multicellular organisms need a circulatory system due to small surface area to volume ratio.

• Blood separated by centrifuge:

  • Blood cells (bottom)

  • Plasma (light straw-coloured liquid, top)

Red Blood Cells (Erythrocytes)

• Made in bone marrow.

• Function: Carry oxygen around the body.

Properties

• Biconcave shape: Large surface area to volume ratio, increases oxygen diffusion.

• No nucleus: Allows more haemoglobin for oxygen transport.

• Haemoglobin: Carrier protein, binds to oxygen forming oxyhaemoglobin.

White Blood Cells

• Main function: Protect against disease-causing pathogens.

• Two main types:

  • Phagocytes (approx. 70%): Engulf pathogens (phagocytosis).

  • Lymphocytes (approx. 30%): Produce antibodies.

Lymphocytes and Antibodies

• Pathogens have antigens (markers).

• Antibodies attach to antigens to destroy pathogens by:

  • Causing bacteria to burst.

  • Making bacteria stick together for easier ingestion by phagocytes.

  • Neutralising toxins.

• Memorycells: Some lymphocytes become memory cells, providing immunity to specific pathogens.

• Secondary immune response: Faster, mass production of antibodies upon re-exposure.

Vaccines

• Trick the body into initiatingan immune response to produce antibodies.

• Contents: Dead pathogen, weakened pathogen strain, modified toxins, or isolated antigens.

Platelets

• Small cell fragments.

• Function: Help blood clot (e.g., when cut) to stop bleeding and prevent infection.

• Produce chemical that converts plasma protein fibrinogen to fibrin, forming a clot.

Plasma

• Over 90% water.

• Function: Transports many substances around the body.

The Heart

• Made of cardiac muscle (never tires).

• Function: Pump blood around thebody and to lungs by contracting (systole) and relaxing (diastole).

• Contains valves to ensure one-way blood flow.