IGCSE Biology 3 Flashcards

• The primary role of red blood cells is to carry oxygen from the lungs to the rest of the body's tissues and transport carbon dioxide back to the lungs for exhalation. (these cells contain a protein called haemoglobin, which binds to oxygen, enabling efficient oxygen transport)
• White blood cells: Some white blood cells, called phagocytes, engulf and destroy pathogens (bacteria, viruses, etc.) through the process of phagocytosis. Lymphocytes, another type of white blood cell, produce antibodies.
• Platelets in clotting - preventing blood loss and the entry of pathogens.
• Plasma acts as a solvent allowing for the transport of blood cells, ions, nutrients, urea, hormones and carbon dioxide

Identifying Red Blood Cells:

• Shape: Look for the characteristic biconcave disc shape, which is thinner in the center than at the edges.
• Size: Red blood cells are typically smaller than white blood cells.
• Nucleus: Red blood cells lack a nucleus.

Identifying White Blood Cells:

• Shape: Generally round, but can vary in shape, especially phagocytes.
• Size: Larger than red blood cells.
• Nucleus: Visible nucleus, which can vary in shape and size depending on the type of white blood cell.

Identifying Lymphocytes and Phagocytes:

• Lymphocytes:These white blood cells have a large, round nucleus that takes up most of the cell, with a thin rim of cytoplasm.
• Phagocytes:These white blood cells can be identified by their irregular shape.

1. Clotting Factors and Thrombin:When a blood vessel is damaged, clotting factors are released, which ultimately leads to the activation of the enzyme thrombin.

2. Fibrinogen to Fibrin:Thrombin acts as a catalyst, converting the soluble plasma protein fibrinogen into insoluble fibrin.

3. Mesh Formation:Fibrin molecules then polymerize, forming long, insoluble threads that create a mesh-like network.

4. Clot Formation:This fibrin mesh traps platelets and blood cells, including red blood cells, forming a clot that seals the wound.

5. Scab Formation:Over time, the clot dries and hardens, forming a scab that protects the wound while new skin cells grow underneath.

A disease-causing organism.

A disease in which the pathogen can be passed from one host to another.

(a) by direct contact, including through blood and other body fluids

(b) indirectly, including from contaminated surfaces, food, animals and air

• Skin: The skin is the body's outer covering and acts as the first line of defence. It is a physical barrier that prevents pathogens from entering the body.
• Nose Hairs: Act as a filter, trapping dust, dirt, and pathogens, preventing them from reaching the lungs.
• Mucus: Mucus is a sticky substance secreted by cells lining various body parts, including the respiratory and digestive tracts. It traps pathogens, preventing them from adhering to cells and causing infection. Mucus can be expelled from the body through coughing, sneezing, or swallowing.
• Stomach Acid:The stomach produces hydrochloric acid, which is highly acidic. This acidity creates an inhospitable environment for many pathogens, killing them before they can cause infection.
• White Blood Cells: They circulate in the blood and lymphatic system and are crucial for fighting infections. They can engulf and destroy pathogens or produce antibodies to neutralise them.

Defence against a pathogen by antibody production in the body.

Proteins that bind to antigens leading to direct destruction of pathogens or marking of pathogens for destruction by phagocytes.

(a) weakened pathogens or their antigens are put into the body

(b) the antigens stimulate an immune response by lymphocytes which produce antibodies

(c) memory cells are produced that give long-term immunity

Passive immunity is a short-term defence against a pathogen by antibodies acquired from another individual, including across the placenta and in breast milk.

A disease caused by bacteria which is transmitted in contaminated water.

The cholera bacterium produces a toxin that causes secretion of chloride ions into the small intestine, causing osmosis of water into the gut, causing diarrhoea, dehydration and loss of ions from the blood.