Red blood cells are specialized for transporting oxygen from the lungs to all cells in the body. Their structure is uniquely adapted to perform this function efficiently:

• Haemoglobin Content: Red blood cells contain a high concentration of haemoglobin, a protein that can reversibly bind to oxygen. This allows them to pick up oxygen in the lungs and release it where it is needed in the body.
• Lack of Nucleus: Red blood cells lack a nucleus, which creates additional space for haemoglobin. This increases their oxygen-carrying capacity.
• Biconcave Shape: Their biconcave disc-like shape (thinner in the middle and thicker at the edges) increases their surface area relative to their volume. This facilitates more efficient oxygen diffusion into and out of the cell.
• Flexibility: Red blood cells are highly flexible, enabling them to squeeze through narrow capillaries without rupturing. This ensures oxygen is delivered to even the smallest and most remote tissues.

Each of these features is closely linked to the red blood cell's role in oxygen transport, optimizing their efficiency in delivering oxygen throughout the body.

Osmosis is the movement of water molecules across a semi-permeable membrane, which allows certain molecules to pass through while blocking others (like a cell membrane). This process occurs along a concentration gradient, meaning water moves from an area of higher water concentration to an area of lower water concentration.

To illustrate this with an example, imagine a tank of water divided into two sections by a semi-permeable barrier. On one side, the water is 80% pure, while on the other side, it is only 40% pure. During osmosis, water molecules will move through the semi-permeable barrier from the side with 80% purity (higher concentration) to the side with 40% purity (lower concentration). This movement continues until equilibrium is reached, where the concentration of water molecules is balanced on both sides, and no net movement occurs.

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Atoms are the tiny building blocks that make up all matter. Imagine an object composed of miniature footballs—this is similar to how atoms form the structure of an object, though on an incredibly smaller scale.

Each atom consists of three subatomic particles: protons (with a positive charge), electrons (with a negative charge), and neutrons (with no charge). The number of each particle varies depending on the type of atom.

The atoms that make up the elements on the periodic table are known as standard atoms. These elements are the most basic forms of matter and serve as the foundation for everything in the universe.

The smallest living unit is the cell, which is organised differently depending on its function. Despite these variations, cells share some common features.

In animal cells, key components include:

• Nucleus: Contains genetic information.
• Cell membrane: Acts as a protective barrier.
• Cytoplasm: The site where most cellular functions occur.
• Mitochondria: Responsible for cellular respiration.
• Ribosomes: Facilitate protein synthesis.

Plant cells have additional specialised structures, such as:

• Chloroplasts: Convert light into energy through photosynthesis.
• Vacuoles: Provide storage and maintain cell structure.

Bacterial cells, on the other hand, are unique in having a cell wall, a feature not present in animal cells. This cell wall plays a crucial role in bacterial survival and is a key target for antibiotics developed by scientists.

Photosynthesis is a vital biochemical process in which plants convert carbon dioxide and water into glucose and oxygen using sunlight. This process plays a crucial role in maintaining the balance of gases in Earth's atmosphere, as plants take in carbon dioxide (exhaled by animals) and release oxygen, which is essential for most living organisms.

Word Equation:

Carbon dioxide + Water → Glucose + Oxygen

Chemical Equation:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

This process occurs primarily in the chloroplasts of plant cells, where chlorophyll absorbs sunlight to drive the reactions.

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Deoxygenated blood from the body returns to the right atrium of the heart via the superior and inferior vena cava. From the right atrium, the blood flows into the right ventricle, passing through the tricuspid valve, which prevents backflow. The right ventricle then pumps the blood to the lungs for oxygenation through the pulmonary artery.

Once oxygenated, the blood returns to the heart via the pulmonary vein, entering the left atrium. From there, it is pumped into the left ventricle, the final chamber of the heart. The left ventricular wall is thick and muscular, allowing it to generate the force needed to pump oxygen-rich blood through the aorta and distribute it to the rest of the body.

he process of cardiac excitation begins with the sinoatrial (SA) node, which generates an action potential (excitation signal). This signal propagates across the atria, triggering their contraction. Upon reaching the atrioventricular (AV) node, the signal experiences a brief delay, allowing the atria to contract before the ventricles are stimulated fully. From the AV node, the excitation is transmitted to His bundle, which runs along the interventricular septum. The bundle of His branches into Purkinje fibres, which distribute the signal throughout the ventricles, causing them to contract and effectively pump blood.