GCSE Biology Notes on Organisation

Principles of Organisation

Think of your body like a perfectly organised company - it all starts with cells as the basic workers. These specialised cells team up to form tissues (like muscular tissue that helps you move), which then combine into organs (like your heart or stomach), and finally create organ systems that run your entire body.

The digestive system is your body's food processing plant, breaking down everything you eat so your body can actually use it. It includes obvious parts like your mouth and stomach, plus behind-the-scenes players like your pancreas (which makes digestive enzymes) and your liver (which produces bile to help break down fats).

Here's where it gets clever - your body uses enzymes as biological catalysts to speed up chemical reactions without getting used up themselves. Every enzyme has a unique active site that fits perfectly with its target substance, like a lock and key. This means each enzyme can only work on one specific job, making your body incredibly efficient.

Key Point: Enzymes are proteins made of amino acids, and their specific shapes determine exactly what job they can do in your body.

Digestive Enzymes and Conditions

Your digestive system uses three main types of digestive enzymes to break down food into molecules small enough to absorb. Carbohydrases (like amylase) convert starch into simple sugars, proteases break proteins into amino acids, and lipases turn fats into glycerol and fatty acids.

Bile plays a crucial supporting role - it's made in your liver, stored in your gallbladder, then released into your small intestine. Since stomach acid makes everything too acidic for enzymes to work properly, bile neutralises this acid and creates the perfect alkaline conditions for digestion.

Enzymes are quite fussy about their working conditions. They need the right temperature - too cold and they work slowly, too hot and they denature (lose their shape and stop working completely). They also need the right pH level, usually around neutral (pH 7), or they'll change shape and become useless.

Remember: Each enzyme has an optimum temperature and pH where it works best - this is why your body maintains such precise internal conditions.

Heart and Blood Vessels

Your lungs sit in your thorax, protected by ribs and separated from your abdomen by the diaphragm. Air travels down your trachea, splits into bronchi (one for each lung), then branches into tiny bronchioles ending in alveoli - microscopic air sacs where oxygen and carbon dioxide swap places with your blood.

Your circulatory system is actually a double loop - one circuit takes deoxygenated blood to your lungs to pick up oxygen, whilst the other pumps freshly oxygenated blood to every organ in your body. Pretty efficient design when you think about it.

Your heart is essentially a muscular pump with four chambers and valves that prevent blood flowing backwards. The process is surprisingly simple: blood flows into the two atria, they contract to push blood into the ventricles, then the ventricles contract to force blood out through major arteries. Your heart even has its own blood supply through coronary arteries that branch off from the main aorta.

Your heart's rhythm comes from natural pacemaker cells in the right atrium that produce electrical impulses. If these fail, doctors can implant artificial pacemakers to keep your heart beating regularly.

Interesting Fact: Your heart beats roughly 100,000 times per day, pumping about 7,500 litres of blood around your body.

Blood Vessels and Blood Components

Arteries, capillaries, and veins each have different jobs and structures. Arteries carry high-pressure blood away from your heart, so they need thick, muscular walls with elastic fibres to handle the pressure. Capillaries are where the real action happens - they're only one cell thick, making it easy for oxygen, nutrients, and waste to diffuse in and out. Veins return low-pressure blood to your heart, so they have thinner walls and valves to prevent backflow.

Blood itself is a tissue with four main components. Red blood cells are shaped like biconcave discs (imagine a doughnut that hasn't been fully punched through) to maximise surface area for carrying oxygen via haemoglobin. They don't even have a nucleus - all that space is dedicated to carrying oxygen.

White blood cells are your immune system's soldiers. Some engulf harmful microbes through phagocytosis, others produce antibodies to fight infections, and some make antitoxins to neutralise toxins. Platelets are cell fragments that help your blood clot when you're injured, preventing blood loss and keeping germs out.

Plasma is the liquid component that carries everything else - it's basically your blood's transport system, moving cells, nutrients, hormones, and waste products around your body.

Quick Calculation: Rate of blood flow = volume of blood ÷ number of minutes. Useful for working out how efficiently blood moves through different parts of your circulatory system.

Coronary Heart Disease Treatments

Coronary heart disease happens when the arteries supplying your heart muscle become blocked by fatty deposits, restricting blood flow and potentially causing heart attacks. It's a major non-communicable disease that doctors can treat in several ways.

Stents are tiny tubes inserted into blocked arteries to keep them open - they're effective long-term with quick recovery times, but carry risks of infection and blood clots. Statins are drugs that reduce 'bad' cholesterol in your blood, slowing down fatty deposit formation, though they need to be taken long-term to be effective.

For severe cases, doctors might use artificial hearts as temporary solutions whilst patients wait for transplants. These mechanical devices are less likely to be rejected by your immune system but can cause bleeding and don't create smooth blood flow. Valve replacements (either biological or mechanical) fix valves that have become stiff or leaky.

Artificial blood substitutes like saline can replace lost blood volume temporarily whilst your body produces new blood cells, though severe blood loss still requires proper transfusions.

Key Point: All these treatments have advantages and disadvantages - doctors choose based on individual patient needs and circumstances.

Health Issues and Risk Factors

Communicable diseases spread from person to person (like flu), whilst non-communicable diseases can't be transmitted between people (like diabetes). Sometimes these diseases interact - for example, people with weakened immune systems are more vulnerable to infections, and some cancers are triggered by viral infections.

Risk factors increase your likelihood of developing diseases but don't guarantee you'll get them. These can be lifestyle choices (smoking, diet) or environmental factors (pollution, access to healthcare). The impact varies - locally it's about individual choices, nationally it's about social deprivation affecting health outcomes, and globally it's about economic development affecting disease patterns.

Some risk factors directly cause diseases. Smoking damages artery walls and lung tissue, obesity can lead to insulin resistance and type 2 diabetes, and excessive alcohol consumption damages your liver and brain. Smoking and drinking during pregnancy harm developing babies.

Scientists identify risk factors by looking for correlations in data, but correlation doesn't always mean causation. Sometimes risk factors are linked to other factors that actually cause the disease - like how high-fat diets correlate with heart disease, but it's actually the resulting high blood pressure that causes the damage.

Important: Understanding risk factors helps you make informed choices about your health, even though they don't guarantee specific outcomes.

Cancer and Plant Organisation

Cancer results from uncontrolled cell growth and division, creating tumours. Benign tumours stay in one place and aren't usually dangerous, whilst malignant tumours spread throughout your body via the bloodstream, invading healthy tissues and forming secondary tumours.

Various risk factors increase cancer chances, including smoking, obesity, UV exposure, and viral infections. However, you can also inherit faulty genes that make you more susceptible. The good news is that cancer survival rates have improved dramatically due to better treatments and earlier diagnosis.

Plants, like humans, have organs and organ systems made of specialised tissues. Epidermal tissue covers the plant surface with a waxy cuticle to reduce water loss. The upper epidermis is transparent for light penetration, whilst the lower epidermis contains stomata for gas exchange.

Palisade mesophyll tissue sits near the top of leaves and contains loads of chloroplasts for photosynthesis. Spongy mesophyll tissue has large air spaces for gas diffusion. Xylem and phloem transport substances and provide structural support, whilst meristem tissue at root and shoot tips allows plants to grow by differentiating into various cell types.

Plant Fact: Plants are basically solar-powered factories - their entire structure is designed to capture sunlight, absorb water and nutrients, and manufacture everything they need to survive.

Plant Transport Systems

Plants have two main transport systems working like a plant's circulatory system. Phloem tubes transport food substances made in leaves to other parts of the plant through translocation - this can flow in both directions depending on where the plant needs nutrients.

Xylem tubes carry water from roots to stems and leaves through transpiration. They're made of dead cells joined end-to-end with hollow centres, creating perfect water highways. Transpiration happens when water evaporates from leaf surfaces, creating a shortage that draws more water up from the roots - like a constant conveyor belt of water movement.

Transpiration rate depends on four main factors. Higher light intensity opens stomata more, increasing water loss. Higher temperature gives water particles more energy to diffuse out. Better air flow sweeps away water vapour, maintaining concentration gradients for diffusion. Lower humidity creates bigger differences between water concentration inside and outside leaves.

You can measure transpiration using a potometer - set up the apparatus, record the air bubble's starting position, then measure how far it moves in a set time. This gives you an estimate of water uptake, which relates directly to water loss.

Guard cells control stomata opening and closing. When plants have plenty of water, guard cells become turgid (swollen), opening stomata for gas exchange. When water is scarce, they become flaccid (limp), closing stomata to conserve water.

Cool Design: Guard cells have thin outer walls and thick inner walls, plus they're light-sensitive - perfect for responding to changing conditions automatically.