Organisation

Tissues and Organ Systems

When similar cells are connected, they form a tissue, like heart tissue. Tissues then combine to form organs, such as the heart, which operates as part of an organ system (e.g., the circulatory system). This hierarchical organization allows for complex biological functions necessary for life.

Digestive System

The digestive system is crucial for breaking down food into useful nutrients. Food enters the stomach where acid initiates the breakdown process. Following this, bile, produced in the liver and stored in the gallbladder, is secreted into the small intestine. Here, it neutralizes stomach acid and emulsifies fats, increasing the surface area for enzymes to act on.

Enzyme Function and Specificity

Enzymes act as biological catalysts, facilitating the breakdown of larger molecules into smaller, absorbable units. For instance, amylase breaks down starch into glucose, found in saliva and the small intestine. Enzymes are specific; carbohydrases, for example, convert carbohydrates to simple sugars, while proteases break down proteins into amino acids, and lipases convert lipids into glycerol and fatty acids. The specificity is explained by the lock and key model, where the substrate must precisely fit the enzyme’s active site to form an enzyme-substrate complex.

Enzyme Activity

The rate of enzyme activity is influenced by temperature and pH. As temperature increases, enzyme activity rises until a point where the enzyme denatures, altering the active site shape. Similarly, extreme pH levels can lead to denaturation. Practical experiments measure enzyme activity (e.g., mixing amylase with starch) by observing color change with iodine—indicating starch breakdown. Optimum pH and temperature are identified where the activity rate is highest.

Nutrient Testing

Food tests are essential for identifying nutrients in food. Iodine indicates starch presence by turning black, while Benedict's solution indicates sugars by changing from blue to orange. Biuret's reagent similarly detects proteins by changing from blue to purple, and lipids can be tested with cold ethanol, which becomes cloudy.

Respiratory System

The respiratory system facilitates breathing and gas exchange—though breathing itself is not respiration, it provides necessary oxygen. Air travels down from the trachea to the bronchi and bronchioles, finally reaching the alveoli. Here, oxygen diffuses into blood vessels, binds to hemoglobin in red blood cells, and is distributed to cells for respiration. Carbon dioxide generated from cellular respiration dissolves in blood plasma, diffusing out to the lungs to be exhaled, with moisture also released during this process.

The Heart and Circulatory System

The heart functions as the central pump of the circulatory system, a double circulatory system meaning blood passes through the heart twice per cycle. Deoxygenated blood returns to the right atrium via the vena cava and moves to the lungs through the pulmonary artery for oxygenation. The left side pumps oxygenated blood out through the aorta. The left ventricle has thicker muscular walls than the right ventricle, as it circulates blood throughout the body.

Heart Function and Conditions

Initiation of heart contraction is controlled by electrical pulses generated near the right atrium, and deficiencies can be managed with artificial pacemakers. Understanding vascular dynamics is crucial: arteries typically carry oxygenated blood and have thick walls to cope with high-pressure flow, while veins return deoxygenated blood and often include valves to prevent backflow. Coronary arteries supply blood to the heart muscle itself; blockages can lead to coronary heart disease (CHD), often treated with stents or cholesterol-reducing drugs (statins).

Cardiovascular and Non-communicable Diseases (CVD)

CVD, defined as a non-communicable disease, develops from internal factors rather than pathogens. Risk factors include obesity, poor diet, smoking, and lack of exercise, leading to conditions like Type 2 diabetes and heart disease. Cancer results from damaged cell division, categorized as benign or malignant based on spread capability.

Plant Organ Systems

Plants also possess organ systems; leaves are essential for photosynthesis, roots absorb water and nutrients, and stems produce new cells. Xylem transports water unidirectionally, while phloem facilitates bi-directional transport of sugars (translocation). Factors such as temperature, humidity, and air movement influence transpiration rates.

Leaf Structure

A leaf's structure supports its function in photosynthesis and gas exchange. The waterproof cuticle prevents water loss, while the upper epidermis allows light passage. The palisade mesophyll is rich in chloroplasts for photosynthesis, and the spongy mesophyll enhances gas exchange efficiency. Vascular bundles (xylem and phloem) and stomata (controlled by guard cells) facilitate these processes, adapting gas permeability to environmental conditions.

In summary, understanding the detailed functions of these biological systems can greatly enhance our comprehension of human and plant physiology and health.