Biology: Cells, Tissues, and Digestion

Cells, Tissues, and Organs

Similar cells group to form tissues.
Tissues form organs, like the heart.
Organs work together in organ systems, like the circulatory system.

Digestion

The digestive system breaks down food into usable nutrients.
Stomach acid breaks down food.
Bile, produced in the liver and stored in the gallbladder, neutralizes stomach acid and emulsifies fats.
Emulsification forms droplets, increasing surface area for enzymes to break down fats faster.
Enzymes are biological catalysts that break down molecules.
Some enzymes break larger molecules into smaller ones, which can be absorbed.
Amylase is an enzyme that breaks down starch into glucose.
Enzymes are specific, they act only on certain molecules:
- Carbohydrases, like amylase, break down carbohydrates into simple sugars.
- Proteases break down proteins into amino acids.
- Lipases break down lipids (fats) into glycerol and fatty acids.
Enzymes work on a lock-and-key principle, where the substrate binds to the enzyme's active site.
This binding only occurs if the substrate's shape matches the active site.
The rate of enzyme activity increases with temperature.
Enzyme activity also increases with pH.
However, both temperature and pH extremes can denature enzymes, altering their shape and rendering them inactive.
The optimum temperature and pH are the conditions where the enzyme works best.

Respiration

Respiration is the process of using oxygen to release energy from food.
Breathing provides the oxygen needed for respiration.
Air travels down the trachea, bronchi, bronchioles, and into the alveoli (air sacs).
The alveoli have a large surface area to facilitate gas exchange.
Oxygen diffuses from the alveoli into the blood, binding to hemoglobin in red blood cells.
Hemoglobin transports oxygen to all body cells for respiration.
Carbon dioxide, a waste product of respiration, dissolves in blood plasma and diffuses back into the lungs to be exhaled.

Circulation

The circulatory system transports blood throughout the body.
The heart is the center of the circulatory system.
It's a double circulatory system, meaning blood passes through the heart twice per cycle.
Deoxygenated blood from the body enters the right atrium of the heart through the vena cava.
The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery.
Oxygenated blood from the lungs returns to the heart through the pulmonary vein, entering the left atrium.
The left ventricle pumps oxygenated blood to the body through the aorta.
The left ventricle has thicker walls than the right, as it must pump blood to the entire body.
Electrical pulses from cells near the right atrium trigger heart contractions.
Arteries carry oxygenated blood away from the heart, except for the pulmonary artery.
Veins carry deoxygenated blood towards the heart, except for the pulmonary vein.
Arteries have thicker walls to withstand higher blood pressure and have a smaller lumen (inner space).
Veins have thinner walls due to lower blood pressure but contain valves to prevent backflow.
Arteries branch into tiny capillaries, with thin walls that allow rapid diffusion of molecules in and out of cells.
The heart requires its own blood supply (oxygen) delivered by the coronary artery.
Blockage of coronary arteries by fatty deposits can cause a heart attack (CHD).
Stents can be implanted to keep blocked blood vessels open.
Statins are medications to lower cholesterol, reducing fatty deposits.
Faulty heart valves can be replaced with artificial ones.

Blood

Blood consists of plasma, red blood cells, white blood cells, and platelets.
Red blood cells transport oxygen.
White blood cells fight infections.
Platelets help clot wounds and stop bleeding.

Non-Communicable Diseases

Non-communicable diseases are caused by internal factors.
Examples include:
- Cardiovascular disease (CVD)
- Autoimmune conditions
- Cancer
- Type 2 diabetes

Communicable Diseases

Communicable diseases are caused by pathogens (viruses, bacteria, fungi) that enter the body.

Cancer

Cancer arises from uncontrolled cell division.
Benign tumors are non-spreading and easier to treat.
Malignant tumors spread to other parts of the body and are more dangerous.

Plant Organs

Leaves:
- Photosynthesis occurs in leaves, producing food for the plant.
- Leaves also release water through transpiration.
Roots:
- Water and mineral ions enter the plant through roots.
- The meristem is located in roots and produces new cells.
Xylem:
- Xylem are long tubes transporting water upwards (unidirectional transport). This is called transpiration.
Phloem:
- Phloem transports sugars, food, and sap both up and down the plant (bidirectional transport). This is called translocation.

Factors Affecting Transpiration Rate

Increased temperature, humidity, and air movement increase the rate of transpiration.

Leaf Anatomy

Cuticle: Waterproof, waxy layer that prevents water loss from the top of the leaf.
Upper epidermis: Transparent outer layer that allows light to pass through to the palisade mesophyll.
Palisade mesophyll: Layer packed with chloroplasts, where most photosynthesis takes place.
Spongy mesophyll: Layer with gaps, increasing surface area for gas exchange.
Vascular bundle: Contains xylem and phloem.
Lower epidermis: Bottom layer with stomata (pores) for gas exchange.
Guard cells: Surround stomata, regulating their opening and closing.