Cell Theory and Components

Study Notes

All living things are made up of cells.
Cells are the basic building blocks of life.
Cells are incredibly small, typically measured in micrometres (μm).
One micrometre is 1000 times smaller than one millimetre.
Bird eggs are a notable exception, being easily visible to the naked eye. The ostrich egg is the largest cell.
Multicellular organisms are made up of many cells.
Unicellular organisms consist of only one cell.

Common Components:
- Cell membrane: A protective outer layer made of proteins that controls what enters and exits the cell.
- DNA: Contains genetic information that determines an organism's traits and instructs cells to function.
- Cytosol: A jelly-like substance that holds organelles in place.
Eukaryotic Cells (Multicellular) have specialized structures called organelles:
- Nucleus: Controls the cell's activities, stores DNA, and contains the nucleolus which makes ribosomes.
- Ribosomes: Produce proteins based on instructions from DNA.
- Endoplasmic Reticulum (ER): A transport network within the cell.
  - Smooth ER: Manufactures fats and hormones.
  - Rough ER: Covered in ribosomes, involved in protein synthesis.
- Golgi apparatus: Modifies, packages, and transports molecules.
- Mitochondria: The powerhouse of the cell, converting sugar into energy (ATP).
- Lysosomes: Contain digestive enzymes for breaking down waste.
- Vacuole: Storage for water and proteins. Plant cells have a large central vacuole, while animal cells have many small vacuoles.
- Chloroplasts: Found only in plant cells, contain chlorophyll for photosynthesis.
- Cell Wall: Found only in plants and fungi, provides structural support.

Plants capture energy from the sun using chlorophyll.
This energy is used to combine carbon dioxide and water to produce glucose (a type of sugar) and oxygen.
The process can be represented as:
- Carbon dioxide + Water → Glucose + Oxygen

Air enters the body through the nose or mouth.
It travels down the trachea and into the bronchi, which branch into smaller bronchioles within the lungs.
At the end of bronchioles, tiny air sacs called alveoli allow for gas exchange, taking in oxygen and releasing carbon dioxide.
The diaphragm, a muscle beneath the lungs, helps facilitate breathing by contracting and relaxing.

The nervous system acts as the body's command center, controlling movement, thoughts, and sensations.
It consists of the brain, spinal cord, and nerves.
The central nervous system (CNS) includes the brain and spinal cord.
The peripheral nervous system (PNS) consists of nerves extending from the CNS to the rest of the body.
The nervous system controls both voluntary and involuntary actions.

The digestive system breaks down food into nutrients your body can use.
The process begins in the mouth:
- Food is chewed and mixed with saliva.
- It travels down the esophagus.
In the stomach:
- Food is mixed with digestive juices.
- It is further broken down.
In the small intestine:
- Most nutrient absorption occurs.
- The liver, pancreas, and gallbladder contribute enzymes and bile to digestion.
In the large intestine:
- Water is absorbed.
- Remaining waste is excreted through the rectum and anus.

The circulatory system (cardiovascular system) transports oxygen, nutrients, and hormones throughout the body while removing waste products (like carbon dioxide).
It includes the heart, which pumps blood, and a network of blood vessels.
Blood vessels include arteries, veins, and capillaries:
- Arteries carry oxygenated blood away from the heart.
- Veins carry deoxygenated blood back to the heart.
- Capillaries facilitate the exchange of substances between blood and cells.