Cell Biology: Characteristics, Structure, and Processes
Characteristics of Living Organisms
- Nutrition: Taking in, absorbing, and assimilating nutrients (organic substances, mineral ions) containing raw materials/energy for growth and tissue repair.
- Plants: Photosynthesis – H2O, CO2, Light
- Excretion: Removal of toxic materials and waste products of metabolism and substances in excess, produced by chemical reactions in cells (respiration).
- Respiration: Breaking down food in cells to release energy.
- Sensitivity: Sensing and responding to changes in the environment (stimuli).
- Reproduction: Producing offspring to prevent extinction of species.
- Growth: Increase in size and mass of organism by increasing cell number and/or size.
- Movement: Change in position or place of an organism or part of an organism.
- Ex: Parts of the plant move very slowly to obtain more light for photosynthesis.
Cell Structure and Organization
All organisms are made of basic units called cells.
- Unicellular Organisms: Made of a single cell.
- Multicellular Organisms: Made of many cells.
Animal and Plant Cells Under the Light Microscope
- Animal (Liver): Cell membrane, nucleus, granular cytoplasm
- Plant (Palisade): Cell wall, sap vacuole, chloroplasts, nucleus
Functions of Cell Structures
- Cell Membrane: Controls what enters and leaves the cell.
- Cytoplasm: Contains organelles and enzymes that speed up chemical reactions inside the cell.
- Nucleus:
- Largest organelle.
- Contains genetic material in the form of DNA.
- Directs all the functions of the cell.
- Chloroplasts:
- Contains the green pigment chlorophyll.
- Carries out photosynthesis.
- Sap Vacuole: Big, central, and permanent vacuole containing a solution of sugar and salts that allows the cell to take in water by osmosis.
- Cell Wall:
- Made of cellulose.
- Protects the cell.
- Gives shape to the cell.
- Prevents the cell from bursting when water flows into it by osmosis.
Differences Between Plant and Animal Cells
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present | Absent |
| Nucleus | Pushed to the side | Central |
| Vacuole | Big, central, and permanent | One to many, small, temporary |
| Chloroplasts | Present | Absent |
| Shape | Regular | Irregular |
| Storage Carbohydrate | Starch | Glycogen |
Magnification and Real Size of Biological Structures
1 mm = 1000 μm
1 cm = 10,000 μm
Magnification: Length of image : Real size
Length of image: Use a ruler to measure the longest dimension.
Length of scale: 1 cm = 1 μm; 6 cm = x. Real size: 6 x 1 / 1 = 6. m = 60,000; 6 cm = x 10,000 times of magnification
Movement In and Out of the Cell
Substances are transported through the cell membrane by diffusion and osmosis.
Diffusion
Diffusion is the passive movement of substances from a high to a lower concentration due to the random motion of the molecules.
There must be a concentration gradient (difference in concentration) for diffusion to take place.
In cells, diffusion takes place through the plasma membrane; therefore, the membrane should be fully permeable to the substance.
In our body, the gases O2 and CO2 diffuse between the alveoli of the lungs and the blood, and between the blood and the tissue cells.
Osmosis
Before Osmosis: semipermeable membrane, strong solution, hypertonic solution, weak solution.
After Osmosis: equally concentrated.
Definition: Osmosis is the passive movement of water molecules through a semipermeable membrane from low solute to higher solute concentration.
Osmosis in Plant Cells
- Hypotonic Solution: Low concentration of solutes.
- When a plant cell is placed in a hypotonic solution, the water flows into the cell, and the cell swells but does not burst because the cell wall prevents it. The cell becomes fully turgid.
- Hypertonic Solution: High concentration of solutes.
- When a plant cell is placed in a hypertonic solution, the water flows out of the cell, and the cell membrane shrinks, leaving a gap between the cell wall and the cell membrane. This is known as plasmolysis.
Osmosis in Animal Cells
When an animal cell is placed in a hypotonic solution, the water flows into the cell; the cell swells and then bursts because it doesn’t have a cell wall to prevent bursting.
When an animal cell is placed in a hypertonic solution, the water flows out of the cell, and the cell shrinks.
Therefore, our body has homeostatic mechanisms to regulate the water balance to prevent our cells from bursting or dehydrating.
Magnification = Size of image : Real size