Cells, Microscopes, and Cellular Processes: A Comprehensive Guide
Microscopes
Electron and Light Microscopes
Electron microscopes have higher magnification and resolution than light microscopes, but can only view dead specimens in black and white, and are relatively expensive. Light microscopes can view both alive and dead specimens in color, and are relatively cheap.
Image size = real size x magnification
Total magnification = objective lens x eyepiece (eyepiece already has a x10 magnification)
Microscope Procedure
- Place the slide on the stage and use clips to secure it in place.
- Set the lowest power objective lens.
- Position the stage just under the objective lens (view from the side).
- Turn the coarse focusing wheel first to adjust the position of the stage.
- Then use the fine focusing wheel to adjust it further.
- Change the objective lens to a higher magnification if needed.
- Make notes on the specimen viewed.
Types of Cells
Eukaryotic Cells
Eukaryotic cells have a nucleus and can build together to form larger organisms.
Prokaryotic Cells
Prokaryotic cells have no nucleus, just floating bits of DNA within the cell, and are single-celled organisms. (Pro = no nucleus)
Plant vs. Animal Cells
Plant cells have a cell wall to provide structure, a permanent vacuole which is full of sap and holds salts, minerals, and nutrients, and chloroplasts containing chlorophyll for photosynthesis.
Bacteria Cells
Bacteria cells have no nucleus, instead, DNA is floating around and plasmids, which are sections of DNA providing genetic variation for the bacteria. They also have flagella to help them swim, a cell wall, and a slime capsule around the outside to protect the cell from physical and chemical attacks.
Specialization and Differentiation
Differentiation
Differentiation is the process by which a cell changes to become specialized for a specific job.
Examples of Specialized Cells
- Xylem and phloem have fewer subcellular structures to allow substances to pass through.
- Sperm cells have more mitochondria for more energy and a streamlined shape to swim faster.
- Nerve cells have a myelin sheath around the axon to insulate it, providing a faster electrical signal.
- Root hair cells have a higher surface area for osmosis.
- Red blood cells have a biconcave shape to hold more oxygen.
Stem Cells
Stem cells are undifferentiated cells, which can divide to produce more stem cells. They can mostly become any type of cell.
Types of Stem Cells
- Adult stem cells can be found in the liver, lining of the small intestine, bone marrow, human embryo, and plant meristem.
- Bone marrow stem cells are multipotent (can become some types of cells).
- Umbilical cord stem cells are pluripotent (can become most types of cells).
- Embryo stem cells are totipotent (can become any type of cell).
Stem Cell Applications
Stem cells can be grown in a lab and be made to differentiate into different types of cells. For example, stem cells could be reproduced to be made into insulin-producing cells for diabetic patients. However, there is a risk of rejection.
In therapeutic cloning, the stem cell is taken from the patient’s embryo, meaning it has their genes, and therefore can be made into any type of cell and have no chance of rejection.
In plants, a meristem can be taken to grow whole species of plants quickly and cheaply, with the same genetic information as the original plant.
Cell Division
Mitosis
- The cell duplicates its subcellular structures.
- The cell expands, and DNA is pulled to either side of the cell.
- The cytoplasm and cell membrane divide, producing two new identical daughter cells.
Meiosis
In meiosis (production of sex cells), the daughter cells divide again to produce four half cells (gametes).
Binary Fission
Binary fission is the same as mitosis, but for bacteria cells. Bacteria cells can divide as quickly as every 20 minutes in the right conditions.
Equation for the total number of bacteria produced in binary fission:
Total time / mean division time = number of divisions
2number of divisions = total number of bacteria produced
Cell Cycle
- Cell growth
- DNA synthesis – chromosomes are now double-stranded
- Further growth and DNA is checked for errors
- Mitosis
- Cytoplasm separates – two cells are formed
- Temporary cell resting period/cell stops dividing
You do not need to know PMAT.
Transport in Cells
Diffusion
Diffusion is the movement of particles from a high concentration area to a low concentration area that does not require energy, and the particles move until equilibrium is reached.
Factors Affecting Diffusion
- Higher concentration gradient = faster diffusion
- Higher surface area = faster diffusion
- Higher temperature = more kinetic energy per particle = faster diffusion
Osmosis
Osmosis is the movement of water molecules from a high concentration area to a low concentration area across a semi-permeable membrane that does not require energy, and the particles move until equilibrium is reached.
Active Transport
Active transport is the movement of particles from a low concentration area to a high concentration area that does require energy.
Gas Exchange in Plants and Animals
Gills, alveoli, red blood cells, villi, and root hair cells have a high surface area for faster diffusion/osmosis.
Osmosis Experiment
- Peel the potato as the skin can affect osmosis.
- Use a cork borer to produce three cylinders of potato (keeps the same diameter).
- Cut to approximately 3cm in length.
- Measure the mass of each potato chunk and record it.
- Place each cylinder in a test tube with different concentrations of sugar solution (0.5M, 0.25M, and distilled water).
- Leave the potatoes for 15 minutes.
- Remove from the solution, pat dry to remove excess water, and measure the mass on a scale. Work out the percentage change of potato mass (if the mass increased, water moved in via osmosis; if the mass decreased, water moved out via osmosis).
- Repeat multiple times and find an average.
- Plot a graph to show the relationship between potato mass and the concentration of the sugar solution.