Knowt
Cells
Types of Cells
Animal Cell
Does not have a cell wall or chloroplast
Small vacuole
Plant Cell
Contains a cell wall
Chloroplast and large vacuole
Bacteria Cell
Prokaryotic, contains no nucleus
No membrane-bound organelles
Cell Categories
Prokaryotic Cells
Lacks a membrane-enclosed nucleus
No membrane-enclosed organelles
Found only in the domains Bacteria and Archaea
Eukaryotic Cells
Contains a nucleus
Other organelles are bound by membranes
Key Cell Organelles and Structures
Mitochondria
Powerhouse of the cell
Site of ATP (energy) production
Cell Membrane
Thin, flexible barrier around a cell
Regulates what enters and leaves the cell
Nucleus
Large membrane-enclosed structure
Contains the cell's genetic material in the form of DNA
Nuclear Membrane
Highly-porous membrane
Separates the nucleus from the cytoplasm
Nucleolus
Found inside the nucleus
Produces ribosomes
Lysosomes (Animal Cell)
Filled with enzymes needed to break down certain materials
Ribosomes
Makes proteins
Vacuole
Stores materials such as water, salts, proteins, and carbohydrates
Endoplasmic Reticulum (ER)
Extensive membranous network
Composed of ribosome-studded (rough) and ribosome-free (smooth) regions
Golgi Apparatus
Modifies and packages proteins for export by the cell
Cytoplasm
Jelly-like fluid inside the cell
Organelles are suspended in it
Cytoskeleton
Network of fibers that holds the cell together
Helps the cell to keep its shape and aids in movement
Nucleoid (Prokaryotic Cell)
Non-membrane-bounded region
Where the DNA is concentrated
Plasmid
Small ring of DNA
Carries accessory genes separate from the bacterial chromosome
Plastid (Plant Cell)
Group of plant organelles
Used for storage of starches, lipids, or pigments
Chloroplast (Plant Cell)
Site where photosynthesis occurs
Cell Wall (Plant Cell)
Rigid layer of nonliving material
Surrounds the cells of plants and some other organisms
Capsule (Bacteria)
Sticky layer that surrounds the cell walls of some bacteria
Protects the cell surface and sometimes helps to glue the cell to surfaces
Pilus (Bacteria)
Short, thick hair-like protein structure
Allows a bacterium to attach to other bacteria and surfaces
Flagellum
Long, hairlike structure
Enables the cell to move
Cell Processes
Mitosis
Part of eukaryotic cell division
Cell nucleus divides
Meiosis
Cell division that produces reproductive cells in sexually reproducing organisms
Homeostasis
Tendency to maintain a balanced or constant internal state
Regulation of any aspect of body chemistry, such as blood glucose, around a particular level
Cell Theory
All living things are composed of cells
Cells are the basic units of structure and function in living things
New cells are produced from existing cells
Example Experiments
Observing Onion Cells under a Microscope
Objective: To identify plant cell structures such as the cell wall, nucleus, and vacuole.
Materials: Onion, microscope, slides, iodine solution, and coverslip.
Procedure: Peel a thin layer of onion skin, place it on a slide, add a drop of iodine solution, cover with a coverslip, and observe under a microscope.
Effect of Different Solutions on Plant Cells
Objective: To observe osmosis in plant cells.
Materials: Potato, sugar solution, distilled water, and microscope.
Procedure: Cut potato slices, place them in different concentrations of sugar solutions and distilled water, observe changes in cells under a microscope.
Bacteria Cultures and Antibiotic Effect
Objective: To observe the growth of bacteria and the effect of antibiotics.
Materials: Agar plates, bacteria samples, antibiotic discs, incubator.
Procedure: Spread bacteria on agar plates, place antibiotic discs on the agar, incubate and observe the zones of inhibition around antibiotic discs.
Redi's experiment, conducted by the Italian scientist Francesco Redi in the 17th century, was a landmark study in the field of biology that aimed to disprove the theory of spontaneous generation. This theory suggested that living organisms could arise from non-living matter.
In his experiment, Redi used jars containing meat. He divided the jars into three groups:
Open jars with meat - these jars were exposed to the air.
Sealed jars with meat - these jars were completely sealed to prevent any air from entering.
Jars covered with gauze - these jars were covered with gauze that allowed air in but prevented flies from laying eggs on the meat.
Over time, Redi observed that only the open jars produced maggots, while the sealed jars and gauze-covered jars did not. This led him to conclude that the maggots arose not spontaneously from the meat, but from fly eggs that were present in the environment. Redi's experiment provided strong evidence against spontaneous generation and laid the groundwork for further studies in microbiology and the understanding of biogenesis.
Pasteur's Experiment (1857): Louis Pasteur conducted a pivotal experiment that further disproved the theory of spontaneous generation and established the principles of microbiology.
Objective: To show that microorganisms in the air cause spoilage and fermentation.
Materials:
Broth in S-shaped flasks
Heat source
Procedure:
Pasteur used S-shaped flasks to allow air to enter but prevent dust and microorganisms from contaminating the broth.
He boiled the broth to sterilize it and kill existing microorganisms.
The flasks were left exposed to air without any additional covering.
Results:
The broth in the S-shaped flasks remained clear and free of microbial growth for a long time, while broth in open flasks became cloudy with microbial growth.
The design of the S-shaped neck trapped airborne bacteria, preventing them from reaching the broth.
Conclusion: Pasteur concluded that microorganisms in the air contaminated the broth, thus supporting the idea that life does not spontaneously arise from non-living matter, but is instead introduced from the environment. This experiment solidified the germ theory of disease and established sterilization techniques in microbiology.
