Science (Bio) Chapter - Fundamental Unit of Life Notes

Observation by Robert Hooke in 1665 of cork under a self-designed microscope revealed structures resembling honeycomb.
Hooke coined the term "cells" from the Latin word for ‘a little room’, marking the first observation of living entities as consisting of distinct units.
Cells are a crucial component in the study of biology today.

Take an onion bulb and peel off the epidermis.
Lay the peel in water on a watch glass to prevent drying.
Transfer a flat piece of peel to a glass slide with a drop of water, then add safranin solution and a cover slip.
Observe the temporary mount under low and high power of a compound microscope (refer to figures of microscope components).

Draw structures observed under the microscope, comparing them to provided figures.

Unicellular Organisms: Single-cell organisms such as Chlamydomonas, Paramecium, and bacteria.
Multicellular Organisms: These consist of multiple cells, which serve different functions (e.g., plants, fungi, and animals).
All multicellular organisms originate from a single cell. Cells divide to create new cells, forming the basis of cellular reproduction.

Cells contain three main components:
- Plasma Membrane: Outer layer regulating entry/exit of substances, acts as a selectively permeable barrier.
- Nucleus: Control center of the cell containing genetic material and governing cell functions.
- Cytoplasm: Fluid that houses organelles and is the site of various metabolic activities.

The plasma membrane separates cell contents from the external environment and is selectively permeable, allowing certain substances to pass.
Diffusion: Process by which substances like CO₂ and O₂ move across this membrane based on concentration gradients.
Osmosis: Special case of diffusion regarding water movement across a membrane; water moves from low solute concentration to high solute concentration.
Types of external solutions affecting cells:
1. Hypotonic Solution: Higher water concentration outside the cell; water enters the cell, potentially causing it to swell.
2. Isotonic Solution: Equal water concentration; no net movement of water; cell size remains constant.
3. Hypertonic Solution: Lower water concentration outside; water exits the cell, causing it to shrink.

Egg Activity: Demonstrates osmosis using de-shelled eggs in different solutions (pure water vs. concentrated salt solution) to observe swelling and shrinking effects.
Dried Fruit Activity: Observing the effect of osmosis on dried raisins or apricots in water and concentrated solutions.

Plant cells have an additional structure called the cell wall, composed of cellulose, providing structural support.
Plasmolysis: Occurs when a plant cell loses water leading the cell membrane to pull away from the cell wall. Demonstrated through Rhoeo leaf activities.
Cell walls allow plants to resist hypotonic media without bursting.

Viewed in onion peel cells and human cheek cells; characterized by a nuclear membrane with pores facilitating material transfer.
Chromosomes contain DNA, responsible for genetic inheritance; organized as chromatin in non-dividing cells.
Nucleoid: Region in prokaryotic cells lacking a defined membrane, distinguishing from eukaryotic cells.

The cytoplasm is the fluid-containing organelles; lacks membrane-bound organelles in prokaryotic cells, distinguishing them from eukaryotic cells.
Viruses do not possess membranes, limiting their classification as living entities until they infect host cells.

ER is a network involved in the transport and synthesis of proteins:
- Rough ER (RER): Studded with ribosomes; site of protein synthesis.
- Smooth ER (SER): Involved in lipid synthesis and detoxification processes.

Comprises membrane-bound sacs; functions to modify, package, and transport cellular products.
Involved in synthesizing lysosomes.

Membrane-bound sacs with digestive enzymes to break down waste and foreign materials. Known as the "suicide bags" of the cell due to their role in autophagy when the cell is damaged.

Known as the powerhouses of the cell, producing ATP through respiration. Possesses dual membranes and independent DNA, indicating their unique role in energy metabolism.

Present in plant cells, types include:
- Chloroplasts: Contain chlorophyll and are crucial for photosynthesis.
- Leucoplasts: Store starches and oils.

Mitosis allows growth and tissue repair, resulting in two genetically identical daughter cells.
Meiosis produces gametes with half the chromosome number of the parent cell, crucial for sexual reproduction.

Cells are the structural and functional units of life, possessing intricate organelles that facilitate their operations.
Understanding cell structure and functions is paramount in biology, highlighting their role in living organisms.