Biology Chapter 5: The Fundamental Unit of Life

The Fundamental Unit of Life

Discovery of Cells

• Robert Hooke discovered cells in 1665 while examining a thin slice of cork
• He observed that the cork resembled a honeycomb structure with many little compartments
• He called these boxes "cells," which is Latin for "a little room"

Cell Structure

• Cells are the basic building units of all living organisms
• Cells have three main features: plasma membrane, nucleus, and cytoplasm
• Each cell organelle performs a special function, such as making new material, clearing waste, and more

Plasma Membrane

• The plasma membrane is the outermost covering of the cell
• It separates the cell's contents from the external environment
• It is selectively permeable, allowing certain substances to pass through while keeping others out
• The plasma membrane allows for the exchange of gases and water through diffusion and osmosis

Cell Wall

• Plant cells have an additional rigid outer covering called the cell wall
• The cell wall lies outside the plasma membrane and is composed mainly of cellulose
• Cellulose provides structural strength to plants
• Cell walls allow plant cells to withstand changes in the surrounding medium without bursting

Nucleus

• The nucleus is a key component of the cell
• It was discovered by Robert Brown in 1831
• The nucleus is responsible for controlling the cell's activities and functions

Cell Division

• Cells divide to produce new cells of their own kind
• All cells come from pre-existing cells
• This process is essential for the growth and development of living organisms

Osmosis

• Osmosis is the movement of water across a selectively permeable membrane
• It occurs when there is a difference in concentration of water or solute between the cell and its environment
• Osmosis can cause cells to swell or shrink depending on the concentration of the surrounding solution
• It is an important process for the exchange of water and nutrients between cells and their environment

Importance of Diffusion

• Diffusion is the movement of substances from a region of high concentration to a region of low concentration

• It is an important process for the exchange of gases and water between cells and their environment

• Diffusion plays a crucial role in the life of a cell, enabling the exchange of essential nutrients and waste products### Cellular Structure and Function

• A cell can lose water through osmosis, leading to shrinkage or contraction of the cell contents away from the cell wall, a phenomenon known as plasmolysis.

Cellular Components

• The nucleus is a central part of a cell, containing chromosomes, which are made up of DNA and protein.
• Chromosomes contain genetic information necessary for constructing and organizing cells.
• The nuclear membrane has pores that allow the transfer of material between the nucleus and the cytoplasm.

Eukaryotic and Prokaryotic Cells

• Prokaryotic cells (e.g., bacteria) lack a nuclear membrane, while eukaryotic cells (e.g., plants and animals) have a defined nuclear region.
• Prokaryotic cells are generally smaller than eukaryotic cells.
• Eukaryotic cells have more complex organelles and a true nucleus.

Cell Membrane and Cytoplasm

• The cell membrane is a selective barrier that separates the cell from its environment.
• The cytoplasm is the fluid content inside the cell membrane, containing many specialized organelles.
• The cytoplasm plays a crucial role in maintaining cellular functions.

Cell Organelles

• Endoplasmic Reticulum (ER):
  • A network of membrane-bound tubes and sheets.
  • RER has ribosomes attached to its surface, involved in protein synthesis.
  • SER is involved in lipid synthesis and detoxification.
• Golgi Apparatus:
  • A system of membrane-bound vesicles, involved in protein modification and packaging.
  • Functions include storage, modification, and packaging of products.
• Lysosomes:
  • Membrane-bound sacs containing digestive enzymes.
  • Involved in cellular digestion and waste removal.
  • Also known as "suicide bags" because they can digest their own cell components.
• Mitochondria:
  • Known as the powerhouses of the cell.
  • Generate ATP through cellular respiration.
  • Have their own DNA and ribosomes.
• Plastids:
  • Present only in plant cells.
  • Types include chromoplasts (colored) and leucoplasts (white or colorless).
  • Chloroplasts contain chlorophyll and are involved in photosynthesis.
• Vacuoles:
  • Membrane-bound sacs involved in storage and digestion.
  • In plant cells, vacuoles are filled with cell sap and provide turgidity and rigidity.

Cell Division

• New cells are formed in organisms for growth, replacement, and reproduction.

• Cell division is a fundamental process of life.### Cell Division

• Cell division is the process by which new cells are made, and it has two main types: mitosis and meiosis.

• Mitosis is the process of cell division that results in two identical daughter cells, each with the same number of chromosomes as the mother cell.

• Mitosis is responsible for growth and repair of tissues in organisms.

• Meiosis is a different process of cell division that involves two consecutive divisions, resulting in four new cells with half the number of chromosomes as the mother cell.

Cell Structure

• The cell is the fundamental organisational unit of life.
• Cells are enclosed by a plasma membrane composed of lipids and proteins.
• The cell membrane is an active part of the cell, regulating the movement of materials between the cell and the outer environment.
• In plant cells, a cell wall composed mainly of cellulose is located outside the cell membrane.
• The cell wall enables cells to exist in hypotonic media without bursting.
• The nucleus in eukaryotes is separated from the cytoplasm by a double-layered membrane and directs the life processes of the cell.
• The ER functions as a passageway for intracellular transport and as a manufacturing surface.
• The Golgi apparatus consists of stacks of membrane-bound vesicles that function in the storage, modification, and packaging of substances manufactured in the cell.
• Plant cells have large membranous organelles called plastids, which are of two types: chromoplasts and leucoplasts.
• Chromoplasts contain chlorophyll and perform photosynthesis, while leucoplasts function in storage.
• Most mature plant cells have a large central vacuole that helps maintain the turgidity of the cell and stores important substances, including wastes.

Cell Types

• Prokaryotic cells have no membrane-bound organelles, their chromosomes are composed of only nucleic acid, and they have only very small ribosomes as organelles.
• Eukaryotic cells have membrane-bound organelles and chromosomes composed of nucleic acid and proteins.

Cellular Functions

• Cells in organisms divide for growth, replacement of dead cells, and formation of gametes for reproduction.
• The plasma membrane is necessary for the survival of the cell, and if it ruptures or breaks down, the cell will die.
• The Golgi apparatus is essential for the storage, modification, and packaging of substances manufactured in the cell.
• The mitochondria is known as the powerhouse of the cell because it generates energy for the cell through cellular respiration.
• Lipids and proteins constituting the cell membrane are synthesized in the ER.
• Amoeba obtains its food through a process called phagocytosis.
• Osmosis is the movement of water molecules from a high concentration to a low concentration through a selectively permeable membrane.

Explore the basics of life sciences, including the discovery of cells and their structures, as observed by Robert Hooke in a cork slice.